Roof Design

OBJECTIVE:-

• For the Given Roof styling, create an ASSEMBLY by developing the essential flanges for the outer roof and creating the reinforcements.

• Provide appropriate dimensions and check for Draft analysis.
• Do a curvature study on the roof and perform calculations to determine the position of the Bow-roofs.

CAR ROOF:-

An automobile roof or car top is the portion of an automobile that sits above the passenger compartment, protecting the vehicle occupants from sun, wind, rain, and other external elements.

Roof is the structure above the wind shield glass having the reinforcement proving the strength to the overall structure and to with stand the over head forces like snow and other load.

REINFORCEMENT:-

The roof is approximatly flat it is very weak and cannot able to with stand the forces like snow and other load , so in order to increase the strength of the roof these reinforcements like front roof rail, central roof rail, rear roof rail and the bow roofs are introduced and joined to the flat surface of the roof with the different joining process.

DESIGN CONSIDERATIONS :

• Visibility criteria
• Head clearance
• Curvature study
• Heat distortion and snow load criteria
• Draft analysis

HEAT DISTORTION STUDY

Bow–Roof Prediction 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

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]

Judgment Condition

OK< 2.7

CASE	L	RX	RY	R	l	T	W	Result
FRR-BR1	2034.876	5738.305	3479.47	4332.121385	326.94	0.75	1.662895614	PASS
BR1-CRR	2034.876	5033.217	5590.492	5297.238351	482.682	0.75	2.063450456	PASS
CRR-BR2	2034.876	3937.649	17415.069	6423.016408	482.341	0.75	2.388537361	PASS
BR2-RRR	2034.876	4286.117	12181.704	6341.119278	302.826	0.75	2.165285658	PASS

Snow Load Prediction 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)

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 front and rear reference point.

Lx = Distance between the Left and Right end of the roof on the Roof BOW [mm]

The width of the roof panel is 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]

Roof panel X curvature radius of length s in Side view

Judgment condition

Qr ≥ 3.1

CASE	RX	RY	LX	Y	IY	S	alpha	T	My	ly	L	Qr	Result
FRR-BR1	2740.019	2030.399	1145.988	423.158	27800	568.281	0.8581304378	0.75	653421.1183	1967.312	326.94	563.6350618	Pass
BR1-CRR	3755.853	3118.854	1093.683	979.96	23300	723.8525	1.15734618	0.75	967565.4659	1967.312	482.682	132.4087518	Pass
CRR-BR2	4292.263	4202.086	1060.007	1539.779	23300	633.754	0.7396827675	0.75	658306.3352	1967.312	482.341	154.9929783	Pass
BR2-RRR	3951.941	4782.797	1046.255	1967.312				0.75		1967.312	302.826		Pass

DRAFT ANALYSIS: