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4 Wind Damage to Buildings
Pages 41-90

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From page 41...
... PREPAREDNESS AND RESPONSE TABLE 3-1 Evacuation Times (hours) 39 August 29 September 1 County Observed Calculated Observed Calculated Hancock, Mississippi 7 9.5 5 8.5 Harrison, Mississippi 11 11.0 9 11.0 Jackson, Mississippi 12 13.0 11 11.5 Mobile, Alabama 11 15.5 12 14.5 Baldwin, Alabama 16 16.0 12 -15.0 Escambia, Florida 12 14.5 10 13.0 Santa Rosa, Florida 7 8.5 7 8.0 Okaloosa, Floridaa 7 14.0 13 14.0 Walton, Florida 7 9.5 10 11.5 Bay, Floridab 11 22.0 11 22.0 aOkaloosa had a partial evacuation on August 29.
From page 42...
... 40 Regional Boundaries HURRICANE ELENA The regional (multicounty) approach to hurricane evacuation studies was taken after a Lee County, Florida, study was frustrated by the fact that evacuees cross county boundaries, thereby making it difficult to consider their effect on Lee's evacuation times and patterns without considering what was occurring in the adjacent counties simultaneously.
From page 43...
... Jackson County had adopted a building code but apparently had no means of enforcing it. The codes in use had been steadily tightened in the light of hurricane experience and by 1969, Gulfport, Biloxi, end Pascagoula had adopted the Standard Building Code.
From page 44...
... These possible causes are now examined in detail. Design Wind Speeds and Pressures The wind force exerted on a component of a building depends upon the local wind velocity and the location of the tributary area transferring the load to the component.
From page 45...
... First, the South Florida Building Code was used for areas within 1,000 It of the shore. Although suffering the same problems regarding fastest-mile and gust wind speeds as the Standard Building Code, it did use a design wind speed of 120 mph and provided velocity pressures at 10-ft instead of 30-ft intervals.
From page 46...
... The upgrading of the Standard Building Code took place as a result of pressure from the metal building industry, and many manufacturers took advantage of the new regulations when they became an alternative procedure in 1982. The shortcomings in assessing design wind pressures are best illustrated by reference to the design pressures that would have been used in the design of buildings that sustained the most serious damage in Elena" namely, flatroofed buildings 10 to 20 It high.
From page 47...
... TABLE 4-3 Mean Recurrence Intervals for Wind Loads in Excess of the Standard Building Code (1974 to 1986, i.e.
From page 48...
... In these circumstances, the design wind load will occur in the presence of the full dead load. In situations where light roofing systems are subjected to high uplift forces, certain steel members might be sized to carry the design wind loads at stresses very close to the yield strength of the material, providing little or no safety margin to accommodate incorrect design pressures or unforeseen occurrences such as window damage.
From page 49...
... In wood construction, the Standard Building Code suggests the use of three Ed nails driven at an angle through a roof truss or rafter into the top plate of the wall, although hurricane requirements contained in the code's Appendix D state that approved hurricane anchors must be used for wooden truss rafters. Fortunately, most coastal jurisdictions have recognized the inadequacy of the toenail connection and require the use of proper anchors, at least for residential construction.
From page 50...
... Table 4-5 indicates the maximum pressures applied during these tests. Based on the requirement for resistance to high local suctions specified by the Standard Building Code for the top surface of the roof, the most stringent classification, 90, would be required for flat roofs in this area.
From page 51...
... Although they have the advantage that they must be designed by a registered architect or engineer in accordance with the Standard Building Code, their plans are not checked, nor is construction inspected by the local building official. This is the responsibility of the state's Department of Education.
From page 52...
... Leakage Almost all flat roofs and some pitched roofs on schools were leaking after the storm. This was probably the result of a combination of factors, including the use of an inappropriate building code, poor design specification, poor installation, and deterioration; it was probably not the result of excessive wind speeds.
From page 53...
