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Originally Posted by ozeco41
I used bending to refer to the bending of horizontal beams and "C" shows a descending beam which will fall across another beam and the result both beams will be bent - one down, one up. As shown in "D"....
Would the joints between the vertical columns and horizontal beams be stronger than the horizontal beams themselves?
Sorry for the delay ... I missed the reference when checking the thread.
There is no simple or single answer - it depends what aspect you have in mind.
In general there are three types of forces which apply to structural members:
- "Axial" which means pull or push (tension or compression) along the length or axis of the member;
- "Shear" which is across the member's cross section and tends to "Shear" it (I trust the circular definition is clear
); AND
- "Bending" which should not need explaining. So a horizontal beam supporting a floor will tend to bend downwards with loads increasing on the floor.
Example 1
__________8
__________V__________
A
___________________A
4
___________________4
A "Beam" with a single point load of 8 pounds/kilos/tonnes/whatevers at the midpoint "V" will be supported at the end points "A" and each will carry half the load.
Example 2
Move "V" to the 1/4<>3/4 point:
_____8
_____V_______________
A
___________________A
6
___________________2
...the loads split 3/4<>1/4
Now the beam in both examples will tend to bend downwards due to the load of "V".
In Example 1
Now for Example 2 and working from the left end the "Bending moment" will be 6 x 1/4 = 1.5. Working from the right 2 x 3/4 = 1.5 (Again working from right end gives same result as from left)
However the "bending moment is less in example two. Stateed in reverse a beam loaded at the quarter point as per Example 2 could support 1/3 more load than one loaded at the midpoint.
So that is the first form of "strength".
"Shear" is the force across the member so in Example 1 the shear force would be the same from the left support to the centre - and it would be 4.
Ditto right to centre this time also 4 but opposite sign which we needn't worry about.
However in Example 2 the shear force in the left quarter of the beam would be 6. So tha shear in Ex 2 is 50% greater than in Ex 1.
Bending moment reduces but shear increases when we move that load.
So, when designing, you have to choose members on both shear and bending and, depending on layout, either shear or bending could be the decider.
Say you have a piece of steel which can take 3 in bending and 5 in shear. It could support Ex 1 but would not do for Ex 2.
And the third "Axial" force is not normally relevant to beams.
So, given that mini lecture in Structures 101, you should see why I cannot answer your question at this stage.
How the connections join beam to column changes the simple example for bending. And both bending and shear strength would depend on how the joins were made.
For my example earlier - ie the bending beam pulling a bend into the columns the column would be relatively weak in bending would be pulled sideways by a force much smaller than the column could take as its axial load.
To apply that pull on the columns the joint of beam to column would almost certainly be similar to the axial strength of the beam. Explanation if needed.
I pause there - you should have enough to see what details I would need before I can better answer your original inquiry.
