Meet one of the CFS-NHERI student researchers: My name is Zhidong Zhang, a third year PhD student in the Thin-walled Structures Group at Johns Hopkins University. I have been in the CFS-NHERI project for more than 2 years. I am conducting research on the seismic resiliency of repetitively framed mid-rise Cold-Formed Steel(CFS) buildings and focused on Steel Sheet Sheathed CFS-Framed shear walls.
I worked on a recently compiled database of 700 CFS-Framed shear wall tests and demonstrate the application of this database for improving the understanding and modeling of cold-formed steel framed shear walls. The initial version of the database was assembled during the development of ASCE41-17 and the database has recently been expanded to include additional tests, additional complete cyclic information from tests, additional fields regarding limit states and code predictions, and placed in a standardized format. Please check this conference paper for further information regarding the database.
Besides, I am working on the development and validation of a high fidelity shell finite element modeling framework in ABAQUS of steel sheet sheathed CFS-Framed shear walls. The models will be used to predict and augment ongoing and future testing in the CFS-NHERI project and to conduct parametric studies to determine improved details and performance. Compared with a number of phenomenological performance-based models, the high fidelity shell finite element-based model can capture the buckling of the steel sheet sheathing, deformations outside of the localized sheathing-to-chord stud fastener zones, cross-section deformations in the cold-formed steel framing, and stiffness reductions due to local and/or distortional buckling of the stud or track. This model is still under development and more work is required before the models can be considered complete. Please check this conference paper for further information regarding the modeling work.
Moreover, in the simulation efforts, it is found that the cyclic nonlinear response of the fastener connection is particularly important and should incorporate the impact of the steel sheet local buckling on the strength and ductility of the connection for seismic performance of screw fastened, steel sheet sheathed shear walls. However, minimal cyclic fastener-level shear test data exists, especially for thin steel sheet – thick framing steel combinations. To provide fastener-level force-deformation response appropriate for cold-formed steel (CFS) steel sheet sheathed shear walls in cyclic load incorporating steel sheet local buckling, A lap shear cyclic testing configuration featuring either one thin steel sheet ply and one thick framing ply or one thin steel sheet ply and two thick framing plies connected by a single fastener with proper sensors is designed. A total number of 156 tests covering a wide range of framing thickness, sheet thickness, fastener type and size, and loading types were conducted. A procedure is developed for idealizing the test results with a multi-segment linear backbone phenomenological model. Parameters developed via the procedure are summarized with the intent of supporting development of high fidelity shell element models.
This post was prepared by CFS-NHERI researcher and Ph.D. candidate at Johns Hopkins, Zhidong Zhang. Contact cfsrc “at” cfsrc.org or Mr. Zhang for further information.