Seismic performance of bridges designed according to AS 5100

Bridges are the critical components of a nation’s transportation system, as closure of an important bridge in the event of an earthquake can disrupt the total transportation network. In Australian standard for bridge design, ASBD (AS 5100-2004), consistent with other major bridge design codes (for example, AASHTO in the USA and CAN/CSA-S6 in Canada), bridges are classified according to their importance levels. The anticipated performances (performance objectives) of the bridges in small to moderate (Return Period, RP= 100 years), design level (RP= 500 years) and large (RP= 2500 years) earthquake events have been specified in major bridge design codes, although not explicitly stated in ASBD for bridge design. It is believed that similar performance objectives should also be anticipated for the bridges designed for different importance levels according to ASBD. However, there appears to be no requirement in the code to check whether such multiple performance objectives have been achieved for the designed bridges. Also, no engineering parameters have been assigned to the anticipated performance objectives. This paper correlates seismic performance objectives (both qualitative and quantitative) with engineering parameters which are based on the data collected from available experimental investigations and field investigations from recent earthquakes. A simple methodology has been developed and validated with experimental results for assessing the performance of bridges designed according ASBD. It has been found that the design rules prescribed in ASBD do not guarantee that intended multiple seismic performance objectives can be obtained. Implicit seismic design rule in the form of Performance Response Modification Factor (PRMF) has been outlined for performance based seismic design of bridges. The implicit design rule has the potential for further development in order to be incorporated in the next generation ASBD.