International Concrete Abstracts Portal

The boundary conditions at the supports of reinforced concrete slabs, specifically the amount of lateral and rotational restraint, dictate how they respond to particular loads. Membrane (in-plane) forces are present in slabs when their boundaries are sufficiently stiff, therefore restricting the slabs from lateral translations in addition to rotations. Increases in compressive strength and ductility in ultra-high-performance concrete (UHPC) introduce additional strength enhancement not present in Normal-Strength Concrete (NSC).

Ten reinforced concrete slabs were quasi-statically tested in a static water chamber that allowed hydrostatic forces to be utilized as a loading technique on the slab. Of the 10 slabs, 4 were simply supported, and the remaining 6 were rigidly restrained. The load-deformation responses of laterally restrained slabs were then compared to those of simply-supported slabs to determine the enhancement due to the boundary conditions (i.e., compression membrane action). The results of these experiments were then compared to the results of response calculations based on plastic theory.

Valuable data on rigidly-restrained UHPC slab response were obtained from the experiments. The experimental results were compared to the results of the associated numerical analyses. Existing plastic theory should be used with caution when calculating the ultimate resistance of UHPC slabs. The experimental and numerical results showed that UHPC slabs with sufficiently rigid boundary conditions have a static resistance two-and-a-half-times greater than the traditional yield-line theory resistance for UHPC slabs due to compressive membrane effects.

Three-dimensional (3-D) finite element analysis (FEA) is considered to examine previously tested and analyzed under static loading reinforced concrete slabs using the FEA software ABAQUS. Four interior reinforced concrete slab-column connections are presented; one slab is without shear reinforcement (SB1) and the other slabs are with shear bolts (SB2, SB3 and SB4) which differ in the amount of the shear bolts. The coupled plasticity damaged model previously calibrated is considered for modeling the concrete. In this research, parametric studies are presented considering different amount and placement of the shear bolts. The adopted FEA model is used to analyze and investigate the failure modes and loads and the crack patterns of the shear reinforced slab-column connections. Finally, the numerical results obtained from the parametric studies are compared to the current design code predictions.

The paper reports tests to investigate shear and punching behavior of voided slabs, part of a research aimed at studying the structural response of such systems. The voids are shaped like a truncated pyramid. The program included a series of twelve slabs, divided into four groups according to the transverse steel arrangement. The slabs were loaded by one or two forces and supported on two sides. This loading scheme was chosen to investigate the load transfer and resistant mechanism in the slab with voids, with the aim of studying the shear transfer at a column. Failures under point loads close to the support correspond to those typical in thick slabs. A combination of two failure modes occurred, with punching and diagonal shear tension. The capacity must be predicted using the concrete cross section reduced by the voids.

Over the last 20 years the Institute of Structural Concrete at RWTH Aachen University has conducted numerous punching tests on interior slab-column connections with different types of punching shear reinforcement. Within the tests, different types and arrangements of stirrups, lattice girders, and double-headed studs were used as punching shear reinforcement. In this paper, the efficiency of the various types of punching shear reinforcement is studied and discussed based on the experimental results of 39 tests on interior slab-column connections. By comparing the failure loads with the punching shear capacities without shear reinforcement according to ACI 318-14 and Eurocode 2 along with the German Annex, respectively, the increase in punching shear resistance with each shear reinforcement system is investigated.

Most methods for the design and analysis of reinforced concrete slabs for punching are based on experiments on slab-column connections, reflecting the situation in building slabs. Slab-column connections with unbalanced moments have also been studied in the past. Experiments indicate that the accuracy of models for asymmetrically loaded slabs is lower than for symmetrically loaded slabs. In this paper, the difference in accuracy between test predictions for symmetrically and asymmetrically loaded slabs is tackled. A plastic model, the Extended Strip Model, is proposed. The results of maximum loads according to this model are compared to experimental results of symmetrically and asymmetrically loaded slabs. The comparison between the proposed Extended Strip Model and the experimental results shows that the model has a consistent performance for both symmetrically and asymmetrically loaded slabs. Moreover, the model has as an advantage that it combines the failure modes of flexure, shear and punching. The proposed model can be used for the analysis of slabs. In particular, it can be used for the assessment of existing slab bridges subjected to concentrated live loads.