ABSTRACT
As the bridge engineering community sets sails to using longer and longer spans, more and more sophisticated analysis models have to be used in the design process. For large pre-stressed concrete and composite bridges built using the incremental launching or free cantilever method, this applies mainly to accurately modeling the erection process in time, with considering the different construction stages, the time dependent behavior (creep and shrinkage), and the required pre-cambering to achieve the design shape after the construction process has been finished.
The erection geometry can only be seriously controlled using a precise structural analysis that considers all the structural stages occurring during the construction of the bridge as well as the effects from the pre-fabricated shapes (where applicable) of the elements. However, the challenges for ultra-long-span bridges such as stay cable or suspended bridges with high pylons and slender steel or concrete decks are mainly related to optimizing the stressing sequence of the cables, to the geometrically non-linear behavior of the structure, and to dynamic problems such as wind-induced vibrations.
One of the significant problems represents cable rupture of cable stays. The problem is also addressed in guidelines for cable-stayed bridge design such as PTI Recommendations (2007) and EC3 (2006) by quasi-static analyses using dynamic amplification factors (DAF) to account dynamic effects, which can be conducted instead of using dynamic analysis.
Bridge engineers are mostly interested in maximum impact of cable rupture to the bridge structure. Cable-stayed bridge design guidelines suggest a semistatic approach for consideration of dynamic impact. PTI (2007) suggestion for DAF is 2.0. EC3 (2006) suggestion for DAF is 1.5. In addition, PTI (2007) allows identification of additional factors in non-linear dynamic analysis to ensure economical – technical design.
Using RM Bridge software has been shown, that DAF coefficients for all elements can be evaluated, using non-linear dynamic analysis with time history functions. Results show, that DAF coefficients for cable-stayed bridges can’t be specified without accurate calculation. Their value depends on location of stay-cable rupture, structural damping, stiffness of structural elements and type of cable stayed – bridge with one, two or more pylons. DAF coefficient can overstep value 2.0, especially in pylon elements (Figure 1). All DAF values should be based on non-linear dynamic calculation, where cable rupture is treated as time dependent load, using time history function. For evaluation of those factors professional bridge software should be used. One pylon cable-stay bridge, DAF of pylon – Mz. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig216_1.tif"/>
Bridge engineers can use RM Bridge for optimization of bridge structural elements and increase structural safety.
