PSI - Issue 44

Andrea Natale et al. / Procedia Structural Integrity 44 (2023) 1768–1775 Andrea Natale et al./ Structural Integrity Procedia 00 (2022) 000–000

1772

5

Fig.3. Case Study: front view The base isolation system designed for the retrofit solution consists of high damping rubber bearings, having a diameter equal to 450 mm, height of 231 mm, total rubber thickness of 126 mm, shape factor of 18.3, vertical stiffness of 516 kN/mm, equivalent horizontal stiffness of 0.50 kN/mm, horizontal design displacement of 147 mm, maximum vertical static load (S.L.U) of 2000 kN, maximum vertical seismic load of 950 kN. The mechanical properties used to characterize the model of the bearing are the following: equivalent stiffness equal to 20000 kN/m, damping equal to 0.15, elastic stiffness equal to 79884 kN/m, post-yielding stiffness equal to 15976.8 kN/m, yielding strength equal to 1005.8 kN, yielding displacement equal to 0.01574 m. The characteristic strength of the steel used for internal reinforcement in RC members is set equal to 453 MPa (Verderame et al. 2011). The record selection is performed with REXEL software (Iervolino et al. 2010), considering 14 records and the 9-return period have been defined. The selected records for the 475 years return period and the spectrum compatibility with reference code acceleration and displacement response spectra are reported in Fig.4.

0.6000

SLV Design TR = 475 years Upper Bound Lower Bound Average Spectrum

1.40

SLV Design TR = 475 years Upper Bound Lower Bound Average Spectrum

0.5000

1.20

1.00

0.4000

0.80

0.3000

S d [m]

S a [g]

0.60

0.2000

0.40

0.1000

0.20

0.0000

0.00

0.00

1.00

2.00

3.00

4.00

0.00

1.00

2.00

3.00

4.00

T [s]

T [s]

(a) (b) Fig.4. Spectrum compatibility for the case study buiding: (a) acceleration and (b) displacement.

4. Numerical Results As described in the section above the equation of motion was solved for 14 records and 9 return periods considering 120 couples of concrete strength and transversal reinforcement ratio and the building in the as-built configuration and for the base isolated configuration. To account for the benefits of the FRP strengthening or demolition/reconstruction.

Direction Y

Direction Y

Direction X

Direction X

3.00

3.00

3.00

3.00

2.00

2.00

2.00

2.00

1.00 Floor [-]

1.00 Floor [-]

1.00 Floor [-]

1.00 Floor [-]

0.00

0.00

0.00

0.00

0.00

0.25

0.50

0.75

1.00

0.00

0.25

0.50

0.75

1.00

0.00

0.25

0.50

0.75

1.00

0.00

0.25

0.50

0.75

1.00

Sa [g]

Sa [g]

Sa [g]

Sa [g]

(a)

(b)

(c)

(d)

Fig.5. Acceleration for a return period for 475 years: (a-c) As-Built Configuration, (b-d) Base isolated configuration.