Reliability of Rotational Behavior of Framing Connections

Recent studies have pointed to the behavior of beam-column connections as having an important effect on stiffness and strength of steel frames, and considerable work has been done to develop analysis methods intended to include not only member, but also connection behavior. Design methods as outlined in the AISC Allowable Stress5 and LRFD6 Specifications authorize inclusion of connection effects under the heading of "Type 3" in the former, and "Partially Restrained" (PR) in the latter. In both analysis and design including connection effects, connection behavior must be known. For typical beam-to column connections of building frames, voluminous, if fragmentary, data are available. Attempts at rational prediction of connection behavior have been less than successful, but empirical expressions, based on test data, of the relation between the applied moment M and the resulting connection rotation q are available. Among these, the most commonly used are those of Frye and Morris. The deterministic moment-rotation curves shown in Fig.1, and others similar, are often based on one single test, and do not account for the scatter which may inevitably be expected of connection behavior, specially if field-bolted. Little is available in the way of replicate tests which might provide a database necessary for statistical prediction of connection behavior. Until such information about reliability of connection behavior is provided, its inclusion in design or analysis rests, at best, on a shaky basis. This paper reports a study the aim of which is to provide a statistical database for the purpose of establishing the degree of reliability of strength and stiffness for one connection type. To this end, nominally identical framing connection specimens from different sources were tested under identical conditions. The individual moment-rotation curves obtained from these tests form the database for probabilistic determination of the reliability with which specified behavior of these connections can be expected.