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Reinforced concrete pile foundations are a common and efficient solution for constructing deepwater bridges that span large bodies of water, such as rivers, seas, or portions of oceans. Many of these bridges are situated in areas with significant seismic hazards. These structures are not only subjected to typical water loads, such as currents and waves but also to earthquake forces. The interaction between these water forces and the structure generates hydrodynamic forces on the submerged parts of the bridges. Thus, accurately estimating these hydrodynamic forces during earthquakes is crucial for ensuring the structural safety of deepwater bridges. This chapter aims to assess the structural response of pile foundation bridge piers when exposed to hydrodynamic forces during earthquakes, utilizing DIANA FE software and parallel computation technology. The study model incorporates the combined effects of currents, waves, and earthquakes, along with the nonlinear behavior of soil and concrete. Using Stokes’s fifth-order wave theory and Morison’s hydrodynamic pressure formula, the wave force was applied as a distributed load on the bridge’s pile foundation. The dynamic excitation characteristics of the pier under elastic conditions were analyzed, considering the influence of currents and waves.
Department of Building and Construction Techniques Engineering, Al-Mustaqbal University, Al-Hilla, Iraq
Ibtisam R. Karim
Civil Engineering Department, University of Technology, Baghdad, Iraq
Saleh I. Khassaf
Civil Engineering Department, University of Basrah, Basrah, Iraq
Ahmed Ashoor
Department of Building and Construction Techniques Engineering, Al-Mustaqbal University, Al-Hilla, Iraq
*Address all correspondence to: dr.riyadh.abdulabbas@uomus.edu.iq
1. Introduction
The growth of the social economy has led to an increased demand for urban transportation, prompting the construction of new broad-span bridges across rivers and canals. These bridge piers, often situated in deep water, must withstand challenging environmental pressures [1]. Completed projects have shown that deepwater pile foundations can meet safety and performance criteria, passing dynamic effect tests related to wind, dampness, and flow. However, their seismic stability, particularly under the combined influence of significant ground motion and wave movement during a massive earthquake, remains to be fully confirmed [2, 3, 4].
Deepwater pile foundations, located several meters below the sea surface, are susceptible to hydrodynamic pressure from water waves and currents, as well as vibration induced by ground motion. The additional moment on the pile results from hydrodynamic pressure due to water waves and currents, affecting the internal forces within the pile [5]. Research on the dynamic response of water structures under seismic and wave action has provided useful insights. For example, Yamada et al. [6] used random vibration to study an offshore structure’s dynamic response, representing waves with a Bretschneider power spectrum and ground motion with a Kanai power spectrum. Karadeniz [7] employed spectrum analysis to examine a three-dimensional structure’s response under deepwater wave and seismic motion, treating both as stochastic processes. Fukusumi et al. [8] simulated waves as harmonic and analyzed dynamic effects influenced by structural stiffness, flow, and fluid density.
Etemad et al. [9] considered pile-soil interaction using the Nogami model to analyze seismic reactions of pile foundations under two scenarios: wave and ground motion in the same and opposite directions. Abbasi and Gharabaghi [10] incorporated nonlinearity into a 3D model of an offshore platform to analyze wave direction’s impact on seismic response. Li et al. [11] used the additional mass method to create a pile-soil-pier-water model, examining dynamic water pressure and water level changes. He and Li [12] applied Morison’s formula and wave theory to investigate seismic responses under combined earthquake and wave actions. Song et al. [13] addressed the issue of seismic response by developing a simplified calculation method for hydrodynamic pressures exerted on slender structures during earthquakes. Their research provides a valuable tool for engineers to efficiently estimate these pressures, which is essential for the design and safety assessment of bridges exposed to seismic activity. This method facilitates the prediction and management of dynamic responses, ensuring that structures can withstand the combined impacts of seismic and hydrodynamic forces.
