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RE: Steel Bar Joists as Bridge Beams[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: <seaint(--nospam--at)seaint.org>
- Subject: RE: Steel Bar Joists as Bridge Beams
- From: "Mike Valley" <mtv(--nospam--at)skilling.com>
- Date: Tue, 5 Dec 2000 09:09:53 -0800
Be careful with what you think KCS joists can do! All concentrated loads must still occur at panel points. Therefore, if the location of the concentrated load can vary (as for moving loads) the "constant shear" is meaningless. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Michael Valley, P.E., S.E. E-mail: mtv(--nospam--at)skilling.com Skilling Ward Magnusson Barkshire Inc. Tel:(206)292-1200 1301 Fifth Ave, #3200, Seattle WA 98101-2699 Fax: -1201 -----Original Message----- From: Effland, Greg [mailto:geeffland(--nospam--at)butlermfg.com] Sent: Tuesday, December 05, 2000 8:28 AM To: seaint(--nospam--at)seaint.org Subject: RE: Steel Bar Joists as Bridge Beams David, One joist that might be of interest is the KCS series of bar joists. These joists are designed to allow a specific joist to handle a specific shear value at any point along the length of the joist. This could be handy in dealing with moving loads such as on a bridge. The KCS series should be available from any supplier that supplies SJI Joists. Vulcraft, SMI Joist, and Canam Steel are 3 examples of suppliers. These are available in lengths up to 60 ft long. Typically the span should not exceed 24x the depth of the joist. If you need longer than 60 ft you should look at LH or DLH joists. If you are unconfortable designing the joists from a table then most suppliers will design the joists based upon loading diagrams supplied by yourself. As far as cross-bridging I would use the SJI recommendations as minimums and possibly increase as desired since the bridge will have moving loads. I would provide some sort of lateral bracing, such as rods, or diaphragm deck (using the bar joists as struts) and not count on the bar joists for lateral loads through weak-axis bending. One thing you might consider is serviceability to keep the bridge from bouncing as the truck moves over it. The KCS joist table provides a gross moment of inertia that could be used for the deflection calcs. Not sure what deflection and vibration limits apply to bridges though. Not sure where you are located but here are a few contacts if you need them. If the locations are not close you could contact the manufacturer of your choice and obtain an address/phone for a closer location. Vulcraft PO Box 637 Brigham City, Utah 84302 (801) 734-9433 SMI Joist Company Highway 32 North PO Box 2000 Hope, Arkansas 71802 (501) 777-8777 (800) 643-1577 Canam Steel Corporation 2000 W. Main St. Washington, MO 63090 (314) 239-6716 if for some reason the area code has changed on this one it might be 473. Hope this helps, Greg Effland, P.E. -----Original Message----- From: PEC - Lake City [mailto:pec(--nospam--at)isgroup.net] Sent: Monday, December 04, 2000 2:06 PM To: Seaint Subject: Steel Bar Joists as Bridge Beams I've been contacted by a local builder who wants to build a bridge connecting two pastures separated by a stream. This will be a private bridge - no government controlled loading criteria, but almost certainly the water management district has jurisdiction. The span is 40', single lane to accommodate a loaded pickup truck (builder says use 7000# total live load). Structure is 2 bar joists @ 7'-0" with 4 x 4 decking - total width of about 12 feet. I have designed a number of bridges, but none using bar joists. In fact, I've never used bar joists for anything since I don't normally do buildings. With that ignorance in mind, can bar joists be successfully used in such an application? I'm concerned about the wheel loads that occur directly over the bar joist - there would be pretty good concentrated loads between panel points. Also, without a rigid diaphragm deck (concrete, for example), I don't see any load sharing for lateral loads. I can see the need for some pretty significant cross-bridging. I've already tried to talk the guy into using precast double tees or even a proprietary arch culvert, but he is stuck on the bar joist idea. Any comments, suggestions, ideas? David Finley, P.E.
- RE: Steel Bar Joists as Bridge Beams
- From: Effland, Greg
- RE: Steel Bar Joists as Bridge Beams
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