When determining the structural performance of an external façade system, typically façade engineers will assess each system for both serviceability and ultimate strength performance.
Each building project will have a pre-determined serviceability limit state (SLS) and ultimate limit state (ULS) criteria.
The (SLS) is the design to ensure that a structure remains functional for its intended use subject to routine (everyday) loading. This includes deflections (movements).
The (ULS) is the design to ensure that the probability of collapse is at an acceptable level – i.e. the façade system will not shear off the building under abnormal or random load conditions.
Manufacturers and distributors of wall and roof cladding may wish to produce load-span design tables for their products based on test results. For comprehensive tables to be developed, the AS4040 series of tests must be considered.
The Australian standard AS4040.0 requires that each different roof or wall cladding product (i.e. different profile, thickness) be tested for three different spans, a short span, an intermediate span and a large span. The panels that have been tested are then able to have design wind strength load span tables prepared that will be valid for spans within the span range tested.
The AS4040 series addresses criteria for both AS1170 and AS4055 (design wind pressures) for commercial and housing buildings respectively, along with deflection limit criteria in accordance with the AS1562.1 standard.
The façade engineer will typically review the test data along with wind load and deflection tables and make judgement as to what an acceptable system is.