Encyclopedia of Natural Hazards

2013 Edition
| Editors: Peter T. Bobrowsky

Tsunami Loads on Infrastructure

  • Dan Palermo
  • Ioan Nistor
  • Murat Saatcioglu
Reference work entry
DOI: https://doi.org/10.1007/978-1-4020-4399-4_347


Tsunami. The Japanese word for “harbor wave.”

Coastal bathymetry. The study and mapping of the submarine ocean floor in near-shore areas.

Inundation. The overflowing of water onto normally dry land.

Loading combinations. The summation of individual force components occurring simultaneously.


Tsunami, meaning “harbor wave” in Japanese, is the outcome of a vertical displacement of a large body of water. It can be triggered by various geological or astronomical phenomena, including: underwater earthquakes occurring along tectonic boundaries, volcanic eruptions, submerged or aerial landslides, and impact from asteroids or comets. In deep, open waters, tsunamis have small amplitudes (wave height), but very long wavelengths. However, as tsunami waves advance toward shorelines they transform. First, the amplitude of the tsunami wave increases due to shoaling, which occurs as the wave is “squeezed” by the up-sloping seabed. Second, the celerity and the wavelength decrease. However, the wave period remains constant. Depending on coastal bathymetry, tsunami waves can break offshore and advance in the form of a hydraulic bore, which is a turbulent, foamy wall of water, or surge in the form of a sudden increase in water level. Both bores and surges cause inundation of low-lying coastal areas. This in turn can significantly impact infrastructure located in the path of the advancing tsunami. The risks associated with tsunami hazard have increased in recent years due to the rapid development of coastal regions. The risk is more severe in low-lying coastal areas in developing countries, as shown in Figure 1, where structures, specifically residential, are often nonengineered and inadequately designed and constructed, thus prone to extensive damage when subjected to extreme events such as earthquakes, wind storms, and tsunamis. Even in developed countries, however, where structures are typically designed for gravity loads, wind-induced lateral loads, and earthquake excitations, they are not generally designed for tsunami-induced loading.
Tsunami Loads on Infrastructure, Figure 1

Overall damage after the 2004 Indian Ocean tsunami (Saatcioglu et al., 2006a).

Tsunami forces on infrastructure

The impact of tsunami-induced forces on coastal protection structures, such as breakwaters, seawalls, reefs, etc., has been previously analyzed by researchers and engineers, particularly in Japan. However, understanding of the adverse effects of the impact of tsunami-induced flooding on near-shoreline infrastructure, such as bridges and buildings, is significantly less developed. Building codes do not explicitly consider tsunami loading, as it is understood that inland structures can be protected by proper site planning and site selection. Therefore, forces generated by tsunami are often neglected in structural design practice. Furthermore, code developers consider tsunami to be a rare event with a long return period. However, depending on the geographical location and tectonic characteristics of the underlying fault lines, major tsunamis can have a recurrence in the order of tens to hundreds of years; therefore, they should be given more attention in building codes. Recent catastrophic events (2004 Indian Ocean Tsunami; 2007 and 2010 Solomon Islands Tsunamis; 2010 Chile Tsunami; 2011 Tohoku, Japan Tsunami) have brought to light the destructive power of tsunami-induced flooding on near-shoreline structures. These events caused major structural damage to infrastructure, devastating coastal communities and resulting in widespread fatalities. Figure 2 illustrates the damage sustained by reinforced concrete structures during the 2004 Indian Ocean Tsunami. The research community has been responding with significant efforts to better understand the phenomenon of tsunami-induced forces and the interaction with structures to provide guidelines for engineers to design or assess infrastructure against such actions. Recent research indicates that forces imposed on structures due to impact of tsunami-induced flooding can be significantly higher than those associated with wind and comparable to or in excess of forces due to earthquake ground shaking (Nouri et al., 2007; Palermo and Nistor, 2009; Saatcioglu, 2009).
Tsunami Loads on Infrastructure, Figure 2

Damage to reinforced concrete buildings after the 2004 Indian Ocean tsunami (Saatcioglu et al., 2006b).

