� To introduce the concept of modeling and to show its usefulness.

� To understand the definition and limitations of a SSS.a SSS.

� To illustrate the SSS method on a simplified box or van structure.

� To show examples of SSS methods representing vehicle structures.

� A plane structural element (or subassembly) that can be considered as rigid only in its own plane. (i.e. flexible to out-of-plane load)

Plane x-y, Plane y-z

� Note :

oTherefore, the SSS is capable of resisting bending moments about the y-axis (My).

(little or no resistance for Mx, Mz)

M = (E/R)IM = (E/R)I

o Structural surfaces are rigid in their plane but flexible with respect to forces normal to it.

M = (E/R)I

Panel Swaged panelPanel Swaged panel

Panel with reinforced hole Pin jointed framework

Windscreen frame Passenger car sideframeWindscreen frame Passenger car sideframe

Bus sideframe

� Note:◦ Stiffening of the panel by swaging or a reinforced

hole can increase the load capacity.

◦ The pin-jointed framework will also provide suitable structural properties for the loads Q1 and suitable structural properties for the loads Q1 and Q2.

◦ A ring frame (windscreen) provide its sufficient corner joint stiffness and sidebeam stiffness.

Pin jointed mechanism Discontinuous rigidPin jointed mechanism Discontinuous rigid

Panel with large cutout

◦ The structure consists of a thin rectangular sheet to which a rod is bonded along each edge.

Consideration

� A cantilever supported at the Rtwith a vertical load Fz at Lt end.

Note: The boom may be attached to the panel by spot welds, rivets, bolts, fold integral or pressing operations

with a vertical load Fz at Lt end.� The vertical boom distributes the

Fz into the panel.� we assume that panel carries only

shear load.

(Panel does not participate in producing internal bending moment at the section)

� If the floor is square and beam are placed at the longitudinal centreline and at the mid-side position.

Substitution:

Note: Note: Note: Note: 1) The payload (Fpl) is shared between the two beam

in proportion to the beam second moments of area2) The ratio can be used for an approximation load

distribution.

� Bending Load Case

� Each of these members is subject to shear and bending load which are functions of their length.

� The floor and roof panels have no loads � The floor and roof panels have no loads acting in their planes.

� Pure Torsion Load Case

� The floor, roof, Lf and Rt hand side wall panel are loaded in complementary shear.

� The load on a rear panel must be correct as the reacted moment from the suspension forces Rr.reacted moment from the suspension forces Rr.

� If the rear panel is removed, it must be replaced by a ring structure or door frame (resist the torsional load)

� If the rear door frame is omitted, so Q4, Q6, and Q5 does not exist. (No shear loads can be transferred)

� Therefore, the floor (or chassis frame under the � Therefore, the floor (or chassis frame under the floor) has to carry the torsion moment from the front to the rear. (SSS is not permissible)

� Represent Vehicle Structures by SSS (Pawlowski,1964)

A typical saloon (sedan)

� Surface (10) and (11) could be regarded as one component.

� An important design feature is the detail of S(9)-the real panel and S(16)-top frame of the S(9)-the real panel and S(16)-top frame of the boot. (torsional stiffness can be severely reduced)

An estate car (station wagon)

� When this model is loaded with torsion moment, the SSS (4),(6),(7),(11),(12),(13),(14),(15) all act as shear carrying member.

� The main bending loads are taken by the longitudinal (1) and (2), the cross-beam (3) and (4) and the sidewalls (5) and (6).

Van structure (courtesy of Ford Motor co.)

� Modelling vehicles with SSS method has revealed problem in the design concept.

� Flexibility in the rear door frame of a simple � Flexibility in the rear door frame of a simple box results in the torsion moment being carried entirely in the floor or chassis frame.

� If the surrounding frame has low stiffness the glass may be loaded excessive. (glass cracking)