Behavior and Design of Eccentrically Loaded Group Bolted Connections Considering

Abstract

Steel structures have many advantages of material and prefabrication characteristics than reinforced concrete structures. In steel structures, group bolted connections and welded connections are typical methods as these prefabrications. Of these, well-designed bolted connections can exhibit excellent ductile behavior through bearing mechanism until the occurrence of bolt shear rupture.

Two approaches exist for design group bolted connections under eccentric load: a traditional elastic analysis and the more accurate (but more complex) ultimate strength analysis. The elastic analysis is widely used for decades because it is very easy to apply. But the elastic analysis brings about more conservative results than the ultimate strength analysis. In the elastic analysis, the behavior between force and deformation of single bolted connections is assumed to be proportional although it shows a nonlinear relationship. To calculate a more accurate capacity of group bolted connection (ultimate strength design), the nonlinear relationship between force and deformation of single bolted connections has to be defined preferentially. However, the current bolt load-deformation relationship, which the basis of the current ultimate strength method, was derived long ago by Crawford and Kulak (1971), is based on one-type of 3/4in-A325 bolt and A36 steel combination. Considering that combination of different bolt sizes and steel specifications are now widely used in designing group bolted connections, the applicability and reliability of the current approach needs to be evaluated.

Each fastener in group bolted connection under eccentric load has different boundary conditions depending on displacement of that. For example, in the case of the fasteners of which displacement is pointing to edge of the connection is governed by end tearing of base steel. Although the fasteners can have that boundary condition, which is open boundary condition, the current design practice only consider closed boundary condition which is governed by bolt shear rupture and excessive bolt hole deformation. Therefore, in this study, single bolt tests with variables such as steel specification, thickness of a base steel, bolt diameter and edge distance were carried out to propose the force-deformation relationship depending on the boundary condition of fasteners.

The test results with the open boundary conditions revealed that the bolt force-deformation relationship is strongly affected by the edge distance, the strength and the thickness of the steel plates. On the other hand, in the tests with the closed boundary condition, the projected area of the bolt hole, the strength and the thickness of the plates were the main factor affecting the force-deformation relationship. From these approach, to propose generalized force-deformation equation of both types single bolted connection, normalization was conducted by current bearing strength, which are and , of each specimen. From the normalized data based on the test results in this study, the force-deformation equation is proposed. Together with the normalized force-deformation relationship, the allowable deformation limit of bolted connections was also proposed considering failure modes of the both boundary conditions. The available deformation capacity should be used as the limit deformation for redistributing the bolt forces in the ultimate strength design of eccentric group bolted connections. It was that the relationship proposed in this study can be used for a more accurate analysis and economical design of a variety of group bolted connections subjected to eccentric shear.