• Structural Engineering and Mechanics
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• v.68 no.5
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• pp.621-632
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• 2018

Soft-story buildings have bottom stories much less rigid than the top stories and are susceptible to earthquake damage. Therefore, the seismic design specifications need strict design considerations in such cases. In this paper, a four-story building was investigated as a case study and the effects of X-braces elimination in its lower stories studied. In addition, the possibility of replacement of the X-braces in soft-stories with equivalent moment resisting frame inspected in two different phases. In first phase, the stiffness of X-braces and equivalent moment-resisting frames evaluated using classic equations. In final phase, diagonals removed from the lowest story to develop a soft-story and replaced with moment resisting frames. Then, the seismic stiffness variation of moment-resisting frame evaluated using nonlinear static and dynamic analyses. The results show that substitution of braced frames with an equivalent moment-resisting frame of the same stiffness increases story drift and reduces energy absorption capacity. However, it is enough to consider the needs of building codes, even using equivalent moment resisting frame instead of X-Braces, to avoid soft-story stiffness irregularity in seismic design of buildings. Besides, soft-story development in the second story may be more critical under strong ground excitations, because of interaction of adjacent stories.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.553-558
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• 1999

As a process of development of composite beam-column connection system, structural tests have been conducted to verify moment resisting performance of the system. The tests have been proceeded by two steps, the first being welding performance test of the steel connection rod and stiffners, and the second overall moment resisting capacity of the fuly assembled system. Ten welding test specimens and four prototype specimens have been used in the test. Good structural performance of welding test specimens has been observed without any single welding failure, and sufficient moment resisting capacity has been proved from the overall performance test, with the moment magnitude in excess of the calculated plastic moment.

• Structural Engineering and Mechanics
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• v.35 no.5
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• pp.617-630
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• 2010

Different types of moment resisting connections are commonly used to transfer the induced seismic moments between frame elements in an earthquake resisting structure. The local connection behavior may drastically affect the global seismic response of the structure. In this study, the finite element and experimental seismic investigations are implemented on two frequently used connection type to evaluate the local behavior and to reveal the failure modes. An alternative connection type is then proposed to eliminate the unfavorable brittle fracture modes resulted from probable poor welding quality. This will develop a reliable predefined ductile plastic mechanism forming away from the critical locations. Employing this technique, the structural reliability of the moment resisting connections shall be improved by achieving a controllable energy dissipation source in form of yielding of the cover plates.

• Journal of the Earthquake Engineering Society of Korea
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• v.17 no.1
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• pp.33-41
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• 2013

Due to a high level of system ductility, steel moment resisting frames have been widely used for lateral force resisting structural systems in high seismic zones. Earthquake field investigations after Northridge earthquake in 1994 and Kobe earthquake in 1995 have reported that many steel moment resisting frames designed before 1990's had suffered significant damages and structural collapse. In this research, seismic performance assessment of steel moment resisting frames designed in accordance with the previous seismic provisions before 1990's was performed. Buckling-restrained braces and shear walls are considered for seismic retrofit of the reference buildings. Increasing stiffness and strength of the buildings using buckling-restrained braces and shear walls are considered as options to rehabilitate the damaged buildings. Probabilistic seismic performance assessment using fragility analysis results is used for the criteria for determining an appropriate seismic retrofit strategy. The fragility contour method can be used to provide an intial guideline to structural engineers when various structural retrofit options for the damaged buildings are available.

• Earthquakes and Structures
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• v.15 no.4
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• pp.383-393
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• 2018

In this study, seismic performance of low and medium-rise RC buildings with wide-beam and ribbed-slab were evaluated numerically. Moment resisting systems consisting of moment and dual frame were selected as structural system of the buildings. Sufficiency of moment resisting wide-beam frames designed with high ductility requirements were evaluated. Upon necessity frames were stiffen with shear-walls. The buildings were designed in accordance with the Turkish Earthquake Code (TEC 2007) and were evaluated by using the strain-based nonlinear static method specified in TEC. Second order (P-delta) effects on the lateral load capacity of the buildings were also assessed in the study. The results indicated that the predicted seismic performances were achieved for the low-rise (4-story) building with the high ductility requirements. However, the moment resisting frame with high ductility was not adequate for the medium-rise building. Addition of sufficient amount of shear-walls to the system proved to be efficient way of providing the target performance of structure.

