Multi-Hazard Mitigation Plan: 07. Earthquakes

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Chapter 7:Hazard Analysis—Earthquakes up to 1S" were observed at Pier 1, the seawall revetment area between Pier 1 and 2, and as localized displacement within the sloping fills abutting the piers. Harbor Building Mitigation Measures With the evolution of building codes, the evaluation of seismic risk in the Hawaiian Islands has gone through substantial change in recent years. Many older buildings would not meet current code requirements for seismic resistance. Harbor buildings that are deemed essential should undergo a thorough existing conditions evaluation to determine potential seismic design and/or construction deficiencies. Wharf and Pier Mitigation Measures Older wharf and pier structures are typically constructed using non-prestressed vertical and battered piles. These piles typically do not have the ductility reinforcing and detailing normally required to resist seismic loads. Four options were identified to improve the lateral resisting system of the existing wharf structures,including: • Install a new independent lateral resisting system with new piles carrying all the lateral loads under the existing deck,tied together. • Install additional vertical piles to share vertical and horizontal loads with existing serviceable piles, again tied together. • Increase the vertical and lateral capacity of existing vertical piles by wrapping piles in fiber-reinforced polymer(FRP)jackets,with doweled and grouted connections. • Add continuous anchor blocks behind the wall with tie rods located perpendicular to the length of the wharf and at opposing 45 degree angles (one in each direction) to resist both transverse and longitudinal seismic loads. Geotechnical Foundation Mitigation Measures Seismic hazards in soils, usually liquefaction or related seismic deformations, can be mitigated using one or a combination of the following soil treatment or ground improvement methods: densification, improvement of drainage characteristics, cementing of the soils, or use of structural elements to resist seismic loads. Structural foundation mitigation for liquefaction can also be used with or in lieu of ground improvements. Piles and micropiles have proven effective against liquefaction hazards by transferring the building loads into non-liquefiable soils, so long as the large horizontal forces can be adequately carried by the piles. Piles and micropiles are not effective when they do not sufficiently extend into non-liquefiable soils or where lateral spread is possible, causing excessively large bending moments in the piles. Planning For each port which may serve as a sole lifeline to its supporting communities,FEMA recommends the following: • Advocate as a highest planning priority to adopt more current standards or codes. • Determine site seismicity and surface ground motions for each critical structure including potential performance, effects of liquefaction and pavement settlements. 7-11 Hawaii Countv Multi-Hazard Mitigation Plan