Furthermore, the seismic hazards specific to certain regions underscore the importance of such studies. Al-Taie and Albusoda [14] examined the earthquake hazard in Iraq, using the Halabjah earthquake as a case study. Their research highlighted the seismic risks prevalent in Iraqi soil and the implications for infrastructure resilience. Understanding these hazards is crucial for designing bridges and other critical structures to endure and perform under earthquake conditions. Together, these studies contribute to a deeper understanding of the challenges posed by seismic activities on slender structures and provide practical solutions to enhance the resilience of infrastructure in earthquake-prone areas.
Recent studies have highlighted various aspects of these interactions. For instance, Li et al. [5] conducted underwater shaking table tests to evaluate the performance of a sea-crossing cable-stayed bridge under the combined action of earthquakes and waves. This research underscores the complex nature of multi-hazard scenarios and their cumulative effects on bridge stability. Similarly, Wei et al. [15] focused on the impacts of wave and wave-current actions on bridge towers, providing valuable insights into the hydrodynamic forces and their implications for structural design. The dynamic behavior of bridge piers under extreme conditions, such as dam-break floods, was explored by Huang and Liu [1]. Their analysis revealed how different directions of impact influence the response of bridge piers, which is crucial for designing resilient structures against such catastrophic events. Another study by Huynh et al. [16] examined the time-dependent seismic fragility of offshore bridges considering scour and chloride ion corrosion, highlighting the importance of accounting for long-term environmental effects in seismic assessments.
Incorporating the most recent studies into the literature review is essential for staying at the forefront of research in the field of deepwater pile foundations and bridge stability. As new methodologies, technologies, and theoretical advancements emerge, they offer novel insights and solutions that challenge and refine existing models and practices. For instance, recent research by Chen et al. [17] introduces an advanced numerical model for analyzing the effects of combined wave and seismic actions on deepwater pile foundations, providing more accurate predictions of structural responses compared to earlier approaches. Similarly, Zhao et al. [18] investigated the dynamic response of bridge piers under complex multi-hazard scenarios, highlighting the limitations of traditional models and proposing new strategies for enhancing structural resilience. By integrating these contemporary studies, the literature review not only reflects the latest developments but also identifies ongoing challenges and opportunities for future research. This dynamic and updated approach ensures that the research remains relevant and continues to advance the field by addressing contemporary issues and leveraging the latest innovations [19, 20].
Xu and Cai [21] conducted numerical simulations to explore how lateral restraining stiffness affects the dynamic response of bridge decks to solitary wave impacts. Their research offers a valuable framework for enhancing bridge deck designs to better withstand wave forces. Additionally, Qu et al. [22] evaluated the vulnerability of coastal bridges in the New York City metropolitan area by examining Hurricane Sandy as a case study. Their findings underscore the importance of robust design and adaptive strategies to safeguard coastal infrastructure against future extreme storm surges and waves.
Despite these studies, two main issues persist: the oversimplification of structures that neglect pile-soil interaction and the inadequate or ignored fluid influence modeling. Updating the literature review to include the most recent studies would ensure that the research remains at the cutting edge, reflecting the latest advancements and discussions in the field. This is essential for maintaining the chapter’s relevance and authority. To accurately simulate the pier-piles-soil-water current-and-wave system under earthquake conditions, a 3D finite element model must be developed. This model should analyze bridge piers’ dynamic responses, including relative displacement, acceleration, shear force, moment responses, and hydrodynamic pressure coefficients.
This case study examines the soil-pile foundation-pier system of a multi-span bridge crossing the Songhua River in northeast China [23]. The bridge pier has a high rectangular cross-section, measuring 4.8 meters in length, 2.4 meters in width, and 15 meters in height. The pile cap features a square cross-section, standing 3 meters tall and 12 meters wide, supported by nine circular piles. These piles are 58 meters in height, with 12 meters extending above the scour line, a diameter of 1.8 meters, and a spacing of 4.5 meters.
