1. Designing for Flood Loads Using ASCE 7 and ASCE 24
4/16/2017
Designing for Flood Loads Using ASCE 7 and ASCE 24
William L. Coulbourne, P.E.

2. Outline Defining minimum design conditions as required by regulations
Flood load considerations for any floodplain
Issues critical to riverine flooding
Issues critical to coastal flooding
Retrofitting

3. Community Flood Regulations
Locally adopted flood map (FIRM) and flood insurance study (FIS)
Local flood ordinance
Local ordinance defines:
Amount of freeboard if any
More restrictive regulations related to foundations, elevation, construction methods
Allowable location for certain types of construction

4. Minimum NFIP Requirements
4/16/2017
Minimum NFIP Requirements
Walled and roofed structures
New construction (some additions)
Substantially damaged/improved structures
Subdivisions and other new development
New and replacement water supply systems and sanitary sewage systems
Apply to
Type of foundation
Height of lowest floor
Use of area below lowest floor
Affect
primarily

5. Most Restrictive Zone Applies
4/16/2017
Most Restrictive Zone Applies
V zone
A zone
A building that has any portion of its foundation in a V zone must comply with V zone requirements

6. All Buildings, All SFHAs
4/16/2017
All Buildings, All SFHAs
Site reasonably safe from flooding
Designed to prevent flotation, collapse, and lateral movement during flooding
Flood-resistant materials
Constructed to minimize flood damage
HVAC/plumbing equipment designed or located to prevent water entry

7. Understanding Flood Maps
4/16/2017
Understanding Flood Maps

8. Base Flood Elevation BFE is regulatory flood elevation
Probability of Exceedance = 1% in any given year (100-year flood)
Flood of this probability has 26% chance of being equaled or exceeded in 30 year period (life of mortgage)
Other flood elevations are frequently provided in Flood Insurance Studies that accompany flood maps
Design Safety Factor is increased elevation = Freeboard

9. 4/16/2017
Riverine A Zone FIRM

10. NFIP: A Zone Requirements
4/16/2017
NFIP: A Zone Requirements

11. NFIP: A Zone Requirements
4/16/2017
NFIP: A Zone Requirements
Enclosures below lowest floor:
Used only for parking, access, storage
At least 2 wall openings:
1 in2 for every 1 ft2 of enclosed area subject to flooding
Bottoms no higher than 1 ft above grade
Coverings, if used, must permit automatic entry/exit of flood waters

12. 4/16/2017
Elevation Example

13. Issues Critical to Riverine Flood Design
Elevation of expected flooding
Velocity of water
Location relative to floodway
Age of flood maps – accuracy of hazard identification
Scale of flood maps – location within floodplain
Risk of damage by flood-borne debris

14. 4/16/2017
Coastal FIRM

15. 4/16/2017
Delaware FIS

16. 4/16/2017

17. Flood Zones based on Wave Height
4/16/2017
Flood Zones based on Wave Height

18. NFIP: V Zone Requirements
4/16/2017
NFIP: V Zone Requirements
Siting:
Landward of the reach of mean high tide.
Restrictions on alteration of sand dunes, mangrove stands
Elevation:
On pilings or columns
Bottom of lowest horizontal structural member of the lowest floor at/above BFE

19. 4/16/2017
NFIP: V Zone Elevation

20. NFIP: V Zone Requirements
4/16/2017
NFIP: V Zone Requirements
Foundation:
Piling/column foundations and buildings anchored
Erosion control structures may not be tied to building or foundation
Use of Fill:
Not for structural support of buildings

21. NFIP: V Zone Requirements
4/16/2017
NFIP: V Zone Requirements
Space Below BFE:
Used only for parking, access, storage
Free of obstructions or enclosed only by non-supporting materials (e.g., insect screening, open lattice, breakaway walls)
Specific requirements for breakaway walls

