FAQ – Bridging

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What are the bridging requirements for double pitch joists?
For any joist where the center of gravity is above the support point, all rows of bridging should be bolted cross bridging.  The number of rows will vary with length, pitch and weight of joist.  A joist manufacturer can give direction on this.


Can bolted bridging be welded in lieu of bolting?
Yes, Erection bridging must be installed prior to the hoisting cable being released, consequently if welding is being placed on erection bridging, the welding must be done prior to the hoisting cables being released.


How much force can a bridging resist?
Bridging is only designed for the lateral stability forces in the joists.  In general those values are in the SJI bridging tables in the specification.  If bridging is intended to brace other components of the structure the size and connections must be indicated on the contract documents.  Normally these systems are independent of the joist system.


Can the bridging be removed after the joists are erected, the deck is in place and construction of the building is completed?
The bridging that is required only for erection stability can be removed. However the bridging needed for lateral stability during the life of the joist cannot be removed without an analysis. Generally the deck provided the lateral stability of the top chord so it might be able to be removed. The bridging generally provides the lateral stability of the BC. The removal of this bridging will require an analysis of the loading as well as consultation with the manufacturer.


When is uplift bridging needed?
Uplift bridging is required whenever the bottom chord goes into compression. This will be true if there are net concentrated up loads.


Do all bridging lines / rows need to be anchored?
All horizontal bridging lines need to be anchored at the ends either by attaching to a beam, wall anchors or with X bridging termination. Anchorage of the bridging is critical to its performance. We are often asked after the joists have been installed if the bridging can be removed to clear the way for mechanical ducts. In most all cases it can, especially if the bridging is X welded or X bolted and as long as the bridging in the adjacent spaces remains to supply the lateral stability to the joist. In the case of horizontal, removing the bridging and terminating the discontinuity with X welded is acceptable.


Is it required that top and bottom chord bridging lines be aligned?
No. The design by the manufacturer may not require that the top and bottom chord bridging be aligned. Special attention should be addressed to bridging anchorage / termination when lines are not aligned.


When bridging interferes with mechanical ducts, can I remove it?
It is possible but an analysis is required. The manufacturer can provide assistance with an alternate bridging layout.

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