Compressive Membrane Action Effects on Punching Strength of Flat RC Slabs

Abstract

The design of reinforced concrete flat slabs in practice can be governed at failure by punching shear close to concentrated loads or columns. Punching shear resistance formulations provided by codes are calibrated on the basis of experimental tests on isolated slabs supported on columns in axisymmetric conditions. Nevertheless, the behavior of flat slabs can be different than isolated specimens due to the potentially beneficial contributions of moment redistributions and compressive membrane actions. Accounting for the significance of these effects, nonlinear finite element analyses are performed with the crack model PARC_CL implemented in Abaqus. This paper aims to investigate a series of punching shear tests on slabs with and without shear reinforcement, different reinforcement ratios and loading conditions accounting for the potential contribution to the enhancement of the punching strength due to compressive membrane action (CMA). The numerical results with a multi – layered shell modeling are then post – processed adopting the failure criterion of the Critical Shear Crack Theory (CSCT). The results pointed out the significant outcomes and differences between standard specimens and actual members showing how the current codes of practice may underestimate the punching capacity.

Robustness improvements for 2D reinforced concrete moment resisting frames: Parametric study by means of NLFE analyses

“…Therefore, the second suggestion 5,14 consists in providing the same reinforcement in the two chords of the beam, making the section symmetrical; • Lateral springs: the presence of the orthogonal structural systems can highly and positively influence the response of the structure when a supporting column collapses, as demonstrated in Refs. [19][20][21][47][48][49][50][51] In general, the horizontal flexural-shear response of the orthogonal beams combined with the slabs can produce "3D effects" with important benefits.…”

“…In fact, in a 3D building, the lateral displacements of a plane frame are limited due to the influence of the transverse structural elements, which stiffen the structure and surely enhance the robustness. 19,20,24,[48][49][50][51] However, it is not straightforward to experimentally calibrate the stiffness of the lateral constraints. 29 The lateral constraint conditions, determined by the transverse beams belonging to the orthogonal framed systems and slabs with one-way joists, have been herein modeled, in a simplified way, by means of elastic translational springs.…”

“…Thirdly, the contribution provided by the orthogonal systems to the frame with continuity and symmetry has been modeled by means of elastic springs. In fact, in a 3D building, the lateral displacements of a plane frame are limited due to the influence of the transverse structural elements, which stiffen the structure and surely enhance the robustness 19,20,24,48–51 . However, it is not straightforward to experimentally calibrate the stiffness of the lateral constraints 29 .…”

Eccentric punching strength of continuous flat slabs—Analysis of different experimental setups

“…In the elastic field, the circular area has a radius of approximately 0.22ÁL from the centre of the column for regular span length. However, as shown by Einpaul et al, 16 Cantone et al, 17 and Kueres et al 18 vertical loading tests on isolated specimens could lead to inaccurate prediction of the behavior of the actual continuous slab. In a continuous slab, moment redistribution occurs shifting the location of the line of contraflexure, furthermore, a continuous slab cannot expand laterally causing axial compression within the hogging moment area.…”

Parametric analysis on punching shear resistance of reinforced-concrete continuous slabs

“…CMA or TMA effects can be evaluated using yield line methods (Bailey, 2001;Burgess, 2017;Dat and Hai, 2013;Gouverneur et al, 2013a;Qian et al, 2015), rigid plastic approach (Park and Gamble, 2000;Rankin and Long, 1997;Wood, 1961) for RC, SFRC and strengthened fibre-reinforced polymer (FRP) members (Zeng et al, 2016), sector models based on axisymmetric assumptions (Einpaul et al, 2015(Einpaul et al, , 2016 and finite-element methods (Belletti et al, 2016;Soares and Vollum, 2015). Membrane action effects on continuous slabs have been recently analysed using nonlinear finite-element analysis (NLFEA) and different modelling approaches, for example using threedimensional (3D) hexahedral elements (Genikomsou and Polak, 2017) or multi-layered shell elements (Cantone et al, 2016). In this paper, the shrinkage effects on concrete cracking and on the punching shear resistance are studied.…”