# Study on New Bolted T-Stub Connection with Inserted Plates under Axial and Cyclic Loads
## 1 Introduction  
Beam-to-column joints are critical to ensuring that beams and columns work together to assemble whole building structures while resisting external loads. The early popular type of steel beam-to-column connection was the welded flange and bolted web, which was deemed capable of providing enough plastic rotational capacity for most seismic applications. However, during the Northridge (1994) and Kobe (1995) earthquakes [1; 2], a number of steel moment-frame buildings experienced unexpected brittle fractures with these types of joints, rather than showing desirable performances. Following investigations mostly focused on understanding the causes of damage to beam-to-column connections, improvements have been suggested for those connections. The main measures to ameliorate traditional beam-to-column connections are as follows: reducing beam sections [3; 4; 5], augmenting welding details of joints [6; 7; 8], strengthening connection parts [9; 10; 11], completely using bolted connections [12; 13] and welding the web of the beam to the column [6; 8; 14; 15]. The design principle of those improved beam-to-column joints is either to strengthen the end of the beam or to weaken the beam section, so that the location of a plastic hinge on the beam can be a certain distance from the column during an earthquake, which deepens the seismic understanding of strong joints and weak components. However, in these improved connections, it is the frame beamsthat are supposed to provide plastic deformation. As the main structures, once the beams are damaged, retrofitting will become quite tough. In order to make the structure return to service after an earthquake, new connection configurations have also been proposed based on the passive control concept [16]. In these joints, the dissipative zones are constituted by replaceable damping devices located at the beam ends, to prevent the plastic engagement of other components and then to achieve the ambitious goal of building frames structures that are free from damage. The stable hysteretic performance of beam-column joints with U-shaped metal energy dissipating elements at the bottom beam flange has been proven in literature [17], but the U-type dissipater could only be fit in the weak axis direction of the connection. Similarly, the beam-column joint with a slit energy dissipater was able to take the upper flange of the beam as the rotation center and successfully concentrate the plastic deformation on the lower dissipater [18]; however, the large volume of the slit energy dissipater will inevitably take occupancy of the available space. Studies working on the integration parameters or optimization of components themselves have also been performed. Research [19] has proposed an hourglass shape for T-stub flange to elevate the energy-dissipation capacity of classical rectangular T-stubs. A variety of geometric dimensions and material types were attempted in [20] to explore the optimal energy dissipation capacity and deformation features of T-stub connections. Solutions for friction dampening have begun to emerge as well. One study [21] proposed a strategy of inserting two friction pads made from metallic or rubber materials between the upper/lower T-stub stem and beam flange based on classical double split tee joints. The dissipation of a large amount of energy by friction pads was achieved, but the structure damage could not be entirely avoided. Low-damage seismic resistant connections, such as sliding hinge joints and asymmetric friction connections with friction interfaces made of brass, steel or aluminum were subsequently investigated [22]. Presently, a novel configuration friction kit was employed containing removable haunches or ribs with slotted holes, and stainless steel friction pads were horizontally or vertically equipped together with L-stubs at the lower beam flange (based on [23]), aiming to detach the friction dampening device from both the bottom beam flange or the column surface and thus simplify the separability.