The foundation of any building is arguably the most important aspect. Without a solid foundation the most well built structures can experience problems including settling, cracking, and in the worst case, collapse. With this in mind it’s important to know what the design requirements are for building foundations as early in the design stage as possible.
Metal Building Foundations and Current Code – Anchorage
The driving force behind any metal building foundation design is the prevailing building codes. As all design professionals know, the design process begins with a thorough analysis of local building design criteria. With the adoption of the 2006 IBC many changes were implemented to the way foundation systems and anchorage are designed. In California for instance, the previous building code, UBC 1997, contained design procedures for anchorage to concrete within the document itself. Currently, under the 2007 CBC, anchorage to concrete is dictated by ACI 318-05 Appendix D.
This change has resulted in a drastic shift in the way anchorage capacities are calculated, which plays a vital role in the way metal building foundation systems are designed. Supplementary reinforcement around anchor groups is all but required now. Appendix D severely limits the capacities achieved from classical “Inverted Punching Shear” type design procedures. With the forces generated by typical metal building frames, both inward and outward, things like ensuring slab continuity and preventing concrete blowout at anchor groups are critical.
Many designers are uncomfortable with the cumbersome equations found in Appendix D. While the new design procedures are much more tedious and difficult to use in solving for a direct solution, the adoption of Appendix D does enable the designer a much broader range of control when it comes to the design of supplementary reinforcement and its effects on anchorage capacity.
The broad scope encompassed in the supplementary reinforcement concept requires designers to be versed in all aspects of concrete and steel behavior. A global picture of the interaction between materials is required to achieve the most efficient designs. In general, the increased complexity is intended to yield increased accuracy and efficiency in a variety of scenarios but this requires designers that are comfortable and capable of using engineering judgment and big picture thinking.
Tags: Design