willowman
Civil/Environmental
- Feb 22, 2020
- 25
Hi all,
I am working on the conceptual design of a cable stayed bridge. The bridge is a composite ladder deck supported by main cable stays which are attached to a curved (anti-funicular shaped) pylon. Each pylon (two at each end of the bridge) is supported by a single back-stay which connects to the edge beams of the deck in the back-span.
During the 'bare steel' phase of the construction i.e. SW of steel, SW of wet concrete and nominal construction load, there is a large compressive force induced in the edge beams of the back span due to the back-stay cable. In its bare steel form, the edge beams are shortening, which is causing loss of tension in the back-stay cable. The loss of tension causes deflection at the tip of the pylon...which causes loss of tension in some of the main stays, resulting in large deflections in the main-span. Evidently I can pre-tension the back-stay cables further to control the pylon tip deflection but this will increase the compression force in the back-span edge beams....which I've found doesn't help my situation.
My question is, would it be common practice to have an additional temporary back-stay cable anchorage to reduce the compression forces directly into the 'bare steel' phase of the back-span? Something like a large counter-weight? Once the concrete of the back and main span decks is cast and cured, the axial stiffness of the deck increases hugely and then the full compression force could be transferred into the deck permanently without experiencing such shortening.
Any feedback or ideas would be greatly appreciated.
Thanks,
I am working on the conceptual design of a cable stayed bridge. The bridge is a composite ladder deck supported by main cable stays which are attached to a curved (anti-funicular shaped) pylon. Each pylon (two at each end of the bridge) is supported by a single back-stay which connects to the edge beams of the deck in the back-span.
During the 'bare steel' phase of the construction i.e. SW of steel, SW of wet concrete and nominal construction load, there is a large compressive force induced in the edge beams of the back span due to the back-stay cable. In its bare steel form, the edge beams are shortening, which is causing loss of tension in the back-stay cable. The loss of tension causes deflection at the tip of the pylon...which causes loss of tension in some of the main stays, resulting in large deflections in the main-span. Evidently I can pre-tension the back-stay cables further to control the pylon tip deflection but this will increase the compression force in the back-span edge beams....which I've found doesn't help my situation.
My question is, would it be common practice to have an additional temporary back-stay cable anchorage to reduce the compression forces directly into the 'bare steel' phase of the back-span? Something like a large counter-weight? Once the concrete of the back and main span decks is cast and cured, the axial stiffness of the deck increases hugely and then the full compression force could be transferred into the deck permanently without experiencing such shortening.
Any feedback or ideas would be greatly appreciated.
Thanks,
