Efficient 3D modelling of punching shear failure at slab-column connections by means of nonlinear joint elements

Failures of isolated slab-column connections can be classified as either flexural or punching. Flexural failure is typically preceded by large deformation, owing to flexural reinforcement yield, unlike punching failure which occurs suddenly with little if any warning. This paper proposes a novel numerical strategy for modelling punching failure in which nonlinear joint elements are combined with nonlinear reinforced concrete (RC) shell elements. The joint elements are employed to model punching failure which limits force transfer from slabs to supporting columns. The shear resistance of individual joint elements is calculated using the critical shear crack theory (CSCT) which relates shear resistance to slab rotation. Unlike other similar models reported in the literature, the joint strength is continually updated throughout the analysis as the slab rotation changes. The approach is presented for slabs without shear reinforcement but could be easily extended to include shear reinforcement. The adequacy of the proposed methodology is verified using experimental test data from isolated internal RC slab-column connections tested to failure under various loading arrangements and slab edge boundary conditions. Comparisons are also made with the predictions of nonlinear finite element analysis using 3-D solid elements, where the proposed methodology is shown to compare favourably whilst requiring significantly less computation time. Additionally, the proposed methodology enables simple calculation of the relative contributions of flexure, torsion and eccentric shear to moment transfer between slab and column. This information is pertinent to the development of improved codified design methods for calculating the critical design shear stress at eccentrically loaded columns

Shear design of short-span beams

Eurocode 2 presents two alternative methods for accounting for arching action in beams. The simplest option is to reduce the component of shear force owing to loads applied within 2d of the support by the multiple a v /2d (where a v is the clear shear span and d is the effective depth). Eurocode 2 also allows short-span beams to be designed with the strut-and-tie method (STM), raising the question of which method to use. This paper presents a simple strut-and-tie model for short-span beams. The stress fields used in the STM are shown to be broadly consistent with those calculated with non-linear finite-element analysis. The STM is shown to give good predictions of shear strength, particularly when the concrete strength is calculated in accordance with the recommendations of Collins and Mitchell. The accuracy of the simplified design method in Eurocode 2 is shown to be highly dependent on the stirrup index. The paper also presents data from eight beams tested by the authors which show that aggregate fracture has little if any influence on the shear strength of short-span beams

Shear design of short-span beams

Eurocode 2 presents two alternative methods for accounting for arching action in beams. The simplest option is to reduce the component of shear force owing to loads applied within 2d of the support by the multiple a v /2d (where a v is the clear shear span and d is the effective depth). Eurocode 2 also allows short-span beams to be designed with the strut-and-tie method (STM), raising the question of which method to use. This paper presents a simple strut-and-tie model for short-span beams. The stress fields used in the STM are shown to be broadly consistent with those calculated with non-linear finite-element analysis. The STM is shown to give good predictions of shear strength, particularly when the concrete strength is calculated in accordance with the recommendations of Collins and Mitchell. The accuracy of the simplified design method in Eurocode 2 is shown to be highly dependent on the stirrup index. The paper also presents data from eight beams tested by the authors which show that aggregate fracture has little if any influence on the shear strength of short-span beams