PunchingShear Resistance of Flat Slabs: Influence of Reinforcement Type and Ratio

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Title: PunchingShear Resistance of Flat Slabs: Influence of Reinforcement Type and Ratio

Author(s): Tetsuya Yamada, Antonio Nanni, and Katsushiko Endo

Publication: Structural Journal

Volume: 89

Issue: 5

Appears on pages(s): 555-563

Keywords: anchorage; bond (concrete to reinforcement); building codes; flat concrete slabs; punching shear; reinforced concrete; structural design; reinforcement spacing; shear properties; slab-column connections; tests; Structural Research

Date: 9/1/1992

Abstract:
As part of a research program to study the performance and design of flat-slab systems, this investigation aimed to determine the effect of shear reinforcement type and ratio on punching shear strength of monolithic slab-to-column connections. The first type of shear reinforcement consisted of hat-shaped units, very advantageous from the points of view of fabrication and field installation. The second type consisted of double-hooked shear bars, more difficult to install but with very efficient anchorage. A total of 13 specimens were fabricated and tested. The dimensions of the slab were 2 x 2 x 0.2 m (79 x 79 x 7.9 in.), with a centrally located column 0.3 x 0.3 m (11.8 x 11.8 in.) in cross section. The column extended above and below the slab for a length of 0.3 m (11.8 in.). Monotonic static load was applied downward at eight points symmetrically distributed around the column center at a distance of 0.75 m (29.5 in.). The specimen was supported by the column stud. Shear reinforcement varied from 0 to 1.53 percent in the first series, and from 0 to 1.98 percent in the second series. Longitudinal bars were placed on both compression and tension sides. The tensile flexural reinforcement was 1.23 and 1.53 percent in the first and second series, respectively. Load, deflection, and strain were monitored (at various locations along the shear and flexural reinforcement) during the tests. Experimental results showed that the hat-shaped reinforcement was not effective because of lack of proper anchorage and large spacing. Double-hooked reinforcement showed high effectiveness, which resulted in a considerable increment of the punching shear resistance of the connection. Comparisons with the provisions of ACI 318-89 were made.