Clayton, Berman, and Lowes 2013
This paper discusses the results of an experimental SC-SPSW subassembly study conducted to gain a better understanding of the system behavior and to verify response and component demand parameters that are used in design. The authors then present the results of a numerical study to verify that proposed design procedures for SC-SPSW systems are capable of achieving intended performance standards. The observations and modeling techniques presented may be used as tools to better inform SC-SPSW design.
System Concept
This system is composed of a steel infill plate with horizontal and vertical boundary elements and PT beam to column connections. The SC-SPSW system resists lateral load and dissipates energy through development of tension field action and yielding in the thin steel infill panel. PT connections provide a self-centering capability to the system. In the SC-SPSW system, PT connections replace typical MR HBE to VBE connections, allowing the connection to rock about the HBE flange and resulting in the formation of a gap. This gap causes the PT strands in the connection to elongate elastically, so damage at the HBE ends is prevented and self-centering is achieved.
The lateral strength of the SC-SPSW was provided by a web plate, which acts as a replaceable energy dissipating fuse in the system. HBE distributed forces from the yielding web below and above the HBE act in the direction of the diagonal tension field. If the maximum moment occurs along the HBE, it becomes susceptible to the occurrence of in span flexural hinging. Development of the tension field leads to a reduction of lateral load resistance in the SPSW. Occurrence of in-span hinging in the HBE can be prevented by using PT. PT connections can be designed to ensure that the maximum moment occurs at the end of the HBE at a specified drift level before the beginning of HBE yielding.
Combining the SPSW and PT frame results in flag-shaped hysteresis, where self-centering is provided by SPSW and the re-centering capability is provided by the PT frame.
Experimental Study, Results and Discussion
Subassemblage testing was conducted to investigate additional SC-SPSW design variations including HBE depth, web plate-to-fish plate connection detailing, and web plate-to-boundary frame connectivity. The experimental subassembly was designed to simulate the boundary condition of a HBE mid-height in a SC-SPSW, resulting in a two-story configuration with PT beam-to-column connections at all three HBEs.
The PT elongation, and thus PT force, was greater in the larger HBE specimens for a given drift demand due to the increase in connection rocking depth. As the development of PT strain energy provides the restoring forces to recenter the frame, the lower PT elongation at a given drift demand caused by a decrease in HBE depth results in a lower recentering stiffness and corresponding PT connection rotational stiffness.
Both the welded web plate-to-fish plate connection and the bolted connection had similar strengths up to 2% drift before the ratio began to decrease with increasing drift. The welded connection had a peak strength that was 85% of the bolted connection, and the welded connection showed signs of web plate tearing prior to the bolted connection. Interestingly, both specimens had nearly identical unloading strength and stiffness even though they had significantly different peak strengths and web plate tearing characteristics.
Connecting the web plates only to the HBEs delayed the onset of web plate tearing while also increasing specimen ductility, when compared to connecting the web plate along all edges. Although the specimen strength is significantly lessened with the web plates connected to the HBEs only, using a HBE-only web plate connection may be desirable in SC-SPSWs for web plate damage mitigation and potential reduction of VBE demands, provided that the web plate thickness is appropriately designed to resist the required lateral loads.
Numerical Model, Analysis and Results
The experimental test setups were modeled and analyzed using OpenSees, employing a diagonal strip model to simulate the web plate. The numerical models were able to adequately predict the specimen response, including yield strength, recentering stiffness and HBE moment demands. The tension-compression strip was better at predicting the reloading and unloading strengths of the SC-SPSW specimens than the tension-only model; however, further research can be done to more accurately simulate the complex web plate behavior.
Reference
Clayton, P. M., Berman, J. W., & Lowes, L. N. (2013). Subassembly testing and modeling of self-centering steel plate shear walls. Engineering Structures, 56, 1848-1857. Chicago.