The seismic behaviour of existing hollowcore seating connections pre and post retrofit

This investigation was part of a greater research initiative regarding the seismic vulnerability of precast hollowcore floor systems. The primary focus throughout the research programme has been to investigate the susceptibility to loss of vertical support of the floor system, from the seating beam. Previous research firstly focussed on identifying and understanding preconceived deficiencies with existing seating connection details. This was followed by the validation of amended, superior performing, 'new' seating connection details. However, little consideration has been given to retrofit techniques for already existing buildings, with potentially poor performing existing seating connections. A two-dimensional, single hollowcore unit, seating connection sub-assembly is used to experimentally investigate the seismic behaviour of previously un-tested existing seating connections pre- and post-retrofit. Three existing seating connection configurations, with the hollowcore unit seated directly on the bare concrete seating ledge and with varying seating lengths were tested. These tests were followed by a fourth retrofitted specimen. Both relative rotation between the hollowcore unit and seating beam, and beam elongation 'pull-off' deformations (resulting from the supporting frame deformations) were imposed on the test specimens. In conjunction with this experimental investigation and with prior knowledge from previous investigations, three primary failure mechanisms for existing hollowcore seating connections are summarised. A suite of conceptual retrofit techniques which target the critical structural weaknesses attributed to causing the primary failure mechanisms are outlined. In general, unfavourable performance was exhibited by the existing seating connections in the experimental investigation, resulting in loss of vertical support of the hollowcore unit under imposed 'pull-off' effects. In contrast, when the retrofit strategy was implemented, a higher level of seismic performance, leading to collapse prevention was achieved. A review is carried out into existing beam elongation numerical models, which are simple and involve only hand-type calculation procedures. The aim of this was to investigate potential methods for predicting the 'pull-off' effects on suspended floor systems. From this, a modification is made to an existing, loading dependent method developed by Matthews (2004). The modified method aimed to more accurately represent the loading dependant nature of beam elongation (and the resulting 'pull-off' effects) as described by Lee and Watanabe (2003). A number of beam elongation predictions for a suite of experimental beam elongation data sets were carried out with the modified method. Good agreement was generally seen, both in terms of prediction of the magnitude of elongation and the shape of the elongation profile