Long-span Steel Bridge Research Articles

Bond-slip models on interfacial behavior between Fe-SMA and steel in hygrothermal environments

Strengthening the existing steel structures to enhance performance can prolong their service life and reduce carbon emissions. Previous studies have employed iron-based shape memory alloy (Fe-SMA) to adhesively and actively retrofit long-span steel bridges in practice, achieving satisfactory repair efficiency. Nonetheless, concerns persist regarding the long-term performance of Fe-SMA-bonded parent structures, principally stemming from the performance degradation of the adhesives in hygrothermal environments. In this study, the damage evolution and debonding mechanisms of Fe-SMA/steel single-lap joints (SLJs) in hygrothermal environments are investigated through 54 lap-shear tests. The evolutionary process of Fe-SMA strain and shear stress within the overlapping zone is assessed, varying with aging time and adhesive type under shear load. Furthermore, the bond-slip models of the Fe-SMA/steel SLJs are put forward, which change with the aforementioned influencing factors in hygrothermal environments. The lap-shear tests demonstrate that the ultimate shear stress of SLJs is transmitted approximately up to 50 mm away from the initial end, with shear stress developing swiftly towards the free end during this phase. In hygrothermal environments, the effective overlapping length of the SLJs is highly contingent on the material properties of adhesives, improving with the prolonged aging time. This study proposes bond-slip models that describe the interfacial performance between Fe-SMA and steel, accounting for the detrimental influence of temperature, humidity, plastic deformation of components and strain relaxation. The experimental outcomes can guide the analysis of the debonding characteristics of Fe-SMA-bonded structures, and the theoretical study can provide reliable predictions for the service performance of reinforcement systems in hygrothermal environments.

Study on Structure-Borne Noise Characteristics of Long-Span Steel Truss Bridge in Urban Rail Transit

The application of long-span steel bridge in urban rail transit is becoming more and more extensive, but the structure-borne noise of steel bridge induced by passing train is also prominent. Research on the structure-borne noise problem of long-span steel bridge in urban rail transit has positive significance in promoting the sustainable development of steel bridge, and improving the quality of sound environment along rail transit. In this work, dynamic receptance principle, finite element method and statistical energy method are combined to establish the structure-borne noise prediction model of the long-span steel bridge, and the rationality and validity of the model are verified based on field measurement results. Based on the prediction model, the noise radiation characteristics of large-span steel truss bridge in urban rail transit are studied, and the following conclusions are drawn: The bridge deck has the strongest acoustic contribution ability, with the contribution rate of 33–44%, followed by the longitudinal web and transverse web, with the contribution rate of 23–30%, followed by the truss chord, with the contribution rate of 5–8%, and the truss web, longitudinal wing and transverse wing have weak contribution ability, with the contribution rate of less than 2%. The acoustic radiation efficiency of steel truss bridge components reaches its peak at the critical frequency, and the critical frequency is determined by the thickness of steel bridge plate components when the material parameters are fixed. Under ordinary track structures, the middle-to-high frequency noise distribution characteristics of large-span steel truss bridge structure are obvious. Damping pad floating slab track can effectively suppress the high-frequency noise of steel bridge, and the overall sound level can be reduced by about 11–14[Formula: see text]dB.

Numerical assessment of the dynamic load allowance on long-span modular steel bridges considering vehicle-bridge interaction

Numerical assessment of the dynamic load allowance on long-span modular steel bridges considering vehicle-bridge interaction

Theoretical investigation and design recommendations for the initial stiffness of Fe-SMA/steel bolted joints in shear

Due to the self-stressing performance and easy-to-install, iron-based shape memory alloy (Fe-SMA) has been successfully applied to the prestressed rehabilitation of deteriorated long-span steel bridges, through bolt anchoring joints. The initial stiffness of Fe-SMA/steel bolted joints affects the transfer and distribution of external load and initial preload, which is significant in investigating the mechanical behavior of Fe-SMA plates for structural reinforcements. However, the current leading design standards for the bolted joints are based on mild steels, whose reliability requires investigation when employing Fe-SMA. For this purpose, the applicability of EN 1993-1-8 in predicting the initial stiffness of Fe-SMA/steel bolted joints is evaluated by experimental and numerical results. A parameter study exploring the influencing parameters of Fe-SMA plate thickness as well as end and edge distances on the initial stiffness of Fe-SMA/steel bolted joints is conducted via the numerical models validated with experimental results. Furthermore, the theoretical formula for predicting the initial stiffness of Fe-SMA/steel bolted joints is proposed. The study indicates that when e/d rises from 1.0 to 4.0, the initial stiffness of single-hole Fe-SMA/steel bolted joints improves by 20% to 35%. The influence of edge distance on the initial stiffness of single-hole Fe-SMA/steel bolted joints is found significant but neglected by EN 1993-1-8. Compared with the recommended formula in EN 1993-1-8, the proposed theoretical formula improves the accuracy by 23% in predicting the initial stiffness of single-hole Fe-SMA/steel bolted joints. The research achievements contribute to the theoretical improvements in the reinforcement design of Fe-SMA in civil engineering.

