Search Results (9)

Strengthening existing structures and bridges allows us to continue using them, increase their reliability, resistance, durability and extend their service life instead of demolishing them and replacing them with new ones. This helps to reduce CO₂ (decarbonization). The use of prestressed CFRP strips represents the use of new modern materials and new technology for strengthening existing bridges. The paper is focused on the use of prestressed CFRP strips for strengthening a concrete bridge made of precast prestressed box girders as the most suitable strengthening alternative in a given case. This is a technology that is more commonly used for strengthening structures, but it is not common to use this technology for strengthening bridges. There are relatively few examples of using this technology for strengthening bridges, also because these are dynamically loaded structures. The paper firstly presents the diagnostics and calculation of the load-carrying capacity of the railway bridge on a narrow-gauge railway line in Štrbské Pleso, Slovakia, and then the strengthening of the given bridge. The bridge is located in the mountains of the High Tatras in the northern part of Slovakia and bypasses two local roads. The bridge was made from the precast prestressed post-tensioned box girders of six single spans. The visual inspection, diagnostics, and verification of real dimensions and material characteristics were requested. The non-destructive and semi-destructive methods of testing were used to determine the geometrical and materials’ properties. After that, the calculation of the load-carrying capacity was done. For this purpose, a numerical 3D FEM model was created. For determining the load-carrying capacity, the standard approach, given in Eurocodes, was used according to provisions, which take into account the modified (lower) reliability levels and their adequate partial safety factors. From the calculation, it follows that the bridge should be strengthened. The strengthening of the superstructure was done using prestressed CFRP strips in the lower part of the box girders. This is one of the first applications of this modern method of strengthening, not only in Slovakia but in Central Europe as well. Full article

In this paper, bridge live load testing was conducted to examine the performance of repairs on a section of a post-tensioned box girder bridge in Oklahoma City, Oklahoma. The live load test was performed with a single/group of truck(s) with known gross weight. The objective of this study was to characterize the behavior of the test bridge span by comparing the performance of a repair in situ as part of the bridge section’s structural response to that of a section known to be sound. To achieve the objective, the structural strain response was collected from several critical locations across the bridge girders. A comparative analysis of bridge behavior was carried out for the results from both the repaired and structurally sound areas to identify any deterioration and adverse changes. The structural strain response indicated an elastic behavior of the tested bridge span under three different load levels. Meanwhile, acoustic emission monitoring was implemented as a supplementary evaluation method. The acoustic emission intensity analysis also revealed an insignificant change in the effectiveness of the repair upon comparing results obtained from both locations. Although there were fluctuations in the b-value, it consistently remained above one across the different load testing scenarios, indicating no progressive damage and generally reflecting structural soundness, aligning with the absence of visible cracks in the monitored area. Full article

This study investigates damage detection in the tendons of post-tensioned segmental box girder bridges, focusing on the vibration-based technique and its application in conjunction with the Precursor Transformation Matrix (PTM). Due to the critical role of bridge tendons in structural integrity, efficient and timely detection methods are essential. The methodology combines theoretical modeling with Finite Element Method (FEM) simulations and empirical data collection to evaluate the PTM’s effectiveness in identifying tendon damage. Key results indicate that the PTM, when paired with vibration analysis, enhances the identification and localization of damage, proving to be a robust method in structural health monitoring. This approach not only speeds up damage detection but also potentially lowers maintenance costs by pinpointing specific damage sites, thereby preventing widespread structural failures. The findings offer a promising tool for ensuring the longevity and safety of post-tensioned bridges. Full article

This article takes a single-tower cable-stayed bridge with a steel-UHPC composite deck steel box girder as the research object and develops different casting plans for the UHPC layer on the bridge deck. It analyzes the influence of factors such as the block casting sequence of the UHPC layer on the bridge deck, whether or not to set up a post-casting section, whether or not to set up bridge deck counterweights and the range of it on the additional deformation and stress of the formed UHPC bridge deck during the construction stage, exploring the impact of various factors on the structural target bridge’s completion status (cable force, bridge completion linearity, bridge deck and steel box girder stress) under different pouring schemes. Research has shown that under the constant initial tension of stay cables, adjusting the pouring sequence of UHPC bridge decks and setting post-pouring sections is not significant in reducing the tensile stress of UHPC bridge decks. The more effective technical measure is to use bridge deck counterweight pouring during construction; the closer the counterweight is to the later stage constant load loading value, the more significant the decrease in UHPC tensile stress is. When factors such as on-site construction conditions, construction period, and labor costs are limited, local weight balancing on the bridge deck can be used. Full article