22. 4/16/2017
V Zone Example

23. Issues Critical to Coastal Flood Design
Elevation of expected flooding
Velocity of water
Depth of waves
Age of flood maps – accuracy of hazard identification
Scale of flood maps – location within floodplain
V Zone vs. Coastal A Zone
Risk of damage by flood-borne debris

24. ASCE 7 Flood Load Requirements
Chapter 5 – ASCE 7-10
Loads during flooding
Hydrostatic
Hydrodynamic
Waves
Impact from debris
DFE – Design Flood Elevation
Load combinations involving flood (Chapter 2 – ASCE 7)

25. Hydrostatic Loads
Force from standing water – either lateral force or vertical force (buoyancy)
fsta = lateral force per unit width
Buoyancy = γ(Volume of displaced water)

26. Hydrostatic loads

27. Hydrodynamic Loads Formula is from FEMA 55 CCM Cd = drag coefficient
ρ = mass density of water (slugs)
A = surface area impacted by the water

28. Hydrodynamic loads

29. Waves (piles) Breaking wave loads on piles
Hb is the height of the wave = 0.78ds
CD = drag coefficient
D = diameter of pile

30. Waves (walls) fbrkw = unit force on a wall from breaking wave (lbs/ft)
Cp = dynamic pressure coefficient

31. Impact from flood-borne debris
FEMA 55 CCM has a “cleaner” version of this formula
Where:
CD and CB are depth and blockage coefficients
CStr is a structural coefficient related to rigidity

32. DFE - definition
And how does that differ from the Base Flood Elevation (BFE)?

33. Strength Design Load Combinations

34. ASD Load Combinations

35. FEMA 55 CCM Flood Load Combinations

36. ASCE 24 Flood Requirements
FEMA funded first pre-standard effort
Wanted more flood provisions in building code
First standard came out 1998
Intended to be for all types of construction and flood conditions
ASCE 24 referenced in IBC
Current version is ASCE 24-14

37. Scope Buildings subject to bldg code requirements
4/16/2017
Scope
Buildings subject to bldg code requirements
Located in flood hazard areas
Applies to new construction or substantial improvements or repairs
See Figures 1-1 and 1-2 for further details
Classification of Structures Table 1-1 is different than ASCE 7 classification table
Table 1-1 titled Flood Design Class of Buildings and Structures

38. Table 1-1 Flood Classification
Use or Occupancy
Flood Design Class
Buildings and structures normally unoccupied and pose minimal risk to public or community (temporary or storage facilities) 1
Buildings and structures that pose moderate risk to public or community should they be damaged or fail during flooding (most buildings including residential, commercial and industrial) 2
Buildings and structures that pose a high risk to public or community should they be damaged or are unable to perform normal function after flooding (large assembly buildings) 3
Buildings and structures that contain essential facilities and services for emergency response and recovery or that pose substantial risk to community at large in event of damage or failure by flooding (hospitals, EOCs, emergency shelters, fire, police, etc) 4

39. Section 1.5 Basic Requirements
4/16/2017
Section 1.5 Basic Requirements
Account for:
Elevation relative to DFE
Foundation and soils
Prior damage
Enclosures below DFE
Flood-resistant materials
Structural connections
Floodproofing
Utilities
Egress
Adverse impacts on others

40. 4/16/2017
IBC and ASCE 24
Appendix G covers Flood-Resistant Construction and references ASCE 24
IRC covers flood resistant design issues in Section R323
Crosswalk document between codes, ASCE 24 and NFIP

41. IRC References Topic IRC Section Basic Flood Resistance R322.1
4/16/2017
IRC References
Topic
IRC Section
Basic Flood Resistance
R322.1
Flood Loads and Conditions
R301.1, Table R301.2(1), R , R
Lowest Floor Elevation
R309.3, R , R
Foundation
R , R , R401
Use of Fill
R , R (3) and (4), R401.2, R
Basements
R , R
Use of Enclosed Areas Below DFE
R309.3, R , R
Example of flood resistant design topics and associated IRC provisions from Step 7 of CodeMaster. In total, 15 separate topics are included under Step 7. In addition to the 7 topics above, the following are also included:
Flood Openings in Below-DFE Enclosures
Breakaway Walls
Flood Damage-Resistant Materials
Mechanical, Electrical Equipment and Systems, Plumbing, Fuel Gas
Dry Floodproofing
High Risk Flood Hazard Areas
Substantial Damage and Substantial Improvement
Documentation, Inspections and Certifications: Lowest Floor Elevation, Flood Openings, Dry Floodproofing, Breakaway Walls, V Zone Design

