Assessment of the vulnerability of Oahu's coastal bridges to storm waves and tsunami inundation

Abstract

This thesis is part of an extensive research project by the University of Hawaii at Manoa Civil and Environmental Engineering and Ocean Resources Engineering Departments to analyze the vulnerability of Hawaii's coastal bridges and ports to storm waves and tsunamis. The main focus of this thesis was the structural evaluation of coastal bridges on the island of Oahu, where the bridge capacities and potential demand during hurricanes and tsunami inundation were compared for potentially at-risk bridges. In addition, a method was been developed to facilitate the organization and archiving of survey data. Of the 26 bridges surveyed, 11 bridges were selected based on the bridge location, number of communities in proximity to the bridge, and the critical service routes that the bridge provided. In addition, the bridges that were determined to be the most exposed to wave forces were favored during the selection process. The chosen bridges were: Kuliouou Stream Bridge, Kahaluu Stream Bridge, New South Punaluu Bridge, Ukoa Pond Bridge, Old Makaha #3A Bridge, New Makaha #3A Bridge, Maipalaoa Bridge, Moanalua Stream Bridge, Kalihi Stream Bridge, and the Nimitz Highway at Aloha Tower Slip Cover #2 and Slip Cover #3. As-built drawings provided by the Hawaii Department of Transportation were used to calculate bridge weights, buoyancy forces, the lateral and vertical connection capacities, and the negative bending strength of the bridges' decks and girders. As a preliminary check of the bridges vulnerability to failure, the capacities of each bridge were then compared to estimated 100-year storm wave forces. From this assessment, it was determined the estimated wave forces that will impact the Kahaluu Bridge, Old Makaha #3A Bridge, and the Maipalaoa Bridge are greater than the calculated bridge capacities and therefore all of these bridges are at risk of failing during a 100-year storm event. If submerged by tsunami inundation, the Ukoa Pond Bridge was determined to be at risk of failing due to buoyancy forces. The Kuliouou Stream Bridge, the New Makaha #3A Bridge, the New South Punaluu Bridge, the Moanalua Bridge, the Kalihi Bridge, and the Nimitz Highway Slip Covers #2 and #3 are all determined to have sufficient factors of safety against wave loads and are not at risk of becoming buoyant if submerged by tsunami inundation, which indicates that these bridges will likely survive a 100-year storm event.