Req help with figuring out old post and beam construction

[Caracal]

On a recent visit to George Washington's Distillery I found posts topped with a cross piece that supported the beams for the floor above (pic provided as attachment) I understand how the scarfed beam is put together but what I cant figure out is how the cross piece and the post are joined and how the beam is them attached to it, if at all??

Can anyone explain how this all fits together?   

 

[Jim_Rogers]

The piece under the scarf joint is called a bolster. It my just be sitting on top of the post, but I don't think so with those wedges showing.
The scarf joint maybe just sitting on top of the bolster.
Or the scarf joint pieces maybe blind pegged down from the top into the bolster.

Welcome to the forum.

Jim Rogers

[Dave Shepard]

Welcome to the Forum! The wedges don't make much sense, unless something strange is going on. :D I don't like to see scarf joints over posts. I wonder if there is any historical influence in the design. I saw a recent small house frame go up on a blog that used a similar scarf joint/bolster design.

[Chilterns]

Caracal,

This kind of assembly is known as a Samson Post and pillow and is generally found in mills and factories where very heavy floor loads are encountered.

Cecil Hewett provides some exploded view illustrations of these on pages 249 - 252 & 255 - 256 in English Historic Carpentry however those wedges are a puzzle.

Do you have more photographs taken from a different angle ?

Chilterns

[Caracal]

The following should give you a good idea of how they are all positioned and provides some more detail from a different perspective. 

The building in the photos is a reconstruction but apparently follows the original methods.  I have seen similar Samson Post and Pillow setups in a large Hammer Mill in Halifax Virginia (not sure of the age)




  

  

 

[hawkins111]

In the top post, what is with the center right joist? Does that not take away from the scarf joint strength? Tom

[Jim_Rogers]

In the top post, what is with the center right joist? Does that not take away from the scarf joint strength? Tom

Yes, most likely it does. However this scarf joint is not a tension joint. If it was then there would be wedges pushing the two halves together.
It is most likely just a joint in two beams to hold up the floor joists. And the pillow block/bolster is doing all the supporting.

Jim Rogers

[Caracal]

Jim, can you or anyone else shed any light on how the post, wedges and pillow block are interacting in this set up?  It would make sense that the beam would be pegged to the pillow block - I assume there is a pocket cut in the post and above that tenon that extends into the pillow block??  I would also assume that there is a shoulder on the post that is supporting the pillow block or is it all resting on the wedges??

[Jim_Rogers]

There seems to be a notch in the scarfed beam for the pillow/bolster block to set into. It is shown on the right hand side in one of the pictures. I think that keeps the pillow block/bolster in place from end to end.

I would assume that there are two tenons on the post, with the gap between them for the wedge and it's matting block to press against the pillow block/bolster and the top end grain of the post. And that there are two matching mortises into the bottom of the pillow block/bolster.
That way they can level the floor above by pounding in the wedge against it's bearing block with the rounded ends.
It could be one of those cases where they didn't know the exact length of the post based on what it is sitting on and needed some way to adjust it up and down to level it out.
But I am just guessing.

Jim Rogers

[D L Bahler]

I am very familiar with bolsters, they are quite common in Switzerland.
There, they are used as an effective means of shortening the span of a timber, or supporting a scarf.
We see them all the time on old bridges (some examples from the 1400's or even earlier) in castles, houses, barns, etc.

They are very common in log buildings where you see an arrangement much like what is shown in the support of roof purlins and floor beams. Wedges are common and, like Jim suggests, are used to adjust the level of an assembly (in a log building, they would be knocked in tight, then withdrawn or even removed later once the walls settle) The forked tenon would be used in this case, with the wedges fitting between the forks, again like Jim suggests. SOmetimes it is blind, like you see here, some times it is a 'bridle' where the forks fit up over on the outside of the block

The cross beam above is usually secured to the block with pegs. Stout pegs are driven into the top of the block, with matching holes  drilled in the cross beam's bottom, which is let down from above and pounded into place. This has proven to be stout enough to last in castle and granary floors for over 700 years...

Unlike directly supporting a beam with a post, where a bolster is used it is proper to place the scarf directly above the post. The load patterns here are much different than they would be without the block, and the beam is not under much pressure above the post (but rather, its forces are concentrated toward the ends of the block.

A bolster block is a very effective way of simplifying post-beam connections.

I am not guaranteeing that is how the structure in question is assembled, but that is certainly one way to do what you see here. That whole assembly looks very European.

[D L Bahler]

 

[Caracal]

Thank you Sir (and Jim)

A very good description that makes lot of sense now.  The structure is a recreation of George Washington's Distillery at Mount Vernon in Northern Virginia.  Given the time of the original construction and the origins of the Master Distiller I would expect that the European influence would have been very strong.

In 1797, George Washington hired a Scottish plantation manager, James Anderson, who encouraged him to build a whiskey distillery next to his gristmill.  This distillery was the largest in America and produced almost 11,000 gallons of whiskey in 1799. - from the Mount Vernon Website

[Chilterns]

Hi Jim,

I think that you are on the right track re double tenon with wedges in between however the outside face of the post is flush with the bolster outside face above and there is no gap between the post top and bolster.

