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Publication Date: 2022/05/22
Amirkabir Journal of Civil Engineering (2588297X) 54(3)pp. 851-868
In this study, the effects of sodium hydroxide solution concentration and sodium hydroxide to sodium silicate weight ratio on compressive strength, tensile strength, and elastic modulus of slag-based geopolymer concrete are investigated. The results of the experiments show that by reducing the ratio of sodium hydroxide to sodium silicate and increasing the concentration of sodium hydroxide, the compressive strength and tensile strength of concrete increase. In addition, by increasing the concentration of sodium hydroxide and reducing the ratio of sodium hydroxide to sodium silicate, the modulus of elasticity decreases, and no clear relationship is observed between compressive strength and modulus of elasticity of geopolymer concrete. Therefore, a mix design with a ratio of sodium hydroxide to sodium silicate equal to 0.4 and a concentration of 6 molarity sodium hydroxide with the highest compressive strength was selected to be used for the second step of the research. The performance of beam-column joints in past earthquakes shows their importance in the performance of concrete moment-resisting frames. Therefore, in the second step of this research, an experimental study is done for two beam-column joints with geopolymer concrete and ordinary concrete. In order to investigate the cyclic behavior of the joint, the experiment is performed according to the loading protocol of ACI 374.1-05. The results of the experiment show that the geopolymer concrete beam-column joint has the acceptance criteria of ACI 374.1-05 regulations, and also, its seismic performance assures that the plastic hinge is generated in the beam properly .
Publication Date: 2022/09/23
Amirkabir Journal of Civil Engineering (2588297X) 54(7)pp. 2713-2738
Peridynamic theory, with a new formulation in the equations of motion, replaces the partial differential equations with integral equations. Due to this capability, it is possible to model crack initiation in any direction without the need to consider crack-growth criteria. One of the main problems in peridynamic theory is its high computational efforts due to its dynamic nature. If the critical time step of the numerical integration is greater than the loading time step, it will increase the cost of calculations. In this paper, using wavelet transform, peridynamic problems under irregular and random impact loads are analyzed. The aim of this study is to increase the computational speed for these problems. The method presented in this paper is investigated on two material models, namely Prototype brittle material and micro-plastic material. In this regard, structures with linear and nonlinear behavior have been analyzed considering the effects of discontinuities (such as cracks) and without considering the effects of discontinuities. The selected structures include two beams. Each beam is subjected to two types of irregular impact loading. The beams are analyzed once with the main impact (wave) function and once with the approximate impact (waves) functions obtained using wavelet transform. Based on the results of linear and nonlinear analyses of this study, it can be judged that the presented method reduces the computational cost by 87% in peridynamic models with linear behavior. It also bring a 94% reduction in computational costs in peridynamic models with nonlinear behavior.
Publication Date: 2026
Soil Dynamics and Earthquake Engineering (02677261) 201
This study presents a new hybrid viscoelastic-hysteretic device, termed the visco-plastic drawing (VPD) damper, designed to provide effective structural vibration control across a wide range of excitation amplitudes. The VPD damper integrates a metallic yielding (MY) component, consisting of rectangular steel plates operating under optimized pure-bending conditions, with a viscoelastic (VE) component composed of shear-deforming layers. The VE part effectively mitigates low-to moderate-amplitude vibrations, such as those from winds, storms, or ambient sources, while the MY part supplies high-capacity energy dissipation during strong earthquakes. This dual mechanism ensures large damping ratios at low story drifts, enhances performance in high-seismicity and high-wind regions, and protects primary structural members from damage under design-level events. The damper's independent configuration avoids direct interaction with vertical load-carrying members. Furthermore, damaged MY plates can be replaced post-event without removing the VE layers, allowing the structure to remain serviceable. Owing to its unique configuration and performance, the VPD damper offers advantages over conventional VE or MY devices, which are typically optimized for only one vibration intensity range. In this study the conceptual design, theoretical considerations, material testing, and cyclic performance of the VPD damper were investigated through both experimental and numerical methods, demonstrating its stable and sustainable hysteretic behavior across a full spectrum of structural demands. Finally, the VPD efficiency and effectiveness in control performance under low to high-amplitude excitations were numerically confirmed according to the lateral responses of a single MRF structure. © 2025 Elsevier Ltd.
Publication Date: 2025
Engineering Structures (18737323) 336
The recently developed metallic-yielding pistonic (MYP) damper is a novel passive control system. It consists of a set of rectangular yielding plates under pure-bending loading conditions. The developed device generally performs as a tension/compression element with rigidity and stability in other directions. In this study, a step-by-step procedure is presented for the design of the structures controlled by this damper under severe earthquakes. The main design objective of this procedure is the perfect seismic protection of the combined control-structure based on the fulfillment of two criteria including fuse-like performance and control sustainability. The first criterion preserves the elastic behavior of the controlled structure (which is defined as the perfect structural protection) under severe earthquakes and the other one is required to be met for the stability of the control system. The study is followed by examination of the procedure through seismic analyses of four 5–20 story moment-resisting buildings as examples of its application. From the obtained results, it was observed that the developed procedure is able to meet all design control objectives for multi-story buildings with acceptable accuracy without requiring any complicated numerical control-structure modeling and nonlinear dynamic analyses. Moreover, the controlled structures experience seismic responses significantly decreased by 67–56 %, 60–46 % and 79–70 % respectively for the maximum lateral drift, shear force and residual drift in average for the stories from the shortest to the tallest structure. © 2025 Elsevier Ltd
Publication Date: 2025
Journal of Constructional Steel Research (0143974X) 235
This study offers a 3D finite element modeling (FEM) and parametric analysis of a novel extended endplate beam-to-column semi-rigid deconstructable external composite joint (DECJ) under cyclic loading. This innovative DECJ is created by connecting the precast geopolymer concrete slab to the top flange of a steel beam using bolted shear connectors, and inserting threaded central reinforcing bars into the column flanges to enhance the demountability of the entire system. The FEM was developed using ABAQUS software and verified against the experimental study results to analyze the structural behavior and failure modes of the proposed DECJ system. The study investigates the effect of various parameters, including the diameter of bolted shear connectors, the degree of shear connection, the ratio of central reinforcing bars, the thickness of the endplate, the thickness and strength of the geopolymer concrete slab, and the bolt diameters of the connection zone. The findings suggest that to prevent the failure of bolted shear connectors, the optimal shear connection degree of approximately 73 %–90 % and the concrete slab thickness of 80-120 mm should be maintained. Additionally, the central reinforcing bar ratio is preferred to be around 0.98 % to avoid the failure of shear connectors and reinforcing bars. Furthermore, the ratio of endplate thickness to connection zone bolt diameter should be between 0.64 and 0.82 to reduce the fracture risks of connection zone bolts. Finally, a new predictive equation is proposed to determine the plastic moment capacities of DECJs with precast concrete slabs, demountable bolted shear connectors, and demountable central reinforcing bars under cyclic loading. © 2024
Publication Date: 2025
Case Studies in Construction Materials (22145095) 22
The significance of finding industrial waste solutions in the construction industry plays a crucial role in the quest for environmental conservation. To reduce the carbon footprint, this research has focused on developing solutions. This study assesses the mechanical properties of water-cured alkali-activated slag concrete (AASC) prepared using a one-part activator, where the dry alkali activator is pre-mixed with slag before water addition. The mix is then reinforced with three types of steel fibers, namely deformed steel fibers (DSF), recycled tire steel fiber (RTSF), and hybrid steel fiber (HSF) at varying volume fractions (0.5 %, 0.75 %, and 1.0 %). Numerous characteristics, including workability, compressive strength, flexural strength, splitting tensile strength, flexural toughness, and SEM observations in short-term, and stress-strain response under uniaxial compression, modulus of elasticity, peak strain and energy absorption in long-term were assessed. According to the test results, compressive strength was largely unaffected by fiber addition, with DSF at 1 % volume (DSF1) achieving the highest strength (58.51 MPa at 28 days). Conversely, optimal compressive strength for RTSF was observed at 0.5 % volume. On the other hand, the concrete mixes' splitting tensile, and flexural strengths increased with the addition of steel fibers achieving maximum values at 1 % DSF. The addition of steel fibers transformed the stress-strain response of one-part AASC mixes from brittle to ductile, with HSF specimens at 1 % volume (HSF1) exhibiting a 50 % increase in strain related to peak stress compared to the reference. Remarkably the HSF1 mix achieved a 421 % increase in toughness at 365 days compared to the reference mix. The DSF1 mix at 28 days and HSF1 at 365 days achieved the highest energy absorption capacity. Overall, the inclusion of 1 % DSF, RTSF, and HSF fibers enhanced the mechanical properties of one-part AASC, with DSF providing the most significant improvements at 28 days. © 2024 The Authors
