> 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/fe-line-loads-fea.md). # FE Line Loads \[FEA] An FE Line Load applies a load **to a line element** rather than to a node: a point load or moment at a position along the member, or a distributed load varying linearly between two positions. The program converts it into equivalent nodal forces and fixed-end moments during assembly. Applying load to the element rather than to nodes is what allows a load to sit **between** nodes, and it produces the correct fixed-end moments without requiring a node at the load position. FE Line Loads **generate load**. They add nothing to stiffness or mass. **Load Case:** The analysis case the load belongs to. With no case assigned it applies nowhere. **Element:** The FE Line, or group of lines, the load acts on. This is a **connectivity** parameter. Pointing at a group applies the load to every member in it — convenient for a deck-wide superimposed load, and a common source of over-application when the group is broader than intended. **System:** Whether the direction below is interpreted in the element's **local** axes or in **global** axes. *Engineering influence.* This is the parameter that most often goes wrong on sloped and curved members. A **global** load acts in a fixed world direction regardless of member orientation — correct for gravity-type loads such as a wearing surface, whose magnitude per unit length is measured along the member. A **local** load follows the member, so it stays perpendicular to a sloped girder — correct for pressure-type loads such as wind on a face. On an inclined member the two differ by the slope angle, and a superimposed dead load entered in local axes on a sloped girder is both reduced and given a spurious axial component. **Direction:** Which axis of the chosen system the load acts along. *Engineering influence.* Combined with the sign of the magnitude, this sets where the load actually goes. A downward load in a Z-up model with a global system is a **negative** magnitude in the Z direction. Note the load is applied **per unit length of the member**, not per unit horizontal projection: on a sloped member, a load defined per horizontal metre must be converted before entry, or the total applied will exceed the intended value by the ratio of member length to horizontal span. ## Point Load **Point Force Magnitude:** A concentrated force applied at a position along the member. **Point Moment Magnitude:** A concentrated moment applied at a position along the member. **Point Load Location (x/L):** The position, as a **fraction of member length** from Node 1 — 0 at the start, 0.5 at midspan, 1 at the end. *Engineering influence.* Because the position is a fraction rather than an absolute distance, it **follows the member if the geometry changes** — useful for parametric models, and a trap if you intended a fixed physical location. A value outside the range 0 to 1 places the load off the member. Position governs the response: a point load at midspan produces the maximum sagging moment, while the same load near a support produces mostly shear and little moment. For a concentrated moment, the position determines where the step in the moment diagram occurs. Both are applied exactly, without needing a node there. ## Linear Load **Force Magnitude at Start / Force Magnitude at End:** Distributed force intensity, in force per unit length, at the start and end of the loaded region. **Moment Magnitude at Start / Moment Magnitude at End:** Distributed moment intensity, in moment per unit length, at each end of the loaded region. **Linear Load Start Location (x/L) / Linear Load End Location (x/L):** The extent of the loaded region, as fractions of member length. *Engineering influence.* Setting start and end magnitudes **equal** gives a uniform load; setting them different gives a linearly varying (trapezoidal or triangular) load — the natural way to model a tapering superimposed load, a soil pressure varying with depth, or a load that ramps across a member. Setting one to zero gives a triangular distribution. The **locations** define a partial-length load. Leaving both at their defaults (0 and 0) applies the load over zero length and therefore applies **nothing** — a load that has been entered with magnitudes but no extent does nothing at all, silently. To load the full member, the end location must be 1. Total applied load is the average intensity times the loaded length, so both the magnitudes and the extent must be right for the total to be right; checking reactions is the only reliable confirmation. Results sensitive to these: span moments and shears, and — because a distributed load produces different fixed-end moments than an equivalent point load — the moment distribution in a continuous structure. ## Verification * Sum the case's reactions and compare against the total applied load computed by hand: average intensity × loaded length. This catches location errors, unit slips and the zero-extent trap in one step. * Display the applied loads and confirm the arrows are on the right members, pointing the right way, and covering the intended extent. * Compare a simply supported span's midspan moment against `wL²/8` for a uniform load, or `PL/4` for a central point load. * For a sloped member, confirm the total load matches what you intended per unit length along the member, not per horizontal metre. * Check that a local-system load stays perpendicular to a sloped member and a global-system load does not, by inspecting the load display. * Confirm a partial-length load starts and ends where you meant, remembering the values are fractions. ## Common mistakes * **Leaving the linear load locations at 0 and 0**, applying the load over zero length so nothing happens. * **Sign error**, applying a gravity load upward. * **Confusing local and global systems on a sloped member**, changing both the magnitude delivered and the direction. * **Entering a load defined per horizontal metre** on a sloped member without converting to per-metre along the member. * **Assuming x/L is a distance.** It is a fraction; entering 5 for "5 metres from the start" places the load well off the member. * **Applying to a group** that contains more members than intended, multiplying the total load. * **No Load Case assigned**, so the load does nothing. * **Expecting the load position to stay fixed** when the model geometry is parametric — the fraction moves with the member. --- # Agent Instructions This documentation is published with GitBook. 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