Weathering Steel Bridges Research Articles

Steel Structures to Withstand the Elements: What Structural Engineers Need to Know about Corrosion

While regimented design processes for load-induced effects in structures are ubiquitous, similar design processes for considering corrosion resistance are lacking. This is a critical gap in the structural engineering profession as material degradation is the most common cause of diminishing structural condition for bridges and other infrastructure exposed to the elements. This results in both safety and financial consequences. This paper addresses this gap by reviewing basic principles governing corrosion, how these corrosion principles translate to real-world environments, commonly available corrosion protection systems, long-term field data assessing corrosion in varied quantified environments and associated conclusions, and practical design and maintenance strategies for improving corrosion resistance. These concepts are connected through a proposed framework for considering corrosion as a limit state that can be applied to all structures. Detailed consideration of uncoated weathering steel (UWS) bridges is provided as a pilot material and structure type for considering corrosion as a limit state. Thoughtful application of these concepts can be used to optimize corrosion resistance, improving life-cycle costs and service lives of civil engineering structures.

Study on the initial corrosion characteristics of weathering steel bridges with corrugated steel webs

In this study, the characteristics and influencing factors of the early corrosion evolution process of the weathering steel (WS) bridge in northwest China were examined, revealing the seldom-studied corrosion evolution law of the corrugated web of weathering steel. The corrosion losses and average corrosion thickness of WS bridge components were measured and evaluated. The results revealed that compared with traditional flat steel webs, the corrosion of corrugated steel webs was enhanced in the vertical direction and at the wave peak, and resulted in a more complex corrosion pattern. The trend of the rust layer on the inner and outer surfaces of the box girder is related to the stage characteristics of the corrosion products. The appearance of microscopic characteristics of the rust layer is periodic, with the rust layer thickness, colour, and particle size varying with the bridge’s location. The development of the corrosion pit followed a lognormal distribution, and the corrosion rate was balanced in the radial and depth directions. These results can serve as a basis for designers or inspectors to design WS bridge structures, select correct corrosion allowances, and improve corrosion monitoring and detection techniques.

Reliability‐based Allowances of Corrosion Losses for Weathering Steel Bridges

AbstractLow demands on maintenance and 100% recyclability cause the growing popularity of weathering steel bridges worldwide. Recent experimental results made it possible to derive generic probabilistic models describing long‐term corrosion losses for various types of weathering steels and exposures. In the contribution, these probabilistic models are applied in reliability assessment. For representative structural members and failure modes, the material allowances for the loss of thickness are derived to achieve a specified target reliability in exposures corresponding to Corrosivity Categories C2 and C3. Numerical analysis reveals that the allowances recommended by the ECCS guideline are generally conservative. For larger sections exposed in C2, a “no allowance” strategy might even be considered. For C3, design allowance of about 0.5‐0.6 mm is then determined by the probabilistic approach.

Influence of Distance from Roads on Corrosion Loss in Weathering Steel Bridges

AbstractThere are numerous steel bridges worldwide, many of which are made from weathering steel. Trademarks of weathering steel, such as Corten (the United States), Atmofix (the Czech Republic), NAW‐TEN and CORSPACE (Japan), or Q345CNH (China) are commonly used. Inland steel bridges are impacted by chloride ions, primarily dispersed into the air by road traffic from de‐icing salt (NaCl) and brine solutions used in winter road maintenance, which can compromise the integrity of the bridges' load‐bearing structures. The quantity of deposited chlorides fluctuates based on the distance from the source, especially for inland bridges, where it is determined by the distance from the road. There is also a difference between the winter season and the rest of the year. The study presents in‐situ measurement data from two sites, analyzing the corrosion loss. Additionally, a regression analysis is conducted to understand the relationship between the distance from the road guide line and the corrosion loss.

