Induced seismicity due to gas extraction in the province of Groningen in the Netherlands has a noticeable impact on building structures. Historic masonry structures in the area, which are non-engineered and lacking empirical design features often present in traditionally seismic regions, are especially vulnerable to dynamic loading. Compounding the problem, gas extraction additionally generates soil settlement, which can induce damage to masonry buildings and thus reduce their capacity to bear seismic loads. The objective of this paper is the evaluation of the performance of a widely used structural intervention method applied in masonry structures in the Groningen region of the Netherlands. This method, initially developed against soil subsidence damage, consists in the embedment of stainless steel helical bars in repointed bed joints. Additionally, diagonal anchors are placed in drilled holes across existing cracks in the masonry. The increase in induced seismicity in Groningen raises the question whether this intervention technique can additionally enhance the behaviour of masonry structures during seismic loading. A masonry wall was experimentally tested in two configurations: a) a pre-damaged state, with simulated damage typical of imposed soil settlement, and b) a post-damaged and postintervention state, this being the wall from the previous configuration after being tested to its maximum base shear and subsequently strengthened. Differences between the two configurations in terms of stiffness, peak force and prevalent damage patterns are discussed. Accompanying the experimental campaign, results of finite element simulations of the strengthened wall are presented. The strengthened wall is simulated using non-linear macro-modelling techniques. The model accounts for the experimentally simulated damage as well as for the damage arising after the testing in the first configuration. The analysis results clarify and quantify the experimental observations on the strengthened wall, particularly as regards stress development and bond-slip in the reinforcement bars. Based on the experimental and numerical results, the effectiveness of the intervention in restoring the strength of the wall and in preventing the re-emergence of major diagonal cracking is confirmed.
- seismic assessment & strengthening
- historic masonry structures
- full-scale testing
- numerical analysis