ارزیابی عملکرد لرزه ای پل قوسی RC
Abstract
1- Introduction
2- Seismic performance analysis
3- Dynamic analysis results
4- Parametric analysis
5- Conclusion
References
Abstract
Reinforced concrete (RC) arch bridges usually sustain remarkable damage from strong earthquakes. To comprehensively investigate the seismic performance of an RC arch bridge, a benchmark RC arch bridge was modeled with the ABAQUS software, and the seismic performance in the longitudinal and lateral directions was determined at different earthquake intensities. In this paper, the seismic responses, i.e., the mid-span drifts, plasticity development, and N-M interactions at the springing, etc., are discussed. The sectional safety factor is proposed to quantitatively describe the damage degree of the springing section under longitudinal excitation. According to the results, this factor successfully indicated the damage status at the springing, and was consistent with the strain development and the N-M interactions. With regard to the lateral excitation, the current design did not consider the contribution from the brace beams. The coupling ratio (CR) is proposed to quantitatively calculate the coupling effect on the two arch ribs from the brace beams. Different CRs were tested to enhance the lateral seismic performance. Finally, the recommended CR was derived.
Introduction
An arch bridge is an effective structure to make full use of the high compressive strength of concrete and masonry material by transferring the gravitational load into the axial force in the main arch [6]. With the development of materials and construction techniques, the amount and scale of arch bridges increased remarkably. However, reinforced concrete (RC) arch bridges are built to cross deep valleys in mountainous areas and are exposed to severe earthquake risk. During the 2008 Wenchuan earthquake in China, more than 100 arch bridges incurred different degrees of damages, with several bridges collapsing completely [7,4,15]. Moreover, extremes were observed in the earthquake damages to RC arch bridges. In other words, serious damage and the complete absence of damage were quite common in the RC arch rib, while instances of moderate damage were rare. The rehabilitation of damaged RC arch bridge was time-consuming and costly [12]. The earthquake hazards attributed to RC arch bridges are still alarming, and a deep investigation into the damage mechanism of the RC arch bridge is needed. Alvarez et al. [1] evaluated the seismic performance of an RC arch bridge by using numerical models with plastic hinges in the SAP2000 software, and the seismic performance was indicated by the evolution of plasticity in critical sections. The plastic hinge models were usually generated under a constant axial force, and no deterioration at the springing was considered. However, the axial force in the arch rib was not constant during the earthquake. Zanardo et al. [16] conducted the seismic performance evaluation of the short span concrete arch bridge, which revealed that the axial force of the springing was significantly affected by the vertical components of the ground motions. Under a fluctuating axial force, the sectional plastic hinge model could not deliver the actual seismic behavior of the arch bridge. During an earthquake, a 40% increase in the axial force can be obtained, and may lead to a significant decrease in the rotation capacity of the springing [13]. Moreover, the coupled axial force and moment effect should be considered when dealing with a large axial force.