Theoretical Question Related to Flitch Plates
Theoretical Question Related to Flitch Plates
(OP)
I understand that Flitch plate beams are usually constructed with a double row of bolts but what if they weren't? What if it were only a single row in the center? Further, what if the steel portion were only in, say, the middle third of the beam? Or equivalently, I suppose, a steel channel reinforcement on the middle third of the beam, again, bolted with only one row of bolts?
It seems to me that compatible deflections and compatible strains would require that the steel be engaged in load sharing and would therefore have value but am I missing something here? Or is the double row primarily for stability, i.e. to prevent buckling?
Thanks.
It seems to me that compatible deflections and compatible strains would require that the steel be engaged in load sharing and would therefore have value but am I missing something here? Or is the double row primarily for stability, i.e. to prevent buckling?
Thanks.






RE: Theoretical Question Related to Flitch Plates
Mike McCann
MMC Engineering
RE: Theoretical Question Related to Flitch Plates
RE: Theoretical Question Related to Flitch Plates
1) as a composite section with calculated "I" and "S" where the steel is almost ineffective for the bending strength due to the neutral axis. Basically the bolting and steel are used for shear strength only.
2) as composite section similar to concrete where the steel is now at a set depth from the compression zone and acts to engage tension forces only. Bolts now engaged horizontally
3) Steel is acting alone for bending strength because by the time it engages, the wood is beyond its strength capacity. Bolts are used to transmit loads only into steel.
______________
MAP
RE: Theoretical Question Related to Flitch Plates
Analysis and Design of arbitrary cross sections
Reinforcement design to all major codes
Moment Curvature analysis
http://www.engissol.com/cross-section-analysis-des...
RE: Theoretical Question Related to Flitch Plates
A single line of bolts at the neutral axis does not constitute a mechanism, kinematic or otherwise. If the Flitch plates run full length, the wood portions and the steel portions would carry load in accordance with their stiffness, provided all parts can do so without buckling.
Archie,
Using Flitch plates over the central third of a beam would not benefit beam strength very much as the moment at each end of the plates is nearly equal to the midspan moment. However, it would reduce deflection.
BA
RE: Theoretical Question Related to Flitch Plates
If I have a single row of bolts at mid-height, for the whole length of the beam, how do I calculate the force on each bolt then?
RE: Theoretical Question Related to Flitch Plates
RE: Theoretical Question Related to Flitch Plates
That is, I was trying to figure out if I need to essentially rebuild the entire frame with steel, effectively ignoring the timber? Or can I cut stop the steel a few feet beyond each connection, with periodic thru-bolts along the way?
I think with the later the moment the steel imposes onto the timber by way of the bolts might prove to be a bit much to bear, literally.
It will take further investigation but in the mean time, any thoughts or suggestions? And sorry, no, I don't have a sketch, unfortunately.
RE: Theoretical Question Related to Flitch Plates
RE: Theoretical Question Related to Flitch Plates
My understanding of the primary reasoning for staggering the bolts is to allow the wood to brace the plate.
There is no shear flow (VQ/It), as hokie points out. This is all stiffness based and the load is transferred from the wood to the steel (typically, it can be the other way around) by bearing through the bolts.
RE: Theoretical Question Related to Flitch Plates
You don't necessarily have to develop the moment at the end of the steel portion. You could just dump the reaction at the end of the steel back on to the wood. So you would then have a point load on your wood beam at the end of the steel portion but you would still have a reduced load where you have steel (because the steel supporting some of the weight). Or do I have this wrong?
EIT
www.HowToEngineer.com
RE: Theoretical Question Related to Flitch Plates
RE: Theoretical Question Related to Flitch Plates
As for the project that caused me to start thinking about this, it sounds like full reinforcement might be the order of the day.