Enhancement of the Sliding Hinge Joint Connection with Belleville Springs
The Sliding Hinge Joint (SHJ) was conceived and initially developed by Charles Clifton from 1998 to 2005 and is now in use in over NZD 4 billion of new buildings. It is a low damage semi-rigid beam to column connection for MRSF seismic-resisting systems, that is intended to be rigid under serviceability conditions, become semi-rigid allowing column to beam relative rotation to occur in a severe earthquake and, at the end of the earthquake, seize up and become rigid again. A further desired criterion is that the MRSF has dynamic self-centring properties so that the post-earthquake residual drift of the building is sufficiently low not to require remedial straightening. Subsequent research under the supervision of Charles Clifton has shown that the post sliding strength and stiffness of the SHJ connection developed by Clifton is appreciably reduced, to the point where re-tightening or replacement of the bolts is likely to be necessary following a severe earthquake. This means the joint still falls short of meeting one of the key original low damage performance requirements of not requiring any structural intervention following a severe earthquake. Indications from research at the Universities of Auckland and Canterbury were that this loss of post sliding strength could be reduced with Belleville Springs, however these could reduce the self-centring ability of the MRSF. Determining the optimum combination of post sliding strength and stiffness retention and self-centring ability was not straight-forward and was the principal focus of this research project. Given the proven attractiveness of the SHJ to engineers and clients, this research work has been of high priority to generate the low damage performance from new SHJ systems that the profession and end-users have been expecting and which current systems will not fully deliver. This research has been undertaken into the highest priority areas identified for further development of the SHJ by previous and ongoing research as well as practical experience, which are as follows: • Proposing the methods of checking and preparing the HSFG bolts on site prior to installation as well as proposing a more accurate way of determining the part turn, to increase the reliability of the delivered installed bolt tension in comparison with the design installed bolt tension. • Proposing a method of tensioning the installed bolts within their elastic range using Belleville Springs to provide an accurate measure of the installed tension. This makes it possible to install the bolts at any desirable elastic preload. • Proposing the optimum configuration of Belleville springs to maintain clamping force after active sliding. This may give better control of the frictional capacity and increase the residual joint strength. • Determining the bolt behaviour, sliding shear capacity, and hysteretic component force-displacement behaviour for the friction component with various options of Belleville springs, using a regime of real scale component testing. • Determining the residual friction component strength when Belleville springs are used. • Investigating the effects of the surface roughness, on the joint sliding behaviour to determine the optimum surface preparation level for the joint’s plies, and to reach to a more accurate coefficient of friction. • Investigating the possibility of using the Sliding Hinge Joint not only in dry internal environments as is recommended currently. • Determining the benefit of surface coating the shim plates using a commercial available Titanium Nitriding process to deposit a very hard coating on the steel shims that form one side of each sliding surface. • Investigating the behaviour of a shim-less Sliding Hinge Joint with an abrasion resistant cleat. • Investigating the behaviour of the Sliding Hinge Joint with abrasion resistant cleat and shims. • The AFC component tests on the MTS machine to establish the optimum level of installed bolt tension. • The SHJAFC component tests using customized Belleville springs to assess the efficiency of using customized Belleville springs in the SHJAFC. • Undertaking an analytical and numerical research on the use of linear springs such as Lurethane spring to establish the design of the linear springs, if they are possibly needed, to make the friction dampers statically and dynamically self centre.
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