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. bill@coulbourneconsulting.com

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

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

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

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

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

Understanding Flood Maps 4/16/2017 Understanding Flood Maps

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

4/16/2017 Riverine A Zone FIRM

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

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

4/16/2017 Elevation Example

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

4/16/2017 Coastal FIRM

4/16/2017 Delaware FIS

4/16/2017

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

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

4/16/2017 NFIP: V Zone Elevation

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

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

4/16/2017 V Zone Example

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

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)

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)

Hydrostatic loads

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

Hydrodynamic loads

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

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

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

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

Strength Design Load Combinations

ASD Load Combinations

FEMA 55 CCM Flood Load Combinations

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

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

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

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

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

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), R322.1.2, R322.3.3 Lowest Floor Elevation R309.3, R322.2.1, R322.3.2 Foundation R322.2.3, R322.3.3, R401 Use of Fill R322.1.4.2, R322.3.2(3) and (4), R401.2, R506.2.1 Basements R322.2.1, R322.3.2 Use of Enclosed Areas Below DFE R309.3, R322.2.2, R322.3.5 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

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, 1612.4   ASCE 24-05:  1.5 Flood Loads and Conditions 1605.2.2, 1605.3.1.2, 1612.4, 3102.7 ASCE 24-05:  1.6 ASCE 7-05:  2.3.3, 2.4.2, 5.3.1, 5.3.2, 5.4 Lowest Floor Elevation 1603.1.7, 1612.4 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

Sections 1.5.2 and 1.5.3 Elevation requirements 4/16/2017 Sections 1.5.2 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

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)

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

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

Chapter 4 Coastal High Hazard Areas 4/16/2017 Chapter 4 Coastal High Hazard Areas V Zones Coastal A Zones Section 4.1.1 Commentary – Hazard ID important Page 51 – explains rationale for Coastal A Zones Elevation requirements Foundation requirements Breakaway walls

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

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

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

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

NJ – Sandy – Loads on Solid Walls

NJ – Sandy – Coastal A Zone

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

4/16/2017 Corrosion example

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

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

NY – Sandy – High-rises

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

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

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

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

NJ – Sandy

Breakaway Wall Design Methods Prescriptive Simplified Performance

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

Breakaway Walls – Prescriptive Method

Breakaway Walls – Prescriptive Method

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

Breakaway Walls – Simplified Method

Breakaway Walls – Simplified Method

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

Questions? bill@coulbourneconsulting.com