5,855 research outputs found
Hydraulic aspects of bridges: assessment of the risk of scour (EX 2502)
No full textThis report presents advice and guidelines which will enable British Rail to assess hydraulic aspects of bridges over water. Possible causes of failure are discussed, and guidelines are presented to assess individual structures with respect to scour. The guidelines are based on bridge geometry and river and catchment characteristics. Features of the bridge and river are discussed and quantified where this is feasible. Recommendations are made concerning relevant data which should be recorded and maintained for each bridge. The guidelines have been designed to allow a bridge to be inspected and assessed in a short time and without special equipment
Evaluation of Bridge Replacement Alternatives for the County Bridge System, HR-365 August 1994
No full textRecent reports have indicated that 23.5 percent of the nation's highway bridges are
structurally deficient and 17.7 percent are functionally obsolete. A significant number of these bridges are on the Iowa county road system. The objective of the investigation described in this report was to identify, review and evaluate replacement bridges currently being used by various counties in Iowa and surrounding states. Iowa county engineers, county engineers in neighboring states as well as private manufacturers of bridge components, and regional precad prestressed concrete manufacturers were contacted to determine the most common replacement bridge types being used. Depending upon the findings of the review, possible improvements and/or new replacement bridge systems were
to be proposed. A questionnaire was developed and sent to county engineers in Iowa and several counties in surrounding states. The results of the questionnaire showed that the most common replacement bridges in Iowa are the continuous concrete slab and prestressed concrete bridges. The primary reason these types are used is because of the availability of standard designs and because of their ease of maintenance. Counties seldom construct these types of bridges using their own labor forces, but instead contract the work. However, county forces are used to construct steel stringer, precast reinforced concrete and timber bridges. In general, 69 percent of the counties indicate an ability and
willingness to use their own forces to design and construct relatively short span bridges (i.e., 40 A or less) provided the construction procedures are relatively simple.
Several unique replacement bridge types used in Iowa that are constructed by county forces
are documented and presented in this report. Sufficient details are provided to allow county engineers to determine if some of these bridges could be used to resolve some of their own replacement bridge problems. Where possible, cost information has also been provided. Each of these bridge types were evaluated for various criteria (e.g., cost effectiveness, conformance to AASI-ITO standards, range of sizes, etc.) by a panel of four Iowa county engineers; a summary of this critique is included. After evaluating the questionnaire responses from the counties and evaluating the various bridge replacement concepts currently in use, one new bridge replacement concept and one modification of a current Iowa county bridge replacement concept were developed. Both of these concepts would utilize county labor forces
Afflux at arch bridges
No full textPresent methods of calculating afflux at bridge crossings have proved inappropriate to bridges with arched soffits. A new method of estimation of afflux at arched structures is presented in this report
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
Becoming an HR strategic partner: tales of transition
No full textThis paper aims to bridge the gap between previous examinations of HR strategic partnership from a role perspective (Truss et al. 2002; Caldwell 2003) and an emerging interest in the social construction of identity (Alvesson et al. 2008). I consider ‘strategic partner’ as a local, flexible social construction framed by the broader occupational context. Based on a year-long ethnographic study, I examine the experiences of HR practitioners ‘becoming’ strategic partners, considering the themes of becoming strategic, becoming a partner and remaining a generalist. Practitioners depict becoming strategic as a ‘release’ from previous constraints, with becoming a partner positioned as filling a gap created by clients’ deficiencies in people management. Meanwhile, tensions develop as strategic partners attempt to retain a say in transactional issues. I reflect on the resulting practical issues while also considering the role of HR practitioners in “the dynamic and socially complex nature of HRM” (Francis 2003: 323)
Integral Bridge Abutment-to-Approach Slab Connection Final Report;TR-539/TR-530, June 2008
No full textThe Iowa Department of Transportation has long recognized that approach slab pavements of integral abutment bridges are prone to settlement and cracking, which manifests as the “bump at the end of the bridge”. A commonly recommended solution is to integrally
attach the approach slab to the bridge abutment. Two different approach slabs, one being precast concrete and the other being cast-inplace concrete, were integrally connected to side-by-side bridges and investigated. The primary objective of this investigation was to
evaluate the approach slab performance and the impacts the approach slabs have on the bridge. To satisfy the research needs, the project scope involved a literature review, survey of Midwest Department of Transportation current practices, implementing a health
monitoring system on the bridge and approach slab, interpreting the data obtained during the evaluation, and conducting periodic visual inspections. Based on the information obtained from the testing the following general conclusions were made: The integral connection between the approach slabs and the bridges appear to function well with no observed distress at this location and no relative longitudinal movement measured between the two components; Tying the approach slab to the bridge appears to impact the bridge; The two different approach slabs, the longer precast slab and the shorter cast-in-place slab, appear to impact the bridge differently; The measured strains in the approach slabs indicate a force exists at the expansion joint and should be taken into consideration when
designing both the approach slab and the bridge; The observed responses generally followed an annual cyclic and/or short term cyclic pattern over time
Steel Diaphragms in Prestressed Concrete Girder Bridges; TR-424, September 2004
No full textOver the years, bridge engineers have been concerned about the response of prestressed concrete (PC) girder bridges that had been hit by over-height vehicles or vehicle loads. When a bridge is struck by an over-height vehicle or vehicle load, usually the outside
and in some instances one of the interior girders are damaged in a bridge. The effect of intermediate diaphragms in providing damage protection to the PC girders of a bridge is not clearly defined. This analytical study focused on the role of intermediate diaphragms in reducing the occurrence of damage in the girders of a PC-girder bridge that has been struck by an over-height vehicle or vehicle load.
