Brittle Punching Shear Failure Research Articles

Punching shear performance of reinforced concrete slab-to-steel column connections incorporating ECC and UHPECC

Unlike the conventional reinforced concrete (RC) slab-column connection, the punching shear generated at the RC slab-to-steel column connection may lead to brittle punching shear failure due to the small area around the steel column. Moreover, the unexpected moments arising from eccentric loading can also lead to the failure of the slab in punching shear mode. This paper proposes employing high-performance concrete (HPC) to fill the critical punching shear zone to improve the punching shear resistance of RC slabs to steel column joints. Experiments on eight RC slabs to steel column connections are reported. The test parameters under investigation are the type of HPC used to fill the critical punching shear zone, the distance (S) of the HPC zone measured from the flanges of the steel column and loading condition (concentric and eccentric). The types of HPC include engineered cementitious composite (ECC) and ultra-high performance ECC (UHPECC). The experimental results show that the proposed techniques can significantly improve the cracking load, elastic stiffness, energy absorption capacity, ductility, failure modes, and ultimate load of the slab-to-column connections. The ultimate load of the tested connections is increased by as much as 33 %, and 28 % for the slabs subjected to concentric and eccentric loading, respectively. However, the ultimate load and energy absorption capacity of the slab with UHPECC having a S value of 1d, where d is the effective depth are lower than those of the control slab. Three-dimensional nonlinear finite element models are developed to simulate the performance of tested slab-to-column connections and validated by experimental results. The parametric study shows that the n (=S/d) value greater than 3.5 has insignificant effects on the ultimate punching shear capacity of the slab. It is demonstrated that the proposed formulas faithfully estimate the ultimate punching shear capacity of slab-to-column connections constructed with different HPCs under concentric and eccentric loadings.

Engineering punching shear strength of flat slabs predicted by nature-inspired metaheuristic optimized regression system

Reinforced concrete (RC) flat slabs, a popular choice in construction due to their flexibility, are susceptible to sudden and brittle punching shear failure. Existing design methods often exhibit significant bias and variability. Accurate estimation of punching shear strength in RC flat slabs is crucial for effective concrete structure design and management. This study introduces a novel computation method, the jellyfish-least square support vector machine (JS-LSSVR) hybrid model, to predict punching shear strength. By combining machine learning (LSSVR) with jellyfish swarm (JS) intelligence, this hybrid model ensures precise and reliable predictions. The model’s development utilizes a real-world experimental data set. Comparison with seven established optimizers, including artificial bee colony (ABC), differential evolution (DE), genetic algorithm (GA), and others, as well as existing machine learning (ML)-based models and design codes, validates the superiority of the JS-LSSVR hybrid model. This innovative approach significantly enhances prediction accuracy, providing valuable support for civil engineers in estimating RC flat slab punching shear strength.

Ultra-high-performance fiber-reinforced concrete flat slabs' punching shear resistance as a function of drop panel thickness

Ultra-high-performance concrete including fibers (UHPFRC) is used to build skyscrapers, towers, and bridges.This type of concrete may have smaller skeletal components than normal concrete. However, flat slabs are thicker than reinforced concrete slabs. Brittle punching shear failure may happen rapidly and abruptly in flat slabs. The punching load was applied to four two-way internal UHPFRC-supported flat slabs: three reinforced concrete flat slabs with 10mm, 14mm, and 18mm drop panels and one control reinforced concrete slab without drop panels. The drop panel thickness enhanced punching shear resistance by 40% at fracture load and 48% at ultimate stress. In addition, deflection, shear strain at the concrete surface, strain in reinforcement, rotation at supports, and fracture inclination angles between top and bottom fibers improved by 30%, 316 percent, 74%, 385 percent, and 1.01 percent at peak load, respectively.

