Keywords

1 Introduction

In recent years, the rise of marine resource development has provided immense opportunities for the global construction of cross-sea bridges [1]. In order to better utilize China's abundant marine resources, the country has constructed numerous marine platforms and cross-sea channels in coastal areas [2], achieving significant advancements in the theory and technology of bridge engineering. Chen et al. [3] took the Qingdao Bay Bridge as an example to predict the service life of reinforced concrete structures in harsh marine environments. Zhao et al. [4] studied the interaction mechanism between waves, currents, and bridge piers under extreme marine conditions caused by hurricanes or tsunamis, revealing the interplay of waves and currents. Simultaneously, with the development of new materials and equipment, an increasing number of bridge construction projects, both domestically and internationally, will face complex hydrogeological conditions. The research on key technologies for the construction of long-span continuous beam bridges over rivers under complex hydrogeological conditions is expected to see further development and widespread application.

Nevertheless, in these complex environments, the construction of waterborne bridges faces a series of unpredictable challenges. For instance, local erosion caused by ocean currents, waves, heavy rainfall, and wind can impact the stability and fatigue life of sea-crossing bridge foundations[5]. The construction process is also influenced by adverse factors such as swift water flow, deep water, significant water level variations, high waves, and the difficulty of water transport during construction. In such situations, the erection of temporary truss bridges can effectively address these issues. Temporary truss bridges can serve as transportation pathways during construction and as construction platforms for the substructure, transforming waterborne construction into land-based construction. This ensures the normal progress of construction in adverse conditions, significantly shortens construction periods, and has therefore found widespread application in bridge construction projects both domestically and internationally.

However, in general, the construction environment for temporary steel truss bridges is often challenging, and the construction of these bridges is significantly influenced by the surrounding conditions. Particularly for temporary steel truss bridges spanning bodies of water, the impact of complex environmental loads such as wind, waves, and currents is substantial. With numerous calculation parameters involved, comprehensive considerations are essential in the design and construction of these truss bridges [6].

Currently, various forms of temporary steel truss bridges have been constructed in China. With the increasing construction of more sea-crossing and river-crossing bridges, as well as the growth in bridge spans, greater water depths for foundation submersion, and the complexity of hydrological and geological conditions, future bridge construction is expected to rely more on temporary construction steel truss bridges. This further highlights the crucial technical requirements for bridge construction under specific natural conditions. On the other hand, while there is extensive research on the interaction between waterborne bridges and waves domestically and internationally [7,8,9], there is limited systematic research on trestle bridge projects over water. Existing references often focus on the assessment of losses and damages for steel trestle bridges [10,11,12,13,14]. Therefore, it is essential to conduct a systematic study on the design and construction of temporary trestle bridges over water.

This paper, based on the Panzhihua Shoupanyan Bridge project, utilizes Midas software to conduct finite element analysis on the structural design of steel truss bridges in high water levels and fast-flowing environments. Additionally, it explores the key construction technologies for safely withstanding floods in the context of high water levels and fast-flowing conditions. The aim is to promote the development of temporary construction truss bridge projects, making the design and construction of truss bridges more scientifically rational. Through an in-depth study of the Panzhihua Shoupanyan Bridge project, we hope to provide valuable experience and technical support for addressing construction challenges in complex conditions such as deep water, high flow rates, and shallow cover layers where navigation is not possible.

2 Project Overview

2.1 Overview of the Shoupanyan Bridge

The Shoupanyan Bridge is situated in Panzhihua City. Spanning the Yalong River, the bridge has a total length of 258.0m and a width of 22.0 m. The bridge features a variable-section prestressed concrete continuous box girder layout. As shown in Fig. 1, Piers 1 and 2 serve as the main piers of the Shoupanyan Bridge, located within the main riverbed, with a height of 26.0 m. The main piers adopt a circular end solid structure, with a pier section dimension of 14.0 m × 3.0 m and rounded chamfers at both ends with a radius of 1.806 m. The abutment dimensions are 16.0 m × 9.2 m × 4.0 m, supported by six bored cast-in-place piles with a diameter of 2.5 m each beneath the abutment.

Fig. 1.
figure 1

The layout of the Shoupanyan Bridge span.

