Double Beam Flexural Strength
Double Beam Flexural Strength
(OP)
Folks,
I am trying to analyze a situation on an existing building where we are trying to add an additional WF beam on top of an existing W beam to boost up the strength. (essentially one W beam stacked up on top of another)
How does one calculate the flexural strength of such a member? Are there prescribed code procedures for this? Can sectional properties (Z, S) be calculated for this section and applied to AISC formulae to calculate the various limit states? In addition welding between the top flange of the existing beam and bottom flange of the new beam will be made for shear flow.
I am trying to analyze a situation on an existing building where we are trying to add an additional WF beam on top of an existing W beam to boost up the strength. (essentially one W beam stacked up on top of another)
How does one calculate the flexural strength of such a member? Are there prescribed code procedures for this? Can sectional properties (Z, S) be calculated for this section and applied to AISC formulae to calculate the various limit states? In addition welding between the top flange of the existing beam and bottom flange of the new beam will be made for shear flow.






RE: Double Beam Flexural Strength
First principles such as parallel axis theorem, same code procedures as elsewhere, yes but use the singly symetric rules,not really shear flow but longitudinal shear yes.
Here is a spreadsheet in ASD to get you started but I cannot verify its accuracy.
RE: Double Beam Flexural Strength
Please explain.
RE: Double Beam Flexural Strength
This is just like a haunch for a portal frame, This member can be treated like a beam in most codes, but it will normally be a slender instead of compact classification.
I attach a spreadsheet by Alex Tomanovich, he has published these free on the web and they are bloody good. Should help you design to AISC 9th Ed. (ASD)
Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that them like it
RE: Double Beam Flexural Strength
Shear flow is a different thing entirely.
It is the flow of shear stress around an unsymetric cross section such as a channel. Look up unsymetric bending and you will see what I mean.
This may seem like pedantics but every engineering tern has a specific meaning and it is best to ensure we use them properly to avoid misunderstandings.
RE: Double Beam Flexural Strength
RE: Double Beam Flexural Strength
If they are separate, then they should be designed to deflect the same, sharing load based on the ratio of their respective I values. For gravity loads, if the top beam sees the load first, then there is no problem. If the bottom beam sees the load, then a connection between the two beams will be necessary to transfer some of the load to the top beam.
It all depends how you design the system as to what you end up doing.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask