Experimental characterization of compressive and shear mechanical properties of field-replicated Kathmandu clay-brick masonry

This study quantifies the strength and stiffness of locally built Kathmandu clay-brick masonry through compression and diagonal-shear tests on field-replicated prisms, component-level strain-gauge tests on bricks and mortars within Kathmandu, and numerical homogenization to connect constituent and assembly behavior. The experimental results show that as-built prism secant moduli and compressive strengths are substantially lower than widely used codal estimates for clay-brick masonry. An empirical fit to the prism data yields the relation $$\:{E}_{m}=125\times\:{f}_{m}$$ (N/mm²), indicating a pronounced discrepancy with the commonly applied IS-based multiplier within Kathmandu. A calibration factor of 0.60 is proposed to reconcile homogenized values with measured prism stiffness, if prism tests are not feasible, for masonry work within Kathmandu. The findings identify mortar quality, joint thickness, interface compliance, and workmanship as primary drivers of the reduced assembly stiffness, and suggest that plastering markedly increases in-plane shear capacity for the tested details. Practical recommendations include using prism-derived $$\:{E}_{m}$$ for global assessments or applying the calibrated reduction when only component data are available, and expanding place-specific paired plastered/unplastered datasets and standardized reporting of workmanship parameters to improve local design and retrofit decisions for Kathmandu. These results represent baseline monotonic mechanical properties only and are not interpreted as indicative of seismic performance, which would require cyclic or dynamic testing.