
Figure: Prestressing cable curves creation in Revit using Excel cable configuration.
The cable curve is the heart for a prestressing concrete bridge. They are configurated from Excel and be the input for both of Revit and Lusas model in ICDAS COB. The cable curves are configurated to obtain compression overall in deck cross section at any section perpendicular to the cables, along the bridge alignment, in quasi-permanent combination of actions. This verification of stress is performed in Lusas Bridge model from which adjustments of the curves found where there are tensile stresses in concrete elements. The new cable curves updated in Excel, and be again the new input for the two models Revit and Lusas. Above show an example of bridge spans 9000+16500+9000mm (1)
To ensure accuracy of geometry in the vicinity of the anchor, a 3D model of the anchorage created in ICDAS COB including strands, anchorage head, anchorage plate, wedges, trumpet and the duct. Freyssinet 13C15 has been chosen as the most applicable in Scandinavian, but the other types can also be easily modified from this model.
The above cable (anchorage and bursting reinforcement) is a 3D cut from Revit model presented in this example. It indicates also that one can document whatever in an ICDAS Revit model using Revit user interface. Realistic view is not just added graphical values to the project but also to ensure the geometry is correct modelled in FEM analysis. ICDAS ensure that because both of Revit and Lusas models are created from the same Excel input. It should be noted that the recess and the anchorage details are not modelled in the global FEM model. But the concrete shell elements do register big concentrated forced from the tendons through beam elements integrated in surfaces creating the shell concrete deck in the vicinity of the anchor (Lusas Prestressed Wizard). Having a good geometry presentation in Revit will help to design a local FEM model here if so desired. This issue refers to analysis part of ICDAS.
Prestressing tendons are designed in center box of the deck cross section. Figure above show a 3D section box at the start of bridge deck. There are 14 cables distributed seven on each side of the deck center alignment. The total prestressing force 14x2720kN yields a compressive stress of about 4MPa over the entire cross section area of the bridge deck, as an experience stress needed for bridge span below 20m carrying vehicle load model 1 and 3 (LM1 & LM3).

Figure above enlarges the 4 cables on each side of the alignment. The seven cables R1-R7 have its own curve due the deck cross section slopes down 2% from the center alignment giving different thickness of deck at the cables position. All the cables designed with the same distance 140mm below top surface of deck over the piers. The seven cable on the left L1-L7 have the same curves as R1-R7, respectively, as the symmetry of the bridge deck.
The cables are located in 570mm distance. The anchorage plate 210mm is located in recess of 310mm width. All the cables are anchored at the same height 330mm above bottom of deck as configurated in the Excel input.
Above show details of the cable at anchorage with reinforcement in vertical view (left) and a top view (right). The concentrated force from a tendon causes splitting forces in both of vertical and transversal directions in the vicinity of the anchor. The bursting reinforcement (splitting) has been designed as crossed hoops (stirrups) as shown above. These stirrups are deduced from the reinforcement used in test prisms and for a concrete cylinder strength equivalent to 24MPa, cf. Freyssinet ETA 06/0226 (European Technical Approval). The first stirrup is located 140mm after the anchorage plate cf. ETA 06/0226. All bursting stirrups are 12 500S instead of 14mm in ETA 06/0226 for easy bending reason. To compensate, there are 5 Y-transversal reinforcement 16mm placing after the anchorage plate as shown in the Top View above (4 reinforcement 16/130mm in ETA 06/0226).
The cable run, anchorage, recess, bursting reinforcement and the deck reinforcement can be checked for any cable using 3D section box. Shown above is cable L1 at the start of deck. ICDAS Revit Material Manual guider the users to navigate in materials folder for materials (appearance) of the bridge components.
Figure: Prestressing tendons & reinforcement, concrete not shown.
Reference
/1/ Prestressing Concrete Bridge using LUSAS 2017, Truc Huynh, Technical University of Denmark, Ballerup Campus. |