Monotonic and Cyclic Tests on Shear Diaphragm Dissipators for Steel Frames

Abstract

This report describes a series of cyclic tests on a yielding shear panel device of the form proposed by U. Dorka (unpublished) at the University of Kassel, Germany. The device consists of a short length of square hollow section (SHS) with a diaphragm plate welded inside it. It is positioned between the braces and the main members of a braced frame, with the diaphragm lying in the plane of the frame, so that it is loaded in pure shear as the frame undergoes lateral deformation. An extensive series of tests on 100 mm square dissipative devices mounted in a single-storey, planar, K-braced frame was successfully performed, under both monotonic and cyclic loads. The devices proved easy and cheap to manufacture, fit, remove and replace. All the devices tested yielded at quite low deformations and sustained very large ductilities without failure. The load carried by the device continued to increase after yield, with a ratio of maximum force carried to yield force of around 1.7 in most tests. While a device with a 2 mm diaphragm appeared to offer the maximum energy dissipation capacity, thinner devices were prone to buckling and to fracture under repeated large- amplitude cycling. A thickness of 3 mm (i.e. thickness to breadth ratio of 0.03) is recommended as offering the best combination of dissipative capacity and robustness. A 3 mm device dissipated approximately 1.3 kJ of energy when the frame in which it was fitted underwent a single displacement cycle of amplitude 30 mm. It is concluded that these devices offer a simple, cheap and robust way of dissipating significant amounts of energy in seismically loaded frames. Some improvements to the rig design and suggestions for further work are offered in section 4.6.