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OCR for page 105
Natural Disaster Studies: Volume Two, Hurricane Elena, Gulf Coast - August 29–September 2, 1985 Appendix A STRUCTURAL FAILURES IN MISSISSIPPI SCHOOLS The following are damage descriptions for the more serious structural failures in Mississippi schools during Hurricane Elena. Pascagoula Vocational High School Annex The annex was exposed to winds from the east. A failure of a windward window appears to have precipitated the removal of the metal deck roof system (Figure A-1). The bar joists supporting the roof had not been securely attached to the top of the wall; indeed, some appeared to have simply rested on the walls (Figure A-2). Pascagoula High School Gymnasium Sunscreens broke loose and smashed the windows, leading to the removal of the compressed wood—fiber (form-board) roof decking. Gautier Junior High School An otherwise well-designed modern school suffered roof damage and the collapse of an in-fill wall of the gymnasium. damage occurred in this area, so the building may have been subjected to uncharacteristically high winds resulting perhaps from a tornado. Dukate Elementary School, Biloxi This school suffered serious damage from northerly winds. A flat-roofed portion of the school experienced failure (Figure A-3). The gymnasium had a steel-framed gable roof. However, winds from the north would have subjected this roof to suctions similar to those of a flat roof. Either the roof-to-wall connection failed and then the walls, lacking top support, collapsed into the gymnasium or a wall collapsed first, exposing the roof to additional internal pressure. There was evidence that the wall reinforcement lacked continuity, and the small bar joists seen hanging from the first steel frame in Figure A-4 appeared to be of insuffi-
OCR for page 106
Natural Disaster Studies: Volume Two, Hurricane Elena, Gulf Coast - August 29–September 2, 1985 Figure A-1 Loss of metal roof deck—Pascagoula Vocational High School. Figure A-2 Bar joist-wall connection—Pascagoula Vocational High School.
OCR for page 107
Natural Disaster Studies: Volume Two, Hurricane Elena, Gulf Coast - August 29–September 2, 1985 Figure A-3 Window and roof damage at Dukate Elementary School, Biloxi. Figure A-4 Collapse of gymnasium at Dukate Elementary School, Biloxi.
OCR for page 108
Natural Disaster Studies: Volume Two, Hurricane Elena, Gulf Coast - August 29–September 2, 1985 cient size to brace the top of the wall properly. An older part of the school and adjacent wood-frame houses were virtually undamaged. Fernwood Junior High School, Biloxi An old masonry chimney crashed through the roof of a classroom. Another wing of the building was being used as a shelter at the time. Central Elementary School and West Elementary School, Gulfport These two schools, approximately 5 miles apart, possessed identical gymnasia oriented in similar directions with similar exposures. They failed at approximately the same time and in the same manner (see Figure A-5 and A-6). The wood roof decking had been attached to the top chord of the roof trusses by toenailed connections to a nailer attached to the chord of the steel trusses. The windows in the upper part of the wall of both buildings had blown in. If this had taken place before the roof failure, it would certainly have resulted in an increased upward wind load on the roof. Both buildings were being used as evacuation centers. Central Elementary School suffered serious roof damage in other parts of the school as well, causing considerable alarm to the occupants and extensive flooding of the building. At the West Elementary School, the damage was considered sufficient to necessitate the evacuation of the occupants by armored personnel carriers to the nearby naval base. Building codes in use throughout the United States State do not prescribe the actual combination of loads to be used in the design of strut purlins. This is Figure A-5 Gymnasium damage, Central Elementary School, Gulfport.
OCR for page 109
Natural Disaster Studies: Volume Two, Hurricane Elena, Gulf Coast - August 29–September 2, 1985 Figure A-6 Gymnasium damage, West Elementary School, Gulfport. because the appropriate data base has not yet been established from wind tunnel tests. The most recent edition of the low-rise design manual for the metal building industry (MBMA, 1986) provides a caveat with regard to this design application but does not specify the loadings to be considered. Engineering judgment is required. One approach would be to consider a worst-case scenario in which the required axial lead is assessed on the basis of main-framing coefficients: coupled with bending lead prescribed from coefficients given for components and cladding. As the two effects do not occur for the same wind azimuth in this case, the approach would appear to be conservative. Perhaps a more realistic scheme would be to consider two lead cases: axial and bending effects based on main-framing coefficients, and bending alone based on component and cladding provisions. Hopefully, wind tunnel researchers will address this problem in the near future. It should be noted that this is only one of many design applications not specifically addressed in codes in which an element or structural assemblage is required to resist both main-framing and high, localized loads.
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