Seismic Resistance Evaluation of Precast Prestressed Concrete Simply Supported I-Girder Bridge by Adopting Non-Linear Static Analysis of Pushover Method

Bridges serve as crucial connections between roadways and are crucial to the transportation sector. Relevant data indicates that concrete bridges make up over 90% of all bridges in China. A bridge is a construction that enables traffic to cross a barrier while keeping in touch with roads or railroads. Throughout history, bridges have played a crucial role in human civilisation and remain an essential component of any transportation network. They serve as essential links for both pedestrian and vehicle traffic and are an integral part of the transport system. The regulations and standards of various areas determine how bridges are classified. Bridge type selection is based on site characteristics, vendor preferences, site hydraulics, profile location, and construction cost. The density and volume of traffic loads, as well as the region that the bridge connects, determine the size of the bridge construction [1-8].

There are two sections to these bridge structural components. The first components are the drainage system, pavement layers, joints, deck, girders or beams, bearings, and security barrier. Superstructure was the name given to them. The foundations, piers, and pier caps made up the second section, which was referred to as the substructure. It is possible to build bridges across obstacles like rivers, roads, and railroads. Bridge constructions may be categorised based on the kinds of supports and materials used. Concrete, pre-stressed concrete, wood, and steel bridges are among the several kinds of bridges based on the materials used in their construction. Simply supported bridges and continuous bridges are two examples of the sorts of supports used in bridge constructions [9-12].

Over the last 20 years, several transportation agencies have made extensive use of precast/prestressed concrete I-girders. These girders offer various benefits, including the capacity to support multiple prestressing strands, a lower girder weight, increased construction stability, and a suitable platform for workers. Despite these benefits, the thin and broad top flange may be a drawback for deck removal since it is more prone to damage. The effect of deck removal on supporting girder performance is examined in this research [13, 14].

Presently, earthquakes are natural disasters that compromise the integrity and functionality of structures. The extent of damage an earthquake inflicts on structures depends on the type of building, the nature of the soil, the technology employed for seismic protection, and, importantly, the building's location. The effects of an earthquake on a specific region predominantly depend on the kind of soil in which the building's foundation is constructed, as earthquakes alter ground motion, leading to foundation failure. Earthquakes produce varying shaking intensities across different places, resulting in differential levels of structural damage in structures at these sites. An earthquake is the shaking of the Earth, or alternatively, the release of energy due to the movement of tectonic plates. This natural calamity has several detrimental impacts on the Earth, including ground shaking, landslides, rockfalls from cliffs, state changes, fires, and tidal waves [15-17].

Decisions for post-earthquake emergency work may be made based on a quick and precise evaluation of the damage to bridge structures after an earthquake. Nevertheless, the conventional methods for assessing structural damage are ineffective, subjective, and time-consuming. Every bridge should be inspected in order to get data on its structural sufficiency and condition. Every kind of bridge should have its damage inspected for the sake of user safety and, often, the local economy. Every component of the bridge is examined throughout the inspection process to determine if it is in excellent condition or requires strengthening or repair. Review reports, site conditions, required tools and equipment, traffic control (if required), and site survey are all included in the inspection plan, as well as structural inspection, which covers deck, superstructure, and substructure examination. Bridges are often regarded as a roadway network's most important component. Any post-earthquake bridge inspection program's main goal should be safety, but maintaining mobility is also crucial because the highway network is required to deliver emergency services, maintain security, provide access for relief and reconstruction, and help the economy recover from a catastrophic event. Seismic damage indices and advanced inelastic analysis programs may improve the assessment process's objectivity and accuracy, but only if they can be proven to be highly dependable. At the moment, these tools are not used enough for engineers to fully trust them [18-26].

Bridge structures must be assessed, strengthened, or repaired after an earthquake. Bridge structural members may be strengthened by adding more load-bearing materials, redistributing loading activities via induced deformation on the structure system, and replacing subpar or faulty elements with better ones. Numerous considerations determine which approach is best for fortifying and repairing the bridge's structural components. The elements include the kind and age of the building, its significance, the amount of strength that must be increased, the kind and extent of damage, the materials that are available, the cost and viability, and aesthetics [27, 28].

Knowledge of structural dynamics, earthquake engineering, and bridge engineering concepts are necessary for the seismic design and analysis of bridges. To make it easier to study, analyse, and build bridges that are vulnerable to seismic stresses, engineers use specialised software tools like CSi Bridge. The superstructure and substructure are often examined independently in bridge study. A grid composed of main girders, transverse diaphragms, and a deck slab usually makes up the superstructure. A grid of line segments makes up the deck slab. The word "girder" is often used in place of "beam" when designing bridges. Because girder bridges work well for building small to medium span bridges, they are often used in the transportation sector. Depending on its design and material, girder bridges are typically less than 50 meters long and cannot span more than 150 meters. Girder bridges are often used for small and medium span bridges; however, they are not the best option for lengthy spans. Steel or concrete may be used to build girders, with concrete girders being prestressed or strengthened [29-31].

Conclusions of this study are:

1. CSI-Bridge Ver. 25 was used to evaluate the seismic structural resistance of bridge structure type precast I-girder prestressed concrete bridge, by adopting pushover non-linear static analysis method, which was located in the center of Hilla City in the middle of Iraq. This bridge has important location in the street No. 60 in Hilla city to transport the traffic volume between capital of Iraq (Baghdad City) and southern provinces.

2. The force-displacement yielding point results revealed that the transversal yielding points are greater than the longitudinal yielding points, with a maximum yielding displacement of 0.02437m and a yielding force of 6121.893kN. This indicates that the seismic action on the transversal bents has little effect and that no damage will be done to the bents if they are subjected to this action alone. However, owing of the high yielding displacement (0.059911m) and yielding force (2352.46kN), the bents will have greater plasticity than elasticity and will be seriously damaged by seismic action in a longitudinal direction.

3. The performance points in transverse direction for all bents are equal and the performance point of shear force and displacement is (v=1205.6kN, D=0.00297m), the performance point of spectral acceleration and spectral displacement is (Sa=1, Sd=0.00297m), and the performance point of effective period and effective damping is (Teff=0.109, Beff=0.05), indicating that the seismic resistance performance of bridge bents in transverse direction is high. Whereas, in longitudinal direction the performance points are more and the performance point of shear force and displacement is (v=1205.77kN, D=0.0130m), the performance point of spectral acceleration and spectral displacement is (Sa=1, Sd=0.0310m), and the performance point of effective period and effective damping is (Teff=0.230, Beff=0.05), showing that the seismic resistance performance of bridge bents is small with low elasticity and stiffness and high plasticity. Therefore, bridge bents capacity cannot resist the demand.

4. The maximum seismic displacement of bridge bents in transverse direction is approximated same and it is 0.087m. Whereas, in longitudinal direction, bridge bents appear higher values of seismic displacement which is equal to 0.662m comparing with transvers direction. Therefore, the dangerous case will appear in the long of bridge structure.

5. The seismic resistance of bridge bents is not enough to resist the lateral horizontal action of earthquake and the stiffness and elasticity of bridge bents need to improve because of the bridge bents arrived to the plastic area and the damages will appear on the bents structure under effects of earthquake action. Therefore, this study suggests to improve the structural performance and seismic resistance of bridge bents by increasing the diameter of bridge piers by 1.6m, 1.8m, and 2m.

The results of yielding points and performance points values of yielding points were increased with increasing the piers diameter. And the seismic displacement decreased with increasing the piers diameter. Indicating that the elastic limit of bridge bents will increase and the bridge piers will resist the earthquake action according to increase in the stiffness and bearing capacity of bridge bents.