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# RE: Timber Truss Gusset Plate

• To: <seaint(--nospam--at)seaint.org>
• Subject: RE: Timber Truss Gusset Plate
• From: "Rich Lewis" <sea(--nospam--at)lewisengineering.com>
• Date: Mon, 10 Jan 2005 16:46:01 -0600

```David,

Thank you for your response.  I'm not sure if this is an insult, or just
pointing out statics.  I understand the joint equilibrium concept.  That
is a theoretical model of sticks.  Now that I'm detailing a 3D joint of
sticks, plates and bolts and I want to make sure the theory doesn't
blind me of the reality of how the overall joint will behave.

I am working with a common work point.  As I see it all the member
forces are transferred into the gusset plate.  The gusset is where all
the X & Y components equalize themselves.  The chord and web members
apply there axial loads to the plates as axial loads.  Why I am
questioning is because I am not 100% convinced that a member like the
sloping diagonal web will not put a perpendicular to grain load in the
bottom chord.  Theory states the vertical component goes into the
vertical web.  But in the real world will there be a perpendicular to
grain force in the bottom chord? It's a matter of lower bolt shear
values, a lot lower.

Rich Lewis
Lewis Engineering

-----Original Message-----
From: David Topete [mailto:davetopete(--nospam--at)yahoo.com]
Sent: Monday, January 10, 2005 11:17 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: Timber Truss Gusset Plate

I would agree that the joint is in equilibrium, and
that the axial member forces are resolved into their
respective vert and horiz components.  So, no, there
should be no/minor perp-to-grain forces on the bottom
chord for example...  I would then to think that the
first quarter undergrad lectures in Statics should be
true.  Otherwise, why would the method of joints be
taught???
David Topete, PE
SF, CA

--- Rich Lewis <sea(--nospam--at)lewisengineering.com> wrote:

> I am designing a timber truss using Parallam lumber.
>  The panel points
> are connected with steel side plates and bolts.
>
> I have a question as to how I see the bolted
> connection designed.  I
> analyzed the truss with a frame analysis program and
> I have all the
> member forces for various load combinations.  I
> modeled the web members
> as pinned ends and the top and bottom chords as
> continuous members.  As
> I see the joint connection design I design the
> number of bolts based on
> the member forces.  The forces in the members are
> primarily axial forces
> so the bolts are designed based on parallel to grain
> values.  The top
> and bottom chords have some minor shear due to the
> continuous modeling.
>
> Let me see if I can explain this further.  I will
> illustrate this with a
> specific joint, a bottom panel joint that has the
> bottom chord
> horizontal on either side, a diagonal going up to
> the top chord and a
> vertical going up to the top chord.  The force from
> the diagonal goes
> into the steel plate.  The vertical component of the
> force is resisted
> by the vertical web and the horizontal component is
> resisted by the
> bottom chords.  The force is distributed to these
> members through the
> gusset plate.  As I see it I don't have any
> perpendicular to grain
> forces in the bottom chord (except the minor shear
> forces) or the
> diagonal or the vertical.
>
> I need a sounding board to bounce my thoughts off
> of.  Am I looking at
> this correctly?  Would this plate put a twisting
> force in the joint that
> bottom chord?  Would
> joint equilibrium negate this possibility?
>
>
>
> Rich Lewis
> Lewis Engineering
>
>
>

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