Bridge Deck Joints Research Articles

Friction stir welded joints in aluminum highway bridge decks: a quality control framework

Friction stir welding (FSW) has shown considerable promise for highway aluminum bridge deck fabrication but lacks specific quality control guidelines for fit-up defects. This study conducts a performance-based (PB) quality control assessment of butt-lap FSW joints for highway bridge decks. Five FSW conditions were simulated, including a standard control welding condition, fit-up defects (gaps and tool offset), and a welding tool’s rotational direction inversion from the standard condition. A rigorous prequalification process established acceptable tolerance levels for fit-up defects: a 3 mm positive offset, a 1.5 mm negative offset, and a 1.5 mm gap. Subsequently, specimens from real aluminium deck extrusions, incorporating the various welding conditions were subjected to fatigue testing. Results showed that the fatigue strength and failure mode were primarily influenced by the weld root microstructure. The FSW tool’s rotational direction significantly influenced fatigue strength due to its impact on the nucleation of the hooking defect in the weld root area, while the impact of fit-up defects on fatigue strength was comparatively lesser. Furthermore, finite element analysis examined the impact of the geometrical features of the root microstructure and the direction of the initial crack propagation on the stress intensity factor range. These findings have practical implications for setting tolerance levels for fit-up defects in aluminum butt-lap FSW joints and optimizing of the quality and fatigue strength of butt-lap FSW joints.

Proactive strengthening of U-rib butt-welded joints in steel bridge decks using adhesively bonded Fe-SMA strips

U-rib butt-welded joints are one of typical fatigue-prone details in early aging orthotropic steel bridge decks, which poses a potential threat to the structural behavior and safe operation of steel bridges. Therefore, it is of great importance to seek out an effective way for retrofitting fatigue cracks. This study proposes an efficient prestressing technique using bonded iron-based shape memory alloy (Fe-SMA) to strengthen cracked U-rib butt-welded joints proactively. A series of static and fatigue tests were conducted on the cracked specimens to investigate the feasibility and fatigue improvement of the proposed technique. Results from the experiments demonstrated that applying prestressing force by heating Fe-SMA strips is a convenient and reliable technique. Activated Fe-SMA strips could introduce significant compressive stresses and provide additional stiffness for the cracked components. This led to a reduction of the mean stress and fatigue stress ranges at the U-rib butt-welded joints under cyclic loading. All the cracked specimens strengthened with adhesively bonded Fe-SMA strips presented excellent fatigue performances, with a maximum equivalent fatigue life extension of 4.09 times compared to the specimen before cracking. Numerical simulation was also performed to better understand the test results. It was demonstrated that prestressed Fe-SMA strengthening could decrease the mode-I stress intensity factor (SIF) at the crack tip, indicating the beneficial effects of the prestressing in retarding crack and its further propagation. In conclusion, the use of adhesively bonded Fe-SMA strips for strengthening cracked butt welds is highly effective in improving the fatigue performance, even better than bonding CFRP.

Fatigue resistance of rib-to-bimetallic steel deck welded joints in orthotropic steel bridge decks

The stainless-cladding techniques have been applied in the top plate of the orthotropic steel decks in the high-speed railway steel bridges to improve the corrosion and wear resistance. The rib-to-deck (RD) welded joint with the stainless-clad bimetallic steel deck plate becomes a new critical fatigue detail. This study firstly examines the fatigue performance of this full-scale new RD joint through six high-cycle constant-amplitude fatigue tests and two beach-mark tests under eccentric over-rib loading. The structural hot-spot stress at the weld toe on the deck plate is obtained by strain gauges and the linear extrapolation method for each RD specimen before the cyclic loading. Experimental results indicate that five RD specimens suffer from the toe-deck failure modes, while the rests encounter root-deck cracking. The fatigue strength of these new RD joints satisfies the FAT100 hot-spot stress S-N curve based on the IIW design recommendation. Numerical simulation is further conducted to investigate the effect of different cracking modes and welding technologies on the fatigue crack propagation behavior of this new RD joint. Root-deck cracking mode shows weakly higher fatigue resistance than the toe-deck failure case. Using the double-side welds between the U-rib and deck plate, and the thickened-edge U-rib technology can slightly enhance the fatigue life in terms of toe-deck cracking mode in contrast with the traditional single-side groove welds. Experimental and numerical validation quantify the excellent fatigue performance of this new RD joint in comparison with the other types of RD welded joints.

