Frequently Asked Questions

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The SJI specifications and Code of Standard Practice cover most bearing seats. If there is nothing in SJI 100-2020 regarding the design of a particular bearing seat, SJI 100-220 Section 4.1a & b apply and the design will be per the requirements of ASIC 360 or AISI S100. If the non-typical joist bearing seat you want to use is not shown in the SJI catalog or Technical Digests, we recommend contacting a joist manufacturer’s engineering department to work out the best solution for your project.

The standard 2½” seat depth should be sufficient; however, going to a 3″ deep bearing seat would be a good idea for the larger 28K- and 30K- joists.

When the joist seat bearing length is less than required bearing length in the SJI specifications, there may eccentricity between the end reaction and the working point where the end web intersects with the top chord centroid. This results in additional top chord bending that needs to be checked. When the bearing length over a masonry wall is less than the SJI specifications, the same is possible; however, the EOR may need to check the wall for possible shear failure due to the shorter bearing or the eccentric load in the wall. If this occurs over an interior beam that does not have a flange wide enough to accommodate two back-to-back joists, there are a couple of options. One is to stagger the joists on each side of the beam. Another is to add a plate on top of the beam flange that will provide the required bearing length.

The three main benefits of using joist bearing seats instead of flush frame connections are: a) lower joist cost for both material and labor, b) lower steel fabrications cost for both material and shop labor, and c) and quicker erection time.

The SJI specifications allow bolting or welding the joist bearing seat to the structure. Bolting can increase the bearing seat uplift capacity. If the joist is subject to axial loads, welding the seat is required; slip critical bolted connection for the bearing seat connection are not recommended.

It is correct that the project’s Engineering of Record is responsible for the connection of the joist or Joist Girder bearing seat to the structure including uplift loading. Although the EOR may not know the thickness of the bearing seat angle, they can control this by specifying the weld size for this connection or by simply specifying the thickness for the bearing seat. For example, if the EOR specifies a 3/16″ fillet weld for the joist bearing seat connection, the joist manufacturer must supply a bearing seat thickness of at least 3/16″ so the specified weld can be developed. In this way the EOR can know the thickness of the bearing seat. FYI – it recommended that the weld size for a K-Series joist not exceed 1/4″.

Yes. It is more economical to install bent plates on the supporting structure to provide a level surface for the joists.

Joist manufacturers do not supply canted bearing seats, as a general rule. These can be attempted when joists are used in hip and valley roof systems. In lieu of installing joists out of plumb, it is recommended that bent plates be installed on the supporting structural steel to provide a level surface of the joists.  If joists are installed out of plumb, special consideration must be given to the bridging. The top chord bridging must be designed for the joist weight effective on the top chord during construction. The bottom chord bridging must be designed for the effective weight while the joists are in service and to prevent rotation of the joist. The bridging will have to be designed for the accumulation of out-of-plane forces caused by the joists being out of plumb. The bearing seat must be designed for the rollover force that will occur due to the joist being out of plumb. the metal deck is considered to brace the joist top chord for the out-of-plane forces in the top chord.

The use of miscellaneous structural steel to transfer the diaphragm shear provides a direct path for the load transfer to the structure. The use of the joist bearing seats to transfer this force can create unintended secondary moments. The joist bearing seat can be designed and manufactured to transfer this force, provided the project’s EOR has considered all the effects of the eccentricity of the force in the structural design.

This will vary depending on the bearing seat depth and angle size used. The SJI has not formally published these values because of the variables involved in the calculation. An approximate value can be obtained by assuming a bearing seat thickness and a 4″ long bearing seat and checking the bending capacity for a given bearing seat depth. The bearing seat thickness can be controlled by the weld specified for the bearing seat connection to the structure.

There is not a common value. The SJI currently does not have published values for bearing seat rollover forces as bearing seat angle sizes, depth and length can vary between projects. Bearing seat angle sizes may be L2x2x1/8″, 3/16″ or 1/4″ for K-Series joists. LH- Series joists seats can be 2½” or 5″ deep and the bearing seat angles can vary more widely than the K-Series.

Joist roll-over is created when the horizontal shears along the building perimeter must be resisted by the joist bearing seat when no structural steel is provided between the joists to absorb the horizontal shear. 

Yes. This would be very helpful to ensure that the joist working point will be over the supporting structure. You can contact an engineer with the joist manufacturer to help coordinate the bearing seat depth for your application. Table 5.4-3 in the SJI 100-2020 provides methods for calculating the joist bearing seat depth for this condition.

Table 5.4-3 in SJI specification ANSI SJI 100-2020 provides formulas that can be used to determine the joist bearing seat depth for this condition.

It may be possible depending on the required top chord angle size. If the joist is installed at a slope, there could be issues with the shallower seat depth. There is usually not a problem with this small a change, however, it is best to check with a joist manufacturer to make sure.

Specifying something and the manufacturer being able to meet that specification are two different things. Specifying a joist with a bearing seat depth less than 2½” can be done; however, joist manufacturers may not be able to design and manufacture a joist to meet that specification. If joists are at a slope, bearing seat depths greater than 2½” may be required.

Yes, for most modifications if the end reaction does not exceed 9200 lbs. the bearing seats will not be affected. Otherwise, the bearing seat weld to the top chord may need to be checked. If the modification involves increased uplift loads, the bearing seats must be checked for their uplift capacity.

For the bolted connection of a joist or Joist Girder to the structure, the steel fabricator is responsible for supplying the bolting materials. For the bolted connection of a joist-to-joist girder, the joist manufacturer is responsible for supplying the bolting material.

There may not be a simple answer to this as fabricators may have different answers. Some may prefer to fabricate the beam seats from plates, while others may prefer to use WTs. Using the same beam seat for all the joist and joist girder connections will always yield the most economical design.

The project’s Engineer of Record is responsible for specifying the connection of the joist or joist girder to the structure. The joist manufacturer will ensure that the supplied joist or joist girder will be capable of obtaining the specified connection.

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