PSI - Issue 11

Mario Fagone et al. / Procedia Structural Integrity 11 (2018) 250–257 Author name / Structural Integrity Procedia 00 (2018) 000–000

251

2

actions. Several strengthening and consolidation techniques have been proposed in the scientific and technical literature to mitigate the seismic vulnerability of masonry structures. Among these, bonding Carbon Fiber Reinforced Polymer (CFRP) sheets demonstrated to effectively improve the structural behavior of both flat (wall panels) (D’Antino et al. 2016; Sinicropi et al. 2015; Paradiso et al. 2013; D’Ambrisi et al. 2013; Briccoli Bati et al. 2015) and curved masonry structural elements (Borri et al. 2011; Foraboschi 2004; Valluzzi et al. 2001; Basilio et al. 2014; Fagone et al. 2017; Briccoli Bati et al. 2013; Cancelliere et al. 2010; Lucchesi et al. 2015; Fagone et al. 2016). As it is well known, the in-plane behavior of masonry walls (mainly defined by initial stiffness, strength and post crack characteristics) mostly contribute to the global structural response of masonry buildings subjected to seismic actions. Thanks to the wide experience gained in research activities concerning masonry structural elements reinforced by CFRP sheets subjected to in-plane loads (Valluzzi et al. 2012; Malena et al. 2017; Freddi and Sacco 2016; National Research Council 2013; Ceroni et al. 2014; Briccoli Bati and Fagone 2008), the main features of the mechanical behavior of such reinforcements are known and quite shared among specialists. Nevertheless, out-of plane failure mechanisms represent a serious life-safety hazard for this type of buildings since they involve an almost instantaneous loss of the wall load bearing capacity for vertical loads. Several research reports in the literature are devoted to the analysis of the effectiveness of CFRP reinforcements externally bonded to masonry walls loaded by out of plane actions (Sistani Nezhad and Kabir 2017; Sorrentino et al. 2016; Bruggi and Milani 2015; Anania et al. 2014; De Felice et al. 2012; Hamed and Rabinovitch 2010; De Santis et al. 2017). Since most of the scientific literature concerns monotonic actions, the experimental program described in this paper seeks to fill the gap in research, concerning the analysis of the effects of load cycles in the out-of-plane behavior of reinforced masonry walls. 2. Mechanical Properties The materials employed in the experimental program described in this paper are analogous to those used in (Caggegi et al. 2014; Fagone et al. 2014; Fagone et al. 2015). The reader can refer to these papers for a comprehensive description of the tests performed to characterize the mechanical properties of the materials. Here, just the main mechanical parameters are summarized for completeness sake. Soft mud bricks, also called solid pressed bricks, have been used to manufacture the specimens. Pressed bricks were preferred to drawn bricks because their material structure (and, consequently, the anisotropy of mechanical properties and the quality of fracture path) resembles the one of traditional soft pressed bricks, that are used in most existing buildings (Briccoli Bati and Ranocchiai 1994). Brick specimens had average compressive strength equal to 20.1 MPa, average tensile strength of 2.5 MPa and Young modulus equal to 8712 MPa. Ready mixed mortar, made with lime and cement as binder, was employed in manufacturing the specimens. Mixed lime and cement mortar was preferred because it exhibits characteristics similar to those of lime mortar, usually employed in historic buildings and traditional architecture, where reinforcement techniques are mainly used for retrofitting and adaptation to standards of structural capacity. The average compressive and (bending) tensile strength, obtained according to (UNI EN 1015-11 2007), was respectively 5.2 and 1.9 MPa.

Table 1. Mechanical properties (declared by the producer) of the reinforcing system components. Nominal thickness Tensile elastic modulus Bending elastic modulus Ultimate tensile strain Characteristic tensile strength

[mm] 0.165

[MPa] 230000

[MPa]

[%] 1.3

[MPa]

Unidirectional carbon fiber fabric

--

2500

Adhesive

-- --

--

3300

> 25

--

Primer

1200

--

--

> 20

A composite material, made of a unidirectional carbon fiber fabric and epoxy resin was used to realize the reinforcement. This was applied to the substrate using a wet lay-up process (with a single layer of carbon fiber fabric), after surface preparation and primer application, according to the producer’s guideline. The main characteristics of the constituent materials, declared by the producer, are summarized in Table 1.