Steel has typically been used in the sluice gate design for well over a century. However, the development of ultra-high performance fibre reinforced concrete (UHPFRC) in the recent decades has presented an interesting alternative to traditional steel sluice gates. The appeal of UHPFRC is based on its extraordinary durability and resistance to most forms of corrosion. Gates produced with the material could function without the need for replacement or maintenance works for extremely long periods of time. Due to higher material strength parameters, UHPFRC elements are also significantly more slender and therefore lighter than their standard concrete counterparts. That makes UHPFRC a potential alternative to traditionally used steel.
A UHPFRC mitre gate had already been designed as a replacement for one of the gates in the Robbengatsluis complex. However, due to the novelty of the solution, there were concerns about whether the design choices and solutions used in the process may have resulted in an overly conservative design. The goal of the project was to redesign the UHPFRC gate, verifying if a more optimal design was possible and which of the available methods of analysis were most suitable in the context of UHPFRC sluice gate design.
The gate’s design was focused around the concept of a plate gate strengthened on its inner side by beam segments running along the edges of the structure and through its most significantly loaded areas. In the project, two main approaches were considered. The first focused on reviewing the analytical design procedure used for the original design. The applied standards and assumptions were reassessed, leading to modifications such as the adoption of alternative analytical formulas, the inclusion of fibre contribution in relevant limit states, and the adjustment of the fibre orientation factor for thin plate segments. Relevant ultimate limit state (ULS) and serviceability limit state (SLS) verifications were conducted. This approach was supported by linear finite element analysis as a conservative estimation of the structure’s behaviour.
The second approach aimed at incorporating nonlinear finite element analysis (NLFEA) to verify the accuracy of the utilized analytical design methods. Additionally, the application of NLFEA allowed for consideration of load redistribution effects, which are of significance in the case of UHPFRC structures. Material tests (compression tests, 3-point bending tests, etc.) had been conducted to prepare the NLFE model of the considered UHPFRC mix and to evaluate material parameters utilized in the analytical design verifications. The nonlinear approach was based on a total strain-based rotating crack model. Two nonlinear numerical solution strategies were developed, one based on plane stress elements and the other based on shell elements. The solution strategies were validated within the framework presented in Model Code 2020. The plane stress element solution strategy was validated by comparing numerical simulation results with literature-based results from 4-point bending tests of reinforced UHPFRC beams. The shell element-based strategy was validated by comparing numerical simulation results with experimental data from one-way plate bending tests conducted by FDN Engineering. It was evaluated that both solution strategies closely predicted the experimental results. The modelling uncertainty of the plane stress element strategy regarding prediction of beam bending capacity was quantified through the application of Global Factor Method. The strategy was then used to evaluate the bending capacity of all beam segments within the structure. The shell-based solution strategy was used to take into consideration load redistribution effects in the critical plate segment.
The numerical results confirmed the accuracy of the applied analytical verifications. Numerical capacities differed from analytical ones by -5.7% to +4.4%, they gave more conservative predictions for low reinforcement ratios and less conservative ones for high reinforcement ratios. Due to the lack of experimental benchmark data for UHPFRC plate segments, nonlinear numerical analysis could not be used to comprehensively evaluate the load redistribution effects for the structure at large, as the modelling uncertainty of the solution strategy could not be estimated. A new design for the UHPFRC mitre gate was prepared based on the revised analytical approach. Among other changes, the new design included altered aspect ratios of beam segments and reductions in segments’ reinforcement. The original design and the new design were compared in terms of the amount of concrete and reinforcement used. The new gate variant required slightly less UHPFRC and significantly lower shear and longitudinal reinforcement ratios, with the total decrease in the amount of reinforcing steel reaching 56.2%.
Reinforcement design was strongly influenced by crack width SLS verifications, which required significantly higher reinforcement ratios than ULS requirements. The dominance of crack width SLS was high enough to nullify any potential benefits from less conservative ULS verification approaches. A review of available information suggested that the applied MC2020 SFRC crack width SLS verification could be improved upon to provide less conservative estimations by either utilizing a UHPFRC-specific code-based analytical verification or applying NLFEA in the process.
The concluding results can be used as a reference point for future attempts at designing UHPFRC mitre gates. Currently available UHPFRC and SFRC design standards provide a good framework for the design of those elements, with significantly reduced material use compared to the previous design. With superior durability, UHPFRC offers a feasible alternative to the use of steel. The proposed plate and beam segment structure is a viable solution for UHPFRC mitre gates of similar dimensions. Efficient design requires a series of material tests to properly quantify the necessary input parameters and the benefits of the utilized material on a case-by-case basis. The new design simplifies manufacturing and improves efficiency without compromising performance.