The Short Bolt Problem
Minor differences between manufacturing standards for bolts and tables that are commonly used by engineers and detailers for selecting bolt lengths can lead to discrepancies between what an engineer or detailer expects and what is actually installed in the joint, in some case leading to bolts being sheared though their threads instead of through their shanks. Jim Swanson, G.A. Rassati, and Chad Larson conducted a study of the issue highlighting the manufacturing tolerances and their consequences on the design of bolted joints, and assessing the risk associated with joints designed with the bolts in the threads-excluded configuration but installed in the threads-not-excluded configuration.
Base-Plate Plate Washers
Steel plate washers used in column base plate and anchor rod assemblies must have sufficient strength and stiffness to fully develop the anchor rods without succumbing to pull-through failure, flexural failure, or cracking. Questions received by AISC’s Solution Center spurred some interest in further investigating the values provided in the Manual. Laboratory testing of assemblies consisting of an anchor rod, plate washer, nut, and base plate were conducted to investigate the performance of the plate washers. Plate washers made of ASTM A572 Gr. 50 material with various thicknesses were tested with threaded rods in five diameters and three grades. After the rods were developed fully in tension, the plate washers were examined for signs of failure and permanent out-of-plane deformation of the plate washers was measured.
Extra-Long Slotted Holes
The AISC Specification (2016) limits the maximum slot length for bolted connections to 2.5 times the bolt diameter. The maximum slot length limitation is based primarily on testing performed in the 1960s at Lehigh University (Allan and Fisher, 1967). The goal of this research project was to provide testing data for the behavior of slip-critical bolts in connections with slots exceeding the maximum length in the AISC Specification. This data will assist in determining if a potential increase in maximum slot length can be justified, providing assistance to the steel industry in allowing more flexible connection designs, in providing more options to accommodate erection tolerances, and in addressing potential field issues.
TNA 144ksi Bolts
Nearly two thousand structural bolts from three grades and five sizes were tested as part of a study validating the performance of TNA 144ksi bolts. The study included tension testing, shear testing, and installation verification for the then new torque + angle installation method. The bolts performed very well and the tightening method consistently produced tension in the assemblies above the minimums required for snug and final tension. Ultimately the bolts were approved as ASTM F3148 Fixed Spline Bolt Assemblies and have been adopted by both the AISC and RCSC Specifications.