A Basic Guide to Steel Bridges: An Engineering Marvel
Larger volume of infrastructure is required to sustain the rapid increase of population and social activities. Infrastructures are essential to back up the growth of economies and to promote well-being of every individual. Bridges for example, are vital to streamline transportation, they are instrumental in connecting communities and bringing necessities to people especially food, shelter, medicine, and education. Thanks to the triumphant journey of mankind in Civil Engineering and in the mastery of bridge designs. The birth of steel bridge almost 150 years ago enabled us to swiftly connect distant regions, bring technologies to remote areas, and establish numerous over-water highways that makes travel time significantly shorter.
Steel bridges becomes a common sight around the world – in cities and rural areas, in wealthy sovereigns and developing countries. They are popular in modern construction due to their strength, durability, and ability to span long distances. Steel bridges come in different types and sizes, from a small pedestrian or Bailey bridge to gigantic suspension bridge that can connect two cities. In this article, we will explore the structural components, types, advantages, and areas of improvement of steel bridges.
Structural Components of Steel Bridges
Structural components of steel bridge vary on its type and size. However, they are typically combination of steel beams, columns, decks, and girders.
Beams – They are steel sections or fabrications that runs continuous from pier to pier to span the gap and support the weight of the bridge. Steel beams are the main structural components of the bridge. They come in different shapes, including I-beams or H-beams, box girders, and trusses.
Columns - They provide vertical support for the bridge and anchorage to the foundation. Being in critical location and conditions, steel bridge columns especially water-borne, are normally reinforced concrete or combination of steel and reinforced concrete. Foundation construction including columns located in bodies of water requires the use of temporary or permanent steel casement to facilitate concrete casting. In some cases, steel columns are jacketed with concrete to provide protection to the steel against corrosion.
Girders – Steel girders can be plate girders or box girders and known as large beams. These steel components provide lateral support for the bridge. Girders has high load bearing capability and are designed to carry large amounts of dynamic and moving loads.
Deck - The deck of the bridge is the roadway or walkway surface that vehicles or pedestrians uses to pass. It is usually made of reinforced concrete or steel. Modern deck designs called as composite deck slabs involve galvanized sheet profiles as a reinforcement against positive moment and formwork for concrete placing at the same time. These galvanized sheet profiles are connected to beams or girders by fasteners or welding. The deck is supported by a series of girders that run parallel to the beams.
Joints – Different structural components are joined together to perform as a single steel bridge. Joints are designed to be rigid or flexible and are achieved by welding or bolting.
Types of Steel Bridges
Bridges or steel bridges are sometimes categorized according to type of traffic they support. In this case, we encounter designations such as pedestrian bridge, highway or road bridge, railway bridge, or the combination of different types.
Pedestrian bridge also called footbridge or overpass is designed solely for pedestrians, in short, an elevated walkway. It comes in different shapes and structural designs – rigid, truss, cable-stayed, arch, and more.
Highway bridge, road bridge, or skyway is an elevated major road structure for vehicles of all types. These types of bridges are constructed to avoid obstructions.
Railway bridge is designed to carry rail transits or passenger trains. The purpose of constructing railway bridge other than avoiding obstructions is to create an isolated, uninterrupted means of transportation which is way faster than the normal means.
While steel bridges are generally classified as above, the types can be further described in detail according to their structural system. In other words, they can be classified according to the make up of their load carrying system. Loads can be carried by girder, cables, trusses, and more.
Girder Steel Bridge – can either be done using truss girder or solid web girder. Solid web girder comes in two types: plate girder or box girder. Plate girders are also known as I-beam or H-beams while box girders have shapes of closed four-sided trapezoids. Plate girders are adopted for simply supported spans of less than 50 meters and box girders for continuous spans up to 250 meters. Truss girders are suitable for bridges at span range of 30 meters to 350 meters.
Arch Steel Bridge – also called tied-arch bridge. Like the girder bridge, the main component structure which is the arch can be built using steel trusses or steel girders. Arch bridge relies on strong foundation, preferably reinforced concrete, that restrains transferred compression forces from the giant arch. Arch steel bridges are competitive options for spans of 200 meters to 450 meters
Cable-stayed Steel Bridge – depends on a tower or pylon that extends high where the high-tension cables or tendons that carries the deck are anchored or tied-up. This type of bridges is economical for spans of 150 meters up to over 500 meters. In this type of bridge support system, the cables originate from the top of pylon and runs directly to the girders at intervals appearing like the ribs of a fan. Towers or pylons are reinforced concrete, fabricated structural steel, or combination
Suspension Steel Bridge – The difference between cable-stayed bridge and suspension steel bridge is the arrangement of the cables or stays. In suspension bridge, the cables supporting the deck are suspended vertically from the main cable. The cables are distributed both at the top and bottom making them in right angle with the deck. The main cables that hold the stays runs from tower to tower and deeply anchored at ground at both ends. Suspension bridges are the best solutions for long span bridges.
Advantages of Steel Bridges
Strength and durability - Steel bridges are strong and durable, with a high strength-to-weight ratio. They can withstand heavy loads and harsh weather conditions.
Long span - Steel bridges can span long distances with minimal or without the need for intermediate supports. This makes them suitable for crossing large bodies of water, valleys, and other obstacles.
Speed of construction - Steel bridges can be prefabricated off-site and then assembled on-site. This enables reduction of construction time due to multiple tasks that can take place simultaneously with each other. It also enhances quality and safety due to controlled production environment and parameters.
Low maintenance - Steel bridges require minimal maintenance, as they are resistant to corrosion and deterioration when properly equipped with protection. This makes them cost-effective in the long run especially with the ability of steel to be relocated, replaced, re-used, and re-cycled.
Aesthetically pleasing – Monumental bridges are mostly steel bridges because they can be designed to be aesthetically pleasing, with unique shapes and designs that complement their surroundings.
Areas of Improvement: Steel Bridges
Corrosion - Although steel is highly resistant to corrosion with the aid of protective measures, it can still be affected by rust over time. This can weaken the structure of the bridge and require maintenance.
Thermal expansion - Steel bridges can expand and contract with temperature changes, which can cause stress on the structure. This requires careful design and construction to avoid damage.
Cost – At some project extent, steel bridges can be more expensive than other materials, such as concrete or wood.
Environmental impact - The production of steel requires significant energy and resources, which can have a negative environmental impact.
Expert Touch on Steel Bridges
For any type and size of steel bridge project, working with the right company from the very start is the key. ESC Steel has a global supply capability of heavy structural steel bridge products which are compliant to international standards.
Today’s broad capability and experience of ESC Steel in Steel Bridge Structures resulted from a long and successful journey in challenging and engaging world-wide projects involving multiples kinds of the following: