Long Bolted Joints

Tension tests of long structural butt splices of A7 steel connected with 7/8-in. high strength bolts provide background for parts of the specification of the Research Council on Riveted and Bolted Structural Joints for structural joints using A325 bolts. Joints proportioned for a tensile stress of 20 ksi and a shear stress of 22 ksi produced a balance ultimate strength design for short connections approximately 16-in. long. In longer connections, end bolts sheared before all bolts could develop their full shearing strength. In short connections, the average shear stress was approximately 85% of the strength of a single bolt, but bolts in a 52.5 in. (16\x + 3–1/2 in.) long connection developed only 60% of the strength. Joints with tight mill scale faying surfaces and bolts tightened by the turn-of-nut method slipped into bearing at a lower limit of slip coefficient of 0.35. When the mill scale was removed with a power tool, the slip coefficient was only 0.20. Limited tests of bolted lap joints provide information on the behavior of bolts in single shear. Several tests of riveted connections give interesting comparative data.