Abstract: A portal building frame formed of asymmetrical metal sections comprises a roof frame member supported on columns by means of knee connectors which telescopically engage with the roof frame member at each end thereof and with the columns. The connectors are secured to the roof frame member and the columns by bolts through both the webs of the metal sections and through flanges thereof, the bolts through the webs being longitudinally spaced by a distance corresponding to the lateral dimension of the webs. The knee connectors are each fabricated with reinforcing plates on the flanges of the metal sections at the joint between the sections forming the connector, and a stiffening plate is welded between mitred ends of the sections to the webs, flanges and reinforcing plates to form the one-piece connector.