• Title/Summary/Keyword: punching failure

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Crack constitutive model for the prediction of punching failure modes of fiber reinforced concrete laminar structures

  • Ventura-Gouveia, A.;Barros, Joaquim A.O.;Azevedo, Alvaro F.M.
    • Computers and Concrete
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    • v.8 no.6
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    • pp.735-755
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    • 2011
  • The capability of a multi-directional fixed smeared crack constitutive model to simulate the flexural/punching failure modes of fiber reinforced concrete (FRC) laminar structures is discussed. The constitutive model is implemented in a computer program based on the finite element method, where the FRC laminar structures were simulated according to the Reissner-Mindlin shell theory. The shell is discretized into layers for the simulation of the membrane, bending and out-of-plane shear nonlinear behavior. A stress-strain softening diagram is proposed to reproduce, after crack initiation, the evolution of the normal crack component. The in-plane shear crack component is obtained using the concept of shear retention factor, defined by a crack-strain dependent law. To capture the punching failure mode, a softening diagram is proposed to simulate the decrease of the out-of-plane shear stress components with the increase of the corresponding shear strain components, after crack initiation. With this relatively simple approach, accurate predictions of the behavior of FRC structures failing in bending and in shear can be obtained. To assess the predictive performance of the model, a punching experimental test of a module of a façade panel fabricated with steel fiber reinforced self-compacting concrete is numerically simulated. The influence of some parameters defining the softening diagrams is discussed.

Alternatives to Enhance Flat Slab Ductility

  • Husain, Mohamed;Eisa, Ahmed S.;Roshdy, Ramy
    • International Journal of Concrete Structures and Materials
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    • v.11 no.1
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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.

Theoretical Assessment of Limit Strengthening Ratio of Bridge Deck Based on the Failure Characteristic (교량 바닥판의 파괴형태를 고려한 임계보강재비의 이론적 산정)

  • 심종성;오홍섭;유재명
    • Journal of the Korea Concrete Institute
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    • v.14 no.1
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    • pp.110-117
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    • 2002
  • In a strengthened bridge deck which received increased service loads, failure patterns of bridge deck vary depending on deck thickness, compressive strength of concrete, yielding strength of reinforcement, reinforcement ratio and additional strengthening ratio. General failure pattern that is most commonly reported as punching shear failure after the main rebar yields, followed by yielding of distributing rebar. In this paper, by Proposing a limit to the amount of strengthening material, a brittle failure can be prevented and a ductile failure mode similar to that developed in unstrengthened deck is derived. In order to calculated the limit strengthening ratio, the yield line theory and previously proposed plastic punching shear model have been used

Slab slenderness effect on the punching shear failure of heat-damaged reinforced concrete flat slabs with different opening configurations and flexural reinforcement areas

  • Rajai Z. Al-Rousan;Bara'a R. Alnemrawi
    • Steel and Composite Structures
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    • v.52 no.6
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    • pp.627-645
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    • 2024
  • Punching shear is a brittle failure that occurs within the RC flat slabs where stresses are concentrated within small regions, resulting in a catastrophic and unfavorable progressive collapse. However, increasing the slab slenderness ratio is believed to significantly affect the slab's behavior by the induced strain values throughout the slab depth. This study examines the punching shear behavior of flat slabs by the nonlinear finite element analysis approach using ABAQUS software, where 72 models were investigated. The parametric study includes the effect of opening existence, opening-to-column ratio (O/C), temperature level, slenderness ratio (L/d), and flexural reinforcement rebar diameter. The behavior of the punching shear failure was fully examined under elevated temperatures which was not previously considered in detail along with the combined effect of the other sensitive parameters (opening size, slab slenderness, and reinforcement rebar size). It has been realized that increasing the slab slenderness has a major role in affecting the slab's structural behavior, besides the effect of the flexural reinforcement ratio. Reducing the slab's slenderness from 18.27 to 5.37 increased the cracking load by seven times for the slab without openings compared to nine times for the initial stiffness value. In addition, the toughness capacity is reduced up to 80% upon creating an opening, where the percentage is further increased by increasing the opening size by about an additional 10%. Finally, the ultimate deflection capacity of flat slabs with an opening is increased compared to the solid slab with the enhancement being increased for openings of larger size, larger depths, and higher exposure temperature.

