Strengthening of steel decks for cable-stayed bridge using ultra-high performance concrete: A case study

Abstract

Fatigue cracking induced by vehicle load is a prevalent problem in orthotropic steel decks. In addition, pavement debonding in steel bridge decks is another familiar issue resulting from low slip resistance in the faying surface between the steel and asphalt concrete. The present study proposed a strengthening method that uses ultra-high performance concrete to stiffen a repeatedly maintained cable-stayed bridge in order to help address these two problems. The existing issues of the real bridge and the corresponding causes were investigated. Following this, an ultra-high performance concrete paving system was designed to improve the stiffness of the orthotropic steel decks. For this paving system, a 45-mm ultra-high performance concrete layer was connected to the deck by welded shear studs. The local stresses at the typical vulnerable fatigue cracking points were determined by means of a finite element model and of a field loading test to evaluate the strengthening effect. The results showed that this strengthening method can prevent the propagation of fatigue cracks. The local stresses of the U-ribs and diaphragms were reduced by 45.4% and 40.0%, respectively. The repaired bridge has sufficient resistance against fatigue cracking based on the in situ observations.

Keywords

bridge engineering fatigue crack orthotropic steel deck pavement debonding strengthening ultra-high performance concrete

Introduction

Bridge structures are a key component of infrastructures, and their long-term performance plays an important role in the transportation systems (Chen et al., 2020; Lu et al., 2019). Under the influence of adverse environments and vehicle load, the degradation of service performance of existing bridges is becoming increasingly prominent, which has attracted widespread attention (Dai et al., 2020; Guo et al., 2020a; Krivy et al., 2016). Orthotropic steel decks (OSDs) have been widely used in long-span cable-stayed bridges and suspension bridges, due to their lightweight, rapid construction, and high strength (Fu et al., 2018; Liu et al., 2019; Zhang et al., 2016). However, orthotropic cable-stayed bridges have an unsatisfactory record of durability (Zhang et al., 2017). The OSD-pavement system is generally adopted in orthotropic cable-stayed bridges. This system consists of pavements, deck plates, longitudinal U-ribs, and transverse diaphragms. All these elements are connected with bonding materials or welded connections, and all parts are exposed to the environment and subjected to considerable local deformations caused by traffic loads. With growing traffic volumes and higher wheel loads, pavement debonding and fatigue cracking become serious safety concerns for the vulnerable structural details of OSDs (Yao et al., 2013).

Insufficient adhesion between the bridge deck and pavement is commonly found in OSDs, leading to the common problem of pavement debonding (Chen et al., 2016; Perez et al., 2007). Over the past few years, even when the adhesion at the interface was designed to deal with the cyclic heavy loads, relative slip has still troubled the deck-paving layer. In addition, the combined influence of insufficient adhesion and insufficient stiffness of bridge decks can further exacerbate the relative slip, eventually causing pavement debonding. Resurfacing is the most widely used method for repairing damaged pavement. However, also through these methods, debonding can appear again, because of the lower stiffness and increasing traffic loads. Therefore, a more efficient repair method is needed.

Fatigue cracking in OSDs mainly initiates in the deck plates, U-ribs, diaphragms, and especially in the welded connections (Cao et al., 2016; Freitas et al., 2010; Liu et al., 2018; Yan et al., 2016). Some researchers have made important contributions in clarifying the mechanism of fatigue cracking in welded connections. The OSDs experience several types of fatigue problems, resulting from high cyclic stresses caused by external vehicle loadings (Xiao et al., 2005; Ya et al., 2011). Residual stresses caused by welding may accelerate the fatigue cracking process (Sim and Uang, 2012; Wang et al., 2019; Wolchuk, 1990). Currently, some studies show that the inadequate stiffness of OSDs is a key feature influencing the onset of fatigue cracks (Kainuma et al., 2016; Shao et al., 2013). It has been acknowledged that improving the stiffness of OSDs is an effective way to optimize its fatigue resistance.

The stiffness of bridge decks can be improved by resurfacing them with high-performance pavement materials (Semendary et al., 2020; Zhu et al., 2020). Steel fiber reinforced concrete (SFRC) and reinforced high-performance concrete (RHPC) have been used to strengthen bridge decks, which can effectively reduce the stress amplitude at vulnerable fatigue cracking sites. However, the two materials possess a high risk of self-cracking. Dieng et al. (2013) used ultra-high performance fiber reinforced concrete (UHPFRC) to renovate existing bridge decks, whereas the flexural strength of UHPFRC was largely affected by the direction of fibers. Recently, a steel-UHPC (ultra-high performance concrete) composite bridge deck has been proposed to reinforce the cracked orthotropic deck (Shao et al., 2013; Zhu et al., 2018b). Steel-UHPC composite bridge decks have been successfully used for small and medium span bridges, but no reports are available for long-span cable-stayed bridges. The purpose of this work is to study a strengthening method for orthotropic steel bridge using UHPC on a cable-stayed bridge.

