Proceedings of Coastal Engineering, JSCE, Vol.3, 2012, November

EXPERIMENTAL STUDY ON THE PRESSURE ACTING
ON STRUCTURES DUE TO TSUNAMI BORE IMPACTRahman Md. Mostafizur1, Tsunakiyo Iribe2 andEizo Nakaza3
1Dept. of Civil Eng. and Architecture, University of The Ryukyus
E-mail: rahman_ku@yahoo.com
2 Dept. of Civil Eng. and Architecture, University of The Ryukyus
E-mail: iribe@tec.u-ryukyu.ac.jp
3Dept. of Civil Eng. and Architecture, University of The Ryukyus
E-mail: enakaza@tec.u-ryukyu.ac.jp

Tsunami bore impacts can exert devastating forces on houses and infrastructures along coastalregions. As such, there is an urgent need to clarify the impact pressure of tsunami bore acting on different
types of coastal infrastructure. This study presents the experimental results on impact pressure of tsunami
bore acting on two types of building model for three cases of tsunami height. The distribution of themaximum pressure and the time integration of pressure history on the front section of building models areshown. This distribution reveals that the strength of the impact pressure of the tsunami bore depends on
the impoundment depth (tsunami height), and the distribution of pressure after the impact of the tsunami
bore depends on the width of the structures.
Key Words : Tsunami bore, impact pressure, building model, maximum pressure, time integration of pressure

1. INTRODUCTION
Tsunamis can have a devastating impact oncoastal areas and have been responsible for some of
the worst natural disasters in human history, forexample, the destruction of communities
surrounding the Indian Ocean in 2004 and thedevastation of the Tohoku region along the Pacific
Coast of Japan in 2011.
Ghobarah et al. (2006), Nistor et al. (2005), andYamamoto et al. (2006) reported that coastal
structures were severely damaged by the tsunami
bore impact. Chen (2011) suggested that sufficientattention should be given to the wave impact onbuildings, as the wind and earthquake loads. Hatori(1984), Iizuka and Matsutimi (2000), Lindt et al.
(2009), Nistor et al. (2009), and Thusyanthan andMadabhushi (2008) performed experiments on theimpact pressure of tsunami bore on variousstructures.
The tsunami-structure interaction is a complex
phenomenon, and researches still need to developprominent information, such as the vertical pressure
impact distribution, cause of pressure impact
fluctuation, damaging status, etc on the structure
due to the tsunami bore impact. In order to clarify
the importance of studies on this interaction,

especially the tsunami bore loading on structures; anexperiment is conducted to reveal the tsunami bore
impact pressure on two types of building model.
The present study focuses on the distribution of themaximum impact pressure and the time integrationof pressure history.

2. RELATED RESEARCH
Chanson (2006), Cross (1967) and Fukui (1963)
experimentally and analytically determined thefeatures of the tsunami bore impact. Ramsden(1996) developed an empirical formula for the bore
impact forces on a vertical wall. Gomez-Gesteiraand Dalrymple (2004) explained the numericalanalysis of bore impact by addressing an existed
dam break experiment. Arnason (2005) carried out
experiments on the hydrodynamic impact on
different structures and primarily discussed theinitial impact phenomena of the hydrodynamic
impact. Nistor et al. (2009) analyzed the vertical
distribution of the bore impact forces and pressureson free-standing structures. Nistor et al. (2009)
introduced several hydraulic elements such as theflow depth, the velocity, and the flow direction of
the tsunami bore, which could play a crucial role
during the impact of the tsunami on coastal- 66 -

structures. They also found that the tsunami-induced
hydraulic bore is a complex phenomenon that could
not be assessed by strictly analytical means.
Therefore, clarification of this phenomenon requires
experimental investigation.
As stated above, few studies have investigatedthe changes in the vertical distribution of tsunami
bore impact pressure for different impoundment
depths (tsunami height) and structural sizes. The
present study reveals the vertical distribution of theimpact pressure of the tsunami bore acting on thefront sections of structures for three impoundment
depths and two types of structure.

