ST. LOUIS COUNTY DEPARTMENT OF PUBLIC WORKS DIVISION OF CODE ENFORCEMENT
APPENDIX A1 WIND AND SEISMIC BRACING GUIDELINE FOR ONE AND TWO FAMILY DWELLINGS AND TOWNHOUSES Lateral Loads All buildings are subject to vertical and lateral loads. Vertical loads consist of people, furniture, snow and the weight of the building itself. Lateral load is primarily wind and seismic forces. In St. Louis County, wind load governs lateral design for one and two family dwellings whereas wind and seismic loads govern the lateral design of townhouses (3 or more attached dwellings in which each dwelling unit extends from the foundation to roof and each dwelling unit has open space on at least two sides). This Appendix A1 may be used to design one or two family dwellings and townhouses. Many designers prefer to use St. Louis County‟s Simplified Bracing Method for Designing a One or Two Family Dwelling located in a wind exposure A or B. This method is commonly referred to as the “Simplified Method." Load Path All loads regardless of whether they are vertical or horizontal must be able to pass load from the areas in which the load is applied to the foundation. This is called the load path. For a simple one story building, the seismic/wind load that acts on a wall is transferred to the roof construction, which acts as a diaphragm. Diaphragms are deep, thin beams and can be any sheathed roof or floor. Once in the roof diaphragm, the load is then resisted by the braced wall panels in the walls which run parallel to the direction of the seismic/wind force. Braced wall panels are basically vertical thin beams that are designed to be stiff enough to transfer load from a diaphragm into the foundation. The load path process would be similar if the building had multiple floors. The load would be passed from diaphragm above to the braced wall panels below until it reaches the foundation. However, since the braced wall panels of the lower floors resist more loads, they have stricter requirements for their design.
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