Publication Date: 2025
Journal of Building Engineering (23527102) 106
This study examines a novel damper designed for installation in cross-braced frames to enhance their cyclic performance, referred to as the Variable Grooved Gusset Plate Damper (VGGPD). The damper comprises a gusset plate with multiple slits arranged around the diagonal braces. The steel strips between the slits undergo significant plastic deformation under in-plane double curvature, ensuring high ductility and effective energy dissipation. The proposed damper is developed through cyclic testing and numerical analysis conducted on cross-braced frames equipped with the VGGPD. The study investigates two configurations of the damper, characterized by variable thickness and variable length, to prevent concentration of plastic deformation in a specific region. The damper plate is divided into four sections, assigning specific thicknesses or lengths to the upper and lower parts, and different specifications to the middle part. The experimental findings indicate that both damper configurations significantly improve the cyclic performance of cross-braced frames, ensuring adequate capacity to accommodate the required deformations. Furthermore, the results underscore the cyclic behavior characterized by stable hysteresis loop shapes and effective energy dissipation during repeated loading cycles. Notably, specimens utilizing the VGGPD system exhibited ductility factors reaching values as high as 8. The VGGPD system, in particular, is capable of achieving a relative drift of up to 5 %, a value that matches the drift observed in special moment frames and surpasses that of special braced frames. Further validation through detailed finite element analysis in ABAQUS supported these findings, with strong agreement between the experimental and numerical results. © 2025 Elsevier Ltd
Publication Date: 2024
Arabian Journal for Science and Engineering (21914281) 49(4)pp. 5447-5466
The lack of a code for preparing one-part geopolymer concrete (GPC) is one of the major obstacles to its wide use. This study adopted one of the most common methods for preparing ordinary concrete, the ACI method, taking into account the most important variables affecting this method and then modified it to suit one-part GPC. Three different sizes of aggregates and four water-to-binder ratios (W/B) were used in preparing the concrete mixtures in this study. In addition, three different proportions of sodium metasilicate were used as the activator, which ultimately resulted in a total of 36 mix designs. Specimens were subjected to various tests, including setting time, workability, and compressive strength. In addition, the material's behaviour was studied using X-ray diffraction and scanning electron microscope. The results indicate that the ACI method is generally applicable for designing geopolymer concrete mixtures with minor adjustments. Consequently, the table used for predicting concrete strength based on a specific water/cement ratio has been replaced with relevant figures that depict the relationship between compressive strength and the water-to-binder ratio. In addition, a step-by-step flowchart has been presented that explains how to design one-part geopolymer concrete. Conducted experiments indicated that the properties of geopolymer concrete are greatly affected by the ratio of W/B and the size of aggregate used in preparing the concrete mixture. Furthermore, the quantity of activators has significant effects on concrete's workability and compressive strength. Results of the experiment suggest that one-part GPC can provide greater compressive strength than ordinary concrete. © King Fahd University of Petroleum & Minerals 2023.
Publication Date: 2024
Journal of Constructional Steel Research (0143974X) 222
Modern construction necessitates eco-friendly structures that minimize carbon dioxide emissions and are designed for easy disassembly, facilitating the reuse of structural components with minimal effort and cost. Facilities employing geopolymer concrete designed for disassembly serve as an exemplary model for such construction. In this research, four full-scale interior demountable steel-concrete composite beam-to-column joints having precast geopolymer concrete slab were conceived, produced, and subjected to cyclic loading tests. A comprehensive examination was conducted on the structural behaviors of interior demountable steel-concrete composite beam-to-column joints, encompassing crack patterns, failure modes, moment-rotation responses, force-displacement curves, strain distributions, shear connector slippage, and energy dissipation. The research examined how the structural behavior of interior demountable composite joints is affected by the diameter of bolted shear connectors and the reinforcement ratio of precast concrete slabs. The results indicated that increased reinforcement in the slab enhances the rotation of the connection, the initial rotational stiffness, the bearing capacity of the joint, and the joint's over-strength. The dissipation of energy is impacted by both the dimensions of the reinforcement in the slab and the diameter of the shear connectors. The joint's stiffness was assessed through an analysis of the bending moment-rotation curve, following the guidelines outlined in Eurocodes 3 and 4. The deformability meets the minimum rotation capacity requirement (0.03 rad) specified by these codes. In summary, bolted shear connectors enable controlled slippage, ensuring a smooth response to applied loads and making this joint well-suited for withstanding cyclic loads, such as those associated with earthquakes. The test results also show that the composite beam to column joints having precast concrete slab and bolted shear connectors can be deconstructed easily at the end of their service life. © 2024 Elsevier Ltd
Publication Date: 2024
Results in Engineering (25901230) 24
A comprehensive understanding of the engineering characteristics of one-part slag-based geopolymer concrete (SBGC) is instrumental in promoting its widespread adoption and optimized design, improving construction practices, and advancing sustainability in the built environment. This study examined the workability, development of compressive strength, tensile strength, modulus of elasticity, and stress-strain behavior of one-part SBGC. The long-term compressive strength of SBGC, under both ambient curing and water curing conditions, has also been examined. Multiple combinations of mixtures were assessed, accounting for diverse factors such as activator ratio, aggregate size, water-to-binder ratio, curing conditions and activator types. This research also proposes new equations for predicting tensile strength and modulus of elasticity for one-part SBGC. The findings reveal that water-cured specimens demonstrate up to 43 % higher compressive strength and 52 % higher tensile strength compared to those cured under ambient conditions. Increasing the activator proportion in the mixture notably accelerates the early-stage development of compressive strength and SBGC's modulus of elasticity. Furthermore, one-part SBGC exhibits a long-term strength development that surpasses conventional concrete by over 20 %. In addition, the stress-strain behavior of SBGC reveals its inherent fragility, marked by near-perfect linear elasticity that abruptly transitions to complete and sudden collapse, distinguishing it from ordinary concrete. Microstructural analyses indicate that elevating the activator ratio reduces the presence of unreacted GGBFS particles and quartz in the mixture, thereby promoting the formation of gel. © 2024 The Author(s)
Publication Date: 2024
Mechanics Based Design of Structures and Machines (15397742) 52(11)pp. 9381-9411
One of the significant obstacles in conducting linear and non-linear time history analysis is its time-consuming nature. In this article, a new downsamlping method based on discrete wavelet transform (DWT) and smoothing is proposed to overcome this problem. In order to assess the precision of this approach, 50,000 linear and non-linear dynamic analyses of single degree of freedom (SDOF) systems and 300 nonlinear dynamic analyses of frame structures have been performed. One hundred Fema440 records were utilized to generate approximate waves up to the third level and the outcomes of this method were then contrasted with those of DWT. It has been demonstrated that the third-level approximate wave produced by DWT, previously considered dependable in other research, generates significant errors in results and the average error (absolute error percentage of the acceleration spectrum) of its third-level approximate wave is approximately 17.5%. On the other hand, the proposed method generated approximate waves with an average error of less than 4.5% across all behavior coefficients and periods and the error rate decreases as the period and behavior coefficient increase. Analysis of steel moment-resisting frames indicated that the lowest error in both methods is achieved for the base shear and across different engineering demand parameters, the average error rate for the proposed method was below 7.5%. Furthermore, caution must be exercised when employing the proposed method for structures with periods shorter than 0.5 s. © 2024 Taylor & Francis Group, LLC.
Publication Date: 2024
JVC/Journal of Vibration and Control (10775463) 30(19-20)pp. 4239-4251
A critical factor obstructing structural resilience is residual deformation after a damaging event. The search for a solution for removing residual deformation has led to the consideration of Shape Memory Alloys (SMAs) that can undergo large deformations and return to their original undeformed shape. This study focuses on an innovative hybrid yielding steel-SMA damper that uses monofilament wire loops. Because of numerous design parameters that affect the performance of this hybrid damper, this research aims to carry out a parametric study to optimize the damper’s performance. The study was conducted at the device level as well as a structural level. At the device level, the key design parameters, including SMA to steel ratio, max imposed strain, and the length of the elements, were evaluated. At the same time, the damper’s effect on the seismic performance of low, mid, and high-rise structures was investigated at the structural-level study. In the end, the results showed that using the damper in strong ground motions successfully reduced the maximum residual drift up to 71%, 97%, and 92% for low, mid, and high-rise structures, respectively. Therefore, it was concluded that the damper could add the self-centering ability to hysteretic dampers while maintaining satisfactory energy dissipation performance. Furthermore, some of the advantages claimed by the developers, including versatility in design and performance, adequate load resistance, and stable behavior, were also confirmed in this study. © The Author(s) 2023.