Investigating Oxide Film Degradation at Arkansas Weathering Steel Bridges

Investigating Oxide Film Degradation at Arkansas Weathering Steel Bridges

Evaluating Arkansas Weathering Steel Bridge Performance

Evaluating Arkansas Weathering Steel Bridge Performance

Rehabilitation of Corroded Steel Bridge Girder Ends using Partial-Height Ultra-High-Performance Concrete Encasement

Beam end corrosion is one of the most prominent types of deterioration on simple-span steel bridges. To address this concern, the Connecticut Department of Transportation and the University of Connecticut have jointly developed a repair method for corroded steel girder ends using ultra-high-performance concrete (UHPC) encasement. In this repair, shear studs are welded to the undamaged portion of the web and encased in UHPC to create an alternate load path for bearing and shear forces. This novel repair method has been implemented in multiple states. The widespread promotion of steel girder end repair with UHPC demonstrates the need for literature on field implementations and alternative designs. This paper advances the findings from a field implementation completed in Connecticut in October 2021, which was the first instance of a partial-height repair in the country, the first application of the repair to a weathering steel bridge, and the first use of flange studs to restore shear capacity at the junction of the web and bottom flange. Two of the girder ends were fully instrumented to collect data on the performance of the repaired locations. The paper presents an overview of the bridge, discusses the design and implementation of the repair, provides short-term monitoring data showing its successful activation, and discusses lessons learned throughout the process. It is anticipated that the findings put forward provide support for the use of UHPC encasement as a promising method for the repair of corroded steel girder ends.

Weathering steel bridge structure after 30 years of service ‐ assessment experience

AbstractThe structure of 531.4 m total length bridge was made in early nineties last century and it was regarded as novelty by that time. The interesting point was that the structure was made of original Polish weathering steel prepared for bridge solutions intently. There were several trouble concerning the bridge service, steel cracks and less than expected patina growth due to the unfavorable conditions inside the box girder. Quite recently the bridge was carefully inspected as it was to be an important issue of the modern motorway. There was a question if the bridge is to be demolished, due to the corrosion and structural problems or to be preserved and extended to meet required traffic volume. There was a careful examination performed including metallurgical, corrosion and structural analysis done. The paper is to present the most important outcomes concerning mainly structural issues, but some weathering steel corrosion observation will be provided as well.

Probabilistic Analysis of Corrosion Rates and Degradation of Weathering Steel Bridges

AbstractCorrosion of weathering steels in outdoor conditions has been observed since their pioneering applications in construction in the 1960s. Changing environmental conditions such as decreasing SO2 concentration and changes in temperature and relative air humidity affect the formation and development of a protective layer of corrosion products on the surface of these steels. The study compares the long‐term corrosion rates of weathering steels according to EN ISO 9224 with the measured rates for various environments in the Czech Republic and abroad, with a focus on sites with high concentrations of chlorides from de‐icing salts. When considering related uncertainties, the corrosion rate models provide estimates in a wide range, and in‐situ measurements can significantly improve corrosion loss predictions. The reliability of bridges made of weathering steels with a well‐developed protective layer is insignificantly affected by corrosion. However, low reliability levels may be experienced in critical details where for example leakage may damage the protective layer of patina.

AUTOMATED PREPARATION GRADE JUDGEMENT SYSTEM FOR WEATHERING STEEL BRIDGES BY DEEP LEARNING

The quality and durability of repair coatings for steel bridges are significantly affected by the surface preparation prior to repair coating. Surface preparation by blasting stipulated by ISO Sa2 1/2 or higher is required as surface treatment before repair coating. The weathering steel bridge have unevenly corroded surface (rust grade D), and it is difficult to evaluate the surface condition by comparing the photographic example. Therefore, there is a high possibility that the difference in evaluation occurs by the engineer. In this paper, the authors attempted to develop a support system to determine preparation grade from the image of blasting. The purpose of this paper is to discuss the accuracy of the trained CNN classifier by the difference in the size of the teaching image data, and to evaluate the performance of the classifier by test data. It was considered that the high value of 83% or more was able to be obtained by the result of all evaluation indices, and the classifier with high performance was constructed by this method.

