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Chapter IV Structural Engineering Aspects of Flood Proofing Flood proofing efforts to keep the water out of buildings fall, in part, within the province of the structural engineer. When flood waters surround a building, they impose loads on the structure and substructure beyond those it normally is designed to withstand. A determination of these loads is a prerequisite of flood proofing efforts. This chapter discusses some of the more common structural problems that could be encountered. Because of the complexity of these problems, building owners who are con- templating flood proofing should engage the service of a prl:iessional engineer who has a working knowledge of structures and who has had experience with hydraulic structures or 1100d proofing. This is necessary to insure that the floocl proofing does not increase dam- ages by creating structural damages.-ruptured walls and floors--in addition to the dam- ages resulting from water contact and disruption. Analyzing the Structural Problem The forces which would act upon a typical building under conditions varying from normal (non-flOod) to partial submergence (flood. with and without subsurface or founda- tion drainage) are graphically presented in Figures 17, 18, and 19. The building cross- section shown is considered representative of that which would be commonly encountered in a flood proofing program. Loading from Structure and Contents.-The weight of the building itself (masonry, con- crete, steel, wc:xxl, etc.), known as dead load, together with the weight of its live load (fur- niture, machinery, merchandise, occupants, etc.) will normally be transmitted through the roof and floor systems to supporting columns and walls and thence to the foundations. These loads generally are transmitted directly to the supporting soil or bedrock under the foundation. Loads of this type will normally be unaffected by flooding and will have the same value for both flood and non-flood conditions. Restraint from Floor and Roof Systems. - Flooding produces large lateral forces on the structure. These forces will be resisted by the building walls, floor, and roof sys- tems. Many commercial and industrial buildings are designed and constructed in a man- ner to provide adequate connection and anchorage between these systems for support and structural unity, but each building must be individually evaluated and strengthened where necessary. Most residential and many light commercial and industrial buildings, however, do not have the necessary anchorage and would require modification to provide it. This would involve adequate transverse bridging in addition to anchorage into the walls around the en- tire perimeter. Steel angles bolted into both the floor system and the walls at their junc- ture would be one method of anchorage. Resultant of Non-Flood and Flood Loading.-The non-flood loading is the force exerted by the soil backfill upon the wall. These pressures depend upon the physical character- istics of the soil particles, the degree of compaction, the moisture content, and the move- 23