• Journal of the Earthquake Engineering Society of Korea
• /
• v.20 no.7_spc
• /
• pp.461-472
• /
• 2016

Damage potential has been investigated for a domestic metropolitan railway bridge subjected to 2016 Gyeongju earthquake which has been reported as the strongest earthquake in Korea. For this purpose, nonlinear static pushover analyses for the bridge piers have been carried out to evaluate ductility capacities. Then, the capacities have been compared with those suggested by Railway Design Standards of Korea. This comparison shows that all piers possess enough safety margins. Nonlinear dynamic time-history analysis has also been conducted to estimate both displacement and shear force demands for the bridge subjected to ground motions recorded at stations in near of Gyeongju. Maximum demands reveal that response under the ground motions remains essentially in elastic. In addition, for a further assessment of the bridge under the Gyeongju earthquake, fragility analyses have been performed using those ground motions. The fragility results indicate that the recorded earthquakes do not significantly affect the damage exceedance probability of the bridge piers.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.20 no.7_spc
• /
• pp.473-483
• /
• 2016

In this paper, seismic performance assessment has been examined for a mid-rise RC building subjected to 2016 Gyeongju earthquake occurred in Korea. For the purpose of the paper, 2D external and internal frames in each direction of the building have been employed in the present comparative analyses. Nonlinear static pushover analyses have been conducted to estimate frame capacities. Nonlinear dynamic time-history analyses have also been carried out to examine demands for the frames subjected to ground motions recorded at stations in near of Gyeongju and a previous earthquake ground motion. Analytical predictions demonstrate that maximum demands are significantly affected by characteristics of both spectral acceleration response and spectrum intensity over a wide range of periods. Further damage potential of the frames has been evaluated in terms of fragility analyses using the same ground motions. Fragility results reveal that the ground motion characteristics of the Gyeongju earthquake have little influence on the seismic demand and fragility of frames.

• Earthquakes and Structures
• /
• v.9 no.3
• /
• pp.639-656
• /
• 2015

Seismic isolation devices are commonly used to mitigate damages caused by seismic responses of structures. More damages are created due to progressive collapse in structures. Therefore, evaluating the impact of the isolation systems to enhance progressive collapse-resisting capacity is very important. In this study, the effect of lead rubber bearing isolation system to increase the resistance of structures against progressive collapse was evaluated. Concrete moment resisting frames were used in both the fixed and base-isolated model structures. Then, progressive collapse-resisting capacity of frames was investigated using the push down nonlinear static analysis under gravity loads that specified in GSA guideline. Nonlinear dynamic analysis was performed to consider dynamic effects column removal under earthquake. The results of the push down analysis are highly dependent on location of removal column and floor number of buildings. Also, seismic isolation system does not play an effective role in increasing the progressive collapse-resisting capacities of structures under gravity loads. Base isolation helps to localize failures and prevented from spreading it to intact span under seismic loads.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.17 no.4
• /
• pp.171-180
• /
• 2013

The purpose of this study is to evaluate the effectiveness of the seismic retrofit performance for a reinforced concrete structure with steel damper. The nonlinear static analysis of the RC frame specimens with and without retrofit using the steel damper was conducted and the reliability of the analysis was verified by comparing the analysis and test results. Using this analysis model and method, additional nonlinear analysis was conducted considering varying stiffness and strength ratios between RC frame and steel damper and the failure mode of RC frame. As the result of the study, the total absorbed energy increased and the damage of RC frame was reduced as stiffness and strength ratios increased. The seismic retrofit performance, evaluated by means of the yield strength, increasing ratio of the absorbed energy and damage of the frame, increased linear proportionally with the increase of the strength ratio. In addition, the seismic retrofit performance was stable for stiffness ratios larger than 4~5. The energy absorption capacity of the frame governed by shear failure was better than that of the frame governed by flexure failure.

• Earthquakes and Structures
• /
• v.2 no.1
• /
• pp.43-64
• /
• 2011

One-dimensional rod theory is very effective as a simplified analytical approach to large scale or complicated structures such as high-rise buildings, in preliminary design stages. It replaces an original structure by a one-dimensional rod which has an equivalent stiffness in terms of global properties. The mechanical behavior of structures composed of distinct constituents of different stiffness such as coupled walls with opening is significantly governed by the local variation of stiffness. Furthermore, in structures with setback the distribution of the longitudinal stress behaves remarkable nonlinear behavior in the transverse-wise. So, the author proposed the two-dimensional rod theory as an extended version of the rod theory which accounts for the two-dimensional local variation of structural stiffness; viz, variation in the transverse direction as well as longitudinal stiffness distribution. This paper proposes how to deal with the two-dimensional rod theory for structures with setback. Validity of the proposed theory is confirmed by comparison with numerical results of computational tools in the cases of static, free vibration and forced vibration problems for various structures. The transverse-wise nonlinear distribution of the longitudinal stress due to the existence of setback is clarified to originate from the long distance from setback.