Publication Date: 2024
Structures (23520124) 60
While cold-formed steel structures have been extensively studied for seismic-resistant construction, existing regulations, and implementation guidelines do not comprehensively address the impact of key design parameters on the seismic behavior of CFS strap-braced shear wall systems. This study investigates the lateral resistance and seismic behavior factor of strap-braced shear walls and compares them with code values, and tries to fully understand the effect of different design parameters on the seismic R-factor of these systems. The effect of parameters such as the strap cross-sectional area, aspect ratio, and distance between the studs is studied using ANSYS finite element software to create datasets for various configurations. The pushover analysis results obtained from this analysis are utilized to perform incremental dynamic analysis, under a set of 22 ground motion records, to evaluate the seismic response modification factor for different residential buildings. For this purpose, one to four-story residential buildings are designed based on four seismic hazard zones: low, moderate, high, and very high and then, they are analyzed. Results of pushover analysis show that increasing the strap cross-sectional area and aspect ratio increases capacity, but changing the distance between studs does not have a significant effect, and the R factor presented by codes is conservative. Incremental dynamic analysis results also indicate that the behavior of studied buildings varies depending on the structure and selected record and the suggested R factor by codes for diagonal straps braced cold-formed steel structures is acceptable for buildings up to three stories in low, medium, and high seismic zones, and for buildings up to two stories in very high seismic zones. Overall, this study shows that strap-braced cold-formed steel shear walls have the potential to achieve higher seismic R-values in comparison to design codes. © 2024 Institution of Structural Engineers
Publication Date: 2024
Structures (23520124) 63
Engineers utilize truss structures constructed from various materials, including timber and steel, to achieve superior performance. The motivation behind employing truss structures lies in their ability to cover larger spans with lighter frameworks compared to traditional structural beam-column framing, resulting in cost-effective and efficient construction processes. This study introduces the concept of the equivalent beam approach, enabling designers to rapidly assess the strength and deflection of truss structures. This approach facilitates a quick estimation of the required truss material costs before conducting more precise finite element analyses. The research begins by comparing the results of equivalent Euler-Bernoulli beam and Timoshenko beam. The findings reveal that Euler-Bernoulli beam method is unsuitable, with an error of approximately 57 %. However, the accuracy of the Timoshenko beam method is contingent on the selection of the Timoshenko shear coefficient. By optimizing this coefficient, the errors in static, frequency, dynamic, stability, and thermal analyses are reduced to approximately 1 %, 5 %, 11 %, 11 %, and 11 %, respectively. To aid engineers in determining the optimal Timoshenko shear coefficient, the paper concludes by presenting an exponential relationship based on the examination of various truss sections. This approach simplifies the calculation of the optimal coefficient, enhancing the overall design process for cost-effective and reliable truss structures. © 2024 Institution of Structural Engineers
Publication Date: 2024
Structures (23520124) 60
This paper evaluates the application of the endurance time method in the optimum performance design of structures using the uniform deformation theory. The structures used in this study include shear-building systems with 5, 10, and 15 stories, and steel moment-resisting frames with 3, 7, and 12 stories. Initially, shear-building systems are optimized to have uniform story ductility ratios at low, moderate and high seismic hazard levels separately using three sets of ground motion records and a compatible series of endurance time acceleration functions. The effectiveness and accuracy of the endurance time method are assessed by comparing lateral force distribution obtained from this method with its corresponding attained from ground motion records. Moreover, as the number of stories and target ductility increases, the compatibility of these two methods improves. However, it is found that the optimum structure at one seismic hazard level does not necessarily lead to the optimum structure at other seismic hazard levels. Next, by adding dampers with gap to the systems, a procedure is suggested to optimize these structures at different seismic hazard levels simultaneously. These dampers are activated at moderate and high seismic hazard levels. Finally, similar optimization algorithm is used for steel moment-resisting frames to make their story drift ratios or plastic hinge rotations uniform along the height at different seismic hazard levels. Results show that combining endurance time method and uniform deformation theory leads to a promising optimization procedure that can significantly reduce computational costs with reasonable error. © 2024 Institution of Structural Engineers
Publication Date: 2023
Mechanics Based Design of Structures and Machines (15397742) 51(7)pp. 3779-3802
This experimental study investigates the behavior of a proposed damper based on austenite Nitinol wires. The damper’s design is so that the wires are always in tension under both tensile and compressive forces. Also, the damper can employ steel wires as a hybrid to enhance the performance of the damper. Steel wires can be employed in parallel with the SMA wires and in the same manner. Therefore, SMA and steel wires are stretched simultaneously in the hybrid damper state. This experimental study includes the process of training the wires and the main cyclic tests with different strain rates which leads to the extraction of the hysteresis curves of the proposed damper. A thermal study is also conducted on the employed shape-memory alloy (SMA) wires during the cyclic loadings. The results indicate that the increase of loading frequency causes the SMA wires to heat; thus, the inner area of the hysteresis curve decreases, resulting in diminished damping capacity. Also, the damper stiffness and the residual strain are increased by using the steel wires. The proposed SMA damper is employed for seismic control of a three-story steel frame to evaluate its efficiency. The results reveal that the residual drift ratios of the controlled structure are significantly decreased. © 2021 Taylor & Francis Group, LLC.
Publication Date: 2023
Soil Dynamics and Earthquake Engineering (02677261) 175
One of the main problems of nonlinear time history analysis is its high computational effort, especially in structures with large number of structural components, high-rise buildings and complex structural systems. The ground motions recorded in recent years also include more recorded points than in the past, which has also increased the required volume of calculations. In this paper, three downsampling methods for reducing calculation costs of nonlinear time history analysis are presented and their applicability is investigated through practical examples of complex structures. These methods include the discrete wavelet transform, the time step correction, and the wavelet time step correction which is introduced in this paper. The efficiency of these downsampling methods is investigated for near-fault and far-fault earthquake records, as well as for records on different soil types. A comprehensive study is performed on five sets of ground motions consisting of 20 records. Each record is filtered up to three stages using one half, one quarter, and one eighth of the number of the main record points. First the linear and nonlinear response spectra based on the original records and the approximate waves are investigated. Subsequently, to evaluate the performance of the methods on more complex structural systems, two three-dimensional structures of 6-story and 15-story are analyzed. The 6-story structure is equipped with viscous dampers, while the 15-story structure has seismic isolators. The results indicate that the wavelet time step correction method has better performance in most cases, compared to the other two methods. It is shown that careful consideration is needed when dealing with earthquake records with high frequency contents. In such situations, one filtering step for the discrete wavelet transform method and two filtering steps for the other two methods are recommended. Also, in practical applications, it is advisable to choose earthquake records exhibiting the least error based on the results of SDOF systems analyses. Employing this technique can significantly cut down computational effort (up to 90%), while maintaining an average error ranging from 1% to 2% for the wavelet time step correction method. © 2023
Ravanbakhshian habibabadi, M. ,
Izadinia, M. ,
Tajmir riahi, H. ,
Hasan meisami, M. Publication Date: 2023
Structures (23520124) 51pp. 351-371
In this paper, 39 U-shaped flexural plate (UFP) dampers have been experimentally tested under cyclic loading taking into account the most the effective parameters such as the width and back to back distance of UFPs. The leg length of UFPs was considered equal to or greater than their back to back distance. First, the relationship between effective parameters of UFPs with their energy dissipation and strength capacity has been investigated to enable their selection for different design purposes. Then, the force–displacement behavior of the samples is comprehensively studied to present a suitable spring model for their numerical analysis in different structures. UFPs with the back to back distance equal their leg length showed larger ductility and smaller force and dissipated energy capacity. Moreover, all UFP specimens had a complete hysteresis loop, and they were reliable if their displacement capacity was defined correctly. In addition, increasing the width of UFP specimens caused an increase in the amount of energy dissipation and shear force but the back to back distance had a more effective role rather than the width. The analytical equations were in agreement with the experimental results for UFPs with the ratio of the back to back distance to the leg length less than 0.85. Finally, the backbone curves of UFPs presented in this paper can be used in their optimal selection for different applications. © 2023 Institution of Structural Engineers
Publication Date: 2023
Structures (23520124) 51pp. 846-879
