Prestressed steel portal frame - is prestressed at its apex to reduce moments in columns

摘要

The portal frame has columns which are hinged at ground level and a pitched beam. This beam (4) is cut at its apex, thus dividing the beam into two parts (4a & 4b). On the top are web plates (7 & 8). Between these is a spacer (11) on the whole assembly is bolted together. Two plates, attached to the bottom flanges, are also bolted together, but without the spacer. The bottom flanges of the beam are drawn together, thereby prestressing the beam. Tensile forces are induced in the bottom flanges. This technique reduces the bending moments in the columns and increases those of the beam.