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Publication Date: 2024
International Journal of Structural Stability and Dynamics (2194554) 25
Proper modeling of the dynamic behavior of the soil significantly affects the accuracy of the soil-structure interaction analysis results. Using nonlinear constitutive models has the highest accuracy in modeling soil behavior under earthquake loading. However, it is not functional for practical engineering purposes because of the high cost and complexity. The equivalent linear method also has many limitations, such as filtering out the high-frequency components of the input excitation, underestimating surface ground motion over long periods, and considerable error in high soil strain levels. The current study aims to present an accurate, simple, and low-cost method to model the nonlinear behavior of clays. This method does not meet the limitations of the traditional methods and fully considers the effect of the influential parameters. The novel central composite design technique was adopted to evaluate the effect of influential variables on the nonlinear behavior of clay and formulate the proposed method. The introduced method is applicable to various building structures, power planets, etc. Numerical analyses performed on the proposed method and nonlinear modeling confirm the accuracy, efficiency, and generality of the proposed method. © 2025 World Scientific Publishing Company.
Publication Date: 2024
Geomechanics and Engineering (20926219) 39(2)pp. 115-129
The present paper aimed to estimate the ground surface settlement induced by excavated circular tunnel in soft soils, taking into account the uncertainties of geometric and geotechnical parameters. To this end, following two-dimensional numerical simulation of the tunnel based on finite difference method in FLAC2D, the ground surface settlement profiles were determined using regression analysis (Gaussian equation). The effect of changes in tunnel geometric parameters (including buried depth C, diameter D and depth distance H of tunnel) and soil geotechnical properties (including modulus of elasticity E, undrained shear strength Su and density γ) based on three dimensionless ratios named depth ratio (C/D), soil strength ratio (γD/Su) and the soil stiffness ratio (E/Su) were studied on the ground surface settlement. The results showed that there is a relationship in the form of Smax/H = f (γD/Su, E/Su, C/D) between the parameters to determine the normalized ground surface settlement induced by tunnel. Therefore, using the gene expression programming (GEP) algorithm and forming a database containing 1000 different simulations in terms of a combination of C/D, γD/Su changes for fixed E/Su ratios (inputs) and Smax/H results (outputs), two powerful empirical equations were proposed as new empirical models to estimate the normalized maximum ground surface settlement. © 2024 Techno-Press, Ltd.
Publication Date: 2022
Iranian Journal Of Science And Technology, Transactions Of Civil Engineering (22286160) 46(1)pp. 157-167
Ordinary buckling-restrained braces have a single-yielding core. A buckling-restrained brace (BRB) with three parallel yielding cores and different yield strengths is, however, introduced in this paper that will expectedly exhibit an improved seismic behavior. The new BRB was constructed using three-yielding steel cores with the different yield strengths of 180, 240, and 360 MPa to be subjected to experimental tests of cyclic axial loading in accordance with the ATC-24 loading protocol. The results obtained were subsequently compared with those obtained for equivalent single-core BRBs. The three-core brace was observed to yield an area of hysteresis loops/dissipated energy considerably larger than that produced by the equivalent single-core BRB. Moreover, the cores with lower yield strengths tended not only to yield sooner but also to dissipate the input energy, while those with higher yield strengths limited both the story drift and the chances of a structural collapse. Finally, the three-core BRBs recorded energy absorption rates and damping ratios by 16.3% and 8.8%, respectively, higher than these of the single-core brace. © 2021, Shiraz University.
