Does anyone have any general engineering experience with queen post barns. What I am looking at is a basic New York style barn 26' x 36'(14'-8'-14' bays). Much of the roof load is transferred to the purlin plates,queen post bents and and then to the tie beams. The tie beams have one support in the middle(with braces) and the queen posts go into the tie beam about 6' 6" from side wall.
My question is how would you calculate the actual amount of load on these tie beams? Additionally, when there is also a floor framed into them, would you have to add both the floor load and the point loads together, in order to size the beam? It seems if you did this,you would need a beam like 12"x24" to support it. However I have taken part in the building of and have seen enough of these frames, that had much smaller beams and have done just fine. Is there something I am missing?
I am new to the engineering aspects of building but I would like to know a little bit more than just floor joist sizing. If anyone has any experience with these frames please share some insights. Thanks tb

Just one post in the middle? Side entry or gable end entry? If it is a gable end entry I would see two post under the tie, running the length of the barn, not one post, it would get in the way. But with the 14-8-14 bay layout it appears to be side entry, in the 8' bay. Is there any sign of other members supporting the ties, as example, stall framing, walls, ladders, dividers of some kind?

What is the size of the typical tie beams seen in the old barns?

Hi TB,

The loads applied to the tie beam would need to include constant dead loads such as the self weight of the various roof and floor members and coverings (tiles, sarking boards, etc.). Then add to this the variable loads like those imposed by the typical items stored in the barn (hay, etc.) and most importantly don't forget the snow, wind & earthquake loads applied to the tie beam by the roof, side wall & foundations.

All of these loads are applied to the tie beam via the various connecting members such as main posts, queen posts, principal rafters, wall plates, sills, braces, intermediate studs, posts, etc.

The effect of all of these loads can be calculated using simple hand cranked approximations but it is much more easily done using a plane frame analysis program where different case study analysis can be made. These case studies will provide you with more than one answer for each of the conditions needing to be checked such as tension, compression, bending, shear & deflection and so you should take the worst values encountered from each of the case studies to size your beam.

Regards

Ken Hume

The short answer is hire an engineer to do this for you. This is what they do.

The guild resource book has a list. Also there is a list on the TFEC site (Timber Framing Engineering Council).

Jim Rogers

When will engineers be replace by apps on the ipad?

Not anytime soon, I'll wager.

Why is that, Joel?

What would it take to add on to Sketchup, a program to size timber?

Not enough demand?

Would it threaten the engineers work?

For what it's worth I believe you are right, not anytime soon.

Hi Tim,

How long have you got ? You might well be looking for an exactitude where this does not exist.

I spent Sunday examining the Abbingdon Long Gallery - a very large 10 bay jettied building which likely dates from 1430 or so and using the miracle of CAD I did a quick timber count and found that the original building had about 1600 or so individual timbers with almost half of these timbers now cut out and removed. Stuff happens over 600 years. The building has slowly yielded and deformed to the point that some of the joints have failed and are now coming apart and some members have fractured but still the building continues to stand.

Poor Design or Ravages of Time ?

I think that I have expressed my views on this forum many times before about the dangers of designing leggy empty buildings that could easily be subject to large deformations leading to disproportionate collapse typically for the reasons outlined above and so one must recognise that "time now" is only an approximation as to the final building configuration that is likely to exist before decay, deformation and loss results in collapse.

After a while it becomes perfectly possible to believe that because someone has examined and calculated how a timber or collection of timbers will perform that this means that everything will be OK but hopefully we have now advanced beyond that point. It's probably more important to examine existing buildings to see what works and what isn't such a good idea. This empirical approach to building is an equally valid approach when compared with calculations. Where calculations really come into their own is when something quite radical or rare is being undertaken i.e. where there is no experience base from which to draw or alternatively where the commercial, technical or risk to life and limb is such that a better understanding of the undertaking is required.

One must recognise in the USA that apart from New England there is probably very little in the way of a historic building experience base from which timber frame engineers and carpenters can draw upon and so an informed engineering partnership between carpenters and engineers might well provide a better result than over reliance on just the carpenter or just the engineer.

I feel a Rumsfeldian moment coming on again - time to adopt the recovery position !

Regards

Ken Hume

Too many variables for a simple solution. The basic calcs are easy, but the infinite number of configurations means that there is no formula that can handle all circumstances. The closest thing might be Finite Element Analysis, but that's a bear to configure even in 2D from what I've been told. CB.

I have heard that excuse before. Infinite number? What is the poor human to do?
http://www.youtube.com/watch?v=MlyTq-xVkQE