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.
Numerical Modelling of Local Cladding-Structure Interaction
The modelling exemplifies the different failure mechanisms that can result due to cladding-structure interaction. Results confirm that common design methods which neglect cladding interaction are inaccurate. The authors intend to continue the research to successively develop improved and innovative low damage cladding-moment resisting frame systems. They also aim to produce simple design tools that provide easy inclusion of the effects of cladding-frame interaction to the seismic response.
Seismic Design Spectra for Nuclear Power Plants
Statistical studies made recently, independently by the Blume and Newmark organizations for the AEC, of a number of earthquakes are reported with a view toward developing recommendations for design response spectra to be used for nuclear power plant facilities. Recommended criteria and design spectra are reported which differ somewhat from previous recommendations but which are generally in accord with current practice. The new recommendations are more rational than previous ones in the sense that they are consistent with the results of a larger number of observations, and will generally tend to agree better with response spectrum calculations made for the same earthquake history with different levels of damping. Recommendations are also included regarding other seismic design criteria for nuclear power plants, including damping values and combination of response components.