This article is organized as follows. First, bridge pavement problems and steel box girders were introduced based on inspection results of the Haihe Bridge. The causes for these issues were also discussed. Next, a repair method was proposed, using an UHPC layer as the sub-base connected to the bridge deck with shear studs. The strengthening procedure was presented. Following that, a finite element (FE) model was established to discuss the local tensile stress of the UHPC layer and to make a comparison between the numerical and the experimental results. Finally, the strengthening effect is validated, and some conclusions were drawn.

Engineering background

The Haihe Bridge, located on the Tianjin Haibin highway, was built in 2002. This was a steel–concrete combined, single-pylon cable-stayed bridge, which consisted of five spans with a total length of 500 m. The tower height was 168 m. Figure 1 shows the overall layout and a cross-sectional view of the Haihe Bridge. This steel–concrete combined structure consisted of steel and concrete box girders in the longitudinal direction. The side span was made with prestressed concrete box girder that was 190 m long. The main span was 310 m, including a 290-m steel box girder and a 20-m connection with a prestressed concrete box girder between the main span and the side span.

Figure 1.

Overall layout and cross-section: (a) layout of the bridge (unit: m) and (b) cross-sectional view of the steel box girder (unit: mm).

The traffic loads were placed in the two lanes in each direction. The depth and the wide of steel girder were 3 and 23 m. The thickness of deck plate, webs, and bottom flange were 14, 14, and 10 mm, respectively. This steel box girder was designed as a double cell box with a trapezoidal cross-section. The thickness of diaphragm was 10 mm (24 mm in stay-cable anchored points). As shown in Figure 1(b), each cell box consisted of 12 U-ribs named #1 to #12 at the upstream side. The U-ribs were 300 mm wide and 6 mm thick. The clear spacing between two U-ribs was 300 mm. The Haihe Bridge is close to the Tianjin port, which is a main freight channel that links the north and the south sides of the Tianjin Binhai New District. The average daily traffic volume of the Haihe Bridge is of 31,486 vehicles and four-axle heavy trucks account for 51.9%.

Description of the bridge problems

Fatigue damage is one of the most significant factors affecting structural performance under service conditions (Guo et al., 2020b; Ma et al., 2020). Conventionally, asphalt binder pavement is widely used in steel–concrete combined bridges. Asphalt pavement plays an important role in increasing the global stiffness of bridge deck systems and in reducing the high-level strains in the surface of the deck plate. However, pavement damage and cracking of the steel box girder gradually appear in the Haihe Bridge due to the long-term effect of cyclic heavy loads.

The pavement damage and cracking of box girder had been repaired several times. For example, a bracing system was added to the non-hanging diaphragm, and the asphalt binder pavement was replaced by a double stone mastic asphalt (SMA) layer in 2011. This strengthening method only had a positive effect in improving the structural performance in the first 2 years. Bridge pavement damage, cracking in the steel box girder, and other issues occurred again due to the continuous growth of traffic resulting from the development of the economy. A detailed bridge field inspection was carried out in December 2013 to investigate the performance of the Haihe Bridge. The detected main problems will be introduced in the following sections.

Bridge deck pavement problems

A bridge inspection was performed 2 years after the previous repair. The inspection results showed that the deck pavement issues include the following: (1) 18 longitudinal cracks with a transverse spacing of 30 cm, as shown in Figure 2(a); (2) 3 network cracks and 10 pit slots; (3) steel–concrete interface debonding in six locations with a maximum area of 320 m², as shown in Figure 2(b).

Figure 2.

Typical diseases of pavement: (a) longitudinal cracking and (b) pavement debonding.

Due to the low stiffness of the steel bridge deck, the negative bending moment is readily produced at the longitudinal rib and at the longitudinal diaphragm position under traffic loads, causing the pavement to be in a flexural-tensile condition. Fatigue cracks occur on the pavement as a result of the continuous effect of stress amplitude. Figure 3 shows the approximate position on the deck and possible cause. The longitudinal cracks in the pavement were mainly located in wheel position with a spacing of about 30 cm in the transverse direction and the crack spacing was approximately equal to the width of the U-ribs.