Punching shear performance of star-shaped steel plates reinforced RC slab-column connections

The progressive collapse of flat plate structures due to brittle punching shear failure of reinforced concrete (RC) slab-column connections is a major concern in structural engineering. This paper proposed an innovative star-shaped steel plates (SSPs) system to achieve an effective yet practical enhancement of the punching and post-punching performance of RC slab-column connections. SSPs were fabricated from thin steel plates, welded together, and placed in the centre of the joint. Engineering cementitious composite (ECC) was also adopted to replace the joint core concrete and work with the SSPs further to improve the punching shear behaviour of the joint. To evaluate the effectiveness of the proposed system, five large-scale RC slab-column connections with different SSPs configurations and concrete materials were tested under monotonic load. The results showed that the initial stiffness of the joint was minimally affected by the presence of SSPs, but the system significantly improved the punching shear strength, post-punching load-bearing capacity, and deformation capacity of the joint. Specimens with ECC and SSPs exhibited an even higher punching shear strength and more ductile post-punching behaviour. The study also found that the optimum enhancement of the punching shear behaviour of the slab-column joint can be realised when the SSPs yield just before the joint experiences punching shear damage. Finally, formulas were developed to reasonably predict the punching shear strength and post-punching load-carrying capacity of the SSPs reinforced slab-column connections.

Enhancing punching shear capacity of flat slab: review of strengthening and repairing techniques

A significant number of concrete flat slabs need to be strengthened against brittle punching shear failure due to conversion of existing buildings, material deterioration, the growth of standards, and detailed defects. Furthermore, there are some traditional approaches to strengthen and repair reinforced concrete slabs which can be either cumbersome or expensive. The repairing of the slabs is very important and not optional because, they will be lost without repairing and reconstruction may not be appropriate due to lack of time or other exceptional circumstances. There were many techniques to strengthening and repair the flat slab depend on suitable way and material availability for strengthening like CFRP sheets, TRM jackets, steel stiffeners, steel bolts, column capital, increasing slab thickness and many other techniques. Typically, the strengthening enhanced punching shear capacity, and the increment may reach 90%. Repair specimens’ punching shear capacity, which may be more than that of the control specimen and the repairing techniques can be used for strengthening. From presented studies, it was found that using the same technique for strengthening and repairing gave better results in strengthening, so strengthening slabs before damages occur is important and enhances resistance better.

Punching shear code provisions examination against the creation of an opening in existed RC flat slab of various sizes and locations

Punching shear is a critical problem in flat slabs directly supported at columns resulting in a high-stress concentration area, increasing the probability of brittle punching shear failure. However, the capacity is reduced by creating an opening that affects the overall behavior of the slab based on its size and location with respect to the loaded area. Furthermore, the design and analysis of the various structural elements are based on international regulations that have major differences in their basis and executions. In this study, the different code provisions in punching shear of RC two-way flat slab without shear reinforcement are examined under various opening sizes and locations using the Nonlinear Finite Element Analysis (NLFEA) procedure using ABAQUS software. A total of twenty-one model has been simulated for examining the prediction accuracy by the ACI318-19, MC2010, and EC2 under the effect of opening size (100, 200, and 300) mm, and locations (zero, 0.25d, 0.50d, 2.0d, 4.0 h, 5.5d, and 6.0d) under two main categories; the critical punching perimeter, and the critical opening location. However, it has been revealed that the proposed value of 0.50d as the critical punching perimeter is the most reliable one; besides, the value of 4 h is enough for defining the position where the effect of an opening could be neglected regardless of its size. Furthermore, it has been found that the column-to-opening ratio (C/O) is a very significant factor in controlling the punching shear capacity prediction accuracy by the different codes. Predictions get more overestimated under larger (C/O) values where increasing the C/O ratio by half increases the ultimate deflection percentage by an average of 22 %, except for those with smaller C/O values of less than 0.5, where it only reaches a maximum value of 13 %. Moreover, code prediction of the ACI318-19 and the MC2010 was found to be overestimated in all cases. In contrast, the EC2 was underestimated with an accurate prediction for an opening location of 2.0d from the column's face. However, it has been found that ACI318-19 is the most accurate one regarding the critical punching perimeter (0.5d) and critical opening location (4.0d).

