Structural Support 1212 Main Street April 15, 2013 Belmar NJ 07719

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1 Structural Support 1212 Main Street April 15, 2013 Belmar NJ New Jersey Department of Community Affairs Division of Codes and Standards 101 South Broad Street PO Box 802 Trenton NJ Subject: Design & Construction For Flood Loads Within Coastal A Zone Tens of thousands (perhaps more than 100,000) buildings in New Jersey will have to be raised in the next four years to comply with the "substantial damage" rule (NFIP & building code) as well as to reduce NFIP flood insurance premiums which will otherwise increase dramatically. There is currently substantial risk of a major problem developing due to deficient design of support systems for new or modified (raised) existing buildings at locations within Coastal A Zones. DCA should address this issue now, before tens of thousands of buildings are supported on deficient support systems. Based on recent discussions with several architects and builders, it appears that houses recently raised in Coastal A Zones are being supported on plain and reinforced block walls with grossly inadequate design capacity to resist lateral forces from flood water. Definition & Meaning of Coastal A Zones Coastal A Zone is defined on FEMA flood maps as an area, within the more general A Zone, that is adjacent to the V Zone. Coastal A Zone, described as an area with "moderate" wave action, is defined by a light brown color and dashed black line on updated flood maps available online. Unfortunately, use of the term "moderate" tends to reduce concern when the focus should be on the fact that wave action must be considered for design in this zone. During phone discussion on April 12, 2012, staff member with Code Enforcement unit of DCA explained that, within past two weeks, NJDEP has officially adopted new flood maps published by FEMA as of December 12, He explained further that this means new flood maps must be used for building design in New Jersey, whether or not a municipality has passed an ordinance to adopt updated flood maps. However, even if new maps are not used, many building locations are still in Coastal A Zone on prior maps. John F Mann, PE Page 1

2 Lack of Design For Lateral Flood Water Forces Key problem is that many designers are not aware of the very large lateral forces from flood water that must be used for design of buildings within Coastal A Zone. This problem appears to be occurring for the following reasons; 1. Vast majority of architects and engineers in New Jersey have never had to design buildings for lateral forces from flood water. Many (perhaps the majority) are incorrectly using prescriptive provisions of IRC 2009 NJ for design of exterior support walls, not the provisions of ASCE IRC 2009 NJ does not include clear requirements for designers to determine lateral forces from flood water. Even though the general code provision for structural design requires design for such forces, code provisions focused on flood zone conditions tend to make designers think that design for floodwater is not necessary at all. Due to lack of any clear, specific requirements, designers tend to neglect design for flood water forces. Such neglect is somewhat understandable when considering lack of provisions for flood water compared to extensive, detailed provisions for wind and even seismic loads in the building code. 3. Within V-Zone, buildings must be supported only on piles (extending above grade) or columns (usually on grade beams supported on piles). In general, lateral loads from flood water against individual piles or columns are relatively small (typically 500 pounds or less). Therefore, even when (as is very often the case) lateral forces from flood water are not calculated by building designer, there is usually no major design deficiency. Since, except for unusual cases, lateral-force calculations are typically not performed for V-Zone conditions, designers tend to neglect such calculations for Coastal A-Zone conditions. 4. Code provisions for flood vents incorrectly imply that use of flood vents eliminates unbalanced water pressure against walls for all conditions. 5. Code officials are generally not knowledgeable about nature and scale of lateral forces due to wave action compared to other lateral forces. Code officials therefore do not recognize grossly deficient design. Failure to design for lateral force due to flood water and wave-action results in grossly deficient structural design. Significance of this deficiency can be realized by comparing design forces due to flood water for Coastal A Zone to other typical lateral forces, as summarized in example in this report. John F Mann, PE Page 2

