Arching in Masonry Walls Subjected to Earthquake Motions

Nonreinforced masonry walls, used as infill panels in concrete frames, are vulnerable elements of buildings when subjected to earthquake loading. Gaps develop at the top of the walls, shortly after construction due to shrinkage of the mortar, and in the event of an earthquake the walls cannot withstand the out-of-plane forces and collapse due to the lack of adequate binding at the top. However, walls confined between rigid supports can display very high resistance to out-of-plane forces through the development of arching action in flexure. Therefore it is recommended, in order to achieve an optimal load-bearing behavior, or rather stability, that the remaining gap at the top of a wall is filled with nonshrinkable mortar some days after the construction of the wall. Shaking table tests, with full-scale walls subjected to transient seismic loads were carried out in order to study the out-of-plane behavior in relation to the characteristics at the top of the walls. A comparison of the measurements with the results from finite element calculations showed a satisfactory correlation.