Publication Date: 2022
Iranian Journal Of Science And Technology, Transactions Of Civil Engineering (22286160) 46(1)
In light of the vast potential for the application of modern energy absorption systems in the structures, the effectiveness of each system should be tested, analyzed, and proved before convincing the structures design companies to use them. In this research, the effectiveness of applying base isolators, viscous and friction dampers and a hybrid system consisted of lead rubber bearing with friction dampers are studied. To quantify the impact of each system, a control structure without any energy absorption system is considered. Base isolators and damper systems are designed according to available international codes. American concrete institute’s codes were used to design the concrete structure frames. All of the considered systems therewith hybrid systems including lead rubber base isolation and viscous dampers have been modeled in ETABS 2018 software. The control structure has an intermediate moment resisting frame with high importance located in a high seismic hazard zone. These models were subjected to time history analysis by using Manjil, Loma prieta, and Imperial Valley Earthquakes records. It was observed that the structural design parameters such as base shears and story drifts were significantly reduced by 76–86% and 44–92%, respectively, compared to the structure without any energy absorption system. Also, the total energy dissipated in the structures equipped with modern energy absorption systems was decreased between 32 and 86% compared to the friction dampers. It should be noted that the studied devices may be used either for the design of a new structure or seismic rehabilitation of the existing structures. © 2021, Shiraz University.
Publication Date: 2021
Amirkabir Journal of Civil Engineering (2588297X) 53(1)pp. 21-34
In this study, by the concept of control structures, a new shell configuration is designed for steel energy dissipative devices. This device is proposed for the protection of structures against earthquake forces. This device is named a nested-eccentric-shells damper (NESD). This damper is made of a large cylindrical shell that surrounded three small cylindrical shells. The conventional methods of welding or metal casting can be applied in constructing the NESD. The configuration of the shell-type components is designed in such a way that to be able as a combination of series and parallel springs. To assess the performance of this damper, numerical analysis, and full-scale testing are applied. Hysteretic loops obtained from the analysis with highly ductile performance are applied to determine the behavior of this proposed damper. The results indicate that the nested-eccentric-shells damper is of a stable behavior in hysteretic loops, and can provide appropriate damped energy subject to cyclic loading. However, to improve the performance and interaction of the internal members of this damper, a thickness ratio modification is proposed for the inner shells. The effectiveness and the usefulness of this modification in the numerical analysis have been proven in this study. © 2021, Amirkabir University of Technology. All rights reserved.
Publication Date: 2020
Earthquake and Structures (20927614) 18(5)pp. 637-648
In this study, a new steel cylindrical shell configuration of the dissipative energy device is proposed to improve lateral ductility and to reduce the damage of the structures against seismic forces. Four nested-eccentric-cylindrical shells are used to constructing this device; therefore, this proposed device is named nested-eccentric-cylindrical shells damper (NECSD). The particular configuration of the nested-eccentric-cylindrical shells is applied to promote the mechanical characteristics, stability, and overall performance of the damper in cyclic loads. Shell-type components are performed as a combination of series and parallel non-linear springs into the in-plan plastic deformation. Numerical analysis with respect to dimensional variables are used to calculate the mechanical characteristics of the NECSD, and full-scale testing is conducted for verifying the numerical results. The parametric study shows the NECSD with thin shells were more flexible, while devices with thick shells were more capacious. The results from numerical and experimental studies indicate that the NECSD has a stable behavior in hysteretic loops with highly ductile performance, and can provide appropriate dissipated energy under cyclic loads. © 2020 Techno-Press, Ltd.
Publication Date: 2019
Iranian Journal Of Science And Technology, Transactions Of Civil Engineering (22286160) 43(4)pp. 835-849
Seismic waves propagate from bedrock through the soil layers and during this propagation they pass different layers of soil and rock until they reach the soil surface. These waves can be amplified or damped by the soil layers. Underground structures response, like tunnels, is related to a number of factors such as soil type and earthquake frequency. In this paper the simulation of the models is done in two-dimensional plain strain system with finite element mesh generation which consists of soil–tunnel using frequency spectrum analysis. All analyses consist of three actual ground motion records with low, intermediate and high-frequency content. Two different clay soils (Normally or Lightly Over-Consolidate Clay and Heavily Over-Consolidate Clay) have been used in free field and models consist of cylindrical tunnel. In this study, the results of both free field (models without structure) and soil–tunnel analysis have been compared to show the effect of the tunnel on responses. Effect of soil–tunnel interaction in all earthquakes with different frequency content on-site response, amplification, acceleration response and stress and strain propagation in the tunnel’s perimeter are discussed. Based on the results of the analysis, acceleration frequency at different depths of models had different characteristics. Both clay soils amplified seismic waves on the soil surface in free filled models and the soil–structure interaction effects on the tunnel dynamic responses. © 2018, Shiraz University.
