Tension and shear behaviour of anchorage systems in limestone structures

Abstract

The use of anchorage as a method for the seismic retrofit of existing structures has persisted as a prominent technique for many years. Despite considerable analysis regarding anchorage performance within concrete, there is comparatively a lack of investigation concerning the behavioural response of anchorage within low strength materials such as sedimentary stone. Buildings in New Zealand which utilise Oamaru limestone in their construction possess a particular susceptibility to postearthquake damage given the weak mechanical properties of the material. In the study reported herein, 84 adhesive anchors were subjected to either tensile or shear testing within limestone blocks sourced from Oamaru, New Zealand. Three anchor diameters (ɸ12, ɸ16, ɸ20 mm) and two adhesives (epoxy adhesive, cement-based grout) were employed in the test regime. 54 anchors were installed at three varying depths of embedment described as a multiple of the anchor diameter (3ɸ, 5ɸ, 10ɸ) and were subjected to monotonic tension loading. The remaining 30 anchors were installed at one constant depth, and were subjected to a semi-cyclic shear loading regime. Acquired data included anchor capacities in limestone under tensile and shear loading, along with several observed types of failure mechanisms. These mechanisms were archetypal of typical anchor failure modes observed in concrete, despite larger zones of influence being exhibited for anchors in tension. Under tension, epoxy anchor behaviour was governed by the limestone strength, whereas grout anchor failure was governed by the bond strength. Anchor capacities in shear for epoxy and grout anchors were similar, however displacements were typically larger for grout anchors due to a low elastic modulus of grout. The influence of moisture content on the mechanical properties of limestone was also investigated, with the results demonstrating a substantial reduction in strength for a minimal increase in moisture content. The study has established a valuable dataset for adhesive anchorage in sedimentary stone. This dataset could be supplemented in future studies via investigations into alternative loading regimes, and/or the construction of limestone walls to investigate how local wall morphology impacts anchorage performance.