Punching Shear Capacity Of Slabs Research Articles

Punching shear capacity of fiber-reinforced concrete suspended slabs: Database analysis and models assessments

The punching shear capacity is critical in the design of suspended slabs. Fiber reinforcement has been introduced to improve the punching shear capacity of these slabs. Several models have been used to predict the punching shear capacity of fiber-reinforced concrete slabs (FRCS). Some of these models accounted only for the contribution of concrete (e.g., ACI 318–19 and CSA-19), while others also accounted for the contribution of reinforcing steel (e.g., JSCE-07 and Eurocode-2 and/or fibers (e.g., fib MC-10). In the present study, experimental results from 240 FRCS and 78 control slabs (without fibers) were collected and analyzed to assess the effect of various parameters and the extent to which these parameters affect the predicted punching shear capacities by various models. Four main parameters, concrete compressive strength, steel reinforcement ratio, fiber reinforcement, and punching shear perimeter, were considered in the assessment of various design and theoretical models. The study revealed that most design-based models underestimate, to varying degrees, the punching shear capacities with large variability. To better capture the dependence of the punching shear capacity on the four main parameters, a new model was proposed for FRCS. The proposed model considers the critical shear perimeter at a distance d from the face of the column and accounts for the fiber contribution as a function of the residual strength parameter obtained from standard beam tests (ASTM C1609). Predictions of the proposed model were characterized by high accuracy and low coefficient of variation (CV).

Punching Shear Behavior of Slabs Made from Different Types of Concrete Internally Reinforced with SHCC-Filled Steel Tubes

The punching shear failure of reinforced concrete (RC) flat slabs is an undesirable type of failure, as it is sudden and brittle. This paper presents an experimental and numerical study to explore the behavior of flat slabs made of different types of concrete under the influence of punching shear. Experimental tests were carried out on four groups of flat slabs, each group representing a different type of concrete: ordinary normal concrete (NC), high-strength concrete (HSC), strain-hardening cementitious composite concrete (SHCC), and ultra-high-performance fiber concrete (UHPFC). Each group consisted of six slabs, one representing an unreinforced control slab other than the reinforcement of the bottom mesh, and the others representing slabs internally reinforced with SHCC-filled steel tubes and high-strength bolts. An analytical equation was used to predict the punching shear capacity of slabs internally reinforced using steel assemblies. A numerical model was proposed using the ABAQUS program, and was validated by comparing its results with our experimental results. Finally, a case study was performed on large-scale slabs. The results showed that using steel assemblies inside NC slabs increased the slab's punching shear capacity but does not completely prevent punching shear failure. Internally unreinforced slabs made of UHPFC and SHCC were able to avoid punching shear failure and collapse in a ductile bending pattern due to the high compressive and tensile strength of these types of concrete. The proposed analytical method succeeded in predicting the collapse load of slabs reinforced with steel assemblies with a difference not exceeding 9%.

Punching Shear Capacity of RC Biaxial Voided Slab – Prediction by Critical Shear Crack Theory

In this study the applicability of critical shear crack theory (CSCT) to biaxial voided slab is investigated, which predicts the punching shear capacity of solid slab. Based on the experimental results of biaxial voided slab available in the literature (40 specimens) the research is carried out. The experimental results showed that the load-rotation behaviour of biaxial voided slab is remain same as that of solid slab except for specimens with void located within 0.5d from face of the column. Further, the punching shear capacity of slab specimens with voids located beyond 2d distance from column face is almost the same as that of the solid slab. Depends on the available load-rotation data modified CSCT was developed depends on the location of the void from face of the column. The predictions were observed to be very scattered with a mean and standard deviation of 0.752 and 0.412, respectively. This is reasonable as the modified CSCT estimates the capacity with respect to the location of voids and ignores the area of void at the section considered. The CSCT approach needs to be further modified by including location and area of void to predict the punching shear capacity of biaxial voided slab with reasonable accuracy.

Prediction of punching shear capacity of concrete slabs reinforced with additional middle-thickness rebar mesh

This paper aims to evaluate the influence of using additional middle-thickness rebar mesh (mid-mesh) on improving the punching shear behavior of interior slab-column connection. Sixteen two-way slabs were cast and tested including different flexural, compression, and mid-mesh reinforcement ratios at different levels of concrete strength. The performance of code-based expressions in predicting the punching shear capacity of reinforced concrete flat plates was also ascertained. The results indicated that using additional mid-mesh showed an increase in the punching shear capacity of slabs reached up to 17.7%. The results also indicated that the ACI 318-19 and CSA A23.1-19 codes underestimate the punching shear strength of tested slabs. Eurocode showed the closest predictions of the ultimate shear load compared to the other design codes investigated in this study. The authors also proposed an equation that can help the designers/engineers to accurately predict the punching shear capacity of intermediate slab–column connection with and/or without additional mid-mesh reinforcement.