INTRODUCTION A. Purpose of Investigation. The design of bolted connections in cold-formed steel structures is based on the present AISI Specification for the Design of Cold-Formed Steel Structural Members. 1 Prior to the development of the design criteria, bolted connections were tested at University of Michigan 2 in the 1940's and then at Cornell University 3,4 in the 1950's. The present design provisions were developed primarily on the basis of the tests conducted by George Winter and his associates at Cornell University. Additional tests were recently made by Popowich 5 on multi-bolt connections and by Dhalla 6 on connections with low ductility steels. In these tests, the specimens were tightened to specified torques, and washers were placed under the head and nut of each bolt. During recent years, bolted connections without washers have often been used in numerous instances. In some cases, the washers were used in the connections, but the bolts may not have been tightened according to the torques previously used in the Cornell tests. In order to study the effect of washers on connection strengths, Chong and Matlock 7 have conducted connection tests with and without washers. It was found that the bearing strengths of the connections were reduced considerably when the washers were eliminated. In addition, the parameters used by Chong and Matlock for evaluation of the tensile strength of bolted connections were slightly different from those used in the AISI Specification. It is the purpose of this investigation to review the available test data first and then to study the applicability of the present design formulas to the connections that do not have washers and/or have improper torques. Thin sheets will be used to make an additional study of the connection strength affected by the pretension of bolts and the behavior of bolted connections. In the study carried out to date, additional parameters, such as d/t and Fu/Fy ratios, have been considered for the evaluation of the connection strength. B. Scope of Investigation The present research project consists of an investigation of the structural behavior of bolted connections, a review of the current design criteria, and the conduct of additional tests to provide new design information if necessary. The following items have been planned for inclusion in this study: 20 1) Analysis of available data 2) Effect of torque or pretension in bolts on bearing strength 3) Tensile strength of connections 4) Effect of d/t ratio on bearing strength, longitudinal shearing strength,and tensile strength of steel sheets 5) Difference between single shear and double shear conditions. In order to achieve the objectives of the investigation, the planned research work includes the following three phases: 20 1) Analysis of available data 2) Analytical and experimental investigation 3) Preparation of recommendations Phase 1 of the investigation was initiated in February 1976. It was carried out by Randall L. Mosby, Research Assistant, and directed by Dr. Wei-Wen Yu, Professor of Civil Engineering at the University of Missouri-Rolla. Phases 2 and 3 will be conducted in future studies. This progress report contains the results obtained from the analysis of the available data. It also includes the plans for future analytical and experimental investigations. The research project was sponsored by American Iron and Steel Institute. The technical guidance provided by the AISI Task Group on Bolted Connections (L.W. Ife, T.J. Jones, R.B. Matlock, and D.S. Wolford, members) and the AISI Staff (A.L. Johnson and D.P. Cassidy) is gratefully acknowledged. Thanks are also due to J.H. Senne, Chairman of the Department of Civil Engineering,for his advice. Acknowledgment is also due to E.B. Gibson, past Chairman of the AlSI Task Group, for his technical guidance.
Civil, Architectural and Environmental Engineering
Wei-Wen Yu Center for Cold-Formed Steel Structures
American Iron and Steel Institute
Missouri University of Science and Technology
© 1976 Missouri University of Science and Technology, All rights reserved.
Report - Technical
Mosby, Randall L. and Yu, Wei-wen, "Bolted connections in cold-formed steel structures" (1976). Center for Cold-Formed Steel Structures Library. Paper 63.