Flood-resistant design and construction are essential to mitigate the devastating effects of flooding on buildings. By incorporating strategic elevation, robust foundations, proper anchorage, and resilient materials, structures can better withstand the impact of floods. This article discusses the critical requirements for designing and constructing flood-resistant structures.
Elevation of Structure
Elevating a structure to meet the design flood elevation (DFE) is a fundamental step in flood-resistant construction. The DFE accounts for wave height relative to a specified flood datum, which is determined based on local flood hazard maps. Elevating the lowest floors to this level minimizes flood damage and improves the building’s overall resilience.
However, certain structures are permitted below the DFE under specific conditions. Parking garages, building access points, and storage areas may be constructed below the DFE if they adhere to enclosed area regulations for the specific flood hazard area. Similarly, nonresidential structures or mixed-use buildings can have their lowest floors below the DFE if they implement dry floodproofing measures. Dry floodproofing involves waterproofing techniques to prevent water penetration into the structure.
Foundation Requirements
The foundation of a flood-resistant structure is a critical component that must withstand extreme flood conditions, including flotation, collapse, and lateral movement. Its design should account for the following:
General Design Criteria:
- Foundations should meet load requirements defined by ASCE 7 to resist the forces of design flood conditions.
- The structure must be stable under combinations of hydrodynamic and hydrostatic forces.
Geotechnical Considerations:
- Soil and strata properties must be assessed to ensure stability.
- Potential issues like expansion, consolidation, liquefaction, scour, subsidence, and erosion must be addressed during design.
Foundation Depth and Wall Design:
- The foundation depth should be adequate to resist flood-induced stresses, as determined by geotechnical analysis.
- Foundation walls must support buoyancy and vertical loads and withstand impacts from debris, hydrodynamic and hydrostatic forces, and lateral loads from wind and soil.
Structural Components:
- Piers, piles, and columns are essential for elevating the structure above the DFE while also meeting load-bearing requirements.
Use of Filling Materials
Filling materials, if used, must be designed to withstand specific flood conditions, including:
- Scour and erosion caused by floodwaters.
- Sudden rises and drops in water levels.
- Prolonged submersion.
In general, fill is allowed in low-risk flood hazard areas, provided it does not increase flood levels or impede floodway conveyance. In high-risk hazard areas, fill may only be used if it does not cause wave run-up, ramping, or deflection of floodwaters that could damage the structure.
Anchorage and Connections
Anchorages and connections are vital for structural stability during floods. They must be designed to resist vertical loads, uplift forces, and lateral pressures. Key considerations include:
- Strong connections between beams, piles, columns, piers, and foundation walls using bolts and welds.
- Securing elements like storage tanks, sealed conduits, and pipes to prevent flotation and lateral movement under flood conditions.
Additional Considerations
Flood-resistant structures should incorporate several other factors:
- Flood-Resistant Materials: Use materials that can withstand prolonged water exposure without significant damage.
- Floodproofing Measures: Implement dry or wet floodproofing techniques as applicable.
- Means of Egress: Design safe exit pathways for occupants during flooding events.
- Utility Installation: Elevate or protect utilities to prevent damage and ensure functionality during floods.
- Mitigation of Adverse Impacts: Design structures to minimize negative effects on surrounding buildings and infrastructure.
Conclusion
Designing and constructing flood-resistant structures involves careful planning and execution to address elevation, foundation stability, anchorage, and other critical factors. By adhering to these principles, buildings can better withstand the destructive forces of flooding, protecting lives, property, and infrastructure in flood-prone areas.