• Earthquakes and Structures
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• 제9권3호
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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.

• Steel and Composite Structures
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• 제25권6호
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• pp.705-716
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• 2017

The objective of this study is to investigate the actual behavior of studs in structures under earthquake load through laboratory tests and numerical simulation. A test program including eighteen specimens was devised with consideration of different concrete strengths and stud diameters. Six of specimens were subjected to monotonically increasing loading while the others were subjected to cyclic loading. Mechanical behavior including the failure mechanism, load-slip relationship, stiffness degradation, energy dissipation and the damage accumulation was obtained from the test results. An accurate numerical model based on the ABAQUS software was developed and validated against the test results. The results obtained from the finite element (FE) model matched well with the experimental results. Furthermore, based on the experimental and numerical data, the design formulas for expressing the skeleton curve were proposed and the simplified hysteretic model of load versus displacement was then established. It is demonstrated that the proposed formulas and simplified hysteretic model have a good match with the test results.

• Earthquakes and Structures
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• 제19권6호
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• pp.485-498
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• 2020

Non-ductile detailing of Reinforced Concrete (RC) frames may lead to structural failure when the structure is subjected to earthquake response. These designs are generally encountered in older RC frames constructed prior to the introduction of the ductility aspect. The failure observed in the beam-column joints (BCJs) and accompanied by excessive column damage. This work examines the seismic performance and failure mode of non-ductile designed RC columns and exterior BCJs. The design was based on the actual building in Tainan City, Taiwan, that collapsed due to the 2016 Meinong earthquake. Hence, an experimental investigation using cyclic testing was performed on two columns and two BCJ specimens scaled down to 50%. The experiment resulted in a poor response in both specimens. Excessive cracks and their propagation due to the incursion of the lateral loads could be observed close to the top and bottom of the specimens. Joint shear failure appeared in the joints. The ductility of the member was below the desired value of 4. This is the minimum number required to survive an earthquake with a similar magnitude to that of El Centro. The evidence provides an understanding of the seismic failure of poorly detailed RC frame structures.

• Steel and Composite Structures
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• 제8권6호
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• pp.491-510
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• 2008

This paper presents a plan and guidelines that were drawn for Korean based research carried out on the fire-resistance of CFT columns. This research was carried out by reviewing the Korean regulations related to the fire-resistance of CFT columns and examining studies which had been made in Korea as well as overseas. The first phase of the study plan was to compare the fire-resistance of square CFT columns without fire protection (obtained through fire-resistance tests and numerical analyses) with estimated values (obtained through fire-resistance design formulas proposed in Korea and overseas). This comparison provided conclusions as outlined below. Fire-resistance tests conducted in this study proved that, when the actual design load is taken into consideration, square CFT columns without fire protection are able to resist a fire for more than one hour. A comparison was made of test and analysis results with the fire-resistance time based on the AIJ code, the AISC design formula and the estimation formula suggested for Korea. The results of this comparison showed that the test and analysis results for specimens SAH1, SAH2-1, SAH2-2 and SAH3 were almost identical with the AIJ code, the AISC design formula and estimation formula. For specimens SAH4 and SAH5, the estimation formula was more conservative than the AIJ code and the AISC design formula. It was necessary to identify the factors that have an influence on the fire-resistance of CFT columns without fire protection and to draw fire-resistance design formulas for these columns. To achieve this, it is proposed that numerical analyses and tests be conducted in order to evaluate the fire-resistance of circular CFT columns, the influence of eccentricity existing as an additional factor and the influence of the slenderness ratio of the columns. It is also suggested that the overall behavior of CFT structures without fire protection within a fire be evaluated through analysis simulation.

• Structural Engineering and Mechanics
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• 제64권5호
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• pp.641-652
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• 2017

In general, conventional analysis and design of reinforced concrete (RC) frame structures overlook the role of beam-column (RCBC) joints. Nowadays, the rigid joint model is one of the most common for RCBC joints: the joint is assumed to be rigid (unable to deform) and stronger than the adjacent beams and columns (does not fail before them). This model is popular because (i) the application of the capacity design principles excludes the possibility of the joint failing before the adjacent beams and (ii) many believe that the actual behaviour of RCBC joints designed according to the seismic codes produced mainly after the 1980s can be assumed to be nominally rigid. This study investigates the relevance of the deformation of RCBC joints in a standard pushover analysis at several levels: frame, storey, element and cross-section. Accordingly, a RC frame designed according to preliminary versions of EN 1992-1-1 and EN 1998-1 was analysed, considering the nonlinear behaviour of beams and columns by means of a standard sectional fibre model. Two alternative models were used for the RCBC joints: the rigid model and an explicit component based nonlinear model. The effect of RCBC joints modelling was found to be twofold: (i) the flexibility of the joints substantially increases the frame lateral deformation for a given load (30 to 50%), and (ii) in terms of seismic performance, it was found that joint flexibility (ii-1) appears to have a minor effect on the force and displacement corresponding to the performance point (seismic demand assessed at frame level), but (ii-2) has a major influence on the seismic demand when assessed at storey, element and cross-section levels.

