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Joist FAQ



Q: How do I become a customer of Vulcraft?

A: Please contact the District Sales Manager at your local Vulcraft office.  They will be able to help you through the process which includes a credit check.


Q: How do I find out what my projected delivery date is for ordered material?

A: Please contact your Project Manager to determine a specific delivery date once the project is “Back from Approval” with all questions answered.



Q: Are joists and joist girders designed to the AISC-ASD Code or AISC-LRFD Code?

A: Joist and joist girder design conforms to the Steel Joist Institute specifications, Allowable Stress Design and Load & Resistance Factor Design.


Q: Do joist welds meet AWS D1.1 Code requirements?

A: Joist welds conform to the Steel Joist Institute specifications, Allowable Stress Design and Load & Resistance Factor Design.


Q: How do you specify joist girders with different joist loads or different joist spacing?

A: In this situation, a special load diagram must be provided showing the required loads and their location on the girder. For more examples, see the Code of Standard Practice COSP in the joist specification.


Q: What information is required to specify bowstring Joists?

A: In addition to loading information, the joist depth at the ends and center depth or the bend radius for the top chord must be provided.


Q: When should a KCS series joist be specified?

A: When point load locations vary between joists or the locations for point loads are not known, a KCS series should be used. The KCS series joist can also be used when non-uniform loading conditions exist. The specifying professional must calculate the maximum moment and shear caused by the various loading conditions and select the KCS series joist that provides the required moment and shear capacity. This information is more specifically addressed in the Vulcraft Steel Joist and Joist Girders catalog.


Q: Can bridging be removed when it interferes with other trade work?

A: Bridging may not be removed as a general rule. However, in certain instances, the Vulcraft engineer may be able to recommend modifications to the bridging requirements. Review any conflicting conditions with the Vulcraft engineer to determine what options are available.


Q: Are there special bridging requirements for bottom chord bearing or cantilever joists?

A: There are special bridging requirements when bottom chord bearing is required or a joist has a full depth cantilevered end condition. A row of diagonal bridging is required to be located near the support for lateral stability. This bridging must be installed as the joists are set in place.


Q: Does Vulcraft have recommended moment connection details for joists and joists girders?

A: The most efficient detail allows for the top moment plate to be welded to the top chord of the joist or girder and the cap plate of the column. This requires the joist or girder seat to be supported by a haunch or seat angle. Additionally, the bottom chord extensions must be welded to the stabilizer plate on the column. The size of the top moment plate, seat angle or haunch, stabilizer plate and all required welds are to be determined by the specifying professional. For recommended details, refer to the Vulcraft Steel Joists and Joist Girders catalog.


Q: Are there special requirements for long top chord extensions on K-series joist?

A: The limitations for standard 2 ½” bearing seats can be determined by reviewing the Top Chord Extension Load Tables in the Vulcraft catalog. When the top chord extensions exceed these limits deeper bearing seats will be required and should be reviewed with the Vulcraft engineer for guidance on the minimum seat depth.  In all instances it is important to make sure that proper clearance is provided for the top chord extension.


Q: Can you design joists for a moving point load at top and /or bottom chords?

A: Yes. Vulcraft has the ability to design for point loads that occur at any panel point along the top or bottom chord of the joist. In addition Vulcraft can design for the effect of a point load located at any point along the top or bottom chord. These loads must be clearly defined to avoid duplicate application or missing the load entirely.


Q: Why does the diagram for the joist substitutes with a cantilevered end show the cantilever and the main-span being the same length?

A: By balancing the lengths, the force is applied to the supporting joist would be balanced by the applied load to the joist for the same loading condition. It is possible to have different lengths of the cantilever and the main-span; however, the supporting joist design must be reviewed.


Q: Are there special design factors that must be considered for scissors and arched joists?

A: These types of joist configurations will produce a horizontal force at the supports. The ability of the supporting structure to resist this horizontal load must be considered by the specifying professional.


Q: Can joist seats be used to transfer lateral loads into the supporting structure?

A: Joist seats can be designed to transfer lateral loads into the supporting structure, however there are limitations. This issue must be looked at on a case by case basis and should be reviewed with a Vulcraft engineer.


Q: How much axial load can joist girder seats transfer into the supporting structure?

A: Axial loads can be transferred into a column through the joist girder seats. The magnitude of load that can be transferred depends upon the chord and seat member sizes used in the girder. This information is more specifically addressed in the joist girder section of the Vulcraft Steel Joist and Joist Girders catalog. As with any special condition, this issue should be reviewed with a Vulcraft engineer.



Q: What is the maximum length and/or depth of a joist or joist girder that can be delivered in one piece?

A: Vulcraft’s fabrication ability on depth and length of joists typically exceeds that which may be legally permitted for delivery. Please contact the Vulcraft location that will be fabricating your project to discuss any restrictions.


Q: What is the minimum length joist that can be built?

A: From a practical and economic standpoint, Vulcraft does not recommend using joist for spans less than 10'-0". For spans less than 10'-0" Vulcraft recommends using the VS (Joist Substitute) series.



Q: What design information is required to specify a composite joist?

A: Joist depth, span and adjacent joist spacing (for exterior and interior conditions), deck type, slab depth above deck, concrete unit weight, concrete F’c, stud diameter, stud length and composite design loads. Composite design loads include:

  • Non-composite Dead Load (concrete, joists, deck and bridging)
  • Construction Live Load (A suggestive minimum is ½" additional concrete plus five 200 lb. Workers.)
  • Composite Dead Load (Includes partitions, mechanical, electrical, fireproofing, floor covering and ceiling.)
  • Composite Live Load (Reduced design live load applying applicable code reductions.) Refer to the current Vulcraft Composite Joist / ECOSPAN Composite Joist catalog for a more complete discussion of this issue



Q: What information does the Vulcraft joist tag show?

A: The metal tag wired to each joist shows the job number, mark number and plant location. The bundle tags shows standard erection warnings, plant location, job number, list number, part quantity, part number, paint color, date and time built.


Q: What paint options are available for joist or deck?

A: Joists and joist girders are provided with no paint or gray shop primer.

Deck is provided with either no paint, gray or white shop primer, or galvanized.

      NOTE: The shop primer is not intended to be a finish coat and must not be expected to perform like one. Please contact the Vulcraft location that will be fabricating your project to discuss available primer options.

Q: Why is there a difference in the weight per foot of the same joist in the load tables and Economical Joist Guide?

A: The weights shown in the load tables are from the Steel Joist Institute and are based on the average weight of that joist for the industry. Weights shown in the Economical Joist Guide are based on the weight of Vulcraft manufactured joists. Since Vulcraft, in some cases, has more available material sizes, the Vulcraft weight is less than other manufacturers.


Q: Why is there a 550 pounds per foot capacity limit in the K-series joists?

A: It is possible to get a K-series joist with a capacity greater than 550 plf; however, this joist must be called out as a special and a loading diagram provided. Loading greater than 550 plf can require chord sizes larger than 2½" and therefore bearing seats deeper than the standard K series 2½".


Q: Why is there not a chart to show the maximum duct openings for the LH-series joists?

A: There is no chart because the panel sizes for these joists have many factors that will govern how the panels are set. Specific requirements for clearances in a given joist should be reviewed with a Vulcraft engineer.