• Journal of the Earthquake Engineering Society of Korea
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• v.10 no.4 s.50
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• pp.85-94
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• 2006

In the design of bridge piers in seismic area, the ductility requirement is the most important factor. In order to enhance the seismic performance of RC columns, it is necessary to make the ductility of columns larger by covering RC columns with steel tubes or confining RC columns by arranging transverse reinforcements such as hoop ties closely. Using core steel composite columns is useful as one of the reinforcing RC columns. In this paper, quasi-static tests on concrete encased composite columns with single core steel or multiple steel elements were performed to investigate the seismic performance of the composite columns. Eight concrete-encased composite specimens were fabricated. The cross-sections of these specimens are composed of concrete-encased H-shaped structural steel columns and a concrete-encased circular tube with partial in-filled concrete. Test parameters were the amount of the transverse reinforcements, type and number of encased steel member. Through the tests, it was evaluated the ductility of SRC composite specimens. It has become clear from the test results that encased steel elements makes the deformation capacity of the columns to be larger. The displacement ductility and lateral strength of specimen with concrete-encased circular tube were indicated the biggest value.

• Structural Engineering and Mechanics
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• v.39 no.3
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• pp.411-425
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• 2011

This paper illustrates the results of a seismic vulnerability study aimed to derive the fragility curves for typical Algerian reinforced concrete bridge piers using an analytical approach. Fragility curves express the probability of exceeding a certain damage state for a given ground motion intensity (e.g., PGA). In this respect, a set of 41 worldwide accelerometer records from which, 21 Algerian strong motion records are included, have been used in a non-linear dynamic response analyses to assess the damage indices expressed in terms of the bridge displacement ductility, the ultimate ductility, the cyclic loading factor and the cumulative energy ductility. Combining the damage indices defined for 5 damage rank with the ground motion indices, the fragility curves for the bridge piers were derived assuming a lognormal distribution.

• Structural Engineering and Mechanics
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• v.45 no.6
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• pp.741-758
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• 2013

In this study, inelastic displacement ratios are investigated for existing systems with known lateral strength considering soil structure interaction. For this purpose, SDOF systems for period range of 0.1-3.0 s with different hysteretic behaviors are considered for a number of 18 earthquake motions recorded on soft soil. The effect of stiffness degradation on inelastic displacement ratios is investigated. The Modified Clough model is used to represent structures that exhibit significant stiffness degradation when subjected to reverse cyclic loading and the elastoplastic model is used to represent non-degrading structures. Soil structure interaction analyses are conducted by means of equivalent fixed base model effective period, effective damping and effective ductility values differing from fixed-base case. For inelastic time history analyses, Newmark method for step by step time integration was adapted in an in-house computer program. A new equation is proposed for inelastic displacement ratio of system with SSI with elastoplastic or degrading behavior as a function of structural period ($\tilde{T}$), strength reduction factor (R) and period lengthening ratio ($\tilde{T}$/T). The proposed equation for $\tilde{C}_R$ which takes the soil-structure interaction into account should be useful in estimating the inelastic deformation of existing structures with known lateral strength.

• Journal of the Earthquake Engineering Society of Korea
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• v.15 no.3
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• pp.11-26
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• 2011

The inelastic displacement ratio is defined as the ratio of the peak inelastic displacement to the peak linear elastic displacement. The inelastic displacement ratio allows simple evaluation of the peak inelastic displacement directly from the peak elastic displacement without computation of the inelastic response. Existing research of the inelastic displacement ratio is limited to piece-wise linear systems such as bilinear or stiffness degrading systems. In this paper, the inelastic displacement ratio is investigated for smooth hysteretic behavior systems subjected to near- and far-fault earthquakes. A simple formula of the inelastic displacement ratio is proposed by using a two step procedure of regression analysis.

• Proceedings of the KSR Conference
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• 2008.11b
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• pp.1012-1017
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• 2008

In this study, We examine closely the capacity spectrum method which a kind of displacement-based method evaluated by displacement of structure as an alternative to the load-based analysis method. The displacement-based method can easily review the strength of structure, seismic performance, ductility. Seismic performance by using capacity spectrum method is divided into design response spectrum and capacity spectrum. We can diagram design response spectrum by deciding the design seismic factor depending on performance target, site classification, seismic level, return period as UBC-97. Capacity spectrum is a load-displacement curve obtained by Push-over analysis considering the geometric parameter and the material parameter. We execute the seismic performance evaluation by using the capacity spectrum method to reinforced concrete pier which has been seismic design. As a result, We confirmed that there is a yield point and a ultimate point close by design response spectrum of UBC-97.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.29 no.6
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• pp.563-569
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• 2016

This paper presents the resizing method of columns and beams that considers column-to-beam strength ratios to simultaneously control the initial stiffness and ductility of steel moment frames. The proposed method minimizes the top-floor displacement of a structure while satisfying the constraint conditions with respect to the total structural weight and column-to-beam strength ratios. The design variable considered in this method is the sectional area of structural members, and the sequential quadratic programming(SQP) technique is used to obtain optimal results from the problem formulation. The unit load method is applied to determine the displacement participation factor of each member for the top floor lateral displacement; based on this, the sectional area of each member undergoes a resizing process to minimize the top-floor lateral displacement. Resizing members by using the displacement participation factor of each member leads to increasing the initial stiffness of the structure. Additionally, the proposed method enables the ductility control of a structure by adjusting the column-to-beam strength ratio. The applicability of the proposed optimal drift design method is validated by applying it to the steel moment frame example. As a result, it is confirmed that the initial stiffness and ductility could be controlled by the proposed method without the repetitive structural analysis and the increment of structural weights.

