> 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/nodal-loads-fea.md). # Nodal Loads \[FEA] A Nodal Load applies a concentrated force and/or moment directly at a node. Use it for equipment weights, a reaction handed over from another model, jacking forces, and any action that genuinely acts at a point. Nodal Loads **generate load**. They add nothing to stiffness or mass. **Load Case:** The analysis case the load belongs to. A load with no case assigned is applied nowhere; it exists in the model and contributes to nothing, with no warning. Loads reach results only through their case and any combination that includes that case. **Node:** The joint the load acts at. This is a **connectivity** parameter. *Engineering influence.* A concentrated load applied at a node is exactly a point load in the mathematics of the model, so in a shell or solid mesh it produces a local stress singularity — the stress at that node rises without limit as the mesh is refined, and any stress read there is a function of mesh size rather than of the structure. Read forces a little away from the application point, or spread the load over several nodes, wherever local stress matters. For frame models this is not an issue. The node must exist in the active structure for the case; a load on a node that is inactive in the current construction stage does nothing. **Coordinate System:** Whether the components below are interpreted in **Global**, **Local**, or a **UCS** (user coordinate system). *Engineering influence.* Global is the usual choice and means the components act along the global axes regardless of the structure's orientation. Local and UCS let the load follow a skewed or superelevated geometry — a braking force along the roadway direction on a curved bridge, or a load normal to a skewed abutment. Selecting the wrong system silently rotates the load: a longitudinal braking force entered as global X on a bridge at 30° skew delivers only part of its magnitude along the road and introduces a transverse component that was never intended. **UCS:** The user coordinate system used when Coordinate System is set to UCS. Ignored otherwise. ## Forces & Moments **Fx / Fy / Fz:** Force components along each axis of the chosen coordinate system. **Mx / My / Mz:** Moment components about each axis of the chosen coordinate system. *Engineering influence, all six.* Each component is applied directly to the corresponding degree of freedom, and the response scales linearly with it in a linear analysis. **Sign follows the axis direction**, so a downward load in a model with Z up is entered as a **negative** Fz — a sign error here is the most common mistake on this object and produces an uplift case that looks superficially plausible. A component applied to a **restrained** degree of freedom goes straight into the reaction and produces no deformation at all — which is why a load applied at a support node can appear to do nothing. Similarly, a **moment applied to a node with no rotational stiffness** — a node connected only to truss elements, or only to solid elements, which have no rotational degrees of freedom — is either absorbed with no effect or makes the model singular. This is a frequent surprise when loading a solid model. A value of zero simply means no load in that component. Results sensitive to these: everything downstream of the case, most directly the reactions, which should always be checked first. ## Verification * Sum the reactions for the case and confirm they equal the total applied load in each direction. This is the single most effective check and catches sign errors, missing cases and coordinate-system mistakes at once. * Confirm the deflected shape moves in the direction you intended. * Check that the load appears in the applied-load display at the node you meant. * For a moment, confirm the node actually rotates; no rotation means the degree of freedom is restrained or has no rotational stiffness. * For a skewed or local-system load, resolve the components by hand and compare against the global reactions. * Compare against a hand calculation of the resulting support reactions for a simple span. ## Common mistakes * **Sign error on a gravity load** — entering a positive Fz in a Z-up model, applying uplift. * **No Load Case assigned**, so the load does nothing at all. * **Wrong coordinate system**, rotating the load away from the direction intended, most damagingly on skewed and curved structures. * **Applying a moment at a node with no rotational stiffness** (truss-only or solid-only connectivity), where it has no effect or destabilizes the model. * **Applying the load at a restrained node** and expecting deformation; it goes directly into the reaction. * **Reading local stress at the application point** in a shell or solid mesh, where the result is a mesh-dependent singularity. * **Applying a load at a node that is inactive** in the relevant construction stage. --- # Agent Instructions This documentation is published with GitBook. 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