The Christchurch Justice and Emergency Services Precinct is a new three building precinct incorporating, a justice building, an emergency services building and a parking building for operational vehicles. Holmes Fire carried out advanced structural fire analyses for the project, specifically the Justice Building, which is a five storey building, consisting of four moment-resisting steel framed structures that are built on a large podium structure. The moment resisting frames consist of concrete filled steel CHS columns and I-Beams. The structural frame also features long span cellular beams which support concrete-metal deck floors.
The building has stringent requirements for structural robustness for seismic and fire resistance, due to the Emergency Operations Centre located in the Emergency Services Building – this will be a centre for emergency response and coordination in the event of a natural disaster. As part
of the design requirement, the secondary steel beams and the composite columns were not proposed to be protected with passive fire protection.
A series of advanced analyses using non-linear finite element analysis were carried out by Holmes Fire to test the robustness and stability of the structure in fire conditions. The analysis consisted of 3D modelling of the structural frame under exposure of a realistic post-flashover fire which incorporated detailed heat transfer analysis of each structural component. The 3D modelling enabled different types of load resisting mechanisms to be included in the analysis, such as tensile membrane action, which would typically not be considered with simpler calculation methods. This allowed the structural design to be safely optimised, whilst avoiding over-design.
The resulting analysis demonstrated that the concrete filled steel hollow section columns and the secondary steel beams did not require additional passive fire protection. This provided significant cost savings for the project through the reduction of passive fire protection to the beams and columns.