If the wedges are driven in then a gap would open up unless the outside face of the tenons are set inboard of the outside face of the bolster thereby making a sliding joint. But that is not what I am seeing !

This is an ace challenge Caracal.

Chilterns
p.s. a bolster is a double width pillow that stretches all the way across a double bed.

[D L Bahler]

***Timber Framers' Field Trip***

[D L Bahler]

Note that in the Castles above (Schloss Thun, Thun Switzerland and Schloss Spiez, Spiez Switzerland) the posts connect to the bolsters AND the floor beams with a very stout bridle joint. So the post captures both timbers.

As to the wedges,

IS this just a reconstruction?
COuld be the carpenter faithfully copied the joinery down to the last detail -including the leveling wedges- but also was able to make the floor underneath level enough that they werent actualy needed (but are still there to look right, and to fill the gap)

Also could be they were made as a 'just in case' and aren't needed at this time -but you never know if the floor might settle in the next 100 years...

[D L Bahler]

have a look at this:

http://travel.usnews.com/features/A_Taste_of_All-American_Whiskey/

Look at the picture (you can read the article, I just looked at the pic)

Someone left out the wedges...

[Caracal]

Good eye.  Yes the wedges are left out in the pictures at the link you sent.  My pictures are a couple of weeks old so they were added at some time after the fancy pictures in the link.  As you said maybe wedges were not required to level the floor and they either added them later for cosmetic reasons or they are needed now that the building has settled somewhat.

I will try to find out on my next visit

[D L Bahler]

Another long shot,
maybe the wedges are not structural, but have something to do with the brewery?

I doubt that, but it is a thought that crossed my mind.

[Thehardway]

Caracal,

I don't presume to "know" the answer to your questions but could propose a couple theories as to the presence of the wedges.



First, we must not assume that everything that is present in a frame is there by original structural design.  In many cases, what is present is a solution to a mistake, a resolution of a failure or a change in the structure after original purpose.  For instance, if a floor was overloaded and broke the support beam, two scarfed beams might be installed to replace it with a bolster and post under the scarf for additional support.  In an original structure this repair would likely be obvious, but in a reproduction structure, it might all look original to design.  I really don't think this is what is going on here though.

My first impression was like Jim's.  It was likely used as a leveling mechanism but if that's the case, one should see a gap where the take up was made. so in my mind I have ruled that out.

I am venturing out on a limb here but I am wondering if this is an upside down, wedged half dovetail joint.

In a horizontal wedged half dovetail the wedge is driven horizontally.  Friction only holds it in place but there are no forces acting against it.  In other cases  (think a kingpost to tie) a wedged dovetail might be inserted from above, a wedge driven in beside it and friction and gravity work together to prevent wedge withdrawal.  But here, there would be nothing to hold the wedge in.  The solution would be to insert the wedge, drive it tight, then saw it off even at the bottom of the bolster and then drive a set of wedges in under it through the post to prevent it from falling out. This would be particularly useful if the post and bolster were being put in under a beam as no wedge could be driven in from above once it was in place.  I have imagined such a joint and its usefulness but never seen in use.  This might or might not be it.

I can't think of any other usefulness for the wedges in that location.  It also explains the ability to leave them out for a time between pictures without an visible adverse effects.

My question now is, if those are double tenons. Why are they flush with the edge of the bolster and how long are they?

This is a good puzzle.

[Brian_Weekley]

I had sent a note to the architecture firm that designed the distillery and asked about the purpose of the wedges in the top of the posts.  This was their response:

Hello, Brian. Those wedges were sometimes found in industrial buildings built of green wood. As the wood dried and shrank, posts would get shorter, beams would get smaller, etc., and a gap could emerge between – in the distillery, for example – the posts and the attic summer brackets. Wood wedges were put in between the top of the post and the bottom of the attic summer brackets and, as the wood dried and a gap was created, the opposing wedges could be tapped to re-establish a firm bearing surface. The distillery was constructed of mostly seasoned wood so the wedges won't be as necessary in this structure, but they are appropriate to the period and building use. There are numerous examples of these wedges in the northern Virginia area, and the specific details recreated here were suggested by a consultant at Colonial Williamsburg, based on a colonial-era warehouse in Petersburg, VA.

I think when the images were taken for the article you reference, the building had just opened and wedges hadn't been put into all of the post-to-bracket connections, but you can see the gaps in the tops of the posts in some of the images. I haven't been out there for a season or two, but I think they are all in there now.

Thanks for your interest. It was a real treat to be able to work on this project. Mount Vernon is a tremendous client and has a wealth of knowledge among its staff, and the buildingwright, craftsmen, and historians that we worked with in design and construction were amazing.

Coincidentally, a new batch of the whiskey distilled there goes on sale tomorrow, though you need to be here to get it. If you aren't in the area, you can always sign up for notification about future sales. http://www.mountvernon.org/whiskeysale

Quinn Evans Architects

[Jim_Rogers]

Thanks for posting that.

Jim Rogers