PERFORMANCE DETERIORATION OF SLOTTED-BOLTED CONNECTION DUE TO BOLT IMPACT AND REMEDY BY RESTRAINERS
The behaviour of slotted-bolted connections when the maximum slip travel exceed the available slot length is presented. The drastic degradation behaviour of slotted-bolted connections under bolt impact is demonstrated. Remedy by means of the concept of restrainers is proposed, which is also advantageous in suppressing the build-up of resonance motion by virtue of the change in system stiffness at different stages. Nonlinear dynamic analyses were performed on a prototype 6-storey steel building equipped with friction dampers with and without restrainers. Three historical earthquake records from California, i.e. the 1989 Loma Prieta, the 1966 Parkfield, and the 1940 El Centro records, were considered in the analyses. In the worst loading case, dampers with restrainers are superior to that without restrainers, resulting in reduction of the peak inter-storey drift by 16% and the peak slip travel by 15%. The shorter slip travel obviously provides extra safety to the system. Increasing the maximum restraining force is generally beneficial in reducing the peak inter-storey drift. However for steel bracings, the restraining force limit should be kept sufficiently below the buckling capacity to avoid buckling of the bracings. Furthermore, a higher restraining force would induce higher storey base shear. Hence, the adequacy of the foundation has to be properly addressed as well in retrofitting of buildings.
Seismic Design Spectra for Friction‐Damped Structures
A simplified seismic design procedure is proposed for structures equipped with an innovative friction-damping system. The system has been shown experimentally to perform very well and could represent a major new development in earthquake-resistant design. This paper first presents an efficient modeling approach for the seismic analysis and design of friction-damped structures. The hysteretic properties of the friction dampers are derived theoretically and are included in a Friction Damped Braced Frame Analysis Program (FDBFAP), which is adaptable to a microcompter environment. FDBFAP is then used to perform a parametric study of the optimum slip-load distribution for the friction dampers. The results of the study lead to the construction of a design slip-load spectrum for the rapid evaluation of the optimum slip-load distribution. The spectrum takes into account the properties of the structure and of the ground motion anticipated at the construction site. The availability of this design slip-load spectrum should lead to a greater acceptance by the engineering profession of this innovative design concept.
Tests of composite beams with web holes
Tests of composite beams comprising a concrete slab supported on a steel deck and a steel wide-flange shape containing large web openings are described. Special attention is directed to the amount of shear connection between slab and steel section in the region of a web hole, and on the effect of construction loads acting on the steel section prior to composite action being effective.It is shown that limited shear connection at the hole will significantly affect the strength when loading produces a high shear-to-moment ratio, and a theory is presented which conservatively takes this into account. The effect of construction loads on unshored construction is shown to be small when these do not exceed 60% of the non-composite beam resistance at the hole.