Steel, Our Most Sustainable Material. Steel vs. Concrete White Paper. Bridge To Build 4 Bridges. Connect with Us. First Last. Enter Email Confirm Email. Over a year period, deferring maintenance of bridges and highways can cost three times as much as preventative repairs. The backlog also increases safety risks, hinders economic prosperity and significantly burdens taxpayers. Preservation efforts can also extend the expected service life of a road for an additional 18 years, preventing the need for major reconstruction or replacement.
Repair work on roads and bridges generates 16 percent more jobs than construction of new bridges and roads. For all these reasons, Congress has repeatedly declared the condition and safety of our bridges to be of national significance. However, the current federal program does not ensure transportation agencies have enough money and accountability to get the job done. Transportation for America is an advocacy organization made up of local, regional and state leaders who envision a transportation system that safely, affordably and conveniently connects people of all means and ability to jobs, services, and opportunity through multiple modes of travel.
Yesterday we had some bad news to deliver: EVs won't be a driving force for equity. Overview Despite billions of dollars in annual federal, state and local funds directed toward the maintenance of existing bridges, 68, bridges — representing more than 11 percent of total highway bridges in the U. The Tension Between Fixing the Old and Building the New In recent years, most transportation agencies have delayed needed repairs and maintenance while focusing their energy on new construction.
At just over miles in length, this is the longest bridge in the world, connecting the major business and cultural centers of Beijing and Shanghai in China. The high-speed rail line that runs over it cuts travel time between the two business hubs by more than 50 percent.
This makes it easier for people to connect between the two cities, which is expected to increase business activity and tourism between them for years to come. This plus-mile sea structure is a system made up of three cable-stayed bridges, an undersea tunnel, and three artificial islands. When this structure is completed later this year, it will reduce travel time between Hong Kong and Macao from 4.
It is expected to increase tourism spending because it makes it easier for visitors to see more of China in the same amount of time. This structure is the primary connector between Malaysia and Singapore. Despite some tension between these two countries, they enjoy a mutually beneficial business relationship. Malaysia supplies commodities, cheap labor, and abundant land to Singapore.
Singapore invests a significant amount of capital in Malaysia, with more than half the visitors from each country arriving via this bridge.
This almost mile-long structure carries vehicular and railroad traffic on a bridge, tunnel, and artificial island between the northern European business powerhouses of Sweden and Denmark. It links together Copenhagen and Malmo, fostering economic growth and cooperation between the two cities. Another interesting feature: The bridge carries utility infrastructure, including a critical cable that is the primary transmitter of internet data between Central Europe and Sweden and Finland.
In return, Sweden has experienced a significant reduction in unemployment and related benefit payouts. It took the record, by almost four miles, from the Lake Pontchartrain Causeway in Louisiana. The bridge makes it simple for people living in Qingdao to work in Huangdao. The money they bring home as wages is expected to spur business growth and development in Qingdao. Bridges are a key driver of economic activity.
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Mexicali has high seismic activity and the structure needs to withstand the seismic loads with good lateral displacement performance. The suspension bridge located at Tacoma Narrows consists of two main structural steel towers supporting a main cable and the main deck is stiffened by two steel girders. A total length of feet m and a span of feet m were covered. It was inaugurated in and became one of the largest bridges in the world.
The main feature of this bridge was the dramatically collapse of the main deck after a few months of inauguration, due to the oscillating movement with the action of the wind flow.
These forces were considered for structural design; however, with a much slower wind velocity, the vibration movement increased with enough speed to make the structure collapse. Looking into Figure 9 , the oscillating movements of the bridge can be observed. Tacoma narrows suspension bridge, under aerodynamic vibrations [ 10 ]. Under research, the main reason for the collapse of the bridge was the concept of resonance, which means, a range of coincidence between the natural frequency of the structure and the frequency of wind thrust loads.
The concept of vibration and resonance is not visible easily and many factors influenced on the event: Very high slenderness ratio of the bridge. After this event, studies on aerodynamics and aero-elasticity topics in the structures increased significantly, developing procedures to simulate these events on structures, including bridges of very large spans. The cable-stayed bridge located in Veracruz, Mexico consists of two main reinforced concrete towers that support the main deck with cable tensors and the slab stiffened by two reinforced concrete girders.