Publication Date: 2018
Transportation Geotechnics (22143912) 14pp. 52-60
Highway construction and maintenance are usually expensive, and cost control efficiency is imperative. Although there are several stabilization methods, soil stabilization with agricultural waste materials, such as rice husk ash (RHA), is among the most eco-friendly and affordable methods. The aim of this study is to experimentally investigate the effects of adding RHA and ordinary Portland cement on the geotechnical properties of the clayey sand sampled from the Sejzi area, which lies east of the city of Isfahan, Iran. First, the oxide compounds of RHA, cement, and soil were determined using the X-ray fluorescence (XRF) test. Five different compounds of the soil with 2, 4, 6, and 8% of cement were mixed, and, later, different percentages of RHA (0, 2, 4, 6, and 8%) were added to determine the unconfined compressive strength (UCS), California bearing ratio (CBR), optimum moisture content (ωopt), and maximum dry density (γd) of the stabilized soil compounds with 7, 14, and 28 curing days. The results showed that by increasing the content of RHA, the ωopt of the specimens increased, while the γd decreased. The 28-day-cured specimen with 6% RHA and 8% cement showed the highest values of UCS and CBR at 25.44 and 18.2 times more than those of the values for untreated soil, respectively. The scanning electron micrograph (SEM) test of the aforementioned stabilized soil was characterized as a well-structured soil matrix with very small pores, which can be attributed to the pozzolanic reactions of the cement and RHA. The effectiveness, abundance, and the low cost of RHA will attract considerable environmental interest in this research. © 2017 Elsevier Ltd
Publication Date: 2016
Mires and Peat (1819754X) 18
To accommodate major civil engineering projects in or in the vicinity of peatlands, it is essential to stabilise peat deposits. On the other hand, the accumulation of waste tyres in recent decades has caused environmental problems around the world. An effective remedy for both issues is to use scrap tyre material to stabilise problematic peat soils. This article reports an experimental investigation of the effects of adding shredded tyre chips on the stability and bearing capacity of peat soil. Peat soil samples from the Chaghakhor Wetland (Chaharmahal and Bakhtiari Province, Iran) were mixed with sand at a constant dosage of 400 kg m-3 and different percentages (0%, 5%, 10%, 15% and 20% by weight) of shredded tyre chips. The unconfined compressive strength, effective cohesion, angle of internal friction and coefficient of permeability were measured for all of these mixtures. The results showed that adding shredded tyre chips significantly improved the geotechnical properties of the peat soil. The mixture with 10% shredded tyre chips showed the highest unconfined compressive strength; the one with 15% tyre chips exhibited the highest ductility; and adding 20% shredded tyre chips provided the highest values for angle of internal friction, effective cohesion and coefficient of permeability. Scanning Electron Micrographs (SEM) showed that the pore spaces in the stabilised peat were mostly filled with sand. © 2016 International Mire Conservation Group and International Peat Society.
