• 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.

• Structural Engineering and Mechanics
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• v.55 no.5
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• pp.1037-1053
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• 2015

This paper presents finite element (FE) based pushover analysis of a reinforced concrete structure with a two-leaf cavity wall (TLCW) to estimate the performance level of this structure. In addition to this, an unreinforced masonry (URM) model was selected for comparison. Simulations and analyses of these structures were performed using the DIANA FE program. The mentioned structures were selected as two storeys and two bays. The dimensions of the structures were scaled 1:1.5 according to the Cauchy Froude similitude law. A shake table experiment was implemented on the reinforced concrete structure with the two-leaf cavity wall (TLCW) at the National Civil Engineering Laboratory (LNEC) in Lisbon, Portugal. The model that simulates URM was not experimentally studied. This structure was modelled in the same manner as the TLCW. The purpose of this virtual model is to compare the respective performances. Two nonlinear analyses were performed and compared with the experimental test results. These analyses were carried out in two phases. The research addresses first the analysis of a structure with only reinforced concrete elements, and secondly the analysis of the same structure with reinforced concrete elements and infill walls. Both researches consider static loading and pushover analysis. The experimental pushover curve was plotted by the envelope of the experimental curve obtained on the basis of the shake table records. Crack patterns, failure modes and performance curves were plotted for both models. Finally, results were evaluated on the basis of the current regulation ASCE/SEI 41-06.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2002.03a
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• pp.349-356
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• 2002

There has been an increasing trend toward the use of pushover analysis as a tool for evaluating the seismic resistant and safety of a building structure in the performance based earthquake engineering field. The ATC-40 document proposed a nonlinear static procedure based on the Capacity Spectrum Method to determine earthquake-induced demand given the structure pushover curve, which a curve representing base shear versus roof displacement. However, the procedure is conceptually simple, iterative and time consuming method and may sometimes lead to no solution or multiple solutions. A new improved method of seismic performance evaluation for moment frame building, which take into account the previously mentioned deficiencies of currently used elastic design procedures, is presented in this paper. The results of nonlinear static and nonlinear time history analysis of an example high-rise steel moment frame designed by the proposed method are presented and discussed.

• Earthquakes and Structures
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• v.14 no.6
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• pp.505-523
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• 2018

Static pushover analyses of typical existing reinforced concrete frames, designed according to the previous generations of design codes in Greece, have established these structures' inelastic characteristics, namely overstrength, global ductility capacity and available behaviour factor q, under planar response. These were compared with the corresponding demands at the collapse limit state target performance point. The building stock considered accounted for the typical variability, among different generations of constructed buildings in Greece, in the form, the seismic design code in effect and the material characteristics. These static pushover analyses are extended, in the present study, in the time history domain. Consequently, the static analysis predictions are compared with Incremental Dynamic Analysis results herein, using a large number of spectrum compatible recorded base excitations of recent destructive earthquakes in Greece and abroad, following, for comparison, similar conventional limiting failure criteria as before. It is shown that the buildings constructed in the 70s exhibit the least desirable behaviour, followed by the buildings constructed in the 60s. As the seismic codes evolved, there is a notable improvement for buildings of the 80s, when the seismic code introduced end member confinement and the requirement for a joint capacity criterion. Finally, buildings of the 90s, designed to modern codes exhibit an exceptionally good performance, as expected by the compliance of this code to currently enforced seismic provisions worldwide.

• Structural Engineering and Mechanics
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• v.35 no.1
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• pp.99-117
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• 2010

Beam-column joints are the key structural elements, which dictate the behavior of structures subjected to earthquake loading. Though large experimental work has been conducted in the past, still various issues regarding the post-yield behavior, ductility and failure modes of the joints make it a highly important research topic. This paper presents experimental results obtained for eight beam-column joints of different sizes and configuration under cyclic loads along with the analytical evaluation of their response using a simple and effective analytical procedure based on nonlinear static pushover analysis. It is shown that even the simplified analysis can predict, to a good extent, the behavior of the joints by giving the important information on both strength and ductility of the joints and can even be used for prediction of failure modes. The results for four interior and four exterior joints are presented. One confined and one unconfined joint for each configuration were tested and analyzed. The experimental and analytical results are presented in the form of load-deflection. Analytical plots are compared with envelope of experimentally obtained hysteretic loops for the joints. The behavior of various joints under cyclic loads is carefully examined and presented. It is also shown that the procedure described can be effectively utilized to analytically gather the information on behavior of joints.

