• Structural Engineering and Mechanics
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• 제11권6호
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• pp.637-650
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• 2001

A structural analysis of cracked R.C. members under instantaneous or sustained loads and imposed displacements is presented. In the first part of the paper the problem of deriving feasible moment-curvature diagrams for a long term analysis of R.C. sections is approached in an exact way by using the Reduced Relaxation Function Method in state I uncracked and the method suggested by CEB in state II cracked. In both states the analysis of the main parameters governing the problem has shown that it is possible to describe the concrete creep behaviour in an approximate way by using the algebraic formulation connected to the Effective Modulus Method. In this way the calculations become quite simple and can be applied in design practice without introducing significant errors. Referring to continuous beams, the structural analysis is then approached in a general way, applying the Force Method and the Principle of Virtual Works. Finally, considering single members, the structural analysis is performed by means of a graphical procedure based on the application of feasible moment-rotation diagrams which allow to easily solve various structural problems and to point out the most interesting aspects of the long term behaviour of cracked R.C. members with rigid or elastically deformable redundant restraints.

• Earthquakes and Structures
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• 제11권4호
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• pp.609-627
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• 2016

Results of an experimental program are presented in this paper for the influence of vertical load on the in-plane behavior of masonry infilled steel frames. Five half-scaled single-story, single-bay steel frame specimens were tested under cyclic lateral loading. The specimens included four infilled frames and one bare frame. Two similar specimens as well as the bare frame had moment-resisting steel frames, while the remaining two specimens had pinned steel frames. For each frame type, one specimen was tested under simultaneous vertical and lateral loading, whereas the other was subjected only to lateral loading. The experimental results show that the vertical load changes the cracking patterns and failure modes of the infill panels. It improves dissipated hysteresis energy and equivalent viscous damping. Global responses of specimens, including stiffness and maximum strength, do no change by vertical loading considerably. Regarding the ductility, the presence of vertical load is ignorable in the specimen with moment-resisting frame. However, it increases the ductility of the infilled pinned frame specimen, leading to an enhancement in the m-factor by at least 2.5 times. In summary, it is concluded that the influence of the vertical load on the lateral response of infilled frames can be conservatively ignored.

• Earthquakes and Structures
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• 제14권6호
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• pp.525-535
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• 2018

This study presents a new beam-column model comprising material nonlinearity and joint flexibility to predict the nonlinear response of reinforced concrete structures. The nonlinear behavior of connections has an outstanding role on the nonlinear response of reinforced concrete structures. In presented research, the joint flexibility is considered applying a rotational spring at each end of the member. To derive the moment-rotation behavior of beam-column connections, the relative rotations produced by the relative slip of flexural reinforcement in the joint and the flexural cracking of the beam end are taken into consideration. Furthermore, the considered spread plasticity model, unlike the previous models that have been developed based on the linear moment distribution subjected to lateral loads includes both lateral and gravity load effects, simultaneously. To confirm the accuracy of the proposed methodology, a simply-supported test beam and three reinforced concrete frames are considered. Pushover and nonlinear dynamic analysis of three numerical examples are performed. In these examples the nonlinear behavior of connections and the material nonlinearity using the proposed methodology and also linear flexibility model with different number of elements for each member and fiber based distributed plasticity model with different number of integration points are simulated. Comparing the results of the proposed methodology with those of the aforementioned models describes that suggested model that only uses one element for each member can appropriately estimate the nonlinear behavior of reinforced concrete structures.

