Author: Arneson, L A Zevenbergen, L W Lagasse, P F Clopper, P E | Size: 6.55 MB | Format:PDF | Quality:Original preprint | Publisher: Ayres Associates, Incorporated | Year: 2012 | pages: 340
This document is the fifth edition of HEC-18. It presents the state of knowledge and practice for the design, evaluation and inspection of bridges for scour. There are two companion documents, HEC-20 entitled "Stream Stability at Highway Structures," and HEC-23 entitled "Bridge Scour and Stream Instability Countermeasures." These three documents contain updated material from previous editions and continued research by NCHRP, FHWA, State DOTs, and universities. This fifth edition of HEC-18 also contains revisions obtained from further scour-related developments and the use of the 2001 edition by the highway community. The major changes in the fifth edition of HEC-18 are: expanded discussion on the policy and regulatory basis for the FHWA Scour Program, including risk-based approaches for evaluations, developing Plans of Action (POAs) for scour critical bridges, and expanded discussion on countermeasure design philosophy (new vs. existing bridges). This fifth edition includes: a new section on contraction scour in cohesive materials, an updated abutment scour section, alternative abutment design approaches, alternative procedures for estimating pier scour, and new guidance on pier scour with debris loading. There is a new chapter on soils, rock and geotechnical considerations related to scour. Additional changes include: a new approach for pier scour in coarse material, new sections on pier scour in cohesive materials and pier scour in erodible rock, revised guidance for vertical contraction scour (pressure flow) conditions, guidance for predicting scour at bottomless culverts, deletion of the "General Scour" term, and revised discussion on scour at tidal bridges to reflect material now covered in HEC-25 (2nd Edition).
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Settlement and heave related movements of bridge approach slabs relative to bridge decks create a bump in the roadway. Several problems arise from these bumps, which include poor riding conditions, potential vehicle damage, loss of vehicle control causing injuries or even casualities, lowered perception of the department’s road works, increased maintenance works, and constant delays to rehabilitate the distressed lanes. All these make this bump problem a major maintenance problem in Texas. Several mitigation methods have been employed, and the results are not always satisfactory. In the present research, two treatment methods were investigated for controlling settlements of approach slabs of new bridge construction. Researchers from the University of Texas at Arlington and the University of Texas at El Paso performed two phases to accomplish these studies. During the first phase, the documented information that covers various methods used so far for approach slab settlement mitigation technologies was compiled and presented. The second and final phase focused on field evaluation studies of deep soil mixing and lightweight embankment fill treatment methods in reducing settlements. A few other technologies were also evaluated for reducing settlements of existing bridge approach slabs. Both design and construction specifications of the new methods that provided effective treatments in field conditions are presented.
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This Primer is intended to be a practical supplement to NCHRP Report 534, "Guidelines for Inspection and Strength Evaluation of Suspension Bridge Parallel Wire Cables," and FHWA Report No. FHWA-PD-96-001, titled "Recording and Coding Guide for the Structure Inventory and Appraisal of the Nation’s Bridges." This Primer will serve as an initial resource for those involved in the inspection, metallurgical testing, and strength evaluation of suspension bridge cables in addition to providing necessary documentation for recording performed inspections, testing, and strength evaluations. Furthermore, this document is intended to provide field inspectors, technicians, and/or engineers with the necessary forms and information they need to perform an inspection.
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Posted by: mahyarov - 10-29-2012, 06:27 AM - Forum: Concrete
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Validation of Prestressed Concrete I-Beam Deflection and Camber Estimates
Author: O’Neill, Cullen R French, Catherine E | Size: 3.34 MB | Format:PDF | Quality:Original preprint | Publisher: University of Minnesota, Twin Cities | Year: 2012 | pages: 205
The camber at the time of bridge erection of prestressed concrete bridge girders predicted by the Minnesota Department of Transportation (MnDOT) was observed to often overestimate the measured cambers of girders erected at bridge sites in Minnesota, which, in some cases, was causing significant problems related to the formation of the bridge deck profile, the composite behavior of the girders and bridge deck, delays in construction and increased costs. Extensive historical data was collected from two precasting plants and MN counties and it was found that, on average, the measured cambers at release and erection were only 74% and 83.5%, respectively, of the design values. Through data collection, analysis, and material testing, it was found that the primary causes of the low camber at release were concrete release strengths that exceeded the design values, the use of an equation for concrete elastic modulus that greatly under-predicted the measured values, and thermal prestress losses not accounted for in design. Fourteen girders were instrumented and their camber measured and the program PBEAM was used to evaluate the influence of various time-dependent effects (i.e., solar radiation, relative humidity, concrete creep and shrinkage, length of cure and bunking/storage conditions) on long-term camber. Once investigated, these effects were included in long-term camber predictions that were used to create sets of both time-dependent and singlevalue camber multipliers. The use of these multipliers, along with modifications made to the elastic release camber calculations, greatly reduced the observed discrepancy between measured and design release and erection cambers.