The structure has a total length of feet m and a span length of feet m. Figure 10 shows an overview of the structure. Coatzacoalcos II cable-stayed bridge overview [ 11 ]. The bridge consists of 15 supports, 14 sections and the main structure. The towers and secondary columns are made of reinforced concrete; the main girder is shaped like a drawer with reinforced concrete and the cable tensors supporting the main deck are made of structural steel.
It was inaugurated in and considered one of the largest structures in Mexico. This cable-stayed bridge is located in the city of Jerusalem and has a total span of feet m. The bridge aims to help the city light trail system and the structure consists of a main tower connecting the structural steel slab using 70 steel cables and reinforced concrete supports. The main feature of this bridge belongs to the architecture and geometry. It was designed by Santiago Calatrava, a world-renowned architect and engineer, and the user can recognize the structure as an unconventional bridge.
As shown in Figure 11 , we can see the special geometry of the main tower and each of the cable tensors, showing a harp shape.
In addition, the main deck has a curved form. Jerusalem cable-stayed bridge [ 12 ]. The structure was inaugurated in marking a symbol in the city of Jerusalem. Due to the great height of the main tower and its harp-shaped geometry, the bridge can be appreciated from any place of the city. Due the large number of variables on the conceptual design of a structure, there is no special formula for determining the best option of a bridge.
Many variables come into play, from the experience of the engineers and architects, to the specific needs of the place, such as topography, soil characteristics and materials availability.
There are several models to describe the general process of design, built, operation and maintenance of a bridge in a general way. One of the most compact flowcharts was proposed by Addis [ 13 ], shown in Figure Model of the bridge design process [ 13 ].
The process for any bridge design consists of input data, regulations, design process and results, explained as follows:. All the information required to start the design process of any bridges is placed in this category and can be classified as public and personal.
Public information refers to all existing bibliography like books, magazines, publications and software available in the industry. These references should include all topics related to bridges such as material properties, construction process, architectural design and structural design. Personal information refers to the experience acquired by engineers, architects and companies dedicated to the construction industry.
All the rules, restrictions and limitations imposed on the process of creating and design fall into this category. All the information processed to be able to build any bridge is placed in this category and can be divided into the description and justification of the results. The description refers to all drawings, including architecture, structural, facilities and roads. The justification refers to all technical information that supports the drawings, from structural engineering to budgets.
In the central part of the flowchart is located the bridge design process, where the input data, regulations and results are interacting together. The design of a bridge implies the imagination of engineers and architects to solve the problem statement, use of the previous knowledge to select the best geometry option and justify the solution with the required calculations.
The flowchart process applies to any type of bridge and can be simple or complicated as required. If we want a successful development of any bridge, there must be a balance between the variables described in Figure Another point regarding the design process of bridge is the selection of the appropriate material and geometry.
Span lengths for various bridge types [ 3 ]. The recommended span range is related directly with budget challenges of each project. As an example, consider the construction of m span length structure which can be developed using a concrete slab and concrete girder, according the recommendations of Table 1. Performing a structural and design of the proposed bridge, we can find the minimum size for the concrete slab and the concrete girders; considering concrete slab, the thickness to support m of span will require a great depth in slab and therefore, a large amount of concrete material will be required; therefore, if we use girders, the amount of material will be less in comparison.
Depending the span range and geometry of the project, the best economical option of bridge selection will be the efficient use of each material mechanical properties, stress-strain relationship and the characteristics of the site. Bridges with steel material can enter into any of each three categories described on Section 3. Depending on the type of steel to be used, yielding allowable stress of the structural steel can vary between 36 ksi MPa and 70 ksi MPa.
Within the steel bridges, the most common geometries are: Straight truss, variable geometry truss or arc-shaped trusses. A steel truss bridge is shown in Figure 13 , with straight truss at the center of the span and variable height near the column supports.
The incremental height on the truss near the columns occurs due an increment axial stress in each truss member. The foundation, anchorage and check slab are made of reinforcement concrete; piers can be made of steel or reinforced concrete, depending the site characteristics. Steel truss bridges for long span lengths. Steel cable-stayed bridge and suspension bridge with general geometry are shown in Figures 14 and Both structures have a main tower supporting the main cables; the difference between these two bridges is the arrangement of the cables.
