Assign - Ignore Rib Spacing dialog

The Assign - Ignore Rib Spacing dialog opens when Assign > Ignore Rib Spacing is selected.

RAM Steel Beam considers the spacing of ribs (flutes) when calculating the number of studs that can be applied to a beam. In some situations the angle of the deck relative to the beam is small such that the number of ribs that cross the beam is relatively low and thus the beam either fails as a composite beam or is designed as a non-composite beam. The engineer can indicate that the spacing of the ribs is to be ignored, allowing the program to design those beams as composite beams. This is assigned on a beam-by-beam basis (i.e., it is not a global criteria).

For beams to which the assignment has been made, the stud spacing is not limited to the rib spacing; rather, the minimum allowable stud spacing is used instead.

There are two options that are related to the calculation of the stud capacity.

Altered Ribs – the Stud Capacity will not be modified from what is currently calculated; the reduction for rib configuration will still be applied.
Split Deck –the Stud Capacity may be modified: the normal reduction for the steel deck profile will not be applied if the beam width is at least 8" for ASD and LRFD design or at least 140mm for BS 5950 design.
8" was chosen for ASD and LRFD because, lacking any explicit requirement in those codes the 2005 Specification's requirement has been adopted which says that for split deck there is no reduction due to the deck configuration if less than ½ of the flange is covered by deck; since the required bearing length for deck is 2", this requires an 8" flange: (2")(2 sides)(2) = 8".

The normal reduction for the steel deck profile will always be applied to CAN/CSA S16-01 and to Eurocode; the stud capacity is not affected by the Split Deck designation.

Dialog Controls

Setting	Description
Ignore Rib Spacing when Determining Stud Spacing	When the deck is skewed with respect to the beam and the angle between the deck and the beam is very small, there may be very few ribs crossing the beam in which to put studs. It is sometimes impossible to fit the number of studs required for minimum composite action due to the long spacing between ribs. In actual construction practice, the required number of studs can be forced to fit either by splitting the deck – forming a concrete haunch down the length of the beam – or by cutting or flattening the ribs as necessary to place the studs. The user can indicate that the spacing of the ribs is to be ignored, allowing the program to design those beams as composite beams. This is done by selecting the Ignore Rib Spacing when Determining Stud Spacing option. When this option is selected, the stud spacing is not limited to the rib spacing; rather, the minimum allowable stud spacing is used instead, when determining the number of studs that can fit along the beam. When overriding the rib spacing the engineer can designate that the deck is either Split or Altered, as shown graphically in the dialog box. The option that is selected for Condition has an impact on the design. Normally this option should not be selected, as it may result in the specification of a quantity of studs that cannot be conveniently placed on the beam (within the ribs) without modifying the deck.
Clear	Select this option to assign to beams to clear the assignment.

Setting

Description

Ignore Rib Spacing when Determining Stud Spacing

When the deck is skewed with respect to the beam and the angle between the deck and the beam is very small, there may be very few ribs crossing the beam in which to put studs. It is sometimes impossible to fit the number of studs required for minimum composite action due to the long spacing between ribs. In actual construction practice, the required number of studs can be forced to fit either by splitting the deck – forming a concrete haunch down the length of the beam – or by cutting or flattening the ribs as necessary to place the studs. The user can indicate that the spacing of the ribs is to be ignored, allowing the program to design those beams as composite beams. This is done by selecting the Ignore Rib Spacing when Determining Stud Spacing option.

When this option is selected, the stud spacing is not limited to the rib spacing; rather, the minimum allowable stud spacing is used instead, when determining the number of studs that can fit along the beam.

When overriding the rib spacing the engineer can designate that the deck is either Split or Altered, as shown graphically in the dialog box. The option that is selected for Condition has an impact on the design.

Normally this option should not be selected, as it may result in the specification of a quantity of studs that cannot be conveniently placed on the beam (within the ribs) without modifying the deck.

Clear

Select this option to assign to beams to clear the assignment.