Steel Highway Bridges Research Articles

Discussion of “ Fatigue Strength of Deteriorated Steel Highway Bridges ” by Patrick D. Zuraski and John E. Johnson (October, 1990, Vol. 116, No. 10)

Discussion of “ <i>Fatigue Strength of Deteriorated Steel Highway Bridges</i> ” by Patrick D. Zuraski and John E. Johnson (October, 1990, Vol. 116, No. 10)

Fatigue Strength of Deteriorated Steel Highway Bridges

The effect of long-term environmental exposure and an extended history of highway loading was quantitatively determined for steel bridge beams that had been in service more than 50 years. Fatigue tests were conducted on specimens removed from the tension flange of truss stringers salvaged from four bridge replacement projects. Based on the fatigue strength reduction factor \IK\df\N determined on a basis of mean fatigue life for all specimens in one bridge, the fatigue sensitivities encountered were less than that associated with an AASHTO Category C welded connection detail. For individual specimens, the maximum \IK\df\N value determined was 3.0. At 36-ksi (248-MPa) stress range, average specimen lives exceeded 300,000 cycles for all bridges, for both center-span (maximum prior stress history) and near-support (insignificant prior stress history) specimens. The corrosion deterioration experienced by the plain (nonwelded) simple-span steel bridge beams in this study caused the average fatigue strength to be reduced by approximately one AASHTO fatigue category.

Reliability Calibration of Fatigue Evaluation and Design Procedures

Fatigue evaluation and design methods were developed in a recent project for steel highway bridges. The evaluation method enables an engineer to estimate the safe remaining life of an existing bridge. The estimate of safe remaining life is needed to make cost-effective decisions regarding inspection, repair, rehabilitation, and replacement. The design method is consistent with the evaluation method. The reliability-based concepts and data base behind the development of these methods are discussed and illustrated through some examples. The evaluation and design methods were calibrated for both redundant and single-load-path bridge components using safety (reliability) indices computed with existing fatigue specifications. The proposed procedures lead, however, to more uniform and consistent safety indices. The evaluation and design methods also follow to a large degree present procedures familiar to highway agencies. These methods, however, contain options to use site-specific traffic and inspection data and improved structural analysis. Both the evaluation and fatigue design methods have been incorporated in two recent guide specifications published by AASHTO.

Probabilistic fracture mechanics application to highway bridges

A probabilistic fracture mechanics model was developed for determining the risk of fatigue failure of steel highway bridges. A deterministic fracture mechanics calculation of crack growth with stochastic inputs for crack growth rate, fracture toughness, initial crack size and load history was used. Stress intensity expressions were compiled from literature for typical AASHTO category bridge details. Statistical distributions for input variables were derived from data reported in literature. The model was found to predict well the short service life of the Yellow Mill Pond Bridge in Connecticut.

Discussion of “ Risk Analysis of Fatigue Failure of Highway Steel Bridges ” by Nur Yazdani and Pedro Albrecht (March, 1987, Vol. 113, No. 3)

Discussion of “ <i>Risk Analysis of Fatigue Failure of Highway Steel Bridges</i> ” by Nur Yazdani and Pedro Albrecht (March, 1987, Vol. 113, No. 3)

鋼道路橋の疲労設計曲線に関するパラメトリック解析

Fatigue design curves of steel highway bridges were analyzed parametrically under computer simulated variable amplitude stresses. Crack propagation life of 4 types of welded joints was estimated by applying the constant amplitude da/dN-ΔK relationship and the liner cumulative damage rule. The configuration of fatigue life curves under variable amplitude stresses varied with the traffic constitution and the beam span particularly in the longer life region. The fatigue limit under variable amplitude stresses for each joint could be defined by using estimated fatigue life curves and Miner's rule.

Risk Analysis of Fatigue Failure of Highway Steel Bridges

A probabilistic fracture mechanics model was developed for determining the risk of fatigue failure of steel highway bridges. The model consists of: (1) Stochastic inputs for crack growth rate, fracture toughness, initial crack size, and load history; (2) a deterministic fracture mechanics calculation of crack growth; and (3) a Monte Carlo simulation to obtain the output variable, i.e., the fatigue life. The following effects on the risk of failure were examined: inspection interval, truck weight, truck traffic, system versus detail reliability, and length of service life extension. The model was applied to three bridges with cover-plated girders. It was found to predict well the short service life of the Yellow Mill Pond Bridge, Connecticut, in which the cover-plate end details began to fail 12 years after bridge opening. The model is particularly useful in determining the risk of extending the service life of a bridge beyond its intended design life.

