Flitch Plate Question

[markenz]

Hi,

I would like to get some input on engineered lumber and steel flitch plate connection requirements.

One example:

60% of moment is carried by the steel and so 60% of load needs to get into the steel.

Can someone please explain why 100% of the reaction should get into the steel at the support? If the wood can take the shear why can't this reaction be "assumed" distributed between on spacing bolts and friction?

Thoughts...

 

[BAretired]

Who says it should?

BA

 

[msquared48]

The allowable bearing stress on the wood member is a lot higher than the allowable shear stress - 2 to 3 times at least.

Getting the load to the existing column through the wood member should be no problem with a properly sixed column or bearing plate.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[MiketheEngineer]

There have been a number of posts concerning this subject. Search on them.

Each FP is different - different wood - different steel sizes, etc.

I usually just see if the steel can carry the moment and the wood the shear to the column or connection. Very conservative but quick.

Bolt it up so that the thin steel plate is well braced. Like top and bottom at about 16''- 24'' oc.

Again - everything depends on loads, sizes etc.

 

[JLNJ]

It seems to me that the stiffeness of the support material and the relative stiffness of the wood and steel beam in bearing will determine how the reaction is transmitted to the support.


For example if the connection is bearing type on a steel bearing plate I can see how virtually all of the reaction will come through the steel portion of the beam and very little through the wood. The wood needs to deform more to take up its share of the load, but since the steel doesn't deform to let that happen the steel to steel bearing sees most of the reaction.

I imagine that a joist seat would behive differently with more load coming through the wood.

 

[markenz]

@Miketheengineer:

See attached if you would like to use it and save a little on the steel. I usually just use the steel depth... results are close enough.

@JLNJ:

Steel is smaller then wood and it bears atop a column, wall, etc. So no chance steel transfers any of the load to support. Only steel to wood beam, wood beam to support.

But if wood handles the shear ok why it is pertinent at the support to provide extra wood/steel connectors. It is a very common practice to do so but the connectors along the beam span IMO do that very thing and through bolt shear and friction creates the composite beam.

 

[hokie66]

A flitch plate beam is not a composite beam. It is beams of two different materials side by side.

The bolts along the length transfer load from the wood to the steel. If the steel does not take the shear into the support, the steel reaction has to be transferred back into the wood.

 

[Lion06]

markenz-

The grouped bolts at the end are usually to get the load out of the steel and back into the wood. The bolts along the length are taking load out of the wood and putting into the steel. If you want to take the reaction through the wood (which is usually the right thing to do), then you need to get the load that accumulated along the length of the steel plate back into the wood at the end of the member so that it can get into the support in bearing.