Publication Date: 2016
Mires and Peat (1819754X) 18
Peat has a high content of water and organic substances. These weak components can cause low bearing capacity and high consolidation settlement under load, which means that peat deposits must usually be stabilised if they are to bear constructions such as buildings or roads. In this study we investigated the performance of waste tyre chips (10% by weight) and sand (400 kg m-3) supplemented with a pozzolanic binder (gypsum, lime or cement) at a range of dosages (5%, 10% or 15% by weight) as a stabiliser for peat soil. Peat samples were taken from a fen peatland at Chaghakhor Wetland in Chahar Mahal and Bakhtiari Province, Iran. In total, 162 test specimens were prepared and subjected to laboratory strength testing (unconfined compression test and direct shear test). Additionally, the pH of each admixture was recorded immediately after mixing, elemental compositions were determined by X-Ray Fluorescence (XRF), and structures were examined using Scanning Electron Microscopy (SEM). It was observed that: (1) the total percentage of pozzolanic compounds in the peat soil was well below the minimum of 70% set by the standard ASTM C 618 (ASTM 2000), so an additive such as cement, lime or gypsum would certainly be required; (2) specimens stabilised with gypsum or lime showed improvements in unconfined compressive strength (UCS), but those stabilised with ordinary Portland cement exhibited the greatest improvement in UCS (up to 12,200%) as well as improvements in the direct shear parameters c and φ; (3) according to the XRF tests, additives such as cement, lime and gypsum introduced considerable amounts of Si, Al, Ca and O, which are important for pozzolanic reactions in peat soils; and (4) on the basis of the results of UCS and direct shear tests, the optimum percentage of the additives tested would be 5%. © 2016 International Mire Conservation Group and International Peatland Society.
Publication Date: 2015
International Journal Of Civil Engineering (17350522) 13(3-4)pp. 213-225
The interactive effects of adjacent buildings on their seismic performance are not frequently considered in seismic design. The adjacent buildings, however, are interrelated through the soil during seismic ground motions. The seismic energy is redistributed in the neighboring buildings through multiple structure-soil-structure interactions (SSSI). For example, in an area congested with many nearby tall and/or heavy buildings, accounting for the proximity effects of the adjacent buildings is very important. To solve the problem of SSSI successfully, researchers indicate two main research areas where need the most attention: 1) accounting for soil nonlinearity in an efficient way, and 2) spatial analysis of full 3D soil-structure models. In the present study, three-dimensional finite element models of tall buildings on different flexible foundation soils are used to evaluate the extent of cross interaction of adjacent buildings. Soil nonlinearity under cyclic loading is accounted for by Equivalent Linear Method (ELM) as to conduct large parametric studies in the field of seismic soil-structure interaction, the application of ELM is preferred over other alternatives (such as application of complicated constitutive soil models) due to the efficiency and reliability of its results. 15 and 30 story steel structures with pile foundations on two sandy and clayey sites are designed according to modern codes and then subjected to several actual earthquake records scaled to represent the seismicity of the building sites. Results show the cross interaction of adjacent buildings on flexible soils, depending on their proximity, increases dynamic displacements of buildings and reduces their base shears. © 2015, Iran University of Science and Technology. All rights reserved.
Publication Date: 2015
Mires and Peat (1819754X) 16
Because peat has high organic content and high natural water content, it is potentially problematic for civil engineering projects involving construction on peatland. Therefore, it is important to understand the physical, chemical and geotechnical properties of the peat. The aim of the study reported here was to investigate the properties of two Iranian peat types. Peat and water samples were collected from sites within two extensive wetland areas (Chaghakhor Wetland and Gavkhuni Swamp) where construction works are planned. Both sites had peat layers more than three metres thick, which were sampled at depths of 0.6, 1.2, 1.8, 2.4 and 3.0 metres below ground level with four replicates per site. Degree of humification was determined in the field. Laboratory tests were conducted to determine the pH of water and peat; and the natural (field) moisture content, organic content, ash content, bulk density, dry density, density of solids, liquid limit, initial void ratio, linear shrinkage, unconfined compressive strength, shear strength and falling-head permeability of each peat sample. We also investigated the elemental compositions and microstructure of the peats using X-Ray fluorescence and scanning electron microscopy. The laboratory tests of physical and geotechnical properties indicated that, for construction purposes, Chaghakhor peat is weaker than Gavkhuni peat. © 2015 International Mire Conservation Group and International Peat Society.
