• Journal of the Earthquake Engineering Society of Korea
• /
• v.28 no.1
• /
• pp.11-20
• /
• 2024

The ductility of the system based on the capacity of each structural member constituting the seismic force-resisting system is a significant factor determining the structure's seismic performance. This study aims to provide a procedure to supplement the current seismic design criteria to secure the system's ductility and improve the seismic performance of the steel ordinary moment frames. For the study, a nonlinear analysis was performed on the 9- and 15-story model buildings, and the formation of collapse mechanisms and damage distribution for dynamic loads were analyzed. As a result of analyzing the nonlinear response and damage distribution of the steel ordinary moment frame, local collapse due to the concentration of structural damage was observed in the case where the influence of the higher mode was dominant. In this study, a procedure to improve the seismic performance and avoid inferior dynamic response was proposed by limiting the strength ratio of the column. The proposed procedure effectively improved the seismic performance of steel ordinary moment frames by reducing the probability of local collapse.

• Journal of Korean Society of Steel Construction
• /
• v.29 no.4
• /
• pp.269-280
• /
• 2017

In this study, seismic performance was evaluated for the exposed column-base plate weak-axis connections of small size steel structures through cyclic loading tests. The primary test parameters are the thickness of base plate, the presence of rib plates, the number of anchor bolts and embedment length of anchor bolts. To investigate the effect of bond performance of anchor bolts on the seismic performance of column-base plate connections, L-shaped round bars and thread bars were used as the hooked anchor bolts in the test specimens. Test results showed that bond performance of anchor bolts and the thickness of base plate significantly affect the structural performance and energy dissipation capacity. In particular, it was found that even if the requirements for minimum thickness of the base plate that is satisfied, the base plate can yield before the capacity of steel column reaches the plastic moment resulting in decreasing the structural performance of the connections. However, the proposed details of the connections might be considered as the partially restrained, that is semi-rigid connections. Consequently, the L-shaped thread anchor bolts is applicable in the exposed column-base plate weak-axis connections of small-size steel structures.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.26 no.4
• /
• pp.263-269
• /
• 2013

In this study, the strain based monitoring method to evaluate the lateral structural response of buildings is presented and an applicability of the proposed method is confirmed through the numerical study. It is assumed that the fiber Bragg grating(FBG) strain sensor is employed to measure the strain response of members due to the excellent properties such as multiplexing, and higher sampling frequency. These properties of FBG sensors is proper for buildings the a lot of sensors are required to monitor the reponses of those. FBG sensors measure the strain response of vertical members and are employed to calculate the curvatures of members using the measured strain responses. Then the lateral displacement, and lateral acceleration is evaluated based on the curvatures of vertical members. Additionally, these dynamic responses of buildings are used to evaluate the dynamic properties of buildings such as the natural frequencies and mode shapes using the frequency domain decomposition(FDD) method. Through the application of nine-story steel moment frame example structure, it is confirmed that the proposed method is appropriate to evaluate the lateral structural responses and dynamic properties of buildings.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.31 no.6
• /
• pp.293-299
• /
• 2018

Steel truss outriggers can be replaced by reinforced concrete walls to control the lateral drift of tall buildings. When reinforced concrete outrigger walls are connected to perimeter columns, not only axial forces but also shear forces and moments can be induced on the perimeter columns. In this study, the shear force of the perimeter column due to the rotation of the outer edge of the outrigger wall is derived as analytic equations and the result is compared with the finite element analysis result. In the finite element analysis, the effects of connecting beams at each floor and the effect of modeling shear walls and outriggers with beam element and plane stress element was analyzed. The effect of the connecting beam was almost negligible and the plane stress element was determined to have greater stiffness than the beam element. The inter-story rotation and the shear force of the perimeter column due to the rotation of the outer edge of the outrigger wall was considerably smaller than the allowable value. Therefore, even if the outrigger wall made of reinforced concrete is applied to a tall building, it is considered that there is no need to study the shear force and moment induced in the perimeter columns.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.12 no.2
• /
• pp.69-80
• /
• 2008

In this study, improved capacity spectrum method (CSM) is proposed. The method can account for higher mode contribution to the seismic response of MDOF systems. The CSM has been conveniently used for determining maximum roof displacement using both demand spectrum and capacity curve of equivalent SDOF system. Unlike the conventional CSM, the maximum roof displacement is determined without iteration using inelastic displacement ratio and R factor calculated from demand spectrum and capacity curve. Three moment resisting steel frames of 3-, 9- and 20-stories are considered to test the accuracy of the proposed method. Nonlinear response history analysis (NL-RHA) for three frames is also conducted, which is considered as an exact solution. SAC LA 10/50 and 2/50 sets of ground motions are used. Moreover, this study estimates maximum story drift ratios (IDR) using ATC-40 CSM and N2-method and compared with those from the proposed method and NL-RHA. It shows that the proposed CSM estimates the maximum IDR accurately better than the previous methods.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.16 no.2
• /
• pp.173-182
• /
• 2003

