PSI - Issue 44

Devis Sonda et al. / Procedia Structural Integrity 44 (2023) 1188–1195 Devis Sonda et al. / Structural Integrity Procedia 00 (2022) 000 – 000

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3. Properties of structural models and devices

In order to evaluate the effects of the introduction of CWST devices, the structural models used for numerical analyses were defined through an analysis on most widespread typologies of existing precast concrete structures. Three different structural typologies have been identified as representative of the most common existing precast structures with friction-based connections. Characteristics of structural models (Model A, B and C) of the three identified case studies used for analyses are reported in Table 1.

Table 1. Properties of models. Model ID Column Height [m] Beam Length [m]

Column Cross Section [mm]

Modulus of elasticity [MPa]

Beam Load [kN/m]

First Period [sec]

Modal Mass [%]

A B C

5.50 5.00 6.50

21.8 14.5 15.0

500x500 500x400 400x400

33345 32836 32836

17.1 15.4 30.6

0.61 0.46 1.22

95.6 94.9 96.6

The aim of performed analyses was to evaluate the effects of the introduction of CWST Sismocell devices in terms of base shear and moment reduction respect to systems with hinged connections. For this reason, the structural models considered in these analyses present columns performing linear elastic behavior, and non-linearity concentrated in beam-column joints. Each CWST, because of its specific behavior, was modeled in Midas GEN using three non-linear links (NLLinks) working in parallel. The non-hysteretic cyclic behavior of the device was modelled as a non-linear symmetric element with property type SLIP bilinear, with two additional NLLinks to simulate the end stroke in compression (Gap) and in tension (Hook), with the stiffness given by the steel threaded bar. The behavior of the devices is represented in Figure 3a, where the force-deformation curve is referred to the single device in compression. In the initial branch O-A the device remains elastic, acting like a hinge and preventing beam column relative displacements, so the lateral seismic force is fully taken by the column. As soon as the force overcome a preset force threshold, the device starts to buckle and the plastic deformation takes place (branch A-B of the curve), limiting the value of the force transmitted to the column. After point B, when the device attains its maximum deformation capacity, the stiffness boosts significantly and seismic action is fully transferred to the column because the joint become rigid. At this step, the device performs as a displacement-limiter between beams and columns. In Figure 3a, F eq is the equivalent plastic force threshold in terms of absorbed energy, and S max is the maximum deformation capacity of the device. In case of ground motions, and in general under cyclic loading, the two devices positioned in one joint, work alternatively. Figure 3b represents the force-deformation law of a couple of devices in case of cyclic loads. In the curve, the blue path shows that, when a load reversal occurs after entering the plastic branch of one of the devices, the connection slides with no force until the recovery of the entire previous deformation.

a

b

Fig. 3. CWST device model: (a) theoretical model; (b) plastic loops of a double CWST Sismocell.