Framing Connections for Square and Rectangular Structural Tubing

The square and rectangular structural tube was introduced as a new structural shape several years ago. In this short period, these shapes have found application in many structures; they have been particularly popular for columns in low-rise buildings such as schools and factories. Other recent applications include space frame and Vierendeel girder construction. Two of the outstanding characteristics of the tubular shape are (a) high efficiency in carrying compressive loads, and (b) clean appearance for exposed framing. In addition, it has exceptional torsional rigidity in comparison to open structural shapes such as the wide flange beam and channelsection. Square and rectangular tubes are now readily available in many sizes and in several grades of steel. While conventional steel design procedures are appropriate for sizing tubular members, there has been considerable question as to the best methods for connecting tubes to tubes and wide flange beams to tubes. The purpose of this paper is to attempt to resolve some of these questions by presenting the results of recent research conducted at Cornell University. Primary emphasis has been on studying the characteristics and behavior of simple connections (AISC Type 2 framing); although some pilot studies have been conducted on rigid connections (AISC Type 1 framing). Both classes of connections will be discussed herein. All tests were conducted on square tubing, but the results should be applicable to rectangular tubing with no significant error.