States [FEA]

A Structure State declares what is present at a given point in the construction sequence, and in what capacity. It associates an element or a group with a stage, and says whether that element contributes stiffness, weight, or both.

This separation is the essence of staged analysis. A segment being lifted contributes weight but not stiffness; wet concrete loads the structure without stiffening it; falsework contributes stiffness but no permanent weight. States are how each of those is expressed.

States control activation and can generate load through their weight factors. They add nothing themselves.

Data

Load Case: The case — normally the stage's case — this state applies in. A state with no case assigned takes effect nowhere.

Object: The specific object whose presence is being declared.

Group: The FE Group whose members are being declared present. Using a group is the normal approach for anything larger than a single element, because it keeps the state definitions to a manageable number as the model grows.

Engineering influence, both. Together these are the connectivity side of the object: they select what is being activated. A group that resolves to nothing activates nothing, and the stage proceeds with less structure than intended — usually visible as a mechanism, a singular matrix, or deflections far larger than expected. Check the group's object count.

Has Stiffness?: Whether the activated elements contribute to the stiffness matrix.

Engineering influence. This is the parameter that distinguishes "load" from "structure". Setting it off while applying weight models material that is present but not yet structurally effective — wet concrete in a deck pour, a segment suspended from a crane, or ballast. The load reaches the structure while the element itself carries nothing.

Setting it on brings the element into the load path from this stage onward, and from that point it attracts force according to its stiffness. When an element becomes stiff is decisive in a staged analysis: a deck made composite early carries a share of subsequent dead load, while the same deck made composite later does not, and the resulting stress distributions differ substantially.

An element that never has stiffness in any state contributes only weight and never carries anything.

Weight Factor X / Y / Z: Multipliers on the activated elements' self-weight in each global direction, for this state.

Engineering influence. This is how the element's own weight is introduced at the right moment in the sequence. In a Z-up model, a factor of −1 in Z applies full self-weight; 0 applies none.

Getting these right is the most common source of error in staged models, in two directions. Applying weight in more than one state double-counts it — the element's self-weight is applied every time a state with a non-zero factor activates it, so a segment declared in several stages is weighed several times. Applying it in none leaves the element weightless for the whole analysis.

Fractional factors have legitimate uses: applying part of a segment's weight as it is progressively lowered onto its bearings, or splitting a pour across stages.

Verification

• Step through the stages in the 3D view and confirm the active structure at each one matches the erection sequence.
• Sum the reactions at the end of the sequence and compare against the total weight of the completed structure. A total that is too high means weight has been double-counted in overlapping states; too low means an element was never given a weight factor.
• Check the object count of each group used by a state.
• For an element intended to be present-but-not-stiff, confirm it carries essentially no force in that stage while its weight still appears in the reactions.
• Confirm that composite action begins in the stage you intend, by checking when the deck starts attracting force.
• Compare deflections at the end of the sequence against expectation; a member that never became stiff shows up as an unexpectedly flexible region.

Common mistakes

• Applying self-weight in more than one state, weighing the same element repeatedly. The total-reaction check is the only reliable way to catch this.
• Never applying self-weight, leaving an element weightless throughout.
• Activating stiffness too early, so a deck or a closure carries load it did not carry in reality.
• Activating stiffness too late, leaving the structure unstable for a stage.
• A group that resolves to nothing, activating no structure at all.
• Sign error on the weight factors, applying self-weight upward.
• Forgetting the wet-concrete condition — modelling a deck pour as immediately composite, which understates girder stress at the most critical moment in its life.