Shear Performance of Epoxy Joints in a Precast Bridge Deck Considering Constraint Effects.

The joint form plays a vital role in the rapid assembly of precast bridge decks for steel-concrete composite bridges. Existing research primarily focuses on studying the shear performance of joints through direct shear tests, which is insufficient to fully reflect the mechanical behavior of joints under the constraint of prefabricated bridge deck panels during actual vehicular traffic. Considering situations such as vehicle loads and external forces acting on precast bridge decks, this study investigates the shear performance of epoxy joints under constraint through an improved shear test. The influence of constraint force, shear key details and interface defects on the shear performance of epoxy joints is investigated. The results reveal that the shear test method employed in this study can realistically reflect the shear performance of epoxy joints in precast bridge decks. Both active and passive constrained epoxy joint specimens exhibited no interface cracks, and their failure modes were identified as shear failure between mid-span supports. Compared with passive constraint, the shear-bearing capacity of epoxy joint specimens under active constraint was increased by 86.1~130.6%. Among the epoxy joint specimens with depth-height ratios of 15/110, 25/110, 35/110 and 45/110, the joint with a depth of 35 mm demonstrated the highest shear strength. Furthermore, the shear performance of epoxy joints significantly deteriorated when the interface defects exceeded 30%, resulting in the failure mode transforming from shear failure to interface failure.

Capacity assessment of segment-to-segment joints in precast unbonded segmental bridge decks under vertical seismic mainshock and aftershocks

Precast segmental construction of concrete bridge decks has become increasingly popular due to short construction time and low cost compared with other construction methods. However, during earthquake excitation the segment-to-segment joints in post-tensioned bridge decks may constitute a weak part of the superstructure, particularly due to the lack of continuous rebar that is present in cast-in-place decks. This research investigates the effects of the vertical component of earthquakes on the joints of the superstructure of bridges in near-fault regions. Specifically, a sample non-continuous precast segmental bridge with unbonded cables and constructed with the span-by-span method, has been studied using a detailed two-dimensional non-linear Incremental Dynamic Analysis (IDA) and Nonlinear Pushover Analysis (NPO). The results indicate that the vertical component of the earthquake could significantly adversely affect the joints’ behavior, especially in the upward direction. This may cause failure in the critical joints at midspan earlier than other common collapse prevention (CP) limit states such as deck sliding on the seat. The joint failure occurs easier in the mainshock-damaged bridge than in the intact one. Hence, the collapse probability can increase by up to 47% for the considered cases.

Fatigue experimental study on full-scale large sectional model of orthotropic steel deck of urban rail bridge

The fatigue problem of orthotropic steel bridge decks of urban rail transit steel bridges has gradually become one of the hot research topics. And it is also a key problem that restricts the further development of rail transit steel bridges. In this paper, the orthotropic steel bridge deck structure of a long-span urban rail transit cable-stayed bridge is studied. Based on the segmental finite element model and full-scale model, the fatigue details of the joint weld between an orthotropic steel bridge deck and U-rib were studied theoretically and experimentally. The theoretical model of the segment is analyzed to obtain the hot spot stress characteristics. On this basis, the full-scale model fatigue test and the fatigue performance evaluation are completed based on the S-N curve. The results show that the fatigue performance of the bridge deck and U-rib joints of the orthotropic steel bridge deck structure model meets the design requirements and has a certain safety reserve. The joint fatigue details of the bridge deck, the U-rib joint weld, and the diaphragm plate are the sensitive areas that are most likely to occur fatigue failure first and need to be paid attention to in the later bridge maintenance and inspection.

