A review of a draft of the ASCE report shows how the engineers analyzed the forensic evidence to parse out the many forces the tsunami inflicted on a variety of structures. The data set includes fluid and impact loads and scouring during inundation and drawdown; hydrostatic forces; buoyant forces; added loads on elevated floors; unbalanced lateral forces; hydrodynamic forces; lateral and uplift pressures of tsunami bore and surge flow; debris impact and damming forces; external and internal debris accumulation and striking forces; scour effects; the shear loads of cyclic inflow and outflow, and transient soil liquefaction.
Building Structural Performance
The report observes that tsunami inundation was between 5 meters to over 30 m. Complete collapse of residential light-frame construction occurred in nearly 100% of affected areas.
In affected commercial and industrial areas, 75% to 95% of low-rise buildings collapsed, with the rate increasing with tsunami height. Despite this, a number of multistory buildings survived without loss of structural integrity of vertical load-carrying systems or foundation. In fact, a significant number of surviving buildings did not appear to have significant structural damage.
“This provides some encouragement regarding the potential resilience of larger modern buildings with robust seismic designs and scour and uplift-resistant foundations,” the report states.
The report recommends a number of factors be considered in design for tsunami risk mitigation, including:
• Structures of all construction types may be subject to general and progressive collapse during tsunami.
• Debris accumulates rapidly during inflow as structures and forests are encountered. Designers should consider debris damming, blockage and strikes. Designs should include resistance to debris.
• Buoyancy should be accounted for and alleviated by openness.
• Structurally boxed-in areas subject to hydrodynamic pressurization of load-bearing walls should be avoided.