• Journal of the Earthquake Engineering Society of Korea
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• v.10 no.1 s.47
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• pp.9-16
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• 2006

The design practice of the lateral resisting system has been traditionally dependent on the experience and know-how of a structural engineer. And the method to reflect the evaluation results of building's capacity on design process doesn't exist. The proposal of a rational design of the lateral load resisting system is based on the available full capacity $(R_{ac})$ of a building and the minimum required capacity $(R_{code})$ suggested in the code. This study suggests thai nonlinear static analysis, which is the estimation of the lateral capacity with the pushover analysis, be included in the existing design procedure of the structure. After finishing the basic structural design, the lateral resisting capacity ol a building is estimated. At the phase of nonlinear static analysis, pushover analysis is peformed to define the fully yielded baseshear $(V_Y)$. When the design wind baseshear $(V_{wind})$ is bigger than the design seismic baseshear $(V_D)$, the value is checked to determine whether or not it is smaller than the $V_Y$. After confirming that it is smaller, the $R_{ac}$ of the structure is computed. If the $V_D$ is bigger at first, only the $R_{ac}$ is computed. When the value of the estimation shows remarkable differences with the $R_{code}$, repetition of the design modification is needed for those approximate to the $R_{code}$. Application of the proposed design procedure to 2-D steel braced RC buildings has proven to be efficient.

• Steel and Composite Structures
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• v.8 no.1
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• pp.53-83
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• 2008

A rational and efficient seismic design methodology for irregular space steel frames using advanced methods of analysis in the framework of Eurocodes 8 and 3 is presented. This design methodology employs an advanced static or dynamic finite element method of analysis that takes into account geometrical and material non-linearities and member and frame imperfections. The inelastic static analysis (pushover) is employed with multimodal load along the height of the building combining the first few modes. The inelastic dynamic method in the time domain is employed with accelerograms taken from real earthquakes scaled so as to be compatible with the elastic design spectrum of Eurocode 8. The design procedure starts with assumed member sections, continues with the checking of the damage and ultimate limit states requirements, the serviceability requirements and ends with the adjustment of member sizes. Thus it can sufficiently capture the limit states of displacements, rotations, strength, stability and damage of the structure and its individual members so that separate member capacity checks through the interaction equations of Eurocode 3 or the usage of the conservative and crude q-factor suggested in Eurocode 8 are not required. Two numerical examples dealing with the seismic design of irregular space steel moment resisting frames are presented to illustrate the proposed method and demonstrate its advantages. The first considers a seven storey geometrically regular frame with in-plan eccentricities, while the second a six storey frame with a setback.

• Journal of the Earthquake Engineering Society of Korea
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• v.19 no.5
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• pp.229-238
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• 2015

For small-size reinforce-concrete buildings, Midas Gen, OpenSees, and Perform-3D, which are structural analysis programs that are most popularly used at present, were applied for nonlinear static pushover analysis, and then difference between those programs was analyzed. Example buildings were limited to 2-story frames with irregular shaped walls. Analysis result showed that there were more differences than for frames only and frames with rectangular walls, but it was not so significant. Nevertheless, the capacity curve were different in some buildings, which is attributed to shape and location of walls, and feature of the analysis program. Especially, selection of automatic or manual input in Midas Gen, or nonlinear wall elements in Perform3D can affect the capacity curve and performance of the buildings. Therefore, the program users should understand the feature of the program well, and then conduct performance assessment. The result of this study is limited to low-story buildings so that it should be noted that it is possible to get different results for mid- to high-rise buildings.

• Journal of the Earthquake Engineering Society of Korea
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• v.19 no.5
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• pp.219-228
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• 2015

For small-size reinforce-concrete buildings, Midas Gen, OpenSees, and Perform-3D, which are structural analysis programs that are most popularly used at present, were applied for nonlinear static pushover analysis, and then difference between those programs was analyzed. Example buildings were limited to 2-story frames only and frames with one or more rectangular walls. Analysis results showed that there was not much difference for frames only based on capacity curves. There were some differences for frames with rectangular walls, but it was not so significant. The global behaviors represented by the capacity curve were not so different, but the feature of each analysis program appeared when the results were analyzed in more detail. Therefore, the program users should understand the feature of the program well, and then conduct performance assessment. The result of this study is limited to low-story frames only and frames with rectangular walls so that it should be noted that it is possible to get different results for frames with non-rectangular walls or mid- to high-rise buildings.

• Structural Engineering and Mechanics
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• v.48 no.5
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• pp.681-695
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• 2013

Performance-based seismic design allows a structure to develop inelastic response during earthquakes. This modern seismic design requires more clearly defined levels of inelastic response. The ultimate deformation of a structure without total collapse (target displacement) is used to obtain the inelastic deformation capacity (inelastic performance). The inelastic performance of a structure indicates its performance under excitation. In this study, a new energy-based method to obtain the target displacement for reinforced concrete frames under cyclic loading is proposed. Concrete structures were analyzed using nonlinear static (pushover) analysis and cyclic loading. Failure of structures under cyclic loading was controlled and the new method was tested to obtain target displacement. In this method, the capacity energy absorption of the structures for both pushover and cyclic analyses were considered to be equal. The results were compared with FEMA-356, which confirmed the accuracy of the proposed method.