Dongde, Yong, Yinke, Yicong, Yunlong, and Shiqiang, 2022
Steel angles are proposed at beam-to-column connections in conjunction with frictional damping and post-tensioned strands in a steel frame in order to provide supplemental energy dissipation under the application of seismic loading. Cyclic loads were applied to eight test subassemblies featuring a beam-to-column connection using an electrohydraulic servo actuator in order to assess the effectiveness of this system under lateral loads, and the experimental results demonstrated seismic dissipation was concentrated into the replaceable steel angles, therefore reducing residual deformation in other components.
System Concept
The proposed system combines different techniques for energy dissipation and self centering into the beam-to-column connections of a steel structure. The primary element for energy dissipation is a replaceable steel angle that is bolted to the beam and the column. The steel angle is intended to experience plastic deformation under the application of seismic loading, therefore dissipating seismic energy by absorbing the lateral loads into a ductile and replaceable component of the system. The beam-column connections also include a web friction device in the beam, which consists of brass plates sandwiched between the beam and the connector with six frictional bolts connecting them with some preloaded tension. The web friction device also is used to dissipate seismic energy through frictional damping.
At each beam-to-column connection, the system also includes post-tensioning strands to provide a self-centering component. Rather than vertical post-tensioning, which can often interfere with the structural columns of the building, the horizontal post-tensioning is used to self-center the structure at each connection in order to reduce the lateral drift of the structure under applied loads. Four post-tensioned strands are used at each connection with some initial stress.
Experimental Study, Results and Discussion
Beam-to-column subassemblies are erected for eight different specimens. Two of the specimens do not have the steel angled connection, while five of the others have two steel angles on both sides of the connection and one has steel angles on one side of the connections. The steel angles vary in size and form, with bolt tension and initial prestress being two other design parameters for the specimens.
Cyclic lateral loading was applied to each of the specimens using an electrohydraulic servo actuator. The initial three cycles were set to a target drift of 0.2%, 0.4%, and 0.5%, and the following cycles were three cycles at each target drift until the lateral loading applied to the system to achieve the target drift was reduced to 85% of the peak applied lateral load. The target drift was observed using linear variable differential transformers.
It was observed that the steel angles increased the seismic performance of the subassemblies through plastic deformation concentrated in the angles to reduce the residual deformation in the remaining components of the subassembly. The thicker steel angles were shown to have a higher energy dissipation capacity, and the steel angles were shown to be quickly and effectively replaceable after seismic loading. A higher prestress for the horizontal post-tensioning also demonstrated an improvement to the seismic performance in terms of the hysteretic response of the system. Overall, steel angles located at beam-to-column connections were shown to be effective at dissipating seismic loading, though more research is needed to assess the effects of the number of steel angles on the seismic dissipation capacity of a system.
Reference
Dongde, S., Tong, Y., Yinke, M., Yicong, X., Yunlong, Y., and Shiqiang, F., (2022). “Experimental study on seismic performance of prefabricated replaceable beam-column connectors using double-sided angle steel,” Journal of Building Engineering, 51. pp. 1-25.