• Journal of the Korea Concrete Institute
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• v.24 no.5
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• pp.517-524
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• 2012

In this study, the effects of the inelastic shear behavior of beam-column joint and the vertical distribution of lateral load are evaluated considering higher modes on the response of RC OMRF using the pushover analysis. A structure used for the analysis was a 5-story structure located at site class SB and seismic design category C, which was designed in accordance with KBC2009. Bending moment-curvature relationship for beam and column was identified using fiber model. Also, bending moment-rotation relationship for beam-column joint was calculated using simple and unified joint shear behavior model and moment equilibrium relationship for the joint. The results of pushover analysis showed that, although the rigid beam-column joint overestimated the stiffness and strength of the structure, the inelastic shear behavior of beam-column joint could be neglected in the process of structural design since the average response modification factor satisfied the criteria of KBC2009 for RC OMRF independent to inelastic behavior of joint.

• Journal of the Earthquake Engineering Society of Korea
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• v.8 no.1
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• pp.39-58
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• 2004

It is very important that predict the inelastic seismic behavior exactly for seismic performance evaluation of a building in the performance based seismic design. Evaluation method of seismic performance based on the pushover analysis reflected in PBSE was developed by some researchers. For the evaluation of inelastic global and local seismic responses by pushover analysis exactly. lateral load distribution should be adjusted and reflected the dynamic characteristics of structural system and various seismic ground motions. And performance point should be determined based on the evaluation of reasonable deformation capacity of a building more exactly. An effective method based on the improved the adaptive lateral load distribution and the equivalent responses of a multistory building is proposed in this study to efficiently estimate the accurate inelastic seismic responses. The proposed method can be used to evaluate the seismic performance for the global inelastic behavior of a building and to accurately estimate its local inelastic seismic responses. In order to demonstrate the accuracy and validity of this method, inelastic seismic responses estimated by the proposed method are compared with those obtained from other analytical methods.

• Earthquakes and Structures
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• v.9 no.2
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• pp.353-373
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• 2015

In this paper, the effects of different types of irregularity along the height on the seismic responses of moment resisting frames are investigated using nonlinear dynamic analysis. Furthermore, the applicability of consecutive modal pushover (CMP) procedure for computing the seismic demands of vertically irregular frames is studied and the advantages and limitations of the procedure are elaborated. For this purpose, a special moment resisting steel frame of 10-storey height was selected as reference regular frame for which the effect of higher modes is important. Forty vertically irregular frames with stiffness, strength, combined-stiffness-and-strength and mass irregularities are created by applying two modification factors (MF=2 and 4) in four different locations along the height of the reference frame. Seismic demands of irregular frames are computed by using the nonlinear response history analysis (NL-RHA) and CMP procedure. Modal pushover analysis (MPA) method is also carried out for the sake of comparison. The effect of different types of irregularity along the height on the seismic demands of vertically irregular frames is investigated by studying the results obtained from the NL-RHA. To demonstrate the accuracy of the enhanced pushover analysis methods, the results derived from the CMP and MPA are compared with those obtained by benchmark solution, i.e., NL-RHA. The results show that the CMP and MPA methods can accurately compute the seismic demands of vertically irregular buildings. The methods may be, however, less accurate especially in estimating plastic hinge rotations for weak or weak-and-soft top and middle storeys of vertically irregular frames.

• Earthquakes and Structures
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• v.23 no.1
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• pp.35-57
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• 2022

This article presents a computationally efficient framework for multi-objective seismic design optimization of steel moment-resisting frame (MRF) structures based on the nonlinear dynamic analysis procedure. This framework employs the uniform damage distribution philosophy to minimize the weight (initial cost) of the structure at different levels of damage. The preliminary framework was recently proposed by the authors based on the single excitation and the nonlinear static (pushover) analysis procedure, in which the effects of record-to-record variability as well as higher-order vibration modes were neglected. The present study investigates the reliability of the previous framework by extending the proposed algorithm using the nonlinear dynamic design procedure (optimization under multiple ground motions). Three benchmark structures, including 4-, 8-, and 12-story steel MRFs, representing the behavior of low-, mid-, and high-rise buildings, are utilized to evaluate the proposed framework. The total weight of the structure and the maximum inter-story drift ratio (IDRmax) resulting from the average response of the structure to a set of seven ground motion records are considered as two conflicting objectives for the optimization problem and are simultaneously minimized. The results of this study indicate that the optimization under several ground motions leads to almost similar outcomes in terms of optimization objectives to those are obtained from optimization under pushover analysis. However, investigation of optimal designs under a suite of 22 earthquake records reveals that the damage distribution in buildings designed by the nonlinear dynamic-based procedure is closer to the uniform distribution (desired target during the optimization process) compared to those designed according to the pushover procedure.

• Wind and Structures
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• v.13 no.1
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• pp.1-20
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• 2010

The recommended factored design wind load effects for overhead lattice transmission line towers by codes and standards are evaluated based on the applicable wind load factor, gust response factor and design wind speed. The current factors and design wind speed were developed considering linear elastic responses and selected notional target safety levels. However, information on the nonlinear inelastic responses of such towers under extreme dynamic wind loading, and on the structural capacity curves of the towers in relation to the design capacities, is lacking. The knowledge and assessment of the capacity curve, and its relation to the design strength, is important to evaluate the integrity and reliability of these towers. Such an assessment was performed in the present study, using a nonlinear static pushover (NSP) analysis and incremental dynamic analysis (IDA), both of which are commonly used in earthquake engineering. For the IDA, temporal and spatially varying wind speeds are simulated based on power spectral density and coherence functions. Numerical results show that the structural capacity curves of the tower determined from the NSP analysis depend on the load pattern, and that the curves determined from the nonlinear static pushover analysis are similar to those obtained from IDA.

