Coordination with main structures
A brief summary of the coordination requirements between the facade engineer and the structural engineer in design phase, for any project, as a minimum:
- Cladding zones. Definition: From outside of the glass to the edge of concrete. We will need some space behind the mullion for bracketing and tolerances (so often forgotten by architects!) Based on the cladding zones, slab edge geometry can be finalized. Further coordination is required for beam locations, PT anchor locations, upstands, step down slabs to accommodate interfaces.
- Space requirements of BMU equipment.
- Expansion joint locations and expected actual movements. Seismic joints.
- Base building inter-storey live load deflection, wind sway, seismic drift, settlements, shortening. The facade system need to cater for these reoccurring movements without deformation or damage. The facade engineer will need actual base building behaviour data, not the design limits, in order to optimize joint sizes and allowances. Every millimeter counts!
- Concrete and main steel tolerances. This will be catered for by a one-off 3-way adjustment within the facade system or bracketry.
- Wind tunnel testing requirements.
- Reactions from facade to slabs. Especially exciting when we design steel trusses or pre-tensioned cable nets to support large glass walls, and these transfer concentrated loads to the main structure! We will provide these and ensure in early design phases that the reactions are considered.
- Reactions from BMU machines. Their weight ranges from 2 tonnes to 40 tonnes, so take it seriously.
- Coordination and scope split for secondary steelwork. We usually design and document exposed steelwork, and steelwork that fits better with the facade contractor's package. The structural engineer shall include additional steelwork, that could be under the main contractor's scope, however we may provide preliminary sizing for those too. Strategical placement of concealed primary steelwork may reduce the amount of required secondary steelwork, hence early layout coordination may bring cost savings.
April Soh and Agnes Koltay gave a CPD accredited presentation on above topic to IStructE (Institute of Structural Engineers) members, invited by the Regional Chapter's board. The presentation took place on the 18th of September, and it is free to download to IStructE members, through the IStructE website. We have included case study examples from our past projects, to demonstrate the coordination process and its benefits: an integrated design documentation that reduces site problems.