Application of discrete wavelet transform for down-sampling earthquake records has been started since 2002. Although the mother wavelet function plays an important role in the accuracy of wavelet transform, there is no study to investigate the effect of this function on dynamic analysis error. In addition, most studies have used a limited number of earthquake records for down-sampling application of wavelet transform. Therefore, in this paper, a comprehensive study is performed on 36 different mother wavelet functions and 100 earthquake records. The linear and nonlinear response spectra of the main records and their down-sampled ones have been used to evaluate the performance of different mother wavelet functions. Approximate waves are obtained for three levels using wavelet transform. Also, dynamic analyses are done for 101 single-degree-of-freedom systems (with a period between 0 and 5 s) and 5 behavior coefficients consisting of more than 7 million analyses. Results show that the Daubechies family of wavelet functions used in previous studies for down-sampling earthquake records often cause errors greater than 15%. But the Biorthogonal wavelet functions which have not been used for down-sampling before, have an error of less than 2.5% and are the best wavelet functions for down-sampling earthquake records. In addition, a method called wavelet functions combination is presented to ensure minimum errors at different levels of down-sampling. In the next step, to evaluate the effect of the wavelet function on the accuracy of dynamic analysis of real structures, 3, 9, and 20 story structures are analyzed using the IDA method and finally, an irregular structure is also analyzed. The results obtained from the nonlinear analysis of these structures show that Biorthogonal wavelet functions can reduce the wavelet error from 27% to 6%. © 2023 Institution of Structural Engineers
Publication Date: 2023
Construction and Building Materials (09500618) 369
The cement production process produces enormous amounts of carbon dioxide (CO2). Hence, using new types of cement, like ternary cement, which contains calcined clay, limestone, and cement clinker, can significantly reduce the CO2 emissions of the cement industry and even increase the mechanical properties and durability of samples. This paper investigates the cement mortar's mechanical and durability characteristics, containing ceramic waste powder (CWP) and limestone powder (LSP) as partial cement substitution. Samples with 5, 10, and 15 % LSP and 10, 20, and 30 % (by weight of cement) CWP as cement substitutes were produced. The mortar specimen tests were performed after 7, 28, and 90 days of curing in the water pool, then compressive strength and alkali-silica reaction (ASR) tests were evaluated. Furthermore, setting time test, thermogravimetric analyses, X-ray diffraction analyses, and scanning electron microscopy (SEM) of cement paste were carried out. The ternary cement mortar containing 10 % CWP and 15 % LSP has the highest compressive strength. Also, the ternary cement mortar containing 30 % CWP and 15 % LSP shows the lowest compressive strength (decreased by 8.5 % compared to the reference sample). In addition, the mix containing 20 % CWP and 15 % LSP has a lower ASR value than the control sample (52 % less). Eventually, SEM images showed the reference sample and the specimen containing 30 % CWP and 15 % LSP have the lowest and highest pores and cavities, respectively. © 2023 Elsevier Ltd
Publication Date: 2023
Journal of Building Engineering (23527102) 78
In this study, the numerical and experimental investigations of a new passive control system recently introduced by the authors are discussed. This system is a metallic-yielding pistonic damper (MYP) in which the lateral excitation is transferred to a set of rectangular metallic-yielding plates under pure-bending loading conditions. The dissipator plates are placed into a steel surrounding rigid box which has only one sliding translational degree of freedom along its longitudinal axis. Based on this configuration, the damper performs as a piston-like axial element under cyclic motions. In this study first, the conceptual design and theoretical basis of the proposed system are presented and then, the details of the MYP numerical and experimental program are discussed. For this purpose, the MYP stability and performance are examined by conducting displacement-control cyclic tests on 12 physical specimens as well as finite element analyses on the corresponding numerical models. According to obtained results, the specimens experiencing ductility values from 15 to 38 during the tests, exhibit a broad range of ultimate capacity from 23 to 245 kN. Overall, the damper is found to have nonlinear behavior with consistent strain hardening and preserve its stability and performance during a large number of consecutive cyclic motions. Moreover, it was found that the MYP control system supplies high levels of damping ratios at low values of the lateral story drift due to its fuse-like performance. © 2023 Elsevier Ltd
Publication Date: 2023
Soil Dynamics and Earthquake Engineering (02677261) 172
Friction tuned mass dampers (FTMDs) are widely used to control the displacement of structures located in seismically active areas. Typically, the frequency and friction ratios of FTMDs are tuned up during design, but this task is complex if real ground motion records are considered. This article proposes a novel and accurate approach to calculate optimum parameters of FTMDs for controlling the displacements of both single degree of freedom (SDOF) systems and multi-story structural frames subjected to real ground motion records. In this study, the SDOF displacement and two FTMD parameters (frequency ratio and friction ratio) are first optimized simultaneously using a Particle Swarm Optimization (PSO) algorithm. A series of sensitivity analyses are then carried out to examine the effect of different structural features (damper movement, variations of optimized parameters and damping) on the optimized SDOF displacements and FTMD parameters given by the PSO. It is shown that, compared to a more established method available in the literature, the PSO algorithm reduces the SDOF displacements by an additional 21% on average. The PSO is then used to obtain optimum parameters of FTMDs and TMDs connected to four moment-resisting frames, and the results from the frames are compared to those from equivalent SDOF systems. This article contributes towards providing more suitable optimization tools for structures fitted with FTMDs, which in turn can lead to more efficient design methods for dampers. © 2023 The Authors
Publication Date: 2022
Journal of Anatomy (14697580) 240(2)pp. 305-322
Statistical data pertaining to anatomic variations of the human talus contain valuable information for advances in biological anthropology, diagnosis of the talar pathologies, and designing talar prostheses. A statistical shape model (SSM) can be a powerful data analysis tool for the anatomic variations of the talus. The main concern in constructing an SSM for the talus is establishing the true geometric correspondence between the talar geometries. The true correspondence complies with biological and/or mathematical homologies on the talar surfaces. In this study, we proposed a semi-automatic approach to establish a dense correspondence between talar surfaces discretized by triangular meshes. Through our approach, homologous salient surface features in the form of crest lines were detected on 49 talar surfaces. Then, the point-wise correspondence information of the crest lines was recruited to create posterior Gaussian process morphable models that non-rigidly registered the talar meshes and consequently established inter-mesh dense correspondence. The resultant correspondence perceptually represented the true correspondence as per our visual assessments. Having established the correspondence, we computed the mean shape using full generalized Procrustes analysis and constructed an SSM by means of principal component analysis. Anatomical variations and the mean shape of the talus were predicted by the SSM. As a clinically related application, we considered the mean shape and investigated the feasibility of designing universal talar prostheses. Our results suggest that the mean shape of (the shapes of) tali can be used as a scalable shape template for designing universal talar prostheses. © 2021 Anatomical Society
Publication Date: 2022
Journal of Constructional Steel Research (0143974X) 194
A new damper with pistonic performance is presented in this research for seismic control of structures. A set of rectangular metallic yielding plates has been considered as the energy dissipating part for this device. The damper is configured in such a way that can provide the loading conditions as pure-bending for this part during cyclic motions. This configuration makes the damper to have an optimized flexural yielding mechanism and consequently a high-level of force capacity and damping ratio. The dissipator part is placed into a steel surrounding rigid box which has only one sliding translational degree of freedom along its longitudinal axis. Accordingly, the device can perform as a tension/compression piston with sufficient stability in other directions. The proposed metallic-yielding pistonic (MYP) damper can be used in various types of structural systems such as moment-resisting or braced frames and even coupled shear wall systems with the capability of dual or multiple-installation in each frame bay. In this research the hysteresis behavior of this damper has been numerically investigated. Then as a parametric study, the effects of various MYP design parameters on the damper hysteretic behavior were studied. Finally, the control performance of this device was seismically investigated in a one-story moment-resisting frame considering possible beam flange out-of-square imperfections. According to observed results, the proposed damping system is high-performance in seismic structural protection at low-value story drifts. Besides, it was able to significantly reduce the structural responses and residual deformations as well as the out-of-plane frame motions. © 2022 Elsevier Ltd
Publication Date: 2022
Structures (23520124) 44pp. 323-342
The direct displacement-based design (DDBD) procedure is well established for designing reinforced concrete and steel moment-resisting frames (SMRFs). However, a limited number of researches is available on optimum DDBD of SMRFs. Furthermore, the nonlinear time-history analysis response of structures designed based on this procedure is inconsistent with its initial assumptions. Design displacement profile is one of the most essential and influential parameters in the DDBD method because it can impress other design parameters. In this paper, an optimum displacement profile is proposed to improve the results of the DDBD procedure via using the particle swarm optimization (PSO) algorithm. In this regard, nine SMRFs with a different number of stories have been designed using the DDBD procedure. Nonlinear time history analyses are performed for these frames using OpenSees software. The models are subjected to a set of 20 ground motion records. Then, PSO algorithm has been used to optimize the displacement profile of the DDBD procedure to achieve uniform drift distribution along with the height of the frames. Finally, based on regression analysis, the optimum design displacement profile for SMRFs with a different number of stories is formulated. The proposed equations show an average reduction of about 20% and 40% in steel usage and design base shear of the frames, respectively, while they have uniform drift along their heights. © 2022 Institution of Structural Engineers
