PSI - Issue 64

E. Michelini et al. / Procedia Structural Integrity 64 (2024) 1967–1974 1969 Elena Michelini, S ł awomir Dudziak, Simone Ravasini, Beatrice Belletti / Structural Integrity Procedia 00 (2019) 000–000 3

ε s or for concrete ε c ) summarized in Table 1 are referred to low-code frames, according to the characteristics of the case-study building analyzed in Section 4. Points on stress-strain curves corresponding to the reaching of these LS are also depicted in Figure 1.

Table 1. Description of structural limit states for RC frame buildings. Structural damage band Description None to slight

Linear elastic response, flexural or shear type hairline cracks in some members, no yielding in any critical section

Limit State 1 (LS1)

LSS1: reinforcement yielding ε s = ε sy

Moderate

Member flexural resistance achieved, limited ductility developed, initiation of concrete spalling

Limit State 2 (LS2)

LSS2: ε s = 0.0125 or LSC2:

ε c = 0.0045

Extensive

Significant repair required to the building, wide flexural or shear cracks, buckling of longitudinal reinforcement may occur

Limit State 3 (LS3)

LSS3: ε s = 0.025 or LSC3:

ε c = 0.006

Complete

Repair of building not feasible either physically or economically, demolition required, could be due to excessive displacement

Limit State 4 (LS4)

LSS4: ε s = 0.045

(a)

(b)

(c)

Fig. 1. Material models: (a) for steel (ABAQUS and Seismostruct), (b) for concrete: Mander (Seismostruct); (c) trilinear model (ABAQUS).

3. Validation of the procedure through comparison with experimental results The above-described procedure is first validated against the results of a well-documented experimental test available from the literature (Li et al., 2016). The considered specimen is constituted by a four-bay, two-storey RC frame, with a net span of 1.50 m, according to the sketch reported in Figure 2(a). The geometrical dimensions and reinforcement arrangement of its elements were first calculated with reference to a full-scale prototype building, and then adapted to the scale of the specimen (1/3 of the real structure), according to Li et al. (2016), to which reference is made for further details. Two different frame configurations, with and without infills, were analyzed in the experimental campaign; in the following, only the bare frame situation is discussed. During the test, a progressive collapse situation was simulated by applying an increasing quasi-static load to the central column. Parameters of material models assumed in FE analyses, which correspond to the values of material properties reported by Li et al. (2016), are as in the following; for reinforcement: Young modulus E s = 200 GPa, yield strength f y = 415 MPa, ultimate strength f t = 588 MPa, fracture strain ε u = 0.126; for concrete (at first floor): compressive strength f cm = 41.3 MPa, tensile strength f ctm = 4.0 MPa, modulus of elasticity E ci = 32 GPa, strain at peak stress ε c1 = 0.00225; for concrete (at second floor): f cm = 31.8 MPa, f ctm = 3.2 MPa, E ci = 31 GPa, ε c1 = 0.0021.