Experimental study on the verification of adequate fatigue test specimen size of U‐rib‐to‐deck joints in orthotropic steel bridge decks

AbstractIn this study, the distribution of residual stress of the substructure model and small coupon specimens in orthotropic steel bridge structures is experimentally and numerically investigated to validate adequate specimen sizes. Blind‐hole drilling and X‐ray diffraction methods are used to capture longitudinal and transverse residual stresses and evaluate the effects of the cutting process. The maximum LRS and TRS were reduced by 16.6% and 15.6% from those that existed before cutting, verifying the proper size of small voucher specimens. The width‐to‐thickness ratio of 6–6.25 of small coupon specimens has proven sufficient to capture the effects of stress triaxiality induced by the residual stress. In the spirit of master S‐N curves in ASME standard, the role of residual stress was represented in the fatigue process and does not be additionally taken into account when predicting the fatigue performances of welded structures using prediction methods based on the S‐N curves.

A Study of Fatigue Crack Propagation Paths at U-Rib Welds in Orthotropic Bridge Decks using a Phased-Array Imaging Technique

In this paper, the fatigue failure mode of single- and double-sided welded joints in orthotropic bridge decks is innovatively investigated with the phased-array imaging technique for verifying the fatigue failure path defined using the traction structural stress method. The full-scale fatigue specimen tests are conducted, and the fatigue depth and length are imaged and sized for the completeness of fatigue crack propagation law. It can be concluded that the fatigue failure mode of single- and double-sided welded joints is proven to be the thickness-through mode, which is consistent with the fatigue failure path defined in the traction structural stress method. The analysis method for calculating the main characters is first proposed, and the fatigue crack propagation law of the crack length and depth in the through-thickness mode is determined for completeness.

Structural and buckling behavior of full-scale slender UHPC columns

Ultra-high performance concrete (UHPC) is a relatively new class of concrete and cementitious materials with much higher strength and durability than conventional concretes. The use of UHPC is currently expanding worldwide from bridge deck joints and connections to full components and larger applications. With the superior mechanical properties of UHPC, future UHPC columns in buildings and bridges will have compact cross-sections and smaller footprint. The main goal of this study is to provide experimental demonstration and reliable datasets of slender UHPC columns to validate current analytical procedures and inform future designs. This paper presents results and discussions from five full-scale UHPC columns (largest set of axially-tested UHPC columns to-date) at a 4 million-lb [∼18,000 kN] testing facility. The specific objectives are to investigate the structural and buckling behavior of slender UHPC columns under concentric axial loading, and assess the current ACI procedure for slenderness effects using the moment magnification method. When the actual material properties of UHPC and longitudinal bars are used for assessment, the ACI equations were found to overestimate the axial load capacity of slender columns by approximately 9%, on average. The study is concluded by design guidance and several recommendations for applying the moment magnification method for slender UHPC columns, which can be readily incorporated into future design codes.

Reinforcement detailing effects on axial behavior of full-scale UHPC columns

Ultra-high performance concrete (UHPC) applications are currently expanding worldwide from bridge deck joints and connections to full components and larger applications. UHPC has superior structural properties relative to other cementitious materials with multiple times the compressive and tensile strength, durability, and ductility. These outstanding mechanical properties of UHPC make it a strong candidate for full structural columns. The goal of this study is to provide experimental demonstration and reliable datasets of UHPC columns to validate current analytical procedures and inform future designs. This paper presents results and discussions from five full-scale UHPC columns tested at a 4 million-lb machine. The first objective is to analyze the experimental behavior of long UHPC columns with negligible slenderness effects and varying reinforcement details, i.e. different longitudinal, transverse, and fiber reinforcement ratios, under concentric axial loading. The second objective is to inspect the validity of ACI 318 equations for estimating the UHPC columns axial compressive strength. The results indicated that using the actual material properties of UHPC and longitudinal bars for ACI 318 equations overestimates the axial load capacity of columns with different reinforcement details by approximately 13% on average. Furthermore, a new strength reduction factor of 0.75 is suggested (instead of 0.85) for estimating axial capacity of UHPC columns with slenderness limit less than 30.

