Design for Eccentric and Inclined Loads on Bolt and Weld Groups

The 8th Edition AISC Manual of Steel Construction introduced the ultimate strength, instantaneous center of rotation method for computation of the tabulated bolt and weld group eccentricity coefficients C. As discussed in detail by Tide1 and Brandt, this marked a major departure from the traditional and conservative elastic analysis employed in the 7th Edition AISC Manual (and previous editions) and which many design textbook authors still emphasize. The reason for the change was the ultimate strength method better reflected the ductility and load redistribution capability within the group by explicit consideration of each connectors characteristic load-deformation curve. The ultimate strength methods connector shape factor effect, somewhat analogous to the plastic section modulus to elastic section modulus ratio for steel beams, consequently accounts for this increase in connection strength. Unfortunately, this type of nonlinear analysis is certainly more complex, it involves trial iterations until satisfactory numerical convergence, thus, is probably only suitable for computerized solutions for those cases not covered by the Manual.