Assessment of the Bill Emerson Memorial Bridge - FTP Directory ...

(a) Isotropic view(b) Plan view4.4.3. CablesFigure 4.2Modeling of girdersThe vibration of cables plays an important role in the overall response of cable-stayedbridges (Abdel-Ghaffar and Khalifa, 1991; Ali and Abdel-Ghaffer 1995; and Ito, 1987).Therefore, appropriate modeling of cables is quite necessary. Ali and Abdel-Ghaffer(1995) also found that the natural frequencies of cables strongly depend on the sag of thecables. Cables are constructed of strands that are made of high strength steel wires. Threetypes of strand configurations are commercially available. They are: (a) helically-woundstrand, (b) parallel wire strand, and (c) locked coil strand.In the Bill Emerson Memorial Cable-stayed Bridge, each cable consists of 19~54 strands,each 15.7 mm in diameter. Parallel to each other, these strands are placed inside apolyethylene pipe, grouted and then sealed to form a single cable. In this bridge, there are atotal of 128 cables in the main span. In the FE model, these cables were simulated byFrame/Cable element, assuming the contribution of every internal wire inside the cable.The modeling of cables is a difficult task because nonlinearities arise from the sagging ofcables. The stiffness, therefore, changes with the applied load. Each cable element wasrestrained in compression to prevent any compression deformation and to simulate itspractical condition on the actual bridge. Since each cable is attached at one end to the topflange of one composite steel girder and at the other end to the work point of the tower,both attachment points are away from the neutral axes of their respective supportingstructural elements (deck and tower). Therefore, two rigid links were introduced to connectthe cable to the neutral axis of the deck and the tower, respectively. The use of rigid linksensures that the theoretical lengths, horizontal angles, and the maximum sag of the cablesare exactly the same as designed. The dimensions and section properties of all cables aregiven in Table 4.3. The cable number can be seen in Figure 4.4.44