Bed joint reinforced repointing is a strengthening method often used in the Netherlands to counteract settlement damage. This strengthening technique consists of cutting a slot in the mortar joint and installing twisted steel bars embedded in a high-strength repair mortar. Due to the increase in seismic activities, triggered by gas extraction in the region of Groningen (northern part of the Netherlands), it is of interest to investigate whether this strengthening technique is efficient against seismic load. In order to characterize the performance of the bed joint reinforced repointing using twisted steel bars, an experimental campaign was conducted at Delft University of Technology. A quasi-static cyclic in-plane test on a full-scale wall was performed; similar tests on unstrengthened specimens were available from a previous experimental campaign [1][2] and were used for comparison. Moreover, small scale pull-out tests were performed to study the interaction between the steel bars and the repair mortar. By comparing the response of unstrengthened and strengthened masonry specimens, it is observed that the use of bed joint reinforced repointing can provide an increase in terms of ductility and displacement capacity, but not in terms of force capacity. Regarding the serviceability limit state, a reduction in crack width and an increase of load at onset of cracking were observed. The preliminary information obtained for the presented case study provides the ground for futher research as well as benchmark for numerical modelling.

The province of Groningen in the Netherlands is experiencing the continuous impact of gas extraction in the form of induced seismicity. Due to the absence of naturally occurring seismicity in the region, the historic building stock of Groningen was constructed without empirical design features typically encountered in naturally seismic regions. Further, gas extraction, in combination with soft topsoil, is responsible for substantial amounts of ground subsidence. This subsidence may compromise the capacity of existing structures to bear seismic loading. Historic masonry structures, particularly those lacking traditional earthquake-resistant features, are vulnerable to seismic loads. Further, their substantial weight, in-plane stiffness, low tensile strength and brittleness renders them vulnerable to settlement-induced damage. Given the cultural significance of architectural heritage, the performance of historic buildings in the Damage Limitation (DL) state is a matter of importance. Additionally, due to the incorporation of both vernacular and monumental architectural heritage buildings in the urban setting, their performance in the Near Collapse (NC) state is as important as that of ordinary building structures. Therefore, methods and techniques for enhancing the behaviour of historic buildings in both States need to be devised and evaluated. This paper focuses on the application and assessment of a retrofitting technique commonly used for damage prevention and repair in unreinforced masonry structures in the Netherlands, namely bed joint reinforced repointing. The technique consists in the embedment of stainless-steel bars in continuous bed joints, as well as their dry placement across cracks in the masonry. The technique is applied on a masonry wall tested under quasi-static cyclic in-plane shear loading for the evaluation of its performance not only in the DL state for which it was conceived, but also in the NC states. The wall features artificially introduced cracks that simulate settlement-induced damage prior to the installation of the bars. A finite element meso-model is used for the simulation of the wall tests, featuring the artificial damage and reinforcement elements. The model is used in non-linear cyclic analyses for the simulation of the experiments. Through experimental testing and numerical modelling, the efficiency of the strengthening technique is evaluated in terms of resulting shifts in wall capacity, stiffness and failure mode. Further comments are provided concerning its applicability and structural compatibility.

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.