Shear Strength of Slabs with Double- Headed Shear Studs in Radial and Orthogonal Layouts

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Title: Shear Strength of Slabs with Double- Headed Shear Studs in Radial and Orthogonal Layouts

Author(s): G. Birkle and W.H. Dilger

Publication: Special Publication

Volume: 265

Issue:

Appears on pages(s): 499-510

Keywords: flat slabs; headed studs; punching; shear; shear reinforcement; slab bridges; studrails.

Date: 10/1/2009

Abstract:
Solid slabs supported directly on columns offer elegant solutions for short span bridges. For buildings, flat slabs are becoming more and more popular. Solid slabs are easy and economical to construct, and for buildings they offer ease of mechanical installations and maximum story height. The slab thickness is primarily governed by deflection/vibration limits or punching shear. The latter may lead to a very brittle and sudden type of failure that can be avoided by increasing the slab thickness, using high-strength concrete, or providing shear reinforcement. The most effective of these is shear reinforcement because it deals directly with the localized problem of punching and it also prevents brittle failure. The main challenges of shear reinforcement are the installation and the anchorage of the shear elements. These problems are most adequately solved by using headed studs mounted on rails. To investigate the effect of layout and the extent of the shear reinforcement on the punching shear resistance, six slab-column connections were tested at the University of Calgary. The tests showed that the strength of the connections and their ductility were significantly enhanced by shear stud reinforcement. They also demonstrated that the radial layout of the studrails as required by Eurocode 2 exhibited no advantage in performance over an orthogonal layout where the studrails were aligned with the orthogonal reinforcing mesh. This is the standard arrangement in North America. The latter is preferable because of the minimal interference with the non-prestressed or prestressed flexural reinforcement. In the present test series, maximum ductility was achieved by extending the shear reinforcement to 4d from the face of the column. Where the shear reinforcement was only extended to 2d from the face of the column, an increase in strength was recorded, but the mode of failure still had to be classified as brittle because the failure surface occurred outside the shear reinforced zone. Providing shear studs spaced at d/2 to a distance 2d from the column and spaced at d between 2d and 4d significantly increased the ductility of the connection. Ductile behavior is especially important for the performance of slab-column connections of bridges and buildings in seismically active zones.