• Journal of Korean Society of Steel Construction
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• v.26 no.5
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• pp.385-396
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• 2014

Traditionally, domestic steel design and construction practice has provided extra shear studs to moment frame beams even when they are designed as non-composite beams. In the 1994 Northridge earthquake, connection damage initiated from the beam bottom flange side was prevalent. The upward moving of the neutral axis due to the composite action between steel beam and floor deck was speculated to be one of the critical causes. In this study, full-scale seismic testing was conducted to investigate the side effects of the composite action in steel seismic moment frames. The specimen PN700-C, designed following the domestic connection and floor deck details, exhibited significant upward shift of the neutral axis under sagging (or positive) moment, thus producing high strain demand on the bottom flange, and showed a poor seismic performance because of brittle fracture of the beam bottom flange at 3% story drift. The specimen DB700-C, designed by using RBS connection and with the details of minimized floor composite action, exhibited superior seismic performance, without experiencing any fracture or concrete crushing, almost identical to the bare steel counterpart (specimen DB700-NC). The results of this study clearly indicate that the beams and connections in seismic steel moment frames should be constructed to minimize the composite action of a floor deck if possible.

• Journal of Korean Society of Steel Construction
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• v.15 no.3
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• pp.261-269
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• 2003

The length of the links in an eccentrically braced frame will dictate the behavior of the frame. Link length controls the yielding mechanism and the ultimate failure mode. For short links, the links' shear forces reach the plastic shear capacity before the end moments reach the plastic moment capacity, and the links yields in the shear, forming a shear hinges. These links are termed "shear links." For long links, the end moments reach the plastic moment capacity before the links' shear forces reach the plastic shear capacity, forming moment hinges. These links are termed moment links." In long links, flexural yielding dominates the response, and very high bending strains are required at the link ends to produce large link deformations. In a shear links, the shear force is constant along the length of the links, and the inelastic shear strain are is uniformly distributed over the length of the links. This permits the development of large inelastic link deformations without the development of excessively high local strains. However, The use of eccentrically braced steel frames for the purpose of architectural cionsiderations such as openings and doors, areis dictating the use of longer links, though. Little data areis available on the behavior of long links under cyclic loading conditions. In This paper documents the results of an experimental program is that was conducted to assess the response of moment links in eccentrically braced frames. Sixteen specimens awere tested using a cyclic load.

• Steel and Composite Structures
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• v.15 no.3
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• pp.323-342
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• 2013

In the case of seismic-resistant composite dual moment resisting and eccentrically braced frames, the current design practice is to avoid the disposition of shear connectors in the expected plastic zones, and consequently to consider a symmetric moment or shear plastic hinges, which occur only in the steel beam or link. Even without connectors, the real behavior of the hinge may be different from the symmetric assumption since the reinforced concrete slab is connected to the steel element close to the hinge locations, and also due to contact friction between the concrete slab and the steel element. At a larger level, the structural response in the case of important seismic motions depends directly on the elasto-plastic behavior of elements and hinges. The numerical investigation presented in this study summarizes the results of elasto-plastic analyses of several steel frames, considering the interaction of the steel beam with the concrete slab. Several parameters, such as the inter-story drift, plastic rotation requirements and behavior factors q were monitored. In order to obtain accurate results, adequate models of plastic hinges are proposed for both the composite short link and composite reduced beam sections.

• Structural Engineering and Mechanics
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• v.59 no.4
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• pp.653-669
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• 2016

Recent earthquakes worldwide show that a significant portion of the earthquake shaking happens in the vertical direction. This phenomenon has raised significant interests to consider the vertical ground motion during the seismic design and assessment of the structures. Strong vertical ground motions can alter the axial forces in the columns, which might affect the shear capacity of reinforced concrete (RC) members. This is particularly important for non-ductile RC frames, which are very vulnerable to earthquake-induced collapse. This paper presents the detailed nonlinear dynamic analysis to quantify the collapse risk of non-ductile RC frame structures with varying heights. An array of non-ductile RC frame architype buildings located in Los Angeles, California were designed according to the 1967 uniform building code. The seismic responses of the architype buildings subjected to concurrent horizontal and vertical ground motions were analyzed. A comprehensive array of ground motions was selected from the PEER NGA-WEST2 and Iran Strong Motions Network database. Detailed nonlinear dynamic analyses were performed to quantify the collapse fragility curves and collapse margin ratios (CMRs) of the architype buildings. The results show that the vertical ground motions have significant impact on both the local and global responses of non-ductile RC moment frames. Hence, it is crucial to include the combined vertical and horizontal shaking during the seismic design and assessment of non-ductile RC moment frames.

• Structural Engineering and Mechanics
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• v.68 no.6
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• pp.647-660
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• 2018

The Incremental Dynamic Analysis (IDA) procedure is currently known as a robust tool for estimation of seismic collapse capacity. However, the procedure is time-consuming and requires significant computational efforts. Recently some simplified methods have been developed for rapid estimation of seismic collapse capacity using pushover analysis. However, a comparative review and assessment of these methods is necessary to point out their relative advantages and shortcomings, and to pave the way for their practical use. In this paper, four simplified pushover analysis-based methods are selected and applied on four regular RC intermediate moment-resisting frames with 3, 6, 9 and 12 stories. The accuracy and performance of the different simplified methods in estimating the median seismic collapse capacity are evaluated through comparisons with the results obtained from IDAs. The results show that reliable estimations of the summarized 50% fractile IDA curve are produced using SPO2IDA and MPA-based IDA methods; however, the accuracy of the results for 16% and 84% fractiles is relatively low. The method proposed by Shafei et al. appears to be the most simple and straightforward method which gives rise to good estimates of the median sidesway collapse capacity with minimum computational efforts.