AUTOMATED PREPARATION GRADE JUDGEMENT SYSTEM FOR WEATHERING STEEL BRIDGES BY DEEP LEARNING

The quality and durability of repair coatings for steel bridges are significantly affected by the surface preparation prior to repair coating. Surface preparation by blasting stipulated by ISO Sa2 1/2 or higher is required as surface treatment before repair coating. The weathering steel bridge have unevenly corroded surface (rust grade D), and it is difficult to evaluate the surface condition by comparing the photographic example. Therefore, there is a high possibility that the difference in evaluation occurs by the engineer. In this paper, the authors attempted to develop a support system to determine preparation grade from the image of blasting. The purpose of this paper is to discuss the accuracy of the trained CNN classifier by the difference in the size of the teaching image data, and to evaluate the performance of the classifier by test data. It was considered that the high value of 83% or more was able to be obtained by the result of all evaluation indices, and the classifier with high performance was constructed by this method.

Fatigue Life Assessment of Key Fatigue Details of the Corroded Weathering-Steel Anchor Boxes of a Cable-Stayed Bridge

In order to study the influence of corrosion on the fatigue life of weathering steel bridges, firstly the nominal stress method is employed to identify the key fatigue details of a typical weathering-steel anchor box of a cable-stayed bridge and then, a multi-scale refined finite-element model for the weathering-steel anchor box is established. The established fatigue-life assessment method for corroded weathering steel is extended to the multi-scale model, the remaining fatigue life for the fatigue details under corrosion are predicted, and the influence of the initial pit size on the fatigue life of weathering steel structures is analyzed. The research results show that corrosion pits can be equated to the introduction of initial cracks in the structure, and the remaining fatigue life for key fatigue details is calculated when the initial crack size is 1 mm, 2 mm, and 3 mm of the fatigue life when the initial crack size is 0 mm, with results of 20.3%, 12.7%, and 11.5%, respectively. Therefore, the research results show that the corrosion pits are equivalent to the introduction of initial cracks in the structure and, even if the initial crack size is small, the fatigue life of the structure is greatly reduced. The fatigue-life assessment method for corroded weathering-steel structures established in this paper is based on the finite element method and fracture mechanics, which offer universal applicability and generalizability and make up for the lack of a fatigue-life assessment method for corroded weathering-steel bridges in service.

Corrosion Assessment of a Weathering Steel Bridge Structure after 30 Years of Service.

The first steel with improved resistance towards atmospheric corrosion, the so-called weathering steel, was patented in the USA in 1933 and was initially used for coal railway cars, and after that, in building and bridge engineering. Weathering steels show higher corrosion resistance than carbon steels in many types of atmosphere due to their ability to form a compact, stable, adherent and protective patina during the time of exposure. Morphological evaluation of the appearance of the corrosion product layer, together with phase analysis of its components, can enable determination of the type of patina and the degree of protection of the steel. To support the visual assessment of a patina, a check based on the qualitative and quantitative phase analysis of its components may be carried out, and the PAI (Protective Ability Index) can be calculated. The estimation of the corrosion processes on original Polish-made weathering steel (12HNNbA) was carried out on a 30-year-old bridge in Poland. There are some structural problems within the deck derived not only from corrosion but also steel cracking, both inside and outside the boxes, at different heights. Fourteen representative samples of patina were analysed and their phase structures were determined by the X-ray powder diffraction method. The PAIs were determined and analysed.

(Invited) Measurement of Salt Abundance on Weathering Steel Structures By Portable XRF

