A RETROFIT SOLUTION FOR UNCODED STEEL RAFTER TO CONCRETE RING BEAM CONNECTIONS

Abstract

Some building contractors in the Caribbean have been constructing non-coded steel rafter to concrete ring beam connections on low budget residential buildings. These connections may resist failure under normal loading conditions, but critical connections fail under moderate to high loads resulting in partial or full dislodgement of the roof. In this study, the performance of non-coded steel rafter to concrete ring beam designs were analyzed in a finite element program and a retrofit solution for the failed uncoded connections were designed and modeled. Nine versions of the connection were identified and consisted of several variations including mechanically anchoring the rebar to the rafter without welds, using one and two rebars, varying the rebar embedment depth and using 90 degree hooks and straight rebars. A standard, code-compliant, bolted-endplate connection was used as the control for the investigation. The connections were analyzed in “ABAQUS” with a bond slip and damage plasticity model. The maximum load resistances were compared with category 1 hurricane loads for the region. The load capacities of all the connections were found to be lower than the control connection but were still adequate for hurricane category 1 loads, with the exception of the connection in which the rebars were mechanically anchored to the rafter without welds. Connections with welds to the top flange of the rafter were less stiff, experienced larger rafter displacements, inflicted less damage on the concrete ring beam, and required less rebar embedment to prevent pull out failure than the connections to the bottom flange.