3 Building Code Requirements Vast majority of existing buildings that must be raised are single-family houses. Design is governed by the Rehabilitation Subcode of the New Jersey Uniform Construction Code (UCC). Work is considered alterations and reconstruction. For design of new foundation elements for new and existing houses, IRC 2009 NJ is generally the applicable building subcode. IRC 2009 NJ briefly notes [R301.1] the need to design buildings for flood loads. Hovever, IRC 2009 NJ does not include any provisions that specify how loads from flood water are to be determined. IBC 2009 NJ governs design of buildings that do not comply with conditions for use of IRC 2009 NJ. For design to resist flood loads, IBC 2009 NJ [1612.4] specifies use of ASCE Problems With Use of IRC 2009 NJ For Flood Loads Per R , buildings at locations where design wind speed is 100 mph or greater must be designed using one of the alternate "methods" listed. As I have noted in previous letters to DCA, this provision has always been ambiguous since it does not clearly state whether the provision is limited to design for wind only. However, as written, it is most reasonably taken to mean that the alternate method should be used for the entire design, even if that was not intended by code authors. ASCE 7-05 is listed as only one of the alternate methods in R Other than R there is no other code provision that addresses design flood loads for buildings in flood zones. Per R , IRC 2009 NJ directs the designer to Section 322. R322.2 and associated provisions govern design of houses in Coastal A Zone. Foundation design is briefy noted in R , which states only that foundations "shall meet the requirements of Chapter 4". Yet, per R401.1, Chapter 4 just refers back to "Section R322", forming an interminable loop of instructions seemingly designed to maximize frustration. If R does in fact mean that entire design of buildings subject to design wind speed of 100 mph or greater must be performed using an alternate method, then the confusion of R and Chapter 4 can be at least partially resolved within current code provisions. John F Mann, PE Page 3

4 However, if R is considered to be limited to design for wind resistance, a major problem exists with code requirements relative to design for flood water loads. The only provision that hints of loads from flood water is R which requires that design must consider "structural loads and stresses from flooding equal to the design flood elevation." However, provisons for flood vents per R confuse this issue since designers tend to think (incorrectly) that flood vents equalize pressure from flood water on both sides of a wall, negating any necessity to consider lateral loads from flood water. Unfortunately, flood vents do not negate very large lateral forces from wave action that must be considered for proper design. R starts with the following statement (with underline made for this discussion); "When a building of otherwise conventional construction contains structural elements exceeding the limits of Section R301 or otherwise not conforming to this code, these elements shall be designed in accordance with accepted engineering practice." R301.1 states the following; "Buildings and structures, and all parts thereof, shall be constructed to safely support all loads, including dead loads, live loads, roof loads, flood loads, snow loads, wind loads and seismic loads as prescribed by this code." Since flood loads are not defined in IRC 2009 NJ (unless R is considered applicable for entire design) the most reasonable conclusion is that; (1) Structural elements required to resist flood loads must be considered "not conforming to this code" per R , and (2) Such element must be designed per "accepted engineering practice". R also states that "engineered design" may be performed by using the "International Building Code", which is IBC 2009 NJ. John F Mann, PE Page 4

5 Flood Water Design Forces per ASCE 7-05 Chapter 5 of ASCE 7-05 includes detailed provisions for determining design forces due to flood water, including wave action. Complete discussion of the provisions of Chapter 5 is outside the scope of this report. However, when wave action is considered, the following key points should be understood; 1. Total lateral force is the sum of hydrostatic force and dynamic force from wave action. Dynamic force from wave action is generally greater than hydrostatic force. 2. BFE includes water from "incident" waves. In the absence of waves, height of flood water ("stillwater") is much lower than BFE. 3. Use of flood vents to equalize water level on opposite sides of wall reduces total inward lateral water pressure by a very small (essentially insignificant) amount. Flood vents only allow water to rise to the "stillwater" elevation, which does not include waves. 4. For design [per Equation (5-3), Figure 5-1 and Figure 5-2], top of water pressure against wall (for hydrostatic and dynamic force) is taken as 1.43 times the difference between base flood elevation (BFE) and grade (ground surface) adjacent to the wall. Top of water pressure for design is generally higher than BFE. The code allows for consideration of wave direction, which may be considered along a line perpendicular to shoreline of the body of water that is the source of flood water. Only those walls impacted directly by waves must be designed to resist specified flood loads. Loads may also be reduced by considering skew angle of wave direction relative to plane of wall. However, conservative approach should be taken when considering wave direction, especially when shoreline geometry is not clearly or easily defined. John F Mann, PE Page 5

6 FEMA Techinal Bulletin 9 The following is from discussion of wave forces in FEMA publication about breakaway walls; "The effect is quite different when a breaking wave hits a wider, relatively continuous, vertical surface, such as a wall. When the crest of a breaking wave impacts a wall, a pocket of air is trapped and compressed by the wave (see Figure 2). As the air pocket collapses, an exceedingly high-pressure burst (i.e., shock wave) impacts the wall, with the force centered around the stillwater level. Peak pressures from a 5-foot breaking wave can be 100 times higher than the safe loading resistance of 10 to 20 psf that is specified for breakaway walls in the NFIP regulations." FEMA P-55 Coastal Construction Manual In the Coastal Construction Manual, FEMA includes the following; "As explained in Chapters 1 and 3 of this Manual, the NFIP regulations do not differentiate between the Coastal A Zone and the portion of Zone A that is landward of the LiMWA. Because Coastal A Zones may be subject to the types of hazards present in Zone V, such as wave effects, velocity flows, erosion, scour, and high winds, this Manual recommends that buildings in Coastal A Zones meet the NFIP regulatory requirements for Zone V buildings (i.e., the performance requirements concerning resistance to flotation, collapse, and lateral movement and the prescriptive requirements concerning elevation, foundation type, engineering certification of design and construction, enclosures below the lowest floor, and use of structural fill see Section )." "LiMWA" is abbreviation for "Limit of Moderate Wave Action". Although this FEMA recommendation is not mandatory, it does highlight the importance of considering forces from wave action in the Coastal A Zone. John F Mann, PE Page 6