The study also investigated whether a steel, intermediate diaphragm would essentially provide the same degree of impact protection for PC girders as that provided by a reinforced-concrete diaphragm. This investigation includes the following: a literature search and a survey questionnaire to determine the state-of-the-art in the use and design of intermediate diaphragms in PC-girder bridges. Comparisons were made between the strain and displacement results that were experimentally measured for a large-scale, laboratory, model bridge during previously documented work and those results that were obtained from analyses of the finite-element models that were developed during this research for that bridge. These comparisons were conducted to calibrate the finite element models used in the analyses for this research on intermediate diaphragms. Finite-element models were developed for non-skewed and skewed PC-girder bridges. Each model was analyzed with either a reinforced concrete or two types of steel, intermediate diaphragms that were located at mid-span of an interior span for a PC-girder bridge. The bridge models
were analyzed for lateral-impact loads that were applied to the bottom flange of the exterior girders at the diaphragms location and away from the diaphragms location. A comparison was conducted between the strains and displacements induced in the girders for each intermediate-diaphragm type.
These results showed that intermediate diaphragms have an effect in reducing impact damage to the PC girders. When the lateral impact-load was applied at the diaphragm location, the reinforced-concrete diaphragms provided more protection for the girders
than that provided by the two types of steel diaphragms. The three types of diaphragms provided essentially the same degree of protection to the impacted, PC girder when the lateral-impact load was applied away from the diaphragm location
Estuarine Muds manual
No full textThis report is an update of the working manual part of 'The hydraulic engineering characteristics of estuarine muds' Report No SR77, December 1986, made in the light of research conducted at Hydraulics Research Ltd (HR) and invited comments received from end users in the industry. A considerable research programme has been undertaken by HR since the publication of Report No SR77 and valuable information has been gained in respect of the behaviour of mud during tidal cycles (Ref 2), the deposition of sediment from flowing water (Ref 20), the consolidation of weak mud beds (Ref 26), the effect of sand on the consolidation and erosion processes (Ref 27) and the response of mud beds under waves (Refs 32 and 33). These findings have been incorporated into this revised manual. Report No SR77 was widely circulated to consulting engineers, contractors, academics and staff at HR, with a request for their views on the reports technical content, style and usability. Approximately half of the recipients replied with helpful and, in many cases detailed comments. Overall, the general impression was positive and encouraging. This report has been drafted with these comments taken into account wherever possible. This report summarises, in an engineering form, the main processes of cohesive sediment behaviour, namely, deposition, consolidation and erosion. The data presented are intended to show the practicing engineer which parameters are important in each of the processes and to enable broad estimates of the rates of deposition, consolidation and erosion to be made based on a limited knowledge of the field conditions. The behaviour of cohesive sediment does vary considerably in quantitative terms from one source to another. Therefore, it is crucial that the engineer appreciates that estimates based on the data presented herewith may well be in error by half an order of magnitude. For most serious engineering problems involving cohesive sediment it would be essential to undertake a detailed study. This would involve some of the following techniques: field measurements, laboratory testing of sediment, numerical modelling of hydrodynamics and sediment transport and physical modelling of hydrodynamics
Performance of Strip Seals in Iowa Bridges, Project TR-437, January 2001
No full textA pilot study was conducted on the premature failures of neoprene strip seals in
expansion joints in Iowa bridges. In a relatively large number of bridges, strip seals have pulled out of the steel extrusions or otherwise failed well before the expected life span of the seal. The most serious consequence of a strip-seal failure is damage to the bridge substructure due to salt, water, and debris interacting with the substructure.
A literature review was performed. Manufacturers’ specifications and
recommendations, practices in the states bordering Iowa, and Iowa DOT design and
installation guidelines were reviewed. Discussions were held with bridge contractors and the installation of a strip seal system was observed. Iowa DOT bridge databases were analyzed. A national survey was conducted on the use and performance of strip seals.
With guidance from the Iowa DOT, twelve in-service bridges with strip-seal
expansion joints were selected for detailed investigation. Effective bridge temperatures and corresponding expansion-joint openings were measured, DOT inspection reports were
reviewed, and likely cause(s) of premature failures of strip seals were proposed.
All of the seals used in the twelve bridges that had the most serious failures were in
concrete girder bridges. Experimental results show that for a majority of these serious
failures, the joint opening at 0° F predicted by the Iowa DOT design equations, the joint
opening at 0° F extrapolated from the experimental data, or both, are larger than the
movement rating of the strip seal specified on the bridge plans. Other likely causes of
premature failures of seals in the twelve bridges include debris and ice in the seal cavity, a large skew and the corresponding decrease in the movement rating of the seal, improper installation, and improper setting of the initial gap
River regime based on sediment transport concepts
No full textRational regime relationships for the width, depth and slope of a river in equilibrium are developed using the Ackers and White sediment transport formula and the White, Paris and Bettess friction relationships, together with a principle of maximum sediment transporting capacity. This concept of maximising the sediment transporting capacity is shown to be equivalent to minimising the slope of the river. The relationships which are developed show good agreement with other empirically derived regime relationships and data from sand channels. Some comparisons are made with data from gravel rivers and the difficulties in applying regime concepts to these rivers are discussed
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