Latour, G Rizzano, A. Santiago, L. Da Silva 2018
Column base joints equipped with friction dampers and threaded bars are investigated to increase self-centering capacity. Friction devices that provide the capacity for energy dissipation, along with pre-loaded threaded bars and disk springs that provide the restorative force in the joints are examined. The proposed column base joints were attached to the MRFs and tested to study the behavior of self-centering connections. Results from experimental tests and numerical simulations of the proposed solutions contribute to ongoing experimental activity considering self-centering connections. Cyclic and pseudo-dynamic tests are performed to understand and verify proposed solutions and improvements in structural systems that undergo seismic loading. Numerical simulations of case study have demonstrated the ability for self-centering CB connection to return structural systems to their initial configuration by successfully pre-stressing threaded bars to act as elastic springs. The experimental results demonstrated the ability for the connection to be repaired in a short time, along with an increased capability to resist lateral seismic loading with negligible increase in cost.
System Concept
The proposed connection combines the concept of a disk spring system with friction devices, alongside high strength pre-loaded threaded bars to ensure self-centering capacity in conditions of seismic loading. Friction dampers in beam-to-column connections dissipate energy in the base plate with friction devices to minimize damage in the foundation and footing of a structure. The proposed connection consists of a slotted column splice equipped with friction pads pre-stressed with pre-loaded bolts located above the base plate joint. A system of disk springs allow deformation in the pre-loaded threaded bars. Models are used to account for the behavior of the system and determine the design of specimen that consists of disk springs in parallel and in series for experimental testing. Threaded bars with disk springs welded to the columns control and recenter the CB to its initial straight position by providing a restorative force in the joints. The disk springs are arranged in parallel and in series to ensure adequate deformability to the connection and an adaptable stiffness-resistance combination.
Experimental Study, Results and Discussion
Cyclic and pseudo-dynamic tests were performed on the columns and two actuators were used to control the compressive load on top of the column. Load cells were installed in the connection to measure the tensile force in the threaded bars and in the two bolts of the friction dampers. LDT displacement transducers were used to measure the vertical displacement in both column sides. Initial pre-load on the bars were adjusted to account for variability in the bolt tightening and initial installation loss. During the experiment, axial force was constant while horizontal load at the top of the column was applied consistently with loading protocols. A total of four cyclic tests were performed with varying axial load ratios of 25% and 12.5%. The results displayed that the threaded bars were successful in providing re-centering capabilities to the structure. Additionally, the dissipative energy component provided by the friction dampers equipped to the base plate successfully minimize damage in base plate connections, therefore increasing repairability and decreasing cost to repair structure after an earthquake. The proposed solution can maintain a building’s ability to dissipate energy in the case of residual seismic loading. The connections have displayed the ability to re-center a building to its initial configuration with the use of pre-stressed threaded bars.
Reference
Latour, G. Rizzano, A. Santiago, L. Da Silva (2018), “Experimental response of a low yielding, self-centering, rocking CB joint with friction dampers,” Soil Dynamics and Earthquake Engineering