How to arm buildings for life in nature's combat zone 



Jerry Machemehl doesn't conduct a 

 research project; he submerges himself 

 in it. Paper is perched over every 

 square inch of his office — coastal maps, 

 erosion studies, aerial photographs, 

 engineering calculations, hurricane 

 records. This is one giant jigsaw puzzle, 

 and Machemehl wants all the pieces 

 out where he can see them. 



"In the past, we've treated a 

 hurricane as if it were a very idealized, 

 organized storm," Machemehl says, 

 "and that's just not the case. Few peo- 

 ple who haven't experienced a 

 hurricane understand what it's all 

 about." 



Machemehl is an engineer, and an 

 associate professor of marine science 

 and engineering at North Carolina 

 State University. He is knee-deep in 

 hurricane studies because, sooner or 

 later, almost every coastal building ex- 

 pected to outlast its mortgage is likely 

 to get a visit from a Hazel or a Connie 

 or a Belle. 



This winter, Machemehl is winding 

 up a Sea Grant study designed to 

 answer two key questions: What parts 

 of the shoreline are most vulnerable to 

 storm damage, and how can property 

 owners armor buildings to survive the 

 sometimes brutal environment of 

 coastal North Carolina? 



Yes, brutal. Sure, the beaches are 

 mild and heavenly most of the year. 

 But come winter, heavy waves and 

 currents rake real estate out to sea. 

 And then there are the hurricanes . . . 



"Many people have not been here 

 and were not on the coast during our 

 major hurricane period in the nineteen- 

 fifties," Machemehl says. "They don't 

 understand the forces that we're deal- 

 ing with." 



In 1954, Hazel, the worst of a series 

 of hurricanes in the state, killed 19 peo- 

 ple and caused an estimated $125 

 million in damage. Of the 357 buildings 

 on Long Beach before the storm, five 

 were left intact afterward. 



Largely because of Hazel, building 

 codes and construction standards have 

 been improved. Practically all 

 beachfront buildings erected since the 

 storm have been elevated to clear most 

 storm tides. But despite these improve- 

 ments, Machemehl says many new 

 buildings going up on the coast will not 

 stand up to a major hurricane. Part of 

 the problem is a lack of information. 



Winds lift and press roofs 



Machemehl says that homeowners are 

 not the only ones who don't know the 

 meaning of "hurricane." 



"I recently found a developer 

 building condominiums on the coast 

 who was not aware that there was such 

 a thing as a hurricane in North 

 Carolina," he says. 



In fact, so little information has been 

 available on the forces of hurricanes 

 that architects and designers working 

 on coastal structures have relied on for- 

 mulas derived for building inland, 

 where the only major force to contend 

 with is gravity. 



"These consulting firms are using 

 manuals written in the nineteen- 

 forties," Machemehl says. "The design 

 engineer does not have an adequate 

 manual for building in the coastal en- 

 vironment." 



Machemehl believes the results of 

 his study, when they are published, 

 will change all that. His first task was 

 to pull together data and technology 

 already available and to initiate new 

 research for some uncharted problems. 



The most familiar culprit is the wind. 

 A hurricane, by definition, has 

 windspeeds of 74 mph or faster. 

 Hurricane Camille, which hit the Mis- 

 sissippi coast in 1969, had gusts record- 

 ed at 220 mph' — twice what North 

 Carolina's coastal building code sets as 

 the "design windspeed" (the force 

 buildings must be able to withstand) 



for structures on the Outer Banks. 

 And, as windspeeds increase, the forces 

 they exert on a building increase 

 manyfold, so that the 125 mph wind of 

 a severe hurricane would exert about 

 five times the force of a 60 mph wind. 



Hurricane winds over 100 mph are 

 infrequent in North Carolina. 

 Meteorologists estimate that such 

 storms occur on the coast about once 

 every 100 years; hence the term "100- 

 year storms." But there are no guaran- 

 tees that two such monsters won't 

 come in the same week. 



"Hurricane-force winds can occur 

 anywhere on the North Carolina 

 coast," Machemehl says. "A rule of 

 thumb would be that any structure 

 built in an area where there are high 

 winds and wave and surge forces 

 should be tied together from the tip of 

 the roof to the bottom of the founda- 

 tion, so that there is an integrity 

 among all the parts, and the structure 

 acts as a unit." 



To "tie" a building together, con- 

 tractors use corrosion-resistant metal 

 straps and anchors, rather than nails 

 alone, to attach roof parts to walls, and 

 wall frames to foundations. 



But designing for high winds, 

 Machemehl says, is far easier than 

 designing a building to withstand the 

 other big bandits in a hurricane: the 

 storm surge and waves. 



The storm surge is a dome of water 

 pushed up by the combination of 

 rotating storm winds and atmospheric 

 low pressure during a hurricane. It is 

 not a wave. It is a gross distortion in 

 the water level that can stretch as 

 much as 100 miles along the coastline. 

 During Hazel, the surge rose 11 feet 

 above mean sea level, topping dunes 

 and submerging whole islands. During 

 Camille, the storm surge rose to 23 

 feet. 



Breaking waves and swells ride the 

 top of this surge inland. In many cases, 

 erosion during the hours preceeding a 

 storm carves away great quantities of 

 sand from the dunes. The weakened 

 dunes can do little to protect the struc- 

 tures behind them. 



"The dunes are only a reservoir of 

 sand," Machemehl says. "They are not 

 really adequate hurricane protection." 



As the water surges inland, more 



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