Comparative structural behavior of bridge deck panels with polymer concrete and UHPC transverse field joints

Precast bridge deck panels are widely used to accelerate bridge deck erection and provide cost savings, better durability, and solving many constructability challenges. Full-depth deck joints with diamond shear key type and ultra-high performance concrete (UHPC) are the most recent commonly used field joints in bridge decks. UHPC has superior mechanical properties and leads to simplified details and joints. However, UHPC might have some constructability and finishing as well as cost and bidding challenges. Thus, exploring the viability of alternative materials for field joints could be beneficial. Poly Methyl Methacrylate Polymer concrete (PMMA-PC) is another popular construction material with superior mechanical properties that have been used for overlays and can provide a potential alternative to UHPC for deck joints. The objective of this study is to investigate and compare the structural performance of using PMMA-PC and UHPC for full-depth precast deck panel transverse field joints. An experimental program was conducted to test three full-scale specimens under vertical loading at the University of Nevada, Reno. Two specimens were identical except for the material used in the joint, i.e. UHPC versus PMMA-PC, while the third specimen used a new proposed joint detail with PMMA-PC. The structural response was evaluated for connection performance under the AASHTO service and ultimate loads, peak strength, damage progression and mode of failure, and local steel reinforcement strains. The results demonstrated that PMMA-PC, and the proposed joint detail, can be successfully used for bridge deck field joints with comparable performance to UHPC field joints.

Structural performance evaluation of ECC link slabs reinforced with FRP bars for jointless bridge decks

Deterioration of traditional mechanical expansion joints significantly affects the durability of bridge structures. Engineered cementitious composites have been proposed as an alternative to expansion joints in bridge decks. ECC link slabs were cast and tested under monotonic cyclic loading. Link slabs, reinforced with fibre-reinforced polymer bars, demonstrated sufficient flexibility to meet the current design protocols. Nonlinear finite element models were constructed based on the experimental data. Depth-span ratio and reinforcement ratio of such link slabs must not exceed 0.12 and 0.72%. Link slab debonded length should be larger than 0.8% to obtain low bending stiffness.

Fatigue Reliability Assessment for Orthotropic Steel Bridge Decks Considering Load Sequence Effects

Fatigue damage accumulations would dramatically reduce the reliability and service life of the orthotropic steel decks. Incorrect fatigue assessment results may be obtained when load sequence effects are omitted. In the present study, fatigue reliability assessments of rib-to-deck weld joints in orthotropic steel bridge decks are conducted with the consideration of load sequence effects. The method, which judiciously considers the fatigue loading history and is derived from the sequential law and the whole-range S-N curve, is first proposed for fatigue reliability calculation. And then, the whole-range S-N curve describing the fatigue propagating process of the rib-to-deck weld joint is introduced. Finally, the developed method is applied to evaluate the fatigue reliability of two rib-to-deck weld joints in an orthotropic steel deck based on long-term measured strain histories. The influence of traffic growth and initial damage on the fatigue reliability is discussed. The results indicate that it is advisable to consider load sequence effects when assessing the fatigue reliability of orthotropic steel decks equipped with long-term strain monitoring systems and the initial damage significantly reduces the fatigue reliability of orthotropic steel decks.

