Development of Headed Bars in Slab-Column Joints of Reinforced Concrete Slab Bridges

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Title: Development of Headed Bars in Slab-Column Joints of Reinforced Concrete Slab Bridges

Author(s): Vasileios Papadopoulos, Juan Murcia-Delso, and P. Benson Shing

Publication: Structural Journal

Volume: 115

Issue: 5

Appears on pages(s): 1393-1406

Keywords: cyclic loading; development length; finite elements; headed bars; large-scale testing; numerical analysis; punching; seismic design; slab bridges

Date: 9/1/2018

Abstract:
This paper presents results of an investigation on the development of headed bars extending from a column into the slab of a reinforced concrete slab bridge. Three full-scale slab-column specimens were tested under quasi-static cyclic lateral loading to determine the minimum embedment length required for the headed bars to develop their full tensile capacity, and the reinforcement details needed in the slab-column joint region to prevent premature anchorage failure, when a plastic hinge forms at the top of the column. The experimental results showed that for 5000 psi (34.5 MPa) concrete and Grade 60 steel, a development length equal to 11 times the bar diameter is adequate for headed bars in slab-column joints designed according to Caltrans specifications with a minimum of 2 in. (50.8 mm) of clear concrete cover. Specimens with shorter embedment lengths were able to develop the moment capacity of the columns and showed significant ductility, but exhibited moderate to severe punching cracks in the cover concrete of the slabs. Finite element analyses of slab-column assemblies showed that punching damage can be eliminated by increasing the concrete cover above the bar heads.