• Title/Summary/Keyword: punching failure

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Experimental and numerical analysis of the punching behavior of RC isolated footings

  • Walid, Mansour;Sabry, Fayed;Ali, Basha
    • Steel and Composite Structures
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    • v.45 no.5
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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%).

Punching shear behavior of recycled aggregate concrete

  • Dan, Saikat;Chaudhary, Manpreet;Barai, Sudhirkumar V.
    • Computers and Concrete
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    • v.21 no.3
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    • pp.321-333
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    • 2018
  • Flat-slabs, being a significant structural component, not only reduce the dead load of the structure but also reduce the amount of concrete required for construction. Moreover the use of recycled aggregates lowers the impact of large scale construction to nearby ecosystems. Recycled aggregate based concrete being a quasi-brittle material shows enormous cracking during failure. Crack growth in flat-slabs is mostly in sliding mode (Mode II). Therefore sufficient sections need to be provided for resistance against such failure modes. The main objective of the paper is to numerically determine the ultimate load carrying capacity of two self-similar flat-slab specimens and validate the results experimentally for the natural aggregate as well as recycled aggregate based concrete. Punching shear experiments are carried out on circular flat-slab specimen on a rigid circular knife-edge support built out of both normal (NAC) and recycled aggregate concrete (RAC, with full replacement). Uniaxial compression and bending tests have been conducted on cubes, cylinders and prisms using both types of concrete (NAC and RAC) for its material characterization and use in the numerical scheme. The numerical simulations have been conducted in ABAQUS (a known finite element software package). Eight noded solid elements have been used to model the flat slab and material properties have been considered from experimental tests. The inbuilt Concrete Damaged Plasticity model of ABAQUS has been used to monitor crack propagation in the specimen during numerical simulations.

Design Method of RC Flat Plate Slab Considering Unbalanced Moment (불균형모멘트를 고려한 RC 무량판 슬래브 설계방법)

  • Song, Jin-Kyu;Sing, Ho-Beom;Oh, Sang-Won;Han, Sun-Ae
    • Proceedings of the Korea Concrete Institute Conference
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    • 2008.04a
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    • pp.149-152
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    • 2008
  • In structural design provision, maximum punching shear stress of slabs is prescribed as combined stress of direct shear occurred by balanced gravity load and eccentric shear occurred by unbalanced moment. This means that the effect of unbalanced moment is considered to decide the punching shear stress. However, from the resistance capacity standpoint, the effect of unbalanced moment strength is not considered for deciding punching shear strength. For this problem, a model to show unbalanced moment-punching shear interrelation was proposed. In the model, the relation between load effect and resistance capacity in unbalanced moment-punching shear was two-dimensionally expressed. Using the interrelation model, a method how unbalanced moment strength should be considered to decide the punching shear strength was proposed. Additionally, a effective width enlargement factor for deciding the unbalanced moment strength of flat plates with shear reinforcements was proposed. The interrelation model proposed in this paper is very effective for the design because not only punching shear and unbalanced moment strengths but also failure modes of flat plates can be accurately predicted.

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Dynamic punching shear tests of flat slab-column joints with 5D steel fibers

  • Alvarado, Yezid A.;Torres, Benjamin;Buitrago, Manuel;Ruiz, Daniel M.;Torres, Sergio Y.;Alvarez, Ramon A.
    • Structural Engineering and Mechanics
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    • v.81 no.3
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    • pp.281-292
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    • 2022
  • This study aimed to analyze the dynamic punching shear performance of slab-column joints under cyclic loads with the use of double-hooked end (5D) steel fibers. Structural systems such as slab-column joints are widely found in infrastructures. The susceptibility to collapse of such structures when submitted to seismic loads is highly dependent on the structural performance of the slab-column connections. For this reason, the punching capacity of reinforced concrete (RC) structures has been the subject of a great number of studies. Steel fibers are used to achieve a certain degree of ductility under seismic loads. In this context, 5D steel hooked fibers provide high levels of fiber anchoring, tensile strength and ductility. However, only limited research has been carried out on the performance under cyclic loads of concrete structural members containing steel fibers. This study covers this gap with experimental testing of five different full-scale subassemblies of RC slab-column joints: one without punching reinforcement, one with conventional punching reinforcement and three with 5D steel fibers. The subassemblies were tested under cyclic loading, which consisted of applying increasing lateral displacement cycles, such as in seismic situations, with a constant axial load on the column. This set of cycles was repeated for increasing axial loads on the column until failure. The results showed that 5D steel fiber subassemblies: i) had a greater capacity to dissipate energy, ii) improved punching shear strength and stiffness degradation under cyclic loads; and iii) increased cyclic loading capacity.

Structural Performance of Reinforced Concrete Flat Plate Buildings Subjected to Fire

  • George, Sara J.;Tian, Ying
    • International Journal of Concrete Structures and Materials
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    • v.6 no.2
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    • pp.111-121
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    • 2012
  • The research presented in this paper analytically examines the fire performance of flat plate buildings. The modeling parameters for the mechanical and thermal properties of materials are calibrated from relevant test data to minimize the uncertainties involved in analysis. The calibrated models are then adopted to perform a nonlinear finite element simulation on a flat plate building subjected to fire. The analysis examines the characteristics of slab deflection, in-plane deformation, membrane force, bending moment redistribution, and slab rotational deformation near the supporting columns. The numerical simulation enables the understanding of structural performance of flat plate under elevated temperature and, more importantly, identifies the high risk of punching failure at slab-column connections that may trigger large-scale failure in flat plate structures.