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The geological conditions at the site of the Shoupanyan Bridge are primarily composed of an 8.6 m layer of conglomerate/gravel sandstone (including 25 cm floating stones) beneath Pier 1, and a shallow covering of 1.2 m conglomerate/gravel sandstone and 9.9 m of silty clay beneath Pier 2.

2.2 Hydrological Conditions

The Shoupanyan Bridge project is located downstream of the Yalong River, with complex hydrological conditions. The Tongzilin Hydrological Station is situated 2.5 km upstream from the bridge site, followed by the Tongzilin Hydroelectric Station at 5.5 km upstream. Due to the control of the hydroelectric station's power generation and the impact of flood discharge during the flood season, the designed bridge site experiences significant daily fluctuations in flow rates. According to hydrological station survey data, during the dry season (November to May), the water flow velocity can reach 3.87 m/s, with a maximum daily flow rate variation of 2500 m3/s. This corresponds to a fluctuation in water level of around 4 m. The flood season occurs from June to October, with the peak flow velocity reaching 5.69 m/s during the main flood period from July to October. The flow rate typically ranges from 3700 to 6500 m3/s. Based on data from the past six years, flow rates exceeding 7000 m3/s occur for a maximum of 7 days during the flood season. Therefore, the design of the truss bridge assumes of normal usage for flow rates below 7000 m3/s.

Table 1. Statistical table of main hydrological parameters for steel truss bridge design.
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3 Structural Design and Analysis of Steel Truss Bridges

3.1 Steel Truss Bridge Structural Design

To facilitate rapid construction and convenient dismantling, the upper structure of the truss bridge adopts an assembled configuration of I-beams and Bailey beams, while the lower structure is designed as a steel pipe pile with steel beam load-bearing structure. The foundation incorporates a combination of bored cast-in-place piles and steel pipe piles. The Bailey steel truss bridge employs a continuous beam structure with a width of 6.5 m. The steel pipe piles for the truss bridge are arranged in pairs, consisting of 630 × 10 mm steel pipes, spaced at intervals of 6.0 m. The top distribution beams of the Bailey beams are two HM488 steel crossbeams, spaced at 0.75 m intervals. Six transverse Bailey beams are arranged, with each beam spaced at 0.9 m intervals. Bridge abutments are set at both ends, with concrete construction walkways cast behind the abutments. Protective railings are installed on both sides of the truss bridge. The specific details of the plan layout for the steel truss bridge are illustrated in Fig. 2.

Fig. 2.
figure 2

Layout plan of the steel truss bridge of the Shoupanyan Bridge across the river.

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3.2 Hydraulic Flood Assessment for the Steel Truss Bridge

Following the structural design outlined above, a comprehensive modeling and analysis were conducted using Midas numerical simulation software. The resulting model is depicted in Fig. 3.

Fig. 3.
figure 3

Model of the steel truss bridge in Midas.

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When analyzing the forces on the pile cap distribution beams and steel pipe piles, the interaction between the steel pipe piles and the soil is simulated using the m-method with a specified parameter of m = 5000 kN/m4. The connections between the upper and lower distribution beams are assumed to be fully pinned, meaning that the bending moment from the upper distribution beams does not transfer to the lower distribution beams. The analysis considers the loads at the design maximum water level and flow velocity. At this point, there are no additional construction loads on the truss bridge or platform. The calculated values for the water flow forces on the steel truss bridge are illustrated in the Fig. 4.

Fig. 4.
figure 4

Results of water flow force calculation on the steel truss bridge.

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Fig. 5.
figure 5

Steel pipe-pile combined stress (MPa).

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Fig. 6.
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Combined stress for the connection system (MPa).

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Fig. 7.
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Shear stress for the connection system (MPa).

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Fig. 8.
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Drilled pile reaction force (kN).

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As shown in Figs. 5, 6, 7 and 8, it can be observed that the maximum combined stress in the steel pipe and connection system is 97.5 MPa, with a maximum shear stress of 5.8 MPa, meeting the design requirements. The maximum vertical reaction force on the drilled pile is 793 kN with no tensile force generated. The design of the steel truss bridge meets the specified requirements.

