Biggest Challenges in Bridge Construction

The major challenges for building urban bridges are the availability of skilled labor, access to urban areas and environmental compatibility.

A worker paints the Anzhaite Long-span Suspension Bridge in Jishou, Hunan, China (Source: The Daily Mail)

Building bridges in megacities with the current scarcity of skilled labor will require a massive recourse to prefabrication. In a few circumstances, prefabricated bridge units will be transported on water with tugs and barges, which will allow the use of heavy, large units. In most cases, prefabricated bridge units will be transported on the ground through congested urban roads, which will lead to the use of light, modular units.

A floating crane lifts prefabricated deck sections onto the San Francisco-Oakland Bay Bridge (Source: San Francisco Public Press)

The availability of deck assembly areas and the interference of construction operations with adjacent infrastructure are additional challenges that will govern the bridge design process. As such, incremental launching construction from aerial platforms will see new applications, especially when combined with on-site welding of field splices among modular bridge units. The welding of field splices will also allow for optimized segmentation of bridge units, diminish the cost of field splices, and will relax the fabrication tolerances of the units.

Size Determines Cost, Cost Determines Everything Else

When constructing a bridge for an urban area, the size of a bridge governs the construction process. in turn, the construction cost of a bridge determines the materials and technology. Technology includes labor and investment in special construction equipment. The quantities of structural materials for a bridge depend on the design loads of the bridge, the flexural and shear span of the bridge units, and the mechanical strength of the material.

The Jiaozhou Bay Bridge in China is the longest sea-crossing bridge in the world (Source: The New York Times)

Small and large-scale bridge projects are both necessary in megacities and demand will only increase in light of the newly emerging megacities all over the world. When looking at both the construction of new bridges and the maintenance of existing bridges, the number of small-scale projects will definitely be larger than the number of large-scale projects. The impact these construction projects will have on the mobility of people and goods within a megacity is massive.

Although one may assume large-scale bridge projects with a larger budget will allow for design optimization and the efficient use of high-grade steels, scale economies in competition with other megacities will govern the availability of construction materials and workforce. Eventually, the scarcity of structural materials will lead to the efficient, eco-friendly use of steel and concrete in large and small-scale bridge projects alike.

Prefabrication and Incremental Launching for Bridge Construction

It is true that small-scale bridge projects have smaller budgets for technology, which limit design optimization and construction mechanization and increase the labor demand. Therefore, small-scale bridges will most likely be procured as packages of multiple bridges to acquire scale economies and a more efficient use of materials with the optimized design of modular units.

On the other hand, large-scale bridge projects allow for massive investment in special construction equipment, which will facilitate the prefabrication of modular bridge units in smart, eco-friendly factories. It will also diminish the labor demand of site assembly and the need for complementary infrastructure in an urban environment, as well as enhance the quality and durability of the final product.

Thus, large-scale bridge projects will be designed for modularity and have prefabricated standardized units with asynchronous production lines. Parts of the bridge will likely have different cycle times, just-in-time delivery, and require minimal site operations. Overall, construction technology and risk management of the trans-disciplinary relationships of mechanized construction will dictate the design of large-scale bridge projects in megacities.

Workers assemble a prefabricated bridge in Pennsylvania, U.S. (Source: Roads and Bridges)

Small-scale bridge projects will take advantage of incremental launching technologies. Launched bridges minimize the interference between deck construction and the obstruction to overpass, and this is a major advantage for urban bridges designed to overpass congested infrastructure. Launched bridges do not require extra clearance to support the deck during construction, which simplifies connecting the bridge with existing roads and railways. Launched bridges do not require additional right-of-way as the deck is built behind the abutment and incrementally pushed into position. Additionally, the construction area is far from the infrastructure to overpass, which minimizes the risk for workers and the traveling public.

Incremental launching applied to a bridge deck construction process (Source: CARLOS FERNANDEZ CASADO S.L)

Materials For the Future Generation of Urban Bridges

Steel and concrete are the most common materials for bridges. In the field of steel bridges, high-grade steel will reduce the self-weight of bridge superstructures and the cost of piers and foundations. New composite systems and mechanized plate corrugation will increase the buckling capacity of unstiffened web panels and compression flanges to avoid the use of welded stiffeners.

In the field of prestressed concrete, new steels for rebar will offer higher strength and corrosion resistance to increase the durability and service life of the next generation of urban bridges. Post-tensioning materials are already extremely efficient, and the challenge will revolve around finding new duct systems and passivating materials to able to avoid the quality concerns raised by cement grouts.