The bridge deck, designed for two-way traffic, spans four lanes and measures 12 meters in width, with a top mass of 7.8 x 10^5 kg. The deck and pier are constructed from C35 concrete, which has Young’s modulus of 31.5 GPa. In contrast, the pile cap and piles use C30 concrete, with Young’s modulus of 28 GPa (Ministry of Communications of China [24]). Figure 1 provides a sketch of the bridge pier with its elevated pile cap support.
Figure 1.
Drawing of the selected case study: (a) geometry of the bridge; and (b) dimensions and details of the bridge members. All dimensions are in meters.
The soil stratification overlying the bedrock is depicted according to [25]. Table 1 lists the soil model parameters used in this study.
According to the study, the border effects on the dynamic response of structures are sufficiently eliminated in this article because the foundation border is sufficiently big to do so. Concrete is used for the dick, pier, cap, and piles, and the plastic-damage model of concrete is used to describe the nonlinear behavior of concrete [26].
The water-bridge interaction that occurs as a result of an earthquake is taken into account in the examination of the dynamic response of bridge structures. The water’s ability to travel is affected by the deformation or movement of these components, and the water’s forces acting on the bridge take the form of hydrodynamic pressure. In a matrix form, the following represents the governing equation of transient structural dynamics (Morison et al., 1950):
Mx¨t+Cx.t+Kxt=FHt+Mx¨gtE1
Where M,C, and K represent the structural mass matrix, damping matrix, and stiffness matrix, respectively. xt,x.t, and x¨t represent the structural relative displacement, velocity, and acceleration vectors, respectively. x¨gt is the acceleration vector of seismic ground motion. FHt is the fluid force vectors exerted on the bridge structure, including current-wave and earthquake-induced hydrodynamic forces.
The dynamic equation of motion can be represented as:
Where ρ is the water density; CM and CD are the coefficients of inertial and drag forces, respectively; V and A is the exposed face volume and area, respectively; x0̇ and x¨0 are the structure absolute velocity and structure associated acceleration, respectively; and u. and u¨ are the water velocity and water-associated acceleration, respectively.
The hydrodynamic force per unit height, P, from Eq. (2) can be presented as shown in Eq. (3):
P=CMρAu¨−x¨0+12CDρBu.−x0̇u.−x0̇+ρAx¨gtE3
Where B is the width of the exposed face.
The first term at the right of Eq. (3) denotes the inertia force, the second term denotes the drag force, and the third term denotes structural effect.
For coastal and offshore structures, the influence of hydrodynamic drag force, represented by combined current and wave actions, on the dynamic response of structures is very important [13, 27, 28]. Therefore, the Morison equation can be modified to account for currents by replacing ‘u.’ by ‘C+W′, where C is the water current speed and W is wave properties and as in Eq. (4):
P=CMρAu¨−x¨0+12CDρBC+W−x0̇C+W−x0̇+ρAu¨E4
The inertial coefficient is calculated by simplifying the inertia force presented in the first part of the equation (Eq. 4) as the following expressions (Eq. 5):
CM=MρHπ4D2u¨−x¨0E5
Where H is water depth and D is the diameter of the pile. As shown in Eq. (5), the hydrodynamic force is proportional to H and D2, and independent of the action of frequency and amplitude.
The drag coefficient is calculated by simplifying the drag force presented in second part of equation (Eq. 4) as the following expressions (Eq. 6):
CD=M12ρHDC+W−x0̇C+W−x0̇E6
As shown in Eq. (6), the hydrodynamic drag coefficient is proportional toH and D, and independent of the current and wave.
A lift force is also connected to the loading on a bridge’s submerged components, in addition to the drag force. Due to the orbital motion of the water particles, this lift force is perpendicular to the velocity vector and rotates around the axis of the members. The influence of the vortex shedding will be visible as noise in the measurements of the drag and inertia components since the magnitude, direction, and period of the lift force are unknown and cannot be applied to Morison’s equation [29, 30, 31].