In suitable environments, weathering steels can be used for bridges without anticorrosion painting, because weathering steels have enough resistance to atmospheric corrosion by the protective rust generated on its surface. While, abundant supply of salt causes serious corrosion damage on weathering steels. Hence, deterioration due to corrosion is found in weathering steel bridges in conditions that salt abundantly supplied. When serious damages with corrosion are found in the components of weathering steel bridges, salt abundance on the components is measured to estimate reason of the corrosion and determine the repairing method. The salt abundance on the components is usually measured by surface salinity checker, which determines salt abundance by electrical conductivity of water that is in contact with an analyzed area. However, measurement of salt abundance by surface salinity checker is difficult for the component with serious corrosion damages, because porous rust or rough surface on the damaged component cause leakage of the contact water during the analysis. Therefore, measuring method for salt abundance without using water is needed to know salt abundance on corroded components for the maintenance of weathering steel bridges.In order to discuss the possibility of salt abundance measurement by portable XRF, characteristic X-ray intensity of Cl-and abundance of Cl- on five types of test pieces of weathering steels were analyzed by portable x-ray fluorescence analyzer (XRF) and gauze wipe method with ion chromatography respectively, in this study. The two types of test pieces are new weathering steels with coating of A-5 or C-5. Three types of test pieces were artificially corroded previously. For the two types of the corroded test pieces, coating with Ra-III or Rc-I were applied after removing rust. The other type of corroded test pieces was used without rust removing and coatings. The rust thickness on the test pieces was about a few 100 µm. To make air-born salt accumulation on each test pieces, sheltered exposure test was performed in the test site on the roof of the three-story building of the National institute of Technology, Matsue College, which is about 10 km far from sea. After that, characteristic X-ray intensity of Cl- on the test pieces was measured by portable XRF. Cl- on the test pieces was sampled by gauze wiping method, and the Cl- abundance was analyzed by ion chromatography. The characteristic X-ray intensity and abundance of Cl- on test pieces with coatings show good correlation (Fig. 1), suggesting that portable XRF is possible tool for measurement of Cl- abundance on the steels. While, the intensity of characteristic X-ray of Cl- on the corroded test pieces without removing rust shows poor correlation with the Cl- abundance. The intensity of characteristic X-ray of Cl- on the corroded test pieces without removing rust is extremely higher than that estimated from its Cl- abundance by gauze wiping method, considering the correlation among the test pieces with coatings. Since Cl- on weathering steels are known to be also in rust [3], completely sampling of Cl- by gauze wipe method is probably difficult for the corroded test pieces. Considering to the correlation line among the test pieces with coatings, the X-ray intensity of Cl- on corroded test pieces without removing rust potentially suggests that Cl- abundance on the test pieces are a few 100 mg/m2. For more accurate measurement of Cl- abundance on weathering steels with rust, the clear relation between characteristic X-ray intensity and Cl- abundance on weathering steels covered with rust should be revealed. To found the relation, method for complete sampling of Cl- on weathering steels with rust is required. In addition, it is needed to investigate detection range of Cl- in rust of weathering steels by portable XRF in terms of depth direction from surface.

THE ANTI-CORROSIVE REPAIR METHODS FOR DEGRADED WEATHERING STEEL BRIDGES

The existing rust with heavy amounts of salinity or anti-freezing agents on the weathering steel bridge surface can lead to serious durability issues. In the event that the anticorrosion functions of weathering steel bridges do not perform satisfactorily, it is necessary to eliminate the cause or to consider the repair coating and the life extension process. In order to achieve the expected life of the repair coating, it is important to perform the correct surface treatment, appropriate surface preparation (near-white blast cleaning, ISO standard Sa2 1/2 equivalent), and the certain removal of rust containing salinity (50 mg/m2 or below). This study provides state-of-the-art techniques on repair method, which is two repair coating methods and one simple repair method for weathering steel bridges. In 2015, some repair methods, with considerable effectiveness, were carried out to actual weathering steel bridges with undesired rust generation. The investigation of three years after repair coating shows that both repair coating film is confirmed to exhibit good corrosion resistance. The weathering steel surface repaired by simple repair method is also in a good state.

VERIFICATION OF REPAIR PAINTING EFFECT OF CORRODED WEATHERING STEEL BY EXPOSURE TEST

Weathering steel generates dense protective rust on the steel surface. Since this protective rust would reduce corrosion speed, weathering steel can be used without any painting. Furthermore, the Life Cycle Cost of unpainted steel bridges would be lower than ordinary painted steel bridges. Due to these advantages, many weathering steel bridges have been constructed in recent years. Unfortunately, the generation of anomalous rust has been reported in some bridges, cause of water leakage or deicer. It is necessary to repair these bridges, but the repair technique for corroded weathering steel has never been established yet. This study aims to clarify the effect of various repair painting for corroded weathering steel by performing an exposure test. The exposure test has been carried out from September 2015 to Okinawa and Yamaguchi. Test in Okinawa is supplied airborne salt, and the test in Yamaguchi is not supplied airborne salt. Specimens, which produced anomalous rust, were repaired by 19 methods and exposed. As a result, it is effective to repair by organic zinc-rich paint in the area with airborne salt. On the other hand, it is appropriate to remove rust and salt on the steel surface by blasting in the area which is not supplied airborne salt.

