Designing infrastructure that can withstand the effects of earthquakes and other natural disasters is a key concern within the construction industry. This article will explore how engineers take into account seismic design to improve the safety of bridges.
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Seismic Design: An Overview
Successful seismic design is crucial for ensuring the safety of populations using infrastructure worldwide. This design is three-fold: designers must take a multi-hazard approach, performance-based requirements must be established, and design teams must work collaboratively.
Earthquake forces are highly dynamic. Additionally, different buildings respond to an earthquake based on their own unique internal and external complexity: it is well-known that not all buildings collapse in a seismic event and receive differing amounts of damage, even ones next to each other.
Seismic modeling during the design stage must exceed minimum safety requirements to ensure that buildings can withstand worst-case scenarios. Furthermore, buildings must be designed with other natural and human-made hazards.
Factors that must be understood by design teams include torsion, damping, ductility, strength, stiffness, building configuration, and structural and non-structural building elements. This leads to better seismic design for both new and retrofitted buildings.
Seismic design principles and strategies are applied in a systematic approach by architects and engineers. Firstly, site conditions are analyzed, then seismic design objectives are established. Finally, appropriate structural systems are selected to be included in the building’s design.
The Application of Seismic Design to Bridges
Bridges, either road, pedestrian, or rail, are commonplace and essential infrastructural elements of urban and rural areas used daily by billions of people worldwide.
Whilst performance-based seismic design procedures are well-established for commercial and domestic buildings such as skyscrapers, there is a more limited application of these concepts to bridges. One type of applicable study is direct displacement-based design (DDBD.)
DDBD principle studies for bridge piers and entire bridges have been in existence since the 1990s. However, these procedures have some major disadvantages currently, such as not being deemed appropriate for final bridge design but are powerful tools for preliminary design stages.
Current codes have not formally adopted DDBD procedures due to their drawbacks, which severely limit the rational seismic design of bridges. This is urgently needed to protect against loss of life and widespread property damage.
Whilst far from perfect, however, current codes such as Eurocode 8 are deemed adequate. These codes have ample margins of safety, protecting new structures against collapse, and can help the design of robust bridges that can withstand seismic events.
Case Study: Using Seismic Dampers on a Cable-stayed Bridge
There are several examples of recent bridge designs which utilize seismic design to improve their robustness and ability to withstand earthquakes. Seismic dampers are one technology that can be applied during the bridge design and construction stages.
Hisgaura Bridge in Colombia is a cable-stayed bridge. Colombia lies near to the Malpeto Plate’s subduction zone, making seismic design of buildings and infrastructure crucial for the country’s government. The deadliest earthquake in Colombia’s history occurred in 1868, which claimed 70,000 lives.
Several rational design elements in the Hisgaura Bridge improve its safety during seismic events, with a noteworthy design element being the use of four fluid viscous damper units on the bridge’s south abutment. These seismic damper units have a capacity of 2,500 kN.
The dampers connect the abutment and the bridge deck, slowing movement by allowing free longitudinal displacement and dissipating seismic energy during an earthquake.
Real seismic event data for the local area was used during the design process to produce a response spectrum, with several configurations studied by the designers. Based on data modeling, viscous dampers were found to be the optimal choice for this essential bridge.
Seismic Design and Bridge Retrofitting
Retrofitting bridges, especially in areas prone to devastating earthquakes, is a key concern for governments worldwide and presents complex challenges. Utilizing seismic design during the process, existing bridges will meet ever-more stringent codes and regulations.
Much of the civil infrastructure network in locales such as the EU, USA, and Japan was constructed between the 1940s and 1970s and is fast approaching the end of its service life. Many bridges and viaducts were built to old codes that do not have the stringent requirements the construction industry of today must adhere to.
The optimal retrofit strategy differs from that of a new build bridge and is based on similar but unique analysis and evaluation of structures at risk of seismic activity. Any design strategy must also avoid disrupting traffic flow and normal bridge operations and ensure cost benefits whilst ensuring adequate seismic resilience.
Seismic retrofitting methods include steel jacketing, GFRP jacketing, transverse bracing or infill walls, span restrainers, seismic isolation, dampers, restrainers, bumper blocks, and spandrel wall strengthening. Different methods are utilized depending on bridge type.
The Future
Deadly earthquakes can occur suddenly and leave vast devastation in their wake, with recent disasters such as the Türkiye & Syria earthquake laying bare the inadequate design of buildings and infrastructure. Sadly, around 20,000 people typically lose their lives in earthquakes every year.
Rational and in-depth seismic design procedures that satisfy the latest codes are urgently needed for new builds and retrofits of essential structures such as bridges and viaducts in earthquake-prone zones.
Whilst undoubtedly an expensive undertaking, the fatalities caused by natural disasters and the economic burden of rebuilding urban areas demands that infrastructure is urgently brought up to standard by rational seismic design procedures.
More from AZoBuild: What are the Different Types of Bridge Foundations?
References and Further Reading
Skokandić, D et al. (2022) Seismic Assessment and Retrofitting of Existing Road Bridges: State of the Art Review Materials 15(7) 2523 [online] mdpi.com. Available at:
https://www.mdpi.com/1996-1944/15/7/2523
Gabor Lorant (2016) Seismic Design Principles [online] wbdg.org. Available at:
https://www.wbdg.org/resources/seismic-design-principles
Pedalta (website) Seismic Design of Bridges [online] pedalta.com. Available at:
https://www.pedelta.com/downloads/5/seismic-design.pdf
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