Comparative study of influential factors for punching shear resistance/failure of RC slab-column joints using machine-learning models

The study of punching shear resistance and failure mode for reinforced concrete (RC) slab-column structures has been constantly highlighted, due to a number of catastrophic punching shear failures in engineering applications. However, mechanics-based punching shear resistance models and failure mode identification models have problems of prediction accuracy and influential factors quantification. In this paper, the prediction models based on machine learning (ML) are proposed to predict the punching shear resistance and failure mode. Compared with other seven ML models, extreme gradient boosting (XGBoost) is selected as the best model, which performance is examined by several performance measures. The prediction process of XGBoost is explained by shapley additive explanation (SHAP) and partial dependence plot (PDP). A comparative SHAP and PDP analysis reveals the relationships between punching shear resistance/failure and influential factors, which cannot be quantified through traditional experimental and theoretical analysis. Furthermore, suggestions for choosing the influential factors are provided to avert the brittle punching shear failure and improve the punching shear resistance of RC slab-column joints.

Comparative study of reinforced-engineered cementitious composites and reinforced-concrete slab–column connections under a vertical monotonic load

The flat slab is a preferred choice for structural design because of its architectural and construction efficiency. However, flat slabs collapse frequently because of brittle punching shear failure of RC slab-column connections, which can be attributed to the low tensile strength and high tensile brittleness of conventional concrete. Engineered cementitious composites (ECC) have excellent tensile properties compared with conventional concrete. The failure modes of reinforced-ECC (RECC) slab-column connections were revealed in a recently published study by authors. In this study, three RC slab-column connections were tested further monotonically in a comparative study of RECC specimens. A specimen with a slab span of 700 mm and the reinforcement ratio of ρ = 0.6% and 1.4%, and a 500-mm span specimen with a ρ = 1.4% were used. The peak and residual specimen strengths were estimated and compared with the test results. The main conclusions were: (1) the punching shear failure of the RECC specimens was delayed significantly compared with the RC specimens. The RECC specimens experienced a flexural-triggered punching shear failure, with ductility ratios from 2.4 to 6.4, whereas the RC specimens usually have zero ductility. (2) The peak RECC specimen load was ~2.0 times greater than that of the RC among the tested specimens. The peak strength of the RECC specimens was estimated by a yield-line mechanism, whereas the peak strength of the RC specimens was estimated by the punching shear-resisting mechanism. (3) The residual RECC load was ~3.0 times greater than that of the RC among the tested specimens. The main contribution to the residual strength of the RECC specimens was by the vertical compound of axial force from steel bars that passed through the punching shear cone. The main contribution to the residual strength of the RC specimens was by the concrete cover spalling strength. (4) The comparative study verified preliminarily the feasibility of improving the punching shear performance by using ECC in slab-column connections.

Experimental and theoretical investigations of UHPC-NC composite slabs subjected to punching shear-flexural failure

This paper presents an experimental study on the punching shear behavior of concrete flat slabs partially reinforced with ultra-high-performance concrete (UHPC). The effects of the area and depth of UHPC on the failure mode and punching shear capacity are investigated. Test results indicate that the application of full-depth UHPC at the punching shear area changed the failure mode from a brittle punching shear failure to a ductile punching shear-flexural failure, while the application of partial-depth UHPC at the punching shear area caused brittle punching shear failure. By using full-depth UHPC, the first crack strength and punching shear strength of the slabs were increased by up to 65% and 117%, respectively. Partial-depth UHPC did not increase the first crack strength and punching shear strength. According to the testing results, the optimal application of UHPC in the flat slabs is to use full-depth UHPC within the area enclosed by a perimeter located at a distance equal to the slab thickness away from the column face. A new energy dissipation ductility index is proposed to characterize the post-peak load energy dissipation ability. Finally, an analytical model based on yield line theory is proposed to estimate the punching shear strength of the flat slabs. The proposed model reached a good agreement with the testing results while the current ACI model, Chinese model and fib MC2010 model under-estimated the punching shear strength of the test specimens.

Punching shear strength of reinforced concrete column footings under eccentric compression: Experiment and analysis

In reinforced concrete (RC) column footings, the soil stiffness can significantly affects the punching shear strength of the foundation slab. The present study conducted eccentric compression tests on three RC column footings considering the complex interaction between the soil and structure, and investigated the load-carrying capacity, displacement distribution, reaction distribution, failure mode, crack development, and strain distribution. The test parameter was flexural reinforcement ratio in the foundation slab. The test results showed that the footing specimen with lower reinforcement ratio was susceptible to brittle punching shear failure, and the flexural reinforcement ratio affected the crack distribution and the spalling of concrete cover. Since only one specimen was used in each flexural reinforcement ratio, however, the test results should be carefully considered. On the basis of the test results including existing studies, the effect of design parameters on the punching shear strength was evaluated. As a result, a new method was developed to predict the punching shear strength by addressing the eccentric compression force.