4 Key Construction Technologies for Steel Truss Bridge

4.1 Pile Foundation Construction

The pile foundation construction involves the use of drilled cast-in-place piles along with steel pipe piles. The pile diameter is 1.2 m, and each section of the steel pipe pile is 10m in length. Given that the truss bridge foundation incorporates embedded rock piles, the construction employs an impact drilling rig. The key to the construction of the pipe pile foundation is to ensure that the steel pipe piles, and the cast-in-place piles are in the same plane and concentric, with their own verticality aligned in a straight line. To achieve this, the construction adopts positioning assistance measures, a level, and a cross-guidance tool.

The specific construction steps are as follows: once the drilled cast-in-place piles are completed and concrete is poured, reinforcement and positioning assistance measures are added around the steel casing. A cross-guidance tool is installed at the top of the casing to ensure concentricity when inserting the steel pipe piles into the cast-in-place piles. The steel pipe piles are then lifted and lowered using a tracked crane, with a level controlling their verticality during the piling process. Once the required alignment is achieved, the insertion of the pipe piles is halted after reaching the designated position before the concrete solidifies.

4.2 Lateral Bracing Construction

After the installation of a row of steel pipe piles, it is crucial to promptly initiate the assembly of lateral bracing between the piles to link the fully driven steel pipe piles into a unified structure, preventing any deviation in their positioning.

The key to successful lateral bracing lies in accurately determining the installation positions. In the lateral bracing installation phase, a precise control method is employed using positioning steel plates and a chain hoist with guidance. The construction process is as follows: initially, measurements are taken to determine the lateral bracing positions, marked with chalk for reference. Subsequently, a positioning steel plate is welded beneath the lateral bracing steel pipe, lifted into the designated position using a chain hoist, and then secured with fixed welds. Full-section welding is then carried out. During the adjustment of lateral bracing positions, a chain hoist is used for additional assistance in positioning.

4.3 Bridge Deck Structure Construction

The bridge deck structure consists of transverse distribution beams and specialized deck panels. The installation of these distribution beams utilizes custom-designed locks, as illustrated in Fig. 9. These custom locks facilitate a more convenient and secure connection between the distribution beams and the Bailey beams. Before laying the distribution beams, the locks are pre-installed on the upper chords of the Bailey beams. During the installation of distribution beams, the fixture's two lips clamp onto the sides of the distribution beam flanges, and securing bolts fasten the fixture, ensuring a tight connection with the flange plate. The connection between the distribution beam and Bailey beam is illustrated in Fig. 10.

Fig. 9.
figure 9

Custom lock for distribution beam-bailey beam connection.

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Fig. 10.
figure 10

The distribution beam-Bailey beam connection

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Once the transverse distribution beams are laid, the installation of deck panels commences. The specialized deck panels have segmented dimensions of 3000 × 10 × 5500 mm, and they are interconnected using custom fixtures. The prefabricated steel panels have slots and bolt holes at the corners and the central length, facilitating connection through custom locks and reserved slots. At the center of the deck panel, a custom fixture is employed to connect with the transverse distribution beams. The application of a series of custom fixtures enhances the stability of the connection between the bridge deck panels and the beams.

5 Conclusion

This study examines the construction of a sea-crossing bridge under complex hydrological conditions, using the construction of the Shoupanyan Bridge in China as an example. The aim is to construct a steel truss girder bridge over water, despite the challenges posed by high water levels and fast currents. The study proposes the following novel techniques to achieve this goal:

  1. (1)

    This task involves achieving precise positioning and vertical control of steel pipes that are inserted into cast-in-place piles during the pile foundation construction stage. This can be achieved using positioning aids, levelling tape, and cross guiding jigs.

  2. (2)

    For the lateral support construction stage, it is recommended to use positioning steel plates and chain hoists to ensure precise control of the lateral support installation position.

  3. (3)

    During deck construction, specially designed fixing devices can be used to connect distributor girders and berth girders, as well as bridge deck slabs.

These technologies improve the safety and reliability of steel truss bridge construction. The deformation of the truss bridge under maximum water flow, as obtained from construction monitoring, is consistent with theoretical expectations. This study presents technical insights and experiences that can be applied to the construction of steel truss bridges under complex hydrological conditions.