Resistance factors for steel highway bridges

Resistance (performance) factors for bridge members composed of rolled and welded steel sections are developed consistent with the live and dead load factors given in the Ontario Highway Bridge Design Code (OHBDC).Ratios of the load components of seven different spans of plate and box girder bridges are used with the statistical data for loads used in the development of the OHBDC. Monte Carlo simulation techniques are used to compose distribution curves for the various resistance functions from distribution curves describing the appropriate geometric properties, material properties, and test/predicted ratios. Using the 0.001 and 0.05 fractiles of the distribution curves so obtained for the resistances, mean values and coefficients of variation are obtained for equivalent lognormal distribution curves.Resistance factors are then developed for the fully plastic moment resistance, the yield moment, the inelastic buckling moment resistance, the elastic buckling moment resistance, the moment resistance of composite sections, and column resistances for slenderness parameter values of 0.8, 1.0, and 1.2. A general resistance factor of 0.93 is recommended for all the resistances and bridges studied. Resistance factors of 0.95 and 0.98 are considered appropriate for the flexural resistance of bridges composed of welded and rolled sections, respectively. Key words: bridges, limit states, Monte Carlo simulation, performance factors, resistance factors, steel, rolled sections, welded sections.

Stress Cycles for Fatigue Design of Steel Bridges

Analytical methods are used to develop design values for the number of stress cycles caused by the passage of a truck across various types of spans of steel highway bridges. Vibration stresses and close truck spacings are shown to have little effect on such design values under normal conditions. For the main longitudinal members in simple‐span bridges, the design value is 1.0 for spans above 40 ft (12 m) and 2.0 for shorter spans. For the main longitudinal members near interior supports of continuous‐span bridges, the design value is 1.5 for spans above 40 ft and 2.0 for shorter spans. For the main longitudinal members elsewhere in continuous‐span bridges, the value is 1.0 for spans above 40 ft and 2.0 for shorter spans. For transverse members, the value is 1.0 if the spacing between members exceeds 20 ft (6 m) and 2.0 for smaller spacings.

Limit-state criteria for load-factor design of steel bridges

Improved limit-state criteria for the design of steel highway bridges are being developed to meet structural-performance requirements specified for different levels of factored loading. The new criteria close some of t gaps between design conditions and actual behaviour. Design against fatigue recognizes the actual spectrum of truck loading and realistic stress ranges that occur in bridges. Autostress design recognizes the ability of continuous steel members to adjust automatically for the effects of local yielding caused by overloads. Maximum load capacity of continuous bridge members is determined with a new plastic-design method for non-compact members. Design examples show weight and cost savings based on currently specified highway-bridge loadings. Alternatively, the new methods will enable bridges to accommodate heavier loads without significant changes in weight.

Impact Factors for Fatigue Design

Theoretical and experimental information is presented on impact factors for the fatigue design of steel highway bridges. Theoretical studies suggest that the impact factors for individual trucks in actual traffic should generally be less than 0.25, but that much higher factors would occur occasionally due to unusual conditions, such as a bump at a critical location. Measurement of impact factors in actual steel bridges confirms these theoretical conclusions. Impact factors approaching 100 percent have been reported in studies aimed at determining peak impact factors for nonfatigue design. However, impact factors determined for individual trucks in traffic, or for test trucks, are generally much lower. This suggests that the impact factors given by the present American Association of State Highway and Transportation Officials (AASHTO) formula are representative of actual bridge loading and, therefore, are generally appropriate for fatigue design, which should be based on typical, rather than extreme, conditions.

Overview of acoustic emission monitoring of rock structures

Overview of Acoustic Emission Monitoring of Rock Structures The acoustic emission technique for monitoring the stability of rock masses in mines was initiated in the late 1930's by Obert and Duvall in the U. S. A. and Hodgson in Canada. The technique, called microseismic monitoring at that time and even to the present, is currently being extended beyond mining into a wide variety of Civil Engineering oriented problems. These include: Monitoring of all types of stressed rock masses in addition to mines (the subject of this paper). Monitoring of a wide variety of soil masses (dams, embankments, foundations, etc.). Monitoring of seepage and grout flow in both rock and soil. Determining in-situ stress history of rock and soil. Monitoring of steel highway bridges and offshore platforms. Monitoring of concrete bridges, dams and buildings. Assessing stability of permanent and temporary anchors, wire rope and other components of larger structural systems. While most of these activities are still in some form of development, they are generally beyond feasibility and are in various stages of implementation. This paper describes the acoustic emission monitoring method as pertains to rock monitoring and some of the directions that equipment manufacturers are currently pursuing. It then briefly describes applications of the method in connection with the monitoring of rock structures.

Discussion on Papers: Corrosion protection of steel highway bridges: Parts I, II and III

"Discussion on Papers: Corrosion protection of steel highway bridges: Parts I, II and III." British Corrosion Journal, 10(1), pp. 8–9

Discussion on Papers: Corrosion protection of steel highway bridges: Parts I, II and III

Discussion on Papers: Corrosion protection of steel highway bridges: Parts I, II and III

Corrosion Protection of Steel Highway Bridges: II Characterisation of bridge locations by corrosion and environmental measurements

Climatological and air pollution factors greatly affect the corrosion damage to steel highway bridges. This paper gives first results of a programme to define quantitative criteria by which the potential corrosivity of a prospective bridge location can be assessed.At seven sites throughout the country, the corrosion rates of a special mild steel, a low alloy steel and zinc are being measured under both open and sheltered exposure conditions. Meteorological and air pollution data are also being collected.To eliminate the considerable delays which can occur in negotiating the building of permanent test compounds, a mobile test rig has been developed, which can be easily transported to any prospective bridge location.From the first year's results, it is apparent that sheltered test specimens give a much closer indication of the corrosivity under a bridge deck than do open exposure specimens. Of the environmental factors, atmospheric chlorides and sulphur compounds are the major factors influencing corrosion rate. It was not possible, at this stage of the work, to produce a correlation between corrosion rates and meteorological data.

