PSI - Issue 44

Michele Angiolilli et al. / Procedia Structural Integrity 44 (2023) 870–877 M. Angiolilli et al./ Structural Integrity Procedia 00 (2022) 000 – 000

874

5

the main joint diagonals (n.6 and 7). The larger crack was the n. 8 (a few millimeters of length). Applying the force V along the positive y direction (see Figs.1 and 2), the LVDT1 is compressed, whereas the LVDT2 is under tension. On the contrary, applying the force V along the negative y direction, the LVDT1 is under tension whereas the LVDT2 is compressed. The right part of Fig. 3 shows the deformation of both the LVDT s (εLVDT) differentiated between the measurements that led to the diagonal under compression or tension. In particular, one can see that tensile deformation tends to be higher than compressive deformation due to the development of micro cracks from the beginning of the test. At the last instant of the test, LVDT1 resulted in tension whereas LVDT2 resulted in compression, meaning that large cracks developed along the diagonal (see crack n. 10 in Fig. 4).

Fig. 3. Load-drift curve (left) and LVDT deformation-drift curves (right) obtained experimentally.

Fig. 4. Crack evolution observed during the experimental test (from 1 to 10).

Experimental tests showed that the joint capacity is slightly lower than the NTC (2018) prevision. In fact, from Formula 7.4.10 of NTC (2018), one can compute a resistance of 262 kN (about 20% overestimation) by considering only the second part of the inequality (i.e. null joint steel rebars) and, therefore, only the concrete tensile strength. Joint shear strength can also be predicted using formulation 4.7 of ACI-352R (2002) for cyclic loading cases that ignore the steel reinforcement contribution and, thus, express the joint strength as a function of concrete compressive strength and the joint geometry. For that code, Vmax is equal to 1011 kN (about 365% overestimation). Several other proposals are currently available for evaluating the shear strength of RC joints (see Lima et al. (2012a)) and are generally based on the sum of two basic contributions related to concrete and steel stirrups. By considering only the first contribution (note that within the contribution of the only concrete, most of the formulations foresee a contribution of the column/beam rebars passing through the joint), one can compute a shear strength of 540 kN according to Sarsam and Philips (1985), in which the contribution of the column longitudinal reinforcement ratio is still considered.