The Allowable Stress Design (AISC-ASD) 9th Edition, published by the American Institute of Steel Construction, provides detailed provisions for designing steel stair systems that are both safe and long-lasting, while also complying with the code. In this approach, both individual structural components and all assemblies (stringers, treads, risers and landings) are analysed using allowable bending, shear and deflection stresses under reasonable loads. Typical loads that are contemplated are uniformly distributed occupant live loads, loads at a mid-span point, and the weight of the stairs structure. Material properties, connectivity information, and dimensions of the members are chosen so that the stresses will not exceed the maximum permissible values of the code.
The one benefit of ASD 9th Edition is that it is easy to calculate, and its level of calculation makes it ideal in the case of new construction as well as retrofitting 89. The steel stairs designed under such an approach are often balanced between the strength and economy through optimisation of section sizes, and relying upon the standard rolled shapes. Connection integrity is also important in this approach; bolting or welding together joints has to be detailed so that forces can be transferred without huge deformation. Although the newer LRFD-based codes are now used extensively in the industry, renovation work or when the engineer has to handle old design documents, the old AISC-ASD 9th Edition is commonly consulted.