42. IBC References Topic IBC Section ASCE-7, ASCE-24
4/16/2017
IBC References
Topic
IBC Section
ASCE-7, ASCE-24
Basic Flood Resistance
1612.1,
ASCE 24-05:  1.5
Flood Loads and Conditions
, , ,
ASCE 24-05:  1.6
ASCE 7-05:  2.3.3, 2.4.2, , 5.3.2, 5.4
Lowest Floor Elevation ,
ASCE 24-05:  2.3, 4.4
Foundation
1612.4, Chapter 18
ASCE 24-05:  1.5.3, 2.5, 4.5
Example of flood resistant design topics and associated IBC provisions from Step 8 of CodeMaster. In total, 15 separate topics are included under Step 8. In addition to the 7 topics above, the following are also included:
Use of Fill
Basements
Use of Enclosed Areas Below the DFE
Flood Openings in Below-DFE Enclosures
Breakaway Walls
Flood Damage-Resistant Materials
Mechanical, Electrical Equipment and Systems, Plumbing, Fuel Gas
Dry Floodproofing
High Risk Flood Hazard Areas
Substantial Damage and Substantial Improvement
Documentation, Inspections and Certifications: Lowest Floor Elevation, Flood Openings, Dry Floodproofing, Breakaway Walls, V Zone Design

43. Sections 1.5.2 and 1.5.3 Elevation requirements
4/16/2017
Sections and 1.5.3
Elevation requirements
References to other sections related to specific situations
Foundation requirements
Design considerations for foundation walls
Use of fill
Anchorage and connections

44. Section 1.6 Flood Loads Refers to Chapter 5 – ASCE 7
4/16/2017
Section 1.6 Flood Loads
Refers to Chapter 5 – ASCE 7
Load combinations reference to ASCE 7
Combining various flood loads is not covered except in FEMA 55 – CCM
Extensive discussion in ASCE 7 Commentary for Chapter 5 regarding loads (covered later)

45. Chapter 2 Requirements for A Zones
4/16/2017
Chapter 2 Requirements for A Zones
Elevation – Table 2-1
Fill
Slabs on Grade and Footings
Openings requirement

46. Table 2-1 Min. Elevation of Top of Lowest Floor
4/16/2017
Table 2-1 Min. Elevation of Top of Lowest Floor
Flood Design Class
Minimum Elevation of Lowest Floor 1
DFE 2
BFE + 1 ft or DFE 3 4
BFE + 2 ft or DFE

47. Chapter 4 Coastal High Hazard Areas
4/16/2017
Chapter 4 Coastal High Hazard Areas
V Zones
Coastal A Zones
Section Commentary – Hazard ID important
Page 51 – explains rationale for Coastal A Zones
Elevation requirements
Foundation requirements
Breakaway walls

48. Table 4-1 Min. Elevation of Bottom of Lowest Horiz. Structural Member
4/16/2017
Table 4-1 Min. Elevation of Bottom of Lowest Horiz. Structural Member
Flood Design Class
Min. Elevation of LHSM relative to Base Flood Elevation (BFE) or Design Flood Elevation (DFE) 1
DFE 2
BFE + 1 ft or DFE 3
BFE + 2 ft or DFE 4

49. ID Coastal HHA and Coastal A Zones
4/16/2017
ID Coastal HHA and Coastal A Zones
Coastal High Hazard Area has SWL 3.8 ft or more above eroded ground elevation which supports a 3 ft wave
Coastal A Zones have water elevation 1.9 ft minimum above eroded ground elevation which supports a 1.5 ft wave

