•Viaduct redesign using Fiber Reinforced Concrete (FRC) as resisting material.•Case study on the replacement of reinforced concrete by FRC.•FRC replaces conventional reinforcement in transversally ...prestressed viaducts.•Serviceability reinforcement due to light-train loads is fully eliminated with FRC.•FRC improves crack opening for large concrete covers while using ULS reinforcement.
An assessment concerning the structural applicability and performance of fiber reinforced concrete (FRC) is presented for different bridge elements and within a design framework. FRC as the main bearing material in structural members has evolved from low-demand applications to increasingly ones, where bending and shear are the main internal forces. In actual applications, this was reflected with initial slab-on-grade cases, through tunnels, and later moving towards elevated slabs. Past experiences show that FRC has notable features regarding ultimate capacity and serviceability performance (i.e., enhanced crack control). These capabilities allowed for optimizations such as material savings, reduction of intensive labor during construction, or extended durability. Considering FRC's enhancements from previous applications, a case study based on the Metrorrey Line 2 light-train viaduct (Mexico) is developed. The case study aims to assess the structural performance that FRC can deliver within bridge geometries, loads, and specific conditions. Two numerical models considering different transversal post-tensioning configurations are developed based on the reference structure. The use of these two numerical models aims to broaden the applicability of this study to most U-shaped light-train viaducts. The design is based on current and future standards and recommendations, being prEN1992-1-1:2021, EN1992-1-1:2004, and fib Model Code 2010. After the numerical models and structural analysis, different sectional analyses at ultimate and serviceability levels are carried out, considering both conventional and fiber reinforced concretes. From the sectional results, FRC can provide reductions to reinforcement quantities at ultimate load levels, which are tied to the initially required reinforcement ratio (in other words, linked to the internal forces existing in the element). When higher reinforcement ratios are necessary, FRC optimizations point toward serviceability limit states, especially on the crack width reduction and the potential to reduce or suppress any additional reinforcement due to crack limitations.
•The paper covers active control implementation in cable-stayed bridges for quasi-static loads, as opposed to the typical approach for extreme winds or earthquakes.•The authors show that natural ...vibration of these bridges and their excitation periods are sufficiently distant one another, hence a quasi-static analysis is available.•A reference state for the control system, the Neutral Moment State, together with a bending moment-axial force gain function are presented.•Both a non-cumulative and a cumulative load pattern are analysed for a particular bridge, with reduction in unbalanced bending moments of 27.1% and 22.8%, respectively.•Considerations to include active control in codes are stated, based on probabilistic risk assessment.
The following paper deals with active control implementation in cable-stayed bridges. Recent developments in structural active control of cable-stayed bridges are focused on the adaptability to dynamic effects produced by earthquakes or extreme winds (El Ouni et al., 2012; Pakos and Wójcicki, 2014; Domaneschi et al., 2015a,b). Nevertheless, no attention has been paid to the static or quasi-static case. As stated by Housner et al. (1996), Song et al. (2006) or Gilewski and Al Sabouni-Zawadzka (2015), active control could also be useful to diminish fatigue in the day-to-day performance of this type of bridges by decreasing stresses adaptively. Indeed, the following paper shows that excitation periods produced by traffic loads and natural periods of vibration of this type of bridges are sufficiently distant one another so as to conclude that a quasi-static analysis can be performed. Filling this gap, the following paper proposes a structural analysis procedure to include active control systems in the design process of cable-stayed bridges, as well as suggestions which ought to be considered in order to include these cases into codes. The results of the paper, studying both non-cumulative and cumulative load cases, show a reduction in unbalanced bending moment referred to the Neutral Moment State of around 25%, depending on the load case. As a result, active control systems compensating quasi-static loading patterns can certainly help engineers optimise the design of these emblematic structures.