Figure 3.

Approximate position on the deck and possible cause.

The cracks usually initiate at the surface of the pavement and propagate down to the bottom of the pavement depth, resulting in bond failure at the steel–concrete interface. Generally, the deck pavement is connected to the steel plate by an epoxy asphalt layer. The strength of adhesion of the bonding material generally decreases with the increase of temperature in warm seasons. Pavement debonding occurred as a result of the combined effects of reduced adhesion and braking force from highly concentrated wheel loads.

Steel box girder cracking

The OSD of the cable-stayed bridge was subjected to cyclic loading. One of the most common problems with steel box girders was fatigue cracking, which may lead to structural performance degradation. Figure 4 shows the welded details and cracking location. Based on the inspection results, the issues of the OSDs were categorized as follows:

Cracking in the diaphragms. After the diaphragm strengthening in 2011, 74 new cracks were observed. These cracks extended from the diaphragm cutout with an average length of 7.3 cm. Figure 5 shows a typical crack. The length of this crack increased from 18 to 30 cm in about 1 year.

Weld cracking in the rib-to-diaphragm joint. Figure 6 shows positions of the cracks in the rib-to-diaphragm joints. The cracks (total of 1116) initiate from the start of the welding site (see Figure 6(a)). Most of these cracks are distributed in traffic lanes (see Figure 6(b)).

Weld cracking in the rib-to-deck joint. There are 126 weld cracks that are mainly distributed in #7–#11 in the transverse direction.

U-rib web cracking distributed in #7–#11 in the transverse direction.

Bridge deck cracking. There were 17 cracks mainly located in the diaphragm-to-deck joint in the longitudinal direction and #10 to #11 U-ribs in the transverse direction, and the average length is 3.9 cm.

Figure 4.

Welded details and cracking position.

Figure 5.

Diaphragm cracks between U-rib #9 and #10.

Figure 6.

Position of the cracks in the rib-to-diaphragm joints: (a) details of welded cracks and (b) distribution of cracks in transverse direction.

Cable-stayed bridges are high-order statically indeterminate structures. External loads influence the cable forces, and the fatigue cracks and other problems have a complex effect on the dynamic response of the structures. The existing fatigue cracks are mainly due to the inadequate stiffness of OSDs. Another cause of fatigue cracking is the large stress amplitude induced by heavy traffic loads. The latest repair of the Haihe Bridge was performed in 2011, and the deck pavement was replaced by a double SMA layer, which made the stress amplitude of diaphragm decreased 37.6% as compared to the virgin condition. However, after a short period, the cracks continue propagating at fatigue-prone zones, which indicates that the stiffness of OSDs needs to be further improved.

The diaphragm cracks and the weld toe fatigue cracks at the rib-to-diaphragm joints are mainly caused by the thin thickness and low stiffness of the diaphragm. U-ribs produce an eccentric rotation under heavy traffic loads, resulting in a stress amplitude increase in the diaphragm cutout. Due to the higher local stress, the fatigue cracks occur easily at the weld toe of the in-plane diaphragm and diaphragm cutout. The girder vertical deformation caused by the live loads may result in an out-plane deformation of the diaphragm. Meanwhile, a secondary stress exists in the diaphragm in the vertical direction. Under the combined effects of the incompatible strain and the secondary stress, the cracks in the diaphragms and weld toe will constantly propagate.

The cracks in the welded joint between the bridge deck and U-ribs are mainly attributed to the low stiffness of the steel bridge deck where it is difficult to resist deformation induced by vehicle loads. The deformation will lead to a relative rotation between the steel deck and U-ribs. Ultimately, fatigue cracks readily initiate from the welded root under repeated traffic loads.

OSD strengthening using UHPC

The problems mentioned above always plague the normal operation of orthotropic steel bridges. Some researchers focused on clarifying the reasons behind these problems by experimental and numerical methods, and proposed different local structural optimization and structural strengthening measures to prevent fatigue cracking of OSDs (Kozy et al., 2011; Zhu et al., 2018a). These measures include the following:

Optimizing the design of OSDs, such as enlarging the dimensions of U-ribs to increase the spacing between longitudinal ribs, transverse ribs, and diaphragms. The number of welds will reduce substantially and so will the fatigue risk of the bridge deck.

Repairing local cracks, such as boring crack-arresting holes to inhibit crack propagation or bonding steel plate to improve local stiffness.