Cable-stayed bridges use a series of cables to support the deck connected directly with the main tower; when the suspension bridges use a main cable supported between the towers and a series of secondary cables supporting the main deck. Steel cable-stayed bridges for long span lengths. Suspension bridges for long span lengths. For both cable-stayed and suspension bridges, the main deck has a high slender ratio due the long span covered and need additional structural elements to increase the stiffness.
Trusses are commonly used to stiff the main deck and allow the wind to flow through these structural elements. Tension stress is developed by the cables, which are the optimal geometry giving a capacity to increase the span length.
Looking into Table 1 , for span lengths higher than ft. Bridges supported by steel girders are shown in Figure The main deck is the combination of the concrete slab, a wide variety of structural steel beam, piers and anchorage geometries. The steel girders can be simply or continuous beams using hot rolled sections or developed by steel plates.
Steel bridges for short and medium span lengths. Steel girders are working with bending stresses, which usually requires more material if it is compared with truss elements. However, according to Table 1 , these types of bridges can be economical competitive for short and medium span lengths due its easy construction procedures and less time-consuming during installation of the girders.
Also, these girders have a great stiffness compared with truss bridges, reducing vibration responses produced by traffic and wind flow. Concrete bridges can be categorized as below or directly on the main structure, as described on Section 3. According to the American Concrete Institute A. There are many advantages of concrete material compared with structural steel, including its capacity to support compression stresses and the availability on construction industry.
Tension stresses are carried out by the reinforcement, making a composite structural material. Within the reinforced, pre-stressed and post-stressed concrete bridges, we can find the following geometries: Arc-shaped concrete below the main deck. Arc-shaped concrete bridge is shown in Figure 17 , which consists of an arc shaped element below all the structure, supporting the piers and the main deck.
The concrete arch-shaped element is working mainly by compression stress due its curvature, taking advantage of the material capacity. Piers are working as flexure-compression stress and the main deck is working as shear and bending stress.
According to Table 1 , the recommended span length for structural and economical purposes is — ft. Concrete bridges for medium span lengths. The principal feature of pre-stressed concrete girders against simply reinforced concrete girders is the increase of the span length without the need of increases the beam height, taking advantage of the effective inertia and providing greater stiffness to the bridge. This geometry type is widely used to build bridges across the cities, highways or interstate roads.
According to Table 2 , there are a wide variety of recommended girders, considering precast pre-stressed or cast-in-place post-stressed concrete with different cross-sectional geometries, taking account the clear span to cover and the material mechanical properties [ 16 ]. Span lengths for various concrete bridge types [ 16 ]. Each construction procedure have its own benefits; for example, precast pre-stressed girders have the advantage of less time installation consuming and minimum frameworks to use compared with cast-in-place post-stressed girders or cast-in-place slabs, but only can be performed a simple cross-sectional area; by the other hand, cast-in place girders can have any desired cross-sectional geometry, which is adaptable and commonly required on any project.
A concrete girder bridge is shown in Figure 18 , considering few types of construction procedures and geometries, using the same piers and anchorage. Concrete bridges for short span lengths. Cast-in-place reinforced concrete slab or T-beams can be used for small span lengths, as recommended in Table 1 , and precast pre-stressed I-beams are used for spans lower than ft. All these types of girders works for bending stress, which limits the span range; however, due its easy construction procedures, are widely used for most common bridges.
Most bridges use structural steel and concrete as main materials. However, there are other materials that can help to complement the structure, depending on some features: Wooden bridges, used for small crosswalks or where span lengths are short and loads are low. Stainless steel, where it replaces carbon steel parts of the bridge, increasing resistance to humidity and environmental factors. Carbon fibers, used as rehabilitation process and perform capacity improvement of existing structural elements.
The general process for the development of any bridge are described in the flow chart showed in Figure 12 and includes planning, design, operation and maintenance procedures.
To ensure the useful life of the bridge, a maintenance plan must be established, depending on the physical and environmental factors.
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