Tsunami Design Forces for ABC Retrofit

Link to Latest Report: September 2019 Progress Report

Background:

The catastrophic damage that tsunamis cause to coastal communities is often exacerbated by the destruction of much of the transportation infrastructure. This destruction delays critical rescue efforts and economic recovery.

The effects of the initial tsunami bore on bridges has been studied analytically and experimentally by a number of researchers. For example, with funding from FHWA and five state DOTs, PEER is currently coordinating a study in which the impact of a tsunami bore on a bridge superstructure was simulated experimentally at the NHERI wave flume at Oregon State University (OSU).

This small project focuses on later, post-bore effects of tsunamis, which can be equally damaging but have rarely been studied. The post-bore effects are dominated by quasi-steady-state, debris-laden flows that cannot be simulated experimentally well in a flume with a transient, piston-generated wave. No data is available to calibrate design or simulation models for this condition.  Such data is needed to develop ABC methods for the retrofit of bridges to resist tsunamis.

Objective:

The main objective of this project is to create datasets that can be used to develop and calibrate design and numerical models that account for flow-structure interaction, rising flow, and debris-induced forces.

Scope:

The proposed research will take advantage of a new wind-wave-current interaction testing facility at the University of Washington. This 18-m long by 1.2-m high by 0.9-m wide facility generates currents with a centrifugal pump that enables quasi-steady flow conditions at a maximum velocity of 1.0 m/s for at maximum depth or 2.0 m at half depth.  Many structures do not experience impact from the wave front of a tsunami; this facility can be used to model the accumulation of debris, and the effect of rising flows on bridges.

The following tasks will be performed to achieve the project objective:

  • Task 1 – Prepare for Tests
    • Establish forces for reference (no debris) flow conditions as a function of fluid velocity and depth. Construct model superstructure with 3D printer.
  • Task 2 – Conduct Tests
    • Measure statistical distributions (at least 20 repetitions of each test) of impact and damming forces for numerous combinations of debris and flow characteristics. Initially, we will guide the debris with wires, so that the debris orientation can be controlled. Later (and more numerous) tests will start debris fields with a particular configuration but then allow the debris to reconfigure themselves as they approach the bridge. The main variables will be: (1) free-field flow depth, (2) free-field flow velocity, (3) # of debris/min., (4) debris shape, and (5) debris orientation..
  • Task 3 – Develop and Document Design Tools
    • Develop tools to estimate the statistical distributions of debris impact and damming forces as a function of the key test variables. The results will be consistent with PBEE procedures in which the likelihood of exceedance of various force levels will be estimated for each configuration. The test data will also be made available to researchers to provide the means to calibrate numerical models. The tools will be documented in a research report, as well as in professional publications.

Research Team:

Principal Investigator:  Dr. Marc O. Eberhard
Co-Principal Investigators: Dr. Michael Motley and Dr. Dawn Lehman
Research Assistant:  N/A