Applying a composite bridge deck with a high-performance wearing course. SFRC, RHPC, UHPFRC, and super toughness concrete (STC) can provide a higher stiffness for the steel bridge deck.

The above strengthening methods are based on the following points: changing the distribution of the stress field at the crack tip, increasing the global stiffness and reducing the stress amplitude at fatigue-prone zones, and strengthening the local stiffness of crack locations and restraining fatigue crack growth. UHPC has an ultra-high compressive strength, rupture strength, and cleavage strength, which can improve the local stiffness of OSDs to a high level. In the present study, the UHPC-based pavement was used to transform a typical steel deck system into a steel-UHPC composite structural system. The Young’s modulus of the selected UHPC was 40 GPa. The Poisson’s ratio and the density were 0.2 and 2800 kg/m³, respectively. The experimental results showed that the compressive strength of UHPC is 140.3 MPa.

Since the cable force is very sensitive to the dead load, the weight of the pavement is strictly limited to keep the dead load in an acceptable range. UHPC was used in the middle traffic lane section with a width of 17.5 m in the transverse direction, and the synthetic rubber layer was used in the remaining area with a total width of 5.5 m. The UHPC—synthetic rubber—pavement system leaded to a 1% reduction in the dead load. The HRB400 grade steel with a diameter of 10 mm and concrete cover of 10 mm was used for steel bar net. It was placed at a spacing of 37.5 mm in the longitudinal and transverse directions. The shear studs, 13 mm in diameter and 35 mm in height, were embedded in UHPC and welded on the steel plates. The UHPC was casted in full cross-section and stream cured at 80°C for 3 days. Figure 7 shows the details of the deck pavement system at the middle traffic lane section.

Figure 7.

Details of the pavement system.

Compared with the traditional strengthening methods, the essential of the proposed method is to improve the local stiffness of OSDs by adding a lightweight, UHPC layer, which has a positive effect in restraining self-cracking and preventing fatigue cracks. In addition, this method has the advantages of high efficiency and convenient operation. The strengthening of the Haihe Bridge was successfully completed in 2015. It took 45 days to finish the entire process, including the conventional maintenance of the steel box. The construction for strengthening of the deck pavement mainly involved the following procedures: (1) removing the original SMA wearing course, (2) sand blasting the bridge deck to create an uncorroded surface, (3) welding shear studs and brushing a corrosion coating, (4) assembling reinforcing bar and formwork, (5) casting the UHPC (45 mm) and steam curing, and (6) paving the epoxy asphalt and the SMA surfacing (30 mm). Figure 8 shows the main construction procedures.

Figure 8.

Construction procedures: (a) steel bar assembling and (b) UHPC casting.

The bridge had been opened to traffic for more than 2 years after strengthening. It should be noted that the traffic was not restricted, and heavy trucks still run on the bridge. Figure 9 shows the present condition of the bridge deck. The deck pavement was undamaged. No new cracks existed in the steel box girder, and the original cracks had not propagated, which indicates the positive effects of the strengthening method.

Figure 9.

Present condition of pavement.

Field loading test and numerical analysis

Strengthening effects on orthotropic bridge steel deck

The stress of the diaphragm, U-ribs, and roof were individually tested using the standard vehicle load to investigate the effects of the UHPC strengthening method. The test was carried out in the SMA pavement and UHPC layer after the strengthening, respectively. Figure 10 shows the loading footprint and six loading scenarios. The standard wheel load is 35 tons, in which the weight of the two rear axles is 14 tons, respectively. The distance between the centers of two wheels is 1.8 m. As Figure 10(b) shows, all vehicle loads act on the same section in the longitudinal direction (vehicle central axis acts on the M15-3 diaphragm, rear wheel acts on section-C1), and the center of the left wheel loads acting on the U-ribs #7–#12 is matched with the scenarios 1 to 6 in the transverse direction.

Figure 10.

Loading footprint and scenarios (unit: mm): (a) load position and (b) different loading scenarios.

The uncracked M15-3 diaphragm was selected to measure the diaphragm stress. The section-C1, 1.4 m apart from the M15-3 diaphragm, was selected to measure the stress of the U-ribs and bridge deck. Figure 11 shows the strain gauge locations in the M15-3 diaphragm and section-C1. The strain rosettes H1–H3 and H1′ were arranged in the M15-3 diaphragm. Three longitudinal strain measuring points (D1∼D3) were placed at the lower surface of the bridge deck between U-ribs #8∼#11. Six longitudinal measuring points (U7∼U12) were arranged in the U-ribs #7∼#12 to obtain the stress response under the test loads.