3. DESCRIPTIONS OF EXPERIMENT
Experiments were performed using an open
channel having a length of 1,100 cm, a width of 60
cm, and a depth of 40 cm. Fig. 1 shows a schematic
diagram of the experimental setup. The dam breakmodel has been adapted to observe the impact
pressure of a tsunami bore on the building model.
Two types of building model (model A: 12  12
 12 cm and model B: 6  6  12 cm) have been
used, and different impoundment depths (30 cm, 20cm, and 10 cm) behind the gate have been set,considering the initial tsunami height. The bottom

slope of the channel is 1/65 towards downstream.
Five pressure sensors have been installed on thefront face of the building model (Fig. 2). However,the upper most pressure sensor did not show goodrecording data. Hence, data from only the first fourpressure sensors, from the bottom to the upper
portion, are considered for analysis. The pressure
sensors have been fixed at positions 1, 3, 5, and 7
cm from the bottom along the center of the crosssection of the building model. These pressure
sensors are labeled the 1st, 2nd, 3rd, and 4th sensors,respectively.
A digital camera has also been installed in orderto provide qualitative information about thecollision of the tsunami bore with the building
model. The tsunami bore pressure based on the time
history on the font face of the building model has
been estimated. The distributions of the measured
impact pressure were then analyzed. Three timetrials have been regulated based on theimpoundment depth for a building model. The
average values of trial data are considered in
discussing the results.

Pressure Sensor

Gate

Building model

Impoundment
80 cm

60 cm

(Filled with water)

160 cm510 cm

Fig.1 Experimental channel with building model: plan view.

4th Sensor
3rd Sensor
2nd Sensor
1st Sensor
Model A

Model B
Fig.2 Building models with pressure sensors.

- 67 -similar gradually declining values from the 1stsensor to the 4th sensor for both models. However,as the impoundment depth increases, the 2nd sensor
exhibits a higher pressure than the 1st sensor. The
differences in the maximum pressure distributions
between the proposed models increase from the 1stsensor to the 4th sensor and the maximum
differences are found at the 4th sensor. Furthermore,these differences become increasingly similar as theimpoundment depth increases. In case of an
impoundment depth of 30 cm, the 4th sensor exhibits
the greatest difference between model A and modelB.
As mentioned above, the tsunami bore can moreeasily pass through the side sections for model B
than for model A, so the wider model A experiences
a higher tsunami height at the upper portion thanthat for the narrower one model B. After the initial
impact of the tsunami bore, the tsunami bore canaccumulate height along the front face of thebuilding model, so that the differences in this heightcause the differences in the maximum pressure
distributions between models.

4. RESULTS AND DISCUSSION
Figs. 3 and 4 show instances of tsunami bore
impacts and the pressure history from the 1st sensor
on models A and B, respectively. Palermo andNistor (2008) demonstrated that the first loading of
the tsunami bore on the structure is the surge
impact, and the second tsunami bore impact is thehydrostatic and hydrodynamic forces on thestructure. In the figures, the first tsunami bore
impact pressures are similar for both models.
However, the pressure distributions are different
between the models. In the case of the narrow model
B, the tsunami bore can more easily pass throughthe side sections than that for the wider model.
Thus, the bore flow around model B can attain ahigh velocity. Therefore, model B shows a higher
pressure at the base than model A.
Fig. 5 shows the maximum pressure distribution
due to the tsunami bore impact on the pressure
sensors of both building models. The maximum
pressure distribution patterns depend on both thetype of building model and the impoundment depth.
In the case of an impoundment depth of 10 cm, thedistribution of the maximum pressure exhibits

Pressure (kPa)

432100102030403040Time (s)Moment of the impact of tsunami and the splash of water

Pressure history

Fig.3 Tsunami bore impacting model A (impoundment depth: 30 cm).

