Compatibility - Precast Floor & Lateral Resisting Techniques
Principal Researcher: Prof. Des Bull
Staff involved: Assoc. Prof. Stefano Pampanin
Students involved: James Jensen , Lisa Woods
Investigation and mitigation of compatibility issues between existing precast floor and lateral resisting systems.
Previous research regarding the seismic performance of existing precast hollow core floor and ductile lateral frame systems has highlighted several behavioural uncertainties. In particular undesirable damage causing incompatibilities has become apparent; the structural integrity at hollow core seating and perimeter connection interfaces can be jeopardised, potentially leading to a partial or even complete floor collapse. Papers have been presented by Matthews, Bull and Mander (i.e. fib conference, Athens, 2003).
James Jensen has completed his testing of hollowcore alternative edge beam connections detailing prior to and after retrofit solutions. An interesting part of his study was to develop a simplified procedure to predict beam-elongation. Results will be presented at the 2007 NZSEE Conference in Palmerston North.
These deformation incompatibilities are a result of conflicting behaviour characteristics of an individual floor system and a ductile frame (or wall) systems; intrinsic frame beam elongation, seating beam rotation, and longitudinal perimeter vertical displacement induce undesirable rotation and displacement demands on the floor systems.
In this project, experimental and analytical investigation on existing and retrofit techniques with the intent to assess and mitigate the effects due to (but not limited to):
Beam elongation
Vertical displacement incompatibility between floors and supports
Diaphragm action when transferring forces between and in to vertical structural elements (primary and secondary).
Preliminary numerical investigations on global compatibility issues during the seismic response have already been carried out as part of the combined work of three 3rd pro students and a current ME student. Further development will comprise the investigation of the efficiency of selective weakening (i.e. disconnection of the floor at defined location and strengthening of collectors, via fastening techniques). Issues regarding diaphragm action arise as a result of selective weakening.
The issues of deformation compatibility between the suspended floor system and supporting frames or walls are not limited to hollowcore systems. Other systems including Double Tees, flat slabs, rib and timber infill, concrete infilled metal profile deck and cast insitu floors need to be reviewed for possible adverse behaviour in the light of the intrinsic deformation compatibility issues highlight here and in existing research. These reviews would be largely desk-top/analytical. The reviews may indicate that some experimental investigations would be warranted.
Ultimately a major super-assembly 3-D building systems comprising of frames, walls and systems will be tested in the as-built and in the retrofitted configuration, respectively. Definition of damage level and performance prior and after the retrofit will be again produced to support the implementation of vulnerability procedures for damage scenario as well as to support/compliment the NZSEE guidelines on earthquake prone structures.