Developed Model of Cold-Formed Steel Shear Walls Based on Its Physical and Mechanical Characteristics

Cold-formed steel (CFS) members form the main structure of lightweight steel frames (LSF). Structures made with these members, due to their lightweight compared to structures made with other building materials, can be considered as an appropriate solution to prevent and reduce earthquake vulnerability in seismic zones. On the other hand, geology evidence shows that due to the high density of active faults in Iran, this zone has a high seismic potential; as a result, it can be found that a large part of the country's population lives in the fault zone. In recent years, regarding the use of lightweight steel structures, providing lateral bearing capacity as a challenging subject has led to various studies in this field. These studies show that the study of the performance of CFS shear walls under near-fault field earthquakes is one of the subjects that has less addressed. In the present paper, the lateral performance of CFS shear walls with flat steel sheet sheathing has been studied based on non-linear dynamic analysis in the near-fault field.

Whereas today, the use of modeling software in the field of lightweight steel structures consider an appropriate alternative to some time-consuming and costly studies with experimental tests. In this research, the OpenSees finite element software has been used for studies. Considering that previous studies in the field of CFS shear walls more focus on static loading (monotonic and cyclic); first, with the help of two presented numerical models, the existing models have been developed for the appropriate ‎prediction of CFS shear wall responses under non-linear dynamic loading. It should be noted that in this research, the use of OpenSees has been preferred over other software for two main reasons: 1) Considering that CFS shear walls with steel sheet sheathing due to the early onset of shear buckling in the sheathing, experience significant pinching of the strength ‎versus displacement response; the presence of an extensive ‎library of materials and elements in the OpenSees, makes it possible to study lateral performance of CFS shear walls with pinching effects without the need for subroutine ‎coding; and 2) The high speed of the OpenSees in modeling and analysis, provides the possibility of numerous calculations and thus the study of the seismic performance of shear walls under multiple earthquakes. Also, considering that often the models presented in OpenSees for modeling CFS shear walls, contain data dependent to experimental tests; one of the most important features of the numerical model developed in this research is the reduce dependence from the conditions and results of experimental tests that provides ‎the modeling of CSF shear walls with new configurations in a simpler way. It can be found that the improvement of numerical models that in defining their data is not so much required time-consuming and costly experimental tests, to study the performance of this type of lateral bearing systems is efficient. Due to this issue in the following, 18 specimens ‎of single-storey CFS shear wall have been modeled with ‎different configurations and have ‎been analyzed and studied in the near-fault field under a set of no pulse-like and pulse-like earthquakes.‎

The results showed that the developed numerical model is able to predict CFS shear wall responses under non-linear dynamic loading and similar to previous studies, in order to appropriate predict the seismic performance of shear walls, it is necessary to consider more details in the numerical model. In order to better evaluating the performance of shear walls, the measurement of the used steels is necessary and a definite result only based on the nominal specifications cannot be reached. The spacing of the fasteners affects the response of the shear wall specimens and in addition, long spaces of fasteners, especially in pulse-like earthquakes, cause undesirable shear wall performance.