New Millennium Building Systems

Here is everything you need to know

Steel joists have a critical role to play in the design of roof systems facing net uplift due to wind loading. Specifically, the uplift resistance provided by the joist seat—along with the capacity of the welds or bolts that connect the seat to the support structure—is vital to the load path of a roof system facing wind uplift.

Engineers, erectors and fabricators often have questions about or are unaware of proper bolted end anchorage of steel joist seats for uplift loads.

Detailed answers to common questions on this important issue

Q: What must occur if the joist seat has slots, but the erector didn’t install bolts?

A: One of two things must happen:

1. Install the bolts or
2. Weld in the slot

If welding in the slot, the weld must be deposited at side of the slot furthest from the edge of the seat, and the remaining weld must be placed at the toes of the seat and away from the slot as shown in figure 2.

Q: Why is welding required in addition to bolting joist seats?

A: To provide lateral stability to the supporting member. Joist seats have long slots; therefore, they may not provide sufficient lateral stability to the supporting member.

Q: What weld size should be used on joists with uplift?

A: The Steel Joist Institute (SJI) recommends a minimum 3-inch-long weld if sufficient bearing length exists. In regions with high wind loading, a larger weld size and/or length may be required to resist the design uplift reactions.

Q: Who specifies the bearing attachment weld?

A: Per the International Building Code Chapter 2207.2 and the SJI Code of Standard Practice section 6.1, the registered design professional specifies the bearing attachment weld.

Conclusion

Pay close attention to slots in joist seats. The uplift resistance of the joist seat is reliant on bolts and/or welds and deviations from the specified attachment could impact its capacity.