& CRITERIA FOR MAXIMUM ELEVATION OF RESIDENTIAL BUILDINGS IN FLOODPLAINS William L. Coulbourne, P.E. Applied Technology Council Manny Perotin, P.E. Atkins Global

& Why This Topic  Currently no technical guidance on limitations  Applications submitted with little to no engineering  Federal dollars sought for elevation in locations where there should be limitations on the extent of elevation

& A Simple Example

& Current Guidance  FEMA HMA Guidance  Limits on height derived from FEMA 550  IRC  Minimum elevation is DFE  V Zones and Coastal A Zones – minimum DFE is BFE + 1 ft.  Unsupported height of 8” RM walls – 8’  ASCE  Minimum freeboard reqd. of 1’

& Technical Issues  Flooding  Concerned with hydrodynamic flood forces and flood-borne debris  Wind  Non-hurricane wind speed areas  Earthquakes  Elevating increases seismic vulnerability  Snow  This study limited snow load to 30 psf

& Design Scenarios  Floods, winds, earthquakes, snow can all occur in separate events  Floods and winds can occur simultaneously  Earthquakes and snow can occur simultaneously  Floods and earthquakes or wind and snow have a very low probability of occurring simultaneously

& Limitations  Flooding  Flood level not above top of foundation  Flood velocity is equivalent to depth (3’ of water = 3 fps)  No hydrostatic pressure  Flood-debris does not control design

& Limitations con’t  Wind  Not in hurricane wind zones  Used ASCE 7-10 wind maps and speeds  Assumed 2-story building with 5:12 roof pitch  Exposure B condition  Building is enclosed  Map shows the shaded area excluded

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& Limitations con’t  Earthquake  Short period acceleration is 60% g  Building weight is 10 psf for floors, 12 psf for roof, 9 psf for walls  Foundation weight assumes concrete  Ground motion taken from ASCE 7-10 maps  Response value for foundations:  RC walls = 4, RM walls = 2, RC columns = 1.5, wood piles = 1  Map shows the shaded area excluded

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& Limitations con’t  Snow  Upper bound snow load is 30 psf  ASCE 7-10 snow map used  Map shows the shaded area excluded

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& Constraints  Foundation wall thickness – 8” to 12”  IRC limitations on height of wall or columns applies  Pier spacings limited to 6 ft. and 8 ft.  No cross-bracing between piers included  Limits on amount of reinforcing steel not exceeded

& Height (ft) Reinforced Concrete Walls 1 Reinforced Concrete Masonry Walls 1 Reinforced Concrete Piers 2 Wood Piles 3 3Wind – 8” 0.5 in 2 Wind – 8” 0.5 in 2 Wind – 16”x16” x 10’ – 2.6 in 2 Wind – 12” dia.x 8’ Seismic – 8” 1.02 in 2 Seismic – 8” 2.05 in 2 Seismic – 16”x16” x 10’ – 13.6 in 2 Seismic – NP 4 5Wind – 8” 0.6 in 2 Wind – 8” 0.6 in 2 Wind – 16”x16” x 10’ – 3.0 in 2 Wind – 12” dia.x 8’ Seismic – 8” 1.9 in 2 Seismic – 8” 3.8 in 2 Seismic – 16”x16” x 8’ – 20.4 in 2 Seismic – NP 4 8Wind – 8” 0.8 in 2 Wind – 8” 0.8 in 2 Wind – 16”x16” x 10’ – 4.2 in 2 Wind – 14” dia.x 8’ Seismic – 8” 3.1 in 2 Seismic – 10” 5.04 in 2 Seismic – 24”x24” x 8’ – 22.4 in 2 Seismic – NP 4 10Wind – 8” 1.1 in 2 Wind – 8” 1.1 in 2 Wind – 16”x16” x 10’ – 5.7 in 2 Wind – 14” dia.x 6’ Seismic – 8” 3.8 in 2 Seismic – 10” 6.1 in 2 Seismic – 24”x24” x 8’ – 26.9 in 2 Seismic – NP 4 12Wind – 10” 1.3 in 2 Wind – 10” 1.3 in 2 Wind – 16”x16” x 10’ – 8.1 in 2 Wind – NP 4 Seismic – 10” 3.4 in 2 Seismic – 12” 5.7 in 2 Seismic – 24”x24” x 8’ – 30.4 in 2 Seismic – NP 4 15Wind – 12” 1.8 in 2 Wind – 12” 1.8 in 2 Wind – 24”x24” x 10’ – 9.4 in 2 Wind – NP 4 Seismic – 12” 3.2 in 2 Seismic – NP 4 Seismic – 24”x24” x 8’ – 34.1 in 2 Seismic – NP 4

& Conclusions  Structures elevated on walls are limited by height to thickness ratios  Structures elevated on piers are limited by pier dimension to height ratios  Designs are controlled by the prevailing hazard – wind or earthquake  Large segment of country could be covered by these study constraints and limitations

& Proposed Funding Restrictions  Project may be proposed when technical parameters presented here are met  Applicant must demonstrate knowledge of the prevailing hazard  Any parameter not met must be determined by engineering analysis  Buildings in V Zones must be designed  Building elevation must be compliant with most restrictive of ASCE 24, IRC or local floodplain ordinance

& Questions?