Publication Date: 2022
Structures (23520124) 46pp. 1345-1368
In this paper, the wavelet transform is used for the first time to reduce the cost of site response analysis calculations for different soil profiles in Isfahan city. This downsampling method was used up to three levels to generate approximate waves from the ground motion records. Site response analysis was done using the one-dimensional equivalent linear and nonlinear method. Down-hole seismic tests of 71 boreholes in Isfahan city were used to make different soil profiles. In addition, 30 ground motions compatible with seismic hazard analysis of this city were selected. Due to the lack of comprehensiveness in previous studies, none of them has definitively indicated which level of wave decomposition is the last reliable wavelet filter. But in this article, for the first time, by performing a data reliability review, it is shown that the last reliable filter for the site response is related to the second level of decomposition. Comparison of the site response analysis using approximate waves and the main records, by performing more than 2100 analyses, showed that wavelet transform could be used up to two levels with the maximum error of 8% in predicting amplification factors. In addition, approximate waves were used for the nonlinear dynamic analysis of structures with different heights located at different soil profiles, and results showed that wavelet transform decreases the cost of calculations up to 50% with a 5% error. © 2022 Institution of Structural Engineers
Publication Date: 2022
Structures (23520124) 39pp. 57-69
Three strengthening methods for RC beam-column joints using NSM steel bars and NSM CFRP strips were experimentally evaluated by cyclic loading. These methods increase joints capacity and prevent the plastic hinge formation near the column while try to minimize destructive task on floor slab. Strengthened specimens and a control specimen of RC beam-column joint from an intermediate moment-resisting frame were constructed on one-half scale and subjected to cyclic loading according to ACI 374.1-05 simultaneously with a constant column's axial load to study their seismic behavior. Experimental results indicated that the proposed methods could increase joints capacity up to 30% compared to the control specimen and two of them improve joints ductility by removing the plastic hinge from the joint core. In addition, the energy dissipation of the retrofitted specimens was increased up to 100% and they experienced less pinching hysteresis behavior. The debonding of CFRP strips in one of specimens showed that the penetration depth of CFRP strips into the core should be increased to avoid this phenomenon. In addition, the anchorage method of the added steel rebar inside the joint core worked well and forces were transferred to the column properly. © 2022 Institution of Structural Engineers
Kohrangi, M. ,
Safaei, H. ,
Danciu, L. ,
Tajmir riahi, H. ,
Ajalloeian, R. ,
Bazzurro, P. Publication Date: 2022
Bulletin of Earthquake Engineering (1570761X) 20(8)pp. 3623-3657
We present a seismic source characterization model for the probabilistic seismic hazard assessment (PSHA) of the Isfahan urban area, Iran. We compiled the required datasets including the earthquake catalogue and the geological and seismotectonic structure and faults systems within the study region to delineate and characterize seismic source models. We identified 7 relatively large zones that bound each region with similar seismotectonic characteristics and catalogue completeness periods. These regions were used for calculating the b-value of the Gutenberg–Richter magnitude recurrence relationship and for estimating the maximum magnitude value within each region. The earthquake recurrence parameters were then used to build a spatially varying distributed earthquake rate model using a smoothed kernel. Additionally, based on a fault database developed in this study and on a local expert’s opinion supported by tenable constraints about their slip velocity, a fault-based model is also created. We further performed sets of sensitivity analyses to find stable estimates of the ground motion intensity and to define alternative branches for both the seismogenic source and ground motion prediction models. Site amplification is considered based on a Vs30 map for Isfahan compiled within this study. The alternative source and ground motion prediction models considered in the logic tree are then implemented in the software OpenQuake to generate hazard maps and uniform hazard spectra for return periods of interest. Finally, we provide a detailed comparison of these PSHA outcomes with both those presented in the 2014 Earthquake Model of Middle East (EMME14) and with the national seismic design spectrum to further discuss the discrepancies between hazard estimates from site-specific and regional PSHA studies. © 2022, The Author(s), under exclusive licence to Springer Nature B.V.
Publication Date: 2021
Scientia Iranica (23453605) 28(1A)pp. 109-123
One of the most prevalent ground motion Intensity Measures (IMs) is the spectral acceleration at the fundamental period of a structure. Previous research has shown that vectorizing scalar IMs leads to a more reliable structural response, particularly in nonlinear regions and near collapse. Furthermore, the nonlinear behavior of ductile structures results in elongation of their "effective period". Therefore, this paper proposes a new approach to selecting ground motion records considering the effect of spectral shape and period elongation. This method contains two disaggregation analyses at the fundamental and elongated periods of the structure. Nonlinear dynamic analysis is conducted on a set of reinforced concrete moment-resisting frames designed based on ACI 318-05 as representatives of modern structures. Results show a considerable decrease in the median collapse prediction, margin against collapse, and dispersion of the structural response. The presented approach can ensure a better prediction of the vulnerability of structures to collapse. © 2021 Sharif University of Technology. All rights reserved.
Publication Date: 2021
Measurement: Journal of the International Measurement Confederation (02632241) 182
A video-based indirect sensing procedure for dynamic identification purposes is presented. To overcome major limitations of video-based methods in real on-site measurements, a novel three step pre-modification, magnification, post-modification process is developed. This process includes revision of the initial input video record in order to delete disturbing objects, utilizing a magnification method to filter the frequency content of the monitored motion and using a revision step for elimination of noises generated during magnification process. Finally, a set of digital signal and image processing analyses are performed on the modified video using virtual visual sensor technology. Based on the results of this research, motion signals of the monitored object are detected. The proposed approach has been used for identification of dynamic characteristics of two historic masonry minarets in Istanbul. Results shows that the proposed procedure is able to assess the dynamic characteristics of the monitored structure with a high-level of accuracy. © 2021 Elsevier Ltd
Publication Date: 2021
Journal of Thermoplastic Composite Materials (15307980) 34(1)pp. 68-101
This article examines the application of simplified Mindlin’s strain gradient theory to free vibration analysis of functionally graded carbon nanotube–reinforced composite (FG-CNTRC) thick rectangular nanoplates resting on Kerr elastic foundation in thermal environment. The theory contains only one length scale parameter corresponding to strain gradient effects. Also, a quasi-3D hyperbolic theory considering transverse shear deformation and thickness stretching effects is employed to present the formulation. In this study, properties of the carbon nanotubes (CNTs) and the polymeric matrix are assumed to be temperature dependent. Distribution of CNTs across the thickness of the nanoplate is considered to be uniform (UD) or functionally graded (FG-X, FG-V, and FG-O). According to Hamilton’s principle and the generalized differential quadrature method, the governing equations and associated boundary conditions are obtained and discretized, respectively. The natural frequencies of FG-CNTRC nanoplates are determined by solving eigenvalue problem. The numerical results of the present formulation are compared with those available in the literature to explain the accuracy of the suggested theories. Then, parametric studies are presented to examine the effects of elastic foundation coefficients, size parameter, temperature change, volume fraction and dispersion profile of CNTs, aspect ratio, length-to-thickness ratio, and different boundary conditions on vibration behavior of FG-CNTRC nanoplates. The results confirmed that size parameter and changes in temperature play an important role in determining natural frequencies. In addition, the shear layer parameter of Kerr foundation has more influence with respect to the coefficients of the upper and lower layers. © The Author(s) 2019.
Publication Date: 2020
JVC/Journal of Vibration and Control (10775463) 26(5-6)pp. 277-305
This paper investigates the buckling and free vibration analysis of functionally graded carbon nanotube-reinforced composite thick rectangular nanoplates resting on a Kerr foundation under different boundary conditions. Quasi-three-dimensional hyperbolic shear deformation theory is employed to study the effects of transverse shear deformation and thickness stretching. To capture the small-size effects of nanoscale dimensions, the nonlocal strain gradient theory is used, which includes nonlocal parameters and length scale of the material. In this study, rectangular nanocomposite plates are reinforced by carbon nanotubes which are assumed to be graded through the thickness direction with four types of distributions, namely, uniformly, FG-O, FG-V, and FG-X. The governing equations and boundary conditions are extracted within Hamilton’s principle. They are discretized and numerically solved by utilizing a generalized differential quadrature method. The critical buckling loads and natural frequencies are determined by solving the eigenvalue problem. The accuracy of present results is validated with those available in the literature. Also, the effect of various factors, such as aspect ratio, length-to-thickness ratio, in-plane loading factor, length scale parameter, nonlocal parameter, volume fraction and dispersion profile of carbon nanotubes, elastic foundation coefficients, and different boundary conditions, on the buckling behavior and free vibration of nanoplates is investigated. © The Author(s) 2019.