Punching shear resistance of strengthened reinforced concrete interior slab–column connections using ultra-high-performance strain-hardening cementitious composite material

The main target of this article is to find out the most applicable strengthening technique to change the brittle punching shear failure of slab–column connection to a ductile one. The considered strengthening technique uses the combined effect of the internal single-leg stirrups and a thin layer of ultra-high-performance strain hardening cementitious composite material provided in either tension or compression side. Thus, 12 slab specimens divided into four groups were prepared and configured. It was found that the slab provided with properly anchored single-leg stirrups with a cross-shaped thin layer of ultra-high-performance strain hardening cementitious composite material at the compression side proved the most efficient technique among all the considered configurations. This technique enabled the slab to sustain a punching load of about 2.38 times that of the control unstrengthened slab. In addition, it exhibited ductile failure showing strain hardening and softening plateaus. Finally, the experimental shear resistances of all the strengthened slabs were compared against the design resistances stipulated by different design standards such as the ECP 203-2007, ACI 318-14, DIN 1045-1, and EC2-2004 codes. It can be concluded that the failure characteristics stipulated by the DIN 1045-1 code showed the most rational results compared with those of the experimental findings.

STRENGTHENING OF INTERIOR SLAB COLUMN CONNECTIONS VIA POST INSTALLED STEEL SHEAR BOLTS

Flat slabs are widely used in construction operations because of their simplicity and ease. However, this type of structures can be subjected to brittle punching shear failure in the slab-column connections. Without shear reinforcement, the slab column connection can suffer brittle punching failure. In order to overcome the risk of brittle punching shear failure in the column vicinity, the use of post installed shear bolts as a transverse reinforcement is investigated in this paper. A set of six half scale reinforced concrete slab column connections were tested under monotonic concentric load. Three of the tested specimens were provided with steel shear bolts after the hardening of the concrete. Results indicated an enhanced punching strength for specimens provided with steel shear bolts. The increase in punching capacity was combined with a significant increase in both ductility and rotational capacity.

The Effect of Anchorage Strength with Anchorage Capacity in Flat Plate

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. This study proposed 3 reinforcements that are increased to bond capacity using lateral bar, the structure test is performed. As performed test result, because slabs not keep enough bond length, slab is failed before shear reinforcement's yield strength duo to anchorage of slip. According to result, FEM analyzed an effect of slab thickness and concrete compressive. The study suggests shear strength formula that possible a positive shear reinforcement in slab-column connection.

Seismic performance evaluation for gravity-designed flat plate frames

Most existing reinforced concrete (RC) buildings in regions of low and moderate seismicity have been designed only considering gravity loads. Gravity-designed RC flat plate frames may be more vulnerable than RC frames with beams and columns owing to the potential for abrupt and brittle punching shear failure at slab–column connections. This study evaluates the seismic performance of gravity-designed three- and seven-storey flat plate frames, which were assumed to be located at sites having low, moderate and high seismic risks. An analytic model for simulating the hysteretic behaviour of slab–column connections obtained from experiments was proposed. It was found that the level of gravity load as measured by the gravity shear ratio significantly affects the inelastic behaviour of flat plate frames. The frames satisfied the basic safety objective (BSO) specified in AISC 41 subjected to ground motions at the Boston site, but not at the Seattle and LA sites.