Existing design guidelines

While several design codes explicitly provide guidelines for flood-induced loads (UBC, 1997; ASCE, 2006; IBC, 2006), a survey of current design codes, design standards, and design guidelines indicates that limited attention has been given to tsunami-induced forces. Four pioneering design documents specifically account for tsunami-induced forces, namely: the Federal Emergency Management Agency Coastal Construction Manual, FEMA 55 (FEMA, 2003), which provides recommendations for tsunami-induced flood and wind wave loads; the City and County of Honolulu Building Code (CCH, 2000), which contains regulations that apply to districts located in flood and tsunami-risk areas; the Structural Design Method of Buildings for Tsunami Resistance (SMBTR) proposed by the Building Center of Japan (Okada et al., 2005), outlining structural design for tsunami refuge buildings; and Guidelines for Structures that Serve as Tsunami Vertical Evacuation Sites, prepared by Yeh et al. (2005) for the Washington State Department of Natural Resources to estimate tsunami-induced forces on structures. Recently, the Federal Emergency Management Agency published Guidelines for Design of Structures for Vertical Evacuation from Tsunamis, FEMA P646, (FEMA, 2008). This document focuses on high-risk tsunami-prone areas, and provides design guidance for vertical evacuation structures. Conservative assumptions have been incorporated in FEMA P646 to ensure safety and security for the public requiring shelter from tsunami flood waters.

Tsunami-induced force components

A tsunami wave imposes significant loading on structures. The parameters defining the magnitude and application of these forces include inundation depth, flow velocity, and flow direction. These parameters mainly depend on tsunami wave height and wave period, near-shore bathymetry, coastal topography, and roughness of the coastal inland. The inundation depth at a specific location can be estimated using various tsunami scenarios (magnitude and direction) and by numerically modeling coastal inundation. The estimation of flow velocity and direction, however, is much more difficult to quantify. Flow velocities can vary in magnitude, whereas flow directions can vary due to onshore local topographic features, as well as soil cover and obstacles. The force components associated with tsunami-induced flows consist of: (1) hydrostatic force, (2) hydrodynamic force, (3) buoyant and uplift forces, (4) impulsive force, (5) debris impact and damming forces, and (6) gravity forces. The reader is referred to Nistor et al. (2009) and FEMA P646 for a comprehensive review of the individual force components.

Hydrostatic force

The hydrostatic force, generated by still or slow-moving water, acts perpendicular to the surface of the structural element of interest. The hydrostatic force, \( {F_{{HS}}} \), can be calculated using the expression in Equation 1, where \( \rho \) is the seawater density, \( g \) is the gravitational acceleration, \( h \) is the maximum water depth or flood level, and \( b \) is the width of the structure or structural element. The force arises from a difference in water levels on opposite sides of the structural element. Equation 1 is based on water being present on one side of a structural element; however, it can be applied for cases where there is a difference in water elevation on two sides of an element.
$$ {F_{{HS}}} = \frac{1}{2}\rho g{h^2}b $$
Equation 1 is based on a triangular pressure distribution, as shown in Figure 3, with height of \( h \) and maximum pressure of \( pgh \) at the base. The point of application of the resultant hydrostatic force is located at one third from the base of the pressure distribution. In the case of a hydraulic bore, the hydrostatic force has a smaller magnitude compared to the hydrodynamic and impulsive forces. However, for surge-type tsunamis, the hydrostatic force may be substantial.
Tsunami Loads on Infrastructure, Figure 3

Hydrostatic force.

Hydrodynamic (drag) force

As tsunami-induced flow encounters a building or structural element, hydrodynamic forces, \( {F_D} \), are applied to the building. The force includes the effect of the flow velocity on all sides of the building or structural element. The general expression for this force is given in Equation 2. Existing codes suggest different drag coefficient, \( {C_D} \), values.
$$ {F_D} = \frac{{\rho {C_D}h{u^2}b}}{2} $$
where \( u \) is the tsunami-induced flow velocity (see section “Tsunami Flow Velocity” below). The flow is assumed to be uniform, and therefore, the pressure is constant through the depth of the flow. The resultant force is applied at the centroid of the projected area. The FEMA 55 document permits the hydrodynamic force to be converted to an equivalent hydrostatic force for flow velocities not exceeding approximately 3.0 m/s. Figure 4 illustrates the hydrodynamic force on a structural element.
Tsunami Loads on Infrastructure, Figure 4

Hydrodynamic force.

Buoyant and uplift forces

The buoyant force, \( {F_B} \), is a vertical force acting through the center of mass of a submerged or partially submerged structure. Its magnitude is equal to the weight of the volume of water displaced by the structure. Buoyant forces can induce stability problems by reducing the resistance of a structure to sliding and overturning. The buoyant force is calculated as follows:
$$ {F_B} = \rho gV $$
where \( V \) is the volume of water displaced by the submerged or partially submerged structure. The effect of buoyancy in combination with hydrodynamic forces result in uplift forces on horizontal structural elements that have been submerged by tsunami inundation. The contribution of the hydrodynamic force occurs from the rapidly rising water level. It can be estimated using Equation 2 by replacing the flow velocity with the vertical component of the flow velocity, and applying an appropriate hydrodynamic coefficient. Figure 5 demonstrates the effects of uplift forces on concrete slab panels after the 2004 Indian Ocean Tsunami due to buoyant and hydrodynamic forces.
Tsunami Loads on Infrastructure, Figure 5

Displaced slab panels due to uplift forces (Saatcioglu et al., 2006b).