Publication Date: 2020
Amirkabir Journal of Civil Engineering (2588297X) 52(3)pp. 581-600
In this paper, numerical analysis of the hybrid lead rubber bearing system with shape memory alloy was investigated by the finite element method using ABAQUS software and the effectiveness of various parameters on its performance was examined. The studied parameters were the bearing dimensions, type of shape memory alloy and its cross-sectional area, the lead core diameter, the thickness of rubber layers and the compressive stress applied on the bearing. In this hybrid bearing, shape memory alloy wires were used as a recovery unit and lead core was used as a unit for energy dissipation. For this purpose, a finite element model of the bearing was modeled using the Abaqus software and the effect of the various parameters mentioned on the bearing performance has been investigated. The results showed that this hybrid bearing has better seismic performance than lead rubber bearing. Finally, depending on what kind of performance is required from the bearing, its specifications can be obtained optimally. © 2020, Amirkabir University of Technology. All rights reserved.
Publication Date: 2020
Smart Structures and Systems (17381584) 25(5)pp. 515-530
A new type of pure torsional yielding damper made from steel pipe is proposed and introduced. The damper uses a special mechanism to apply force and therefore applies pure torsion in the damper. Uniform distribution of the shear stress caused by pure torsion resulting in widespread yielding along pipe and consequently dissipating a large amount of energy. The behavior of the damper is investigated analytically and the governing relations are derived. To examine the performance of the proposed damper, four types of the damper are experimentally tested. The results of the tests show the behavior of the system as stable and satisfactory. The behavior characteristics include initial stiffness, yielding load, yielding deformation, and dissipated energy in a cycle of hysteretic behavior. The tests results were compared with the numerical analysis and the derived analytical relations outputs. The comparison shows an acceptable and precise approximation by the analytical outputs for estimation of the proposed damper behavior. Therefore, the relations may be applied to design the braced frame system equipped by the pure torsional yielding damper. An analytical model based on analytical relationships was developed and verified. This model can be used to simulate cyclic behavior of the proposed damper in the dynamic analysis of the structures equipped with the proposed damper. A numerical study was conducted on the performance of an assumed frame with/without proposed damper. Dynamic analysis of the assumed frames for seven earthquake records demonstrate that, equipping moment-resisting frames with the proposed dampers decreases the maximum story drift of these frames with an average reduction of about 50%. © 2020 Techno-Press, Ltd. http:/www.techno-press.org/?journal=sss&subpage=7
Publication Date: 2020
Structures (23520124) 25pp. 256-267
K-shaped bracing is one of the lateral load resisting systems used in Cold-Formed Steel structures. Recently, some researches have been conducted to obtain further information about the seismic performance of the CFS using K-shaped bracings under monotonic and cyclic loads. In this research, the seismic performance factor of this structural system is under study. To determine the proper value of this factor, a non-linear finite element model of this structural system is developed using OpenSees software, and the cyclic behavior of this model is verified with previous experimental results. Several structures designed in accordance with Iranian seismic code were modeled using the verified model, and incremental dynamic analysis is performed on these structures. The analysis was performed according to FEMA P695 procedures using a ground motion set consisting of 22 earthquake records. Eventually, the studies showed that the seismic performance factor of 2 is a proper value for the cold-formed steel frames with K-shaped bracings. Also, as another result, the increase in the number of stories and the site's seismic risk will increase the structure's collapse probability. Furthermore, the height limitation proposed by seismic codes for this system seems to be somewhat conservative and it can be concluded that usage of the K-shaped bracing system is possible for taller structures in zones with low seismicity risk. Finally, it can be concluded that the K-shaped bracings might not have a suitable performance due to ductility issues. © 2020 Institution of Structural Engineers
Publication Date: 2020
Structural Design of Tall and Special Buildings (15417808) 29(16)
Steel braces reduce the interstory drifts of steel structures under earthquake excitations; however, severe earthquakes could still cause some notable residual drifts in the structures. The reduction of these residual drifts decreases post-earthquake retrofitting costs. This study investigates the seismic performance of steel frames equipped with a proposed self-centering damper, using shape-memory alloy (SMA) wires. For this purpose, incremental dynamic analyses are carried out on the steel frames of 3, 7, and 12 stories with self-centering dampers of different capacities. The results of cyclic tests validate damper numerical modeling. The results indicate that the proposed damper limits the residual drifts. Also, fragility curves illustrate that the damper reduces the exceedance probabilities of limit states associated with residual story drift. The comparison among three design cases demonstrates that the most appropriate capacity for SMA dampers happens when it obtains the average capacity value required for equality between damper stiffness and strength and braces stiffness and strength, respectively. This particular design will eventually lead to the most efficient scenario in cases of performance and cost. © 2020 John Wiley & Sons, Ltd.
Publication Date: 2020
Earthquake and Structures (20927614) 18(2)pp. 215-222
In this paper: slit steel rubber bearing is presented as an umovative seismic isolator device. In this type of isolator. slit steel damper is an energy dissipation device. Its advantages in comparison with that of the lead rubber bearing are its simplicity in manufacturing process and replacement of its yielding parts. Also, slit steel rubber bearing has the same ability to dissipate energy with smaller value of displacement. Using finite element method in ABAQUS software, a parametric study is done on the performance of this bearing. Three different kinds of isolator with three different values of strut width, 9, 12 and 15 mm, three values of thickness, 4, 6 and 8 mm and two steel types with different yield stress are assessed. Effects of these parameters on the performance characteristics of slit steel rubber bearing are studied. It is shown that by decreasing the thickness and strut width and by selecting the material with lower yield stress, values of effective stiffness, energy dissipation capacity and lateral force in the isolator reduce but equivalent viscous damping is not affected significantly. Thus, by choosing approprilate values for thickness, strut width and slit steel damper yield stress, an isolator with the desired behavior can be achieved. Finally, performance of an 8-storey frame with the proposed isolator is compared with the same frame equipped with LRB. Results show that SSRB is successful in base shear reduction of structure in a different way from LRB. © 2020 Techno-Press, Ltd.
Publication Date: 2019
International Journal of Steel Structures (20936311) 19(3)pp. 747-759
Using the perforated yielding shear plates as an energy dissipated device instead of lead core in rubber bearing is assessed in this paper. The advantage of this innovative isolator compared to lead rubber bearing is the ability of being replaced easily and its less displacement with high ability of energy dissipation. Three different isolators with perforated shear plates with hole cross-section of 15%, 18%, and 33% of cross-sectional of plate surface area are investigated. Three types of shear plates of 2, 3 and 4 mm thicknesses made of two types of steel with different yield stress are assessed. By decreasing the shear plate thickness and increasing the number of the plate holes and selecting the shear plate with lower yield stress, the effective stiffness and the amount of energy dissipation and lateral force in the isolator are reduced. Changing shear plate thickness and number of holes do not affect the viscous damping, while increasing the plate yield stress increases viscous damping. Therefore the choice of the shear plate with appropriate thickness, number of holes and plate yield stress can lead to an isolator with acceptable behavior. The suggested isolator can achieve similar characteristics of lead rubber bearing at 50% shear strain and therefore its design basics should be defined differently rather than lead rubber bearing. © 2018, Korean Society of Steel Construction.
Publication Date: 2019
Journal of Constructional Steel Research (0143974X) 161pp. 385-399
A new yielding damper with pure torsional mechanism is introduced and investigated in this paper. Story shear force is transferred to the proposed device using special details to produce pure torsion without shear force and bending moment in the damper pipes. Hence, energy dissipation capacity of damper material could be efficiently used. Some relationships for structural characteristics of the proposed damper including initial stiffness, yielding and ultimate strength and load-displacement relation, are derived analytically. This is done by assuming a bi-linear curve for steel material considering its strain hardening. Ten specimens of this pure torsional damper were tested under cyclic loading. The hysteresis curves indicate a stable and well-shaped cyclic behavior. Results also show high energy absorption capacity and ductility for this damper. Widespread yielding and uniform stress distribution across the entire thickness of the pipe wall of the damper results in high equivalent viscous damping ratio from 38% to 48%. The structural characteristics of the tested specimens were compared with analytical relationships. In addition, a parametric study was conducted based on the analytical equations. © 2019 Elsevier Ltd
Publication Date: 2019
JVC/Journal of Vibration and Control (10775463) 25(9)pp. 1558-1571
A new hybrid isolator consisting of elastomeric bearing, sliding parts and yielding dampers named friction–yielding–elastomeric bearing (FYEB) is proposed. In this hybrid isolator, the friction–yielding part has an energy absorption feature, where the rubber pad has re-centering and vertical bearing capacity. For this purpose, an X-shaped metal damper with different number and thickness, and sliding surfaces with different friction coefficients is applied and the effect of vertical load variations on the results is assessed. Using the hysteresis force-displacement diagrams of different FYEB and lead rubber bearing (LRB) with the same dimensions at shear strains of 50, 100, and 150%, effective horizontal stiffness, energy dissipation, equivalent viscous damping, and lateral force at each loading cycle are assessed and compared. It can be concluded that the proposed isolator has a more suitable and stable performance at all shear strains than LRB. In addition, by changing FYEB parameters, a wide range of performance can be achieved. © The Author(s) 2019.
