Abstract

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.

Abstract

In the last two decades, the province of Groningen, located in the North-East of the Netherlands, has been subjected to an increasing number of earthquakes induced by gas extractions. The existing building stock is mainly composed by unreinforced masonry (URM) buildings not conceived to resist seismic loads. The need of reducing the vulnerability of these buildings by means of retrofit interventions, led to the development and adoption of a new guideline (NPR9998:2018). As regards the seismic assessment of URM buildings using nonlinear static analysis, the guideline includes significant differences with respect to Eurocode 8, which is adopted in other European countries. The more significant differences lay in the description of failure mechanisms and constitutive laws of piers and spandrels, inthe identification of limit states and in the calculation of seismic demand. In the last years, the assessment and retrofit in the region has been carried out using software based on an equivalent-frame strategy: among these, the 3Muri software has been widely adopted. The solver of this program is the research software TREMURI. In this work, a new version of the solver adopted by the software 3Muri, complying with the requirements of the new Dutch guideline, was developed; the tool was then validated with simple examples. To illustrate the specificities of the new guideline, the seismic assessment of a building representative of one of the most widely diffused URM building typologies in the area was performed.