Bridge–structure interaction analysis of a new bidirectional and continuous launching bridge mechanism
Introduction
Incremental launching is an inexpensive and useful technique to erect bridge structures. This method is based on pushing the bridge structure using several devices which provide the friction force needed to move the bridge. This method has been applied since the nineteenth century in Europe and it is currently very widely used around the world [1], [2]: Bridge over the Caroni River (Venezuela); Bridge over the Danube river (Müller, Austria); Bruggen Viaduct over the Sitter river (Switzerland); Vaux Viaduct between Lausanne and Bern (Switzerland), and so on. Initially, the friction-based launching method was only used for concrete structures, due to the high normal load provided. However, steel structures can currently be launched by friction [3], [4]. Some of the most important bridges in the world were made using this technique, such as the Millau Viaduct in France, which was built from 2001 to 2004, or the “Arroyo Las Piedras viaduct”, the first composite steel–concrete high-speed railway bridge built in Spain [5]. Although this technique is very widely used, it has several disadvantages which must be overcome in order to improve constructions methods [6], [7].
An important problem in ILM is the local stress in the cross section which gives rise to the patch loading phenomenon. This structural local failure is the most important effect in the case of steel bridges and it is an important research line currently [8], [9], [10]. The normal load on the launching devices is not distributed and uniform, so the normal reaction exerts a local force in the bridge structure which can cause the collapse of the bridge. Previous authors studied the non-uniform distribution of bearing stress on a launching shoe [11]. In that study the authors developed an analytical model which describes the distribution of the support’s reaction. They demonstrated that the normal load applied on the launching shoe is a concentrated load in the center of the launching shoe instead of being a uniform distribution of reaction over the whole load-bearing surface. Other authors studied strategies for analysis of construction stages, showing the internal stress redistribution due to restrained creep [10].
Based on previous works, it is known that the interaction between the bridge and the launching devices is very important. This contact surface is very important in order to ensure the correct launching using the friction force. In this sense, this paper presents a numerical study of the structural interaction between a bridge and a new device to launch structures by friction force [12]. This paper provides a valuable contribution to the civil engineering field focused on a new method for launching bridges by a continuous and bidirectional mechanism. The structural interaction between the bridge and the mechanism which pushes the bridge is studied by numerical methods following the process utilized in other research works in which these methods were used successfully [13], [14].
The authors of this paper have worked in a new design to launch bridges using friction force. This new design improves the current methods, obtaining a new procedure that is more efficient, economical and safe. The current methods of launching bridges need several hydraulic jacks to place the bridge in its final position [3], [4], [7]. Vertical and horizontal launching jacks move the bridge using the force of friction as is shown in Fig. 1. The procedure of launching the bridge using this system is as follows: first, the vertical jacks provide the necessary force between the mechanism and the bridge, then horizontal jacks move the bridge structure forward. In order to induce the displacement by friction force, a surface contact is necessary between the bridge and the launching device. Pushing the bridges is a frequently used technique in spite of several problems. This research group has worked on this method for years in order to improve launching safety, as well as to decrease the operation time and to achieve higher average speed in the launching process.
There are some shortcomings in the current launching method [3], [7], [15]:
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Auxiliary systems are needed in order to control the launch and make sure it is safe.
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The average speed of launching is low because the current mechanisms work at very low speed.
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The method is discontinuous due to the retraction of the launching jacks. For this reason, there is a lot of dead time which are inefficient.
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The current method is unidirectional because the structure only pushes forward. Backward displacement is obtained using other auxiliary systems. For this reason, the launching procedure is slow and expensive when backward displacement is required.
For these reasons, the study of the structural interaction between the bridge and the launching mechanism is a very important research line to avoid problems during the launching procedure [10], [11]. It is very useful to analyze the adaptation of the new launching device to the deformed shape of the bridge structure when this is being built. Furthermore, the concentrated load in the steel webs of the bridge during the launching process is an important problem in the current launching methods. The new launching device developed in this innovative paper improves the web’s behavior under patch loading effects because the normal reaction is distributed among several support links.
In summary, the statement of the problem is based on the current limitations of bridge launching procedures and the research significance is demonstrated by means of the development of a new mechanism for continuous launching of heavy structures.
Section snippets
DCACLM for heavy structure displacement
In order to improve the launching method, a new device able to provide a continuous and bidirectional displacement has been designed. This system pushes the superstructure using the force of friction. This new device was patented by the authors of this paper in 2011 (WO 2013/001114A1) [12]. This patent is referred to in this paper as DCACLM.
Two design factors were taken into account:
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The bidirectional and continuous displacement.
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The high normal load which has to be supported.
The DCACLM device
Mathematical model
The methodology applied in this paper is based on the substructuring technique which reduces a complex non-linear model to a single superelement, which is the bridge structure in this case.
The mathematical model of the superelement used, MATRIX 50 [22], [23], is a matrix format of an arbitrary structure which does not have a fixed geometrical identity. The first step in the analysis introduces a superelement as one of its element types, this process is named “use pass”. In the second step,
Cases studies
In bridge erections, specifically in large bridge constructions, the construction stages are usually as important as the service life. This is due to the stress distribution within the bridge structure and also other aspects such as the joints among the structure segments or the launching forces of the launching devices on the structure and so on. These problems in construction methods have been studied for years by other authors using non-linear numerical methods [11], [10]. In this paper the
Conclusions
A numerical study of the structural interaction between the bridge structure and a new launching device is presented in this paper. This study was carried out using the substructuring technique with which two complex numerical models are reduced to a simplified numerical one. The numerical model used takes into account several phases of launching in the construction process, as well as three different positions of the new launching device.
The results obtained for each case studied are shown in
Acknowledgements
The authors express deep gratitude to the GICONSIME and GITECO Research Groups at Oviedo University and Cantabria University, respectively, for their useful assistance and the anonymous comments and suggestions of the reviewers. This work was partially financed with FEDER funds by the Spanish Ministry of Science and Innovation through the Research Project BIA2012-31609 and the Gijon City Council through the SV-13-GIJON-1.7 Project. We would also like to thank Swanson Analysis Inc. for the use
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