How to Overcome Extreme Cold to Provide Optimal Installation Solutions for Prefabricated Highway Steel Bridges in Mongolia?

As a bridge engineer from a professional steel structure bridge production and export company, we have rich experience in providing customized installation solutions for prefabricated highway steel bridges in harsh environments. In 2013, we successfully completed a HD200-type Bailey bridge project in Mongolia, which is a multi-span prefabricated highway steel bridge with a load capacity of 50 tons and a total length of 150 meters. Mongolia is characterized by extremely harsh construction conditions, especially its extreme cold climate, large temperature differences and strong wind and snow, which brought unprecedented challenges to the on-site installation of the bridge. This article will elaborate on the definition of prefabricated highway steel bridges, the installation methods and key challenges in Mongolia’s extreme cold environment, and how our company solved the installation problems to provide the optimal solution for the customer, and finally answer the common questions from customers in cold regions.

1. What is a Prefabricated Highway Steel Bridge?

A prefabricated highway steel bridge is a modular, assembled structural system, which is widely used in transportation infrastructure construction, especially in regions with harsh construction conditions and urgent traffic needs. Its main components, including truss pieces, crossbeams, bridge decks, connecting pins and supports, are all prefabricated in professional factories with standardized production processes and strict quality control, which ensures the precision and stability of each component. After production, these light-weight and easy-to-transport components are transported to the construction site by land or sea, and then quickly assembled into a complete and usable highway bridge according to the designed procedures, without the need for complex on-site pouring or large-scale construction equipment.

Compared with traditional cast-in-place concrete bridges, prefabricated highway steel bridges have unique advantages: fast on-site installation speed, strong adaptability to harsh environments, recyclability, and low impact on the surrounding environment. The HD200-type Bailey bridge, adopted in our 2013 Mongolia project, is an upgraded type of prefabricated steel bridge, which has higher structural strength, better load-bearing capacity and stronger stability, and is especially suitable for large-span and heavy-load transportation needs in harsh environments like Mongolia.

2. Installation Methods and On-site Challenges of Prefabricated Highway Steel Bridges in Mongolia’s Extreme Cold Environment

Mongolia is located in a cold temperate zone, with a typical continental extreme cold climate. The winter temperature can drop to -40℃, with annual temperature difference of nearly 70℃, and frequent strong wind and snow weather. In addition, most construction sites are located in remote grassland or hilly areas, with poor transportation conditions, shortage of construction equipment and limited professional construction personnel. In such an environment, the installation of prefabricated highway steel bridges needs to adopt targeted methods, while overcoming various harsh on-site factors.

2.1 Main Installation Methods in Extreme Cold Environment

Combined with Mongolia’s on-site conditions, we mainly adopted two installation methods for the 150-meter multi-span HD200-type Bailey bridge project: cantilever launching method and segmented assembly method, which are both suitable for extreme cold environments and can minimize the impact on permafrost.

The cantilever launching method is the core installation method for the project. Its principle is to assemble the bridge components on one bank first, then use simple equipment such as winches and jacks to push the assembled bridge sections forward section by section, and set a nose frame at the front end to balance the cantilever moment and prevent structural deformation caused by extreme cold. This method requires simple equipment, fast construction speed, and can minimize on-site operation time, reducing the impact of extreme cold on construction personnel and equipment.

The segmented assembly method is used for the middle span of the bridge. We divided the 150-meter multi-span bridge into several segments, assembled each segment on the ground near the bridge site, and then hoisted and connected them one by one. This method can reduce the difficulty of high-altitude operation, ensure the installation precision, and avoid the damage of components caused by long-time exposure to extreme cold.

2.2 Key On-site Installation Challenges to Overcome

The extreme cold environment in Mongolia brought three core challenges to the bridge installation, which are the key factors we need to focus on solving.

First, the impact of extreme cold on materials and equipment. When the temperature drops to -30℃ to -40℃, the steel materials will appear cold brittleness, and the toughness and ductility will decrease significantly, which may lead to component cracking during installation. At the same time, the lubricating oil of construction equipment such as winches and jacks will solidify, resulting in equipment failure and affecting the normal progress of installation. In addition, the permafrost layer at the construction site is thick, and improper operation will easily cause permafrost disturbance, leading to uneven settlement of the bridge foundation and affecting the structural stability of the bridge.