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Posted by: mahyarov - 10-29-2012, 06:25 AM - Forum: Concrete
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Lateral Load Distribution for Steel Beams Supporting an FRP Panel
Author: Poole, Harrison Walker | Size: 3.62 MB | Format:PDF | Quality:Original preprint | Publisher: Kansas State University's Center for Transportation Research | Year: 2012 | pages: 162
Fiber Reinforced Polymer (FRP) is a relatively new material used in the field of civil engineering. FRP is composed of fibers, usually carbon or glass, bonded together using a polymer adhesive and formed into the desired structural shape. Recently, FRP deck panels have been viewed as an attractive alternative to concrete decks when replacing deteriorated bridges. The main advantages of an FRP deck are its weight (roughly 75% lighter than concrete), its high strength-to-weight ratio, and its resistance to deterioration. In bridge design, the American Association of State Highway and Transportation Officials (AASHTO) provides load distributions to be used when determining how much load a longitudinal beam supporting a bridge deck should be designed to hold. Depending on the deck material along with other variables, a different design distribution will be used. Since FRP is a relatively new material used for bridge design, there are no provisions in the AASHTO code that provides a load distribution when designing beams supporting an FRP deck. FRP deck panels, measuring 6 ft x 8.5 ft, were loaded and analyzed at Kansas State University (KSU) over the past 4 years. The research conducted provides insight towards a conservative load distribution to assist engineers in future bridge designs with FRP decks. Two FRP panels were tested using two different support configurations. The continuous panel test was completed throughout the year of 2007 while the simple span and cantilever tests were completed November, 2010 through January, 2011. Load increments of 5 kips from 0 to 20 kips were analyzed in this report. From strain results, load ratios for beams were developed and a distribution ratio for each tests setup was determined. Additional testing was completed on the simple span in order to determine the moment curve for a beam with different loading scenarios. These moment curves provided the researchers with insight that would determine an effective load distribution length of the panel bearing on the supporting beam.
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Posted by: mahyarov - 10-29-2012, 06:22 AM - Forum: Concrete
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Nanotechnology-Based System for Damage-Resistant Concrete Pavements
Author: Al-Rub, Rashid K Abu | Size: 3.97 MB | Format:PDF | Quality:Original preprint | Publisher: Texas A&M University | Year: 2012 | pages: 124
The focus of this study was to explore the use of nanotechnology-based nanofilaments, such as carbon nanotubes (CNTs) and nanofibers (CNFs), as reinforcement for improving the mechanical properties of Portland cement paste and creating multifunctional and sensing concrete. Due to their ultra-high strength and very high aspect ratios, CNTs and CNFs have been excellent reinforcements for enhancing the physical and mechanical properties of polymer, metallic, and ceramic composites. Very little attention has been devoted to exploring the use of nanofilaments in the transportation industry, however. Therefore, this study aimed to bridge the gap between nanofilaments and transportation materials. This was achieved by testing the integration of CNTs and CNFs in ordinary Portland cement paste through state-of-the-art techniques. Different mixes in fixed proportions (e.g., water-to-cement ratio, air content, admixtures) along with varying concentrations of CNTs or CNFs were prepared. Different techniques commonly used for other materials (like polymers) were used in achieving uniform dispersion of nanofilaments in the cement paste matrix and strong nanofilament/cement bonding. Small-scale specimens were prepared for mechanical testing in order to measure the modified mechanical properties as a function of nanofilament concentration, type, and distribution. With 0.1% CNFs, the ultimate strain capacity increased by 142%, the flexural strength increased by 79%, and the fracture toughness increased by 242%. A scanning electron microscope was used to discern the difference between crack bridging and fiber pullout. Test results showed that the strength, ductility, and fracture toughness can be improved with the addition of low concentrations of either CNTs or CNFs.
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Development of Supplemental Resistance Method for the Design of Drilled Shaft Rock Sockets
Author: Sandford, Thomas C | Size: 5.70 MB | Format:PDF | Quality:Original preprint | Publisher: University of Maine, Orono | Year: 2011 | pages: 186
Rock Socketed Drilled Shafts have been used on a variety of projects, especially bridges, in areas with bedrock close to the surface. The large loads that these foundation structures can resist make them more practical than alternatives, such as pile groups, in certain situations. However, the current conservative design practices are based on the performance of Rock Socketed Drilled Shafts in soft rock formations. The current design practice for axial capacity often neglects one of the two resisting forces, usually end bearing. In areas, such as New England, with good quality hard rock, Rock Socketed Drilled Shafts have been found to have ultimate axial capacities 7-25 times the predicted value. The goal of this research is to develop a design method that utilizes the full potential of Rock Socketed Drilled Shafts in hard rock. A finite element model using constitutive relationships and surface interactions was created to replicate Rock Socketed Drilled Shafts in hard rock. The model was calibrated by duplicating results from five Osterberg load tests on shafts in hard rock. For the purpose of this research hard rock is classified as having an unconfined strength greater than 30 MPa. After calibrating the model, the model was used to show performance of shafts of various sizes founded in rock of two different qualities. The performance results were used to develop a design method for Rock Socketed Drilled Shafts based on service limit criteria. This research revealed that portions of both resistance forces, end bearing and side shear, can be used together in the design of Rock Socketed Drilled Shafts if service limit state criteria are considered. This method applies to well cleaned sockets and primarily hard rock. This method can be used with equations for nominal resistance as well as Osterberg tests.