Analysis of Traveling Wave and Combined Site Effect of Long-Span Upper-Bearing Concrete-Filled Steel Tubular Arch Bridge

In order to study the traveling wave effect and combined site effect of long-span steel tube concrete-filled arch bridge, a 400-m span bridge of the same type is taken as an example, and a large-mass time-history analysis method with multipoint input of recorded seismic waves is used. A total of 11 kinds of traveling wave excitations and 9 kinds of combined site excitations under 4 types of typical sites are carried out to calculate the structural response, and the chord axial force ratio and displacement changes are compared and analyzed. The results show that the long-span arch bridge also has nonuniform seismic excitation conditions in the lateral and vertical directions, and the spatial effect of the structural response is significant; under the traveling wave excitation, the change of the axial force ratio of the chord has a certain periodicity, and it is not the larger the axial force ratio is, the larger the axial force ratio is; the X direction has a significant influence, the maximum axial force ratio of the vault under the design condition is 6.26, and the changes in the Y and Z directions are relatively gentle, but there are still nearly two times the working condition; after the same amplitude modulation of different recorded waves, under the uniform excitation, the axial force is similar, but the displacement is quite different; under the unidirectional traveling wave excitation, the displacement in the X and Z directions shows an accelerating and increasing trend toward the vault. When it is relatively consistent under the unidirectional combined site excitation, and the axial force ratio changes under small and then increases, the L/4–3L/8 segment has a significant impact; the axial force ratio changes are the combined site excitation in different directions are spatially random; three under the combined site excitation. The axial force ratio in the orthogonal direction changes greatly. When the hard field is transformed into the soft field, the axial force ratio decreases, and the displacement increases continuously.

Using Deep Learning-Based Defect Detection and 3D Quantitative Assessment for Steel Deck Pavement Maintenance

Efficient distress detection and identification analysis are of great significances for long-span steel bridge deck pavement maintenance. This paper proposes a pavement distress recognition method based on road quality detection equipment and deep learning. Firstly, the sub-block image is used as the processing unit, and the three-dimensional image is divided into fracture surface element and background surface element. A pavement crack recognition network (PDRNet) based on convolutional neural network is proposed, which is used for automatic recognition of pavement background element and pavement crack element. Then, considering the pixel-level neighborhood characteristics of cracks in 3D pavement images, the PDRNet model is used to detect and quantitatively evaluate pavement cracks, which combines the crack elevation detection method to extract the complete contour of cracks in the crack surface element. Finally, the distress database containing three-dimensional markers is integrated into the pavement maintenance management platform. Results show that the PDRNet proposed in this paper has high prediction accuracy on the verification set and shows good robustness to various distress, and the average accuracy is above 88%. The established spatial-temporal integration platform overcomes the communication bottleneck between different types of data, and is important to improve the maintenance management level and predict the long-term development of distress.

Comprehensive evaluation and data analysis of field pavement distress for epoxy asphalt pavement on steel bridge deck

Epoxy asphalt mixtures are widely used as the paving layer of long-span steel bridges due to their excellent properties, such as high strength, and resistance to fatigue. However, like any material exposed to environmental factors and traffic loads, epoxy asphalt mixtures may undergo certain changes over time, leading to performance deterioration. At present, the statistical analysis on the in-situ pavement condition of steel bridge paving is insufficient. Therefore, more than 12,000 distress data from various in-service steel bridge deck pavements were collected and analyzed, and the main distress characteristics were also summarized. Using random forest and long short-term memory (LSTM) regression models, the evolution of decay pavement distress was evaluated, and the importance of different variables in distress development was quantified. The key findings include that linear crack, map crack, and patching are the dominant pavement distress, accounting for over 90 % of the pavement layer. The observation of an evident increase in pavement distress development after 9–11 years of service. The cumulative number of equivalent axial loads (CEASLs) and service year exhibit the strongest correlation with distress intensity. The importance calculation results show that service year and CESALs are identified as the most influential factors in distress development on steel bridge decks.