Second, the impact of strong wind and snow on construction safety and quality. Mongolia often has strong wind and snow weather during the construction period, which not only affects the stability of the assembled bridge sections, but also increases the difficulty of high-altitude operation and brings great safety risks to construction personnel. At the same time, snow accumulation on the bridge deck and components will increase the load of the bridge, and the freezing of snow water will also affect the connection between components, reducing the installation quality.

Third, the shortage of on-site construction conditions. Most construction sites in Mongolia are remote, with no stable power supply and limited living conditions for construction personnel. The shortage of professional construction personnel and the difficulty in transporting construction materials also bring great obstacles to the smooth progress of the installation work. Moreover, the low temperature will affect the welding quality, easily causing cold cracks and pores in the welds.

3. How Our Company Solved the Installation Problems in Mongolia’s Extreme Cold Environment

In view of the harsh on-site conditions in Mongolia, our company took a series of targeted measures to overcome the challenges of extreme cold, large temperature difference and strong wind and snow, and successfully completed the installation of the HD200-type Bailey bridge, providing the optimal solution for the customer.

First of all, we optimized the design of bridge components and installation process to adapt to the extreme cold environment. Before the project started, our professional engineers conducted a detailed on-site investigation, analyzed the local climate conditions and permafrost characteristics, and optimized the HD200-type Bailey bridge components. We selected high-strength steel with excellent low-temperature toughness, which can still maintain good mechanical properties at -40℃, avoiding component cracking caused by cold brittleness. At the same time, we optimized the connection mode of components, adopted anti-freezing connecting pins and sealing materials, and applied special anti-corrosion and anti-freezing coatings to the components to prevent corrosion and freezing damage. For the welding process, we selected special low-temperature welding materials (E5016-G low-temperature welding rods) and optimized the welding parameters, implementing preheating at 80-100℃ and post-welding heat treatment at 200-250℃ to avoid weld cold cracks.

Secondly, we took effective measures to protect construction equipment and minimize permafrost disturbance. For construction equipment such as winches and jacks, we used special low-temperature lubricating oil and installed thermal insulation devices to ensure that the equipment can work normally in extreme cold. At the same time, we optimized the installation route and construction sequence, adopted lightweight construction equipment, and minimized the pressure on the permafrost layer to avoid permafrost melting and disturbance. We also set up temporary thermal insulation sheds at the construction site to protect the assembled components and construction personnel from the impact of strong wind and snow, ensuring the installation quality and construction safety. Referring to the winter construction insulation experience in cold regions, we built a "thermal insulation system" for the construction site, using thermal insulation quilts and warm air guns to maintain a positive temperature environment for key operations.

Thirdly, we strengthened on-site technical guidance and personnel training to improve the efficiency and quality of installation. Considering the shortage of professional construction personnel in Mongolia, our company sent a professional technical team to the site to conduct on-site guidance and training for local construction personnel, teaching them the key points of component assembly, equipment operation and safety protection in extreme cold environments. We also formulated a scientific construction schedule, arranged construction tasks reasonably, and avoided construction in the coldest period of the day, ensuring the physical health of construction personnel and the smooth progress of the project. In addition, we prepared sufficient spare parts and emergency materials to deal with equipment failure and sudden wind and snow weather in a timely manner, ensuring that the installation work was not interrupted.

Finally, we established a strict quality inspection system to ensure the structural safety and service performance of the bridge. During the installation process, we conducted strict inspection on each component and each installation link, focusing on checking the connection tightness of components, the flatness of the bridge deck and the stability of the foundation, and timely corrected any problems found. After the completion of the installation, we conducted a comprehensive load test and safety inspection on the bridge, ensuring that the bridge met the 50-ton load requirement and could adapt to the extreme cold climate and strong wind and snow environment in Mongolia. The entire project was completed 10 days ahead of schedule, which was highly recognized by the customer.

