PSI - Issue 44

Francesca Ferretti et al. / Procedia Structural Integrity 44 (2023) 2254–2261 Ferretti et al./ Structural Integrity Procedia 00 (2022) 000–000

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2.3. Diagonal compression test setup and interpretation Diagonal compression tests were performed in accordance with the ASTM E519 Standard with the goal of studying the shear behavior of the analyzed masonry samples. Tests were carried out under displacement control in order to capture both the pre-peak and the post-peak behavior. A hydraulic actuator with a maximum capacity of 500 kN was used for applying the diagonal compression load at a rate of 0.01 mm/s. All the samples were monotonically loaded up to failure. Linear potentiometers, with a stroke of 50 mm and approximate gage length of 1230 mm, were placed on both sides of the masonry panels along the diagonals, to measure the shortenings or elongations. The setup of the test is shown in Fig. 4.

Fig. 4. Test setup for diagonal compression test.

For the interpretation of the diagonal compression test, the elastic interpretation is here adopted (Calderini et al., 2010), with the following stress state at the center of the panel:

P

P

0.56 ;

1.05

 

 

(1)

A

A

n

n

where A n is the net cross sectional area of the panel, evaluated as the product between the thickness and the average between the dimensions of the sample and P is applied diagonal load. In this configuration, the principal directions in the middle of the panel are aligned with the diagonals and the principal stresses at failure can be calculated as:

P A

P A

0.5 ; u

1.62

f

  

  

u

(2)

, t M

I

II

n

n

where f t,M is the masonry diagonal tensile strength and P u is the panel failure load. Since during the tests elongations and shortenings were measured along the two diagonals, the shear strain γ can be determined as: (3) where ε c and ε t are the compressive and tensile diagonal deformations, respectively, and they are calculated as the average of the corresponding deformations on both sides of the specimen. The shear modulus G was calculated using the experimental shear stress vs shear strain curve as the secant modulus between 1/10 and 1/3 of the failure load. 3. Experimental results The unreinforced masonry specimen (Fig. 5 a ) failed with the appearance of a main crack along the compressed diagonal. Cracking began in the center of the specimen at the maximum load (Table 4) and swiftly spread to the c t     