Up to now, the erection control procedure of bridges exhibiting non-linear behaviour as well as being built in stages, has presented almost insoluble problems. The missing structural engineering tool was the one, which gives the building contractor and consultant the ability to determine the effects-in terms of both deformation and force-of constraining the structure into a certain pre-defined position in any stage of construction. This missing erection control tool has finally been produced. The erection control facility described in this paper accurately controls the position and the forces in the segments in non-linear (as well as linear) structures built using the stage-by-stage construction method. The paper describes how the program provides various procedures for compensating the errors found on site and how it is used to apply the correction to subsequent construction stages-on a smear basis-spreading the error compensation to the pre-camber over all subsequent construction stages up to the end of the construction.

Wherever built, suspension bridges attract public attention due to their size and conspicuousness. However, the long spans combined with extraordinary slenderness yield outstanding challenges. First of all, in any case the slenderness and kinematical conditions of these structures bring about large displacements due to the permanent loads. Therefore, the shape of the bridge is a non-linear function of the loading, deviating to a great extent from the hypothetical "stress-less" shape. The form finding process is a complicated iterative process if done in the conventional way. As an alternative, the Additional Constraint Method has been provided in the program RM2006 in order to find and optimize the shape of the suspension cables and the hangers. A further great challenge is the simulation of the erection process. Further on, un-symmetric loading due to traffic causes large displacements and requires non-linear traffic analyses. Last but not least, a major engineering challenge of long suspension bridges is their susceptibility to wind induced vibrations. The Hardanger Bridge project is used as a descriptive example for an integrative procedure including form finding, simulation of the erection process, and detailed analysis with considering geometric non-linearity and dynamic impacts like wind induced vibrations.

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Over 30 years of experience in structural analysis in a wide range of applications. Dorian Janjic, born 1960, civil engineering degree from the Faculty of Civil Engineering, Sarajevo. 15 years of experience in technical research, software development. Marko Heiden, born 1973, civil engineering degree from the Technical University of Graz in 2000. Currently working as a project engineer with TDV-Austria. Involved in many international high-speed railway projects during the last few years Summary The design of long span cable-stayed bridges can prove tedious when it comes to finding an appropriate strategy for the stay cable tensioning procedure. The design concept for achieving the appropriate tensioning procedure in cable stay bridges is often based on finding the forces in the individual cables that give rise to certain allowable structural displacements, moments or stress distributions in the girder and the pylons at the end of construction. The stressing forces and the sequence of stressing for all the cables needs to be optimised to meet these pre-defined requirements as closely as possible. The calculation procedure described in this paper models every construction stage in detail with the tensioning of each individual cable being firstly considered as unit-loading cases acting on the currently active structural system and influencing all previously applied unit-loading cases. The effects of the other loading cases appropriate to the construction procedure affecting all previously constructed parts (such as self weight of the new segment, traveller relocation etc.) are also calculated. The displacements and the internal forces from each construction stage are accumulated and the values are subdivided into "constant" (i.e. self weight.) and several "variable" components-each "variable" component being connected to one of the unit loading cases. A system of equations is built up by comparing these accumulated values with the initial design requirements. The result from the equation reduction is the intensity factors for all the unit-loading cases to achieve the predefined constraints (displacements, moments, stresses). The dynamic software procedure works equally well for both linear and non-linear structures with the effects of Creep & Shrinkage being fully considered. The benefit from this method is achieving an optimal tensioning strategy which results in reduced stressing actions with consequent huge time saving and cost saving during construction. The concept is illustrated by the analysis of the Verige Bridge that crosses the Bay of Boka Kotorska in Montenegro.

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