Design proposal for bolted angle members in compression

Abstract

The type and size of the rotational restraints at the gusset plates near the member’s ends (provided by the adjacent structure) are crucial for the prediction of the compression member capacity of bolted angles. This was highlighted by the authors by means of experimental and numerical investigations in the past. Due to the eccentric connection on only one leg, additional bending moments are acting on the member, leading to a complex load carrying behaviour with flexural and/or lateral torsional buckling phenomena. Detailed analytical models for the estimation of appropriate spring stiffness values have been developed for several practical applications in buildings and two-bolt connections at both member’s ends. The investigated connection details comprise a simply fixed gusset plate (e.g. as attachment to concrete walls), a joint to the flange of an I-shaped section and a joint to the web of an I-shaped section via a gusset plate. Based on that, a design model was developed for bolted angle members with rotational spring restraints at both member’s ends and an eccentric compression loading N, in order to calculate the compression capacity NR. Within this paper, the proposed design procedure is presented. Moreover, the thereby determined resistances NR,model are compared with the results of sophisticated 3D finite element calculations NR,FEM that consider the actual boundary conditions and the eccentric load introduction as well as equivalent geometric imperfections. The finite element model has preliminary been calibrated on the experimental test results. The comparison indicates that the resistances based on the proposed design procedure are slightly conservative compared to the real behaviour of the angle member. In addition, the large increase in capacity (compared to the simply supported reference case) is highlighted. Therefore, it is concluded that the new design proposal is able to predict the compression member capacity of bolted angles safely and economically.