Under-deck Cable-stayed Bridges Research Articles

Full-Range Modeling of Underdeck Cable-Stayed Bridges

Full-Range Modeling of Underdeck Cable-Stayed Bridges

Dynamic behaviour of steel–concrete composite under-deck cable-stayed bridges under the action of moving loads

The dynamic response of under-deck cable-stayed bridges with steel–concrete composite decks under moving loads is presented, and different parameters are considered. The vibrational modes with a strong contribution in the response, the key parameters that control the modal frequencies, and those that reduce the maximum accelerations registered on the deck in a cost-effective manner, are identified. It is found that relatively high accelerations occur and that these can be increased by large load eccentricities. It is also found that maximum accelerations are conditioned by the amplification and cancellation speeds of the loads. Increasing the depth of the deck is determined to be the most effective way to reduce the maximum accelerations. Decks formed by I-beams seem to be quite appropriate from the perspective of dynamic behaviour, while box sections tend to increase the overall cost of the bridge. The findings provide effective strategies to define the most efficient configurations that satisfy the limit state of vibrations, which is critical for this type of bridge.

Non-linear stability of under-deck cable-stayed bridge decks

The stability of comparatively more slender decks of under-deck cable-stayed bridges is studied, by considering both the critical loads and the post-buckling behaviour. A potential energy approach is applied to a simplified discrete link and spring model that allows for an exact non-linear formulation of the equilibrium equations. The physical response is found to be dependent on the ratio of the axial stiffness of the cable-staying system to the flexural stiffness of the deck. The influence of several parameters is analysed and unstable mode interaction is observed to occur under certain geometric conditions. The presented analytical model is compared with a non-linear finite element model that shows good correlation. Finally, some design criteria and recommendations are suggested, which are relevant for designers of this innovative typology of cable-stayed bridges.

Design Criteria of Under-Deck Cable-Stayed Composite Bridges for Short and Medium Spans

Under-deck cable-stayed bridges are innovative bridge schemes that can lead to lightweight and highly efficient construction. However, the design of slender bridges may be governed by the vibrations under traffic live loads. After a historical review of bridges with under-deck cable-staying systems and the consequent research, the dynamic response of medium- and short-span bridges is analysed. Eccentric traffic loads are shown to increase accelerations considerably, and the second vertical mode is found to be the main contributor to the response. A parametric study shows the strong influence of resonance effects in the maximum accelerations registered on the deck. In addition, under-deck cable-staying systems are found to be more appropriate for medium-span than for short-span bridges from the dynamic viewpoint. Moreover, for medium spans, much more slender decks can be achieved compared with conventional bridges without cable-staying systems. Finally, some design criteria are provided that may be useful for structural designers.

Serviceability limit state of vibrations in under-deck cable-stayed bridges accounting for vehicle-structure interaction

Verification of the serviceability limit state of vibrations due to traffic live loads can be neglected in conventional types of concrete road bridges but becomes critical in the design of slender structures like under-deck cable-stayed bridges. The novelty of the work presented in this article is that an innovative vehicle-bridge interaction model is employed, in which realistic wheel dimensions of heavy trucks, road roughness profiles and the cross slope of the road are considered in nonlinear dynamic analyses of detailed three-dimensional finite element models. An extensive parametric study is conducted to explore the influence of the bridge parameters such as the longitudinal and transverse cable arrangement and the support conditions, in addition to the load modelling, road quality, the wheel size, the transverse road slope and the vehicle position and speed on the response of under-deck cable-stayed bridges. It has been observed that the vibrations perceived by pedestrians can be effectively reduced by concentrating the cable-system below the deck at the bridge centreline. The Fourier amplitude spectrum of the acceleration at critical positions along the deck proved that the response of under-deck cable-stayed bridges is not dominated only by contributions at the fundamental mode and, consequently, the conventional deflection-based methods are not valid to assess the users comfort. Instead, Vehicle-Bridge Interaction analyses are recommended for detailed design, considering the wheel dimensions if the pavement quality is bad and/or if the wheel radius is large. Finally, we verify through multiple approaches that the comfort of pedestrian users is more critical than that of vehicle users. However, the comfort of vehicle users is shown to be significantly affected when the road quality is poor.

Developments in under-deck and combined cable-stayed bridges

Under-deck, cable-stayed bridges and combined cable-stayed bridges constitute two innovative bridge types that have been designed and built on relatively few occasions over the last 30 years, in most cases by renowned structural engineers, such as Leonhardt, Schlaich, Virlogeux, Manterola, Robertson and Cremer. In these bridge types, the stay cables have unconventional layouts: either below the deck, in the case of under-deck cable-stayed bridges, or above and below the deck, in the case of combined cable-stayed bridges. In this paper, a general and critical overview of the current state-of-the-art is outlined, addressing issues related to proposals, built bridges and research. Significant attention is paid to their highly efficient structural behaviour and unconventional design criteria, both of which lead to a significant reduction in the amount of required materials, in comparison with conventional bridges without stay cables, and thus allow for sustainable design. Other advantages of these bridges, such as multiple construction possibilities, strong aesthetic characteristics and their broad range of potential applications, are also stressed.

