Shear in One-Way Slabs under Concentrated Load Close to Support

Headnote

One-way slabs under concentrated loads are generally designed for shear by checking the beam shear resistance and the punching shear resistance over an effective width. Only a small number of test data regarding the shear resistance of one-way slabs subjected to concentrated loads is currently available. To be able to better evaluate the shear resistance of one-way slabs, a series of experiments was carried out on continuous one-way slabs (5 m x 2.5 m x 0.3 m [16.4 ftx 8.2 ftx 11.8 in.]) subjected to concentrated loads close to the supports, in which the load position, transverse reinforcement ratio, and concrete strength were varied. The test results are compared with code provisions and a method developed by Regan. The results show a different behavior in shear for slabs under concentrated loads than for beams.

Keywords: effective width; experiments; one-way slabs; punching; shear.

(ProQuest: ... denotes formulae omitted.)

INTRODUCTION

Shear in reinforced concrete one-way slabs loaded with a concentrated load is typically checked in two ways: 1) by calculating the beam shear resistance over a certain effective width resulting from a chosen horizontal load spreading assumption between the load and the support; and 2) by checking the punching shear resistance on a perimeter around the load. The beam shear (one-way shear) capacity formulas in codes are derived from experiments on beams. The tested beams generally have a total width smaller than their depth. The shear resistance of a slab subjected to a concentrated load should not be calculated over its entire width b, but over a certain effective width beff. The shear force calculated from the maximum shear stress over the effective width should equal the shear force resulting from the shear stress distribution over the entire width. In practice, horizontal load spreading is assumed to be less than 45 degrees from the load toward the support (Fig. 1). The lower limit for the effective width is taken in Dutch practice as 2d for loads in the central area of the width and d for loads near the edge or corner of the slab. The punching shear (two-way shear) capacity in code formulas is developed for two-way slabs. Most empirical methods for punching shear are derived from tests on slab-column connections.

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