• Structural Engineering and Mechanics
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• v.33 no.3
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• pp.261-284
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• 2009

The seismic behavior of a framed structure with chevron-type buckling restrained braces was investigated and their behavior factors, such as overstrength, ductility, and response modification factors, were evaluated. Two types of structures, building frame systems and dual systems, with 4, 8, 12, and 16 stories were designed per the IBC 2003, the AISC LRFD and the AISC Seismic Provisions. Nonlinear static pushover analyses using two different loading patterns and incremental dynamic analysis using 20 earthquake records were carried out to compute behavior factors. Time history analyses were also conducted with another 20 earthquakes to obtain dynamic responses. According to the analysis results, the response modification factors turned out to be larger than what is proposed in the provision in low-rise structures, and a little smaller than the code-values in the medium-rise structures. The dual systems, even though designed with smaller seismic load, showed superior static and dynamic performances.

• Earthquakes and Structures
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• v.5 no.1
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• pp.1-22
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• 2013

Soft storey failure mechanism is a common collapse mode for masonry-infilled (MI) reinforced concrete (RC) buildings subjected to severe earthquakes. Simple analytical equations correlating global with local ductility demands are derived from pushover (PO) analyses for seismic assessments of regular MI RC frames, considering the critical interstorey drift ratio, number of storeys and lateral loading configurations. The reliability of the equations is investigated using incremental dynamic analyses for MI RC frames of up to 7 storeys. Using the analytical ductility relationship and a coefficient-based method (CBM), the response spectral accelerations and period shift factors of low-rise MI RC frames are computed. The results are verified through published shake table test results. In general applications, the analytical ductility relationships thus derived can be used to bypass the onerous PO analysis while accurately predicting the local ductility demands for seismic assessment of regular MI RC frames.

• Journal of Korean Association for Spatial Structures
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• v.22 no.3
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• pp.41-48
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• 2022

The purpose of this study is to evaluate seismic performances of a modular house system developed by a simple 4-clip fastening method and double metal assembly made of lightweight metals. In order to evaluate structural and non-structural seismic performances of the system. Shaking table test was carried out with full-scale modular units, and a nonlinear pushover analysis was performed to obtain suitable seismic responses for story drifts, displacements, force resistances and dynamic properties of the system. Through 3D analysis and shaking table test, the current method of lightweight modular metal unit assembly and systems with seismic performance of a 4-clip fastening type modular house were demonstrated safe and effective to seismic design.

• Journal of Korean Society of Steel Construction
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• v.22 no.3
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• pp.281-291
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• 2010

In this study, a five-story steel frame was designed in accordance with KBC2005 to evaluate the effects of the beam-column connection on the structural behavior. The connections were designed as fully rigid and semi-rigid. The fiber model was used to describe the moment-curvature relationship of the steel beam and the column, the power model for the moment-rotation angle of the semi-rigid connection and the three-parameter model for the hysteretic behavior of the steel beam, column, and connection. The structure was idealized as separate 2-D frames and as connected 2-D frames. The peak ground accelerations of four earthquake records were modified in a time-history analysis for the levels of the mean return period and for the maximum base-shear force in a pushover analysis. The top story displacement, base-shear force, story drift, demanded ductility ratio for the semi-rigid connection, maximum bending moment of the column, beam, and connection, and distribution of the plastic hinge were examined in the time-history analysis. The frame with the semi-rigid connection yielded a lower base-shear force, less magnitude, and increasing ratio in the bending moment of the column, beam, and connection than the frame with a fully rigid connection. The TSD connection was deemed to have secured the economy and safety of the sample structure that was subjected to seismic excitation for the Korean design level.

• Journal of the Earthquake Engineering Society of Korea
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• v.8 no.1
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• pp.67-76
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• 2004

This study presents the evaluation of CSM(Capacity Spectrum Method, ATC-40) in developing fragility curves for a sample concrete bridge. The CSM is originally developed as one of the simplified procedures for building structures, while this study adopts the CSM to develop fragility curves of bridge structures. Four(4) different approaches are demonstrated and the fragility curves developed are compared those by the nonlinear time history analysis. Fragility curves in this study are represented by lognormal distribution functions with two parameters and developed as a function of PGA. The sixty(60) ground acceleration time histories for the Los Angeles area developed for the Federal Emergency Management Agency (FEMA) SAC(SEAOC-ATC-CUREe) steel project are used for the bridge analysis. The comparison of fragility curves by the CSM with those by the time history analysis indicates that the agreement is excellent for one of the methods investigated in this study. In this respect. it is recommended that the demand spectrum might be improved according to the guidelines suggested in this study. However, this observation might not always apply, depending on the details of specific bridge characteristic

• Wind and Structures
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• v.31 no.2
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• pp.143-152
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• 2020

