Asymmetric Friction Connection (AFC) design for seismic energy dissipation

Abstract

Asymmetric Friction Connections (AFCs) are used to dissipate seismic energy via friction. AFC strength is affected by moment–axial force–shear force (MPV) interaction. Current MPV models do not consider the increase in bolt tension due to bolt rotation as bolts are assumed to yield axially during AFC assembly. A MPV model is proposed for AFCs considering the increase in bolt axial tension due to bolt rotation, and elastic or elasto – plastic bolt axial behaviour. A parametric study is presented describing the relative impact and effects of bolt rotation, bolt thread, ultimate strength, friction coefficient at the sliding interfaces, and bolt axial relationship. The predicted AFC strength is validated against experimental data from 60 tests of AFCs with Grade 8.8 bolts and Bisalloy 400 shims, and 18 experimental tests with Grade 8.8 bolts and Bisalloy 500 shims. The proposed MPV model considering elasto-plastic bolt axial behaviour better matches the experimental data with average absolute errors of 0–18% for AFCs with M16, M20 and M24 bolts, and of 55–79% for AFCs with M30 bolts. Finally, the model validation indicates the current in practice overstrength and understrength factors of 1.40 and 0.70 can be used with this particular model in design to consider: (i) the variability of the sliding strength due to the bolt fabrication and assembly issues; and (ii) the degradation of sliding surfaces.