Tsunami-like flow induced force on the structure: Prediction formulae for the horizontal force in quasi-steady flow phase

ABSTRACT Amongst extreme hydrodynamic events are bore- and surge-type flow motions that are observed in the context of storm surges induced by tropical cyclones, but also occur when tsunami or flash floods strike. Coastal houses built on elevated pile foundations have suffered less damages in recent extreme hydrodynamic events since the water could pass beneath the floor slabs decreasing the exertion of forces onto structures. To date, research pertaining to horizontal and vertical forces on elevated structures is still scarce. Specifically, previous research may not be applicable to cases of bore-type inundation interacting with elevated coastal structures. This work hence aims to model non-elevated and elevated coastal structure, and to deepen insight into forces with a focus on the structural elevation. For this purpose, large-scale experimental tests were performed on a uniform 1:15 slope in combination with an adjacent horizontal plane. Idealized residential buildings on a length scale of 1:5 were designed to simulate loading conditions of broken solitary waves on slab-on-grade and elevated buildings. A wide range of horizontal forces between 0.1 and 10 , vertical forces between 0.5 and 7.5 and overturning moments up to 4.5 were measured. In accordance with the experimental results, design equations were derived.

Large-scale physical modeling of broken solitary waves impacting elevated coastal structures

Tsunami-like flow induced forces on the structure: Dependence of the hydrodynamic force coefficients on Froude number and flow channel width in quasi-steady flow phase

It is more common to introduce the parapet/recurve/wave return wall over the existing structure, such as a vertical seawall or composite structure, to reduce the overtopping efficiently. The advantage of a recurve wall on top of the sea wall has been studied in the past in regards to wave interaction and overtopping. However, their efficiency in protecting the inland structure during extreme events such as flooding during a tsunami is unexplored. The present study addresses the effect of a vertical seawall with recurve in reducing the dam break surge simulating tsunami-induced forces on an inland structure. The study compares the momentum transferred on the landward structure behind a Vertical seaWall (VW) and a vertical wall with the Large ReCurve on the top (LRC) during overtopped conditions. The outcome from the numerical simulation shows an insignificant contribution due to the LRC in reducing the force on the inland structure compared to the VW, albeit delaying the impact time. However, the LRC performed slightly better in the case of a low-rise wall located near the inland structure than the VW. Furthermore, a low-rise VW increases the force and overturning moment on the inland structure compared to no-wall conditions. Both the LRC and the VW reduced the horizontal force on the structure linearly with the increase in height. An exponential decrease in the overturning moment was observed on the landward structure with the increase in the height of the VW or the LRC. Design equations are proposed for the forces and overturning moment reduction based on the height of the VW or the LRC.

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Tsunami-like Flow-Induced Forces on the Landward Structure behind a Vertical Seawall with and without Recurve Using OpenFOAM

Subgrid-scale modeling of tsunami inundation in coastal urban areas

Tsunami impact on infrastructure along the coast causes severe destruction, loss of human lives and negative influence on the economy. When tsunami propagates towards the coastline, the flow often resembles a bore which propagates with a high velocity and takes everything on its way, including heavy objects. When reaching the structure, this water-driven debris induces a kind of impact force and magnifies the load on structures along the coast. The present study is aimed to measure the load of tsunami-borne debris on a building constructed near the shoreline. In many situations, tsunami or any flood nearshore resembles a surge caused by a dam-break event; therefore, to model this process, we conducted our experiments by setting up a dam-break arrangement in a wave flume of 72.5 m length, 2 m wide and 2.5 m deep at the Department of Ocean Engineering, IIT Madras, India. A Froude scale of 1:20 was adopted for modelling the coastal structure and the debris placed over a beach slope of 1:30. The hydraulic bore was generated by a sudden opening of the gate of the tank. We considered three water depths of 0.8, 0.9 and 1.0 m. The debris was modelled as a box-shaped structure weighing 4.2, 5.6 and 6.0 kg. A video camera was used to capture the surging of the hydraulic bore and to study the character of debris motion during impact. The impact forces acting on the structure due to debris were measured with a load cell. The acquired data were further analysed and discussed.

S. Harish

Papers

Tsunami-like flow induced force on the structure: Prediction formulae for the horizontal force in quasi-steady flow phase

Impact of Flow-Driven Debris on Coastal Structure During Tsunami Bore