A soil-piles-pier model, illustrated in Figure 2, was created using parallel computation technologies and the DIANA software. The model employs a dynamic plastic-damage approach to accurately represent the dynamic behavior of concrete bridge components, modeling them as an assembly of beam elements. For the soil, a viscous-plastic memorial nested yield surface model was utilized to capture its dynamic nonlinearity [32, 33, 34]. The soil is modeled as an assembly of 8-node solid elements, assumed to be saturated and undrained during an earthquake, with a Poisson’s ratio of 0.49.
Figure 2.
Finite element mesh of the model.
The foundation soil model covers an area of 1000 meters by 1000 meters by 50 meters. To address the effects of region truncation on wave propagation, a 3D time-domain viscoelastic artificial boundary was applied. The soil layer corresponding to the bedrock surface was selected based on a shear wave velocity exceeding 500 m/s. The model includes 2242 piles, distributed across beam elements, and comprises a total of 2280 nodes, capturing the dynamic properties under cyclic loads.
Figure 2 presents the finite element mesh of the entire system, showcasing the detailed configuration and distribution of the soil, piles, and pier components.
The exact dynamic response of the bridge pier to the combined effects of earthquake-induced ground motion, waves, and water currents was simulated. The 100-year current-wave characteristics of the field area are detailed in Table 2. Figure 3 depicts the simulation setup and boundary conditions applied to the model. In the simulation, only the transverse (y-axis) direction of the bridge was considered for current and wave water loads. All simulations began with a water level of 12 meters.
Return period (Year)
Current velocity (m/sec)
Wave height (m)
Wave period (sec)
Wave length (m)
Wave velocity (m/sec)
100
2.5
0.5
4.5
8.5
4.5
Table 2.
Current-wave parameters.
Figure 3.
Distributed impact loads along the build model.
By simulating these interactions, the model provides insights into how the bridge pier behaves under complex dynamic conditions, which is essential for understanding its structural resilience and for informing effective design and safety measures. It is possible to determine that CD= 1.2, CM= 2. 0, and CA= 1.0. in accordance with the Environment Conditions and Load Standard.
In this chapter, the acceleration-time history of the Halabjah earthquake, which struck Baghdad on November 12, 2017 [35], was selected as the input seismic excitation to evaluate the structural response of the model. The earthquake’s original accelerogram, with a peak ground acceleration (PGA) of 0.11 g at 41.5 seconds, spans a total ground excitation time history of 200 seconds. Figure 4 illustrates the acceleration-time histories for the longitudinal and transverse horizontal components of this seismic event. To investigate the impact of different earthquake motion amplitudes, three peak acceleration levels (0.05 g, 0.10 g, and 0.20 g) at a frequency of 20 Hz were considered. The finite element model was analyzed under deepwater conditions for the combined loads of current-wave and earthquake, taking into account the imposed boundary conditions.
Figure 4.
Acceleration-time history of Halabjah earthquakes in Baghdad.
The analysis of the structural stability of the bridge pier begins with evaluating the displacement relative to the bottom of the pier and the absolute acceleration of the pier top. These metrics are crucial for understanding the pier’s seismic response and overall structural stability.
The displacement of the pier top relative to its bottom is a critical factor in assessing earthquake-induced deformation in the pier’s seismic design. Similarly, the absolute acceleration of the pier top significantly influences deck motion under bedrock ground motion. Figure 5 presents the relative displacement of the pier and the peak acceleration resulting from earthquake ground movements at different peak ground accelerations (0.05 g, 0.10 g, and 0.20 g), with and without the influence of current and wave.
Figure 5.
Relative displacement and acceleration responses of the pier.
Hydrodynamic pressure significantly alters the pier’s reactivity, reaching its peak near the top of the pier and affecting the relative peak displacement response. The data indicate that the peak relative displacement of the pier top increases gradually as the hydrodynamic pressure changes the pier’s reactivity. The relative peak displacement under the combined current-wave and earthquake actions is greater than under earthquake alone. This increase in displacement response decreases with higher input accelerations from 0.05 g to 0.20 g. Specifically, with an input acceleration of 0.05 g, the peak relative displacement is more pronounced due to the current-wave impact, while for input accelerations of 0.10 g and 0.20 g, the effect of the current wave diminishes, as shown in Figure 5(a).
