Roof challenge

Aim: To Design Roof and its various reinforcements considering the styling data given and verify the positions of Roof bow/Roof rails as per snow load or heat distortion criterias.

The following is the material and thickness categories used in Roof designs.

The number of bow roofs depends on the type of roof and CAE requirements for oil canning or snow loads.

Input:

Section for Roof bow:

Section for Front/Rear Roof rails:

The Roof Consist of following components apart from the roof panel,

1) Front Roof Rail

2) Rear Roof rail

3) Front Roof bow

4) Rear Roof bow

5) Center roof rail and reinforcement

6) Brackets for accesories mounting.

Front Roof Rail:

It is a integral part of the roof connecting the front windshield area and connects to the BSO on the sides, consist of mounting provisions for headliner and other accesories.

Center Roof Bow

This mostly consist of additional reinforcement and brackets for light and accesories mounting, depending on position of Sun roof the bow positions change

Additional roof Rails: Depending on requirements one or two additional rails are added for strength and roof crush requirements.

Rear Roof Rail:

It is of two types depending on the tailgate types and joins with the tailgate and rear panels.

The joinery between the roof panel and roof bow is usually done by mastic for which identification marks are provided along the roof rail.

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]

BOW	RX	RY	R	I	L	t	W	OK/NOK
1&2	5686.9	2622.83	3589.953447	360	2030.5	0.75	1.6	OK
2&3	5009.4	5901.4	5418.937779	495.4	2030.5	0.75	1.98	OK
3&4	3988.7	10465.7	5776.031878	450	2030.5	0.75	2.1	OK
4&5	3280.6	15043.7	5386.54816	312.2	2030.5	0.75	1.7	OK

From the above table the Roof passes the bow roof criteria.

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

Section Study is also done for one or two roof rails.

Z=I/Y

1.706*10^4

Y= 134/2 = 67

S = 2.54*10^4

With this the Roof panel and its reinforcements are designed as per required criterias