Fatigue behavior of corroded non-load-carrying bridge weathering steel Q345qDNH fillet welded joints

Fatigue behavior of corroded non-load-carrying fillet welded joints exposed to atmosphere in Nanjing for 1-year which were made of bridge weathering steel Q345qNH was explored in this paper. Fatigue tests were conducted on 8 specimens which were under 8 stress ranges, fitted S-N curve and lower bound of 95% survival probability were established. It was found that fatigue strength dropped by 26.2% after 1-year exposure compared to uncorroded specimens, the design S-N curve for non-load-carrying fillet welded joint in Eurocode 3 is still satisfactory for fatigue assessment of this batch of specimens. Fractography analysis revealed that fatigue cracks always originated from multiple corrosion pits, geometries of corrosion pits were quantified by surface morphology analysis. Numerical simulation of mixed-mode fatigue crack propagation was conducted, it is found that taking the geometry of the deepest pit as the equivalent initial crack and orienting the crack in the direction normal to the maximum tensile stress plane could predict fatigue lives safely and satisfactorily. The research provides reference for design and fatigue assessment of uncoated weathering steel bridges.

The anticorrosive repair coating system for degraded weathering steel bridges

The anticorrosive repair coating system for degraded weathering steel bridges

Inspection and evaluation strategy for uncoated weathering steel bridges

Uncoated weathering steel can significantly reduce the life cycle cost of bridges and the difficulty of maintenance during operation. However, weathering steel is not a maintenance-free material. Design and construction errors, topography, de-icing salt and other factors are likely to cause severe corrosion of weathering steel. Therefore, effective inspection and maintenance planning is essential to ensure that weathering steel bridges can reach expected service life. Weathering steel bridges must be regularly inspected to check the corrosion of weathering steel in important parts, and evaluations shall be made to develop maintenance plans. Previous investigations show that the appearance of weathering steel’s rust layer can effectively judge its stability. Therefore, the corrosion condition of weathering steel can be judged by different rating of the appearance of the rust layer. Meanwhile, corresponding maintenance measures will be formulated.

Corrosion-Fatigue Evaluation of Uncoated Weathering Steel Bridges

Uncoated weathering steel (UWS) bridges have been extensively used to reduce the lifecycle cost since they are maintenance-free and eco-friendly. However, the fatigue issue becomes significant in UWS bridges due to the intended corrosion process utilized to form the corrodent-proof rust layer instead of the coating process. In this paper, an innovative model is proposed to simulate the corrosion-fatigue (C-F) process in UWS bridges. Generally, the C-F process could be considered as two relatively independent stages in a time series, including the pitting process of flaw-initiation and the fatigue crack propagation of the critical pitting flaw. In the proposed C-F model, Faraday’s law has been employed at the critical flaw-initiation stage to describe the pitting process, in which the pitting current is applied to reflect the pitting rate in different corrosive environments. At the crack propagation stage, the influence of pitting corrosion is so small that it can be safely ignored. In simulating the crack propagation stage, the advanced NASGRO equation proposed by the NASA is employed instead of the classic Paris’ law, in which a modified fatigue limit is adopted. The fatigue limit is then used to determine the critical size of pitting flaws, above which the fatigue effect joins as a parallel driving force in crack propagation. The model is then validated through the experimental data from published articles at the initiation stage as well as the whole C-F process. Two types of structural steel, i.e., HPS 70W and 14MnNbq steel, have been selected to carry out a case study. The result shows that the C-F life can be notably prolonged in the HPS 70W due to the enhancement in fatigue strength and corrosion resistance. Besides, a sensitivity analysis has been made on the crucial parameters, including the stress range, stress ratio, corrosive environment and average daily truck traffic (ADTT). The result has revealed the different influence of the above parameters on the initiation life and propagation life.