Publication Date: 2014
Electronic Journal of Geotechnical Engineering (discontinued) (10893032) 19(X)pp. 7141-7163
Earthquake hazard zonation is the most important step towards seismic risk assessment and mitigation strategy in densely populated regions. The city of Isfahan, as an important industrial and historical center, is considered among the major economic and cultural poles in Iran. In addition, the existence of seismic evidence and several identified faults emphasizes the need for conducting seismotectonic studies and the development of seismic zonation for this city. In this regard, first, the main faults of the studied area were identified using the digital data from the satellite photos, and their conditions were corroborated by field observations. Then, a probabilistic seismic hazard assessment (PSHA) was conducted using SeisRiskIII software. The first outcome in the current study was preparation of the seismic hazard zoning maps for different hazard levels (according to the Building and construction Iranian Earthquake Code (Std. No. 2800)). Using selected compatible acceleration time histories from past earthquakes, the second was the development of the geotechnical amplification conversion functions corresponding to different soil conditions on bedrock, using SHAKE2000 software, which is based on the application of one-dimensional equivalent linear method (ELM). The results include the distribution maps of average shear wave velocity of the soil, the maximum horizontal acceleration on the ground surface, and the amplification ratio. According to these maps, the PGAs at ground surface and the amplification ratios range between 0.25 g to 0.5 g and 0.9 to 1.9, respectively. © 2014 ejge.
Publication Date: 2012
Journal of Constructional Steel Research (0143974X) 79pp. 83-90
The earthquake loads imposed to the structures are generally much more than what they are designed for. This reduction of design loads by seismic codes is through the application of response modification factor (R-factor). During moderate to severe earthquakes, structures usually behave inelastically, and therefore inelastic analysis is required for design. Inelastic dynamic analysis is time consuming and interpretation of its results demands high level of expertise. Pushover analysis, recently commonly used, is however, a simple way of estimating inelastic response of structures. Despite its capabilities, conventional pushover analysis (CPA) does not account for higher mode effects and member stiffness changes. Adaptive pushover analysis (APA) method however, overcomes these drawbacks. This research deals with derivation and comparison of some seismic demand parameters such as ductility based reduction factor, R μ, overstrength factor, Ω, and in particular, response modification factor, R, from capacity curves obtained from different methods of APA and CPA. Three steel moment-resisting frames of 3, 9 and 20 stories adopted from SAC steel project are analyzed. In pushover analyses for each frame, eight different constant as well as adaptive lateral load patterns are used. Among the main conclusions drawn is that the maximum relative difference for response modification factors was about 16% obtained by the methods of conventional and adaptive pushover analyses. © 2012 Elsevier Ltd. All rights reserved.
Publication Date: 2011
WIT Transactions on the Built Environment (17464498) 120pp. 173-173
In design of low rise structures the effects of soil-structure interaction are often ignored. However, these effects are considerable for heavy structures such as skyscrapers or multi-level highway structures. The existence of this interaction phenomenon can also be extended to the adjacent buildings. For example, in an area congested with many nearby tall buildings, to account for the proximity effects of adjacent buildings will become critical. Previous few studies conducted in this area, were limited to 2D finite element plain-strain models. Assuming plain-strain for foundation soil may be valid, however, for a building structure which has limited dimensions in plan, this assumption could be erroneous. In the current study, in order to capture the proximity effects on the response of adjacent buildings under earthquake motions, 3D models of 15 and 30 storey building structures on group piles are used. The foundation soils considered are clay and sand. Dynamic analyses are performed under horizontal components of several actual earthquakes. Three different combinations of two adjacent buildings are considered, 1) two 15-stories, 2) two 30-stories, and 3) one 15- and one 30-stories. Seismic soil-structure interaction analyses in this study are based on direct method. Foundation soil behavior is assumed to be equivalent linear while structures are assumed to behave in elastic range. Results show that the interaction of adjacent buildings depends on structural heights, type and depth of the foundation soil, frequency content of the earthquake records, the type of proximity and the distance between the adjacent buildings. © 2011 WIT Press.
