3 research outputs found
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Effectiveness of Small Onshore Seawall in Reducing Forces Induced by Tsunami Bore: Large Scale Experimental Study
Tsunami force and pressure distributions on a rigid
wall fronted by a small seawall were determined experimentally
in a large-scale wave flume. Six different
seawall heights were examined, two of which were exposed
to a range of solitary wave heights. The same
experiment was done without a seawall for comparison.
The measured wave profile contained incident
offshore, incident broken, reflected broken, and transmitted
wave heights measured using wire resistance
and ultrasonic wave gauges. Small individual seawalls
increased reflection of the incoming broken bore front
and reduced force on the rigid landward wall. These
findings agree well with published field reconnaissance
on small seawalls in Thailand that showed a correlation
between seawalls and reduced damage on landward
structures.This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by Fuji Technology Press. The published article can be found at: http://www.fujipress.jp/JDR/.Keywords: tsunami inundation, tsunami defense strategy, tsunami hazard mitigation, tsunami risk reduction, wave force
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Evaluation of Tsunami Loads on Wood Frame Walls at Full Scale
The performance of full-scale light-frame wood walls subjected to wave loading was examined using the Large Wave Flume of the Network for Earthquake Engineering (NEES) Tsunami Facility at Oregon State University. The hydrodynamic conditions (water level and bore speed) and structural response (horizontal force, pressure, and deflection) were observed for a range of incident tsunami heights and for several wood wall framing configurations. The walls were tested at the same cross-shore location with a dry bed condition. For each tsunami wave height tested, the force and pressure profiles showed a transient peak force followed by a period of sustained quasi-static force. The ratio of the transient force to quasi-static force was 2.2. These experimental values were compared to the predicted values using the linear momentum equation, and it was found that the equation predicted the measured forces on the vertical wall within an accuracy of approximately 20% without using a momentum correction coefficient. The experiments also showed that the more flexible 2x4 wall resulted in lower peak forces when compared to the 2x6 walls subjected to similar tsunami heights. However, the 2x6 walls were able to withstand larger waves before failure.Keywords: light-frame wood walls, impact, tsunami mitigation, tsunami forces, tsunami damageKeywords: light-frame wood walls, impact, tsunami mitigation, tsunami forces, tsunami damag
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An analysis of wave forces on prototype walls under tsunami loading
This thesis is comprised of two manuscripts based on a laboratory experiment conducted to examine realistic wave forcing on a vertical wall subjected to tsunami loading. The first manuscript examined tsunami force and pressure distributions on a rigid wall that was fronted by a small seawall. Six different seawall heights were examined, two of which were exposed to a range of solitary wave heights. The same experiment was done without a seawall for comparison. The measured wave profile contained incident offshore, incident broken, reflected broken, and transmitted wave heights measured using wire resistance and ultrasonic wave gauges. Results showed that small individual seawalls increased reflection of the incoming broken bore front and reduced force on the rigid landward wall. These findings agreed well with published field reconnaissance on small seawalls in Thailand that showed a correlation between seawalls and reduced damage on landward structures.
The second manuscript examined cross-shore variation of tsunami loading as the loading scenario changed from an impulse to a quasi-steady bore. In this study tsunami force and pressure distributions on a rigid wall were determined experimentally in a large scale wave flume, and forces were examined experimentally at three different cross-shore locations. Incident offshore and incident broken wave heights measured using wire resistance and ultrasonic wave gages, and velocity was measured using acoustic-Doppler velocimeters. Force and pressure profiles were measured using load cells and pressure transducers. At each cross-shore location, the force and pressure profiles showed an impulse peak followed by a period of sustained force. This type of profile was seen for each wave height tested, and as expected as wave height increased the value of the maximum impulse force also increased. By examining force time histories, it was also found that while the hydrostatic pressure distribution accurately depicted the force profile during the period of sustained force it was significantly less reliable during the impact period. It was found that as the rigid wall was moved further offshore the peaks were less pronounced and the corresponding maximum impulse force values decreased. Thus, as the wall was moved onshore the loading scenario transitioned from impact to a quasi-steady bore-like loading condition. The sustained forces measured experimentally verified the empirical formula for steady state force presented by Iizuka and Matsutomi (2000). This theoretical formula was also presented by both the FEMA Coastal Construction Manual (2000) and the City of Honolulu Building Code (2003) as the “hydrodynamic force.