Publication Date: 2018
International Journal Of Civil Engineering (17350522) 16(11)pp. 1643-1653
In this paper, the seismic performance of cold formed steel shear walls sheathed by fiber cement boards (FCB) is investigated. Of particular interest is the seismic response modification factor of FCB shear walls. Nonlinear incremental dynamic analyses of multi-story cold formed steel framed structures were carried out following an approach adopted by FEMA-P695 on the description of building seismic behavior. Different scaled earthquake records in three different earthquake prone regions located on low, medium and high seismic risk zones in Iran were taken into account. One, two and three story CFS archetype buildings were analyzed using models created in OpenSees software to predict structural performance of the buildings. Nonlinear dynamic time history analyses were carried out employing OpenSees software utilizing 2D models of a FCB braced wall tower. A stick model was created whose behavior was fitted to the lateral resistance versus deformation of each story that braced elements in the model. The elements were defined via material Pinching4 to construct a uniaxial material exhibiting pinched load-deformation response and demonstrate degradation under cyclic loading. The results show that most relevant codes which suggest the value of seismic response modification factor equal to 2 for cold formed steel shear walls sheathed by FCB are acceptable only for up to three story buildings in low seismic risk zone, up to two story in medium seismic zone and one story in high seismic risk zone. © 2018, Iran University of Science and Technology.
Publication Date: 2015
Scientia Iranica (23453605) 22(1)pp. 92-106
Developing the concept of performance based analysis and design has made nonlinear dynamic analysis an efficient method for quantification of the seismic response of structures. Generally, this analysis is done utilizing accelerograms, which are ground motions obtained from earthquakes. This research is focused on assessing the seismic structural response of a comprehensive set of reinforced concrete moment resisting frames under excitation of real accelerograms and ground motions that are spectrally matched to a target spectrum. The matching process is conducted in the time domain, and the ASCE 7-05 spectrum is used as the target spectrum. Comparisons are provided for a number of ground motion parameters and the effect of spectrum matching has been investigated. Additionally, the variation of structural response and the degree of compatibility and conservation of real and spectrally matched ground motions have been extensively discussed. It is shown that spectrum compatibilization effectively decreases the variation of structural response. However, the measure of observed bias thoroughly depends on the height of the structure. Finally, fragility curves of structural performance are provided and it is indicated that consideration of modeling uncertainties results in obtaining a fragility curve with reasonable resemblance to that obtained from real ground motions. © 2015 Sharif University of Technology. All rights reserved.
Publication Date: 2015
Soil Dynamics and Earthquake Engineering (02677261) 78pp. 46-60
During strong earthquakes, adjacent structures with non-sufficient clear distances collide with each other. In addition to such a pounding, cross interaction of adjacent structures through soil can exchange the vibration energy between buildings and make the problem even more complex. In this paper, effects of both of the mentioned phenomena on the inelastic response of selected steel structures are studied. Number of stories varied between 3 and 12 and different clear distances up to the seismic codes prescribed value are considered. The pounding element is modeled within Opensees. A coupled model of springs and dashpots is utilized for through-the-soil interaction of the adjacent structures, for two types of soft soils. The pounding force, relative displacements of stories, story shears, and plastic hinge rotations are compared for different conditions as the maximum responses averaged between seven consistent earthquakes. As a result, simultaneous effects of pounding and structure-soil-structure interaction are discussed. © 2015 Elsevier Ltd.
Publication Date: 2015
International Journal Of Civil Engineering (17350522) 13(1)pp. 112-125
Incremental launching is a widespread bridge erection technique which may offer many advantages for bridge designers. Since internal forces of deck vary perpetually during construction stages, simulation and modeling of the bridge behavior, for each step of launching, are tedious and time consuming tasks. The problem becomes much more complicated in construction progression. Considering other load cases such as support settlements or temperature effects makes the problem more intricate. Therefore, modeling of construction stages entails a reliable, simple, economical and fast algorithmic solution. In this paper, a new Finite Element (FE) model for study on static behavior of bridges during launching is presented. Also a simple method is introduced to normalize all quantities in the problem. The new FE model eliminates many limitations of some previous models. To exemplify, the present model is capable to simulate all the stages of launching, yet some conventional models of launching are insufficient for them. The problem roots from the main assumptions considered to develop these models. Nevertheless, by using the results of the present FE model, some solutions are presented to improve accuracy of the conventional models for the initial stages. It is shown that first span of the bridge plays a very important role for initial stages; it was eliminated in most researches. Also a new simple model is developed named as "semi infinite beam" model. By using the developed model with a simple optimization approach, some optimal values for launching nose specifications are obtained. The study may be suitable for practical usages and also useful for optimizing the nose-deck system of incrementally launched bridges. © 2015, Iran University of Science and Technology. All right reserved.
Publication Date: 2015
Proceedings of the Institution of Civil Engineers: Structures and Buildings (09650911) 168(8)pp. 578-592
The capability of endurance time analysis as an appropriate tool in performance-based earthquake engineering is assessed in this paper. Seismic performance of a comprehensive database of reinforced concrete moment-resisting frames is studied using endurance time and time history analysis. Ground motions used in this study are spectrally matched to the design spectrum which was used for the generation of the input motions of endurance time analysis. This matching facilitates the comparison of the results of two methods at different seismic hazard levels. Comparisons are done for different engineering demand parameters and the pros and cons of the endurance time method are discussed. The endurance time method is shown to provide an estimate of maximum inter-storey drift ratio, roof displacement and plastic hinge rotations that is very close to the results of time history analysis. This method can also correctly predict the distribution of displacement and lateral forces over all storeys. Results are compared with the results of pushover analysis, and the endurance time analysis results are found to be more compatible with the results of time history analysis. In addition, in most frames, the coefficient of variation of engineering demand parameters is less for endurance time analysis than for time history analysis. Results show that input motions of the endurance time method, generated based on a design response spectrum, can be used to assess frames at different seismic hazard levels correctly. © 2015, Thomas Telford Services Ltd.
Publication Date: 2015
Structural Design of Tall and Special Buildings (15417808) 24(4)pp. 300-315
In this paper, seismic collapse of reinforced concrete moment frames is assessed using endurance time (ET) analysis. A set of 30 frames that incorporate deterioration of concrete components is used for this assessment. Application of ET method for collapse assessment of structures is explained, and its accuracy for this purpose is evaluated by comparing its results with incremental dynamic analysis results. Input motions for ET analysis are generated based on ASCE7-05 design spectrum, and also accelerograms used for incremental dynamic analysis are spectrally matched to the same spectrum. Distribution of different engineering demand parameters over frames height and their values at collapse occurrence are compared for two methods. Results show that spectral accelerations in which collapse occurs in both analyses are very similar for most of the frames, and ET method can appropriately predict the collapse mechanisms of the structures especially for taller frames. Accuracy of ET method in collapse assessment of reinforced concrete moment frames is satisfactory, and this method can be used as a good estimator for study of collapse mechanisms with much less computational effort. Copyright © 2014 John Wiley & Sons, Ltd.
Publication Date: 2014
2025 29th International Computer Conference, Computer Society of Iran, CSICC 2025
The strength of an earthquake ground motion is usually quantified by an Intensity Measure (IM). This IM is used to predict the response of a structure. Traditionally scalar intensity measures were used for selecting ground motions and exerting them on structure but vector valued intensity measures consist of spectral acceleration and epsilon tend to show more reliable responses for nonlinear analysis. Epsilon as the index of spectral shape is an innovative approach that was developed by Baker and colleagues. This index (defined as the measure of the difference between the spectral acceleration of a record and the mean of a ground motion prediction equation at the given period) tries to refine ground motions in order to obtain comparable responses. The complete dependence of this index in the given period makes some ambiguities in response of the structure in nonlinear region. Therefore the focus of this research is on selecting ground motions in accordance with obtained target epsilon from disaggregation analysis in the first step. Since period elongation alters the period of structures, another disaggregation analysis was performed and an alternate set of ground motions based on new period and target epsilon was selected. Finally a nonlinear time history analysis was performed for new parameters. A set of reinforced concrete four story three bay moment resisting frames that were designed based on ACI 318-05 was used. Nonlinear characteristics of Ibarra model were considered in these frames in order to obtain the most realistic results. These ground motions are selected based on a spectral shape index and exerted on frames using OpenSees. It is shown that period elongation has considerable effect on spectral shape and consequently the response of the structure will alter.
