• Computers and Concrete
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• 제20권6호
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• pp.731-738
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• 2017

Reinforced concrete flat plates consist of slabs supported directly on columns. The absence of beams makes these systems attractive due to advantages such as economical formwork, shorter construction time, less total building height with more clear space and architectural flexibility. Punching shear failure is usually the governing failure mode of flat plate structures. Punching failure is brittle in nature which induces more vulnerability to this type of structure. To analyze the flat plate behavior under punching shear, twelve finite element models of flat plate on a column with different parameters have been developed and verified with experimental results. The maximum range of variation of punching stress, obtained numerically, is within 10% of the experimental results. Additional finite element models have been developed to analyze the influence of integrity reinforcement, clear cover and column reinforcement. Variation of clear cover influences the punching capacity of flat plate. Proposed finite element model can be a substitute to mechanical model to understand the influence of clear cover. Variation of slab thickness along with column reinforcement has noteworthy impact on punching capacity. From the study it has been noted that integrity reinforcement can increase the punching capacity as much as 19 percent in terms of force and 101 percent in terms of deformation.

• 한국방재학회:학술대회논문집
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• 한국방재학회 2008년도 정기총회 및 학술발표대회
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• pp.37-40
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• 2008

The study is an experimental test on full-scale flat plate slab-column interior connection. The punching shear on the flat plate slab-column connection can bring about the reason of the brittle punching shear failure which may result of collapsing the whole structure. From the development of residential flat plate system, the shear reinforcement is developed for preventing the punching shear. For making sure of the punching shear capacity, developed for shear reinforcement in slab-column connection, the structural test is performed. The dimension of the slabs was 2620*2725*180mm with square column (600*800mm). The slabs were tested up to failure monotonic vertical shear forces. The presences of S/S bar and wire mesh substantially increased the punching shear capacity and the ductility of the slab-column connections.

• Computers and Concrete
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• 제25권4호
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• pp.355-367
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• 2020

This paper proposed a numerical investigation based on finite elements analysis (FEA) in order to study the punching shear behavior of reinforced concrete (RC) flat slabs using ABAQUS and SAP2000 programs. Firstly, the concrete and the steel reinforcements were modeled by hexahedral 3D solid and linear elements respectively, and the nonlinearity of the used materials was considered. In order to validate this model, experimental results considered in literature were compared with the proposed FE model. After validation, a parametric study was performed. The parameters include the slab thickness, the flexure reinforcement ratios and the axial membrane loads. Then, to reduce the time of FEA, a simplified modelling using 3D layered shell element and shear hinge concept was also induced. The effect of the footings settlement was studied using the proposed simplified nonlinear model as a case study. Results of numerical models showed that increase of the slab thickness by 185.7% enhanced the ultimate load by 439.1%, accompanied with a brittle punching failure. The punching failure occurred in one of the tested specimens when the tensile reinforcement ratio increased more than 0.65% and the punching capacity improved with increasing the horizontal flexural reinforcement; it decreased by 30% with the settlement of the outer footings.

• Steel and Composite Structures
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• 제45권5호
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• pp.665-682
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• 2022

In the current study, punching behavior of Reinforced concrete (RC) isolated footings was experimentally and numerically investigated. The experimental program consisted of four half-scale RC isolated footing specimens. The test matrix was proposed to show effect of footing area, reinforcement mesh ratio, adding internal longitudinal reinforcement bars and stirrups on the punching response of RC isolated footings. Footings area varied from 1200×1200 mm2 to 1500×1500 mm2 while the mesh reinforcement ratio was in the range from 0.36 to 0.45%. On the other hand, a 3D non-linear finite element model was constructed using ABAQUS/standard program and verified against the experimental program. The numerical results agreed well with the experimental records. The validated numerical model was used to study effect of concrete compressive strength; longitudinal reinforcement bars ratio and stirrups concentration along one or two directions on the ultimate load, deflection, stiffness and failure patterns of RC isolated footings. Results concluded that adding longitudinal reinforcement bars did not significantly affect the punching response of RC isolated footings even high steel ratios were used. On the contrary, as the stirrups ratio increased, the ultimate load of RC isolated footings increased. Footing with stirrups ratio of 1.5% had ultimate load equal to 1331 kN, 19.6% higher than the bare footing. Moreover, adding stirrups along two directions with lower ratio (0.5 and 0.7%) significantly enhanced the ultimate load of RC isolated footings compared to their counterparts with higher stirrups ratio (1.0 and 1.5%).

• Computers and Concrete
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• 제23권3호
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• pp.217-233
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• 2019

This paper describes the numerical modelling of an interior slab-column connection to investigate the punching shear resistance of reinforced concrete (RC) slabs under fire conditions. Parameters of the study were the fire direction, flexural reinforcement ratio, load levels, shear reinforcement and compressive strength of concrete. Moreover, the efficiency of the insulating material, gypsum, in reducing the heat transferred to the slab was assessed. Validation studies were conducted comparing the simulation results to experiments from the literature and common codes of practice. Temperature dependencies of both concrete and reinforcing steel bars were considered in thermo-mechanical analyses. Results showed that there is a slight difference in temperature endurance of various models with respect to concrete with different compressive strengths. It was also concluded that compared to a slab without gypsum, 10-mm and 20-mm thick gypsum reduce the maximum heat transferred to the slab by 45.8% and 70%, respectively. Finally, it was observed that increasing the flexural reinforcement ratio changes the failure mode from flexural punching to brittle punching in most cases.

