Author Topic: Free span with hammer beam truss Qs (Read 3475 times)

Rooster · « **on:** August 16, 2009, 03:41:48 PM »

I have a potential client who is looking into building a 70ft wide free-span timberframe shop with about an 8/12 +/- pitch saltbox roof.

(That's what I thought!!)

What is the widest building width that a hammer beam truss can appropriately span?

Or has anyone built a timberfame girder truss to span long widths?

Looking for options and direction, ..."no need to re-invent the wheel"

Rooster

Raphael · « **Reply #1 on:** August 16, 2009, 06:50:07 PM »

This is definitely one for the engineers. Wrangling the assymetrical forces of a saltbox roof under a single truss will be quite a challenge, have you got a sketch?

I've seen hammer beams spanning ~60ft and suspect some cathedrals go even wider, but these are buttressed structures. A scissors truss might be another option.

As for the TF girder, I haven't done it but it's essentially the same problem as a bridge.
The Guelph bridge (a 1992 guild project) is 120' clear span.

moonhill · « **Reply #2 on:** August 16, 2009, 08:19:43 PM »

I would say the possible client does not understand the hammer beam "truss". Is this their idea? Did it come from a glossy magazine? Buttress indeed.

If the building is 70' wide how long is it?

I have an engineer now looking at a 36' queen rod truss for my next possible up coming job.

Tim

Rooster · « **Reply #3 on:** August 17, 2009, 02:32:31 AM »

Thanks guys,

I haven't received a sketch yet, but I do know that the building is divided up into two halves...one end is a 42ft wide x 56ft gambrel roof style, two story draft horse barn, which also has 14ft x 56ft lean-to additions attached to each side.

42 +14+14=70ft

The other end of the building is the 70ft x100ft free span, saltbox style roof, timberframe farm and mechanics/ maintenence shop.

70ft x 156ft total footprint.

He likes the look of old timber and is asking that it be made out of used barn material. I have built a 51ft Multiple Kingpost truss covered bridge, so I feel more comfotable with that sort of system. I also looked at some of the Guild's truss literature and found a couple of Queen/King truss combinations that would work for a shorter span. We are still in the early stages of planning, and I have a couple of alternatives/compromises to propose if needed.

Tim,

30-36ft Queen trusses with hanging support rods are very common in Wisconsin Dairy barns built between c.1890-1920. Let me know if you want to pick my brain on that one.

Rooster

Mad Professor · « **Reply #4 on:** August 17, 2009, 05:52:27 AM »

I been in some churches with large span hammer truss design. The walls are mortared stone with a substantial buttress, also of stone, to support the outward thrust of each truss.

I think you will also have to consider a heavy snow load..........

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