Hurricane Katrina 29 th August Preliminary Damage Survey Wyndham Partners Consulting, Limited

Transcription

1 Hurricane Katrina 29 th August 2005 Preliminary Damage Survey Wyndham Partners Consulting, Limited Copyright All rights reserved.

2 A Brief Reconnaissance of Hurricane Katrina Hurricane Katrina may be the most severe catastrophe experienced by the insurance industry to date. Similar to Camille in 1969, the combination of storm size and unique Gulf Coast under sea terrain made this event both deadly and costly. The casualty statistics are still unclear for Katrina, but the casualties are already triple those of Camille. Similar to Camille, in Katrina a dome of water slammed into the coastline with devastating effects. Studies of Katrina and her aftermath should provide considerable information on future hurricane risk and begs the question of how much society has improved in preparing for and dealing with such extreme catastrophes. Craig Tillman, President of Wyndham Partners Consulting Ltd., spent many hours in the field with the Florida Coastal Monitoring Program (FCMP) team led by Dr. Kurt Gurley of the University of Florida, Gainesville, and Dr. Forrest Masters of Florida International University and the International Hurricane Research Center, Miami. The result was a rapid survey of the affected areas. This report summarizes two surveys of the damaged areas of Katrina conducted by this team. Due to significant logistical problems (traffic, blocked roads, bridges out, etc.), the team was focused on getting instrumentation equipment extracted and completing an overview of the devastation, rather than undertaking detailed surveys. We were able to get a quick tour of much of the affected stretch of coast from Florida s state-line to slightly west of New Orleans. A follow-up detailed survey focusing on the highest wind areas is planned by the Institute for Business and Home Safety (IBHS) in the coming weeks. After inspecting several different regions affected by the event, three tiers of damage emerged from the varying degrees of intensity inside Katrina s swath of destruction: Tier 1: Vast stretches of coastline experienced complete devastation from the storm surge and accompanying wave action effects. Both residential and commercial structures in this tier were completely overwhelmed by this effect, and many were literally swept from their foundations. Structures that remained were largely ISO Construction Class 5 and 6 1 mid to high-rise buildings, but even these structures sustained massive damage to their lower stories. In this tier, storm surge and wave action forces greatly surpassed that delivered by the wind alone. Tier 2: Near-coastline areas experienced the devastating effects of both wind and flood without the velocity effects brought on by direct wave action. In some cases this was simply the surge line moving further inland, causing widespread flooding to low lying areas near the coast. This tier also includes areas in and around New Orleans where man-made flood protection systems failed. Depending on the location s coincidence with Katrina s wind footprint, as well as the local topography, either wind or flood damage could dominate the cause of loss to structures. Especially within ¼ mile of many coastline areas, flooding 1 ISO Class 5 Modified Fire Resistive includes buildings having exterior walls, floors and roof constructed of masonry or other fire-resistive material with a fire resistance rating of one hour or more, but less than two hours. ISO Class 6 Fire Resistive includes buildings having exterior walls, floors and roof constructed of masonry or other fire-resistive material with a fire resistance rating of not less than two hours. 1

3 effects due to storm surge were complete. From approximately Biloxi to Bay Saint Louis this flooding was accompanied by some of the greatest winds delivered by Katrina. In other areas, however, such as much of New Orleans, the effects of flood waters were overwhelming. The flood damage in New Orleans overshadowed the effect of wind, which was comparatively moderate relative to other areas under Katrina s influence. Tier 3: The balance of areas affected by Katrina s footprint were impacted exclusively by the high winds brought by the hurricane. In these areas, as we have seen in numerous hurricanes in the past, the vulnerability of a particular structure was a function of the velocity of wind experienced and the type of construction employed. We observe that the continuing lesson is attention to detail in construction techniques, provision of wind resistive features in local building codes, adherence and enforcement of those codes, and finally, responsible owner actions to apply further loss reduction measures well before the hurricane was a threat. This is the case for both commercial and residential occupancies. A Battered Coastline The coastline from Biloxi, Mississippi, to Bay Saint Louis was subjected to extreme storm surge and wave action. It is served by a 26 mile stretch of Highway 90, supporting major resort and gaming businesses. Both Biloxi and Gulfport saw large surge heights running to 2 stories and penetrating inland up to ½ mile or more. We note that Camille had storm surge with heights of 25 feet. 2 Photos 1 through 6 show a common sight along this coastline, with waterfront and near-coast properties destroyed by very high storm surge topped with pounding wave action. In many cases, there is clear evidence the water reached heights of feet (two stories) and traveled inland at times more than ½ mile. What was striking was that often the only element of a structure left was the foundation. Indeed, with the exception of ISO Class 5 and 6 construction, most buildings along this coastal stretch were completely swept away. The photos call into question design critical decisions on such structures including the use of breakaway walls, sacrificial first stories, and the likelihood of seeing high storm surge coupled with storm driven waves during the design life of the building. Photo 4 shows new construction where first story foundation piers were used in anticipation of future storm surge effects. The resulting debris from many of these beachfront buildings was carried far inland by the storm surge causing further damage to near-coastal properties. Photo 5 shows one such property apparently collapsed by the debris flow. Note that this home s roof shingles appear intact typically shingles of this type begin to fail at 80mph wind speeds. 2 Sheets, R Catastrophic Hurricanes May Become Frequent Events in Caribbean and along the United States East and Gulf Coasts in Hurricanes of Edited by Ronald Cook and Mehrad Soltani. American Society of Civil Engineers, December. 2