50. Section 4.5 Foundation Requirements
4/16/2017
Section 4.5 Foundation Requirements
Designed to minimize forces on the system
Foundation system must be free of obstructions
Structures supported on piles, columns, or shear walls
Top of spread footings, mat, or raft foundations must be below eroded ground surface
Piles must be used in erodible soils

51. Free-of-Obstruction T.B.
4/16/2017
Free-of-Obstruction T.B.
Wave Loads on Solid Walls:
This is why the CCM promotes
V Zone open foundation requirements in Coastal A Zones

52. NJ – Sandy – Loads on Solid Walls

53. NJ – Sandy – Coastal A Zone

54. Chapter 5 Materials Metal and corrosion Other materials
4/16/2017
Chapter 5 Materials
Metal and corrosion
Other materials
FEMA T.B. on corrosion

55. 4/16/2017
Corrosion example

56. Chapter 6 Flood proofing Methods
4/16/2017
Chapter 6 Flood proofing Methods
Dry flood proofing
Wet flood proofing
Need for human intervention important
Not allowed to bring noncompliant residential buildings into compliance
Dry flood proofing permitted for commercial buildings with licensed professional seal

57. Chapter 7 Utilities Electrical service Plumbing systems HVAC systems
4/16/2017
Chapter 7 Utilities
Electrical service
Plumbing systems
HVAC systems
Elevators

58. NY – Sandy – High-rises

59. Other sections Building access Decks, porches, etc Garages Pools Tanks
4/16/2017
Other sections
Building access
Decks, porches, etc
Garages
Pools
Tanks

60. ASCE 24 RE: ASCE 7 Flood loads
4/16/2017
ASCE 24 RE: ASCE 7 Flood loads
Chapter 5
Structural systems shall be designed to resist flotation, collapse and permanent lateral displacement
In flood hazard areas, design must be based on the design flood
Effects of erosion and scour shall be included in calculation of loads

61. Breakaway wall loads Loads on breakaway walls designed for largest of:
4/16/2017
Breakaway wall loads
Loads on breakaway walls designed for largest of:
Wind load
Earthquake load
10 psf
Not to exceed 20 psf unless:
Wall designed to collapse from flood that is less than design flood
Foundation designed for load combination specified in Chapter 2
Have found by calculation that small waves (1.5 ft or less) will not govern in areas where wind speed is a minimum of 140 mph; walls would have to be designed for wind
Flood loads should be applied to walls as unit loads not equivalent forces at the Stillwater level

62. FEMA T.B - Breakaway Walls
4/16/2017
FEMA T.B - Breakaway Walls
Refer to FEMA Technical Bulletin 9

63. NJ – Sandy

64. Breakaway Wall Design Methods
Prescriptive
Simplified
Performance

65. Breakaway Walls – Prescriptive Method
Walls subject to > 10 psf and < 20 psf
Wall heights between 6 and 9 ft. Columns or piers spaced between 8 and 12 ft.
Wind speed does not exceed 110 mph (ASCE 7-05) except 100 mph for areas within 4 ft of corners
Method permitted for all seismic design categories
Walls serving as backup for brick or stone veneer that might be damaged by deflection may not be designed using this method

66. Breakaway Walls – Prescriptive Method

67. Breakaway Walls – Prescriptive Method

68. Breakaway Walls – Simplified Method
Wall heights between 6 and 9 ft. Columns or piers spaced between 8 and 12 ft.
Wind speed between 110 mph (ASCE 7-05) and 140 mph
Method permitted for all seismic design categories
Walls serving as backup for brick or stone veneer that might be damaged by deflection may not be designed using this method
Use Tables to look up designs

69. Breakaway Walls – Simplified Method

70. Breakaway Walls – Simplified Method

71. Breakaway Walls – Performance Method
Design must be performed by design professional
Method is always permitted
Expected to be used when neither of the other 2 methods can be satisfied

72. Questions?