Pressure (kPa)

4321001020Time (s)Moment of the impact of tsunami and the splash of water

Pressure history

Fig.4 Tsunami bore impacting model B (impoundment depth: 30 cm).

- 68 -7A (H=10cm)
A (H=20cm)

Sensor Position (cm)A (H=30cm)
B (H=10cm)

5B (H=20cm)
B (H=30cm)

31012345Maximum Pressure (kPa)

1614121086420Time integration of pressure（kPa.s）

Time integration of pressure（kPa.s）

Fig.5 Maximum pressure distribution (A: model A, B: model B).

BA010

1st Sensor （1 cm）
2nd Sensor （3 cm）
20Time (s)

30

16
14
1210864
2040

B

A
1st Sensor （1 cm）
2nd Sensor （3 cm）
0

1020Time (s)3040

Fig.6 Time integration of impact pressure for impoundment depths of 20 cm (left) and 30 cm (right) on the 1st and 2nd16
1412108642016141210864
20Time integration of pressure（kPa.s）

Time integration of pressure（kPa.s）

sensors (A: model A, B: model B).

3rd Sensor (5 cm）
4th Sensor (7 cm）

AB
01020Time (s)3040

3rd Sensor (5 cm）
4th Sensor (7 cm）

AB

01020Time (s)30Fig.7 Time integration of impact pressure for impoundment depths of 20 cm (left) and 30 cm (right) on the 3rd and4th sensors (A: model A, B: model B).

- 69 -40

Figs. 6 and 7 show the time integration of thepressure history for impoundment depths of 20 cm
and 30 cm. Fig. 6 shows the time integration ofpressure based on the base level sensors (1st and 2ndsensors), whereas Fig. 7 shows the time integrationof pressure based on the upper level sensors (3rd and4th sensor).
In Fig. 6, the pressure integrations obtained
from the 2nd sensor for both models exhibit similarvalues at the beginning of impact, compared to thatfrom the 1st sensor. However, after a few moments,
the pressure integration of the 1st sensor exhibits
higher values than that of the 2nd sensor for bothmodels. On the other hand, the pressure integrationof the 2nd sensor for model B exhibits higher values
than that for model A. Nevertheless, similar patterns
can be observed on the 1st sensor for both models.
As mentioned above, due to the existence of thehigh-velocity flow around model B, it can have ahigher impact pressure near the base, as comparedto that for model A. Hence, the 2nd sensor, which isalmost at the level of the water surface during bore
impact and thereby facing high flow velocity,
exhibits a large difference between the pressure
integrations obtained from model A and model B.
Fig. 7 shows the pressure integrations from the3rd and 4th sensors, where the 4th sensor pressure
integration for model A takes higher values than thatfor model B. Furthermore, this line always passes
below the 3rd sensor pressure integration line.
Although the 3rd sensor pressure integration exhibits
higher values for model A in the case of an
impoundment depth of 20 cm, the pressure
integration from this sensor shows a similar pattern
for both models. In these cases, the bore height infront of the models affects the strength of thepressure for both models.
The time integration of pressure also depends on
the impoundment depth and the width of model, asobserved in the maximum pressure distributions
shown in Fig. 5.

5. CONCLUSIONS
Tsunamis can cause immense physical, social,and financial damages to coastal communities.
However, these losses could be reduced by applying
a proper design process to infrastructures in coastal
regions. Considering the recent high frequency oftsunami events, it is important to develop methodsby which to minimize the destruction to coastal
structures caused by tsunami bore impact.
The present study revealed experimentally thefeatures of tsunami bore impact on building models.
Tsunami bore pressure depends on both the initialtsunami height (impoundment depth) and the widthof the structure. The upper leveled of the widerbuilding (model A) experiences higher pressuresthan that of the narrower building (model B). On theother hand, the time integration of pressure for thenarrower building takes higher values than that for
the wider building.
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- 70 -(Received June 15, 2012)