• Journal of the Korea Institute of Building Construction
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• v.15 no.6
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• pp.569-577
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• 2015

Recently, the concept of seismic design has changed from prescriptive to performance based design. For the performance based design with the specified target performance of the structure, it is necessary to execute the inelastic structural analysis to predict precisely the actual behavior of the structure. To address this issue, the seismic performance of the 5-story RC moment-resisting frames designed in accordance with KBC2009 is evaluated through push-over analysis and economic analysis is conducted focused on the direct construction costs. The results show that the ordinary and the intermediate moment-resisting frame are evaluated to meet the required performance design criteria and that the direct construction costs of the two frames are similar. However, although the special moment-resisting frame designed with strong column-weak girder philosophy satisfies the required performance design criteria, the direct construction cost is uneconomical compared with other frames. Therefore, although the intermediate moment-resisting frame of design category D is prohibited in IBC2012, the ordinary and the intermediate moment-resisting frame are estimated to be more reasonable than the special moment-resisting frame for the design of 5-story RC moment-resisting frame.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2000.10a
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• pp.233-238
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• 2000

The purpose of this study is to outline the analysis procedure for evaluating the performance of moment resisting steel frames. For this purpose, three ordinary moment resisting frames are designed in compliance to UBC 1994. The evaluation is performed by nonlinear static procedures using two analytical models. Only one analytical model using panel element can reflect the panel zone deformation explicitly. The limit values in FEMA 273 are used as guidelines of predicted demand parameters by which the performance of OMRFs may be assessed.

• Journal of the Earthquake Engineering Society of Korea
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• v.27 no.1
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• pp.13-24
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• 2023

In this study, alternative seismic force-resisting systems for plant structure supporting equipment were designed, and the seismic performance thereof was compared using nonlinear dynamic analysis. One alternative seismic force-resisting system was designed per the requirement for ordinary moment-resisting and concentrically braced frames but with a reduced base shear. The other seismic force-resisting system was designed by accommodating seismic details of intermediate and unique moment-resisting frames and special concentrically braced frames. Different plastic hinge models were applied to ordinary and ductile systems based on the validation using existing test results. The control model obtained by code-based flexible design and/or reduction of base shear did not satisfy the seismic performance objectives, but the alternative structural system did by strengthened panel zones and a reduced effective buckling length. The seismic force to equipment calculated from the nonlinear dynamic analysis was significantly lower than the equivalent static force of KDS 41 17 00. The comparison of design alternatives showed that the seismic performance required for a plant structure could be secured economically by using performance-based design and alternative seismic-force resisting systems adopting minimally modified seismic details.

• Steel and Composite Structures
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• v.19 no.2
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• pp.467-484
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• 2015

Seismic performances of dual steel moment-resisting frames with mixed use of rigid and semi-rigid connections were investigated to control of the base shear, story drifts and the ductility demand of the elements. To this end, nonlinear seismic responses of three groups of frames with three, eight and fifteen story were evaluated. These frames with rigid, semi-rigid and combined configuration of rigid and semi-rigid connections were analyzed under five earthquake records and their responses were compared in ultimate limit state of rigid frame. This study showed that in all frames, it could be found a state of semi-rigidity and connections configuration which behaved better than rigid frame, with consideration of the base shear and story drifts criterion. Finally, some criteria were suggested to locate the best place of the semi-rigid connections for improvement of the seismic performance of steel moment-resisting frames.

• Structural Engineering and Mechanics
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• v.87 no.1
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• pp.69-84
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• 2023

The use of steel pipe dampers (SPD) as fuses or interchangeable elements in the steel moment-resisting frames (MRF) is one of the newest methods for improving seismic performance. In the present study, the performance of steel pipe dampers in MRF has been investigated. Evaluation of MRF with and without SPD models were performed using the finite element method by ABAQUS. For validation, an MRF and MRF with steel pipe dampers were modeled that had been experimentally tested and reported in previous experimental research and a good agreement was observed. The behavior of these dampers in frames of 3, 6, and 9 stories was studied by modeling the damper directly. Nonlinear time history dynamic analysis was used. It was observed that by increasing the number of stories in the buildings, steel pipe dampers should be used to perform properly against earthquakes. The installation of steel pipe dampers in steel moment-resisting frames shows that the drift ratio between the floors is reduced and the seismic performance of these frames is improved.