• Steel and Composite Structures
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• v.46 no.5
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• pp.591-609
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• 2023

In some buildings, the lateral structural response of steel framed buildings depends on the shear walls and it is very important to study the behavior of these elements under near-field seismic loads. The link beam in the opening of the shear wall between two wall plates is investigated numerically in terms of behavior and effects on frames. Based on the length of the beam and its bending and shear behavior, three types of models are constructed and analyzed, and the behavior of the frames is also compared. The results show that by reducing the length of the link beam, the base shear forces reduce about 20%. The changes in the length of the link beam have different effects on the degree of coupling. Increasing the length of the link beam increases the base shear about 15%. Also, it has both, a positive and a negative effect on the degree of coupling. The increasing strength of the coupling steel shear wall is linearly related to the yield stress of the beam materials, length, and flexural stiffness of the beam. The use of a shorter link beam will increase the additional strength and consequently improving the behavior of the coupling steel shear wall by reducing the stresses in this element. The link beam with large moment of inertia will also increase about 25% the additional strength and as a result the coefficient of behavior of the shear wall.

• Earthquakes and Structures
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• v.25 no.2
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• pp.99-112
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• 2023

This paper investigates the influences of Soil-Structure Interaction (SSI) on the seismic behavior of two-dimensional reinforced concrete moment-resisting frames subjected to Far-Field Ground Motion (FFGM) and Near-Field Ground Motion (NFGM). For this purpose, the nonlinear modeling of 7, 10, and 15-story reinforced concrete moment resisting frames were developed in Open Systems for Earthquake Engineering Simulation (OpenSees) software. Effects of SSI were studied by simulating Beam on Nonlinear Winkler Foundation (BNWF) and the soil type as homogenous medium-dense. Generally, the building resistance to seismic loads can be explained in terms of Incremental Dynamic Analysis (IDA); therefore, IDA curves are presented in this study. For comparison, the fragility evaluation is subjected to NFGM and FFGM as proposed by Quantification of Building Seismic Performance Factors (FEMA P-695). The seismic performance of Reinforced Concrete (RC) buildings with fixed and flexible foundations was evaluated to assess the probability of collapse. The results of this paper demonstrate that SSI and NFGM have significantly influenced the probability of failure of the RC frames. In particular, the flexible-base RC buildings experience higher Spectral acceleration (Sa) compared to the fixed-base ones subjected to FFGM and NFGM.

• Steel and Composite Structures
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• v.20 no.5
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• pp.1155-1171
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• 2016

Post-tensioned (PT) steel moment resisting frames (MRFs) with semi-rigid connections (SRC) can be used to control the hysteretic energy demands and to reduce the maximum inter-story drift (${\gamma}$). In this study the seismic behavior of steel MRFs with PT connections is estimated by incremental nonlinear dynamic analysis in terms of dissipated hysteretic energy ($E_H$) demands. For this aim, five PT steel MRFs are subjected to 30 long duration earthquake ground motions recorded on soft soil sites. To assess the energy dissipated in the frames with PT connections, a new expression is proposed for the hysteretic behavior of semi-rigid connections validated by experimental tests. The performance was estimated not only for the global $E_H$ demands in the steel frames; but also for, the distribution and demands of hysteretic energy in beams, columns and connections considering several levels of deformation. The results show that $E_H$ varies with ${\gamma}$, and that most of $E_H$ is dissipated by the connections. It is observed in all the cases a log-normal distribution of $E_H$ through the building height. The largest demand of $E_H$ occurs between 0.25 and 0.5 of the height. Finally, an equation is proposed to calculate the distribution of $E_H$ in terms of the normalized height of the stories (h/H) and the inter-story drift.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.21 no.5
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• pp.429-437
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• 2008

In this study the progressive collapse potential of braced frames were investigated using the nonlinear static and dynamic analyses. All of nine different brace types were considered along with a special moment-resisting frame for comparison. According to the pushdown analysis results, most braced frames designed per current design codes satisfied the design guidelines for progressive collapse initiated by loss of a first story mid-column; however most model structures showed brittle failure mode. This was caused by buckling of columns after compressive braces buckled. Among the braced frames considered, the inverted- V type braced frames showed superior ductile behavior during progressive collapse. The nonlinear dynamic analysis results showed that all the braced frame model structures remained in stable condition after sudden removal of a column, and their deflections were less than that of the moment-resisting frame.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2002.09a
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• pp.266-273
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• 2002

Pushover analysis is frequently used for evaluation of seismic performance and determination of seismic demand of a building structure in the current structural engineering practice field. However, pushover analysis has a advantage for estimation of seismic demands, which cannot account for the contributions of higher modes to response or for a redistribution of inertia forces because of structural yielding and the associated changes in the vibration properties of the structures. Recently, Chopra and Coel(2001) derived uncoupled inelastic dynamic equation of motion with several assumptions in the pushover analysis. By using this approach, pushover analysis for each mode is carried out and modal pushover analysis method, which can consider higher mode effects of the building, was suggested. The principle objective of this study is to introduced the modal pushover analysis by Chopra et al.(2001) and investigated the applicability and validity of this method for the steel moment frames subjected to various earthquake ground motions.