Structural Design

How much do we currently Design ?
The state-of-the-art FEM Software is used to compute the stresses in the structure under its current stiffness configuration. Then:

• The local peak stresses are checked vs. the yield stress of the material to: compute the strength of the structural members vs. elastic-brittle failure.
• The strength of the welded joints is checked vs. Normative Codes (see ASME [3] ) to: compute safety factors (worth up to 30%) that raise the stiffness of the members in compensation of the weakness of the joints.
• The weight of the structure results so penalized by the safety factors, that further attempts to redesign the structural members is hardly worth the effort.

Thus current ‘design’ boils down from its function of project into just assessing the safety of the structure vs. Normative Codes.

Optimal Design
CASoft produces the Optimal Design of a structure by combining three new computational procedures:
Structural Optimization; (see Product)
Virtual Welding; (see next Expert)
Design by Analysis; (see next Expert)

The Structural Optimization procedure in CASoft operates in the following steps:

• Optimal structural stiffness
  the Optimal Optimization feature computes the stiffness distribution across the structural members that produces the minimum total weight.
• Welded joints
  For joints of structural relevance:
  a. set the weld parameters that produce welds of Quality, i.e.
  - free from the distortions induced by shrinkage;
  - ductile under increasing load, up to forming plastic hinges;
  b. compute the ultimate loads on the welded joints, obtaining the ultimate safety factors.
  NOTE:
  step a. is derived from the existing Quality Protocols, or is computed by a new Virtual Welding model;
  step b. is obtained with a Mechanical analysis of plastic hinge models.
  Because of the scalability of Virtual Welding models, such data can often be derived from previous designs.
• Design by Analysis a. store into the Data Base of CASoft the safety factors computed for welded joints;
  b. rerun Structural Optimization, now accounting for safety factors on the welded joints;

In the end, CASoft will design the optimal structural configuration, that produces:
minimum weight of the structural members;
maximum ultimate strength on the welded joints.

Fig. 1 – Table of optimal stresses in the members, case STb1

====MODEL data
User =CASoft Reference =WManual
Model =ZSTb1 Units =[lb,in]
Problem =Structural

MOdules =1
name uaisc
type 4
uaisc-> MOd list ADD
FRames =1
name FRaxy
type 4
from uaisc
scale move rotate recur
X 120 0 0 3
Z 120 0 0 0
BMname BMOd
BMOd-> BMO List ADD
FRaxy-> FRa List ADD
STrucs =1
name STruz
type 4
from FRaxy
scale move rotate recur
Z 0 0 0 1
BFname FRaxy1
FRaxy1-> BFR List Add
STruz-> STr List ADD
Materials =1
ASTM36 prob 3
Lin ym: 2.9e+007 sy: 36000
====BCond =3
BFRame Fraxy
BC name pin4 prob 3
var 1 type 1 val 0 Add
var 2 type 1 val 0 Add
var 3 type 5 val 0 Add
face 4
BFRame Fraxy
BC name pin3 prob 3
var 1 type 1 val 0 Add
var 2 type 1 val 0 Add
var 3 type 5 val 0 Add
face 3
BFRame Fraxy
BC name py prob 3
var 2 type 2 val -17.35 Add
face 6
====endModelData