Failure Modes in Piled Embankments (말뚝으로 지지된 성토지반의 파괴형태)

  • 홍원표;윤중만;서문성
    • Journal of the Korean Geotechnical Society
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    • v.15 no.4
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    • pp.207-220
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    • 1999
  • Model tests were performed to investigate the failure modes in embankments on soft ground supported by piles with cap beams. In the model tests, Jumunjin standard sand was placed on simulated cap beams and soft ground. The cap beams are placed perpendicular to the longitudinal axis of the embankment. The colored sand and the Jmniin standard sand were placed one after the other above cap beams and soft ground to make lateral stripes with 3mm thickness in the embarkment. The colored sand was prepared by coating the Jumunjin sand with black lead powder. The photographs illustrate the two characteristic modes of failure in embarkments. One is the soil arching failure and the other is the punching shear failure. The failure mode depends on the height of embankment and the space between cap beams. That is, if the embankment is high enough compared with the space between cap beams, it will fail in arching failure. On the other hand if the embarkment is relatively low or the space between piles is too wide, it will fail in punching shear failure. The soil arching develops in embarkment as a semicylindrical arch with a thickness equal to the width of the cap beam. And the soil wedge developed above the cap beams remains intact during both arching and punching failures. The boundary of punching shear failure of the displaced soil mass can be defined on the basis of observation of the photographs.

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Shear Strength Model for Interior Flat Plate-Column Connections (무량판 슬래브-기둥 내부 접합부에 대한 전단강도모델)

  • Choi, Kyoung-Kyu;Park, Hong-Gun
    • Journal of the Korea Concrete Institute
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    • v.22 no.3
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    • pp.345-356
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    • 2010
  • An alternative design method for interior flat plate-column connections subjected to punching shear and unbalanced moment was developed. Since the slab-column connections are severely damaged by flexural cracking before punching shear failure, punching shear was assumed to be resisted mainly by the compression zone of the slab critical section. Considering the interaction with the flexural moment of the slab, the punching shear strength of the compression zone was evaluated based on the material failure criteria of concrete subjected to multiple stresses. The punching shear strength was also used to evaluate the unbalanced moment capacity of the slab-column connections. For verification, the proposed strength model was applied to existing test specimens subjected to direct punching shear or combined punching shear and unbalanced moment. The results showed that the proposed method predicted the strengths of the test specimens better than current design methods in ACI 318 and Eurocode 2.

An Experimental Study on Punching Shear of Simplified Composite Deck (초간편 강합성 바닥판의 펀칭 전단에 관한 실험적 연구)

  • Yoon, Ki-Yong;Lee, Sung-Yol;Yi, Gyu-Sei;Kim, Sang-Seup
    • Journal of the Korean Society of Hazard Mitigation
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    • v.9 no.5
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    • pp.23-30
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    • 2009
  • According to Korea Highway Bridge Design Code the bridge deck is designed by the strength design method and is regarded as a beam possessing the unit width based on the bending theory. By many researches it is revealed that the existing bridge deck is failed by punching shear. For evaluating the ultimate capacity of bridge deck it is important to estimate the behavior of bridge deck under the punching shear. For the punching strength it is difficult that the existing research results are applied to the simplified composite deck. In this study for comparing characteristics on punching shear the punching shear tests on simplified composite deck and RC deck are performed. The punching shear strength of simplified composite deck is compared with several bridge design codes.

The Failure Model of RC Flat Plates Considering Interrelation between Punching Shear and Unbalanced Moment (불균형모멘트와 펀칭전단의 상관관계를 고려한 철근콘크리트 무량판 슬래브의 파괴모델)

  • Choi, Jung-Wook;Song, Jin-Kyu;Song, Ho-Beom
    • Journal of the Korea Concrete Institute
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    • v.20 no.4
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    • pp.523-530
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    • 2008
  • In structural design provision, maximum punching shear stress of slabs is prescribed as combined stress in direct shear occurred by 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. In this paper, a model considering interrelation between unbalanced moment and punching shear was proposed. In the model, the relation between load effect and resistance capacity in unbalanced moment and 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, effective width enlargement factors for deciding the unbalanced moment strength of flat plates with shear reinforcements were proposed. The interrelation model proposed in this paper is very effective for the prediction of the behavior of slab-column connection because not only punching shear and unbalanced moment strengths but also failure modes of flat plates can be accurately predicted.

Punching Shear Strength of Slab-Column Interior Connection Considering Anchorage Performance of Shear Reinforcements (전단보강재의 정착성능을 고려한 슬래브-기둥 내부접합부의 뚫림전단강도)

  • Jung, Hyung-Suk;Choi, Hyun-Ki;Chung, Joo-Hong
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.26 no.2
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    • pp.51-58
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    • 2022
  • Flat plate slab is cost-efficient structural system widely used in high rise building, apartment and parking garages. But flat plate-column connections are so weak against punching shear failure that it may cause collapse of overall structure. In this study, spiral type shear reinforcement which increases the shear strength and ductility of the plate-column connection and has good workability was proposed. And experimental test was performed to verify the punching shear capacity of spiral type shear reinforcement. The current code does not accurately estimate the punching shear strength of slab-column connection with shear reinforcement because slab is so slender that punching failure may occurred before shear reinforcement reached yield stress. Therefore modified equation of ACI code for punching shear strength was proposed base on finite element analysis using LUSAS program, and data analysis from CEB-FIP database.

Numerical investigation on punching shear of RC slabs exposed to fire

  • Sadaghian, Hamed;Farzam, Masood
    • Computers and Concrete
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    • v.23 no.3
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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.