> For the complete documentation index, see [llms.txt](https://docs.openbrim.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.openbrim.org/templates/openbrimfea/loads-fea/static-loads-fea/global-line-load-fea.md). # Global Line Load \[FEA] A Global Line Load applies a distributed force or moment along a **polyline path** defined by a set of points, distributing it to whichever elements in the nominated group lie along that path. Use it for barrier and parapet weights, lane loads, services running along the deck, and any linear load whose position is defined geometrically rather than by naming elements. It survives re-meshing, which makes it the practical choice for a load that must stay on a line while the mesh beneath it changes. Global Line Loads **generate load**. They add nothing to stiffness or mass. ## Line Load **Load Case:** The analysis case the load belongs to. With no case assigned it applies nowhere. **Group:** The FE Group whose elements can receive the load. *Engineering influence.* The load is distributed onto elements **within this group** that lie along the path. A path that runs outside the group's elements delivers nothing, silently. This pairing of a path and a group is the crux of the object: both must be right, and neither is validated. **Points:** The polyline defining the load path, edited in its own sub-sheet. *Engineering influence.* The path defines both **where** the load acts and **how long** it is, and the total load applied is intensity × path length. A path that stops short of the deck end under-applies the barrier weight over the last portion of the span; a path that overshoots applies load beyond the structure, where it is lost. Because the path is geometric, it does not automatically follow a change in the structure's extent. On a curved bridge the polyline must have enough points to follow the curve — too few and it cuts across the arc, shortening the path and placing load off the intended line. **Fx / Fy / Fz:** Distributed force intensity in each direction, in force per unit length. **Mx / My / Mz:** Distributed moment intensity, in moment per unit length. *Engineering influence.* Intensity times path length gives the total applied load, and response scales linearly with it in a linear analysis. **Sign follows the axis direction** — a downward barrier weight in a Z-up model is a **negative** Fz. Note the intensity is **per unit length along the path**, so on a sloped or curved path it is not the same as per unit horizontal length; a quantity taken off a plan drawing must be converted before entry. Applying an eccentric line load — a barrier at the deck edge — produces both vertical load and torsion about the deck's centroid. That torsional effect is part of the point of placing the load geometrically, and it is lost if the load is simplified onto the centreline. **Convert to Node Load:** When enabled, the distributed load is resolved into equivalent concentrated loads at nodes rather than applied as a distributed load along the elements. *Engineering influence.* Node conversion is simpler and more predictable, but it loses the correct fixed-end moments that a genuinely distributed load produces within a member — the total load and the overall response are close, while local moments between nodes are not. Leave it off unless you specifically need nodal application; if it is on, ensure the mesh is fine enough that the discretized load is a fair representation. **Coordinate System:** Whether the components are interpreted in **Global**, **Local**, or a **UCS**. **UCS:** The user coordinate system used when Coordinate System is set to UCS. Ignored otherwise. *Engineering influence.* Global suits gravity-type loads. Local follows the path, which is what a pressure-type load along a curved or superelevated alignment needs. On a curved deck the two diverge continuously along the path, so the choice matters more here than on a straight member. ## Verification * Sum the case's reactions and compare against intensity × path length computed by hand. This catches a path that misses the group, a path shorter than intended, and unit slips in one step. * Display the applied loads and confirm the line follows the intended alignment with no gaps at either end. * On a curved structure, check that the polyline has enough points to follow the curve rather than cutting the chord. * Confirm the eccentricity produces the torsion you expect, by comparing against a case with the load on the centreline. * Check the sign by inspecting the deflected shape. * If Convert to Node Load is on, compare against the distributed case and confirm the difference is acceptable for the mesh density. ## Common mistakes * **A path that lies outside the group's elements**, so the load is silently lost. * **Too few polyline points on a curve**, shortening the path and misplacing the load. * **A path that does not span the full length** it should, under-applying the total. * **Sign error**, applying barrier weight upward. * **Using a plan-length intensity on a sloped or curved path** without converting. * **Simplifying an eccentric load onto the centreline** and losing the torsion. * **Leaving Convert to Node Load on with a coarse mesh**, distorting local moments. * **No Load Case assigned**, so the load does nothing. --- # Agent Instructions This documentation is published with GitBook. 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