30,467 research outputs found
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
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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
Letter to the editor by Co-Chair of Lavender Bridges
No full textThis January 30, 1986 letter to the editor signed Co-Chair, Lavender Bridges addresses the front-page article in the Western Carolinian from January 23 titled “Addressing gay concerns: Lavender Bridges recognized.” The author was misquoted in the article and wishes to set the record straight. Lavender Bridges, an anonymously founded student organization open to all individuals, aimed to promote awareness of lesbian and gay lifestyle, provide lesbian and gay resources, and increase communication with all students and community members. The first organizational meeting took place October 10, 1985 and was officially recognized by the office of Student Development on December 13, 1985. The last mention of the group appeared in the October 10, 1991 issue of the Western Carolinian.Dear Mr. Editor,
I'd like to calf your attention to
the significance of language and
the importance of the use of
particular words to convey the
intended meanings of one person
(or group) to another. Specifically,
I refer to the article about Lavender
Bridges in your January 23 issue.
The only quotation in the
article was carefully planned and
the words were carefully selected
with the intention to convey clearly
that this orgainzation would NOT
address "specific concerns of
sexual orientation" more than
broader concerns affecting all
individuals in a society regardless
of one's sexuality. I am adamant
that if you are to quote an
individual (and in this particular
case you were able to copy from a
written quote) their specific
selection of words must be
considered and carefully
conveyed. On behalf of Lavender
Bridges, I will reiterate the specific
and correct quote that was
Western Carolinian
(704) 227 7267 Western Carolina University PO Box 66Culiowhee, North Carolina 28723
The WESTERN CAROLINIAN is published
weekly by the Publication Board of Western Carolina
University. It is an independent student publication
intended for the article:
"While Lavender Bridges
specifically addresses the
concerns of lesbian and gay
students, attendance is not a
reflection of sexual orientation. The
group wishes to extend an
invitation to any individual who is
interested in learning more about
the issues surrounding a lesbian or
gay lifestyle.
In addition, sexual orientation
is not the only area of one's lifestyle.
We assume labels only to begin
defining and clarifying for
ourselves and others who it is that
we really are. For gay people, this
mea ns eve n creati ng new words or
using old words for newer
concepts. We are no more strictly
sexual beings than bisexuals or
heterosexuals. What we are
though, has been overshadowed
by the labels which have been
used to create frightening myths
about us.
Sincerely,
Co-Chair, Lavender Bridge
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
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
Linear oscillations of axisymmetric viscous liquid bridges
No full textSmall amplitude free oscillations of axisymmetric capillary bridges are considered for varying values of the capillary Reynolds number C-1 and the slenderness of the bridge Λ . A semi-analytical method is presented that provides cheap and accurate results for arbitrary values of C-1 and Λ ; several asymptotic limits (namely, C>> 1, C>>1, Λ >> 1 \ {and} \ |π -Λ |>> 1 ) are considered in some detail, and the associated approximate results are checked. A fairly complete picture of the (fairly complex) spectrum of the linear problem is obtained for varying values of C and Λ . Two kinds of normal modes, called capillary and hydrodynamic respectively, are almost always clearly identified, the former being associated with free surface deformation and the latter, only with the internal flow field; when C is small the damping rate associated with both kind of modes is comparable, and the hydrodynamic ones explain the appearance of secondary (steady or slowly-varying) streaming flow
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-steady Phenomena in the Vibration of Viscous Cylindrical Long Liquid Bridges
No full textThis paper deals with the dynamic response of long cylindrical viscous liquid bridges subjected to an oscillatory microgravity field whose frequency varies linearly with time. The problem has been solved by using a one-dimensional model for the dynamics, derived from Cosserat theory for continuum, in which the axial velocity is considered to be constant over each cross-section of the liquid column. The dynamic response of the liquid bridge has been obtained by applying the Laplace transform to the problem formulation. The results obtained show that a variable -frequency excitation could give rise to erroneous measurements of the resonance frequencies of viscous liquid bridges
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
Alternative Solutions to Meet the Service Needs of Low Volume Bridges in Iowa; TR-452, June 2004
No full textThere is a nationwide need for a safe, efficient and cost effective transportation
system. An essential component of this system is the bridges. Local agencies perhaps
have an even greater task than federal and state agencies in maintaining the low
volume road (LVR) bridge system due to lack of sufficient resources and funding.
The primary focus of this study was to review the various aspects of off-system bridge
design, rehabilitation, and replacement. Specifically, a reference report was developed
to address common problems in LVR bridges. The source of information included
both Iowa and national agencies. This report is intended to be a “user manual” or
“tool box” of information, procedures and choices for county engineers to employ in
the management of their bridge inventory plus identify areas and problems that need to
be researche
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