PSI - Issue 37

Gonçalo Ribeiro et al. / Procedia Structural Integrity 37 (2022) 89–96 Ribeiro et al. / Structural Integrity Procedia 00 (2019) 000 – 000

94 6

frequency of 100 Hz was used in the numerical simulations. The frequency of the responses is around 2.4 Hz, which is approximately the vertical natural frequency of the damaged structure. Additionally, results show that the maximum deflection for scenario (iv) is equal to 58.2 mm (maximum deflections for the other scenarios are similar), which is very close to the established SLS limits. Thus, the imposed deformations on the upper floors would not have any damaging consequences.

1.00 1.05 1.10 1.15 1.20 1.25 1.30 1.35 1.40 1.45 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 Dynamic amplification coefficient t rise (sec)

Scenario (i) - Longitudinal trusses Scenario (i) - Transverse trusses Scenario (ii) - Longitudinal trusses Scenario (ii) - Transverse trusses Scenario (iii) - Longitudinal trusses Scenario (iii) - Transverse trusses Scenario (iv) - Longitudinal trusses Scenario (iv) - Transverse trusses

Fig. 5. Dynamic amplification coefficients for the sudden loss of a structural member and sensitivity analysis of the t rise

17 19 21 23 25 27 29 31

Trise = 0 sec Trise = 0.1 sec Trise = 0.3 sec Trise = 0.5 sec Trise = 1.0 sec Trise = 2.0 sec

-20

-30

-40

-50

Axial force(MN)

Displacement (mm)

-60

0

1

2

3

4

5

0

1

2

3

4

5

Time (sec)

Time (sec)

Fig. 6. (a) time-history of the vertical displacement of the elements adjacent to the failure when scenario (iv) occurs; (b) time-history of the axial force in the diagonal of the central longitudinal truss adjacent to the core, in Zone 1, when scenario (iv) occurs

3.6. Members and connections’ design The overall design of the transfer system was determined by the serviceability behavior with respect to deflections. The design of the members of the transfer structure for the ULS was based on the provisions of EN 1993-1-1 and EN 1994-1-1. Regarding the longitudinal trusses, the chords have the same cross-section throughout their entire length, whereas the dimensions of the web members (diagonals and verticals) were optimized according to their internal forces. Also, for the simplicity of the connections, it was decided that the web member widths must be lower than the chord widths. The chords are embedded in RC slabs, which provides fire protection and composite behavior, and the bond between the steel members and the concrete is achieved by headed studs. The connections of the steel trusses to the RC cores are critical elements of the system. They must be sufficiently strong and rigid to ensure a fixed support condition at the RC core walls. Several options were considered, but the one that was found most advantageous was to connect both sides of the core where the trusses meet through a set of post-tensioned Diwidag bars.

3.7. Deflection control

The design criteria adopted were the following: (i) long-term deflection must not exceed L/250 for spans and L/125 for the cantilevers, and (ii) the deformation imposed on non-structural elements must not exceed L/500 for spans and L/250 for the cantilevers, where L represents the length of the span or cantilever. The characteristic load combination, rather than the quasi-permanent one, was used to calculate the deflections, in order to ensure that the building does not have excessive deformations even under rare loading scenarios.