One of the major components of transportation systems and networks are bridgernstructures, and earthquake is one of the natural effects which cause catastrophic damage tornbridge structures and leads to the transportation networks to be malfunctioned. Therefore,rnbridge structures should be functional before and after earthquake because these bridgesrnserve for emergency during and after the earthquake.rnDifferent parameters may have different effect under different seismic loadings;rntherefore, their effect need to be assessed on seismic performance of the bridges. Undesiredrnfailures can be prevented through a comprehensive understanding of dynamic load naturernand bridgeâ€™s structural response while keeping the cost-safety balance. Many structuralrnparameters such as geometry of the bridge and properties of the material of the bridge affectrnthe dynamic response of the bridges. Furthermore, the bridge structural response could bernsignificantly changed by characteristics of dynamic load. In most cases, involvement ofrnnumerous parameter and complexity require the designer to investigate the bridge responsernvia numerical study.rnParametric studies were carried out using probabilistic approach for 2-spanrnprestressed I girder bridges. The effects of bridge deck thickness (superstructure mass),rnconcrete compressive strength, reinforcement steel yield strength of and skew angle on thernbridges seismic response were studied using nonlinear time history analyses (probabilisticrnapproach). The effect of the variation of these four parameters on the response of thernstructure is analyzed to determine their effect on seismic performance of the bridge.rnComputer software, CsiBridge 20 is used to analyze the bridge.rnFor this thesis, a 2-span prestressed I girder bridges with integral abutments isrnselected and a detailed inelastic three-dimensional model is created for bridges withrndifferent parameters. A set of nonlinear time history analysis (NTHA) for a ground motionrnsuite has been performed using these created models to compute the fragility analysis ofrnthe bridges. Modified bridges of the original bridge are modeled by varying one of eachrnparameter and simulated repeatedly for pushover analysis and assessment of seismicrnfragility of modified models. The above parameters affecting fragility curves and seismicrndemands of these bridges have been examined using the outcomes from fragility analysis.In probabilistic seismic evaluation one of the popular tools is fragility curves. For arngiven seismic intensity level the probability of bridge reaching or exceeding a particularrndamage level is given by fragility curves which are conditional probability statements. Inrnthis study, different parameters of a two-span continuous prestressed girder concrete bridgernhave been assessed for seismic performance analysis. Results of dynamic analysis of thernprestressed girder bridge subjected to suit of ground motions is used to develop analyticalrnfragility curves.rnIt is observed that some parameters significantly affect fragilities, but not others; thernskew angle and yield strength of reinforcement steel are the most influence parametersrnaffecting the system fragility while the concrete compressive strength and bridge slab deckrnthickness (superstructure mass) have a very small influence on the bridge.