Experimental study of lightly reinforced concrete walls upgraded with various schemes under seismic loading

The 2011 off the Pacific coast of Tohoku Earthquake clarified the weakness of lightly reinforced concrete (RC) walls with opening (spandrel, wall pier, wing wall) in residential and government office buildings. Lightly RC walls are not a critical structural component, but their damage often impaired functions of buildings after earthquakes although it did not jeopardize safety. In order to avoid the suspension of building function due damage to lightly RC walls, it is very important to have proper upgrading schemes to improve the seismic performance. An experimental study was carried out on three full-scale wall specimens upgraded with various schemes to improve the seismic behavior of shear-type damage of lightly RC walls. Two specimens were upgraded using additional RC panel and ultra-high strength fiber reinforced concrete (UFC) panel to prevent shear failure. The other specimen had upgraded reinforcement details to increase shear capacity and flexural ductility. The test results were compared with past lightly RC wall test as a reference wall, which failed prematurely in shear reproducing the failure observed in the field. The changes of ultimate failure mode and the damage process were observed. Three upgraded specimens showed ductile and stable behavior with less damage compared with the reference wall. Adding RC and UFC panels improved the behavior of lightly RC wall and prevented crack formation at the central part of the wall panel. Increasing the amount of horizontal reinforcement and providing confinement in the boundary regions controlled the opening of crack width and made structure more ductile.