• Earthquakes and Structures
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• v.14 no.1
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• pp.21-32
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• 2018

Prefabricated structures are constructed by bolted connections of separated members. The design and analysis of these structures are generally performed by defining fully hinges for the connection of separated members at the joint of junction. In practice, these connections are not fully hinged. Therefore, the assumption of semi-rigid connections (restrained or partially fixity) instead of fully hinge connections is a more realistic approach for bolted connections used in the prefabricated elements. The aim of this study is to investigate the effects of semi-rigid connections on seismic performance of prefabricated structures. Nonlinear static analysis (pushover analysis) of a selected RC prefabricated structure is performed with SAP2000 structural analysis program by considering various partially fixity percentages for bolted connections. The target values of roof displacements obtained from the analyses according to ATC-40, FEMA-356, FEMA-440, and TEC-2007 codes are compared each other. The numerical results are given in tables and figures comparatively and discussed. The results show that the effects of semi-rigid connections should be considered in design and analysis of the prefabricated structures.

• Structural Engineering and Mechanics
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• v.28 no.6
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• pp.727-747
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• 2008

In the framework of the SPEAR (Seismic PErformance Assessment and Rehabilitation) research Project, an under-designed three storey RC frame structure, designed to sustain only gravity loads, was subjected, in three different configurations 'as-built', Fiber Reinforced Polymer (FRP) retrofitted and rehabilitated by reinforced concrete (RC) jacketing, to a series of bi-directional pseudodynamic (PsD) tests under different values of peak ground acceleration (PGA) (from a minimum of 0.20g to a maximum of 0.30g). The seismic deficiencies exhibited by the 'as-built' structure after the test at PGA level of 0.20g were confirmed by a post - test assessment of the structural seismic capacity performed by a nonlinear static pushover analysis implemented on the structure lumped plasticity model. To improve the seismic performance of the 'as-built' structure', two rehabilitation interventions by using either FRP laminates or RC jacketing were designed. Assumptions for the analytical modeling, design criteria and calculation procedures along with local and global intervention measures and their installation details are herein presented and discussed. Nonlinear static pushover analyses for the assessment of the theoretical seismic capacity of the structure in each retrofitted configuration were performed and compared with the experimental outcomes.

• Earthquakes and Structures
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• v.7 no.3
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• pp.333-347
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• 2014

Multi-scale model can take both computational efficiency and accuracy into consideration when it is used to conduct elasto-plastic seismic response analysis for complex steel bridges. This paper proposed a method based on pushover analysis of member sharing the same section pattern to verify the accuracy of multi-scale model. A deck-through type steel arch bridge with a span length of 200m was employed for seismic response analysis using multi-scale model and fiber model respectively, the validity and necessity of elasto-plastic seismic analysis for steel bridge by multi-scale model was then verified. The results show that the convergence of load-displacement curves obtained from pushover analysis for members having the same section pattern can be used as a proof of the accuracy of multi-scale model. It is noted that the computational precision of multi-scale model can be guaranteed when length of shell element segment is 1.40 times longer than the width of section where was in compression status. Fiber model can only be used for the predictions of the global deformations and the approximate positions of plastic areas on steel structures. However, it cannot give exact prediction on the distribution of plastic areas and the degree of the plasticity.

• Earthquakes and Structures
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• v.16 no.6
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• pp.655-664
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• 2019

Behavior factor of a structure plays a crucial role in designing and predicting the inelastic responses of it. Recently, irregular buildings have been interested in many designers. To design irregular structures, recognizing the inelastic behavior of them is necessary. The main objective of this study is to determine the behavior factor of irregular Reinforced Concrete Moment Resisting Frames (RCMRFs) via nonlinear Incremental Dynamic Analysis (IDA). To do so, first, several frames are designed according to the regulations of the Iranian national building code. Then the nonlinear incremental dynamic analysis is performed on these structures and the behavior factors are achieved. The acquired results are compared with those obtained using pushover analysis and it is shown that the behavior factors acquired from the nonlinear incremental dynamic analysis are somewhat larger than those obtained from pushover analysis. Eventually, two practical relations are proposed to predict the behavior factor of irregular RCMRFs. Since these relations are based on the simple characteristics of frames such as: irregularity indices, the height and fundamental period, the behavior factor of irregular RCMRFs can be achieved efficiently using these relations. The proposed relations are applied to design of four new irregular RCMRFs and the outcomes confirm the accuracy of the aforementioned relations.

• Structural Engineering and Mechanics
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• v.82 no.5
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• pp.667-678
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• 2022

Moment-resisting frames (MRFs) are among the most conventional steel structures for mid-rise buildings in many earthquake-prone cities. Here, a simplified performance-based methodology is proposed for the seismic collapse capacity assessment of these buildings. This method employs a novel multi-mode pushover analysis to determine the engineering demand parameters (EDPs) of the regular steel MRFs up to the collapse prevention (CP) performance level. The modal combination coefficients used in the proposed pushover analysis, are obtained from two metaheuristic optimization algorithms and a fitting procedure. The design variables for the optimization process are the inter-story drift ratio profiles resulting from the multi-mode pushover analyses, and the objective values are the outcomes of the incremental dynamic analysis (IDA). Here, the collapse capacity of the structures is assessed in three to five steps, using a modified IDA procedure. A series of regular mid-rise steel MRFs are selected and analyzed to calculate the modal combination coefficients and to validate the proposed approach. The new methodology is verified against the current existing approaches. This comparison shows that the suggested method more accurately evaluates the EDPs and the collapse capacity of the regular MRFs in a robust and easy to implement way.