Shear cracking in concrete box-girder bridges, which could cause excessive deflection during the serviceability limit state, cannot be effectively avoided by code-guided design. While elastic shear deformation only accounts for a small proportion of total deformation for un-cracked reinforced concrete (RC) beams, the magnitude of after-cracking shear deformation becomes comparable to flexural deformation for RC beams. However, there is still a lack of practical models to predict the after-cracking shear deformation of RC beams. First, six thin-webbed I beams were tested to investigate the shear stiffness degradation mechanism and the decrease ratio. Then, a very simple truss strut angle formula, which is the crucial parameter for shear stiffness, was established. Furthermore, a stiffness degradation rule for partially cracked beams was proposed considering the influence of concrete tension stiffening, which is essential for predicting the development process of after-cracking shear deformation. Finally, directly measured shear strains were used to validate the proposed shear stiffness model. The results showed that the shear stiffness drops to about 30~40% of the original stiffness after the first diagonal crack, and the remaining shear stiffness is only about 10% of the original one when the stirrup yields. Increasing the stirrup ratio is a more effective method to control shear stiffness degradation for diagonally cracked RC beams. Also, the proposed shear stiffness model well captures the main features of the shear stiffness degradation, and it provides a relatively accurate prediction of the equivalent shear stiffness at the post-cracking stage. Full article

A new bridge construction method, combining semi-precast elements and in situ concrete, has been developed at TU Wien, with the aim of decreasing erection time. In the course of construction using this new method, structural conditions arise that render a more detailed investigation necessary. By connecting a precast, thin-walled box girder to a bridge segment located on a pier by means of post-tensioning, a joint is created. By casting in situ concrete on the bottom and top slabs, the joint can be bridged with longitudinal reinforcement; however, the unreinforced vertical joints in the webs remain. This detail is a specific characteristic of the LT-bridge construction method and needs to be further investigated and assessed, as the question arises as to how this circumstance affects the torsional bearing behavior of the bridge superstructure. Torsion tests described in the literature consider ordinary box girders with longitudinal reinforcement or post-tensioned segmental bridges without longitudinal reinforcement at the joints. Therefore, the new reinforcement layout at the joints had to be investigated experimentally. Two large-scale thin-walled box girders—one without joints in the webs and the other with unreinforced joints in the webs—were tested, allowing for a direct comparison of conventionally manufactured bridges and those erected with the new bridge construction method. Furthermore, we investigated whether the results of common calculation methods corresponded to the experimental findings. Full article

A three-dimensional non-linear finite-element model (FEM) was constructed using a commercial software (ATENA-Studio) to investigate the transverse load distribution behavior of adjacent precast prestressed concrete box-girder bridges. An innovative connection between box girders was used, where transverse post-tensioning was applied at the top flanges only eliminating the need for intermediate transverse diaphragms. The FEM was validated in terms of deflections, strains, cracking and ultimate loads against experimental results previously reported by the authors. The validated FEM was then used to perform a parametric study investigating the influence of adding concrete topping, load location, and bridge width on the transverse load distribution behavior of the newly developed connection. The results of the FEM demonstrated the efficiency of concrete topping in limiting mid-span deflections up to 25%. Additionally, the maximum live load moment distribution factors (LLMDFs) for different load locations and bridge widths were evaluated. Full article

The design of a structure is generally carried out according to a deterministic approach. However, all structural problems have associated initial uncertain parameters that can differ from the design value. This becomes important when the goal is to reach optimized structures, as a small variation of these initial uncertain parameters can have a big influence on the structural behavior. The objective of robust design optimization is to obtain an optimum design with the lowest possible variation of the objective functions. For this purpose, a probabilistic optimization is necessary to obtain the statistical parameters that represent the mean value and variation of the objective function considered. However, one of the disadvantages of the optimal robust design is its high computational cost. In this paper, robust design optimization is applied to design a continuous prestressed concrete box-girder pedestrian bridge that is optimum in terms of its cost and robust in terms of structural stability. Furthermore, Latin hypercube sampling and the kriging metamodel are used to deal with the high computational cost. Results show that the main variables that control the structural behavior are the depth of the cross-section and compressive strength of the concrete and that a compromise solution between the optimal cost and the robustness of the design can be reached. Full article

The goal of sustainability involves a consensus among economic, environmental and social factors. Due to climate change, environmental concerns have increased in society. The construction sector is among the most active high environmental impact sectors. This paper proposes new features to consider a more detailed life-cycle assessment (LCA) of reinforced or pre-stressed concrete structures. Besides, this study carries out a comparison between two optimal post-tensioned concrete box-girder road bridges with different maintenance scenarios. ReCiPe method is used to carry out the life-cycle assessment. The midpoint approach shows a complete environmental profile with 18 impact categories. In practice, all the impact categories make their highest contribution in the manufacturing and use and maintenance stages. Afterwards, these two stages are analyzed to identify the process which makes the greatest contribution. In addition, the contribution of CO₂ fixation is taken into account, reducing the environmental impact in the use and maintenance and end of life stages. The endpoint approach shows more interpretable results, enabling an easier comparison between different stages and solutions. The results show the importance of considering the whole life-cycle, since a better design reduces the global environmental impact despite a higher environmental impact in the manufacturing stage. Full article