Study on Seismic Performance of Cold-Formed Steel-Straw Bale Structure System

The cold-formed steel（CFS） structure system has the characteristics of lightweight components, fully assembled construction（without the need for large machinery at construction site）, fast and simple connection, safety and reliability, and is suitable for the construction of low and multi-story buildings in rural areas. Straw building is a highly energy-efficient building type, which can create a natural and comfortable indoor environment for residents, and has a good effect of energy saving and emission reduction. When the building is abandoned, the straw can also be biodegraded. Straw is rich in reserves and has the ability to sequester carbon, which has gradually become a green building material that has attracted attention. In the traditional CFS structure system, the platform inter-story connection is complicated, with weak connection strength and stiffness, and is prone to failure. The ledger-framed inter-story connection is prone to local buckling, as the studs bear the additional bending moment transmitted by the floor joists. The enclosure materials such as mineral wool, expanded polystyrene, extruded polystyrene are difficult to be widely used in rural buildings due to high energy consumption and high cost in the production. This paper proposed a platform-balloon type CFS-straw bale structure system, which combined CFS with straw bale and improved the platform CFS structure. This system meets the needs of green buildings and low energy consumption, and has unique advantages and large development space in rural areas. In order to investigate the seismic performance of the structure system subjected to earthquake, the finite element models of platform CFS structure, platform-balloon CFS structure, and platform-balloon CFS-straw bale structure were established respectively based on the actual project, and the natural frequencies of the three were obtained. The nonlinear time-history analysis of ground motion was carried out, and the seismic responses of the three subjected to different levels of earthquake were compared, including acceleration response, displacement response, and base shear-top displacement curve. It can be seen from the construction process of the actual project that compared with the platform CFS structure, the platform-balloon CFS structure has fewer components, simple joint configuration, convenient installation and good integrity, which is suitable for application in rural areas. The first three natural frequencies of platform-balloon CFS structure are higher than those of the platform CFS structure. Under the most unfavorable ground motion, the peak base shear force, peak roof displacement, and peak inter-story displacement of platform-balloon CFS structure are smaller than those of platform CFS structure, and the maximum inter-story drift of the structure meets the limit requirements of JGJ 227—2011 "Technical Specification for Low-rise Cold-fromed Thin-walled Steel Buildings" and GB 50011—2010 "Code for Seismic Design of Buildings". Those results indicate that the structural stiffness and seismic performance of the platform-balloon CFS structure are better than those of the platform CFS structure. Considering the influence of the straw wall, the peak base shear and peak roof displacement of the platform-balloon CFS structure are reduced by 12.5% and 30% respectively, indicating that the viscoelastic mechanical properties of straw wall can reduce the seismic response of CFS structure.