Search results for "Deck"
showing 10 items of 25 documents
Concrete arch bridges built by lattice cantilevers
2013
In this paper a study about concrete arch bridges built by lattice cantilevers is presented. Lattice cantilevers are partial structures composed of deck, arch, piers and provisional steel diagonals, organized as reticular cantilever girders, in order to build arch bridges without the use of centrings, supports or temporary towers. Characteristics of this construction methodology with its variants are explained together with their implications in the erection sequence. Partial elastic scheme method is implemented in order to find initial forces of temporary cables and a forward analysis is carried out to follow the actual sequence of construction, by extending a procedure already applied to …
Construction sequence analysis of long-span cable-stayed bridges
2018
Abstract In cantilever construction of long-span cable-stayed bridges the stressing sequence of stays is fundamental for establishing the final configuration of the bridge. The structural behaviour of these bridges is usually evaluated through a forward staged construction analysis, in which the values of the prestressing forces to be applied to stays are the main unknowns. A unified procedure for determining the initial cable forces and for analyzing the entire sequence is presented here, considering the geometric nonlinearity of stays through the Dischinger equivalent elastic modulus. The target is the simultaneous determination of the initial cable forces with the simulation of the const…
Increasing the Capacity of Existing Bridges by Using Unbonded Prestressing Technology: A Case Study
2014
External posttensioning or unbonded prestressing was found to be a powerful tool for retrofitting and for increasing the life extension of existing structures. Since the 1950s, this technique of reinforcement was applied with success to bridge structures in many countries, and was found to provide an efficient and economic solution for a wide range of bridge types and conditions. Unbonded prestressing is defined as a system in which the post-tensioning tendons or bars are located outside the concrete cross-section and the prestressing forces are transmitted to the girder through the end anchorages, deviators, or saddles. In response to the demand for a faster and more efficient transportati…
The influence of time-dependent phenomena in segmental construction of concrete cable-stayed bridges
2011
Construction stages of a cable-stayed bridge are characterized by a sequence in which geometric configuration, restraints and consequently stress and strain patterns vary many times till the final arrangement is achieved. When construction of concrete bridges is made by cantilever method the influence of time-dependent phenomena becomes significant. In this study an evaluation of stay stressing procedures is given by taking into account creep and shrinkage in cantilever construction of concrete cable-stayed bridges. A methodology of stay stressing is proposed with the final target of reaching the desired geometric configuration. Comparison with classical analyses performed by backward metho…
A parametric study of curved incrementally launched bridges
2013
Abstract The structural behaviour of incrementally launched bridges in the construction stages depends on different parameters involving deck, nose, supports and guide devices, because static schemes vary continuously with the advance of the deck above the piers. For this reason temporary stresses in the deck, during launching, are rather different from those occurring in service life. Horizontally curved launched bridges also present the effects of torsion induced by geometric curvature. A parametric study is presented in order to analyse the influence of design parameters on the construction of these bridges. Analyses were carried out by extending to curved beams a procedure based on the …
Adjustable prestressing for construction stages of incrementally launched bridges
2014
Incrementally launched bridges, which are generally built with the static scheme of a continuous beam on supports, change their scheme several times during launching. In these different configurations, internal forces vary and bending moments of opposite signs occur in the same sections for different positions of deck during advancement. In these bridges, two different kinds of prestressing are necessary: a temporary one during launching and a definitive one in service life. In this study, the possibility of implementing automatic adjustable prestressing for the launching stages is investigated; the launch prestressing is partially supplied by a system which can change the tension value in …
Using FEM simulation to predict structural performances of a sailing dinghy
2017
The use of finite element method (FEM) tools is proposed to investigate the structural response of an eco-sustainable sailing yacht to different loading conditions, typical of those acting during regattas. The boat is, in particular, a 4.60 m dinghy with the hull and the deck made of an hybrid flaxâcork sandwich and internal reinforcements made of marine plywood. A preliminary activity has consisted in the refitting of an existing model in order to reduce the hull weight and to improve performances during manoeuvrings. These tasks have been interactively simulated in the virtual environment of the boat CAD model, where longitudinal and transversal reinforcements were enlightened and the m…
Influence of secondary torsion on curved steel girder bridges with box and I-girder cross-sections
2015
Steel curved girder bridges are largely used today in motorways and railways. They are often composed of thin-walled crosssections, entirely made of steel or with an upper concrete slab. The deck may have I-girders or box cross-sections: in any case curved girders are subjected to twisting moment, associated with bending, even for dead loads. Moreover, in thin-walled sections the influence of non-uniform torsion becomes sizable with respect to Saint Venant torsion, modifying the state of tangential stresses in the section and introducing axial stresses due to warping being prevented. Open sections of I-girder bridges are especially subject to these phenomena and warping can be significant n…
A Mixed Approach for Determination of Initial Cable Forces in Cable-Stayed Bridges and the Parameters Variability
2015
The determination of initial cable forces in cable-stayed bridges is an important first step in design and analysis of the structure under external loads. Adjustments of stay forces are often required during construction in order to assure the requested behaviour of the bridge in terms of final geometrical configuration and internal force distribution. An accurate assessment of the stay tensioning system allows designers to obtain a good result at the end of construction, by considering the parameters involved as deterministic quantities, assuring the observance of the execution tolerances during works. Actual loads and their variations need instead a stochastic approach which can give usef…
Synthesis and structural characterization of ethylene copolymers containing double-decker silsesquioxane as pendant groups and cross-linkage sites by…
2018
Abstract The copolymers of ethylene with the double-decker silsesquioxane (DDSQ) were synthesized by copolymerization with the use of metallocene and bis(phenoxy-imine) catalysts. The influence of the kind of the catalyst and polyreaction conditions on the performance of copolymerization as well as on the properties of the copolymers was studied. Depending on polyreaction parameters, the DDSQ contents in the copolymer varied in the range of 0.93–11.53 wt% which determined the compositions and the structural properties of copolymers. DDSQ incorporated into the polymer chain could constitute pendant groups in the main chain or it could act as a cross-linking agent. The ethylene/DDSQ copolymer…