... In many cases, such structures are more exposed because of extensive parking areas and are usually more vulnerable to high internal pressure because of large glazed areas. During Elena, most of the flat roofs of commercial structures leaked, and loose gravel from the roofs sometimes caused serious damage nearby.
From page 54...
... ~2 FIGuRE4-2 Roofmembr~ed~magem ashopping maH,Gauden ~Ii~i~Ii~i~I~i~I~! ll~lllllll~lllI~ll<~?
From page 55...
... ~ ~~ TO BEGS - ~1 1I \1 l Elf ffffff ~ ~!
From page 56...
... , but the structural system proved inadequate because of poor connections. This was also true of many small, nonengineered commercial structures using unreinforced masonry walls with steel or wood roof construction (Figures 4-10 and 4-11~.
From page 57...
... WIND DAMAGE TO BUILDINGS 55 FIGURE 4-7 Collapse of Payless Shoe Store, Pascagoula. FIGURE 4-8 Barjoist-to-wall connection, Payless Shoe Store, Pascagoula.
From page 58...
... :.: ::: ~ ~. ~ ~ ~- :: ~` .:: .; ~ : ~ ~ Hi= ~ FIGURE 4-9 Mortar failure at roof anchor, Payless Shoe Source, Pascagoula.
From page 59...
... WIND DAMAGE TO BUILDINGS 57 FIGURE 4-10 Loss of wood roof from masonry-walled building (note sign) , Gautier.
From page 60...
... Clearly, this attention to detail pays off and shows that it is quite possible to build small commercial structures that can survive hurri canes. Motels A number of motels sustained roof damage of the type shown in Figure 4-12.
From page 61...
... Newer buildings benefited from the requirement to use hurricane anchors to connect the roof to the walls and the walls to the foundation, but both old and new dwellings probably derived their major benefit from shelter provided by neighboring buildings and trees. Nevertheless, virtually all buildings came through a storm close to the "once-in-SO-year event" with very little damage.
From page 62...
... dO USE _ a _ SSSS~-~S^ ~ ! ~ S _ FIGURE 4-14 Damaged house using metal deck Ioof, Pascagoula.
From page 63...
... Although these buildings were probably never subjected to a detailed structural analysis, they had certain features that would have made the direct use of the Standard Building Code difficult or inappropriate. The roofs were of a shape not covered by the code.
From page 64...
... In another respect, the Standard Building Code is ill equipped to deal with this particular location, since the code assumes all buildings are located in open country. For most locations, this assumption is conservative.
From page 65...
... FIGURE 4-18 Anchor failure in mobile home, O=~. FIGURE 4-19 S~uc~ra1 damage to w~1-~chored mobile home, Gautier.
From page 66...
... Two factors appear to be primarily responsible. First, as mentioned earlier, the Standard Building Code has undergone extensive revisions during this time.
From page 67...
... O ~ (1205) SBC-1969 -24 -31 _ _~E -25 rartlally Eliclosed Enclosed -30 _39 -39 -48 -66 -75 +27 +27 _ -35 +27 +35 -31 ~ -43 ~20' ~ ~ (: /~ FIGURE 4-20 Component and fastener loads for design wind speeds of 100 mph.
From page 68...
... FIGURE 4-22 Preengineered warehouse buildings at Ingalls Shipyard. Wind damage limited to older building (top)
From page 69...
... On the negative side, a number of metal building systems performed in a less than satisfactory manner and sustained damage ranging from minor cladding failures to loss of an entire end bay of the building. Some of these FIGURE 4-23 Preengineered metal buildings and conventional construction on west bank of Ingalls Shipyard.
From page 70...
... No damage ~ muldp~se mete budding 1 1111~11 1llll+llll~1+11111+1+1+11111111+1+11161111+1111111111111111111 1 1111111~1 1 lI111111+++~+++ 11 1[1~ FIGURE 4-27 Fast Baptist Church of Lyman. Wind dodge to complex of metal buildings lamed lo glass breathe due lo Chrome Debra.
From page 71...
