SHAKE TABLE TESTING OF SEISMICALLY RESTRAINED CLAY BRICK MASONRY PARAPETS
Earthquake Spectra, 34(1)
Scope and methodology
Past earthquakes have repeatedly served as reminders of the hazards posed by unreinforced masonry parapets. Observed failure modes have included several cases where adopted retrofit techniques were inadequate to effectively secure parapets during earthquake-induced shaking.
The aim of this research was to provide professional structural engineers with valuable experimental data on the dynamic behaviour of commonly used parapet bracing systems and to propose cost-effective alternative solutions.
Shake-table testing was conducted on nine full-scale solid-clay-brick masonry parapets in both an as-built condition and after retrofitted using various techniques.
Ultra-weak mortar tends to crumble, resulting in a wide spread cracking and in the collapse of non-retrofitted masonry portions of the parapet, such as the area above the securing members.
Steel and timber diagonal bracing improved the seismic capacity of parapets by eight times in comparison to as-built parapets. If durability measures are addressed, timber bracing can be considered a cost-effective alternative.
The addition of vertical strong-backs further improved the performance, sustaining twice the acceleration recorded for braced parapets.
The connection of the vertical strong-backs to the parapet should be designed to transfer the induced base shear loads into the supporting structure.
Due to insufficient development length below the parapet, the post-tensioning retrofit was unable to prevent the out-of-plane failure and hence further investigation is required. Nevertheless, performance were 20% lower than steel-braced parapets.