• 한국구조물진단유지관리공학회 논문집
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• 제14권1호
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• pp.148-155
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• 2010

본 연구는 지하주차장 건물의 바닥구조를 구성하기 위한 방안으로서 프리스트레스를 도입한 일방향 장선구조인 MRS공법을 제안하고, MRS공법의 연속단 접합부에 대한 구조실험을 수행함으로써 휨거동 특성과 접합상세의 적정성을 평가하였다. 연속단 접합부는 4개의 실험체를 제작하였으며, 연속단 접합부에 부모멘트가 작용하도록 실험을 수행하였다. 실물크기로 제작한 MRS 연속단 접합부는 접합부의 구조상세와 상관없이 충분한 휨강성의 발현과 함께 연성적인 휨파괴 거동을 보여주었다. 특히 지붕층에 위치한 MRS 연속단 접합부는 큰 값의 부모멘트를 저항하기 위한 인장철근의 양을 최대철근비 이하로 설계할 수 있으며, 최종파괴 모드는 휨에 의해 지배되는 거동특성을 보여주었다. 따라서 제안된 MRS공법은 우수한 지압성능과 연속단 구축이 용이한 접합부 상세를 갖는 것으로 평가되었다.

• 콘크리트학회논문집
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• 제26권3호
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• pp.287-297
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• 2014

최근 증가 추세에 있는 화력발전소 건설에 있어서, 터빈 기초 구조물은 규모가 매우 큰 매스콘크리트이다. 매스콘크리트의 수화열은 구조물의 품질과 공기 등에 중대한 영향을 미치는 요인 중 하나이므로, 수화열 제어를 위한 적절한 방안은 필수적이다. 이 연구에서는 국내 복합화력발전소 터빈 기초 시공에 앞서 수화열 해석을 통하여 수화열 균열 발생 가능성을 예측하고, 수화열 제어 방안으로서 콘크리트 배합 및 양생방법 변경을 제안하였다. 콘크리트 배합은 기존 1종 보통시멘트 콘크리트 배합에서 슬래그시멘트 콘크리트 배합으로 변경을 제안하였고, 기존 양생포 및 살수양생방법을 개선하기 위하여 매스콘크리트 중심부와 표면부의 온도를 모니터링하여 온도차를 일정수준 이하로 일정하게 유지시켜주는 양생자동화시스템을 적용한 양생방법을 제안하였다. 실제 시공시에는 슬래그콘크리트 배합을 사용하고, 2기의 동일한 터빈 기초 구조물에 대하여 각각 보온양생공법과 양생자동화시스템을 적용하여 양생방법에 따른 온도균열 제어효과를 비교하였으며, 2기의 매스콘크리트에서 온도, 변형률 모니터링 및 균열 조사를 통하여 수화열 제어 효과를 평가하였다.

• Earthquakes and Structures
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• 제11권3호
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• pp.407-420
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• 2016

The aim of this study is to investigate the effect of vertical ground motion (VGM) on seismic behavior of reinforced concrete (RC) regular frame with construction joints, and determine more proper modeling method for cast-in-situ RC frame. The four-story RC frames in the regions of 7, 8 and 9 earthquake intensity were analyzed with nonlinear dynamic time-history method. Two different methods of ground motion input, horizontal ground motion (HGM) input only, VGM and HGM input simultaneously were performed. Seismic responses in terms of the maximum vertex displacement, the maximum inter-story drift distribution and the plastic hinge distribution were analyzed. The results show that VGM might increase or decrease the horizontal maximum vertex displacement depending on the value of axial load ratio of column. And it will increase the maximum inter-story drift and change its distribution. Finally, proper modeling method is proposed according to the distribution of plastic hinges, which is in well agreement with the actual earthquake damage.

• Structural Engineering and Mechanics
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• 제10권1호
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• pp.1-15
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• 2000

It is inevitable that every space truss structure would be under some form of direct member loading. At least the structure self weight certainly affects the members directly, and in structures involving top concrete slabs or cladding, their weight is also likely to apply some lateral pressure on the members. In spite of that, direct member loading is usually ignored in space truss designs and assumed to lead only to a negligible effect on truss performance. This study is intended to explore this point and identify the actual effects that can arise from direct member loading, and eventually provide an answer to the question of whether the current design practice is satisfactory or certain modifications would be needed. After presenting two analytical techniques to allow the study of space trusses with laterally loaded members, the paper describes a wide parametric study involving practical-size space trusses with different configurations, aspect ratios, boundary conditions and number of chord panels.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1999년도 봄 학술발표회 논문집
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• pp.210-217
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• 1999

This paper deals with the analysis for column shortening of RC frame structure considering the construction sequences. The time-dependent effects of concrete are taken into consideration in this study to simulate the actual structural behavior. The stiffness matrix of a beam element is derived on the bases of the layer approach, dividing a section with imaginary layers. Creep and shrinkage strains at each layer are calculated by using the first-order algorithm based on the expansion of creep compliance. Finally, the correlation studies with the purpose of analyzing the time-dependent behavior of building structure are conducted using the analytical model proposed in this study.