Louisiana Highway Construction Cost Trend after Hurricanes Katrina and Rita

The objective of this study was to reveal the trend in highway construction costs following Hurricanes Katrina and Rita in Louisiana. The means of measuring highway construction cost was the Louisiana Highway Construction Index, an index made up of the cost of labor, equipment, and six major materials used in highway construction. Data from projects let by the Louisiana Department of Transportation and Development from the second quarter of 2003 to the second quarter of 2007 were used to track the change in construction costs. Index values from hurricane-impacted areas (GO Zones) were compared with those in Non-GO Zones. The indices revealed that two quarters after Hurricanes Katrina and Rita, the highway construction cost jumped about 20% statewide and 51% in GO Zone. Two years after the hurricanes, the cost has stabilized to around 30% increase over the pre-Katrina and Rita period. This study provides valuable information for the state agency to estimate cost escalation in ongoing projects and to estimate future disaster response to highway construction costs.     

New Orleans Levee System Performance during Hurricane Katrina: 17th Street Canal and Orleans Canal North

Centrifuge modeling of the 17th Street Canal and Orleans Canal North levees was performed in this study. During hurricane Katrina the levees on the 17th Street Canal failed, leading to breaches in the outfall canal in the city. Two mechanisms were observed in the centrifuge modeling that could cause a breach. First, a water-filled crack formed in front of the floodwall as the water in the canal rose above the top of the levee. The levees on the 17th Street Canal, which were supported on clay foundations, failed when this cracking led to a translational (sliding) failure in the clay layer commencing at the toe of the floodwall. The levees at Orleans Canal North, where failure did not occur, were also modeled to demonstrate that the model tests could successfully simulate failure and nonfailure conditions. The centrifuge model tests identified the importance of the crack formation in relation to the stability of the floodwall. These tests also confirmed that levee geometry, floodwall depth of penetration, and the underlying soil profile were all critical to the performance of the system under flood loading.     

Analysis of the Stability of I-Walls with Gaps between the I-Wall and the Levee Fill

Following Hurricane Katrina an extensive investigation of the performance of floodwalls in the New Orleans area was undertaken by the U. S. Army Corps of Engineers and others. This investigation included detailed study of failures of cantilevered sheet pile “I-walls” during the hurricane. An important lesson from this investigation was that gaps can form on the canal side of I-walls as the water rises in the canal and causes the I-wall to deflect. Once formed, these gaps filled with water, resulting in significantly higher loads on the walls. Gap formation was a key factor in several I-wall failures, and modeling such gaps correctly is clearly an important aspect of analyzing I-wall stability. This paper describes simple procedures for estimating the depths of gaps behind I-walls, for calculating the loads to which they are subjected, and for including them in stability analyses. The effects of gaps on the stability of the 17th Canal and the London Avenue Canal I-walls are discussed.     

New Orleans Levee System Performance during Hurricane Katrina: London Avenue and Orleans Canal South

Hurricane Katrina was one of the worst natural disasters in U.S. history. The effects of the hurricane were particularly devastating in the city of New Orleans. Most of the damage was due to the failure of the levee system that surrounds the city to protect it from flooding. This paper presents the results of centrifuge models conducted at Rensselaer Polytechnic Institute and the U.S. Army Corps of Engineers simulating the behavior of the levees at London Avenue North and South that failed during Hurricane Katrina. Those levees failed without being overtopped by the storm surge. Also included are the results of a centrifuge model of one levee section at Orleans Canal South, which did not fail during the hurricane. The key factor of the failure mechanism of the London Avenue levees was the formation of a gap between the flooded side of the levee and the sheetpile. This gap triggered a reduction of the strength at the foundation of the protected side of the levee. The results are fully consistent with field observations.     

Performance of Roof Tiles under Simulated Hurricane Impact

Widespread damage to tile roofs over the last few years, even for weaker hurricanes, has raised concerns regarding construction practices and codes. An experimental study was carried out for clay and concrete roof tiles with adhesive- and mortar-set attachments using a “Wall of Wind” apparatus. The estimated peak 3-s gust wind speeds achieved in the simulations were 31.5 and 57.9?m/s (70.5 and 129.5?mi/h), as defined by the ASCE 7 Standard. Tests were conducted for winds from the 0° direction and subsequently, unless the roofs suffered significant damage, from the 50° direction. The research objectives were to assess roof-tile performance and observe failure modes in simulated hurricane conditions, and obtain wind pressure data allowing comparisons of measured pressures with pressures for components and cladding specified in the ASCE 7-05 Standard. Comparisons of pressure time histories for different tile systems showed that the external pressure on a tile is strongly influenced by the surface geometry of the tile. The concrete tile roof with mortar set showed the best performance among all tested roofs. Workmanship was found to be a major factor to roof-tile performance. Test results also suggested that the ASCE 7-05 pressure coefficient values are conservative for assessing wind loads acting on individual tiles.     

Hydrodynamic Investigation of Coastal Bridge Collapse during Hurricane Katrina

A number of U.S. coastal bridges have been destroyed by hurricanes, including three highway bridges in Mississippi and Louisiana during Hurricane Katrina (2005). This paper addresses three fundamental questions on the coastal bridge failures: (1) what were the hydrodynamic conditions near the failed bridge during the hurricane; (2) what was the cause of the bridge collapse; and (3) what was the magnitude of the hydrodynamic loading on the bridge under the extreme hurricane conditions. Guided by field observations of winds, waves, and water levels, two numerical models for storm surges and water waves are coupled to hindcast the hydrodynamic conditions. Fairly good agreement between the modeled and measured high watermarks and offshore wave heights is found, allowing an estimate of the surge and wave conditions near the bridges in nested domains with higher resolutions. The output of the coupled wave-surge models is utilized to determine the static buoyant force and wave forces on the bridge superstructure based on empirical equations derived from small-scale hydraulic tests for elevated decks used in the coastal and offshore industry. It is inferred that the bridge failure was caused by the wind waves accompanied by the storm surge, which raised the water level to an elevation where surface waves generated by strong winds over a relatively short fetch were able to strike the bridge superstructure. The storm waves produced both an uplift force and a horizontal force on the bridge decks. The magnitude of wave uplift force from individual waves exceeded the weight of the simple span bridge decks and the horizontal force overcame the resistance provided by the connections of the bridge decks to the pilings. The methodology for determining the hydrodynamic forcing on bridge decks can be used to produce a preliminary assessment of the vulnerability of existing coastal bridges in hurricane-prone areas.     

Hurricane Bonnie wind flow characteristics as determined from WEMITE

The Wind Engineering Mobile Instrumented Tower Experiment (WEMITE) successfully gathered high-resolution wind speed data from within Hurricane Bonnie as it made landfall near Wilmington, North Carolina, on 27 August 1998, at 04:00 UTC. This data is used to inspect the variations in turbulent characteristics of the wind during the passage of the storm. Specifically, turbulence intensities, integral scales, gust factors and power spectral densities are evaluated. Results indicate there is general agreement with the Krayer/Marshall gust factor curve, additional low-frequency energy in the longitudinal power spectral density compared to various model spectra, and a wide variation in integral scales even within the same roughness regime.