• Structural Engineering and Mechanics
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• 제87권6호
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• pp.615-624
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• 2023

The focus of this study is on the structural behaviour of reinforced concrete beams in which basalt fiber and SBR latex were added and the cement was partially replaced with 10% of hypo sludge. Eight different mixes of reinforced beam specimens were tested under static loading behaviour. The experiments showed, the structural behaviour with features such as load-deflection relationships, crack pattern, crack propagation, number of crack, crack spacing and moment curvature. A stress-strain relationship to represent the overall behavior of reinforced concrete in tension, which includes the combined effects of cracking and mode of failure along the reinforcement, is proposed. The structural behaviour results of reinforced concrete beams with various types of mix were tested at the age of 28 days. The investigation revealed that the flexural behaviors of hypo sludge reinforced concrete beams with addition of basalt fiber and SBR latex was higher than that of control concrete reinforced beam. The specimen (LHSBFC) with 10% hypo sludge, 0.25% Basalt fiber and 10% SBR latex showed an increase of 5.08% load carrying capacity, 7.6% stiffness, 3.97% ductility, 31.29% energy dissipation when compared to the control concrete beam. The analytical investigation using FEM shows that it was in good agreement with the experimental investigation.

• Structural Engineering and Mechanics
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• 제89권1호
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• pp.77-91
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• 2024

During strong seismic events, inelastic shear deformation occurs in beam-column joints. To capture inelastic shear deformation, an analytical model for beam-column joint in reinforced concrete (RC) frame structures has been proposed in this study. The proposed model has been developed using a rotational spring and rigid links. The stiffness properties of the rotational spring element have been assigned in terms of a moment rotation curve developed from the shear stress-strain backbone curve. The inelastic rotation behavior of joint has been categorized in three stages viz. cracking, yielding and ultimate. The joint shear stress and strain values at these stages have been estimated using analytical models and experimental database respectively. The stiffness properties of joint rotational spring have been modified by incorporating a geometry factor based on dimensions of adjoining beam and column members. The hysteretic response of the joint rotational spring has been defined by a pivot hysteresis model. The response of the proposed analytical model has been verified initially at the component level and later at the structural level with the two actually tested RC frame structures. The proposed joint model effectively emulates the inelastic behavior precisely with the experimental results at component as well as at structural levels.

• 한국지진공학회논문집
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• 제6권4호
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• pp.31-37
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• 2002

최근에 용접 수평헌치로 보강된 내진 철골 모멘트 적합부의 응력 전달모형 및 설계법이 Lee-Uang에 의해 새로이 제안된 바가 있다. 본 연구에서는 반복재하 실물대 실험을 통하여 이 설계방안의 타당성을 실험적으로 확인하고 응력집중에서 기인하는 헌치단부의 균열을 방지할 수 있는 효과적인 상세도 제안하고자 하였다. Lee-Uang의 방안에 의해 설계된 3개의 시험체는 모두 설계의도에 부합되게, 헌치단부의 외측에서 형성된 소성힌지에서 0.04 radian에 달하는 뛰어난 소성회전능력을 발휘하였다. 도한 헌치단부에 구배를 주고 처공하거나 또는 보 웨브 스티프너를 헌치의 웨브로 부분적으로 또는 완전히 연장하는 상세에 의해 헌치단부의 균열발생을 효과적으로 방지할 수 있음을 실험적으로 입증하였다. 아울러 해석적으로 예견되었던 헌치 웨브의 스트럿 거동도 스트레인 계측을 통하여 실험적으로 입증하였다.

• 한국지반공학회논문집
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• 제35권2호
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• pp.5-17
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• 2019

철도하중 및 지진하중 재하 시 궤도지지말뚝 구조의 동적 거동 평가를 위해 동적원심모형 실험을 수행하였다. 실험의 변수는 연약지반의 깊이와 성토체의 높이로 결정하였으며, 총 4가지 경우에 대해 실험을 수행하였다. 연약지반 깊이는 실제 연약지반층에 고속철도를 부설한 호남고속철도의 익산-정읍 구간의 시추주상도를 분석하여 결정하였으며, 성토체의 높이는 일반적인 고속철도의 성토체 높이 범위의 하한 값과 상한 값으로 결정하였다. 실험 결과, 연약지반 깊이 대비 성토체 높이 비율이 높을 수록 말뚝에 작용하는 최대 휨모멘트 값이 크게 평가되었다. 또한, 실험조건 내에서 부설되는 궤도지지말뚝 구조는 단주기 지진파에 대해서는 국내 내진설계 기준의 최대 지진하중인 0.22g에 대해서까지 안전한 것으로 확인되었다. 그러나, 장주기 지진파에 대해서는 재현주기 2400년 지진인 0.22g로 가진시 말뚝의 균열 모멘트가 초과되었다. 일련의 실험결과를 바탕으로, 본 논문에 기술된 연약지반 깊이와 성토체 높이 범위 내에서 궤도지지말뚝 일반 단면에 대한 연약지반 대비 성토체 높이 비율 기준을 제시하였다.