Moreover, the bottom of the pier is subjected to greater earthquake forces, leading to concrete cracking and the formation of a plastic hinge. This reduces the flexural rigidity of the pier’s bottom section, causing a decrease in acceleration and an increase in relative displacement. The pier’s acceleration increases in the upper area due to the higher inertial impact of the structure. However, the acceleration at the top and bottom of the pier remains relatively homogeneous, as depicted in Figure 5(b). In conclusion, the analysis shows that the acceleration at the top of the pier induced by the combined action of current waves and earthquakes is minimal compared to that under earthquake action alone.
6.2 Internal forces and plastic hinge formation
During an earthquake, the pier can sustain damage and develop a plastic hinge when the internal force response at a specific location exceeds its bearing capacity. In a single-column pier, the potential plastic hinge zone is typically located at the lowest portion of the pier. This chapter compares the shear force and moment at the pier bottom under earthquake action alone and under the combined actions of earthquake and current-wave impacts to analyze the effect on the pier’s internal forces.
Figure 6 depicts the maximum shear force and moment response of the pier. It clearly illustrates that the shear force at the pier bottom is significantly greater than in the higher sections (Figure 6a). The substantial force acting on the pier bottom increases the likelihood of plastic hinge formation in this area during an earthquake. Additionally, the moment at the pier bottom within the first 6 meters is notably higher than at other locations along the pier (Figure 6b).
Figure 6.
Shear force and moment responses of the pier.
When subjected to a 0.05 g acceleration, the current-wave impact on the pile body is negligible. However, when the earthquake excitation increases to 0.10 g and 0.20 g, the forces acting on the pier body become more pronounced, indicating a visible increase in internal force responses under these conditions [36, 37]. This highlights the significant role that combined earthquake and hydrodynamic pressures play in the structural behavior and potential damage mechanisms of deepwater bridge piers.
During an earthquake, the plastic hinge area is readily produced at the bottom of the piers, where hydrodynamic pressure can have a significant impact. Therefore, for the seismic design of piers in deep water, it is crucial to account for the current-wave effects [38]. Several measures can be implemented to enhance the seismic performance of the piers under these conditions: Firstly, improved Connection of Longitudinal Steel: Extending the pier longitudinal steel to better connect with the cap or capping beam ensures that the strength of the steel is fully utilized, thereby improving the structural integrity and resilience of the pier under seismic loads. Secondly, use of Confining Stirrups: Implementing round or spiral stirrups with small spacing can effectively constrain the horizontal deformation of the core concrete. This confinement helps to maintain the structural integrity of the concrete under the combined actions of seismic and hydrodynamic forces.
By integrating these measures, the effects of hydrodynamic pressure can be more effectively addressed in the seismic design of deepwater bridge piers, thereby enhancing their stability and performance during earthquakes.
The Kd, Ka, Ks, and Km shows the hydrodynamic pressure influence coefficient of the relative displacement, acceleration on the top of the pier, and the shear force, moment at the bottom of the pier separately. Therefore, the influence of hydrodynamic pressure on the peak dynamic response of bridge piers tends to emphasize peak acceleration and the interaction with earthquake waves, even though this influence can be less straightforward to discern. Across various parameters, the average impact reveals distinct trends:
Relative displacement experiences minimal alteration due to hydrodynamic pressure, indicating that its influence is negligible in comparison to other factors. In contrast, acceleration at the top of the pier shows a significant response, with hydrodynamic effects contributing up to a maximum of 11%. This underscores the substantial impact of currents and waves on the pier’s acceleration dynamics during seismic events.