Publication Date: 2013
2025 29th International Computer Conference, Computer Society of Iran, CSICC 2025 2(January)pp. 1637-1646
Most recent seismic codes include response modification factor in the definition of equivalent lateral forces that are used for the design of earthquake resistant buildings. The response modification factor, used to reduce the linear elastic design spectrum to account for energy dissipation capacity of structure, is the central feature of force-based seismic design. The main goal of this paper is the assessment of Endurance Time (ET) method results accuracy in the evaluation of response modification factors and estimation of strength and stiffness deterioration effects on them according to frame performance evaluation. To reach this goal a sample set of steel moment-resisting frames (3, 7 and 12-story) are designed and ET results are compared to Incremental Dynamic Analysis (IDA) ones as an evaluation base. In order to model deteriorating connections, frames are also modeled using concentrated plastic springs. ET analysis is a new dynamic pushover procedure in which structures are subjected to gradually intensifying acceleration functions and their performances are assessed based on their responses. It is observed that although the results of ET analysis are not exactly consistent with the results of IDA, the ET analysis can reasonably assess the response modification factors and strength and stiffness effects in most cases. Also, considering the great amount of computational efforts that should be done for evaluating response modification factors and the effects of strength and stiffness on them by IDA analysis, ET analysis can evaluate them and the performances of structures with less analysis.
Publication Date: 2011
Procedia Engineering (18777058) 14pp. 3237-3244
In Endurance Time (ET) method gradually intensifying acceleration functions are created in a manner that the linear and nonlinear response spectra of them, while being proportional to average of real earthquakes spectra, intensifies in a uniform manner with time. These functions are used as input functions for nonlinear time history analysis of structures and performance of structures is assessed based on the maximum time duration that they can meet the specified performance objectives. In this paper, application of the ET method in nonlinear seismic analysis of structures has been investigated. Numerical procedures and optimization techniques that are used for the production of acceleration functions are described. A set of three acceleration functions have been applied to various steel moment frames and the results of analysis are compared to the results of IDA analyses. ET results of different frames approved that this method can be a good instrument to estimate IDA results with reasonably good accuracy using a few number of time history analyses. It is proved that this method can be used in nonlinear analysis of structures as a powerful tool but more research in this area is required before ET method can be recommended for practical applications. Selection.
Publication Date: 2011
Engineering Structures (18737323) 33(9)pp. 2535-2546
In this paper, application of a new dynamic procedure called Endurance Time (ET) method in seismic analysis of steel frames is explained. In this method, structures are subjected to gradually intensifying ground shaking and their performance is assessed based on their response considering relevant design criteria at each intensity level. By considerably reducing the number of time history analyses for assessment of structural response at different intensities, this procedure tends to pave a way for practical performance based design of structures. The accuracy of ET method in predicting the response of structures in linear and nonlinear analysis is investigated by considering a set of steel frames. Different material models consisting of elastic-perfectly plastic, stiffness degrading and strength deteriorating models are considered. Application of ET method in assessment of frames that incorporate fluid viscous dampers as seismic mitigation devices is also demonstrated. It is shown that ET analysis can estimate the results of full response history analysis with reasonable accuracy at different excitation levels. ET analysis results are also shown to be reasonably consistent for different material models. Specific issues that should be considered for a successful ET analysis, including the potential loss of accuracy at highly nonlinear excitation levels are discussed. Capability of ET method in predicting collapse capacity of the studied frames is discussed. © 2011 Elsevier Ltd.
Publication Date: 2010
Journal of Constructional Steel Research (0143974X) 66(6)pp. 780-792
In the endurance time (ET) method, structures are subjected to a specially designed intensifying ground acceleration function and their performance is judged based on their response at various excitation levels. A range of equivalent intensities can be covered in a single numerical or experimental simulation, thus significantly reducing the computational demand as compared to full nonlinear response-history analyses. The applied excitation intensity at various times has been correlated with those of the scaled ground motions. Response spectra of seven ground motions on stiff soil were used to produce intensifying acceleration functions that at each time window produce a response spectrum that is compatible with the template spectrum and proportionally scale up with time. The drift ratios and plastic hinge rotations compare well with those from ground motions in steel frames with various numbers of stories and bays. The locations of plastic hinges are also predicted quite satisfactorily by ET analysis. The sensitivity of the results to the selection of a particular set of ground motions is also studied. © 2009 Elsevier Ltd. All rights reserved.
Publication Date: 2009
Journal of Applied Sciences (discontinued) (18125654) 9(10)pp. 1817-1832
Endurance Time (ET) method has been introduced as a lime-history based dynamic analysis procedure. In this method, structures are subjected to a gradually intensifying acceleration function. Performance of the structures is assessed based on the length of the time interval that they can satisfy required performance objectives. In this study, some fundamental concepts of ET method are explained and the potentials and limitations of this procedure in nonlinear seismic analysis of SDOF structures are investigated. A numerical optimization procedure for generating ET acceleration functions that are compatible with ground motions are explained. Results of ET analysis for inelastic SDOF systems are compared with ground motions analysis results for different strength ratios, ductilities and damping ratios. The accuracy of ET method in predicting the response of SDOF systems with stiffness degradation and strength deterioration is also investigated application of ET method in performance based earthquake engineering is described by an example of a single degree of freedom system. The results show that the approximations of ET method are in good agreement with the exact response history results of the similar ground motions for different nonlinear systems. It is shown that ET acceleration functions optimized in linear range considering long periods can be used in nonlinear analysis with reasonable accuracy. © 2009 Asian Network for Scientific Information.
Publication Date: 2009
Asian Journal Of Civil Engineering (15630854) 10(5)pp. 559-577
Endurance Time (ET) method is a new dynamic analysis procedure that aims at estimating seismic performance of structures by subjecting them to predesigned intensifying acceleration. These acceleration functions are designed in a way that they approximately simulate earthquakes with different intensities through their duration. Performance of the structure is judged based on its behavior for different intensity measures through time. A set of three acceleration functions have been produced using the ET concept by applying optimization techniques. These acceleration functions are designed in such a way that their response spectrum, while complying with typical code design spectra, intensify uniformly with their duration. Potential applications of this method are described by evaluating the performance of sample SDOF and MDOF systems. The pros and cons of ET method are investigated. The feasibility of application of ET method as a tool in performance based seismic analysis and design is discussed.
Publication Date: 2009
Scientia Iranica (23453605) 16(5 A)pp. 388-402
The Endurance Time (ET) method is a new dynamic pushover procedure in which structures are subjected to gradually intensifying acceleration functions and their performance is assessed based on the length of the time interval that they can satisfy required performance objectives. In this paper, the accuracy of the Endurance Time method in estimating average deformation demands of low and medium rise steel frames using ETASOf series of ET acceleration functions has been investigated. The precision of the ET method in predicting the response of steel frames in nonlinear analysis is investigated by considering a simple set of moment-resisting frames. An elastic-perfectly-plastic material model and a bilinear material model with a post-yield stiffness equal to 3% of the initial elastic stiffness have been considered. For frames with an elastic-perfectly- plastic material model, which are P - Δ sensitive cases, the ET analysis for the maximum interstory drift ratio somewhat underestimates the nonlinear response history analysis results. The difference between the results of the ET analysis and the nonlinear response history analysis for the material model with 3% post-yield stiffness is acceptable. The consistency of the base shears obtained by the two methods is also satisfactory. It is shown that, although the results of the ET analysis are not exactly consistent with the results of ground motions analysis, the ET method can clearly identify the structure with a better performance even in the case of structures with a relatively complicated nonlinear behavior. © Sharif University of Technology, October 2009.
Publication Date: 2006
5pp. 331-338
During construction of one of the Sahand cooling towers due to slip forming performance some imperfections were raised mostly between elevation of +30 and +40 meter. It was evaluated that some points of the shell should be repaired. In constructing the cooling tower from elevation +40 to +60 meter these imperfections were removed and the cooling tower was constructed with no problem until the elevation +130 meter. In this paper reasons of generation of geometric imperfections in Sahand cooling tower are clearly shown and possible ways for preventing them are discussed. Applied repairing method for Sahand cooling tower is explained in detail. Geometrical imperfections of the constructed cooling tower are measured using photogrammetric techniques. The detailed three dimensional models for both perfect and imperfect cooling towers are made using finite element method. Different analyses for different loading of such structures are done and the results are compared. For the cooling tower with imperfections the wind load is applied in 12 directions around the circumference of it so that the effects of imperfections can be seen well. Critical buckling load factors are obtained for both models by linear and nonlinear analysis. The results of analysis of imperfect cooling tower shell are used for checking the design of it. Results show that the maximum values for circumferential and vertical stresses are appeared between level +30 to +40. The increase of circumferential stress is usually more than increase of vertical stresses. This high increase appears locally in some parts of cooling tower shell. The difference of displacements in cooling tower shell in two models is negligible. The critical buckling safety factor of the imperfect model is greater than the perfect one. There is not a large difference between the values of this factor for different wind load directions. © 2006 by School of Engineering and Technology, Asian Institute of Technology.
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