Effect of earthquake load pattern on the response of two-column bridge bents with in-fill wall retrofit

• PI: M. Saiid Saiidi
  
• Co-PIs: David Sanders, Ahmad Itani
  
• Research assistant: Christ Olaegbe
• Sponsor: California Department of Transportation
  
• Project monitor: Saad El-Azazy

Project summary

In-fill wall retrofit has been used in many multi-column bridge bents in California and elsewhere. Some of the in-fill walls are connected to the cap beam while others are stopped short of the bottom of cap beam with a 6-in. gap to facilitate construction.

The focus of the present study is on the walls with a gap at the top. A recent shake table test at the University of Nevada, Reno, revealed that in the retrofitted model the lateral load has to transfer through the cap beam, the top of the columns adjacent to the gap, the lower part of columns, and then to the wall.

In that test the model was subjected to a series of simulated earthquakes starting with small amplitudes and then gradually increasing amplitude in successive runs. The frame failed under a simulated Sylmar-Northridge record with input peak acceleration of 1.2g.

The objective of the current test is to study the lateral load path in an identical specimen under a strong simulated Sylmar record with target peak acceleration of 1.2g without subjecting the bent to other earthquake motions with lower amplitudes.

Test information

• Scale: 0.25
• Specified concrete compressive strength: 5 ksi in the frame; 4 ksi in the wall
• Specified grade of steel: Gr. 40 in the frame; Gr. 60 in the wall
• Earthquake record: Northridge-Sylmar 1994