Residual stress measurement at the weld root of rib-to-deck welded joints in orthotropic steel bridge decks using the contour method

This paper presents a comprehensive study on measuring residual stress (RS) distribution at the weld root of rib-to-deck joints using the contour method (CM). Two different cutting techniques were performed at the weld root to examine their influence on the distribution of mapped RS. A fully automated data processing code was developed to prepare and treat the raw measured displacements where the smoothed displacements were printed out as constraints normal to the cut surface. Linear elastic calculations were carried out to map RS distribution across the cut surface. Different boundary conditions (BCs) cases were also studied to examine their influence on the resulting energy as well as RS distribution. The results provide full 2D maps of RS distribution across the cut surface. The results reveal compressive RS is induced at the weld root for the two cutting techniques. It is also noticed that the applied cutting techniques influence the distribution of mapped RS. Further, the examined BCs cases show a small influence on the resulting energy while they have a negligible impact on the general distribution of mapped RS. Moreover, 2D stress maps were prepared by means of the plane strain condition to provide a general image of RS distribution, especially at the weld root. The results obtained by the plane strain condition give a good understanding of the induced RS distribution at the weld root for the two cutting techniques.

Numerical modeling and design sensitivity of structural and seismic behavior of UHPC bridge piers

Advanced behavior of Ultra-high performance concrete (UHPC) is attracting a growing interest among the construction industry worldwide. Currently, UHPC is commonly used in precast bridge deck joints and connections. As the UHPC market grows, the material will have a great potential to extend to larger structural applications. However, there is no guidance yet on best practices or optimum structural designs that fully utilize the UHPC superior mechanical properties for larger components. The objective of this study is to better understand the overall behavior, failure mechanism, and effect of reinforcement and design details of UHPC bridge columns using detailed finite element modeling. The pushover response of a two-column bridge pier with the typical geometry and gravity loads obtained from a representative California bridge is investigated when UHPC is used instead of conventional concrete for the columns. A detailed sensitivity/parametric analysis is conducted to assess the effect of different steel fiber ratio, longitudinal reinforcement ratio, and steel grades of reinforcement bars on the overall structural behavior of the columns. The total strain crack model, as readily implemented in DIANA FEA, is utilized with user-defined input to model the UHPC constitutive material behavior. The UHPC stress-strain relationships in tension and compression are independently defined using uniaxial curves from the literature. For comparison, the two-column bent of conventional concrete is modeled and used as the reference case to evaluate the relative increase in load capacity of the UHPC bridge columns.

Effect of crack-closure treatment on fatigue durability of cracked rib-to-deck welded joints in steel bridge decks

To evaluate the effect of treating long cracks with the impact crack-closure retrofit (ICR) technique, three rib-to-deck welded specimens with a crack length of about 100 mm were tested. The metallographic structure, crack section, crack propagation life, and stress variation were analyzed. Finite-element models were also developed, and some optimal values of certain parameters are suggested according to the simulated results. The results show that new crack sources are generated on both sides of the ICR-treated region because of the stress distribution. The fatigue lives of cracked specimens with long cracks are significantly improved by the technique. Considerable residual compressive stress is also induced, and so it is suggested that the optimal impact angle to be applied to real bridges should be 70°. The stress at the weld root is distributed uniformly with the crack closed, and the optimal crack-closure depth is 4 mm. To evaluate the effect of different crack-closure depths in tests, it is recommended that a hot-spot stress method which is extrapolated by three reference points should be adopted.

Fatigue assessment of longitudinal rib-to-crossbeam welded joints in orthotropic steel bridge decks

Fatigue cracks at rib-to-crossbeam welded joints in orthotropic steel decks (OSDs) accelerate degradation of steel bridges. This research aims to investigate fatigue cracking characteristics of rib-to-crossbeam welded joints, and assess the fatigue strength of the welded joints through fatigue testing and finite element analysis. Nine large-scale specimens were tested under static and fatigue loading to explore the failure mode, fatigue life, and failure process. The fatigue test results were compared with the fatigue strength values recommended in different design specifications. Based on the hot spot stress and notch stress approaches, SN curves for rib-to-crossbeam welded joints were derived and compared with the existing fatigue test data. The results indicate that fatigue cracks that initiate from the weld end at the weld toe controls the fatigue resistance of the rib-to-crossbeam welded joints. A statistical analysis was performed to study the probability distribution of the fatigue strength.

