PSI - Issue 44

Fabrizio Comodini et al. / Procedia Structural Integrity 44 (2023) 1076–1083 Author name / Structural Integrity Procedia 00 (2022) 000–000

1079

4

2.4. Seismic capacity assessment A finite element model with non-linear behavior beam elements has been developed. The model adopted using plastic hinges is the one based on concentrated plasticity. Preliminarily, linear analyses were carried out to identify the representative parameters of the modal dynamic response. The main periods of vibration are: T1 = 1.99 s X direction, T2 = 1.27 s Y direction and T3 = 1.21 s Z direction.

b)

a)

Z

Y

X

Fig. 3. 3D Finit Element Model a) front view; b) posterior view

Non-linear static analyzes were then developed to determine the safety level of the construction through the coefficient ζE, defined as the ratio between the seismic action associated with the capacity of the structure and the expected seismic demand for new constructions. The seismic capacity of the structure was assessed concerning the safeguard of life limit state (SLV) and the damage limit state (SLD), referring to the following three distinct verification conditions: bending collapse (SLV), collapse shear (SLV), and inter-floor displacement (SLD). Table 1 shows the main results of the seismic assessment of the safeguard of life limit state (SLV) (NTC2018).

Table 2 Results of seismic assessment Collapse mechanisms

Seismic Capacity (C)

Seismic Demand (D)

Ratio C/D

ξ E

ag/g

Return Time

ag/g

Return Time

Shear collapse Flexion collapse

0,033 0,072 0,011 0,227

7

0,227 0,227 0,227 0,227

712 712 712 712

0,15 0,32 0,05 > 1,0

38

Joint collapse

1

Foundations collapse

712

The values of the seismic capacity of the structure are very low The first mechanisms of collapse occur for a seismic demand with a return period of less than 30 years. Of the four mechanisms investigated, the most critical is that relating to the strength of the unconfined beam-column joints. Setting aside the vulnerability associated with the unconfined joints, which will be resolved by localized interventions, the lower capacity value is that associated with the shear mechanisms of the external columns of the transverse direction. The shear collapses of the columns depend on the low amount of transverse reinforcement, but above all on the twisting effects caused by the irregularity in the plan of the building and by the significant eccentricity between the center of the masses and the center of the stiffnesses. These effects are amplified by the low stiffness of the structural system in both directions. 3. Seismic improvement The seismic improvement interventions aim to raise the building's seismic capacity to a minimum value equal to 60% of the expected performance level for a new building concerning the SLV. Furthermore, the planned intervention strategy is based on the need to limit, as much as possible, any interactions with the internal spaces,