Published: December 2012 | Category: Activity management , Research programme , Research & reports | Audience: General
Bridge damage, especially due to pounding and unseating at expansion joints has been observed in almost all major earthquakes. It is the result of large relative displacements of girders, in excess of the designed gap width and seating length.
Research shows that relative displacements of neighbouring bridge segments depend on the fundamental frequencies of the adjacent structures, spatially varying ground motions and soil-structure interaction (SSI).
To evaluate the significance of the influence of these factors, three identical bridge models with a scale ratio of 1:125 were tested using shake tables. Another study involved one of these models pounding with movable abutments.
Lastly, another scaled model of 1:22 was field tested to study the SSI effect in comparison with the fixed-base results. The scaled models were designed in accordance with the principles of similitude.
The results obtained by isolating and varying each individual influence factor are presented and discussed in this report. The results show that the spatially varying effect of ground motions increases the maximum relative displacements and pounding forces between adjacent bridge girders even if adjacent segments have the same fundamental frequency.
Recommendations are made for new bridge design which will take into consideration the spatially varying effect of ground excitations.
Keywords: fundamental frequency, NZTA Bridge manual, relative displacement, seismic design, spatially varying ground excitations