... at the time Elena came ashore. Regrettably, economic conditions and the competitive nature of low-rise construction may have encouraged some members of the industry to continue to use the older provisions even though the improved alternative procedures had been adopted by the Standard Building Code in 1982.
From page 72...
... Loss of watertightness also proved to be a problem for many other buildings, including the new Vocational High School in Pascagoula and several buildings located at the Jackson County campus of the Mississippi Gulf Coast Junior College (Figure 4-28~. A number of multistory buildings, including an apartment building in Ocean Springs (Figure 4-29)
From page 73...
... Building sustained no wind damage.
From page 74...
... Although of an unusual shape and in a very exposed location, these relatively heavy concrete-shell roofs had apparently been properly designed to resist the expected wind loads.
From page 75...
... WIND DAMAGE TO BUILDINGS 73 FIGURE 4-31 Collapsed roadside shelter at rest area on Interstate Highway 10. All units failed.
From page 76...
... FIGURE 4-33 Column-to-roof connection of shelter of Figure 4-31. HURRICANE ELENA FIGURE 4-34 Failure of highway sign on Interstate 10.
From page 77...
... WIND DAMAGE TO BUILDINGS 75 FIGURE 4-35 Failure of sign in Moss Point. FIGURE 4-36 Broadwater Beach Marina in BiloxiJGulfport area.
From page 78...
... Nearly all the buildings on the island are nonengineered. The area is under the jurisdiction of Mobile County, which has adopted the Standard Building Code.
From page 79...
... It is likely that the design wind speed, as defined by the Standard Building Code in effect at the time, was achieved during Hurricane Elena and may have been slightly exceeded at the western end of the island, which was closer to the eye of the storm than the anemometer station. The design wind speeds on most of the Gulf and South Atlantic coasts are similar to those on Dauphin Island.
From page 80...
... 78 HURRICANE ELENA FIGURE 4-38 Minor damage to old military building, near Fort Gaines, Dauphin Island.
From page 81...
... WIND DAMAGE TO BUILDINGS FIGURE 4-39 Well-constructed modern building, near Fort Gaines, Dauphin Island. FIGURE 4-40 Undamaged older beach house with steep-pitched roof and protected windows, Dauphin Island.
From page 82...
... , Dauphin Island. ally the result of failing to follow the nailing schedule of the Standard Building Code.
From page 83...
... :~ ~ ~ . ~ _ FIGURE 4-42 Roof damage showing the influence of roof shape, Dauphin Island.
From page 84...
... . Mobile County's building regulations do not specify the type of hurricane strap or anchor to be used, but virtually all of the buildings that sustained serious damage used the type of anchor described in class B construction (lightduty hurricane anchors)
From page 85...
... elevated 8 ft above the ground and adjacent to the ocean on Dauphin Island, SBC1 was in fact more appropriate. Furthermore, the amended Standard Building Code (SBC2)
From page 86...
... These forces, however, vary considerably depending on the shape of the roof, the weight of the roof, the degree to which the windward wall is open, the size of roof overhangs, and the local wind speed and direction. Ironically, those structures that failed could probably have been saved had they used anchors of slightly higher capacity or doubled up on the ones used.
From page 87...
... WIND DAMAGE TO BUILDINGS FIGURE 4-44 Loss of roof, Isle Dauphin Country Club, Dauphin Island.
From page 88...
... The built-up roof was stripped from a high percentage of the buildings by the storm, resulting in water damage to almost all units. Two preengineered metal buildings were sited near the bridge connecting
From page 89...
... Considering the damage sustained by many schools on the mainland, it is interesting to note that the small wooden school on Dauphin Island survived with very little damage, as it had in Hurricanes Frederic and Camille (Figure 450~. Yet, it probably experienced the highest wind speed of any school affected by Elena and probably had the smallest amount of professional input in its design.
From page 90...
... oo oo FICURE 4-48 This preeng~eered mead ~m scram ~~ on Delphi It'd suf~red only minor Dante ~ Cubicle Elena. (Note damage ~ sign ~ foreground)


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