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MEASUREMENT OF FOUNDATION STRAINS UNDER LATERAL LOADS
Author: Long, R P Healy, K A CAREY, P J Powers, M | Size: 1.37 MB | Format:PDF | Quality:Original preprint | Publisher: University of Connecticut, Storrs | Year: 1976 | pages: 81
A cooperative field work effort was developed to evaluate the resistance to lateral loads of poles set in augured holes and surrounded by well graded backfill, and the effect of pole diameter on strength and stiffness. Theoretical aspects of soil-pole interaction, poles in cohesionless soil, and poles in precompressed clay are discussed as well as non-homogeneous soil conditions and theoretical assumptions. Methods of testing are reviewed, and tests in dense sand, glacial till and clayey silt, are detailed. Field test results are discussed, and model tests in sands are described. Design considerations are set forth, and a design example is described. It is concluded from the study that directly embedding poles is, in many cases, an economical method of setting the poles to resist lateral forces. The behavior of directly embedded poles depends on the stress-strain characteristics of the soil surrounding the pole to a distance of approximately 3 pole diameters. The stiffness of glacial till can be reduced by the method of excavating the hole to receive the pole. The study also showed that the stress-strain properties of clays and disturbed glacial till are time dependent; this must be considered in the design.
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STUDIES ON BOND AND CRACKING OF STRUCTURAL CONCRETE
by Homayoun H. Abrishami, June 1994
Department of Civil Engineering and Applied Mechanics
McGill University, Montreal, Canada
A thesis submitted to
the Faculty of Graduate Studies and Research
in partial fulfilment of the requirements for the degree of
Doctor of Philosophy
ABSTRACT
This thesis presents new testing methods to study the bond characteristics of reinforcing
bars and pretensioned strands. For reinforcing bars, the new technique, which simulates a more uniforrn bond stress, enabled the study of both pullout failures and splitting faiiures. Variables studied included concrete cover, bar size and the erfect of epoxy coatings on the bars. Analytical expressions for predicting the bond stress versus slip response and the bond stress distribution for different types of pullout tests are developed. For pretensioned strand, the testing technique enabled the study of the bond characteristics along toth the transfer and the flexural bond lengths. Equations for predicting the trasnfer development lengths are given.
The tensile behaviour of concrete members reinforced with a single reinforcing bar are studied. Variables studied included concrete strength, presence of steel fibres, bar size and the effect of epoxy coatings on the bars. Both transverse cracks and splitting cracks were studied and a factor accounting for the influence of splitting cracks on tension stiffening is introduced. A procedure for predicting the response of tension members, accounting for the concrete coyer and bar size and the presence of steel fibres is given. Equations are suggested to deterrnine the transfer length and crack spacing.
Experimental investigations were carried out to study the post-cracking behaviour of bearns
without stirrups. The influence of concrete strength and the presence of epoxy-coated reinforcement on the crack development, type of cracking, ductility and failure mechanism are discussed. Typical slab-colurnn connections found in parking structures were tested, simulating the construction stages. The effects on crack development of both concrete quality and the presence of epoxy coatings on the reinforcement were studied. Modification factors for predicting crack widths in bearns and two-way slabs, accounting for the presence of epoxy coatings, are given in a forrn suitable for implementation in codes of practice.
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Models for flexural cracking in concrete; the state of the art by
A. Borosnyoi and G. L. Balazs
Structural Concrete, 2005 - 6 No 2
Crack formation presents a complex mechanical and geometrical question to be modelled. The available crack
width formulations are often based on simplifications. A rigorous formulation of crack widths should be based on
the integration of strain differences of reinforcement and concrete between cracks, due to the accumulated slips.
In this paper an extensive literature review on crack widths and crack spacing is presented. The basic intention of
the present paper is to summarise the development of flexural crack models and collect the most relevant formulae
for crack spacing and crack width. It reports not only the possible improvement of design or research equations but
also the appearance of new types of reinforcements with different characteristics from those of steel
reinforcements. This state-of-the-art Report is a contribution to the work of fib TG 4.1 ‘Serviceability Models’.
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