Tomoki KOBASHI, Nariaki NAKAYASU, Nobutaka SHIMIZU, Ryoichi KANNO and Kikuo IKARASHI Cold-formed steel members are widely applied in columns and other axial members in steel structures. One of the key issues in design of cold formed steel is local buckling strength under axial compression. As a means to avoid premature local buckling, we have paid an attention to the application of octagonal section members. In this paper, we conducted numerical analyses (Finite Strip Analysis and Finite Element Analysis) and stab column tests, to investigate both the elastic and the post buckling strengths of octagonal section members including those where the adjacent plate elements have different width-thickness ratios. These tests and numerical analysis results indicated that the post buckling strengths of the plate elements were affected by the restraining effect from the adjacent plate elements. However, the overall strengths of the members were in line with those estimations by the traditional effective-width method, where simply supported conditions were assumed. This was caused possibly by a trade-off effect between the adjacent plate elements on their local buckling strengths.
The number of cold-formed steel framed houses is increasing and they tend to be built as apartment houses rather than detached houses. Along with this trend, heavy-floor impact sound insulation performance of the houses is expected to be improved. In order to meet this expectation, experimental test and numerical analysis are carried out, using the really-constructed houses as specimens. The results indicate, 1) in order to improve the heavy-floor impact sound insulation performance of cold-formed steel framed houses, sound pressure in a frequency band of 63 Hz has to be reduced, 2) floors of cold-formed steel houses tend to vibrate in a perpendicular direction to floor joists axis in the low-ranged frequency band, which is caused by the anisotropy of floor bending stiffness, 3) considering the vibrating mode shape, to improve sound insulation performance, it seems one of the solutions to increase the floor bending stiffness of weak axis, and 4) the possibility of the suggested solution is confirmed through the on-site test.
In-plane stiffness of dryly built-up steel floor made of flat and corrugated plate is evaluated with using theoretical formulation and physical test. They indicate, 1) dryly built-up floor alone can satisfy required stiffness; 2) it is difficult to satisfy required stiffness when the floor is connected to beam by self-drilling screw; and 3) stiffness of built-up steel floor can be estimated by theoretical formulation shown herein with the accuracy between 0.8 and 1.4 as the ratio of test result to the theoretical value.
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