349,217 research outputs found
Modelling Extreme Traffic Loading on Bridges Using Kernal Density Estimators
No full textInnovations on Bridges and Soil-Bridge Interaction (IBSBI 2011), Athens, Greece, October 13-15, 2011Kernel density estimators are a non-parametric method of
estimating the probability density function of sample data. In this paper, the
method is applied to find characteristic maximum daily truck weights on
highway bridges. The results are then compared with the conventional
approach.Deposited by bulk impor
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Optimum design of composite prestressed concrete girder railway bridges
No full textThis paper deals with the formulation of design optimisation of pretsressed concrete bridges. The bridge is of a slab-on-girder type, hence modeled as an equivalent orthotropic plate. The whole bridge system is considered as a simply supported right angle plate. Following linear elastic behaviour, the governing fourth order differential equation of the plate for patch load is solved in order to find out load distribution on the girders forming the bridge as well as the deflections and internal forces at critical sections of the whole bridge. The optimisation problem is formulated for various cross sectional geometries including rectangular, symmetrical I, unsymmetrical I, box, T and inverted T sections. The design variables are the main cross sectional dimensions, prestressing force and tendon eccentricity. The objective function comprises the cost of concrete material, formwork and prestressing steel tendons. The constraint functions are set to satisfy design requirements as per British Standards for bridges (BS 5400). Nonlinear optimisation method based on sequential unconstrained minimisation technique (SUMT) is employed to achieve optimum bridge configuration for specific design parameters of span length, concrete compressive strength and railway loading patterns. A purpose built computer program is set up to carry out the solution of the design optimisation problem efficiently in terms of time and effort. A typical example of unsymmetrical I-section having a small bottom flange as compared to the top flange width with composite deck effect is presented. The results show that the total cost increases as the span increases due to the increase of the initial prestressing force. Furthermore, the total cost decreases as the concrete compressive strength increases in spite of the increasing of the prestressing force. This is due to decrease of the overall depth, top and bottom flange widths, hence leading to a smaller girder size. Such finding will encourage engineers to adopt high strength concrete for bridges as it will help reducing not only the initial cost but also the life cycle cost of the bridge over its entire life
Maximum dynamic stress on bridges traversed by moving loads
No full textMost current research on dynamic effects due to traffic load on simply supported bridges focuses on the mid-span section of the bridge, since this location corresponds to the worst static bending moment. However, the maximum total moment allowing for dynamics, may differ considerably from the maximum moment at mid-span. This paper shows how the maximum can occur in a section relatively far from mid-span with a significant difference in magnitude.Other funderJournal websitewww.bridgesjournal.comEuropean 6th Framework Programme ARCHES (Assessment and Rehabilitation of Central European Highway Structures)Publisher requires the journal URL to appear on the record: www.bridgesjournal.com. Could use Description web link: Journal website as in http://hdl.handle.net/10197/2437? - AV 1/11/2010 au ke SB. 15/11/'1
Non-Axisymmetric Effects on Long Liquid Bridges
No full textThe stability of long liquid bridges under non-axisymmetric disturbances like a microgravitational force acting perpendicular to the liquid bridge axis or a non-coaxiality of the disks is analyzed through an asymptotic method based on bifurcation techniques. Results obtained indicate that such non-axisymmetric effects are of higher order than those produced by axisymmetric perturbations
Feasibility Study of Strengthening Existing Single Span Steel Beam Concrete Deck Bridges; HR-214, June 1961
No full textIowa has the same problem that confronts most states in the United States: many bridges constructed more than 20 years ago either have deteriorated to the point that they are inadequate for original design loads or have been rendered inadequate by changes in design/maintenance standards or design loads. Inadequate bridges require either strengthening or posting for reduced loads. A sizeable number of single span, composite concrete deck - steel I beam bridges in Iowa currently cannot be rated to carry today's design loads. Various methods for strengthening the unsafe bridges have been proposed and some methods have been tried. No method appears to be as economical and promising as strengthening by post-tensioning of the steel beams. At the time this research study was begun, the feasibility of posttensioning existing composite bridges was unknown. As one would expect, the design of a bridge-strengthening scheme utilizing post-tensioning is
quite complex. The design involves composite construction stressed in an abnormal manner (possible tension in the deck slab), consideration of different sizes of exterior and interior beams, cover-plated beams already designed for maximum moment at midspan and at plate cut-off points, complex live load distribution, and distribution of post-tensioningforces and moments among the bridge beams. Although information is available on many of these topics, there is miminal information on several of them and no information available on the total design problem. This study, therefore, is an effort to gather some of the missing information, primarily through testing a half-size bridge model and
thus determining the feasibility of strengthening composite bridges by post-tensioning. Based on the results of this study, the authors anticipate that a second phase of the study will be undertaken and directed toward strengthening of one or more prototype bridges in Iowa
Comparative structural response of two steel bridges constructed 100 years apart