• 한국구조물진단유지관리공학회 논문집
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• 제26권2호
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• pp.51-58
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• 2022

플랫 플레이트는 매우 경제적인 구조시스템으로서 고층건물과 아파트, 지하 주차장등에 널리 쓰인다. 하지만 기둥-슬래브 접합부가 뚫림전단에 취약하기 때문에 건물의 연쇄붕괴로 이어질 수 있는 단점이 있다. 이에 본 연구에서는 뚫림전단강도 증가, 연성능력 향상, 시공성면에서 뛰어난 나선형 철근 전단 보강재가 제안되었으며, 실험을 통해 나선형 철근 전단보강재의 강도를 평가하였다. 현행 기준은 전단보강된 슬래브-기둥 접합부의 뚫림전단강도를 정확하게 예측하지 못하고 있다. 그 이유는 전단보강재가 설치되는 슬래브의 두께가 얇을경우 정착길이가 확보되지 못하여 전단보강재가 항복강도에 이르기 전에 파괴가 일어나기 때문이다. 이에 본 연구에서는 유한요소해석 프로그램 LUSAS ver14.3을 이용하여 나선형 전단보강재의 보강성능에 영향을 미치는 변수를 분석하여 강도보정계수를 도출하였다. 또한 CEB-FIP 데이터뱅크에 수록된 실험체의 회귀분석을 통해 전단보강된 슬래브-기둥 접합부의 뚫림전단강도 산정식을 제안하였다.

• International Journal of Concrete Structures and Materials
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• 제11권1호
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• pp.161-169
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• 2017

Flat slab systems are vastly used in multi-story buildings because of their savings in story height and construction time, as well as for their flexibility in architectural remodeling. However, they frequently suffer brittle punching-shear failure around columns, especially when subjected to lateral loads. Therefore, seismic codes labeled flat slabs as non-ductile systems. This research goal is investigating some construction alternatives to enhance flat slab ductility and deformability. The alternatives are: adding different types of punching-shear reinforcement, using discreet fibers in concrete mixes, and increasing thickness of slab around columns. The experimental study included preparation and testing of seven half-scale interior slab-column connections up to failure. The first specimen is considered a reference, the second two specimens made of concrete mixes with different volumetric ratios of polymer fibers. Another three specimens reinforced with different types of punching-shear reinforcement, and the last specimen constructed with drop panel of inverted pyramidal shape. It is found that using the inverted pyramid-shape drop panel of specimen, increases the punching-shear capacity, and the initial and the post-cracking stiffnesses. The initial elastic stiffnesses are different for all specimens especially for the slab with closed stirrups where it is experienced the highest initial stiffness compared to the reference slab.

• 한국구조물진단유지관리공학회 논문집
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• 제10권3호
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• pp.211-218
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• 2006

본 연구에서는 거주형 무량판 구조의 뚫림 전단을 방지하기 위한 연속 절곡된 전단 보강근을 개발하였다. 이를 적용한 슬래브-기둥 접합부에 있어 개발 전단 보강근의 뚫림 전단 성능을 평가하기 위하여, 구조 성능 실험을 수행하였다. 실험 변수는 전단보강근이 없는 경우, 개발 전단보강근을 사용한 경우, 헤드 스터드를 사용한 경우이다. 수평하중에 대한 저항성능을 평가하기 위하여 일정축력하에서의 이력 하중 실험을 수행하였다. 실험결과는 전체 변위 및 접합부 강도 등으로 평가되었다. 이러한 결과로부터, 개발된 전단보강근이 층간변위비 거동에 있어 우수한 성능을 보유함을 확인할 수 있었다.

• Structural Engineering and Mechanics
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• 제66권2호
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• pp.203-215
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• 2018

A large body of experiments have been conducted to date to evaluate the punching shear strength of flat slab-column connections, but it is noted that only a few of them have been considered for the development of the ACI Code provisions. The limited test results used for the development of the code provisions fall short of predicting accurately the punching shear strength of such connections. In an effort to address this shortfall and to gain an insight into the factors that control the punching shear strength of flat slab-column connections, we report a qualified database of 650 punching shear test results in this article. All slabs examined in this database were tested under gravity loading and do not contain shear reinforcement. In order to justify including any test result for evaluation punching shear database, we have developed an approved set of criteria. Carefully established set of criteria represent the actual characteristics of structures that include minimum compressive strength, effective depths of slab, flexural and compression reinforcement ratio and column size. The key parameters that significantly affect the punching shear strength of flat slab-column connections are then examined using ACI 318-14 expression. The results reported here have paramount significance on the range of applicability of the ACI Code provision and seem to indicate that the ACI provisions do not sufficiently capture many trends identified through regression of the principal parameters, and fall on the unsafe side for the prediction of the punching shear strength of flat slab-column connections.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.48-51
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• 2004

This paper is to study the response of flat plate slab-column connections consisting of various types of shear reinforcement and steel plate subjected to gravity loadings, mainly punching shear forces using the non-destructive testing, spectral analysis of surface waves and structural experiments. The base specimen failed due to punching shear generated from the gravity. The three other types of slab shear reinforcement and steel plate showed effective in resisting punching shear for these types of connections under gravity loading. This study has focused in evaluating the velocity response of a Surface wave during the early age as the poured concrete specimens have been hardened, the possibility of damage detection in the slab-column connection and the relationship between the punching shear forces and the surface wave velocities under the condition that the punching shear forces had gradually increased until the flat plate slab in slab-column connection had been failed.