Figure 11.

Strain gauge locations in M15-3 diaphragm and section-C1.

FE modeling

This section focuses on the effects of the UHPC strengthening method on the decrease of stress amplitude in fatigue-prone details. To improve the calculation efficiency, only a standard segment shown in Figure 1(b) of steel box girder was separately analyzed before and after the strengthening. The FE analysis was performed by ANSYS. The LINK8 elements were used for the modeling of steel bars. The SHELL63 elements and BEAM189 elements were selected for the main girder and shear studs, respectively. The UHPC was simulated by SOLID45 three-dimensional (3D) elements. The joints at the junction between shear studs and UHPC, and at the junction between bottom of shear studs and steel deck were fully coupled. The connection between UHPC and steel deck at the position of welded shear studs was considered, while the transverse shear resistance in other positions was neglected. It was assumed that the vertical deformation of UHPC layer is consistent with that of steel deck.

The boundary conditions were as follows. At the ends of the model, the segment was restrained to avoid any displacement in longitudinal direction. Symmetry constraints were imposed on the symmetrical plane of the girder for simplify calculation. Due to that, the loading position was far away from the ends of the segment. According to Saint Venant’s principle, the above boundary conditions have insignificant effect on the stress analysis. In addition, the initial cable forces were calculated by continuous girder method. The horizontal component of the cable forces at the anchored points and the uniform load from other segments were imposed to one end of the model.

The original OSDs consist of a double SMA layers, each 30 mm in depth. Due to the low elastic modulus of SMA, the stiffness improvement of bridge deck by SMA is not obvious. Besides, the present study ignores the wearing layer of SMA, while the sub-base of SMA is still retained. Ignoring the SMA slightly increases the stress in the UHPC layer, which is a safety consideration. Similar process method is also suggested by previous studies (Shao and Cao, 2018) to improve the calculation efficiency. It should be point out that although the SMA has low stiffness, it certainly distributes the wheel contact stress greatly. Thus, ignoring the SMA in the model makes the comparison of stresses before and after strengthening biased. Future studies on the accurate modeling of the SMA are required.

The loads directly act on the top flange of the steel box girder or of the UHPC layer. For the loading test, three-axle truck weight is 35 ton. Table 1 shows the physical mechanical parameters of the bridge deck. Figure 12 shows the standard FE segment model.

Figure 12.

A standard finite element segment model.

Table 1.

Physical mechanical parameters of bridge deck.

Parameters	Steel box girder	UHPC
Young’s modulus/GPa	210	40
Poisson’s ratio	0.3	0.2
Density/(kg/m³)	7850	2800
Coefficient of thermalexpansion	1.18E–5	1E–5

UHPC: ultra-high performance concrete.

Comparison between experimental and numerical response

Figure 13 shows the numerical and the measured maximum stress at various U-ribs under scenarios 1 to 6, where the dashed lines represent the average stress. As Figure 13 shows, the experimental observations are in a good correlation with the numerical values pre- and post-strengthening. The average numerical stress and the measured stress after strengthening are reduced by 45.4% and 52.7%, respectively, which indicates that the UHPC has a significantly positive effect on reducing the stress of U-ribs.

Figure 13.

Comparison between numerical and measured stress in U-ribs.

The principal stress of the M15-3 diaphragm near the U-ribs is shown in Figure 14. The observed results agree well with the numerical value pre- and post-strengthening. The measured principal stress before strengthening in the measuring points H1 and H2 are 93.8 and 91.6 MPa, respectively. This high stress level may be one of the main reasons for the diaphragm cracks (see Figure 5). With an enhancement of the OSD stiffness after strengthening, the average stress in the measuring points H1, H2, and H3 is reduced by more than 40.0%. The principal stress of H1′ has been kept at a reasonable level, and no cracks are found in the daily inspections.

Figure 14.

Principal stress of M15-3 diaphragm.

Figure 15 shows the stress values in the measuring points D1, D2, and D3. As previously mentioned, the bridge deck cracks only appeared in the #10 and #11 U-ribs in the transverse direction, and no severe cracking troubles the bridge deck. All numerical and measured values were less than 8.0 MPa. This keeps the three measurement positions in a low stress state. In the original case, the measured tensile stress values were 7.0, 6.2, and 7.6 MPa, which were much lower than the tensile strength of the steel bridge deck. The measured tensile stresses after strengthening decreased to 3.6, 2.9, and 3.0 MPa, and the decrease rates were 49%, 53%, and 61%, respectively.

