Top-and-seat-angle connections and end-plate connections: snug vs. fully pretensioned bolts

Abstract

The effect of partially pretensioned bolts has been examined through research conducted at the ATLSS center of Lehigh University. Extended end-plate and top-and-seat-angle connections incorporating fully pretensioned and snug-tight bolts were tested. Fully pretensioned bolts were tightened to 70% of their ultimate strength (as specified by AISC), and snug bolts were tightened to between 30% and 40% of their ultimate strength.† A W27×94 beam section was connected to a W14×193 column section for the tests considered. All material was 50 ksi steel, and A325 1-in. and 1 1/8-in. diameter bolts were used for all connections. Snug-tightened end-plate connections performed essentially the same as their fully pretensioned counterparts. Snug connections were nearly as stiff as the fully pretensioned connections at moderate loads, and the ultimate strength was the same for either case. Snug-tight connections actually behaved stiffer during the course of reversal loading. Top-and-seat-angle connections were designed to resist moment by using equally large angles attached at the top and bottom beam flanges. The snug-tight connection for multiple bolt rows behaved stiffer and stronger than its fully pretensioned counterpart. Two modes of behavior are proposed for these cases. The snug-tight connection also reacted less adversely to load reversal, and its load-deformation response remained linear over a larger range of loading.