The wind design of buildings is typically based on strength provisions under ultimate loads. This is unlike the ductility-based approach used in seismic design, which allows inelastic actions to take place in the structure under extreme seismic events. This research investigates the application of a similar concept in wind engineering. In seismic design, the elastic forces resulting from an extreme event of high return period are reduced by a load reduction factor chosen by the designer and accordingly a certain ductility capacity needs to be achieved by the structure. Two reasons have triggered the investigation of this ductility-based concept under wind loads. Firstly, there is a trend in the design codes to increase the return period used in wind design approaching the large return period used in seismic design. Secondly, the structure always possesses a certain level of ductility that the wind design does not benefit from. Many technical issues arise when applying a ductility-based approach under wind loads. The use of reduced design loads will lead to the design of a more flexible structure with larger natural periods. While this might be beneficial for seismic response, it is not necessarily the case for the wind response, where increasing the flexibility is expected to increase the fluctuating response. This particular issue is examined by considering a case study of a sixty-five-story high-rise building previously tested at the Boundary Layer Wind Tunnel Laboratory at the University of Western Ontario using a pressure model. A three-dimensional finite element model is developed for the building. The wind pressures from the tested rigid model are applied to the finite element model and a time history dynamic analysis is conducted. The time history variation of the straining actions on various structure elements of the building are evaluated and decomposed into mean, background and fluctuating components. A reduction factor is applied to the fluctuating components and a modified time history response of the straining actions is calculated. The building components are redesigned under this set of reduced straining actions and its fundamental period is then evaluated. A new set of loads is calculated based on the modified period and is compared to the set of loads associated with the original structure. This is followed by non-linear static pushover analysis conducted individually on each shear wall module after redesigning these walls. The ductility demand of shear walls with reduced cross sections is assessed to justify the application of the load reduction factor "R".

• Journal of the Earthquake Engineering Society of Korea
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• v.7 no.1
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• pp.9-16
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• 2003

To evaluate the seismic performance of multistory building structures use an equivalent SDOF model to represent the resistance of the structure to deformation as it respond in its predominant mode. This paper presents a method of converting a MDOF system into an equivalent SDOF model. The principal objective of this investigation is to evaluate appropriateness of converting method through perform nonlinear time history analysis of a multistory building structures and an equivalent SDOF model. The hysteresis rules to be used an equivalent SDOF model is obtained from the pushover analysis. Comparing the peak inelastic response of a moment resisting reinforced concrete frames and an equivalent SDOF model, the adequacy and the validity of the converting method is verified. The conclusion of this study is following; A method of converting a MDOF system into an equivalent SDOF model through the nonlinear time history response analysis is valid. The representative lateral displacement of a moment resisting reinforced concrete frames is close to the height of the first modal participation vector \ulcorner$_1{\beta}$${_1{\mu}}=1$. It can be found that the hysteresis rule of an equivalent SDOF model have influence on the time history response. Therefore, it necessary for selecting hysteresis rules to consider hysteresis characteristics of a moment resisting reinforced concrete frames.

• Earthquakes and Structures
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• v.24 no.6
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• pp.393-404
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• 2023

This paper presents the application of hybrid-simulation-based adapter elements for the non-linear two-scale analysis of reinforced concrete frames with masonry infills under seismic-like demands. The approach provides communication and distribution of the computations carried out by two or more remote or locally distributed numerical models connected through the OpenFresco Framework. The modeling consists of a global analysis formed by macro-elements to represent frames and walls, and to reduce global degrees of freedom, portions of the structure that require advanced analysis are substituted by experimental elements and dimensional couplings acting as interfaces with their respective sub-assemblies. The local sub-assemblies are modeled by solid finite elements where the non-linear behavior of concrete matrix and masonry infill adopt a continuum damage representation and the reinforcement steel a discrete one, the conditions at interfaces between concrete and masonry are considered through a contact model. The methodology is illustrated through the analysis of a frame-wall system subjected to lateral loads comparing the results of using macro-elements, finite element model and experimental observations. Finally, to further assess and validate the methodology proposed, the paper presents the pushover analysis of two more complex structures applying both modeling scales to obtain their corresponding capacity curves.

• Journal of the Earthquake Engineering Society of Korea
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• v.21 no.2
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• pp.105-114
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• 2017

Nonlinear analysis for seismic performance evaluation of existing building usually takes 4~5 times more than linear analysis based on KBC code. To obtain accurate results from the nonlinear analysis, there are a lot of things to be considered for nonlinear analysis modeling. For example, reinforcing layout, applied load and seismic details affect behavior of structural members for the existing building. Engineer-oriented computerized system was developed for engineers to evaluate effective seismic performance of existing buildings with abiding by seismic design principles. Using the engineer-oriented program, seismic performance evaluation of reinforced concrete building was performed. Nonlinear hinge properties were applied with real time multiple consideration such as section layout, section analysis result, applied load and performance levels. As a result, the building was evaluated to satisfy LS(Life Safety) performance level. A comparison between engineer-oriented and program-oriented results is presented to show how important the role of structural engineer is for seismic performance evaluation of existing buildings.

• Structural Engineering and Mechanics
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• v.51 no.1
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• pp.131-140
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• 2014

This study focuses on seismic behaviour of tall piers characterized by high slender ratio. Two analysis models were developed based on elastic-plastic hinged beam element and elastic-plastic fiber beam element, respectively. The effect of the division density of elastic-plastic hinged beam element on seismic demand was discussed firstly to seek a rational analysis model for tall piers. Then structural seismic behaviour such as the formation of plastic hinges, the development of plastic zone, and the displacement at the top of the tall piers were investigated through incremental dynamic analysis. It showed that the seismic behaviour of a tall pier was quite different from that of a lower pier due to higher modes contributions. In a tall pier, an additional plastic zone may occur at the middle height of the pier with the increase of seismic excitation. Moreover, the maximum curvature reaction at the bottom section and maximum lateral displacement at the top turned out to be seriously out of phase for a tall pier due to the higher modes effect, and thus pushover analysis can not appropriately predict the local displacement capacity.