4 Photo 1. A typical commercial structure along coastal highway 90 between Biloxi and Gulfport. Note that the first and second stories were ravaged by storm surge. Photo 2. Detail photo of steel frame superstructure disfigured by storm surge. A large high-rise hotel complex is adjunct to the riverboat (shown in background above). See Photo 3 below for an aerial perspective. 3

5 Photo 3. As pictured in Photo 2, this is an aerial perspective showing the casino riverboat in permanent dock (left side) adjacent to a high-rise hotel complex. It appears that much of the damage to the hotel was due to pounding and flying debris from the floating casino. This emphasizes the need to assess exposing buildings in anticipating a structure s wind vulnerability. Photo 4. A structure near downtown Biloxi, Mississippi. Note the damage to the first and second story. The roof is apparently undamaged and upper story windows intact. 4

6 Photo 5. A near-coastal house collapsed by storm surge augmented with debris from buildings destroyed up stream. Photo 6. A beachfront hotel just east of Gulfport, Mississippi. Note all that remains is the reinforced concrete frame and roof diaphragm. All cladding and interior improvements have been cleared from the structure by storm surge. 5

7 In our survey of the coastline from Biloxi to Gulfport, all of the casino riverboats (actually barges) sustained massive damage. The high storm surge in combination with wind and wave forces probably caused the barges to strain and then break their moorings. What followed was a rather violent transport of the barges beyond the beachfront, and in some cases collisions with other structures inland (see Photos 7, 8 and 9). Photo 10 is a NOAA produced aerial photo of two riverboat barges resting inland of their original moorings. Photo 7. Riverboat casino completely ravaged by the storm surge. The casino was transported from its permanent moorings to several hundred feet inland. 6

8 Photo 8. Most of the riverboat barges ended up resting many yards inland after a rather violent transport of the barge beyond the beachfront. In some cases, as pictured here, barges collided with other structures inland. This barge collided with the corner of the building pictured on the right, the barge then pivoted around to its final resting place. Note the standing seam roof and roof equipment seem to be intact on the barge both elements that are often found to be especially vulnerable to high wind forces. Photo 9. Ariel photo of eastside of Biloxi, where two riverboat barges came onshore. Inset shows detail of riverboat that collided with a mid-rise structure. Note the inland extent of the debris pattern into the more residential sections of the city. 7

9 Photo 10. View of mooring attachment detail on the barge hull superstructure. These details call into question the design criteria used for such details. The design should contemplate performance under the coincident forces of severe winds, severe storm surge, and wave action. Further from the center of destruction, the coastline from Ocean City to Slidell was also devastated by the effects of storm surge and wave action. In Fountainbleau, just west of Pascagoula, a small coastal community of resort homes was completely wiped out. This 2-½ mile stretch has approximately 30 homes, which were all built on a story of stilts to avoid flooding. The damage scene along the coastal road revealed only the skeleton of each foundation; little evidence of the homes once there remained (see Photo 11). In this area, the storm surge was the primary damage mechanism. For the few homes that were spared total destruction due to their slightly higher elevation, a combination of wind and wave wash effects still caused devastating damage (see Photo 12). Here the storm surge was at least in the 15 foot range. Photos 13 and 14 show an aerial view of the destruction along this coastal road. 8

10 Photo 11. A typical post and pier (stilt) foundation for beachfront homes. All other parts of the structure were washed away by storm surge effects. Photo 12. Beachfront home, still standing but showing severe wave action and surge effects. Note that the standing seam roof looks intact, implying less severe wind speeds. 9