Response of under-deck cable-stayed bridges to the accidental breakage of stay cables

Under-deck cable-stayed bridges with prestressed concrete decks have recently been shown to be appropriate structural types for highway overpasses. However, doubts have emerged regarding their capability to withstand the accidental breakage of stay cables, due to collisions with heavy vehicles, without collapsing. In this paper, two distinct parametric analyses are conducted on two different bridges, each of which is representative of this bridge type, in order to study their response due to the breakage of stay cables. The response is assessed through fully dynamic analyses, rather than pseudo-dynamic analysis (via the use of dynamic amplification factors), since the latter method has been shown to be un-conservative in some cases. In both parametric analyses different scenarios, i.e., different parameters, relating to the type of breakage, the time over which breakage occurs, the number of broken stay cables, the type of deviators and the amount of applied traffic live load are considered. In the present study, the capability of this bridge type to easily overcome this accidental action, with a higher degree of safety than that required by codes, is clearly demonstrated. In fact, the analysed bridges do not reach any ultimate limit-state even if 40% of their stay cables are suddenly broken when 100% of the traffic live load is applied. In addition, a set of design criteria closely related with this issue are established.

Structural behaviour and design criteria of under-deck cable-stayed bridges and combined cable-stayed bridges. Part 1: Single-span bridges

This paper examines two new types of bridges, namely under-deck cable-stayed bridges and combined cable-stayed bridges, for prestressed concrete road bridges with single-spans of medium length. Both bridge types offer many advantages over conventional schemes in several aspects, such as structural efficiency, enhanced construction possibilities, and both economic and aesthetical considerations. They are very slender structural types with a very high structural efficiency, for which the materials used in the deck are reduced to one third of that in conventional bridges without stay cables. In this paper, the most important aspects of the structural behaviour of these bridge types are set out through the description of a careful selection from an extensive collection of bridges designed and analysed by the authors in a previous research project. In addition, a detailed set of design criteria for these bridge types is presented, based on the results of the extensive parametric study undertaken in the aforementioned research project.

Structural behaviour and design criteria of under-deck cable-stayed bridges and combined cable-stayed bridges. Part 2: Multispan bridges.

This paper deals with the application of under-deck cable-staying systems and combined cable-staying systems to prestressed concrete road bridges with multiple spans of medium length. Schemes using under-deck cable-staying systems are not suitable for continuous bridges, as they are not efficient under traffic live load and only allow for the compensation of permanent load. However, combined cable-staying systems are very efficient for continuous bridges and enable the design of very slender decks (1/100th of span) where the amount of materials used is halved in comparison with conventional schemes without stay cables. In this paper, the substantial advantages provided by combined cable-staying systems for continuous bridges (such as high structural efficiency, varied construction possibilities, both economic and aesthetical benefits, and landscape integration) are set out. Finally, design criteria are included.

Two new types of bridges: under-deck cable-stayed bridges and combined cable-stayed bridges — the state of the art

At least 20 cable-stayed bridges have been built over the last 30 years that cannot be classified under existing typologies for cable-stayed bridges. These structures represent two new types of cable-stayed bridges that we herein define as "under-deck cable-stayed bridges" and "combined cable-stayed bridges." The evolution of these new bridge types is explored through consideration of the different proposals and structures that have been built throughout this period, pointing out the innovations made in each of them. In this paper we propose a new classification system for bridges prestressed by means of tendons into which these two new bridge types will fit. Studies that have been made of these structural types are also highlighted. On the basis of the aforementioned, we describe the state-of-the-art for these structural types, compiling and cataloguing information, documents, and knowledge that were previously highly dispersed. Lastly, we make a critical analysis of the current situation and draw some key conclusions.Key words: under-deck cable-staying, combined cable-staying, cable-stayed bridges, extradosed prestressing, intradosed prestressing, prestressing.

Parameters governing the response of under-deck cable-stayed bridges

In the past quarter century, a number of bridges have been built that do not fit into the conventional types of cable-stayed bridges. These are under-deck cable-stayed bridges and combined cable-stayed bridges. In this paper we define the first of these two types and set out its mechanisms of response. We then establish and analyze the parameters that determine the permanent response and the response to live load of these bridges. Lastly, we draw conclusions relating to their behaviour and define design criteria for them with the aim of making cable-staying systems highly efficient and allowing the design of much lighter and slimmer structures.Key words: unconventional cable-stayed bridges, under-deck cable-stayed bridges, combined cable-stayed bridges.