Experimental research and numerical analysis of welding residual stress of butt welded joint of thick steel plate

The thickness of steel plates used in the member has gradually increased to meet the load-bearing capacity requirements of long-span steel bridges. As the primary connection method of thick steel plate, welding will result in considerable welding residual stress with complex distribution. Large welding residual stress will significantly impact the performance of steel bridges. In this paper, the distribution of residual stress in welded thick steel plate is systematically studied, a specimen with a thickness of 80 mm was designed and fabricated, and the welding residual stress was measured by X-ray diffraction. The finite element model was established and verified by test results. Subsequently, the finite element calculation of the welding residual stress of steel plates with thicknesses of 20, 40, 60, 80, and 100 mm was carried out, and the distribution of surface residual stress and the influence of plate thickness on residual surface stress were studied; then the spatial evolution mechanism of welding residual stress was studied, and the distribution of residual stress inside steel plate and the influence of plate thickness on the distribution of residual stress were revealed. The results show that the surface and internal residual stresses of 20–100 mm thick plates have good symmetry on the paths perpendicular to the weld seam, and asymmetry only occurs in the weld seam and heat-affected zone where the stress fluctuates. On the paths perpendicular to the weld seam, the stress in the X direction transitions from the “M” shape distribution on the surface to the “Π” shape distribution inside for 20–40 mm thick plates, and the residual stress near the weld seam gradually changes from compressive to tensile; The distribution of stress in the X direction in the 80–100 mm thick plate has experienced the transition from “M” shape to “Π” shape to “M” shape, and the stress near the weld seam has experienced the transition from compressive to tensile to compressive. The stress change in the X direction of the 60 mm thick plate is between the above two cases. On the path of internal stress along the thickness, the maximum stress in the X direction is 310–400 MPa for 20–40 mm thick plates, which appears at about 1/2 plate thickness. The maximum stress in the X direction for 60–100 mm thick plates is 400–480 MPa, which appears at 0.2–0.3 times the thickness of the plate from the upper surface. The results could serve as a reference for welding residual stress analysis and guide optimization design of steel bridges made of thick steel plate.

Dynamic load allowance of long-span modular steel bridges

Modular steel bridges are structures whose construction is based on regular prefabricated truss units. This presents several advantages, such as rapid and easy deployment, high adaptability to the terrain and reduced construction costs. However, they generally face operational restrictions for span lengths greater than 60m. Recent technological innovations search to overcome these limitations and develop modular structures with larger spans. Hence, the main objective of this work is to evaluate the dynamic effects on long-span modular steel bridges. The present contribution provides a study on two modular bridge typologies, considering different span lengths from 120 to 140m. A 3D coupled vehicle–bridge model is used to analyse the vehicle–bridge interaction and the dynamic load allowance of the structures. The vehicle is represented as a multibody truck system and the bridges are modelled with the finite element method. Several types of randomly-generated road irregularities are considered on the bridge deck. The effect of each type of irregularity is evaluated on the dynamic load allowance of the bridges. The results obtained reveal the notable influence of road irregularities that involve abrupt vertical displacements that excite the vehicle mode shapes. In addition, it is observed that dynamic load allowance indices tend to decrease with longer spans and higher speeds, except when a resonance is produced.

Study on in-plane double-crack propagation in the rib-to-deck welded toe of steel-bridge

The fatigue problem of two in-plane cracks in rib-to-deck welded toe of orthotropic steel bridge decks is an important issue. Traditionally, related work focuses on single-crack propagation in these joints; however, many practical observations have shown that the initial weld cracks of structures are characterized by multiple cracks in a small range. Thus, the main goal of this paper is to investigate the mechanism of and guidelines for in-plane double-crack propagation in rib-to-deck welded toe of orthotropic steel bridge decks. In this paper, the rib-to-deck welded toes in the orthotropic steel deck of the Anqing Yangtze River Bridge are taken as the background. Based on extended finite element method theory, single-crack propagation theory and the multiple-crack coalescence law, the stress intensity factors at the crack tip are calculated by the interaction integral method, and the propagation directions are determined using the maximum energy release rate (Merr) criterion. The whole process of in-plane double-crack propagation, coalescence and failure in rib-to-deck welded toe of long-span steel bridge decks and their fatigue life are simulated according to the principle of an equivalent crack front. Meanwhile, the most unfavorable conditions of cracking parameters are determined by changing the spacing and shape ratio of the two cracks. Then, the fatigue loading experiment is carried out on equal proportion specimens under appropriate cracking parameters. The results reveal the whole process of in-plane double-crack propagation in rib-to-deck welded toe of orthotropic steel bridge decks, and the verification shows that experimental results agree well with the simulation results.