No full textThis paper presents a comparative numerical analysis of the structural behaviour and seismic performance of two existing steel bridges, the Infiernillo II Bridge and the Pinhao Bridge, one located in Mexico and the other in Portugal. The two bridges have similar general geometrical characteristics, but were constructed 100 years apart. Three-dimensional structural models of both bridges are developed and analysed for various load cases and several seismic conditions. The results of the comparative analysis between the two bridges are presented in terms of natural frequencies and corresponding vibration modes, maximum stresses in the structural elements and maximum displacements. The study is aimed at determining the influence of a 1 century period in material properties, transverse sections and expected behaviour of two quite similar bridges. In addition, the influence of the bearing conditions in the global response of the Pinhao Bridge was evaluated
Stability of liquid bridges between twisted elliptical disks
No full textThe influence in the stability of long liquid bridges supported between two elliptical-shaped disks of their main axis relative orientation is investigated. A numerical continuation method capable of finding equilibrium shapes, both stable and unstable, is used to calculate a series of equilibrium shapes supported by disks of increasing eccentricity for different relative orientation of the disks axis. The stable or unstable character of each of the shapes is calculated to determine the position of the stability limit and its characte
Experimental determination of dynamic allowance for traffic loading in bridges
No full textTransportation Research Board 89th Annual Meeting, Washington DC, 2010-1-10 to 2010-1-14Bridge codes adopt values for dynamic allowance in traffic load models that are necessarily conservative
to cover for an entire range of bridges with different mechanical characteristics, boundary conditions, and the large
number of uncertainties associated to the vehicle-bridge interaction problem. A further level of conservatism occurs
due to the independent manner in which the governing static load and the corresponding allowance for dynamics are
specified. In particular, certain bridges are not susceptible to high levels of vehicle-bridge interaction when loaded
by a critically heavy vehicle or a critical combination of vehicles. Recent advances in Bridge Weigh-In-Motion
technology allow not only to collect information on the weights, spacings and speeds of the traffic loads traversing a
bridge, but also to separate the maximum static strain from the total measured strain using a filtering procedure. In
this paper, maximum static and total load effects are collected and analysed for three different sites as part of the
European project ARCHES (6th RTD framework programme). Bridge measurements are used to discuss the
dynamics of the most frequent truck classes and the entire traffic sample. The measurements reveal a decrease in
percentage increment in dynamics and a reduction on the variability of the dynamic increment as the static load
effect increases. This phenomenon can be of particular relevance in the assessment of the dynamics of extreme
loading cases.Deposited by bulk impor
Theoretical and Experimental Analysis of Stability Limits of Non-Axisymmetric Liquid Bridges under Microgravity Conditions
No full textThe stability of nonaxisymmetric liquid bridges under microgravity conditions is investigated. The influence on the stability of an almost cylindrical liquid bridge of axisymmetric effects like its volume, a small axial acceleration acting on it, and unequal-diameter supporting disks, as well as that of nonaxisymmetric perturbations like small lateral acceleration and noncoaxial supporting disks, has been analyzed by using standard bifurcation techniques. An expression for the maximum length of a liquid bridge, including all the above-mentioned effects, has been obtained. In addition, the effect on the stability of liquid bridges having noncoaxial supporting disks has been experimentally studied within the constraints of an Earth laboratory by using millimetric liquid bridges. Analytical and experimental results show that each one of the nonaxisymmetric perturbations like the ones here considered (lateral acceleration and eccentricity) can be, from the point of view of stability, as critical as axisymmetric perturbations. In addition, it is demonstrated that when both nonaxisymmetric perturbations are not negligible, the coupling of both perturbations can be a stabilizing effect on the liquid bridg
A mathematical model for assessment of material requirements for cable supported bridges: implications for conceptual design
No full textRecent technological developments have led to improvements in the strengths of materials, such as the steel and wire ropes used in the construction of cable supported bridges. This, combined with technological advancements in construction, has encouraged the design of structures with increasing spans, leaving the question of material and environmental costs behind. This paper presents a refined
mathematical model for the assessment of relative material costs of the supporting structures for
cable-stayed and cable suspension bridges. The proposed model is more accurate than the ones published to date in that it includes the self weight of the cables and the pylons. Comparisons of material requirements for each type of bridge are carried out across a range of span/dip ratios. The basis of comparison is the assumption that each structure is made of the same material (steel) and
carries an identical design load, q, exerted by the deck. Calculations are confined to a centre span of a three-span bridge, with the size of the span ranging from 500 m to 3000 m. Results show that the optimum span/dip ratio, which minimises material usage, is 3 for a cable-stayed (harp type) bridge, and 5 for a suspension structure. The inclusion of the self weight of cable in the analysis imposes limits on either the span, or span/dip ratio. This effect is quantified and discussed with reference to
the longest cable-supported bridges in the world completed to date and planned in the future
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