# Tendons \[FEA] Tendons define prestressing strands or bars used in post-tensioned or pre-tensioned concrete structures. They describe the tendon geometry (path profile), material properties, friction parameters, and jacking forces used in prestress loss calculations and staged construction analysis. ## Geometry **Path Variation:** Defines how the tendon profile varies along the element. Controls the shape of the tendon path (e.g., parabolic, harped, or straight). Right-click this cell for actions: *Path Points...* opens the tendon path point editor for defining control points along the tendon profile; *Path Equation...* opens the parameter editor for defining the path using mathematical equations. Right-click any field in this spreadsheet for the action *Prestressing Details...* which displays the full tendon force profile including all friction and anchor set losses. **Start Station:** The station along the alignment where the tendon begins. Defines the longitudinal starting position of the tendon path. **End Station:** The station along the alignment where the tendon ends. Defines the longitudinal ending position of the tendon path. **Start Offset:** The transverse offset of the tendon from the alignment reference line at the start station. **End Offset:** The transverse offset of the tendon from the alignment reference line at the end station. **Start Elevation:** The vertical position (elevation) of the tendon at the start station, measured from the reference datum. **End Elevation:** The vertical position (elevation) of the tendon at the end station, measured from the reference datum. **Rotation:** Rotation angle of the tendon path about its longitudinal axis. **FEGroup (Load Dist. Elems):** The FE group containing the elements to which the tendon prestress forces are distributed. The tendon forces are distributed to the line or surface elements within this group based on proximity. **Load Dist. Elem. Type:** The type of finite elements used for load distribution (e.g., line elements or surface elements). Controls how the equivalent tendon forces are applied to the structural model. **Properties** **Material:** The prestressing material assigned to the tendon. Provides tensile strength, modulus of elasticity, and relaxation properties for loss calculations. **Prestressing Type:** Specifies whether the tendon is pre-tensioned or post-tensioned. This determines which loss mechanisms are applicable and how the tendon interacts with the concrete during staged construction. **Post-tension Type:** For post-tensioned tendons, specifies whether the tendon is bonded or unbonded. Bonded tendons have grout injected into the duct after stressing, while unbonded tendons remain free to move within their sheath. **Exposure:** The exposure condition of the tendon (e.g., internal or external). This affects the friction parameters and loss calculations. **Anchor Set Length:** The length of strand slip (anchor set) at the stressing end. After jacking, the strand slips slightly when the anchor is set, causing a loss of prestress near the anchor. **Wobble Friction Coeffcient:** The wobble friction coefficient (K) accounts for unintentional misalignment of the tendon duct. It represents friction loss per unit length due to imperfections in the duct placement and is used in the Freyssinet formula for friction losses. **Curvature Friction Coeffcient \[1/rad]:** The curvature friction coefficient (μ) accounts for intentional curvature of the tendon path. It represents friction loss per unit angle change and is used in the Freyssinet formula for friction losses along curved tendon profiles. ## Jacking **# of Strands:** The number of individual strands in the tendon bundle. Together with the strand area, this determines the total prestressing steel area. **Strand Area:** The cross-sectional area of a single strand. The total tendon area is computed as (# of Strands × Strand Area). **Jacking Method:** Specifies how the tendon is stressed. Options typically include stressing from the start end only, the end only, or both ends simultaneously. This affects the friction loss profile along the tendon length. **Start Jacking Force:** The jacking force applied at the start end of the tendon. This is the force applied by the hydraulic jack before any losses occur. **End Jacking Force:** The jacking force applied at the end of the tendon. This is the force applied by the hydraulic jack at the far end. Only applicable when the jacking method involves stressing from the end or both ends. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.openbrim.org/templates/openbrimfea/geometry-fea/tendons-fea.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.