Filling the Design Gap: Structural Performance of Locally Produced Hollow Sandcrete Blocks Under Combined Axial and Lateral Loading

Hollow sandcrete blocks are among the most widely produced walling materials in Nigeria, yet design guidance for their performance under combined axial compression and lateral loading, as experienced by ground-floor walls in multi-storey masonry structures, is largely absent from Nigerian standards. This study addresses this gap by experimentally characterising the structural performance of locally produced hollow sandcrete blocks under combined loading, using specimens sourced from manufacturers in Ibadan, Enugu, and Maiduguri, representing three geopolitical zones. Wall panels measuring 1,200 mm by 1,200 mm were constructed and tested in a biaxial loading rig, allowing simultaneous application of controlled axial precompression and increasing lateral load. Tests were conducted at three axial load levels corresponding to one, two, and three storey equivalent wall stress intensities. Failure modes, crack initiation loads, ultimate capacities, and out-of-plane deflections were documented. Results indicate a clear interaction between axial load and lateral resistance, with moderate axial precompression of 0.2 N/mm2 improving lateral resistance by 28 percent above the unloaded panel capacity, while higher axial loads of 0.5 N/mm2 reduced lateral resistance by 17 percent through amplified second-order effects. Blocks from Ibadan exhibited the highest compressive strength but lowest lateral load ductility, while Maiduguri blocks showed the greatest variability in geometric dimensions, affecting panel construction consistency. The study proposes interaction diagrams for use in the design of load-bearing sandcrete block walls under combined loading and recommends their incorporation into the forthcoming revision of NIS 87. Keywords: sandcrete blocks, combined loading, wall panels, masonry design, lateral load.