Effect of openings and shear bolt pattern in seismic retrofit of reinforced concrete slab–column connections

This study addresses seismic retrofit of reinforced concrete flat slab–column connections against punching shear failure. The tested slabs are retrofitted using shear bolts. These bolts were developed for installation in existing slabs by drilling holes around columns or concentrated load application points and then tightening against the slab surfaces. Slabs with and without openings are investigated. The effect of the pattern of shear reinforcing elements around the column area, namely orthogonal and radial is also investigated. This paper describes tests on six flat slab–column specimens; three with two openings at the column and three without openings. Among each of the three specimens in a group, one has no shear reinforcement; one is retrofitted in the orthogonal pattern; and one in the radial pattern. The test results, comparisons of the behavior of the specimens, and comparisons with the current code formulas are presented and discussed. The results indicate that shear bolts increase lateral drift capacity and ductility of the slab–column connections.

► Investigation of shear bolts as seismic punching shear retrofit for RC slabs.
► Shear bolts increase strength and ductility.
► Strengthened slabs have the capability of undergoing large lateral drifts.
► Both radial and orthogonal patterns of shear bolts were effective.
► Retrofit in radial pattern is difficult due to interference from flexural rebars.