Bridges can be constructed with irregular pier height due to variation of foundation pier height between initial design height and actual pier height at the construction site. And by this condition, the distribution of pier stiffness is affected. Consequently, the seismic performance of the bridge can be affected. So, in this study, the seismic performance of irregular pier height bridges are evaluated on selected Melkademo River. Three types of bridges are considered such as, simply supported bridge (SSB), continuous bridge (CB) and monolithic bridge (MB), to differentiate which bridge is more seismically vulnerable, to identify critical bridge type for variation of pier height condition, to understand the seismic demand distribution, to suggest a technical measurement that should be taken for variation of pier height and to prepare interaction chart for circular pier. The seismic evaluations are performed using modal response spectrum dynamic analysis and pushover analysis in CSiBridge 2018 software. The results are mainly focused on the deflected mode shape, base shear force, fundamental time period, pier forces and pier displacements. From the result it is obtained that, simply supported and continuous bridge are more seismically vulnerable than monolithic bridge. However, continuous bridge is relatively less seismically vulnerable compared to simply supported bridge due to their continuity of super-structure that gives a better stability and strength. On the other hand, simply supported bridge and continuous bridge are more critical than monolithic bridge for variation of pier height condition. Since, the support condition of pier in simply supported and continuous bridge act as cantilever, such kind of bridges are highly sensitive for variation of height than piers of monolithic bridge, which is considered as fixed –fixed ended. By definition, critical means the rate of change of seismic response is high on specified bridge type. And the critical bridge type should get more attention during the design and construction in order to reduce the seismic vulnerability due to variation of pier height. In addition, when bridges are supported by irregular pier height, non-uniform seismic demands and performances are distributed. And shorter pier become more seismic vulnerable than longer pier because it is subjected to higher seismic moment, shear force and it have limited ductility capacity. Another important result observed on variation of pier height, when pier height is decreased, it become more stressed on its pier but other pier become less stressed and when pier height is increased, it become less stressed on its pier but other pier become more stressed. In addition, nondimensional -interaction charts are prepared for circular reinforced concrete pier section.