플랫 플레이트 구조에서 전단보강체의 정착성능에 따른 전단보강효과

플랫 플레이트는 실의 배치가 지속적으로 바뀌는 오피스와 같이 유연한 공간의 배치를 위해 그 사용처가 증가하고 있다. 플랫 플레이트 구조를 사용함에 있어서 실무에서의 주요 문제는 슬래브-기둥 접합부에서 발생는 뚫림 전단 파괴에 대한 적절한 보강을 해주는 것이다. 이 연구에서는 플랫 플레이트 구조의 내부 슬래브-기둥 접합부에 대한 실험을 수행하였다. 세 가지의 특수한 전단 보강근이 구조물 전체의 파괴를 유발시킬 수 있는 플랫 플레이트 슬래브-기둥 접합부의 취성적인 뚫림 전단파괴를 방지하기 위해 제안되었다. 총 네 가지의 프랫 플레이트 실험체가 수직 방향의 단조 가력에 의해 수행되었다. 전단 보강근은 뚫림 전단강도를 높여주는 역할과 취성파괴를 방지하는 역할을 해 주었다. 수행된 실험에서 전단보강근이 충분한 정착길이를 확보하지 못하여 전단보강근의 항복 이전에 파괴가 일어났다. 실험 결과를 통한 FE 모델의 검증이 이루어졌으며 검증된 FE 모델을 통해 전단보강근의 부착 성능에 대한 변수 분석이 수행되었다. 주요 변수는 슬래브의 두께, 콘크리트의 압축강도였으며 전단보강근의 성능을 산정할 수 있는 방법을 제시하였다.

Development of FRP Shear Bolts for Punching Shear Retrofit of Reinforced Concrete Slabs

A fiber-reinforced polymer (FRP) shear bolt system has been recently developed at the University of Waterloo in Canada. The system is used to protect previously built reinforced concrete (RC) slabs against brittle punching shear failure. The system requires drilling small holes in a RC slab around the perimeter of a column, inserting bolts into the holes, and anchoring the bolts at both external surfaces of the slab. Many existing RC slabs have been built without any shear reinforcement. Also, many of these slabs are in corrosive environments, e.g., parking garages, where the use of deicing salts accelerates reinforcement corrosion and concrete deterioration. Therefore, FRPs are ideal materials to be used for such retrofit. The challenge, however, is the development of mechanical end anchorages for FRP rods that are efficient, aesthetic, cost effective, and that can be installed on site. The research presented in this paper includes development of FRP bolts with mechanical anchorages and the results of testing done using the developed systems. A new anchorage technique for the FRP rods based on crimping the rod ends with the aluminum fittings was developed. The testing was done on isolated slab-column specimens representing interior slab-column connections in a continuous flat plate system. The specimens were subjected to simulated gravity loading. The developed FRP bolts worked very well in improving the performance of the slab-column connections and showing the benefits of using FRP in punching shear retrofit of reinforced concrete slabs in corrosive environments.

An Experimental Study on Shear Reinforcement Methods of Interior Flat Plate-Column Connections

This research is an experimental study on full-scale interior slab-column connections of flat-plate. Three types of shear reinforcements were proposed to prevent brittle punching shear failure that could result in collapse of whole flat plate structures. A series of four flat plate specimens including a specimen without shear reinforcement and three specimens with the reinforcements was tested. The dimension of the slabs was 2620*2725*180mm and the specimens had a 600*800mm square column at the center of the slabs. The slabs were tested up to failure using monotonic vertical shear forces. The presences of the shear reinforcements substantially increased punching shear capacity and ductility of the interior slab-column connections.

불균형모멘트를 받는 슬래브-기둥 접합부를 위한 래티스 전단 보강

초록 · 키워드 목차 오류제보하기 등록된 정보가 없습니다. ABSTRACT1. 서론2. 실험체 개요 및 설치3. 실험 결과4. 래티스의 성능 및 상세의 영향5. 결론참고문헌 요약

래티스 철근을 이용한 무량판-기둥 접합부의 전단보강

Flat plate-column connections are susceptible to brittle punching shear failure, which may result in collapse of the overall structure. In the present study, a new shear reinforcement for the plate-column connection, the lattice shear reinforcement was developed. Experimental study for the lattice shear reinforcement was performed. Shear strength and ductility of the specimens reinforced with the lattice bars were compared with those of unreinforced specimens. The test results showed that the strength and ductility of the specimens with the lattice shear reinforcement were improved by 1.37 and 9.16 times those of the unreinforced specimens, respectively. These results indicates that the lattice shear reinforcement is superior in ductility to the shear stud-rail which is popular in U.S. Based on the test results, the design method for the lattice shear reinforcement was developed.