In a word, “yes”. We provide information on HSS connections so that design engineers pay attention to member compatibility issues before the job is let. We suggest the design engineer be directed to the Handbook (9thedition) Part 3, pages 3-89 to 3-98. Since the behaviour and resistance of welded HSS connections are not always intuitive, their detailed design should be undertaken with scrutiny.
Engineers involved in HSS connections should take into account some of the basic considerations that you will find in the Handbook, which I’ve paraphrased and summarized below:
1. HSS members should not be selected on the basis of minimum mass. - Sounds familiar?
2. Remember that the “connection resistance” is a function of the relative dimensions and wall thicknesses of the members. It is frequently less than the capacity of the connected member.
3. Do not specify “connect for member capacity” to avoid unnecessary reinforcement.
4. Try using square and rectangular HSS which are much easier to fabricate than round HSS.
5. Avoid connections whose members are the same width. The maximum branch member’s width should be equal to or less than the main member’s minus about 5 or 6 times the wall thickness of the main member.
6. Choose branch members that have thin walls relative to the main member.
7. Do not specify full penetration welds automatically as they are seldom justified.
8. Do not specify ultrasonic inspection as this has limited application to HSS connections.
Engineers involved in these types of connections should also read pages 3-90 to 3-91 for additional considerations. Here are a few:
1. Reduce the number of different size members for optimum economy.
2. Use simple gap connections as much as possible as they are usually the most economical.
3. If fatigue is an issue, consider using overlap connections of at least 50%.
There are also several recommendations as to when the connection eccentricity effect in primary and secondary bending moments can be ignored or should be considered. There are useful suggestions for improving connection efficiency and weld effectiveness as a function of dimensional parameters of the connected members and in terms of the inclination of web members. Finally, if the engineer is to really get into HSS truss design, a “must” is Packer and Henderson’s Design Guide: Hollow Structural Section Connections and Trusses, published by CISC:
www.cisc-icca.ca/publications/technical/design/hsscx/ Here is my final note to engineers: If the truss you are designing is going to be Architecturally Exposed Structural Steel, it is essential that you pay particular attention to member compatibility at the design stage and prior to bid time to avoid reinforcement that architects will find unacceptable and to reduce cost. Read the Handbook pages on the subject, the reference suggested, and do not hesitate to contact fabricators on such issues. Fabricators are more and more often called upon early in the project to assist. To find a fabricator in your region, consult our membership directory or call one of the regional marketing directors. Such contact information may be found on our website:
www.cisc-icca.ca