Corrosion Protection of Steel Highway Bridges: I Full scale trials of paint systems

Full scale trials of ten paint systems, applied on the plate girders of the Loudwater Viaduct, are described. The best performance during four years of exposure was given by a solvent less epoxy system, but its application requirements were stringent and may be difficult to meet in practice. For high corrosivity sites, a chlorinated rubber paint system should give a good performance with easy application, although transportation damage between fabrication shop and site may be a problem. A general conclusion is that aluminium pigment should be excluded from conventional micaceous iron oxide paints. In several instances aluminium has been leached out as aluminium salts leading to deterioration. of the paint system and rusting of the substrate.The importance of the micro-climate to which sheltered bridge steelwork is exposed is discussed. Steel girders are not washed by rain and the combination of corrosive contaminants and long periods of wetness can be a particularly severe condition for paint coatings under a bridge deck. Further research on the characterisation of bridge sites and evaluation of priming paints has been initiated.

Corrosion Protection of Steel Highway Bridges: III. Protective primers for the underside of steel bridges

AbstractThe objective of this research contract, for the Department of the Environment, was to assess the behaviour of the various primer types, commonly used on structural steel in the special environment under road bridges. In the first instance unrusted steel was used in order to reduce the number of variables. The work has shown that even in this sheltered situation the protection afforded by primers is dependent on the water resisting qualities of the binder as well as on the inhibitive pigment used.. The results also demonstrated that, by choice of a particularly aggressive site (Norfolk Bridge, Shoreham), assessments of relative performance of different primers could be made almost as rapidly as, and more reliably than, by artificial laboratory tests. Further work is in hand to explore the effects of paint binder more thoroughly and to assess the effects of rust contamination before blast cleaning and priming.

Vibration and Deflection of Steel Bridges

Designers wish to provide highway bridges with adequate strength, service lives uninterrupted by fatigue damage, durable riding surfaces, and comfortable crossings for pedestrians and occupants of moving vehicles. Among the criteria employed in the design of steel multistringer highway bridges are limitations on the slenderness and flexibility of the stringers. These limitations commonly lead to bridge designs which need extra embankment and right-of-waywhere vertical clearances are tight and prevent economical applications of high strength steel. It is less clear how they contribute to the desired qualities noted above. The objectives of this paper are: (1) to explore the actual effects of stringer flexibility and slenderness on the quality of highway bridges, and (2) to suggest improved criteria which may help the designer achieve a high quality, economical structure. The objective of this paper is to show the effects of the slenderness and flexibility of multistringer steel highway bridges on their strength and serviceability. Slenderness affects the amount of steel required for bridge stringers and has an associated secondary influence on the dead weight ofthe bridge. Flexibility affects responses to static (slowly moving) loadings and to dynamic loadings.

Load Factor Design for Steel Highway Bridges

In 1965 an advisory committee was formed by American Iron and Steel Institute to review current bridge design practices and to develop design recommendations for a more consistent and efficient use of steel in highway bridges. That committee, drawn from highway bridge engineers, university professors, and steel industry representatives, initiated a study that resulted in the Tentative Criteria for Load Factor Design of Steel Highway Bridges. The Tentative Criteria were presented to the AASHO Committee on Bridges and Structures in 1968 and were published in 1969 as AISI Bulletin 15. The Criteria in the bulletin were supplemented by a commentary that explained the origins of various provisions, provided supporting evidence, and cited basic references. After a year of study and certain modifications, the Criteria were adopted by the AASHO Committee on Bridges and Structures in 1970 as an alternate design method and were published in the 1971 AASHO Interim Specifications.

ON AN APPROXIMATE ANALYSIS OF SIMPLY SUPPORTED BOX GIRDER BRIDGE

As a means of the beam bridge design, hitherto, has been adopted two-dimensional calculation method ; hence, main beams, floor systems and floor slabs were calculated separately. With the recent progress and development of steel highway bridge constructions and the generalization of stress measurings, it is insufficient to treat in customary means the beam bridge design, and the necessity of three-dimensional consideration has been recognized. Inasmuch as main beams of box girder bridges have especially considerable width, it is evidently inadequate to treat them as an assemblage of rods. Accordingly, in this paper, the deformation and stress of a simply supported box girder bridge with steel plate floor were three dimensionally analyzed and its approximate solution was proposed, the reliability of which was confirmed by model experiment. Further the cooperation of the floor slab in the load distribution was considered.