Enhancement of Bonding and Mechanical Performance of Epoxy Asphalt Bond Coats with Graphene Nanoplatelets.

Improving bonding and mechanical strengths is important for the application of bond coats used in the construction of steel deck bridges. Graphene nanoplatelets (GNPs) are attractive nanofillers for polymer modification because of their low cost, ultra-high aspect ratio, and extraordinary thermal and mechanical performance. In this paper, GNPs were used to reinforce the epoxy asphalt bond coat (EABC). The morphology, viscosity-time behavior, contact angle, dynamic mechanical properties, and mechanical and bonding strengths of GNP-reinforced EABCs were investigated using laser confocal microscopy, a Brookfield rotational viscometer, a contact angle meter, dynamic mechanical analysis, a universal test machine, and single-lap shear and pull-off adhesion tests. GNP dispersed non-uniformly in the asphalt phase of EABC. The viscosity of the neat EABC was lowered with the inclusion of GNPs and thus the allowable construction time was extended. The existence of GNPs enhances the hydrophobicity of the neat EABC. When adding more than 0.2% GNP, the storage modulus, crosslinking density and glass transition temperatures of both asphalt and epoxy of the neat EABC increased. The mechanical and bonding properties of the neat EABC were greatly enhanced with the incorporation of GNPs. Furthermore, the mechanical and bonding strengths of the modified EABCs increased with the GNP content. GNP-reinforced EABCs can be utilized in the pavement of long-span steel bridges with long durability.

Experimental Research of Welding Residual Stress of Butt Welded Joint of Thick Steel Plate

The thickness of steel plates used in the structure has gradually increased to meet the load-bearing capacity requirements of long-span steel bridges. Thick steel plate welded by arc welding process will result in considerable welding residual stress with complex distribution. Large welding residual stress will significantly impact the performance of steel bridges. At present; residual welding stress of thick steel plates is not considered enough in bridge engineering; which could lead to potential dangers in safety. In this paper; a butt welded joint with a thickness of 80 mm was designed; the residual welding stress was measured by X-ray diffraction method; and the distribution of residual stress in the direction perpendicular to the weld seam and along the direction of the weld seam is analyzed; and the distribution pattern of welding residual stress in thick steel plate is systematically studied. It is found that in the area near the weld; the stress in the direction along the weld seam is more significant than that in the perpendicular direction; the peak stress in the direction perpendicular to the weld seam usually appears in the weld seam and the heat-affected zone; and the maximum value tends to appear close to the last weld bead on the surface; on the path perpendicular to the weld seam; the stress in the direction perpendicular to the weld seam is distributed in a “Π” shape; the stress in the direction along the weld seam is distributed in an “M” shape; and the stresses in the direction along and perpendicular to the weld seam are symmetrically distributed; however the axis of symmetry may appear anywhere in and around the weld seam. The results could serve as a reference for welding residual stress analysis and guide optimization design of steel bridges made of thick steel plates.

Fatigue Resistance Analysis of the Orthotropic Steel Deck with Arc-Shaped Stiffener

The orthotropic steel deck is widely used in long-span steel bridges due to its simplicity and efficiency. The welded joint of the U-rib to e deck panel area is extremely sensitive to fatigue cracks. In this study, an orthotropic steel deck with an arc-shape stiffener was proposed that aimed to alleviate the fatigue cracks and enhance the fatigue resistance in long-span steel bridges. Based on the Mingzhu Bay steel bridge, the proposed steel deck FE model was first established. Then, the moving vehicle load was applied to investigate the impact of the arc-shape stiffener on the fatigue stress amplitude and distribution. The Miner fatigue cumulative damage theory was employed to evaluate the fatigue life of the orthotropic steel deck with arc-shaped stiffener, and comparative analyses were carried out. Finally, the results show the maximum stress of the orthotropic steel deck with an arc-shaped stiffener is reduced by 15%, and the fatigue life is improved by 40% compared with the OSD.

