Design and Construction Requirements for Flood Prone Building Structures

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Design and construction requirements such as elevation of structure, foundations, anchorage and connections, use of fill and other factors for flood resistant building structures are discussed.

Fig.: Foundation of Flood Resistant Building Structure

Design and Construction of Flood Prone Building Structures

Elevation of Structure

Significant flood resistant improvement can be obtained if the structure has the lowest floors elevated to design flood elevation. Design flood elevation includes wave height relative to a datum determined based on the flood hazard map of the area.

Fig.: Specified Flood Datum

Parking garages, buildings access, and storages are permitted to be constructed below design flood elevation if the enclosed area reach the conditions of enclosed areas applicable to specific flood hazard area. Lastly, nonresidential structures and nonresidential portion of mixed use structure are permitted to have lowest floor below design flood elevation provided that they meet requirements of dry flood proofing. The dry flood proofing is a combination of measured that makes structures waterproofing.

Fig.: Structure Elevated to be Flood Resistant

Foundation Requirements of Flood Resistant Structures

The foundation of flood resistant structures needs to be designed and constructed in such a way that withstands design flood circumstances. It should have adequate capacity to resist flotation, collapse, and permanent lateral movement under the critical load combinations that provided by ASCE 7. Furthermore, the foundation design of flood resistant structures should depend on the geotechnical characteristics of soil and strata beneath the foundation and on the soil foundation interaction. Added to that, it should take reduced structural capacity and instability due to expansion, consolidation, liquefaction, local scour, subsidence, and erosion into account if such incidents are expected to be occurred. Regarding foundation depth, it is specified based on the geotechnical consideration. It needs to meet foundation requirements that described above. As far as foundation walk is concerned, it must withstand flood borne debris impact, hydrodynamic, hydrostatic, wind, soil, and other lateral load that may be imposed during flood design condition. Apart from lateral loads, foundation wall shall be designed and constructed to support buoyancy and vertical loads that imposed during design load conditions. Regarding piers, piles, and columns, they are used to raise the structure above design flood elevation in addition to meet requirements of the foundation of flood resistant structure.

Use of Filling Materials

When fill is used, it should be designed and constructed to withstand flooding conditions for instance scour and erosion due to floods, quick rise and drawdown of flood water, and prolonged inundation. Fill used in flood hazard areas apart from high risk hazard area is allowed unless it is leads to increase flood level while base flood discharge is occurred and it declines flood way conveyance. Lastly, fill is permitted to be used in high risk hazard flood area if it is not cause wave run up, ramping, or deflection of flood water that damage the structure.

Anchorage and Connections

Anchorages and connections in the structures need to be designed and executed to withstand the influence of vertical loads, uplift forces, and lateral loads. Beams shall be connected to piles, columns, piers, and foundation walls adequately using suitable means such as bolts and welds. Sufficient anchorages need to be installed for storage tanks, sealed conduits and pipes, and other structures that may suffer from lateral movement and floatation during design flood condition.

Other Factors for Flood Resistant Building Structures

Other factors that need to be accounted for during the design and construction of flood resistant structures include use of flood resistant damage materials, flood proofing, means of egress, utilities, and adverse impact to surrounding structures.