Redesign of bridges Twentekanaal in UHPC MSc Thesis 7 March 2021 Company Witteveen+Bos MSc thesis project Redesign of bridges Twentekanaal in Ultra-High Performance Concrete Document MSc Thesis Status Final version Version D1.0 Date 7 March 2021 Author ing. M. Dorland Student id 4719980 Degree programme MSc Civil Engineering Track Structural Engineering – Concrete Structures Company Supervisors ing. T. Petersen RC ir. A. ten Voorde Supervisors TU Delft Dr. ir. Y. Yang Dr. ir. M.A.N. Hendriks Dr. ir. S. Grünewald PREFACE This report comprises my MSc thesis, which focusses on the redesign of existing bridges across the Twentekanaal in Ultra-High Performance Concrete. By finalizing this project, I am concluding my master studies at TU Delft, that were preceded by my bachelor studies in Arnhem. During my studies I have discovered my interest in structural design, concrete structures and, especially, existing structures. It is because of this reason that I decided to search for a graduation topic within this field. Existing structures provide both opportunities and challenges to engineers and society. The importance of reliable infrastructure for society is evident, and structures such as bridges and viaducts are essential links in the network. The ‘vervangingsopgave’ as faced by the Dutch infrastructural sector is therefore not only a purely technical challenge, but it is of relevance to society as a whole. The development of new concepts that provide durable and sustainable solutions in dealing with existing structures may therefore be very promising and beneficial. The potential of one of such concepts will be demonstrated in this report. It involves the application of UHPC to redesign existing concrete structures by applying new UHPC decks in combination with the reuse of existing foundations. Writing a thesis is an uphill process. Moreover, the strange times we are in has added another dimension to this challenge. Thus, it becomes even more important to thank those who played a role in this endeavour. First of all, I would like to mention and thank Yuguang Yang, Max Hendriks and Steffen Grünewald from TU Delft, for their interest in the topic and their constructive feedback. I am also grateful to my colleagues from Witteveen+Bos. I would especially like to thank Tom Petersen, who has guided me through the process of shaping and managing the project, and Arjan ten Voorde, who shared his knowledge on structural design and has helped me finding my way through the process of bridge design. Finally, I would like to thank my parents, for their support during my seven and a half year of study, and my girlfriend, who has been so understanding and patient. I hope that this project may yield a small contribution to finding solutions to deal with the ‘vervangingsopgave’, and that it will spark the curiosity and enthusiasm of others to explore innovative solutions within the field of existing structures. Wishing you a pleasant reading, Maarten Dorland Delft, 7 March 2021 SUMMARY Within the Dutch infrastructure there is the challenge of having to replace or strengthen a large number of existing structures within the upcoming years. This challenge also provides the opportunity to develop new concepts, the promising concept described in this report involves the application of UHPC to redesign the decks of existing concrete bridges in combination with the reuse of existing foundations. It is expected that by applying UHPC a higher slenderness and lower self-weight can be achieved compared to the existing structures, which compensates for the increased variable loads. This would increase the reusability of existing foundations, resulting in saving time and material and in reducing hindrance and environmental impact. The Twentekanaal comprises many bridges of which various have similar characteristics and were built in the same period. This canal was therefore selected as the topic of this project. The main question of the project is what the redesign of the existing bridges across the Twentekanaal in UHPC should be like in order to obtain a design which complies to the current standards and enables the reuse of the existing foundation of the bridges without having to modify them due to the increase of vertical variable loads. To limit the scope of the project, the new deck should be constructed using prefabricated beams. Not all bridges could be considered in-depth simultaneously. Therefore, one representative bridge was selected after which the results for this bridge would be generalised onto all other relevant bridges across the canal. The Eefdesebrug was selected for this task. This concrete tied arch bridge across the canal near Zutphen was selected for its span, which is 68 m, and its year of construction, which was 1955. To determine the full potential of the project, it was investigated up to what extent the results for the Eefdesebrug could be projected onto other bridges across the canal. An inventory was set up containing all bridges, in total 37 bridges or bridges part of larger engineering structures were identified, characterised and compared based on bridge category, year of construction and dimensions. This resulted in a total of twelve bridges with similar characteristics, to which the results of the redesign of the Eefdesebrug could potentially be generalised to. After the potential of the project had been determined, the focus was placed on the redesign of the Eefdesebrug, which was carried out following a stepwise approach. The design stage was decomposed into four phases: the preliminary design, detailed design, optimization and final design. After each phase, the global goal of the project was reflected by means of a weight comparison with the existing bridge. The design would be based on the Eurocode, supplemented by the AFGC-SETRA 2013 guideline, because the Eurocode is not applicable to UHPC. The first design phase, the preliminary design, focussed on establishing the first dimensions of the deck and determining the feasibility of the project goal based on the self-weight of the new design. The preliminary design resulted in a 26% increase of the self-weight of the structure compared to the existing bridge. However, given the conservative approach, the large number of possible improvements and the potential to optimisation, the project goal was deemed to be feasible. During the detailed design phase, a more complete and accurate analysis was performed to obtain better insight into the structural behaviour of the bridge, and to identify the best options for optimization. The various improvements and refinements incorporated in the design and design approach resulted in a 33% reduction of self-weight compared to the preliminary design and a 16% reduction compared to the existing structure. The goal of the optimization phase was to achieve a further reduction of the self-weight, by means of varying the dimensions as obtained during the previous phase. New dimensions were established based on capacity, concrete cover, spacing between pretensioned strands and overall stability of the beam, using the results of the detailed design as the starting point. The optimizations resulted in an additional 18% decrease of the self-weight compared to the detailed design. It was concluded that with the given type of cross section and the chosen approach, only limited room remained for further weight reduction. The design stage was therefore concluded. This final design comprises pretensioned box beams with a slenderness of 36, resulting in a 32% reduction of self-weight compared to the existing bridge. In addition to the design verifications, executional aspects were also considered in the design. The two most stringent criteria were the maximum number of pretensioned prestressing strands and the transportation and placement of the beams. By means of a reference project the transportation and placement of the beams was proven to be feasible. In the final design the number of strands was brought back below the maximum number of strands that can be applied in practice. With the design stage concluded, the global assessment of the existing foundation was carried out. A criterion for reuse of the existing foundation was formulated: the summation of vertical forces due to the permanent actions and variable actions in the new situation should be smaller than or at most equal to the summation of those forces in the existing situation. The permanent loads of the existing structure were determined based on design drawings. To determine the variable loads, the GBV 1950 and VOSB 1938 were consulted; these former codes were most likely used for the design of the existing bridge. Because of differences in safety philosophies between these former codes and the Eurocode and uncertainty in the safety margin used in the original design of the existing foundation, the comparison was carried out without the use of partial load factors. The results of the comparison indicated a 32% decrease of the self-weight between the final design and the existing structure, while the variable loads increased with 31% between the VOSB 1938 and the Eurocode. In total the vertical forces on the foundation decreased with 21%. As typical for concrete bridges of larger spans, the self-weight of the existing Eefdesebrug was the largest contributor to the vertical loads. The criterion for reuse of the existing foundation was therefore satisfied and the possibility of reuse of the foundation of the Eefdesebrug without modifications for increased vertical variable loads had therewith been demonstrated. It was subsequently investigated what may be expected if the solution for the Eefdesebrug would be applied onto the group of twelve aforementioned bridges. Using the results for the Eefdesebrug it was possible to estimate the dimensions for the other bridges and to consider the vertical forces acting upon the foundations. The remark was made that for bridges with smaller spans additional unfavourable effects may occur in the results that are not covered by projecting the results for the Eefdesebrug directly onto these bridges.