7 Example of Flood Water Design Load; Crawlspace Summary results for example with exterior walls around crawlspace, from actual house within Coastal A Zone, illustrates the problem; Top of support wall 11.0 feet BFE 10.0 feet Grade 6.0 feet *** Top of water pressure feet Total hydrostatic force Total dynamic force Total lateral force 1,021 PLF (along length of wall) 1,300 PLF 2,321 PLF *** Per provisions of ASCE 7-05 Even for this relatively low wall (5 feet above grade), total lateral force is very large relative to capacity of "conventional" construction intended by IRC 2009 NJ. With top of water pressure about 9 inches above top of wall, total lateral force against foundation wall is 2,273 PLF. Lateral resistance required along top of wall (1,053 PLF) is much greater than shear capacity of standard nailed connections for wood-framed construction and even greater than shear capacity provided by enhanced methods such as light-gage steel connectors. Structural steel angle with two 1/2-inch bolts through joist would be required for each floor joist. Steel angle would also have to be connected to foundation wall with bolts. Comparison of design flood water force (per ASCE 7-05) to other lateral forces (for same 5- feet height of wall above grade) highlights the very large difference between flood water force and other forces typically encountered by designers; Condition Hydrosatic; Water at top of wall Backfill; Soil at top of wall (120 pcf; Ke = 0.33) Wind at 25 psf Lateral Force 780 PLF 525 PLF 125 PLF John F Mann, PE Page 7

8 Flood Water Forces For High Walls For many houses, lower-level space will be used as a garage, such that height of walls supporting the lifted house will be 8 feet or more. For height of wall 8.0 feet above grade, and BFE 1.0 foot below top of wall, total lateral force from flood water is 6,685 PLF (against wall). Only a thick reinforced concrete wall could resist such large lateral force. Even then, unless the wall was designed as cantilever retaining wall with large base, there would be no practical way to provide required lateral resistance (3,262 PLF) along top of wall without concrete floor slab or structural steel framing. Incorrect Information Published by State Agencies The following (from NJDEP web site) is an example of incorrect and misleading information being published by state agencies; "Wet flood-proofing refers to measures that allow floodwaters to enter a building, and thereby balance hydrostatic pressure on the structure during a flood. A non-residential building that cannot feasibly be dry flood-proofed can be wet flood-proofed. Wet flood-proofing generally includes using flood-resistant materials, protecting mechanical and utility equipment, and using openings or breakaway walls. A garage or crawl space with flood vents is an example of a wet flood-proofed area. Note: although wet flood-proofing is allowable in limited circumstances, it may have significant ramifications on flood insurance costs." This statement is misleading (at best) since it does not directly address wave action in Coastal A Zone. The mere noting of "breakaway walls" is not sufficient, especially when the incorrect claim is made that flood vents for "garage or crawl space" is adequate. As previously discussed in this report, flood vents do not equalize very large lateral pressure from wave action. John F Mann, PE Page 8

9 Recommendations After investigation of as-built and planned construction within Coastal A Zone areas as may be warranted, DCA should take the following actions as soon as feasible; Issue letter to construction officials and building subcode officials emphasizing the importance of plan review, focusing on need for designers to use ASCE 7-05 for design of elements to resist flood water. Highight this issue in Construction Code Communicator. Issue letters to New Jersey Board of Architects and New Jersey Builders Association, highlighting need for careful design if exterior walls are to be used for support of house within Coastal A Zone. Emphasize that an architect should obtain advice from qualified professional engineer if the architect is not qualified to perform structural design of such elements, especially when such exterior walls are more than 3 feet above grade. Consider modifications to NJ version of current and future model building code, specifically addressing flood water design loads. Copies; New Jersey Board of Architects New Jersey Board of Professional Engineers & Land Surveyors New Jersey Builders Association John F Mann, PE Page 9