Roof Design
Introduction:
The roof of a car or other vehicle is the top part of it, which protects passengers or goods from the weather. The roof also protects the passenger from any injury when the car gets crashed or is rolled over or something heavy falls on the roof.
DESIGN CONSIDERATION-
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Visibility criteria
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Head clearance
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Curvature study
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Hear distortion and snow load criteria
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Draft analysis.
CALCULATIONS
Heat Distortion Curvature Study-
This study is used to find out and predict the heat distortion temperature at where the material starts to soften when exposed to a fixed load. So in order to avoid bending or damage of the roof based on this calculation we will decide the position on the roof bows on the roof.
Formula-
W = [1.73 x 10^(-3) x L] + [1.85 x 10^(-8) x (R^2)/t] + [ 1.10x10^(-3) x l] - 2.68
Judgement Condition : OK< 2.7> 3.1
Where,
L = Roof Length in X-Direction[mm](Roof dimension in 0-Y)
R = Roof curvature
R = 2(Rx*Ry)/(Rx+Ry)
Rx = X curvature
Ry = Y curvature
t = Roof plate thickness [mm]
l = Bow Roof Span [mm]
Snow Load Criteria-
We predict the snow load in this of the roof bows and then place and change the design of the load accordingly to satisfy the condition.
Formula-
Qr =[Iy x t2] / [α x s x [(Rx + Ry)/2]2 x 10-8]
Note: The Qr value given over here is correct. There was a typo error in the formula given in the video.
Where
α = My x Lx2 x 10-12 , My = Y(Ly-Y)
Judgement condition = Qr ≥ 3.1
250 ≤ s ≤ 380
t = Roof plate thickness [mm]
Ly = Distance between the front and rear roof Rails on the Vehicle along with 0Y[mm]
Length of Roof panel with the center point between Roof rail Front /Rear as the reference point of the front and the rear.
Lx= Distance between the Left and Right end of the roof on the Roof BOW [mm]
Width of the roof panel exposed on the surface.
Y = Distance front Front Roof Rail to Roof BOW[mm]
s= Distance for which Roof BOW bears divided load [mm]
s = L1/2 + L2/2
Iy = Geometrical moment of inertia of Roof BOW (Y cross-section )[mm4]
Rx = Lateral direction curvature radius of roof panel Y cross-section on Roof BOW [mm]
Roof panel curvature Radius of the Length Lx in Front view
Ry = Longitudinal Direction curvature radius of the Roof panel X cross-section on Roof BOW [mm]
1.For front roof rail and Bow1:
Iy = 1553.9 mm^4
Y = 698.1mm
My=Y(Iy−Y)=698⋅(1553.9−510.3)=532549.08My=Y(Iy-Y)=698⋅(1553.9-510.3)=532549.08
Lx=1147Lx=1147
α=My⋅L2x⋅10−12=532549.08⋅11472⋅10−12=0.7α=My⋅Lx2⋅10-12=532549.08⋅11472⋅10-12=0.7
S=L12+L22=896+445.72=478S=L12+L22=510.32+445.72=478
Rx=4510.3897mmRx=4510.3897mm
Ry=2629.5791mmRy=2629.5791mm
t= 0.75mm
Qr=Iy⋅t2α⋅S⋅[Rx+Ry2]2⋅108=1553.9⋅0.7520.7⋅478⋅[4510.3897+2629.57912]2⋅108=27.30Qr=Iy⋅t2α⋅S⋅[Rx+Ry2]2⋅108=1553.9⋅0.7520.7⋅478⋅[4510.3897+2629.57912]2⋅108=27.30
Judgemental criteria is Qr>3.1
Conclusion:
So from this project, we learned types of roofs and reinforcement used to increases the strength of roof and design the roof according to the heat distortion criteria and snow load conditions and how to join the front roof rail, central roof rail, rear roof rail and Bows to the roof.Learned to position the bows so that we can pass the judgemental conditions of the snow load condition and hear distortion criteria.