Punching‐shear strength of reinforced concrete slabs subjected to unidirectional in‐plane tensile forces

Abstract

Some reinforced concrete slabs are subjected simultaneously to concentrated loads and unidirectional in-plane tensile forces. This the case of the top slab of a box girder bridge where hogging bending moments take place at the intermediate supports. Then, the in-plane tensile forces may reduce the punchingshear strength under concentrated loads. This paper describes an experimental campaign carried out to investigate the effect of unidirectional in-plane tensile forces on the punching-shear strength of RC slabs. A total of, five slabs (1,650 × 1,650 × 120 mm), subjected to different levels of in-plane tensile forces were tested under a concentrated load up to failure. As observed, the punching-shear strength diminishes almost linearly as the tensile force increases, up to a certain point associated to concrete cracking. From that point on, the reduction of punching strength is larger since the tensile force at the crack must be resisted by the reinforcement, which yields prematurely.

Experimental investigation of the shear strength of one‐way reinforced concrete (RC) slabs subjected to concentrated loads and in‐plane transverse axial tension

“…Once the second test load ended and the slab was unloaded, the test up to failure was started, applying the load by a controlled displacement at a rate of 0.005 mm/s. In support of the experimental campaign, a finite element model using software package Simulia Abaqus was developed, taking as reference previous works carried out by the authors 20 and Nana et al 21 This model was initially used to predict the tests results and to design the auxiliary structures of loading and support. Once the test on the control slab was performed, the numerical model was calibrated with the obtained result (Figure 9) and used to predict the shear strength of the rest of Type-A slabs under the corresponding value of the external force applied.…”

“…Taking into account the existing plane of symmetry at the middle of the slab, parallel to the spanning direction, both in geometry and loading, only half of each slab was modeled, considering the corresponding boundary conditions in the symmetry plane. The numerical model was inspired in a similar model developed by the authors to study the influence of in‐plane tensile forces on the punching‐shear strength of RC slabs, 20 but also recommendations given in Nana et al, 21 as the use of an explicit quasi‐static solution or a linear evolution of the damage parameter, in both tension and compression.…”

“…The values used to define the yielding surface were modified from those proposed in Fernandez et al 20 to adjust the simulation of the type‐A control slab to the results obtained in the laboratory (Figure 9), and are collected in Table 7. For the steel reinforcement, a bilinear stress–strain diagram was used, considering perfect plasticity.…”

“…A total of five 1650 × 1650 × 120 mm slabs, simply supported on two parallel linear supports, were cast at the Laboratory of Technology of Structures and Materials of the Universitat Politècnica de Catalunya (UPC). The dimensions of the slabs tested in the context of this experimental campaign were conditioned by punching‐shear tests previously performed by the authors, 20 with the aim of reusing the tensioning system built for that occasion. In order to ease the placement, alignment and removal of the whole set‐up within the portal frame where the main hydraulic jack of the laboratory is installed, the point load was decided to be applied at the center of the slabs.…”