Publication Date: 2000
Canadian Journal of Civil Engineering (03151468) 27(3)pp. 563-580
The use of uniform hazard spectra for obtaining the seismic design forces is being considered for the next version of the National Building Code of Canada. Such spectra provide the spectral accelerations of a single-degree-of-freedom system for a range of periods but for a uniform level of hazard. One of the issues that need to be resolved before uniform hazard spectra are used in the design of multistorey buildings is the adjustment required in the base shear to account for the higher mode effects present in a multi-degree-of-freedom system. This issue is examined through analytical studies of the response of idealised elastic and inelastic multistorey building frames to ground motions representative of the seismic hazard in the eastern and western regions of Canada. Representative values are obtained for the adjustment factors that must be applied to the design base shear and to the base overturning moment.
Publication Date: 2000
Shock and Vibration Digest (17413184) 32(1)pp. 67-67
The use of uniform hazard spectra for obtaining the seismic design forces is being considered for the next version of the national building code of Canada. Such spectra provide the spectral accelerations of a single-degree-of-freedom system for a range of periods but for a uniform level of hazard. One of the issues that needs to be resolved before uniform hazard spectra are used in design is the adjustment required in the base shear to account for the higher mode effects present in a multi-degree-of-freedom system. This issue is examined through analytical studies of the response of idealized multistorey building frames to ground motions representative of the seismic hazard in east and west Canada.
Publication Date: 1998
Canadian Journal of Civil Engineering (03151468) 25(1)pp. 1-15
Observations during many earthquakes have shown that building structures are able to sustain without damage earthquake forces considerably larger than those they were designed for. This is explained by the presence in such structures of significant reserve strength not accounted for in design. Relying on such overstrength, many seismic codes permit a reduction in design loads. The possible sources of reserve strength are outlined in this paper, and it is reasoned that a more rational basis for design would be to account for such sources in assessing the capacity rather than in reducing the design loads. As an exception, one possible source of reserve strength, the redistribution of internal forces, may be used in scaling down the design forces. This is because such scaling allows the determination of design forces through an elastic analysis rather than through a limit analysis. To assess the extent of reserve strength attributable to redistribution, steel building structures having moment-resisting frames or concentrically braced frames and from 2 to 30 storeys in height are analyzed for their response to lateral loading. A static nonlinear push-over analysis is used in which the gravity loads are held constant while the earthquake forces are gradually increased until a mechanism forms or the specified limit on interstorey drift is exceeded. It is noted that in moment-resisting frames the reserve strength reduces with an increase in the number of storeys as well as in the level of design earthquake forces. The P-Δ effect causes a further reduction. In structures having braced frames the main parameter controlling the reserve strength is the slenderness ratio of the bracing members. In these structures, reserve strength is almost independent of both the height of the structure and the effect of building sway.
Publication Date: 1996
Canadian Journal of Civil Engineering (03151468) 23(5)pp. 1051-1063
The Geological Survey of Canada is currently producing a suite of new hazard maps for Canada. These maps take into account the additional recorded data obtained during the past 13 years, as well as the new geological and tectonic information that has recently become available. They provide elastic spectral acceleration values for a uniform probability of exceedance of 10% in 50 years. A method of using the uniform hazard spectral values to obtain design response spectral curves for different values of ductility is presented here. The method uses two spectral values obtained from the hazard maps, the peak spectral acceleration for the site and the spectral acceleration corresponding to a period of 0.5 s. Empirical expressions are developed to represent the design response spectra. It is shown that by using inelastic spectral accelerations rather than the elastic spectral values in association with a reduction factor, the new method provides a more reliable estimate of the design forces.
University of Isfahan
Address: Isfahan, Azadi Square, University of Isfahan