Traction structural stress analysis of fatigue behaviors of rib-to-deck joints in orthotropic bridge deck

In this study, a traction stress method is adopted for analyzing some of the unique fatigue behaviors observed in a series of recent experimental studies on rib-to-deck joints in orthotropic steel bridge decks. It is found that the traction-based structural stress definition is not only effective for describing the relevant stress state responsible for each of the four fatigue failure modes, but also mesh-insensitive in finite element computation. The latter attribute is essential for achieving a reliable evaluation of the most likely failure mode possible out of four typical failure modes for a given joint design (including exact weld dimensions) under specified loading conditions. As such, effective means of avoiding undesirable failure mode, e.g., Type 4 (i.e., weld root cracking), can be examined, e.g., by increasing either weld fillet size and/or weld penetration. Furthermore, the rib-to-deck joint fatigue test data investigated in this study are shown falling within the scatter band of the traction stress based master S-N curve adopted by ASME Div Code since 2007, implying that data transferability exists among these three sets of test data obtained independently by different laboratories.

A Whole-Range S–N Curve for Fatigue Assessment of Steel Orthotropic Bridge Decks

The fatigue assessment of orthotropic bridge decks under routine traffic loading is a significant task to ensure the serviceability and safety of steel bridges. The sequential law computes fatigue damages using whole-range [Formula: see text]–[Formula: see text] curves and sequential stress histories and has been proven to provide more realistic results than Miner’s rule under variable amplitude loading. In this paper, a whole-range [Formula: see text]–[Formula: see text] curve covering the very low-cycle region, the low-cycle region, the finite life region, the high-cycle region, and the very high-cycle region is proposed for the sequential law to evaluate the fatigue performance of steel orthotropic bridge decks. The mathematical model of the whole-range [Formula: see text]–[Formula: see text] curve is first deduced based on the partially known [Formula: see text]–[Formula: see text] curve recommended in steel bridge design codes. The properties of the whole-range [Formula: see text]–[Formula: see text] curve are then explained from the geometrical point of view in the double logarithm coordinates system. Finally, rib-to-deck joints in steel orthotropic bridge decks are used as a case study. Fatigue test data are used to validate the proposed model. The whole-range [Formula: see text]–[Formula: see text] curve, with a 97.5% survival limit, is established for fatigue assessment of rib-to-deck joints in real bridges. The results show that the proposed whole-range [Formula: see text]–[Formula: see text] curve allows a good fit of experimental data and excellent agreement with code [Formula: see text]–[Formula: see text] curves in the finite life region and provides an effective extrapolation from the finite life region to the whole range of cycle numbers.

Fatigue Reliability Evaluation of Orthotropic Steel Bridge Decks Based on Site-Specific Weigh-in-Motion Measurements

The fast-growing traffic loads may become a safety hazard for existing bridges especially in developing countries. One of the problems induced by heavy traffic loads is the fatigue damage accumulation of the welded joints in steel bridge decks. This study utilized a stochastic traffic flow model and a novel computational framework for estimating fatigue reliability of orthotropic steel bridge decks using site-specific traffic data. The stochastic traffic flow is demonstrated as an effective approach for converting the probabilistic characteristics of the site-specific traffic data into the fatigue stress spectrum modeling of steel bridge decks. In addition, the traffic growth and control measures can be considered in the stochastic traffic flow for lifetime fatigue reliability estimation of the bridge deck. The proposed computational framework involves a meta-model approximated by neural networks that can greatly reduce the computational effort. Orthotropic steel bridge decks in a long-span suspension bridge is chosen as prototype to illustrate the effective of the stochastic traffic flow model and the computational framework. Numerical results show the following conclusions: firstly, the efficiency and accuracy of the framework is associated with the number of training samples, where approximately 180 training samples is essential for training the 6-types of meta-models; secondly, a annual growth rate of the vehicle weight of 0.5% leads to the fatigue reliability index of the bridge in the 100th year decrease from 5.94 to 0.92. The numerical result may provide a theoretical basis for how to control overloaded trucks for ensuring the bridge safety.