Techniques

Raising tip: lifting a post straight up

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From Daizen News, June 2013

During a raising, lifting the post straight up from the top will help place it accurately and safely. We calculate the weight of the member and place a proper screw that we can hook into the dead-volume center, so the lift is controlled.

The hook used to do this is called a transport ankor, and it’s sold by Würth. We countersink and inset the screws, so that we don’t need to climb up the top of the post after it’s set to take the screw out.

Because we pre-stain our timbers, no damage is allowed. The anchors eliminate the strap that would otherwise go around the member. Also, we protect the corners of the post bottom by enclosing it in a box before the post is lifted. This is a money saving preparation  that we strongly recommend.

We include a gasket around the bottom of each post as part of the building envelope.

A nylon-based plate makes a thermal barrier as well as preventing moisture transfer to the post’s end grain. Then our famous Japanese epoxy anchor system goes in to secure the post to the foundation.

 

 

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How important is a gasket?

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From Daizen News, March 2013

The photo below shows a thermal image from a blow door test, superimposed over a shot of the house itself. A blow door test forces air through the house to determine where heat is escaping. The tongue-and-groove decking and, especially, one triangle

along the roof are areas of air leakage. Since they are in the upper part of the house, the heat loss is tremendous.

The air-tight joints with gaskets that we use prove that our joinery is not causing the heat loss. In one spot, where a beam intersects the roof plate via a wood housing, we thought a gasket was not needed. But the photo shows a distinct air leak. What we learned from this test result will change our frame joint details immediately; and with this knowledge, the leak was easy to fix.

More on an air-tight joint.

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In progress: a curved dome

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from Daizen News  1 April 2012

We’re in the process of erecting a dome for a sun room in a house. Daizen is one of the few sources in B.C. that produces grain-matched, bent, structural timber on a regular basis. To do this, we have developed an entire system, including our proprietary heavy duty clamps.

There is a huge difference between bending a curve and a cut-out curve. Curved beams that are bent retain their continuous fibre, which is what’s required to withstand a compression and tension load. But cut-out timbers simply cut a shape out from a larger timber. This approach is not only limited in size; it can also disconnect most of the fibres entirely, eliminating its usefulness as structural timber. Also, a cut-out curve may split, especially if it is not cut out from free-of-heart-center (FOHC) timber, again limiting the size potential.

A curved beam truss, or a dome as in these pictures, is a structural member, feasible only by bending. In a setting of mostly right angles and straight lines, bent structural timber is not only functional—it’s also refreshing in its roundness.

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Dai goes to the source

  |   Newsletter, Techniques

From Daizen News 1 March 2012

Part of an exchange Dai had with Max Closen, of My-Ti-Con Timber Connectors.

“Hi Max, at December’s CWC engineer workshop in Kelowna, I was surprised by your placing of anchor screws from the main posts. I would always insert screws from the floor beam side, like a spike, but your method makes more sense.

I believe others think as I do. Can you explain for my readers why it’s better to send the anchor screw in from the main post that receives the floor beam?”—Dai

Max says,

Here’s why. Fig. 1 below shows a typical joist-to-beam connection with ASSY structural wood screws installed at an angle. Installing screws on an angle uses their strongest property: withdrawal resistance.

Fig. 1. Insertion, at angles, of ASSY wood screws.

Commonly, screw-type fasteners are not driven into the wood on an angle but instead positioned perpendicular to a member’s surface. In perpendicular insertion, the weakest property of a screw-type fastener, its dowel action, is in force. A simple experiment can explain the difference.

Experiment:

  1. Take a ¼ x 4-in. wood screw and drive half of its length into the wood. Now bend the screw over. Notice how easy it was to bend the screw.
  2. Take a second screw and drive it into the wood under the same conditions. Now try to pull that screw out. As you saw, the screw didn’t want to come out from the wood. The same principle applies for the connection shown in Fig. 1, where the screw is driven in on an angle to the wood grain of the joist.

The two blue arrows in Fig. 1 indicate the correct direction for screw installation in order to maximize its capacity in this connection. The starting point of installation—whether from the top of the beam or the bottom of the joist—is up to the installer.

The red arrow indicates the least efficient installation direction. Installing the fastener as shown in red will not put the screw in tension and therefore will not use the screw’s high withdrawal resistance.

The range of the installation angle  between the wood grain of the joist member and the screw axis is typically  (Fig. 2). Here you see an application of the basic trigonometric functions we all learned in high school (a2 + b2 = c2).

Fig. 2.  Definition of angle  .

I caution against installing screws at angles smaller than 30°. As the angle decreases between the wood grain and the fastener axis, end grain application occurs and reduced capacities must be considered.—Max

ASSY structural wood screws are made in Germany by SWG Production, a  member of the  WURTH Group. Statements made here are to the best knowledge and understanding of the author and shall be confirmed by the structural engineer of record of the project. My-Ti-Con Timber Connectors Inc. and its owners assume no liability.

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