This work presents a study of the structural behavior of segmental concrete beams with external prestressing, focusing on the response of these structures under shear. Six tests have been performed ...on beams to evaluate their shear response and load-carrying capacity at different levels of prestressing. To obtain design guidelines about reinforcement detailing in such structures, the structural response under combined flexure and shear has been carefully inspected. Moreover, to evaluate the possible benefits that the use of steel fiber-reinforced concrete (SFRC) could carry, tests were conducted on both conventional and SFRC elements. PUBLICATION ABSTRACT
AbstractThe objective of this research has been to design, develop, and evaluate experimentally a modified type of construction joint of limited length between concrete slab segments. The design ...concept is based on an anchorage hook of reduced development length stiffened by transverse reinforcement bars. The purpose of this paper is to investigate the mechanical behavior of the joint in terms of stiffness and strength for an application that requires high durability, which often leads to serviceability problems such as cracking and water leakage at transverse joints. This can regularly appear in bridges. Additionally, bridge decks are structures that are subjected to repeated loading such as traffic loads, making it necessary to evaluate the behavior of joints under fatigue load. Therefore, studies focusing on the strength, stiffness, and serviceability of the joints must be carried out. This paper investigates experimentally the fatigue behavior and strength of loop joints with regard to the loop bar diameter, loop joint width, and applied load ranges. These results were compared with the behavior of RC slabs without joints. A total of eight slabs were fabricated for fatigue loading tests, and the failures of the different specimens (with loop joints and without) were obtained. From the test results, the mechanical behavior of the slabs with loop joints was confirmed to be similar to that of the slabs without joints. The experimental loop joint design was found to perform correctly under fatigue loads.
This paper presents the results of a test program on externally prestressed concrete beams. Five monolithic and three segmental beams were tested in bending and in combined bending and shear. The ...most significant results are presented such as carrying capacity, prestressing steel stress increase at ultimate, shear behavior of open joints. Conclusions on ultimate load capacity of externally prestressed beams and influence of the tendon length on this capacity are obtained. These tests have been used to validate a numerical finite element model already presented.
Rain combined with wind action provoking vibration has been observed in the longest stays of the Alamillo cable-stayed bridge in Sevilla (Spain). The maximum displacements observed are in the order ...of magnitude of 0.5 m and have caused discomfort problems to the pedestrian circulation across the bridge. The paper shows the analytical and experimental studies carried out to analyse the possible solutions and also the steps developed to stop the vibration phenomenon. In 2004, a dynamic test in the cables was envisaged to measure the actual damping in the cables. It became clear that damping in the cables was very low and the solution required the installation of dampers. The damping devices had to be in accordance with the relevant aesthetic constraints of the structure. The installation of the damping devices took place during 2007. After the installation of the damping devices, a new dynamic test was carried out in February of 2008 to check if the level of damping introduced by the dampers was appropriate. During the tests performed in 2004, the natural frequencies of vibration were also obtained at the same time than damping. The comparison between the two sets of natural frequencies (1992 and 2004) allow to extract important conclusions about the correct performance and condition state of the bridge as well as the evolution of forces in the cables after 12 years of construction due to creep in the tower.
The authors present a great work, with an impressive number of experimental results, and should be congratulated. Nevertheless, the discussers have some comments and suggestions. In the introduction ...of the article, it is stated that the shear keys serve three functions: aligning the segments during erection, transferring the shear force between segments during service, and ensuring durability of the tendons against corrosion. However, the crucial function of resisting shear during the construction of balanced cantilever bridges, when the epoxy has not hardened and acts like a lubricant, is not mentioned. It is very difficult to extract definite conclusions from the test program because the object of the research is very dependent on the concrete tensile strength. This magnitude can be derived from the concrete compressive strength with a significant scatter, which of course will be more important for concrete compressive strength in the range of 30 MPa to 80 MPa, as those considered in the test program.
This work presents a study of the structural behavior of segmental concrete beams with external prestressing, focusing on the response of these structures under shear. Six tests have been performed ...on beams to evaluate their shear response and load-carrying capacity at different levels of prestressing. To obtain design guidelines about reinforcement detailing in such structures, the structural response under combined flexure and shear has been carefully inspected. Moreover, to evaluate the possible benefits that the use of steel fiber-reinforced concrete (SFRC) could carry, tests were conducted on both conventional and SFRC elements. PUBLICATION ABSTRACT
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