ABSTRACT

In the ASD Specification, design of semi-rigid framing systems is allowed under the Type 2 (simple framing) or Type 3 (semi-rigid) construction provisions. Type 2 construction assumes that, insofar as gravity loading is concerned, the beams and girders are simply-supported members and so their design is carried out without considering the effect of rotational restraint from the connections. However, for lateral loading the design is based on the assumption that the full beam end moments are to be transmitted to the columns. In simple terms, this means that, as far as the design of beams and girders is concerned, the connections are assumed to be pinned, but as far as the design of columns is concerned, the connections are assumed to be rigid. This design approach often results in an overdesign for the beams and an underdesign for the columns. Although frames with less than ten stories designed according to Type 2 construction are safe (Ackroyd and Gerstle,

1983; Ackroyd, 1987a; Cook and Gerstle, 1987a, b), it has been shown that the actual factors of safety for these frames often fall below their intended value (Cronembold, 1986).