Hello,

I would like to apply basic structural design equations (deflection, bending, shear etc.), but have a question:

Is a girt housed at both ends(or any beam for that matter) considered a "beam fixed at both ends"? OR would I still apply the "simple" beam equations?

Which joints would constitute a "fixed" connection?

Many thanks to any who can shed light on this.

Cheers,

Stephen Lenser

Hi Stephen,

Regarding to housing the beam I have to say that the beam cannot be considered as fixed at the ends. No type of simple housing shall be considered as "fixed" in terms of "rigid" connection. Housing takes care of vertical load transmision from beam to post.

House that could be considered as rigid would have to be deep at least 2x height of the beam, which is not the case...

Regarding to formulas I want to make sure we both talk about the same... so, let me give you an example:
loading conditions would be same: uniformly distributed load, full length
Given formulas give us maximum vertical deflection of beam at midspan

A)
joint type: hinges on both sides
D = 5/384 * (w * L^4)/(E*I)

B)
joint type: fixed on both sides (no x,y,z movement alloved, no rx,ry,rz rotation alloved)
D = 1/384 * (w * L^4)/(E*I)

I, personaly, evaluate all beams as they have hinges on both sides, as it is recomended to do so for general steel/wood constructions. The point is rotation, if you can imagine joint where the beam fails in bending (since it is easier to picture than shear) before joinery, you have a rigid connection. Anyway, there is very limited amount of "joints" that could be clasified as fixed or semi-fixed (in terms of wooden joinery - no steel incorporated):

• shouldered thru half dovetail tenon with wedge
• housed thru tenons with shear keys/wedges (anchor beam joint)
• posts buried into the ground

(continuous beam should be evaluated as continuous beam not as sevaral beams with "fixed" ends).
I can post comments and pictures if you are interested....
.
Best regards,
Michal Zajic

Thank you Michal for your response -- this is the information that I needed. I will use the non-fixed equations (e.g. your example 'a') to calculate bending, deflection, shear etc.

If you have additional information about continuous beams and can share that would be appreciated.

Many thanks for the quick response.