In equivalent static nonlinear analysis and in energy-based design, the structures are generally transformed into an equivalent SDOF system. In this study the seismic energy demands in multi story structures, such as three-, eight-, and twenty-story steel moment-resisting frames(MRF), buckling restrained braced frames(BRBF) and a damage tolerant braced frame(DTBF), are compared with those of equivalent single degree of freedom(ESDOF) systems. Sixty earthquake ground motions recorded In different soil conditions, which are soft rock, soft soil, and neat fault, were used to compute the input and hysteretic energy demands in model structures. In case the modal mass coefficient is less than 0.8, the effects of higher modes are considered in the process of converting into ESDOF According to the analysis results, the hysteretic and input energies obtained from 3 story and 8 story MRF and DTBF agreed well with the results from analysis of equivalent SDOF systems. However in the 20 story BRBF the results from ESDOF underestimated those obtained from the original structures.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.18 no.1
• /
• pp.37-43
• /
• 2014

In current seismic design code, steel moment frames are classified into ordinary, intermediate, and special moment frames. In the case of special moment frames which have large R-factor, economic design is possible by reducing the design lateral force. However, there is difficulty for practical application due to constraints such as strong column-weak beam requirement. This study evaluated if steel intermediate moment frame could maintain enough seismic capacity when the R-factor is increased from 4.5 to 6. As for the analytical models, steel moment frames of 3 and 5 stories were categorized into four performance groups according to seismic design category. Seismic performances of the frames were evaluated through the procedure based on FEMA P695. FEMA P695 utilizes nonlinear static analysis(pushover analysis) and nonlinear dynamic analysis(incremental dynamic analysis, IDA). In order to reflect the characteristics of Korean steel moment frames on the analytical model, the beam-column connection was modeled as weak panel zone where the collapse of panel zone was indirectly considered by checking its ultimate rotational angle after an analysis is done. The analysis result showed that the performance criteria required by FEMA P695 was satisfied when R-factor increased in all the soil conditions except $S_E$.

• Journal of Korean Society of Steel Construction
• /
• v.13 no.4
• /
• pp.351-361
• /
• 2001

The connections are classified as rigid, semi+rigid, or pinned. There are two classification systems, EC3 adn Bjorhovede et al., representatively. The EC3 boundary between rigid and semi-rigid connections is in on the whole restrictive in term of the stiffness as well as the moment capacity of connections. The boundary specified by Bjorhovede et al. may not be sufficient to assure the behavior of rigid frames in some cases. In this study, it is proposed the new classification system for steel connection that depends on the reduction factor(R) of critical buckling load for unbraced semi-rigid frame expressed by the stiffness ratio($\rho$) of beam to column and the stiffness ratio(k) of connection to beam. Finally, it is examined by experimental data that new classification criteria provides a practical boundary compared wit hteh existing classifications.

• Journal of Korean Society of Steel Construction
• /
• v.19 no.6
• /
• pp.663-670
• /
• 2007

Column-tree beam-to-column joints are widely used in moment-resisting frames in Korea. In this study, we proposed four different arrangements for weak-axis moment-resisting beam-to-column connections, which are more economical than the conventional connection, while developing similar structural performance. We investigated the proposed connections whose connection details were different from the conventional one. The experiment was also conducted on a total of five beam-to-column joint specimensto verify the structural performance of the proposed connections. All four connections proposed in this study were found to be more economical that the conventional connection. Three out of four specimens with proposed details were able to developa structural performance similar to that of the specimen with the conventional detail.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.24 no.5
• /
• pp.569-576
• /
• 2011

In this paper a new analysis procedure for evaluation of progressive collapse resisting capacity of a structure was proposed based on the nonlinear static analysis procedure. The proposed procedure produces analysis results identical to those obtained by the linear static analysis procedure specified in the GSA guidelines without iteration, therefore saving a lot of computation time and excluding the possibility of human errors during the procedure. To verify the validity of the proposed procedure, the two methods were applied to the analysis of a reinforced concrete moment frame and a steel braced frame subjected to loss of a first story column and the results were compared. According to the analysis results, the two methods produce identical results in the prediction of progressive collapse and the hinge formation. As iterative analysis is not required in the proposed method, significant amount of analysis time is saved in the proposed analysis procedure.