Impulsive force

The impulsive force, \( {F_S} \), is a short duration load generated by the initial impact of the leading edge of a tsunami bore on a structure. Due to a lack of detailed experiments specifically applicable to tsunami bores running up the shoreline, the calculation of the impulsive force exerted on a structure is subject to substantial uncertainty and has not been universally validated. Dames and Moore (1980) suggested an impulsive force, known as surge force, as follows:
$$ {F_S} = 4.5\rho g{h^2}b $$
where \( h \) is the surge height, usually assumed equal to the inundation depth or flood level. This expression is based on a triangular pressure distribution, as illustrated in Figure 6, extending \( 3h \) in height, with a corresponding maximum pressure of \( 3pgh \) at the base. Thus, the point of application of the resultant surge force is located at a distance \( h \) from the base of the pressure distribution. The surge force as given in Equation 4 results in excessively large forces. Conversely, FEMA P646 proposes an impulsive force equal to 1.5 times the hydrodynamic force, based on experimental results reported by Ramsden (1996) and Arnason (2005), as provided in Equation 5:
$$ {F_S} = 1.5{F_D} $$
Tsunami Loads on Infrastructure, Figure 6

Surge force.

Debris impact and damming forces

Tsunami-induced flooding traveling inland carries debris such as floating automobiles (as illustrated in Figure 7), floating pieces of buildings, drift wood, boats, and ships. The impact of floating debris can induce significant forces on a building, leading to structural damage or collapse (Saatcioglu et al., 2006a). The debris impact forces, \( {F_i} \), in its simplest form, can be estimated from the following momentum expression:
$$ {F_i} = m\frac{u}{{\rm Delta t}} $$
where \( m \) is the mass of the body impacting the structure, \( u \) is the approach velocity of the impacting body (assumed equal to the flow velocity), and \( \rm Delta t \) is the impact duration taken equal to the time between the initial contact of the floating body with the building and the time the floating body comes to rest. FEMA P646 provides additional methods for calculating the debris impact force. The impact force acts horizontally at the flow surface or at any point below it. The impact force is to be applied to the structural element at its most critical location. Depending on the assumed debris mass, this force may not represent a significant contribution to the total lateral tsunami load relative to the other force components. However, it is significant in the design of the structural member that is subjected to the impact.
Tsunami Loads on Infrastructure, Figure 7

Impact of a floating vehicle during 2004 Indian Ocean tsunami (Saatcioglu et al., 2006a).

Debris impacting a structure can cause accumulation of debris, as depicted in Figure 7, leading to a damming effect. The forces generated due to damming can be estimated from the hydrodynamic force (Equation 2) by replacing \( b \) with the width of the debris dam.

Gravity forces

Drawdown of the tsunami-induced flooding can result in retention of water on structural flooring systems. This phenomenon imposes additional gravity loading on the structure, which must be considered in design.


Classic wave-breaking formulas are applicable for the case of wave breaking directly onto coastal structures, such as breakwaters, piers, and docks. Tsunami waves, however, depending on the near-shore bathymetry, tend to break offshore and approach the shoreline in the form of a rapidly moving hydraulic bore. Furthermore, inland infrastructure is generally not affected by the action of wave breaking occurring at the shoreline.

Tsunami flow velocity

The hydrodynamic force is proportional to the square of the flow velocity. Thus, uncertainties in estimating velocities result in large differences in the magnitude of the resulting hydrodynamic force. Tsunami inundation velocity magnitude and direction can vary significantly during a major tsunami. Current estimates of the velocity are crude; a conservatively high flow velocity impacting the structure at a normal angle is usually assumed. Also, the effects of run-up, backwash, and direction of velocity are not addressed in current design documents. A number of guidelines and researchers have proposed estimates of velocity for given tsunami inundation levels, such as Murty (1977), Camfield (1980), FEMA 55 (Dames and Moore, 1980), Kirkoz (1983), CCH (2000), Iizuka and Matsutomi (2000), Bryant (2001), and FEMA P646 (2008).

