The behavior and design of unstiffened seated-beam connections

The purpose of this thesis is two-fold. The first is to investigate the behavioral causes of a steel connection failure accident, and the second is to develop a new and rational method for the design of unstiffened seated-beam connections. To this end, the thesis is divided into four parts. Part One introduces the background information regarding the steel connection failure accident that occurred in November 1993 during the construction of the Chicago Postal Building Addition. Detailed information about the accident site is presented and the load condition on the critical connection evaluated. Also, the objective and scope of the study are defined and the general approaches are outlined. Part Two presents a comprehensive analysis on the fundamental behavior of unstiffened seated-beam connections. The current AISC/LRFD design procedure is reviewed and inconsistencies are noted. Interactions between connection components are discussed and more rational and accurate models for strength calculations are developed. Part Three describes two experimental programs that are designed to verify the analytical work. The first test program, with a total of 55 seat angle specimens for 26 different cases, is conducted to investigate the postal building accident. The second test program, with a total of 72 seat angle specimens for 40 different cases, is conducted with aim to develop a new and rational design method. The major test variables of the experimental study involves beam setback, angle thickness and beam-to-angle attaching bolts. The final part of the thesis addresses the design methodology of the seated connections. The validity of various theoretical methods is assessed by comparing analytical predictions with experimental results. The new design method, including tabulated design strength and illustrative examples, is presented in the format ready for adoption in the specifications. At the end of the thesis, a conclusion regarding the causes of the connection failure accident is formulated and the practical implication of this research suggested