Compressive Bearing Capacity Experiment of Brick Walls Under Vertical Loads Considering the Mortar Compaction Process

Total floor areas of existing masonry structures in China cover 25 billion square meters. A significant proportion of these structures were classified as Grade C or D following a safety assessment. The compaction of masonry mortar occurs concurrently with an increase in vertical loads from upper-story walls and floor slabs. This condition may alter the actual compressive bearing capacity due to the compaction effect on the mortar of ground-floor walls. However, this effect is not addressed in the Chinese Code for Design of Masonry Structures. This study involved designing 12 brick walls using mortar with design strength grades of M2.5, M5, and M7.5, as determined by compressive testing. Each group simulated the ground-floor walls of four-, five-, and six-story masonry structures, considering the combined effects of vertical loads and mortar compaction, respectively. The results showed that, during mortar curing in ground-floor walls, the cracking load and ultimate load capacity of the wall models increased with progressively increasing loads from upper-floor walls and slabs. This is possibly due to the compaction effect on the mortar, which benefits the mortar density and the bonding performance between the mortar and brick. Due to the higher initial porosity and weaker bonding of low-strength mortar, the cracking load capacity of low-strength mortar walls under preloading increased significantly more than was observed in high-strength mortar walls. Conversely, owing to the high correlation between ultimate load and compressive strength, higher mortar strength had a more significant effect on the ultimate loads of the brick wall specimens under preloading. An increase in ultimate load capacity exhibited a linear relationship with the number of structural layers. This study can inform the safety assessment of existing masonry walls.