PSI - Issue 44

Fabio Mazza et al. / Procedia Structural Integrity 44 (2023) 147–154 Fabio Mazza et al. / Structural Integrity Procedia 00 (2022) 000–000

3

149

The steel moment resisting frame is designed following the Building Law of Japan (Design Standard for Steel Structures (2017)), with a safety factor equal to 1.5, according to a beam collapsing mechanism with column base yielding. Nominal yield strength values of 325 N/mm 2 and 295 N/mm 2 are used for steel beams and columns, respectively, while a cylindrical compressive strength of 36 N/mm 2 is assumed for concrete. With the aim of recording the displacements along the X and Y in-plan directions during the experimental campaign, optical displacement sensors and accelerometers have been placed at two opposite corners (i.e. nodes 1 and 6 shown in Figure 1 at all levels).

Table 1. Geometrical properties for columns and beams of the fixed-base and base-isolated structures (unit in mm). Column Type Material Cross-section B H t w

t f

C1 C2 C3 B1 B2 B3 B4 B5

Steel Steel Steel Steel Steel Steel Steel

Square Hollow Square Hollow Square Hollow Cross-section

250 250 100 200 150 150 100 B

250 250 100 400 400 300 200 600 H

16

- - -

9 6 8 6 t w

Beam Type

Material

t f

I-shaped I-shaped I-shaped I-shaped

13 19

6.5 5.5

9 8

Concrete

Rectangular

1300

-

-

2.2. Base-isolated test structure

A scaled base-isolated three-storey steel framed hospital building (Figure 2), built adjacent to the fixed-base one, is analysed for experimental and numerical investigations (Blind Prediction Contest (2020)). In-plan configuration for the isolation level (Figure 2a) and level 3 (Figure 2d) consists of 5 m and 6 m single bays along the X and Y directions, respectively. At the intermediate levels (Figures 2b and 2c), a suspended overhang is present, placed at the middle of the left floor side, with a length of 3.4 m along the X direction and 3.0 m along the Y direction. Concrete counterweights (5 m long and 1 m high) for the cantilever floor are placed at the first two levels (Figures 2a,b), with a width of 1 m and 0.42 m respectively. The superstructure consists of three levels of 3.5 m height, for an overall height of 10.5 m. One-way concrete slabs are placed at all levels, 15 cm thick for levels 1 and 2 and 60 cm thick for the isolation and top (third) levels. Rectangular RC beams are placed at the isolation level (Figure 2a), whereas I shaped beams constitutes the resisting system at the other levels (Figures 2b,c,d), together with four steel columns with square hollow section. Dimensional details of structural elements are reported in Table 1.

(a) Isolation level.

(b) Level 1.

(c) Level 2.

(d) Level 3.

Figure 2. Plan views of the base-isolated test structure (unit in cm).

The steel moment resisting frame is designed following the Building Law of Japan (Design Standard for Steel Structures (2017)), considering a base-isolation system constituted of four identical low-friction curved surface sliding bearings (CSSBs) L60-150-600 (NIPPON STEEL (2019)), with an ultimate displacement ( d c ) equal to 600 mm, a radius of curvature ( R ) of 4.5 m and a nominal friction coefficient ( µ 0 ) equal to 0.013, accounting for an effective vibration period ( T iso ) equal to 4.5 s. Material properties are the same of the fixed-base structure. Optical displacement sensors have been placed at two opposite corners at all levels (i.e. nodes 1 and 4 shown in Figure 2).