Figure 15.

Stress in the measuring points of section-C1.

Local stress analysis on UHPC

The local stress at U-ribs and diaphragms can be obtained from the FE or field loading test. However, it is difficult to directly obtain the local stress in the UHPC layer from field loading test. The main goal of the comparison between experimental and numerical values of diaphragm stress and U-rib stress is to verify the accuracy of FE model. After that, the finite element method (FEM) calculation can be used to investigate the stress of UHPC layer.

The above analysis showed that the UHPC-based pavement system effectively reduces the stress amplitude at the vulnerable fatigue cracking sites. The increased structural integrity is attributed to the application of shear studs. In this section, the local tensile stress of UHPC is also analyzed by the FEM. Figure 16 shows four operating scenarios. The positions of the maximum tensile stress are selected to measure the transverse and longitudinal tensile stresses: the top of the web (UHPC-1); the top of U-ribs, UHPC-2 between the two diaphragms, and UHPC-3 in the top of U-ribs–diaphragm; and the top of the diaphragm (UHPC-4).

Figure 16.

Tensile stress testing points in different scenarios: (a) top of the longitudinal ribs, (b) top of U-ribs between the two diaphragms, (c) top of U-ribs–diaphragm, and (d) top of two-diaphragm spacing.

The tensile stress in the UHPC layer of the FE model was calculated. The maximum tensile stress values are shown in Figure 16, in which the notations “TS” and “LS” represent the transverse and longitudinal stress, respectively. As Figure 16 shows, the tensile stress in transversal direction was generally larger than that in the longitudinal one. In addition, the stress distribution in diaphragm and web were much higher than that in the middle span of diaphragm. The maximum and minimum tensile stress were 10.85 and 1.32 MPa in the transverse direction, and 10.84 and 1.16 MPa in longitudinal direction, respectively. Therefore, the calculated maximum stress range in the UHPC layer was 9.69 MPa. Previous studies showed that the fatigue life can approach to 3.1 million cycles when the stress range of the UHPC layer ranges from 0 to 21.3 MPa (Cao et al., 2016). The calculated stress range in this article is much lower than that in previous works. Therefore, the UHPC strengthening method can prevent the propagation of fatigue cracks in the UHPC layer.

Conclusion

The present study introduces a strengthening method using UHPC on the OSDs of a cable-stayed bridge. This material provides an effective and convenient methodology for reducing the stress amplitude and improving the stiffness of the Haihe Bridge. From the experimental and analytical results, the following conclusions can be drawn:

Fatigue cracks generally occur in the diaphragm, rib-to-diaphragm joint, and rib-to-deck joint, which is mainly attributed to insufficient stiffness of the diaphragms and bridge decks.

The vertical deformation and rotation of the U-ribs under the traffic load readily produce tensile cracks at the opening of diaphragm. The vertical deformation of the bridge deck and the relative rotation between the bridge deck and U-rib lead to fatigue cracks at the weld root.

Comparing with a deck with a typical asphalt overlay, this strengthening method reduces the stress of the U-rib and diaphragms by at least 45.4% and 40.0%, respectively. The UHPC and the OSD can be well bonded due to the shear studs, which reduce the risk of pavement debonding. The tensile strength of UHPC can satisfy the required maximum stress.

No new cracks and crack propagation are found in the OSDs after strengthening under the real operating condition based on the in situ observations. The repair method has prominent advantages and technical feasibility in improving the service condition of the orthotropic steel bridges.

The proposed method is validated by a real cable-stayed bridge, which is also applicable for some other structures with OSDs. It required a long period to observe the fatigue cracking behavior of the enhanced structure subjected to real repeated load. Future studies are also required, including small-scale fatigue tests in laboratory conditions and fatigue performance assessment using multiscale FE analysis method.

Footnotes

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The study reported here is financially supported by the National Natural Science Foundation of China (51778068), the Natural Science Foundation for Excellent Young Scholars of Hunan Province (2019JJ30024), the Key Research and Development Program of Hunan Province (2019SK2171 and 2019RS2035), the Training Program for Excellent Young Innovators of Changsha (kq1802012), and the Hunan Provincial Innovation Foundation for Postgraduates (CX20190638). The support is gratefully acknowledged.

ORCID iDs

Yafei Ma

C.S. Cai

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