Meanwhile, the influence on shear force and moment at the bottom of the pier is more modest, averaging around 4%. Although these forces are affected by hydrodynamic pressures, the magnitude of their alteration remains relatively consistent across different scenarios. This consistency suggests that while hydrodynamic factors do affect shear and moment, their overall effect is less pronounced compared to acceleration.
These findings underscore the critical role of earthquake ground motion characteristics in determining how currents and waves influence the dynamic behavior of bridge piers. By understanding these interactions, engineers can better design and reinforce piers to withstand the combined challenges of seismic activity and hydrodynamic forces, ensuring robust structural performance in deepwater environments.
The findings from the structural stability analysis of bridge piers under combined seismic and hydrodynamic forces reveal important insights for enhancing engineering practices. By delving into the practical applications of these findings, we can significantly influence engineering practices, safety standards, and bridge design principles in seismically active coastal regions.
Engineers should incorporate hydrodynamic pressure considerations into seismic design models. This involves using computational fluid dynamics (CFD) simulations to estimate hydrodynamic forces and integrating these forces into structural analysis software. The application of improved longitudinal steel connections and the use of confining stirrups can significantly enhance the strength of bridge piers. This will require revising standard reinforcement detailing practices to include these techniques as mandatory for coastal bridges.
Engineers should regularly evaluate the dynamic responses of bridge piers to varying peak ground accelerations. This can be achieved by implementing advanced structural health monitoring systems that continuously measure and analyze pier responses during seismic events and storms. By understanding these dynamic responses, engineers can adjust design parameters such as damping ratios and natural frequencies to improve the performance of bridge piers under combined loading conditions.
Design codes should be updated to include guidelines for evaluating the combined effects of seismic and hydrodynamic forces. This means specifying design loads that reflect the interaction of these forces, ensuring that safety margins are adequate for both seismic activity and wave impacts. Transitioning from prescriptive to performance-based design codes can provide more flexibility in achieving safety objectives, allowing for innovative solutions tailored to specific site conditions.
Safety standards should mandate regular inspections that specifically look for damage caused by seismic and hydrodynamic forces. This can involve using non-destructive testing methods such as ground-penetrating radar and ultrasonic testing. Maintenance protocols should address identified vulnerabilities, including corrosion of reinforcement due to seawater exposure and structural damage from seismic activity. This ensures the long-term durability and functionality of bridge piers.
Engineers should adopt a performance-based design approach that sets specific objectives for pier performance under combined loading conditions. This includes defining acceptable levels of damage and functionality post-event. Exploring solutions such as seismic isolation systems, which decouple the pier from ground motion, and energy-dissipating devices, which absorb and dissipate energy from both seismic and hydrodynamic forces, can enhance resilience.
Future research should focus on developing advanced simulation techniques that accurately model the interaction between seismic and hydrodynamic forces. This includes using multi-physics software that can simulate complex interactions. Conducting field studies to validate simulation results and refine design criteria is essential. This can involve monitoring the performance of existing coastal bridges during seismic and storm events to gather real-world data.
By expanding on these practical implications, we can ensure that the research not only advances theoretical knowledge but also provides tangible benefits for practitioners and policymakers, ultimately leading to safer and more resilient coastal bridge structures.
8. Expanding the scope of case studies or simulations
Incorporating a broader range of case studies or additional simulations is essential for gaining a more nuanced and comprehensive understanding of how seismic and hydrodynamic forces impact bridge structures in different settings. By extending the scope beyond a single case study or simulation, researchers can explore how various geographical and environmental factors influence the behavior of bridge piers under combined seismic and hydrodynamic loads. This expanded approach not only enriches the research findings but also improves the generalizability of the results, making them applicable to a wider range of real-world scenarios.
