PSI - Issue 44

Alessandra Maione et al. / Procedia Structural Integrity 44 (2023) 1372–1379 Alessandra Maione et al. / Structural Integrity Procedia 00 (2022) 000 – 000

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1. Introduction It is widely recognized that the vulnerability to out-of-plane failure mechanisms is one of the main causes of damage to masonry buildings exposed to seismic events (Abrams et al. 2017). To prevent such failure mechanisms, improving wall connections can play a significant role since they allow a box like behavior of masonry buildings (Casapulla et al. 2021, Solarino and Giresini 2021, Giresini et al. 2021). For this purpose, the use of pultruded fiber-reinforced polymer (FRP) bars as strengthening systems based on grouted anchors is gaining increasing attention, thanks to several interesting features of FRP materials such as their resistance to corrosion, the low weight-to-strength ratio, and the easy installation (Ceroni and Prota 2009). Some experimental investigations have addressed the bond behavior of FRP grouted anchors, even if on different types of bars and masonry, identifying typical failure modes and the related pull-out strengths ( Paganoni and D’Ayala 2014, Panizza et al. 2015, Giresini et al. 2020, Ceroni and Di Ludovico 2020). Based on regression analyses of the experimental data, analytical formulations have also been developed to predict the pull-out strength and the influence of the significant parameters (Ceroni and Di Ludovico 2020). On the other hand, the effectiveness of grouted anchors has also been tested on full-scale specimens of masonry connections highlighting the improved out-of-plane response ( Maddaloni et al. 2016, Melatti and D’Ayala 2021). However, despite the pioneering experimental investigations on full-scale specimens, assessing the performance of strengthened masonry systems is still a matter of ongoing research. In this framework, Maione et al. (2021) have proposed a modeling approach for the OOP response of masonry systems strengthened by FRP grouted anchors, which is based on the non-linear kinematic approach of limit analysis and adopts the frictional macro-block model of masonry developed by Casapulla et al. (2018 and 2021) for unreinforced masonry. It was validated against the experimental results presented by Maddaloni et al. (2016) and applied to T-shaped walls. In this paper, two novelties are introduced to improve such a model: i) the definition of the expected failure mechanism for the strengthened system, which considers the hinge position variability along the height of the wall in addition to the crack inclination angle; ii) the proposal of a simplified design-oriented approach to evaluate the contribution to the stabilizing moment due to the anchors. The proposed simplified approach is compared to the approach of Maione et al. (2021) to verify its reliability in predicting the horizontal capacity of the strengthened system. Then, it is used to design strengthening solutions for a T-shaped masonry connection and to investigate on the influence of the main design parameters on its performance. 2. A modeling approach to assess masonry wall connections strengthened by FRP grouted anchors This section summarizes the modeling approach proposed and validated by Maione et al. (2021) to assess the horizontal capacity of masonry wall connections strengthened by FRP grouted anchors and introduces the two novel contributions mentioned above. The analysis refers to a T-shaped connection defined by an OOP-loaded wall and a single orthogonal wall (Fig. 1a), but it can easily be extended to the cases of two or more orthogonal walls. The adopted grouted anchors consist of carbon fiber-reinforced polymer (CFRP) tubes wrapped in a stainless-steel fabric to enhance the bond with the grout, for which the pull-out test carried out by Ceroni and Di Ludovico (2020) showed a mixed failure mode, i.e., a masonry cone detachment associated with slippage at the grout/masonry interface. The experimental load-slip curves T-s related to three tests are represented in Fig. 1b together with the average bi linear relationship proposed by Maione et al. (2021); this latter, also adopted in this paper, is characterized by the following parameters: T * = 40.5 kN, K 1 = 32.4 kN/mm, K 2 = -1.2 kN/mm, s 1 = 1.25 mm, s u = 36.3 mm, being T * the assumed pull-out strength. 2.1. Limit analysis of a T-shaped connection strengthened by FRP grouted anchors The approach proposed by Maione et al. (2021) extends the rigid macro-block model developed by Casapulla et al. (2018 and 2021) from unreinforced to strengthened masonry systems out-of-plane loaded; based on that, the kinematic method of limit analysis is used to assess the horizontal capacity of the strengthened system in terms of the minimum load multiplier of the gravitational loads. This is found among all the load multipliers related to the possible failure mechanisms of the strengthened system.