Beam fails with Control Summary showing Concentrated Load(B0) or (Bn).
This indicates that a large load from above has been applied to a conservative square area and may be causing the top of the member to fail in stress perpendicular to grain.
A 3.5” wide contact surface along its top edge is assumed, based on a worst-case 2x4 wall plate or 4x4 post. BCI® / AJS® joists have a fixed capacity for any concentrated loading condition, while rectangular products are analyzed by a compression perpendicular to grain stress check.
This load will need to be evaluated by a qualified designer based on the actual square area applied to the top of the beam using the actual product design values.
Here is a link to the technical note (GE-23) from engineering:
https://s3-us-west-2.amazonaws.com/bcframer/Other/GE-23_Vertical_Load_Transfer_Over_Bearings.pdf
New Information under development:
At one time the industry enhanced the criteria for establishing the concentrated load capacities for concentrated and distributed loads. These changes were captured in ESR-1040 as updates to Table 2, Allowable Rim Board Design Capacities. Now instead of just using Fc Perp times an assumed bearing area, there’s also a test for buckling of the cross section as a short column. I believe there’s some testing involved as well and so we chose a range of depths and grades to test to establish our design values (Jeff would be able to talk you through the logic). These new capacities were implemented in software and continue to be used today.
Here's the details to reproduce the BC Calc output for both load types from the job you sent in:
In this project you are seeing an interesting consequence of the choices made in establishing the design values and the impact of multiple ply beams.
- The 5.25” beam uses the 3.5” value from Table 2 because we didn’t establish capacities for wider widths. It’s at a disadvantage from the start.
- When plies are taken into consideration, we use the number of plies times the single ply value as the capacity. 2x the single ply capacity is greater than the single ply 3.5” capacity.
- Both of the above combine to create a scenario where the single 5.25” beam has less capacity than it’s equivalent section as a built up beam.
I’ve added Jeff as he may want to reconsider how we report capacities in ESR-1040 and/or how we implement them in software when it comes to multiple ply beams. As it stands today, what you have observed isn’t a software bug, but it definitely is a confusing outcome relative to what you would intuitively expect to occur.