8.1 Understanding variations across different conditions
A single case study or simulation often reflects a specific set of conditions, such as the seismic activity levels, hydrodynamic forces, and environmental settings present at that location. By broadening the range of case studies, researchers can examine how these factors vary across different regions and conditions. For instance, bridges in coastal regions might face different wave patterns, tidal ranges, and seismic risks compared to those in other locations. By including a variety of case studies, researchers can identify patterns and differences in bridge responses, such as how varying intensities of waves and different seismic magnitudes affect the stability and performance of bridge structures. This approach helps to uncover potential vulnerabilities and design challenges that may not be evident from a single case study.
8.2 Enhancing the generalizability of findings
Expanding the scope of research through diverse case studies and simulations enhances the generalizability of the findings. While a specific study provides valuable insights into the conditions of a particular site, a broader approach allows for the examination of how well the results apply to different environments and scenarios. For example, by analyzing bridge piers under various earthquake magnitudes, hydrodynamic pressures, and geographical settings, researchers can develop more universally applicable design principles and safety guidelines. This broader perspective helps to ensure that the design recommendations and engineering practices developed from the study are robust and effective across a range of conditions, rather than being limited to the specifics of one case.
8.3 Application to design and safety standards
The insights gained from a more comprehensive set of case studies can directly inform the development of improved design standards and safety protocols for bridge construction and maintenance. For example, if the expanded research reveals that certain design features perform well across different conditions, these features can be incorporated into standard design practices. Conversely, if the research uncovers new challenges or limitations, these findings can lead to revisions in safety standards and design guidelines. Ultimately, a broader scope of research helps engineers and policymakers develop more effective and adaptable strategies for designing resilient bridge structures capable of withstanding diverse environmental and seismic conditions.
9. Practical implications for bridge design and maintenance in seismic zones
9.1 Design modifications for seismic resilience
The research findings emphasize the importance of incorporating specific design modifications to enhance the seismic resilience of bridges in seismically active zones. These modifications aim to address the combined effects of seismic forces and hydrodynamic pressures on bridge piers and other structural elements. Here are several design modifications based on the study’s results:
Extend the longitudinal steel reinforcement within bridge piers to improve the connection between the pier and the cap beam. By increasing the length and strength of the steel reinforcement, engineers can better transfer seismic forces from the pier to the cap beam, reducing the risk of structural failure. This modification helps to maintain the structural integrity of the bridge during strong seismic events and prevents premature damage.
Implement round or spiral stirrups with smaller spacing in the core concrete of bridge piers. These stirrups provide additional confinement to the concrete, enhancing its ductility and strength under seismic loads. This design feature helps to manage deformation and reduce the likelihood of cracks forming in the concrete, which can weaken the structure during an earthquake.
Incorporate seismic isolation devices such as elastomeric bearings or sliding bearings into bridge designs. These systems absorb and dissipate seismic energy, reducing the forces transmitted to the bridge structure. Seismic isolation systems can help to limit the amount of movement and damage experienced by the bridge during an earthquake, improving its overall resilience.
Design piers with features that address the effects of hydrodynamic pressures from currents and waves. For example, engineers can use tapered or streamlined pier shapes to reduce drag and minimize the impact of wave forces. Additionally, designing for the worst-case hydrodynamic scenarios ensures that piers can withstand both seismic and wave-induced loads.
These design modifications are directly informed by the study’s findings and provide practical solutions for engineers to enhance the seismic performance of bridges in seismic zones.
9.2 Maintenance strategies for long-term durability
In addition to design modifications, effective maintenance strategies are crucial for ensuring the long-term durability and safety of bridges in seismically active areas. The following maintenance practices are recommended based on the study’s insights:
Implement a routine inspection schedule to assess the condition of bridge piers and other critical components. Inspections should focus on detecting signs of damage such as cracks, deformations, and corrosion. Regular assessments help identify issues early and prevent minor problems from escalating into significant structural failures.
Install monitoring systems to measure hydrodynamic pressures and currents affecting the bridge piers. These systems can provide real-time data on environmental conditions and help engineers evaluate how well the bridge is performing under current and wave forces. Data from these systems can guide maintenance decisions and inform future design improvements.