• Steel and Composite Structures
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• 제43권3호
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• pp.327-340
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• 2022

A vast amount of experimental and analytical research has been conducted related to the seismic behavior and performance of concrete filled steel tubular (CFT) columns. This research has resulted in a wealth of information on the component behavior. However, analytical and experimental data for structural systems with CFT columns is limited, and the well-known behavior of steel or concrete structures is assumed valid for designing these systems. This paper presents the development of an analytical model for nonlinear analysis of composite moment resisting frame (CFT-MRF) systems with CFT columns and steel wide-flange (WF) beams under seismic loading. The model integrates component models for steel WF beams, CFT columns, connections between CFT columns and WF beams, and CFT panel zones. These component models account for nonlinear behavior due to steel yielding and local buckling in the beams and columns, concrete cracking and crushing in the columns, and yielding of panel zones and connections. Component tests were used to validate the component models. The model for a CFT-MRF considers second order geometric effects from the gravity load bearing system using a lean-on column. The experimental results from the testing of a four-story CFT-MRF test structure are used as a benchmark to validate the modeling procedure. An analytical model of the test structure was created using the modeling procedure and imposed-displacement analyses were used to reproduce the tests with the analytical model of the test structure. Good agreement was found at the global and local level. The model reproduced reasonably well the story shear-story drift response as well as the column, beam and connection moment-rotation response, but overpredicted the inelastic deformation of the panel zone.

• 한국건설순환자원학회논문집
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• 제11권4호
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• pp.484-492
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• 2023

본 연구에서는 전기화학적 염화물 추출(ECE) 완료된 RC 보의 구조적 거동을 기존에 주로 사용되었던 부착 강도 측정이 아닌 3점 재하 시험을 통해 분석했다. 그 결과, ECE 처리에 의해 콘크리트 보의 휨 강성은 저하되었으나, 최대하중 측면에서 강도는 향상되는 것으로 나타났다. 또한, ECE에 의해 인장 변형률이 증가하여 인장 균열에 대한 저항성은 향상되었으며, 관성 모멘트 감소율은 감소하였다. 이러한 구조적 거동 측면의 이점에도 불구하고 연성 및 휨 강성은 저하되었다. 콘크리트보의 휨 강성은 선형 탄성 범위에서 유효 단면적의 손실로 인해 감소됐고, 실제로 인장변형에 의해 파손된 상태에서 단면 2차 모멘트는 약 70 %의 손실되었다. 그러나 이러한 단면 손실에 의한 관성 모멘트 감소율은 ECE에 의해 더 낮아졌는데, 이는 균열에 대한 저항성이 증가되는 반면, 변형량이 증가되어 사용성 측면에서의 위험성은 더 증가됨을 의미한다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 가을 학술발표논문집(II)
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• pp.399-404
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• 1998

Analysis of partially prestressed beams in which cracking under service loads is allowed requires a knowledge of geometric cross section properties such as neutral axis, centroid, area and moment of initia of this cracked transformed section. Especially an exact calculation for the stresses of steel and concrete and the width of crack and the amount of deflection can be obtained with accrurate prediction of neutral of centroidal axis location. In this paper, the procedures for predicting the centroidal axis location of partially cracked prestressed concrete members, using the compatibility of deformation of concrete and steel are formulated and compared with Dilger`s computed results. And also the computed results according to this paper are compared with Branson`s experimental results.