Effect of Foundation Depth on Cable Stayed Suspension Hybrid Bridges by Considering Soil Structure Interaction

The immense Infrastrutural development has induced a greatly increased desire and preference for long to super long . Cable supported bridges , comprising of Cable Stayed and/or Suspension Bridges generally constitute for Long to super long span bridges These are popular , also, due to its enhanced popularity owing to the aesthetics / marvelous architectural appearance. Supplimentarily,, owing to its flexibility besdides the complicities for analysis, design and execution(construction); the priority of such bridges are high. Cable Stayed Suspension Hybrid Bridge (CSSHB) has an added advantage additional bit of leeway in inclination over suspension bridge as well as cable stayed bridge. Herein, the response of the bridge as a whole ( inclusive of super and substructure , the foundation, and the soil underlying and/or surrounding the foundation plays a pivotal role in behavioral aspect of bridge thereby for its design and/or analysis. As Soil Structure interaction is an important element in the understanding of seismic structure failure, yet it is very complex to analyse.The damage caused with foundation of bridges in earthquake(s) has emphasized the importance of understanding SSI. Thus, Soil-structure interaction (SSI) analysis evaluates the collective response of the bridge structure / system. Here, an attempt is made to understand the SSI effect Cable stayed Suspension Hybrid Bridge (CSSHB) with H shaped Pylon ( bridge similar to that of Bridge at LingDing Strait China is considered in the study); for that FEM model is prepared with different foundation depth and different soil conditions(spring and dashpots ( Kelvin element) is adopted for Soil modeling for simulation of SSI effects), using SAP2000 software. The effect of SSI cannot be generalized as it purely is site specific. The depth of the foundation plays a vital role in bridge response. SSI effect increases time period of the structure by about 5-8 %. Bridge founded on stiff and soft clayey soil proves a more rigid connection as compared to sandy soil.