Full-span precasting has been employed in thousands of spans of high-speed railway projects and in hundreds of spans of light-rail transit projects. Both steel and prestressed concrete bridges will be present in the mass transit systems of megacities, and both types of bridges are perfectly compatible with steel decks should high-grade steel turn out financially competitive over prestressed concrete in the megacity-oriented life cycle cost analysis.

Modern large-scale bridge projects are designed for 75 or 100-year service life in the USA. The use of renewable protective materials can easily meet this target in steel bridges, but the evolution of design loads and service conditions of urban bridges is hard to predict. Steel bridges offer a major advantage over prestressed-concrete bridges from this point of view, as they are more adaptable and can be modified, strengthened and adapted to new use conditions.

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For global companies it is often not easy to build successful CSR programs overseas due to differences in cultures, customs, and laws. However, the POSCO Group is working to form strong relationships with local communities near its offices and plants by being attentive to the local issues and actively working to find solutions together with the communities.

POSCO Vietnam helps improve homes with the POSCO Steel Village

Since 2009, POSCO Vietnam has been working to understand the needs of the local communities near its plant. By combining the needs of the community with the capabilities of POSCO and its group companies, POSCO was able to improve local housing through its POSCO Steel Village, POSCO Steel Bridge, and POSCO Steel Playground initiatives.

On November 30, 2016, POSCO Vietnam received the Excellent CSR Prize, the most prestigious prize from the Korean Minister of Trade, Industry, and Energy at the 6th Korea-Vietnam CSR Awards in 2016. The award ceremony was held at the KOTRA Hanoi Office on December 28.

In particular, because POSCO Vietnam handles various licenses and permits for steel bridge construction, they formed a volunteer group with members from various POSCO partners. POSCO A&C participated in the design, SS-VINA supplied section steel products, and POSCO E&C processed and built the bridge.

The POSCO Steel Bridge project is seen as a model CSR activity by the local communities and the Vietnamese government. As a result, POSCO Vietnam was awarded with the Excellence in CSR designation, the most prestigious award from the Korean Minister of Trade, Industry and Energy at the 6th Korea-Vietnam CSR Awards on December 28, 2016.

POSCO Steel Village (left) will contain 104 households and is slated for completion in April 2017. The POSCO Steel Bridge in Vietnam (right) was completed in January 2016.

POSCO partners with local schools in Myanmar

In Myanmar, POSCO has been working to provide resources to local schools. Since 2014, POSCO E&C formed sisterhood ties with nearby secondary schools and signed an agreement to work with the National University of Arts and Culture in Yangon. POSCO E&C has donated educational materials and equipment, repaired educational facilities, organized cultural exchange activities, and built rainwater storage & drinking water facilities. More recently, POSCO has been leading the way in making improvements to the safety of Yowa Village. By partnering with POSCO’s 1% Sharing Foundation, they were able to build a bridge in the village with POSCO steel.

For these efforts, Myanmar-POSCO E&C recognized for its contributions to Myanmar’s local communities in the 2016 Myanmar Excellent CSR Company Awards that were held in Yangon, Myanmar in December 13, 2016.

Hyun-ik Choi (right), head of POSCO E&C Myanmar, receives the Prize of the Minister of Strategy and Finance of Myanmar from U Aung Naing Oo, Director General of DICA and General Secretary of MIC. The 2016 Myanmar Excellent CSR Company Awards took place at the Sedona Hotel in Yangon, Myanmar, on December 13.

POSCO Krakatau gives back to Indonesia

In Indonesia, the Krakatau POSCO Social Enterprise (KPSE) has been working to support secondary education, create jobs at the steel mill, and return profits to the local communities in Cilegon, Indonesia, where the steel mill is located.

KPSE, co-founded by the POSCO 1% Sharing Foundation and KOICA, was awarded for its efforts at the ‘2016 Korea-Indonesia CSR Forum and Awards Ceremony’ that was hosted by the Korean Embassy in Indonesia and KOTRA on December 15, 2016.

KPSE manager and acting CEO Jang-gon Jeon (2nd from the left) and Andi Soko, officer of personnel management and general affairs at PT.KP (2nd from the right) stand with KPSE employees after receiving the Prize of the Director of the Indonesian Investment Coordinating Board. The awards ceremony took place at the ‘2016 Korea-Indonesia CSR Forum’ held at the Shangri-La Hotel in Indonesia.

POSCO Group’s overseas subsidiaries have been recognized for their broad contributions in CSR. POSCO Group will continue to promote win-win growth in partnership with local communities at home and abroad based on the Group’s unique values that recognize the overseas market as a partner and not as a business target.

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