## 2 Beam-to-Column Connections
### BCC-3: Curved-Slotted Hole Device Combined with Perfobound Connectors  
The third system differs from BCC-2 in these two main features: the central friction plate is extended throughout the concrete core of the beam, by developing a so-called Perfobond connector; the T-stub on the top is bolted to a horizontal plate welded to the Perfobond connector, while the top reinforcement of the beam is welded to the same plate. This solution results in a stiffer connection where M20 bolts of class 10.9 are adopted for making the sliding system (Figure 3a). In BCC-3, the internal lever arm is \(z_{3}\) = 374 mm  
Figure 2: Solution BCC-2: (**a**) detail of the system; (**b**) cyclic response; and (**c**) plastic deformations at peak.  
and \(\alpha_{3}=68^{\circ}\). In this model, the HSTCB is modeled with linear tetrahedra (C3D4) while all other FE types are solid linear bricks (C3 DBR) and two-node beams are used for the steel reinforcement of the column. Cohesive interaction is used for modeling steel-to-concrete bond in the beam according to the analytical model proposed by [PERSON] et al. [28], while a perfect bond is assumed in the RC column. Frictional behavior is set for the damping device components, adopting the same parameters used in BCC-2 model.  
The FE model developed presents a slightly different setup scheme because the bottom end of the column is loaded with a lateral force which applies a cyclic displacement parallel to the beam axis; moreover, the column is preloaded with an axial force. Moreover, the compressive strength of concrete is f\({}_{\text{c}}\) = 30.31 MPa and the Young's modulus E\({}_{\text{c}}\) = 30,683 MPa. The steel elements are modelled adopting a multi-linear behaviour with hardening phases and material rupture [29; 30]. Three cyclic analyses are performed for 0.5 \(M_{d}\), \(M_{d}\), and \(M_{rd}\) = 1.5 \(M_{d}\), defining cycles with amplitude \(\pm\Theta_{y}\), \(\pm\)4\(\Theta_{y}\), and \(\pm\Theta_{\text{max}}\) = \(\pm\)7\(\Theta_{y}\), the yielding chord rotation being \(\Theta_{y}\) = 7 mrad. This loading scheme is chosen according to the code ACI 374.2R-13 [31] with the aim of achieving multiples of the yielding chord rotation. However, only the three aforementioned amplitudes have been adopted in order to contain the computational time demand of the analysis. The results are reported in Figure 3b. It can be observed that the stiffer top connection is able to prevent the shifting of the rotation center, allowing more stable hysteresis cycles. The cycles are wide and proportional to the different values of preload in the bolts. Figure 3c reports the strain state at the maximum rotation, for the cycles developed at \(M_{d}\) value. The figure shows that the steel elements of the friction damper are elastic, with localized plastic strain concentrations at the end of the  
Figure 3: Solution BCC-3: (**a**) detail of the system; (**b**) cyclic response; and (**c**) plastic strains at maximum rotation for \(M_{d}\) = 165 kNm.  
intersection between the bottom plate of the truss and the sliding holed plate. The upper T-stub assumes higher inelastic strain values in the section devoted to develop the rotation center of the system.