Modelling assumptions

loadtracer is a load rundown, not a design. These are the assumptions it makes, and where they can differ from a hand calculation.

Stiffness

Beams have a unit, uniform EI. A member’s size does not affect how it distributes load.

Continuity

A beam over more than two supports is continuous, and distributes load as a prismatic continuous beam would. This can differ from simple-span hand calculations. A heavily loaded long span can lift the end of a short adjacent span: the reaction at that support is then an uplift, and is carried down as one.

Support fixity

The first support of a beam is a pin and the others are rollers, unless the support has a fixity ("pin", "roller" or "fixed").

Reaction order

A transfer_reaction_index refers to the source member’s supports sorted along the member, which is how papermodels orders them. Coincident supports are kept (so the indexes still line up), but only the first is modelled, and it reports the reaction.

Walls

A wall’s reaction maps onto the member below in the same direction, from the part of the wall over that member (the source extents) to the part of the member under the wall (the target extents). Both are measured from each member’s start, which is the papermodels convention. When the two lengths differ (e.g. from rounding in the drawing), the load is scaled so that the force is unchanged.

Walls on overlapping supports

When two members support the same part of a wall, how the load divides between them depends on their stiffness, which the graph does not carry. loadtracer applies the overlap to both and records an issue. Fix the markup so each part of a wall bears on one member.

Columns

Columns are concentric. Point load locations on a column are ignored.

Loads off a member

Load that falls past the end of a member (common where a trib area is drawn wider than its joist) is moved to that end as a point load. The total load is kept, and an issue is recorded.

Load directions

The inplane and out_of_plane directions are carried through, but only gravity loads are covered by the tests.

The robustness audit covers how each of these was tested, and the input that loadtracer corrects, reports or rejects.