• Computers and Concrete
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• v.10 no.1
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• pp.1-18
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• 2012

This paper presents the details of studies conducted on hollow concrete block masonry (HCBM) units and wall panels. This study includes, compressive strength of unit block, ungrouted and grouted HCB prisms, flexural strength evaluation, testing of HCBM panels with and without opening. Non-linear finite element (FE) analysis of HCBM panels with and without opening has been carried out by simulating the actual test conditions. Constant vertical load is applied on the top of the wall panel and then lateral load is applied in incremental manner. The in-plane deformation is recorded under each incremental lateral load. Displacement ductility factors and response reduction factors have been evaluated based on experimental results. From the study, it is observed that fully grouted and partially reinforced HCBM panel without opening performed well compared to other types of wall panels in lateral load resistance and displacement ductility. In all the wall panels, shear cracks originated at loading point and moved towards the compression toe of the wall. The force reduction factor of a wall panel with opening is much less when compared with fully reinforced wall panel with no opening. The displacement values obtained by non-linear FE analysis are found to be in good agreement with the corresponding experimental values. The influence of mortar joint has been included in the stress-strain behaviour as a monolith with HCBM and not considered separately. The derived response reduction factors will be useful for the design of reinforced HCBM wall panels subjected to lateral forces generated due to earthquakes.

• Journal of the Korea Concrete Institute
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• v.26 no.2
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• pp.159-169
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• 2014

This study generalizes the lateral load-displacement relationship of reinforced concrete shear walls from the section analysis for moment-curvature response to straightforwardly evaluate the flexural capacity and ductility of such members. Moment and curvature at different selected points including the first flexural crack, yielding of tensile reinforcing bar, maximum strength, 80% of the maximum strength at descending branch, and fracture of tensile reinforcing bar are calculated based on the strain compatibility and equilibrium of internal forces. The strain at extreme compressive fiber to determine the curvature at the descending branch is formulated as a function of reduction factor of maximum stress of concrete and volumetric index of lateral reinforcement using the stress-strain model of confined concrete proposed by Razvi and Saatcioglu. The moment prediction models are simply formulated as a function of tensile reinforcement index, vertical reinforcement index, and axial load index from an extensive parametric study. Lateral displacement is calculated by using the moment area method of idealized curvature distribution along the wall height. The generalized lateral load-displacement relationship is in good agreement with test result, even at the descending branch after ultimate strength of shear walls.

• Earthquakes and Structures
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• v.9 no.3
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• pp.455-480
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• 2015

In the last decade, displacement-based (DB) methods have become established design procedures for reinforced concrete (RC) structures. They use strain and displacement measures as seismic performance control parameters. As for other simplified seismic design methods, it is of great interest to prove if they are usually conservative in respect to more refined, nonlinear, time history analyses, and can estimate design parameters with acceptable accuracy. In this paper, the current Direct Displacement-Based Design (DDBD) procedure is evaluated for designing simple single degree of freedom (SDOF) systems with specific reference to simply supported RC bridge piers. Using different formulations proposed in literature for the equivalent viscous damping and spectrum reduction factor, a parametric study is carried out on a comprehensive set of SDOF systems, and an average error chart of the method is derived allowing prediction of the expected error for an ample range of design cases. Following the chart, it can be observed that, for the design of actual RC bridge piers, underestimation errors of the DDBD method are very low, while the overestimation range of the simplified displacement-based procedure is strongly dependent on design ductility.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.671-676
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• 1999

Because of relatively heavy dead weight of concrete itself and unavoidable heat of massive concrete in bridge piers, circular hollow columns are widely used in Korean highway bridges. Since the occurrence of 1995 Kobe earthquake, there have been much concerns about seismic design for various infrastructures, inclusive of bridge structures. It is, however, understood that there are not much research works for nonlinear behavior of circular hollow columns subjected to earthquake motions. The ultimate of this experimental research is investigate nonlinear behavior of circular hollow reinforced concrete bridge piers under the quasi-static cyclic load, and then to enhance their ductility by strengthening the plastic hinge region with glassfiber sheets. It is concluded from quasi-static tests for 7 bridge piers that energy dissipation capacity and curvatures for a given displacement ductility factor $\{\mu}=frac{\Delta}{\Delta_y}$are about 20% higher for the seismically designed columns and about 70% higher for the retrofitted piers than the nonseismically designed columns in a conventional way.