• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2001.04a
• /
• pp.446-453
• /
• 2001

System-level ductility is an essential parameter for seismic performance evaluation of multistory building structures. The ductility demands for single degree of freedom structures or individual structural members can be determined easily. However, there is no clearly established method to determine the ductility demands for structural systems. The system ductility demands are estimated in this study by the equivalent SDOF system methods and proposed method which used the representative responses obtained from the MDOF systems directly. And seismic performance of building structures is evaluated by the modified Capacity Spectrum Method using the representative responses, and the result was compared with those of the inelastic time history analysis.

• Journal of the Korea Concrete Institute
• /
• v.16 no.3 s.81
• /
• pp.357-367
• /
• 2004

In this paper, the effect of cumulative damage for reinforced concrete bridge piers subjected to both single and multiple earthquakes is investigated. For this purpose, selected are three set of accelerograms one of which represents the real successive input ground motions, recorded at the same station with three months time interval. The analytical predictions indicate that piers are in general subjected to a large number of inelastic cycles and increased ductility demand due to multiple earthquakes, and hence more damage in terms of stiffness degradation is expected to occur. In addition, displacement ductility demand demonstrates that inelastic seismic response of piers can significantly be affected by the applied input ground motion characteristics. Also evaluated is the effect of multiple earthquakes on the response with shear. Comparative studies between the cases with and without shear indicate that stiffness degradation and hence reduction in energy dissipation capacity of piers are pronounced due to the multiple earthquakes combined with shear. It is thus concluded that the effect of multiple earthquakes should be taken into account for the stability assessment of reinforced concrete bridge piers.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.30 no.1
• /
• pp.132-138
• /
• 2002

Of srategic importance nowdays is the development of high performance spacecraft bus. In this study, optimization for spacecraft structure is performed under the framework of coupled load analysis which is a branch of component mode synthesis with constrained mode and modal transient analysis. unlike the traditional method which uses the quasi-static table supplied by launch vehicle contractor, the present method adots the load results of previous coupled load analysis. It if shown that the proposed method can serve as a effective tool for the optimization spacecraft structure in the early stage of design and weight reduction by numerical example.

• Journal of the Korea Concrete Institute
• /
• v.14 no.4
• /
• pp.578-588
• /
• 2002

An experimental study was conducted to investigate the effectiveness of transverse reinforcement in reinforced concrete tied columns subjected to monotonically increasing axial compression. Eighteen large-scale columns(260$\times$260$\times$1200 mm) were tested. Effects of main variables such as the concrete compressive strength, the tie configuration, the transverse reinforcement ratio, the tie spacing, and the spatting of the concrete cover were considered. High-strength concrete columns under concentric axial loads show extremely brittle behavior unless the columns are confined with transverse reinforcement that can provide sufficiently high lateral confinement pressure There is a consistent decrease in deformability of column specimen with increasing concrete strength. Test results were compared with the previous confinement model such as modified Kent-Park, Sheikh-Uzumeri, Mander, and Saatcioglu-Razvi model. The comparison indicates that many previous models for confined concrete overestimate or underestimate the ductility of confined concrete.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.27 no.3
• /
• pp.137-145
• /
• 2014

We present a design sensitivity analysis(DSA) method for multiscale problems based on bridging scale decomposition. In this paper, we utilize a bridging scale method for the coupled system analysis. Since the analysis of full MD systems requires huge amount of computational costs, a coupled system of MD-level and continuum-level simulation is usually preferred. The information exchange between the MD and continuum levels is taken place at the MD-continuum boundary. In the bridging scale method, a generalized Langevin equation(GLE) is introduced for the reduced MD system and the GLE force using a time history kernel is applied at the boundary atoms in the MD system. Therefore, we can separately analyze the MD and continuum level simulations, which can accelerate the computing process. Once the simulation of coupled problems is successful, the need for the DSA is naturally arising for the optimization of macro-scale design, where the macro scale performance of the system is maximized considering the micro scale effects. The finite difference sensitivity is impractical for the gradient based optimization of large scale problems due to the restriction of computing costs but the analytical sensitivity for the coupled system is always accurate. In this study, we derive the analytical design sensitivity to verify the accuracy and applicability to the design optimization of the coupled system.

