Ravi Jangid

Dynamic Analysis and Seismic Response Control of High-Speed Railway Bridges

India has announced several high-speed railway (HSR) corridors between major cities to meet the mobility needs of the growing population. The advent of faster trains in these new high-speed railways, along with increased demands on infrastructure, has made dynamic effects a key design factor for railway bridges. As the current HSR is being built on viaducts and bridges, the dynamic behavior of these structures for high-speed trains is an essential factor in their design to ensure the safe operation of trains. Also, few proposed HSR corridors traverse through moderate to high seismic zones (Zone III to V). Designing these corridors in the high seismic zone also brings new seismic challenges.

 Seismic Isolation of HSR Bridge

The first high-speed rail (HSR) corridor in India, built on viaducts and bridge structures, is currently under construction between Mumbai and Ahmedabad. This corridor passes through seismic Zone III, whereas future corridors are planned to be constructed in Zones IV and V according to Indian seismic codes. Achieving the seismic performance goals of HSR bridges through conventional seismic design measures in higher seismic zones is challenging and uneconomical. Seismic isolation technology, successfully deployed to ensure the seismic safety of highway and railway bridges in the past, may also be utilized for HSR bridges. However, HSR bridges are subject to stringent serviceability requirements, including limits on deck end rotations (in-plane and out-of-plane), mid-span deflection (in-plane), deck acceleration, and rail stresses. Hence, the implication of seismic isolation in HSR bridges brings significant challenges. As the isolator deformation increases transverse displacement of girder, the in-plane girder end rotation and rail stress are increased.

                   Fig. Numerical model of HSR bridge                                                                     Fig. FEM model of HSR bridge

 Impact Factor for HSR Bridge

As the operational speed for the current HSR bridge will be 320 km/hr, attention is required in the design of HSR bridges to consider the dynamic impact factor for such speeds. Existing codal provisions only provide dynamic impact factors up to 160 km/hr, which are not applicable for high speeds. Accurate estimation of the dynamic impact factor is essential to ensure safe design and satisfy stringent serviceability criteria. To estimate the impact factor, different types of simplified model representations are used, such as moving point-size mass, moving finite-size mass, and moving sprung mass over a beam. Additionally, the effects of different parameters on the dynamic impact factor are studied, such as span length, axle spacing, and the number of axles. The dynamic impact factor of the bridge is determined using numerical and finite element methods, and the results are compared.

                                       Fig. Multiple sprung mass                                                       Fig. FEM model of multiple finite size mass

Influence of strength dependent stiffness on seismic design 

The conventional method of seismic design of structures considers the lateral natural period to remain constant during the design process. However, the relatively newly proposed yield point spectra based method instead considers a constant yield displacement as the primary criteria. This article provides a critical comparison of both of these methods through case studies. The conventional method is found to be safe but uneconomic, while the yield point spectra based method is challenging to implement and earthquake data specific. A new iterative technique is proposed in this article, which is based on the methodology of the conventional analysis process but takes into account the main feature of the yield point spectra based design, i.e., to maintain constant yield displacement by varying strength and stiffness accordingly. It is anticipated that the proposed seismic design method will appeal to the designers due to its procedural familiarity and conceptual superiority. Further details can be referred from published Journal Paper .