What structural software is for
What the software does
Section titled “What the software does”It calculates what it was given: the members, actions and supports in the model, to the standard that was set.
What it does not do: decide whether the model is right.
Where the mistakes arise
Section titled “Where the mistakes arise”In the actions
Section titled “In the actions”Wrong snow zone, wrong terrain category, a forgotten action, a badly formed load combination. The calculation then produces a flawlessly wrong result.
In the restraint conditions
Section titled “In the restraint conditions”The most sensitive point in a thin-walled structure: the restraint lengths and the restraint against twist directly determine the capacity. If the model is more optimistic than reality, the structure will be weaker than the paper. Restraint.
In modelling the connections
Section titled “In modelling the connections”Pinned or fixed, eccentricity, where the load is introduced. Reality is rarely ideal.
In the standard settings
Section titled “In the standard settings”Which standard, which edition, with which national annex parameters. That is a setting, not an automatism. The national annex.
The two kinds of model
Section titled “The two kinds of model”The global model
Section titled “The global model”The whole structure together: load path, bracing, stability, foundation reactions. Built in general structural software.
Member-by-member checking
Section titled “Member-by-member checking”Detailed verification of the thin-walled sections with the effective cross-section and the stability modes. Often done by the LGS design software, which also produces the layout and the manufacturing output.
The two complement each other: one looks at the system, the other at the members.
The duty to check
Section titled “The duty to check”A software result always has to be checked:
- by order-of-magnitude estimate: is the result plausible,
- by looking at the deformed shape: does the structure move as expected,
- by summing the reactions: does the load going down match the load applied,
- by hand-checking the governing members.
Responsibility
Section titled “Responsibility”Responsibility for the design rests with the qualified engineer. The software is a tool — the signature does not belong to the program. Designer qualifications.
The point
Section titled “The point”The software calculates the model, not reality. Most of the engineering work is building the model and judging the result — not the calculation.