TheBridgeEng

Stay cable — catenary geometry & unstressed length

Stay-cable catenary

One stay, anchor to anchor. Give the horizontal and vertical offsets and the cable force, pick a cable, and the tool returns the exact catenary: curve length L_c, sag f, elastic stretch ΔL_s and the unstressed (cutting) length L_o — the number the cable is actually ordered against — plus the tangent angles at both anchorages and the force utilisation against MBL.

Stay elevation — chord vs catenary

Unstressed length Lₒ (cutting length)

—m

Curve length L_c

—m

Elastic stretch ΔL_s

—mm

X — horizontal offset L_h106m

20310600

Deck anchorage to pylon anchorage, measured horizontally.

Y — vertical offset L_v54m

5152300

Height of the pylon anchorage above the deck anchorage.

Cable system

Wires n

f_u MPa

Sheathing

Cable force & modulus

Tension T (mean) kN

E kN/mm²

T is the mean cable force, as the chord-projection H = T·cosθ is taken directly from it — no iteration. Under service load a stay normally sits at 0.35–0.45 MBL.

Tension utilisation T / MBL—

00.45 MBLMBL

Step	Quantity	Value	Note

Field notes — what to watch for

Fabrication length is the deliverable here — the difference between chord and catenary length is millimetres that either fit or don't at the anchorage. Sag matters twice: geometry, and the effective stiffness of the stay (Ernst modulus) that your global model needs. This tool was checked against real as-built cable schedules before release.

Inputs are saved on this device · reset to defaults