 | Tie-joists
In this article:
This article will primarily deal with the connection of the bottom chord to the column or girder. For information on top chord connections, please refer to our Joist Shoes article in the June 2006 edition of Canam Info-Tech. This article will also address considerations related to tie-joists which structural engineers must take into account in the building design.
Standard connection details and recommendations
A tie-joist is a joist with its top and bottom chords attached to a column or girder by means of specific connections.
Generally, no load is transferred to the bottom chord through these connections. Most bottom chord connections are formed by means of an angle welded to the column and a tie-joist plate shop-welded to the joist (Figure 1).
Figure 1
However, this type of connection is no longer Canam's first choice for tie-joists. It is now recommended to use a connection with a stabilizer plate (Figure 2), which is an effective and simpler design. This type of connection is also easier to erect and exhibits excellent lateral stability.
Figure 2
The steel fabricator supplies the column with the steel plate attached at the location of the joist bottom chord. The plate is inserted between the vertical legs of the bottom chord angles during erection of the tie-joist.
Standard connection details are available in the Documentation Center on the Canam website and can be downloaded in PDF format or AutoCAD (DWG).
Why use Canam standard connection details?
Canam standard connection details offer a number of benefits, including:
- Uniformity of fabrication details
- Faster verification of plans
- Reduced margin of error
The connection details must be used as presented in the Documentation Center, but if not, please notify Canam.
The Canam standard connection details are divided into joist types according to the letters W, X, Y and Z, in the order in which Canam recommends them (W being the first recommendation and Z the last).
Special cases
Non-standard connection details
- For architectural or other reasons, it may not be possible to use the Canam standard connection details. In these situations, the use of fabricator connection details is acceptable, keeping in mind that Canam standards are highly recommended for the reasons mentioned above.
End moments and axial loads
- If specified on the structural drawings, tie-joists can resist axial loads or end moments. In such cases, the connection details must be modified so that the tie-joists resist the loads by utilizing additional welding or round holes.
Considerations for design engineers
When Canam’s standard joist types are used, the designer must consider the column as being restrained only to the top chord of the tie-joists and not to the bottom chord. Canam will not consider any load in the connection of the bottom chord of the tie-joist, unless otherwise specified on the drawings or in the specifications.
As stated in the article The process of specifying joists in the August 2005 edition of Canam Info-Tech, “External forces to be resisted by joists need to be shown on plan views. Joists being part of moment frames should have their end moments broken down by load types.”
A section or detail of the end moments being transferred from the joists to the supporting structure must be shown on the design drawings. The direction, magnitude and types of loads are essential information for the joist designer to achieve an effective and economical design.
The end moments, as specified by the building designer on the plans or in the specifications, result from the analysis of a frame with defined inertias. It is recommended that the building designer specify the required minimum and maximum limits of inertia to ensure that the frame corresponds to the analysis model.
Information
For more information, please contact our experts:
- Telephone: 1-877-499-6049
- Online: Joists
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