Robust optical displacement measurement of bridge structures in complex environments

A robust optical displacement measurement method is proposed herein for long-span bridges by considering complex environmental interference, such as illumination changes, system disturbances, and remote calibrations. First, to reduce the centroid shifts caused by lighting changes from the ambient or target itself, a center detection algorithm with an area-consistency constraint was applied. Optimized algorithm can reduce the noise variance by about half in the static laboratory experiment, which shows better illumination robustness than the adaptive threshold-based method. Second, to overcome the lower accuracy of 6-D camera pose tracking in remote measurements and limited correction effects of the widely used relative displacement method, a novel correction method with better implementability as well as accuracy was proposed for typical environmental vibrations. Third, an integrated real-time standing optical displacement sensor was developed for outdoor tests. In particular, a system combining a kilometer-level rangefinder and high-power laser designator was designed to achieve fast and fine object distance calibrations. Finally, the proposed method was applied to a short-span concrete bridge and a long-span steel bridge. The extracted displacement time histories at multiple points and deflection shapes at certain moments are expected to provide rich data for further performance evaluations.

Two-step approach for fatigue crack detection in steel bridges using convolutional neural networks

The advent of parallel computing capabilities, further boosted through the exploitation of graphics processing units, has resulted in the surge of new, previously infeasible, algorithmic schemes for structural health monitoring (SHM) tasks, such as the use of convolutional neural networks (CNNs) for vision-based SHM. This work proposes a novel approach for crack recognition in digital images based on coupling of CNNs and suited image processing techniques. The proposed method is applied on a dataset comprising images of the welding joints of a long-span steel bridge, collected via high-resolution consumer-grade digital cameras. The studied dataset includes photos taken in sub-optimal light and exposure conditions, with several noise contamination sources such as handwriting scripts, varying material textures, and, in some cases, under presence of external objects. The reference pixels representing the cracks, together with the crack width and length, are available and used for training and validating the proposed model. Although the proposed framework requires some knowledge of the “damaged areas”, it alleviates the need for precise labeling of the cracks in the training dataset. Validation of the model by means of application on an unlabeled image set reveals promising results in terms of accuracy and robustness to noise sources.

Experimental study of the deformation recovery characteristics of steel deck pavement materials

Steel deck pavement material and steel decks require good cooperative deformation ability. The deck system of a long-span steel bridge is flexible, and its pavement is repeatedly subjected to tensile stress and compressive stress; therefore, the steel deck pavement material requires a strong capability to recover from the deformation. The internal stress of the pavement material is the force driving its deformation and recovery. In this study, based on the characteristics of steel deck pavement materials, a repeated creep progressive loading recovery test (RCSR) was proposed to measure the internal stress. In addition, the theoretical solution of the internal stress of the material in the nondestructive stage was derived. The test results show that the RCSR test is effective and accurate in determining the internal stress of the steel deck pavement materials. The recovery modulus of a material can be defined by measurement and calculation of the internal stress. Moreover, different materials can be used to characterize the recovery modulus of a steel deck. Based on the theoretical solution of internal stress, the theoretical solution of the recovery modulus was deduced and calculated. The test value was used to determine the accuracy of the theoretical solution of the recovery modulus. The results were used to verify that the recovery modulus is the inherent property of the material in the nondestructive stage and is not affected by the additional conditions of the test. The internal stress and recovery modulus of three typical steel deck pavement materials were measured and calculated in this study. The test results show that an epoxy asphalt mixture has the largest recovery modulus, which indicates that under the same stress level, the internal driving force for the deformation recovery of this mixture is greater, and its deformation recovery ability is strongest.

Multiscale fatigue damage evolution in orthotropic steel deck of cable-stayed bridges