11 Photo 13. NOAA airborne photo showing coastal development where many homes were washed away. Picture reveals only two structures left standing, all others are demolished with only their foundation showing. The service road is completely washed out. 10

12 Photo 14. Swath of coastal and near-costal section showing gradation of storm surge effects. The photo covers approximately a 1/4 mile on its width -- from coastline going inland. Nearest the coastline is a large lighthouse that was washed from its foundation; it is approximately 70 feet in height. Inland about 1/10 mile more homes can be seen with their roofs intact. Closer to shore the storm surge wiped homes off their foundations. Further inland along the same stretch of coastline, it was clear the storm surge effect was less catastrophic due to the lack of velocity and sheer flooding height. However, it still resulted in widespread water damage. These homes also displayed moderate wind damage, but this damage was reduced due to the shadowing effect from the forest in which these homes were situated. Of course, numerous incidences of trees hitting homes were observed, but for the most part, trees themselves were not severely damaged (Photo 15). 11

13 Photo 15. Typical damage to inland properties not subjected to wave action, but still sustaining flood damage. Note the tree density surrounding the home and lack of damage to roof, roof leading edge or shutters. Elsewhere, there was ample evidence of the incursion of storm surge far inland. Traveling east from the Florida state line along the I-10 freeway, many stretches had visible signs of storm surge over wash (Photo 16). The FCMP team previously observed at least 20 foot surge early Monday morning after deploying scientific instrumentation. Many highway bridges between Biloxi and Bay St. Louis sustained damage. A considerable amount of debris is still there, including large fishing boats and barges lodged between bridge spans (Photo 17). 12

14 Photo 16. Large Aircraft Fuel tank transported by storm surge to freeway roadside. Photo 17. Tugboat dragged inland by storm surge until finally colliding with Interstate Highway Bridge. This bridge was closed for repair as it sustained many similar collisions along its span. 13

15 High Wind Effects Inland Damage from wind was observed from Pascagoula to the suburbs of New Orleans, which are areas situated inland from the severe storm surge and wave action. The most common damage observed was roof failure in the more vulnerable classes of construction due to internal pressurization. Of particular interest were newer vintage apartment buildings. We observed several examples of three story apartment/condominium structures that experienced significant gable end failures leading to progressive destruction of the roofs. One such example is a complex in Ocean Springs that displayed severe damage (see Photos 18, 19 and 20). This complex was located 2-¼ miles from the coast. Note that breaches to the roof of such a structure may cause significant water damage to all three floors. Photo 18. Apartment complex near Ocean Springs, MS (east of Pascagoula). Note the gable end failures on each building, causing progressive damage to the balance of the roofing systems. These failures were observed in every building in the complex. Note aluminum siding, OSB (oriented strand board) sheathing and lack of gable end bracing. 14

16 Photo 19. Another view of the apartment complex in Ocean Springs. Note that water damage propagated to all stories of the building. Photo 20. More severe roof damage initiated by a gable end failure and followed by progressive failure of the balance of the roof systems. Note siding (aluminum) stripped from end wall, as well as potential channeling effect of stairway opening possibly increasing uplift forces in the area. 15

17 Similar gable end failures in newer apartment complexes were observed just east of Gulfport. One complex, located approximately 2-½ miles from the coast, displayed significant construction deficiencies in the assembly of roof elements, in the design of gable ends (which in this case appeared decorative and unnecessary), in the weakness of soffit installations and in the poor attachment methods of the roof sheathing to the roof rafter system. Specifically, the use of staples in irregular patterns made this system especially vulnerable. This type of construction would not meet building code provisions in South Florida. (Photos 21 through 25). Photo 21. Apartment complex near Gulfport, Mississippi. Note severe siding failures, decorative shutters, use of oriented strand board (OSB) and complete gable end failure (truss is lying on the roof). 16

18 Photo 22. Use of OSB sheathing with simple stable attachment methods. Photo 23. Attachment point of sheathing to roof rafter. Note the twin hole pattern from use of simple staple attachment methods. 17

19 Photo 24. Note soffit failure problems that may have increased uplift forces from the underside of the roof, possibly compounding vulnerability of weakly attached roof sheathing. However, roof overhang is shorter than seen in other regions, which reduces overall windage of this component. Photo 25. Failure of gable end siding (apparently only using insulating material behind aluminum siding) leading to failure of weakly attached roof sheathing panels. Note that rafter spacing is 24 on center which is a weaker system for the roof/wall connection. 18

