Seismic Assessment Of Reinforced Concrete Arch Bridge In Nepal:a Case Of 2015 Gorkha Earthquake

The numerous old arch bridges in the major highway of the higher seismic zone of Nepal are designed without or with insufficient seismic loads considerations inducing partial damage or collapse in the major seismic events.As an imperative infrastructure in the mountainous roads,their adequate seismic design is vital in disaster resilience.The recent Gorkha earthquake on 25 April 2015 in central Nepal triggered the performance assessment of arch bridges during the earthquakes as well as build back better on the formerly established guidelines.In this Investigation,we perform a detailed assessment based on the performance of numerical simulation of the reinforced concrete arch bridge with respect to the ground motions of Gorkha earthquake.Impact of the earthquake on the bridge and the loopholes in the guidelines of bridge seismic design in this region is investigated.The FE model of the existing bridge is created using Open Sees platform.Seven ground motions from different earthquakes around the world selected from the peer ground motion database are input to the FE model.The displacement capacity of the bridge is determined from pushover analysis.Non-linear time history analysis is carried out applying two orthogonal ground motions to the FE model at an incident angle with 15° increments,through 180° to determine the influence of the angle of incidence of ground motion on bridge response and check the sufficiency in provisions in present guidelines.Structural responses observed are near the capacity of the bridge,and the undermines the safety of the bridge under possible seismic hazards in this region.The result demonstrates that though the bridge did not damage but is vulnerable that implies the need for strengthening measures.However,seismic design force calculated from the revised code is reliable.Moreover,clear deficiency in the seismic design guidelines was seen needing special regard on the effect of ground motion incident angle.Structural responses such as stress-strain,axial compression force,displacement,and acceleration are found higher in other incident angles than conventional directions(0°,90°)with maximum increment up to 80 %.Further,the bridge is strengthening with CFRP,and the sufficiency of the retrofit intervention is evaluated through the nonlinear time history analysis of the retrofitted model.The evaluation shows a satisfactory result ensuring the safety of the bridge in possible seismic hazards in Nepal Himalayas.