• Earthquakes and Structures
• /
• v.13 no.6
• /
• pp.539-549
• /
• 2017

Existing reinforced concrete frame buildings designed for vertical loads could only suffer severe damage during earthquakes. In recent years, many research activities were undertaken to develop a reliable and practical analysis procedure to identify the safety level of existing structures. The Incremental Dynamic Analysis (IDA) is considered to be one of the most accurate methods to estimate the seismic demand and capacity of structures. However, the executions of many nonlinear response history analyses (NL_RHA) are required to describe the entire range of structural response. The research discussed in this paper deals with the proposal of an efficient Incremental Modal Pushover Analysis (IMPA) to obtain capacity curves by replacing the nonlinear response history analysis of the IDA procedure with Modal Pushover Analysis (MPA). Firstly, In this work, the MPA is examined and extended to three-dimensional asymmetric structures and then it is incorporated into the proposed procedure (IMPA) to estimate the structure's seismic response and capacity for given seismic actions. This new procedure, which accounts for higher mode effects, does not require the execution of complex NL-RHA, but only a series of nonlinear static analysis. Finally, the extended MPA and IMPA were applied to an existing irregular framed building.

• Structural Engineering and Mechanics
• /
• v.69 no.3
• /
• pp.243-255
• /
• 2019

Utilization of fiber beam-column element has gained considerable attention in recent years due mainly to its ability to model distributed plasticity over the length of the element through a number of integration points. However, the relatively high sensitivity of the method to modeling parameters as well as material behavior models can pose a significant challenge. Residual drift is one of the seismic demands which is highly sensitive to modeling parameters and material behavior models. Permanent deformations play a prominent role in the post-earthquake evaluation of serviceability of bridges affected by a near-fault ground shaking. In this research, the influence of distributed plasticity modeling parameters using both force-based and displacement-based fiber elements in the prediction of internal forces obtained from the nonlinear static analysis is studied. Having chosen suitable type and size of elements and number of integration points, the authors take the next step by investigating the influence of material behavioral model employed for the prediction of permanent deformations in the nonlinear dynamic analysis. The result shows that the choice of element type and size, number of integration points, modification of cyclic concrete behavior model and reloading strain of concrete significantly influence the fidelity of fiber element method for the prediction of permanent deformations.

• International Journal of Naval Architecture and Ocean Engineering
• /
• v.12 no.1
• /
• pp.743-754
• /
• 2020

This study provides an insight of the nonlinear behavior of the Offshore Wind Turbine (OWT) structure using the distributed plasticity approach. The fiber section beam-column element is applied to construct the finite element model. The accuracy of the proposed model is verified using linear analysis via the comparison of the dynamic characteristics. For collapse risk assessment of OWT, the nonlinear effects considering the earthquake Incident Angle (IA) have been evaluated first. Then, the Incremental Dynamic Analysis (IDA) has been executed using a set of 20 near-fault records. Lastly, fragility curves are developed to evaluate the vulnerability of structures for different limit states. Attained results justify the accuracy of the proposed approach for the structural response against the ground motions and other environmental loads. It indicates that effects of static wind and wave loads along with the earthquake loads should be considered during the risk assessment of the OWT structure.

• Structural Engineering and Mechanics
• /
• v.83 no.6
• /
• pp.811-824
• /
• 2022

Despite its disadvantages, soft story can reduce the damage to the upper floors by concentrating drift in that specific story provided that large drifts are avoided. Gapped-Inclined Brace (GIB) with reduced P-delta effects and the control of soft story stiffness makes it possible to take advantage of the soft story in buildings and increase their capacity for energy dissipation. OpenSees software is used in this study to validate and modify the GIB model's shortcomings. Also, the analysis method for this element is changed for design. The modified element is evaluated in 3D analysis. Finally, to retrofit an existing building, this element is used. Based on the Iranian seismic code, a six-story reinforced concrete building is modelled and studied with 3D analysis. In this building, the construction shortcomings and elimination of infills on the ground floor cause the formation of a soft story. Results of nonlinear static analysis, nonlinear dynamic, and incremental dynamic analysis using both components of seismic acceleration applied to the structure at different angles and the fragility curves indicate the improvement of the retrofitted structure's performance using the modified element to reach the required performance level following the retrofit code.

• Earthquakes and Structures
• /
• v.22 no.6
• /
• pp.585-595
• /
• 2022

Using the nonlinear static procedures has become very common in seismic codes to achieve the nonlinear response of the structure during an earthquake. The capacity spectrum method (CSM) adopted in ATC-40 is considered as one of the most known and useful procedures. For this procedure the seismic demand can be approximated from the maximum deformation of an equivalent linear elastic Single-Degree-of-Freedom system (SDOF) that has an equivalent damping ratio and period by using an iterative procedure. Data from the results of this procedure are plotted in acceleration- displacement response spectrum (ADRS) format. Different improvements have been made in order to have more accurate results compared to the Non Linear Time History Analysis (NL-THA). A new procedure is presented in this paper where the iteration process shall not be required. This will be done by estimation the ductility demand response spectrum (DDRS) and the corresponding effective damping of the bilinear system based on a new parameter of control, called normalized yield strength coefficient (η), while retaining the attraction of graphical implementation of the improved procedure of the FEMA-440. The proposed procedure accuracy should be verified with the NL-THA analysis results as a first implementation. The comparison shows that the new procedure provided a good estimation of the nonlinear response of the structure compared with those obtained when using the NL-THA analysis.