Estimation of Fatigue safety for PSC Bridge Decks (PSC 바닥판의 피로 안전성 평가)

  • 김영진;이정우;주봉철;김병석;박성용;이필구
    • Proceedings of the Korea Concrete Institute Conference
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    • 2002.05a
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    • pp.525-530
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    • 2002
  • This study is peformed to propose the slab deck for the composite bridge with two girders. Considering the characteristics of the long span and the construction conditions in korea, a cast-in-place PSC deck was proposed for that bridge. To examine structural behaviors and safety of the proposed PSC deck, two real scale partitions of deck(12m$\times$3.2m) were tested under the fatigue loading. In the test, the failure mode and behaviors of each specimen, and the ultimate load carrying capacity of the two-girder-bridge deck were identified. Generally, the failure of concrete bridge deck is caused by the local punching shear stress resulting from the moving wheel load. Even though its ultimate flexural capacity is sufficiently larger than the demand, it could be failed by the punching shear fatigue. Therefore, the fatigue safety of the proposed PSC deck should be checked.

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Nonlinear modeling of flat-plate structures using grid beam elements

  • Tian, Ying;Chen, Jianwei;Said, Aly;Zhao, Jian
    • Computers and Concrete
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    • v.10 no.5
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    • pp.489-505
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    • 2012
  • This paper presents a simplified grid beam model for simulating the nonlinear response of reinforced concrete flat-plate structures. The beam elements are defined with nonlinear behavior for bending moment and torsion. The flexural stiffness and torsional strength of the beam elements are defined based on experimental data to implicitly account for slab two-way bending effects. A failure criterion that considers the interaction between the punching strength and slab flexural behavior is incorporated in the model. The effects of bond-slip of slab reinforcement on connection stiffness are examined. The proposed grid beam model is validated by simulating large-scale tests of slab-column connections subjected to concentric gravity loading and unbalanced moment. This study also determines the critical parameters for a hysteretic model used to simulate flat-plates subjected to cyclic lateral loading.

Ductility of Column-Slab eoint in R/C Flat Plate System (플랫 플레이트 구조의 기둥.슬래브 접합부 연성에 관한 연구)

  • 김형기;박복만
    • Journal of the Korea Concrete Institute
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    • v.12 no.4
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    • pp.113-119
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    • 2000
  • The R/C flat plate system provides architectural flexibility, clear space, reduced building height, simple formwork, which consequently enhance constructibility. One of the serious problems in the flat plate system is brittle punching shear failure due to transfer of shear force and unbalanced moments in column-slab joint. Recently, the flat plate system accompanied with shear walls to resist the lateral loads is applied to high-rise buidings. Although the flat plate system is not considered in design as part of the lateral load-resisting system, it is required that this system keeps the ductile behavior for the lateral displacement of the building. However, it is unclear whether the column-slab joint possesses ductility enough to survive the lateral deformation. The objective of this paper is to investigate the major parameters that influence the ductility of R/C flat plate system by examining the existing experiments on column-slab joint. The effects of gravity load and shear reinforcement on the ductility of the flat plate system are presented.

The Development of Momentum Conversion Type Micro Punch System using Elastic Collision (탄성충돌을 이용한 운동량 보존형 마이크로 펀치 시스템의 개발)

  • 장인배;장현철;최근형;김병희;김현영
    • Transactions of Materials Processing
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    • v.12 no.2
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    • pp.128-133
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    • 2003
  • In this study, the momentum conservation type punching mechanism for micropunching system was developed to avoid the punch failure in the misaligned status between the punch and die. The punching energy can be precisely controlled by the falling height of the projectile mass and the intermediata mass, which contacts with the punch, transmit the energy to the punch with the same contact condition. The potential energy of the projectile mass is converted to kinetic energy at the light weight punch that the projection speed into the sheet metal workpiece can be accelerated. The butt formation characteristics for the alignment condition and for the projection speeds are investigated to verify the feasibility of the proposed punching mechanism.

The Effects of Steel Fibers on the Behavior of Slab-Column System (강섬유를 보강한 슬래브-기둥 시스템의 거동에 관한 연구)

  • 최응규;강경수;김묵한
    • Proceedings of the Korea Concrete Institute Conference
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    • 1998.04b
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    • pp.553-558
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    • 1998
  • Two-way slab-column specimens were tested under monotonic loading increased up to punching shear failure to investigate the beneficial effects of fiber-reinforced concrete. The parameters for experiments are the placement of fibers within the immediate column region, the placement on the entire surface of the slab, and no placement of fibers. The effects of these parameters on the punching shear capacity, negative moment cracking. and stiffness of the two-way slab specimens were studied. According to the results the addition of steel fibers in the slab around the column results in a significant improvement in the performance including the increase of punching shear resistance, greater post-cracking stiffness and smaller crack width at service load levels.

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