Tsunami-induced loading combinations

The design documents previously discussed do not explicitly provide loading combinations to estimate the maximum tsunami load for design. In the case of SMBTR, the tsunami load is determined from a single force component that is equivalent to the surge force. FEMA 55 provides load combinations for flood loads, which include wave breaking. However, modifications are necessary to derive loading combinations that are directly applicable to tsunamis. Yeh et al. (2005) recommended that tsunami shelters located in the inundation zone, but inland, be designed for hydrodynamic (drag) and debris impact. The surge force that is generated due to the formation of a turbulent bore is neglected, since Yeh et al. (2005) consider dry-bed test conditions only where the initial impulsive force does not exceed the drag force. Dias et al. (2005) proposed two loading combinations: point of impact and post-submergence. The point of impact considers the initial impact of the tsunami wave and is estimated as the sum of hydrodynamic (drag) and hydrostatic force components on the upstream face of the structure. The post-submergence includes hydrodynamic (drag) on the upstream face, hydrostatic forces on the upstream and downstream faces, and buoyancy. The impact of debris is not explicitly included in either of the load combinations. Pacheco and Robertson (2005) analyzed structures to various inundation levels. In the estimation of the tsunami load, FEMA 55 was followed and wave-breaking forces were omitted. For columns directly exposed to the tsunami wave, the load was estimated as a combination of hydrodynamic and debris impact forces. The tsunami load for structural walls placed parallel to the shoreline, (and perpendicular to the flow of the tsunami), was considered as the maximum of two combinations: (1) The combined effect of hydrodynamic and debris impact forces, and (2) the surge and debris impact forces. Nouri et al. (2007) proposed loading combinations specifically for turbulent bores generated by tsunamis, as shown in Figure 8. Two combinations were developed, which were based on modifications of those recommended by Dias et al. (2005). The first combination (Initial Impact) considers the first arrival of the tsunami bore on a structure, and includes the combined effect of surge and debris impact forces. The second combination (Post Impact) considers the flow of the tsunami bore around the structure. Hydrodynamic, debris impact, and hydrostatic forces are combined to determine the lateral loading. Consideration is also given to buoyancy, which can cause sliding and overturning instability. The more recent FEMA P646 document provides separate tsunami force combinations for a structure and the individual structural elements. For the structure as a whole, three loading combinations are described. The first is a combination of the impulsive forces on structural members located at the leading edge of the bore and drag forces on all previously submerged members behind the leading edge. The second combines a single impact force with drag forces on all structural members. Finally, the third considers the effect of debris damming with drag forces on all structural members. In, addition, the buoyant and hydrodynamic uplift forces should be considered in all load combinations. The design of tsunami load can be readily incorporated in building codes and combined with other loads. Given that a tsunami is considered to be an extreme event, load cases adopting the philosophy of seismic loading have been suggested (Palermo et al., 2009). FEMA P646 has also provided load combinations consistent with ASCE (2006).
Tsunami Loads on Infrastructure, Figure 8

Tsunami loading combinations: (a) Initial impact; (b) Post impact (Nistor et al., 2009).

Design considerations

Appropriate construction and layout design of a structure located in a tsunami-prone area can reduce the risk of damage during a tsunami event. Tsunami forces increase proportionally with exposed area and nonstructural elements that remain intact during the impact of the tsunami-induced flooding. Therefore, it is prudent to orient buildings with the shorter side parallel to the shoreline. Further, structural walls should also be oriented, if possible, to minimize the exposed area. Exterior nonstructural elements located at lower levels should be designed with a controlled failure mechanism that is triggered by the initial impact of the tsunami. This concept, known as breakaway walls, reduces the amount of lateral load that is transferred to the lateral force resisting system of the structure. Conversely, however, breakaway walls may result in an increase in debris loading. The use of rigid nonstructural exterior components, while providing protection to buildings from flooding, increases the lateral loading.


Recent catastrophic tsunamis (2004 Indian Ocean Tsunami, 2007 and 2010 Solomon Islands Tsunamis, 2010 Chile Tsunami, 2011 Tohoku, Japan Tsunami) have emphasized the destructive power of tsunami-induced flooding as it propagates overland and impacts near-shoreline infrastructure. As a result, research has evolved to improve our understanding of the forces associated with tsunamis and the interaction between tsunami-induced flow and infrastructure. Currently, force components and loading combinations have been proposed to assess and design structures against tsunami forces. The force components include hydrostatic, hydrodynamic, buoyant and uplift, impulsive, debris impact and damming, and gravity. There is, however, uncertainty in both the estimation of the component forces, as well as the total tsunami load that should be considered. Future efforts, including experimental and analytical studies, are being directed toward a better understanding of the forces that should be considered in design of infrastructure located in tsunami-prone areas.



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Copyright information

© Springer-Verlag Berlin Heidelberg 2013

Authors and Affiliations

  1. 1.Department of Civil EngineeringUniversity of OttawaOttawaCanada