4. Common Questions and Answers from Customers in Cold Regions

In the process of undertaking prefabricated highway steel bridge projects in cold regions such as Mongolia, we often receive various questions from customers. The following are the most common questions and our professional answers, helping customers better understand the application of prefabricated steel bridges in extreme cold environments.

4.1 Design Standards of Prefabricated Steel Bridges in Extreme Cold Environments

Q1: What design standards do your prefabricated highway steel bridges adopt, and can they adapt to the extreme cold environment in Mongolia? A1: Our prefabricated highway steel bridges, including the HD200-type Bailey bridge in the 2013 Mongolia project, mainly adopt international universal standards and local standards of Mongolia. We strictly follow ISO 683-11 (Structural Steel - Part 11: Steel for Bridges) and ISO 3834 (Welding Quality Requirements) for design and production, and also refer to BS 5400 standards to ensure structural safety and durability. In view of the extreme cold environment, we have added special design requirements for low-temperature resistance, such as selecting low-temperature-resistant steel materials, optimizing the structural design to resist cold brittleness, and strengthening the anti-corrosion and anti-freezing treatment, which can fully adapt to the extreme cold climate in Mongolia with temperatures as low as -40℃.

4.2 Service Life and Post-maintenance in Extreme Cold Environments

Q2: What is the service life of the prefabricated highway steel bridge in Mongolia’s extreme cold environment, and what post-maintenance work is needed? A2: Under the condition of standardized maintenance, the service life of our HD200-type prefabricated steel bridge can reach 15-25 years in Mongolia’s extreme cold environment. We use high-strength low-temperature-resistant steel and adopt a composite anti-corrosion system (epoxy zinc-rich primer + epoxy micaceous iron intermediate paint + polyurethane topcoat) to effectively resist corrosion and freezing damage. In the later period, it is only necessary to regularly inspect the connecting components, anti-corrosion coatings and bridge foundations, tighten loose pins in time, touch up paint for damaged coatings, and clear snow and ice on the bridge deck in time, which is simple and low-cost. Regular inspection of welds and permafrost foundation is also required to avoid potential safety hazards caused by cold cracks or permafrost disturbance.

4.3 Installation Time and Construction Personnel Requirements

Q3: How long does it take to install a 150-meter multi-span HD200-type prefabricated steel bridge in Mongolia’s extreme cold environment, and how many construction personnel are needed? A3: For the 150-meter multi-span HD200-type Bailey bridge project in 2013, we completed the entire installation work in 25 days with 12 construction personnel (including 4 professional technical personnel from our company and 8 trained local personnel). The installation time is affected by the span of the bridge, climate conditions and on-site equipment. We will optimize the construction schedule according to the actual situation, avoid construction in extreme weather, and ensure the installation efficiency. For similar projects, the installation time can be adjusted between 20-30 days according to the specific conditions.

4.4 Adaptability to Permafrost and Wind and Snow

Q4: Can the prefabricated steel bridge adapt to the permafrost environment in Mongolia, and how to avoid the impact of strong wind and snow? A4: Yes, our prefabricated steel bridge is specially designed for permafrost environments. We adopt lightweight components and optimized foundation design to minimize the disturbance to permafrost and avoid uneven settlement caused by permafrost melting. For strong wind and snow, we strengthen the structural stability of the bridge, set anti-wind pull rods, and take temporary thermal insulation and snow-clearing measures during installation to ensure that the bridge can resist strong wind and snow and maintain stable operation. The HD200-type Bailey bridge is also designed with pre-arched degree to reduce vertical deflection and enhance wind resistance.

5. Conclusion

The HD200-type prefabricated highway steel bridge project in Mongolia fully demonstrates our company’s professional strength in providing customized installation solutions for harsh environments in 2013. Facing the extreme cold, large temperature difference and strong wind and snow in Mongolia, we overcame various challenges through component optimization, process improvement, equipment protection and technical guidance, successfully completed the project and provided the optimal solution for the customer. As a professional steel structure bridge production and export company, we will always adhere to the principle of "customer-oriented and technology-led", adjust the installation method according to the actual on-site conditions of customers in cold regions, provide high-quality products and professional technical support, and help customers solve the problems of bridge installation in harsh environments.