Developing and testing a sprayable overlay of strain hardening cement-based composite for retrofitting of unreinforced load bearing masonry walls

[摘要] ENGLISH ABSTRACT: In the Western Cape Province (South Africa) a large number of multi-storey buildings, built withunreinforced load bearing masonry (URM) were constructed before seismic resistance becamea design standard requirement in 1989. The region lies in a light to moderate seismic zone inSouth Africa. It is foreseen that these buildings perform poorly during seismic activities dueto their brittle in-plane shear failure mode. Retrofitting of existing URM structures are noeasy task and few solutions have been suggested. A spray-able Strain Hardening Cement-basedComposite (SHCC) overlay as retrofitting material is proposed for the materials superior tensileand shear properties while applying the overlay is simple.SHCC is a fibre reinforced composite designed to form multiple fine cracks under tensile, shearand flexural load. The cracks are controlled to small widths, whereby significant toughness, orenergy dissipation, is realised, while maintaining its resistance.This thesis report results of determining the applicability and performance of retrofitting URMwalls with a sprayable overlay of SHCC produced with local available material.A spray-able SHCC was optimized for spray-ability as well as good adhesiveness to the masonry.Tensile strain capacity was tested throughout to determine the optimal mix having desirablefresh and hardened properties. SHCC free shrinkage, as well as the restrained shrinkage on thesurface of the SHCC overlay were measured. The tests showed that restrained overlay shrinkagedid not lead to visible debonding or cracking.The interfacial bond and multiple cracking for energy dissipation in a seismic event were investigatedusing the triplet shear test. The preferred failure mechanism is described and designedfor by restricting the overlay thickness to allow multiple crack formation in the overlay, insteadof overlay debonding. Design guidelines to ensure that energy dissipative failure mechanismsindeed occur during in-plane shearing action are presented. The tests showed that the SHCCoverlay is a viable solution as the shear strength and energy absorption capacity increased manifold.Results from large scale shear wall validation tests are presented and the data was used toformulate a design model. The tests showed that multiple cracks form in the overlay, along withan increased in-plane shearing resistance compared with reference URM walls.It can be concluded that spray-able SHCC is a viable retrofitting solution for the seismic resistanceof URM and further development and testing is encouraged to optimize and implementthe use of this retrofitting strategy.

[发布机构] Stellenbosch University