Stress rate sensitivity of masonry units bound with hydraulic lime mortar

Abstract eng:
It is well established that most construction materials behave differently under static and dynamic loading. The stress-rate sensitivity of concrete, steel and rock has been intensively investigated. However, the literature on the timedependent response of masonry joints is scarce, particularly with regard to bond behaviour in historical stone masonry. This paper describes the dynamic response of sandstone masonry units bound with hydraulic lime mortars. A drop weight impact machine was used to generate stress rates in the range of 1kPa/s to 107kPa/s. The dynamic impact factor and stress rate sensitivity were evaluated for the flexural strength of the mortar and for the bond strength and further, the pattern of failure was noted for each mix and loading rate. Based on a related study, polypropylene micro-fibres were incorporated at 0%, 0.25% and 0.5% volume fraction into the mortar. Results show that although hydraulic lime mortar is stress rate sensitive, the dynamic impact factor is overestimated by existing CEB-FIP models. Further, the stress rate sensitivity of the bond strength decreased with an increase in the fibre content. Also, where as the mode of failure in the masonry units under quasi-static loading was through fracture at the mortar-block interface, the failure plane transferred to within the mortar under dynamic loading, particularly with fibre reinforcement.

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