20 From Biloxi, Mississippi to Slidell, Louisiana damage attributable to hurricane force winds was observed from the highway (traveling west) beginning at about Pascagoula, Mississippi. This was close to where FCMP had their first instrument deployed. Access was limited here but visible damage started around Mobile, where large metal structures displayed some damage. Near Biloxi and Gulfport, severe damage was observed from the highway. We were unable to approach Slidell due to police blockades, but reports indicated devastating effects. Urban Flooding and Wind Effects in New Orleans The New Orleans metropolitan region was striking in the lack of severe wind damage to both residential and commercial structures. Instead, we observed damage mainly related to severe flooding effects. Entering the city via the causeway over Lake Pontchartrain, we observed some minor structural damage including failed glass brick walls (Photos 26 through 30) and window damage from debris hitting buildings. Other structures were observed to have negligible damage. Indeed there is a fair amount of evidence that overall wind speeds were not that strong. Photo 26. Glass block curtain wall failure probably due to debris striking structure. 19

21 Photo 27. Overall light damage to ISO Class 4 and 5 commercial construction panels blown out and windows broken. Foreground shows a damaged billboard. Photo 28. Strip center slightly west of downtown New Orleans. Note little window, awning, light post or signage damage. 20

22 Photo 29. Hospital just southwest of downtown New Orleans. Negligible damage. Photo 30. Upper story window damage on the Wyndham Hotel. 21

23 In Dr. Masters estimation 3, downtown New Orleans experienced at most mph 1-minute sustained and 110-mph 3-second gust wind speeds, which are basically Cat 1 winds adjusted to open exposure (terrain). This estimate takes into account instrument records taken from FCMP deployments approximately 9 miles south of New Orleans as well as field observations of damaged and non-damaged structures within New Orleans. Major flooding was observed in most areas that we were able to view in and near downtown New Orleans. As shown in Photo 31, residential areas were mainly flooded and displayed little evidence of severe wind damage. Flooding created significant access problems for us. Photo 31. Typical flooded areas in residential sections west of the business district of New Orleans. Note minimal tree or structural damage from wind. In downtown New Orleans, we observed some roof damage (see Photo 32) as well as many broken windows on high rise structures (Photo 33). Overall, there was not a pattern of significant damage to commercial structures. Indeed, the low-rise commercial structures adjacent to the business district had only light damage by our observations (Photos 34 and 35). Due to the insidious damage cause by even moderate flood levels, many of the structures sustained high loss ratios from flooding effects alone. 3 Masters, F Personal communication on September

24 Photo 32. Downtown New Orleans Riverwalk Mall. This structure sustained significant roof damage. Photo 33. Views of downtown buildings mainly damage to windows due to debris from adjacent exposures (such as the Superdome s roof). 23

25 Photo 34. Typical low-rise commercial structure just south of downtown New Orleans. Note roof equipment is intact. Photo 35. Typical strip center just south of downtown New Orleans. Note signage and awnings are intact. Further south and east of New Orleans, residential areas only displayed light damage from winds; much of the damage was due to trees and other minor failures. Much of the inventory at risk was older residential structures on moderately treed lots (see Photos 36 and 37). Photo 36. Light to moderate residential damage just a few miles southeast of New Orleans. 24

26 Photo 37. Typical residential structures showing light damage a few miles southeast of New Orleans. Conclusions On a human scale, Katrina emphasizes how especially vulnerable our urban populations are to natural and man-made disasters. As we deal as a society with Katrina s aftermath, the insurance industry is specifically challenged to understand the financial ramifications of the event, as well as gain better knowledge for managing these risks going forward. Wyndam Partners Consulting, Limited (WPC), a wholly owned subsidiary of RenaissanceRe Holdings Ltd., provides consulting services to insurance companies, program managers and other insurance industry participants. This Damage Survey is neither an advertisement of nor a solicitation to purchase (re)insurance in any U.S. jurisdiction, but is intended to provide the estimates and opinions of WPC. These estimates and opinions are solely those of WPC. The readers of this Damage Survey should not rely on any of the general information herein, but should contact an appropriately licensed broker to obtain complete information regarding the terms and details of the products we and our affiliates offer and their availability in particular jurisdictions. WPC s affiliates Renaissance Reinsurance Ltd. and Glencoe Insurance Ltd. operate only from Bermuda and are not admitted in any other jurisdictions. The information in this Damage Survey, or as may be reflected in or relate to any of our or our affiliates coverages or products, should not be construed in any way as legal, tax, business, financial or accounting advice. For any questions on these or any related matters, please refer exclusively to your own professional advisor. We assume no obligation to update the information or estimates herein. 25