Study On The Stability In Plane Of Portal Frame With Rotational Restriction Of Simple Column Base

The Standardization Institute of Chinese Construction enacted Technical specification for steel structure of light-weight buildings with gabled frames (CECS102:2002) in 2002. In the Specification, two kinds of column bases which have one plate and two or four anchor bolts are the most popular in portal frames and are considered as pinned bases when the stability for wedge-shaped column of portal frame is checked. It simplifies the design greatly. However, it has been proved that the two kinds of column bases (especially the base with four anchor bolts) actually have remarkable ability of rotational restrict with the deduction of theory and experiments. The rotational restrict of column base certainly improved the stability of the frame, but how much can the restrict increase the stability? And how to use the advantage in design?On the above-mentioned issue, it is compared in the this paper that the research was made before on the rotational restricted stiffness of column base. With experimental information and relational analysis, it is introduced that the variational-stiffness column base modeling which is relative with axial force and moment. And the codes are made with second-order non-linear finite element methods for analyzing overall stability of portal frame. A lot of cases are computed with computer for stability of one-bay portal frame loaded by typical loads. After that, it is compared with the results of non-restrict column base. It is concluded that the column base with 4 anchor bolts has considerable anti-rotational ability, and the overall stability in plane of portal frame is remarkably strengthened by the ability. This advantage could be used in design, save lots of materials. And simple measures are introduced. And the anti-rotational ability of column base with 2 anchor bolts is neglectable. Moreover, the actual stability is less than Specification's when the diameter of anchor bolts and the thickness of column base plate are too small. So it is suggested that no improving the overall stable capacity when column base is consisted of 2 anchor bolts. But when the structure of column base is ensured, the Specification's stable capacity could be used safely.