For bridges equipped with seismic isolation systems, regular maintenance of these devices is essential. Engineers should inspect isolation bearings for wear and tear, ensure that damping mechanisms are functioning correctly, and perform necessary repairs or replacements. Maintaining these systems ensures they continue to provide effective protection against seismic forces.
As new research findings become available, maintenance protocols should be updated to incorporate the latest knowledge and best practices. Staying informed about advancements in bridge engineering and applying new insights can lead to improved maintenance strategies and enhanced bridge performance.
These maintenance strategies help to ensure that bridges remain safe and functional over time, addressing both existing and emerging challenges in seismically active regions.
9.3 Development of comprehensive design guidelines and standards
The research findings also highlight the need for the development of comprehensive design guidelines and safety standards for bridge construction in seismic zones. These guidelines should include:
Detailed Design Criteria: Develop detailed design criteria that incorporate the combined effects of seismic forces and hydrodynamic pressures. Guidelines should specify design requirements for structural elements, including the use of specific materials, construction techniques, and safety factors.
Best Practices for Seismic and Hydrodynamic Design: Establish best practices for engineers to follow when designing bridges for seismic and hydrodynamic forces. These practices should be based on the latest research findings and include recommendations for addressing common design challenges.
Guidance for Risk Assessment and Management: Provide guidance on how to assess and manage risks associated with seismic and hydrodynamic forces. This includes methods for evaluating potential risks, developing risk mitigation strategies, and preparing for emergency response in the event of a seismic event.
By developing these guidelines and standards, engineering practices can be standardized to ensure that all new bridge projects meet high safety and performance criteria.
This study thoroughly investigated the dynamic response of pile foundation bridge piers under the combined influence of earthquake ground motions and hydrodynamic pressures from currents and waves. Utilizing the Halabjah earthquake excitation, Morison hydrodynamic pressure formula, and nonlinear models of soil and concrete, the research comprehensively assessed the structural behavior of bridge piers subjected to these complex loading conditions. The following conclusions were drawn:
The study revealed that under combined current-wave and earthquake actions, the pier’s relative peak displacement was significantly higher compared to conditions with only earthquake forces. This underscores the substantial influence of hydrodynamic pressures on the displacement dynamics of bridge piers during seismic events.
The analysis indicated that while hydrodynamic effects had a noticeable impact on acceleration, particularly at the pier top, the magnitude of this influence was less pronounced compared to relative displacement. Hydrodynamic pressures contributed up to an 11% variation in acceleration, highlighting their role in modifying the dynamic response but indicating a more moderate influence compared to displacement.
Hydrodynamic pressures also affected the shear force and moment at the bottom of the pier, with an average influence of around 4%. This suggests that while these forces are influenced by currents and waves, their overall alteration remains relatively consistent across different scenarios.
The study established a clear connection between the characteristics of earthquake ground motions and the effects of current-wave loads on the pier’s dynamic response. This relationship underscores the importance of considering seismic and hydrodynamic interactions in the design and analysis of pile foundation bridge piers.
It is imperative to incorporate current-wave effects into the seismic design criteria for pile foundation bridge piers spanning seas and oceans. Neglecting these hydrodynamic forces can compromise the safety and reliability of such structures during seismic events.
Further research is needed to enhance the understanding of hydrodynamic pressure effects on bridge dynamics. Future studies should focus on refining models to better simulate the complex interactions between structural systems and random actions such as currents, waves, and earthquakes. This will improve the accuracy and reliability of dynamic response predictions and seismic analyses for bridge structures.
Acknowledgments
The corresponding author extends his thanks to Al- Mustaqbal University for the financial support for the research.
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Written By
Riyadh Alsultani, Ibtisam R. Karim, Saleh I. Khassaf and Ahmed Ashoor
Submitted: 18 June 2024Reviewed: 20 June 2024Published: 03 October 2024
Open access peer-reviewed chapter - ONLINE FIRST
