Steel: Bridging

So before any metal deck goes on top of open web joists or beams, there needs to be lateral stability of the joists. In this case, when an open web joist is very slender, it's very deep compared to its width, there's the danger of lateral buckling of the joists. So before any deck goes on, they put some bridging on the top and the bottom cord of those open web joists, tying them all together. Then they can go ahead and put the metal deck. Otherwise, they're too flimsy individually and they need to be tied together and prevented from buckling laterally. So as long as the span is less than 60 feet of the joist or the slender beam, then horizontal bridging will do the job. As we see in this picture, the profile is usually an angle of the bridging. So now they can go ahead and put the metal deck and there's no danger of lateral buckling of the joist. If, however, the span is greater than 60 feet of the open-web joist, then they use, instead of horizontal bridging, they use diagonal bridging. And it's important to note that if this open-web joist were to buckle, it would send, whether the horizontal or the X bridging, it would send it into compression. And so slenderness is an issue. The length of the bridging to its least dimension is called the slenderness ratio, and it is limited. The manufacturer specifies the spacing of the X bridging, the horizontal bridging, and it specifies the size of the bridging. Everything is calculated based on slenderness because it could go into compression. Okay, so here's some diagonal bridging versus horizontal bridging and a close-up. And the idea is to keep that bottom chord from wobbling. So this picture probably shows it best. I have a top chord that is made of angles, and in this picture, the web is also a single angle. But what could happen is this would go out or maybe it comes in. So to keep that from happening, there's either horizontal bridging, top and bottom of the open web joist cords, or diagonal bridging as we saw in this image, to keep that bottom tied carefully or closely. Once that deck goes in there, there's a lot more lateral stability. But the bridging is essential before the deck goes in there.