## 3 Seismic Numerical Analysis
### Modeling Procedure in OpenSees
#### 3.2.1 Types of Connections Used for Modeling
In this model, the dimensions of the Weston beam are considered as the dimensions of the connection spring to assign a three-line behavior. A three-line torsion spring or two two-line torsion springs can be used in one of the connection corners. In order to achieve low ductility and less energy absorption (corresponding to the connections of structures before the Northridge earthquake), a Welded Unreinforced Flange with Welded Web connection (WUF-W) is assumed. In this type of connection, the beam wing is connected directly to the column wing using full penetration welding. Moreover, the beam die is connected to the beam die by corner welding with a corner weld and to the column wing by penetration welding. The rotational capacity specified in the regulations for the initial reduction in the horizontal direction is \(\Delta\). Figure 5: An overview of an example of a simple connection used (conventional connections before the Northridge earthquake). Figure 6: An overview of an example of the RBS-type connections used (conventional connections after the Northridge earthquake). the initial resistance is equal to the following equation. This type of connection is used in structures with a special bending frame system. On the other hand, in order to achieve high ductility and absorb more energy (corresponding to the connections of structures after the Northridge earthquake), other types of connections, such as RBS have been used, which act as semi-rigid connections. This type of connection is also used for structures with a special bending frame system. This type of connection was also used after the 1994 Northridge earthquake, in which the connection is stronger than the beam. This type of connection is created by separating a part of the upper and lower wings of the beam at a certain distance from the connection point of the beam to the column. By doing this, the reduced area of the cross-section of the beam is the area that surrenders due to force. The reduced area of the beam wing acts as a factor to prevent sudden connection failure. The rotational capacity is defined according to the FEMA350  
Figure 8: Schematic view of the Panel-Zone element used in modeling connections after the Northridge earthquake (corresponding to the RBS connection). Figure 7: Schematic view of the Panel-Zone element used in modeling simple connections before the Northridge earthquake. guideline for starting the initial resistance reduction mode based on the following equation where the height of the beam (\(\mathrm{d_{b}}\)) is in inches [25]. \[\mathrm{\theta_{sd}}=0.06\,\sim 0.0003\mathrm{d_{b}} \tag{2}\]  
On the other hand, due to the high lateral stiffness of these braces, the drift of the floors is easily responsive to service loads, but in comparison with the flexural frame system, it has a slight addition of resistance in the lateral capacity. In all the models studied in this paper, according to the recommendation of [PERSON] (1996), the inelastic beam-column element in OpenSees software has been used [22]. In the mentioned paper, force-based frame elements with distributed plastics and cross-section discretization in the form of fiber modeling have been used. In this model, in order to consider the possible buckling under axial loads, an initial defect in the system geometry is used in the form of an initial curvature. Here, the initial defect value of 0.08% of the initial limb length is placed at the end of the limb [22]. The Panel-Zone element has been used to model the connections in the bent frames. As mentioned before, the fiber model has been used in modeling the connections for the bracing frame, and the modeling of the connection bracing frame has been modeled in a simple way. It should be mentioned that, as mentioned before, in order to model the joints in OpenSees software, the length of the plastic joint has been used as a criterion for applying rigidity and semi-rigidity.