• Computational Structural Engineering
• /
• v.10 no.4
• /
• pp.281-290
• /
• 1997

Current seismic design code is based on the assumption that the designed structures would be behaved inelastically during a severe earthquake ground motion. For this reason, seismic design forces calculated by seismic codes are much lower than the forces generated by design earthquakes which makes structures responding elastically. Present procedures for calculating seismic design forces are based on the use of elastic spectra reduced by a strength reduction factors known as "response modificaion factor". Because these factors were determined empirically, it is difficult to know how much inelastic behaviors of the structures exhibit. In this study, lateral strength required to maintain target ductility ratio was first calculated from nonlinear dynamic analysis of the single degree of freedom system. At the following step, base shear foeces specified in seismic design code compare with above results. If the base shear force required to maintain target ductility ratio was higher than the code specified one, the lack of required strength should be filled by overstrength and/or redundancy. Therefore, overstrength of moment resisting frame structure will be estimated from the results of push-over analysis.

• Journal of the Korea Concrete Institute
• /
• v.19 no.5
• /
• pp.529-537
• /
• 2007

The purpose of this study is to discuss how strength and ductility of each system in low-rise reinforced concrete buildings composed of extremely brittle, shear and flexural failure lateral-load resisting systems have influence on seismic capacities of the overall system, which is based on nonlinear seismic response analyses of single-degree-of-freedom structural systems. In order to simulate the triple lateral-load resisting system, structures are idealized as a parallel combination of two modified origin-oriented hysteretic models and a degrading trilinear hysteretic model that fail primarily in extremely brittle, shear and flexure, respectively. Stiffness properties of three models are varied in terms of story shear coefficients, and structures are subjected to various ground motion components. By analyzing these systems, interaction curves of demand strengths of the triple system for various levels of ductility factors are finally derived for practical purposes. The result indicates that demand strength levels derived can be used as a basic information for seismic evaluation and design criteria of low-rise reinforced concrete buildings having the triple lateral-load resisting system.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.14 no.2
• /
• pp.37-47
• /
• 2010

In order to attain enhanced seismic performance of RC bridges, premature shear failure prior to the achievement of target ductilities of the piers should be prevented. For this purpose, a reliable shear strength evaluation is required. The shear strength of an RC column subjected to a lateral force decreases with an increase in ductility. Many empirical equations for the shear strength have been proposed by many researchers. However, there are many discrepancies in the initial shear strength in the low ductility range, and in the decrease rate according to the ductility. In this study, a new empirical equation of shear strength considering the displacement ductility effect has been proposed, in which the initial shear strength equation proposed by the authors was revised on the basis of the investigation of many other researchers' test results. The resulting improvement in accuracy is confirmed by comparison with other empirical equations.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.14 no.6
• /
• pp.85-92
• /
• 2010

Recently the earthquake occurrences in Korea are likely to increase. Therefore, the facilities such as bridges and tunnels under the unexpected earthquakes need to be enhanced. Especially most of the subways previously built before 1988 have not been seismically designed, so their seismic safety requirements are required to be inspected and/or reinforced. In this study, the seismic reinforcement using FRP-ductile material layered composites was proposed to reinforce for the subway columns. Material properties of FRP-ductile material layered composites were calculated by laboratory tests considering the laminated conditions of the composites. Numerical simulations were performed using the experimental results of the specimens and the calculated properties of the composites. Seismic performance varied according to the types of composites: ductile material, number of layers, fiber orientations.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.12 no.5
• /
• pp.47-56
• /
• 2008

This study was performed to evaluate the effect of Response modification factors (R-factor) in 3-, 9- and 20- story steel Moment Resisting Frame (MRF) buildings. Each structure was designed using a R-factor of 8, as tabulated in the 2000 International Building Code provision (IBC 2000) and Korea Building Code (KBC) 2008. In order to evaluate the maximum and minimum performance expected for such structures, an upper bound and lower bound design were adopted for each model. Next, each analytical model was designed using different R-factors (8, 9, 10, 11, 12) and four different structural periods with the original fundamental period. For a detailed case study, a total of 150 analytical models were subjected to 20 ground motions representing a hazard level with a 2% probability of being exceeded in 50 years. In order to evaluate the performance of the structures, static push-over and non-linear time history analysis (NTHA) were performed, and displacement ductility demand was investigated to consider the ductility capacity of the structures. The results show that the dynamic behaviors for the 3- and 9-story buildings are relatively stable and conservative, while the 20-story buildings show a large displacement ductility demand due to dynamic instability factors. (e.g. P-delta effect and high mode effect)