This paper investigates multiscale fatigue damage evolution in deck-to-rib (DTR) joints of orthotropic steel deck (OSD) of a long-span cable-stayed steel bridge under traffic loading with consideration of micro short crack nucleation and growth as well as macro long crack propagation. Multiscale finite element modelling and substructure techniques are jointly used to model a long-span cable-stayed bridge and simulate multiscale fatigue damage evolution in DTR joints. The polycrystal microstructure together with the crystal plastic constitutive model are used to model the fine-grained heat-affected zone of a DTR, in which micro short crack nucleation and growth are simulated considering the randomness of grain size and orientation. The polycrystal microstructure is embedded in a substructure while the substructure is coupled with the multiscale model of the bridge under traffic loading. After the micro short crack in the microstructure grows up to an initial long crack length, three-dimensional macro long crack propagation is simulated in the substructure including the effect of mixed crack modes by fracture mechanics. As a case study, the multiscale fatigue damage evolution in the DTR of the OSD of the Stonecutters cable-stayed bridge in Hong Kong under moving vehicles is simulated using the proposed method. The simulation results indicate that the proposed multiscale fatigue damage evolution model can describe the entire damage process from micro crack nucleation to macro crack propagation. The case study shows that the macro crack propagates rapidly from the initial macro crack and the period of micro short crack nucleation and growth is longer than the macro crack propagation period.

Mapping temperature contours for a long-span steel truss arch bridge based on field monitoring data

The temperature-induced response of long-span steel bridges can be more significant than the structural responses associated with operational loads or structural damage. These responses depend on the spatio-temporal temperature variation in bridge members, including the effective temperature and temperature difference within members. Bridges are designed to withstand the extreme temperature variations predicted for a given site. Hence, numerous studies have employed statistical analysis techniques to provide critical information for the design and maintenance of bridges during life cycles. However, the correlation between the effective temperature and temperature difference is usually ignored, which can result in inaccurate assessment of the extreme temperatures in members. In this work, the joint probability distribution for the temperature variation in a long-span steel truss arch bridge is investigated based on field monitoring data. The extreme temperature variations are mapped on contours with relevant return periods; the results show that the probability distribution of the effective temperature can be described using the normal distribution; the weighted sum of two lognormal distributions can describe the distribution of temperature difference. Moreover, extreme values of the effective temperature and temperature difference do not occur concurrently. The effective temperature and temperature difference in the structural member directly exposed to solar radiation vary significantly, while the temperature of the shaded member can be assumed uniform, which is mainly affected by air temperature. The study leads to more accurate estimation of the temperature extremes in long-span steel truss arch bridges, which is of great importance for proper design and maintenance of bridges.

Investigation of the Fatigue Vehicle Load for a Long-span Steel Bridge Based on Nine Years of Measured Traffic Data

ABSTRACT This study conducts a rational investigation of nine years of traffic monitoring information concerning the Jiangyin Yangtze River Bridge within which the traffic flow, vehicle composition, vehicle load and axle-weight features are analyzed and discussed. Based on the annual analysis of traffic information, it is observed that compact cars weighing less than 30 kN account for 61% of the total traffic volume. According to the number of axles, wheelbase and axle groups, the vehicles in the traffic flow are classified into 11 representative types. Among them, two-axle vehicles form the major category, accounting for 80% of the total traffic flow. Statistical analysis of the gross vehicle weight and axle weight indicates that the gross vehicle weight follows a bimodal normal distribution, whereas the axle weight follows diverse distributions, including a normal distribution and an extreme distribution. In addition, by using equivalent damage theory, five equivalent vehicle models are established according to measurements of the axle weight and wheelbase. Finally, a six-axle fatigue-loaded vehicle model is proposed and discussed.

UHPC-based strengthening technique for orthotropic steel decks with significant fatigue cracking issues

Fatigue cracking is a common drawback of orthotropic steel decks (OSDs), especially for long-span steel bridge decks, and it is difficult to repair such decks effectively. This paper proposes an ultrahigh performance concrete (UHPC)-based strengthening technique for OSDs with significant fatigue cracking issues. A multiscale finite element (FE) model based on the Wuhan Junshan Yangtze River Bridge is established. Analysis results show that the vehicle-induced stress values in the OSD are significantly reduced. However, the maximum tensile stress at the bottom of the UHPC layer is 12.9 MPa under the vehicle load, indicating that the UHPC layer is at risk of cracking. Two alternative retrofitting schemes for the UHPC layer are presented. One involves reinforcement by adding one-story transverse steel bars, and the other involves adding steel strips to strengthen the bottom of the UHPC layer. Transverse bending tests were conducted to compare these two schemes. The results show that the tensile strength of the UHPC layer strengthened with 80-mm-wide steel strips could reach 43.2 MPa, and that this was the superior scheme. A test involving 10 million fatigue-loading cycles was conducted to evaluate this steel strip strengthening scheme. The results indicate that the UHPC layer has a fatigue life of 8 million cycles. Thus, the fatigue life of OSDs with significant fatigue cracks can be improved using this strengthening technique.