Vantare Slide Cutout Structure Reinforcement

[davidbrady]

Here's a load, shear, and moment diagram for a typical bus. It's a simplified model based on a uniform load distribution and unequal length overhangs:



R1 and R2 are the loads at the front and rear axles respectively; these are also the maximum shear forces. M is the max moment between the axles. From the literature:

R1 = wl(l-2c)/2b,
R2 = wl(l-2a)/2b, and
M = R1(R1/2w-a).

For this model I'm only looking at the beams added by Vantare along with Prevost's intermediate span connecting the Vantare beams. Vantare added a beam under each slide out to restore strength after it cutout the Prevost sidewalls to make room for the slides. This gives me the following measurements:

a: 24"
b: 316"
c: 134"
w: 49 lbs/in

Since the bus is symmetrical I'm focusing on a 1/2 bus model. My H3 weighs approximately 50,000 lbs, or 25,000 lbs per side. I'm conservatively assuming all this weight bears down on the wall beam composed of a 16" high Vantare section followed by a 32" high Prevost section followed by another 16" Vantare section:



And, with an applied distributed face load (in green) and axle support constraints:



The salon slide situates itself on top of the left Vantare beam while the stateroom slide is supported by the right Vantare beam. The span of this set of beams is 474 inches which after subtracting 3550 lbs of unsprung weight comes to a linear load of 49 lbs per inch.

Using the above formulas for R1, R2, and M, I get:

R1: 7571 lbs
R2: 15656 lbs
M: 33594 ft-lbs

If I resolve this moment about the extreme faces of my Vantare beam's upper and lower chords, I get a tensile force of 20156 lbs acting in compression along the top chord and a 20156 lb force acting in tension along the bottom chord.

I ran an FEA on the sidewall to check the theoretically computed values. Loaded up at 49 lbs/in and with axle constraints in place, here are the results for:

Deflection:
, ,

Tensile Force:
, , , and

Tensile Stress:
, ,
You can see the maximum tensile stress is less than 16,000 psi, which is below the fatigue strength for low carbon steel of roughly 28,000 psi and well below the steel's ultimate tensile strength of roughly 55,000 psi.


Next I want to compare these results to the original Prevost wall beam, more to come...