More efficient and economical designs are needed to replace or retrofit the nation’s sub-standard bridges.
By Roumen V. Mladjov, S.E., P.E.
Every year in January, the National Bridge Inventory publishes data on the condition of the highway system. It contains information on the total number of bridges and the total bridge deck area per state and the summary for the country including “sub-standard” (structurally deficient or functionally obsolete) bridges (Reference 1). An excerpt of these reports from years 1995 to 2015 is shown in Table 1.
According to the U.S. Department of Transportation, at the end of 2015 there were 661,845 highway bridges in the country with a total bridge deck area of 369,109,088 square meters. More than 142,900 of these bridges, with a bridge deck area of 99,809,000 square meters, are sub-standard; this constitutes 27 percent of all bridges (based on percentage of deck areas). The area of sub-standard bridges is more than 1.07 billion square feet!
The situation is even worse in specific states. For example, in California the deficient bridge area is 33.2 percent; in Pennsylvania, 42.2 percent; in Massachusetts, 57.2 percent; in Rhode Island, 57.4 percent; in New York State, 58.8 percent; and in the District of Columbia, 63.8 percent. In several states, sub-standard bridge structures constitute more than 50 percent of all bridges. This is an alarming situation that is absolutely unacceptable for the U.S. A well-developed and maintained transportation system is vital for the country’s economy.
While all components of the transportation infrastructure are important, improvement of sub-standard bridges is critical. A failure or even serious damage to a bridge may cost lives and will close a highway for a long period of time.
The current poor condition of our bridge infrastructure is not an isolated case. Until the 1980s, American bridge engineering led the way in design and construction of the best and longest spans and most efficient bridges (Reference 2). All professionals around the world looked to American engineers to learn how to build good bridges. It is not the same any longer, and we are lagging behind in the competition for the best bridges. This fact, combined with insufficient funding and less than optimal planning and management, has contributed to the current poor condition of our bridges.
What should be done to improve the situation and what are the options for such improvement?
First option — The simplest solution is to continue without any change. While there is some small improvement in the numbers (see Table 1), the recent yearly improvement is less than 0.41 percent; it is negligible compared with the need. For the last 20 years, from 1995 to 2015, the average yearly improvement is 0.42 percent for the country, 0.24 percent for California, and 1.1 percent for New York State. Assuming that the deterioration rate for bridges does not increase, the current pace of improvement will require 66 years to replace or retrofit the sub-standard bridges in the country!
In addition, during these 66 years more bridges will end up becoming sub-standard. The bridges that are today in relatively good condition but already 40 or 50 years old, will be 100 to 115 years old at the end of the 66-year period with a good chance to be added to the sub-standard category. With these newly deteriorated bridges, the overall recovery period will extend even further (78 years at the current yearly pace of improvement). Obviously, this is not a viable solution.
Second option — Increase funding significantly for bridge recovery, dedicating more funding every year until the sub-standard bridges become a very small percentage of the total. The current situation is worse than critical. This is well known, and politicians are raising the issue of deteriorating infrastructure and the need for its improvement. Unfortunately, politicians’ solution seems to be simply, “We need more money to fix the infrastructure!”
It is important to clarify that “transportation infrastructure” includes roads (highway and railway), the bridges for these roads, necessary new roads and bridges, as well as maintenance, repair, and replacement of existing roads and bridges, airports, and marine ports. This article reviews only the problem with the necessary replacement or retrofitting of sub-standard highway bridges.
If the budget could allocate unlimited funding specifically for fixing sub-standard bridges, this would be the easiest solution. However, even for a rich country like the U.S., multiple necessities do not allow unlimited funding for any single issue. As 99,800,000 square meters of bridges cannot be replaced or retrofitted in one year, let us consider selecting a very aggressive period of five years for the recovery in order to allow for necessary organizing, planning, and providing structural design for all sub-standard bridges. A recovery in five years will require an average of $85 billion per year, or altogether $425 billion (see Table 2 below).
However, despite the desire of federal and local administrations to improve the infrastructure, considering all the other important items on the budget, allocating such amounts in so short a period is unrealistic.
A future substantial improvement of the economy might allow a significant increase of funding for the infrastructure in the budget compared with the current year. If the administration would like to reduce the unacceptable period of 66 years for recovery to 10 or 15 years, that would require allocating significantly larger amounts to this issue in each yearly budget. Even if such a dramatic increase could be delivered, neither the design nor the bridge construction capacity could meet such a steep increase in demand all at once.
Third option — Increase the efficiency of new replacement structures in order to build more bridges (bridge deck areas) with the same amount of funding.
One of the common negative impacts on infrastructure improvement is the use of inefficient structures. It is time to realize that a bridge is not better when more steel, concrete, or millions of dollars are expended for its construction; a bridge is more efficient when it functions as designed with less steel, concrete, and millions of dollars! The number of sub-standard bridges will not be reduced significantly if transportation departments continue to select and build very inefficient structures.
One striking example of an inefficient structure is the recently competed replacement of the almost 80-year-old East Span of the San Francisco-Oakland Bay Bridge in California. The 195,000-square-meter new structure is comprised primarily of a concrete segmental bridge (Skyway) and a steel self-anchored suspension bridge. It took 14 years to build at a cost of $6.5 billion, which equates to $33,330 per square meter. The average unit cost for bridges with similar spans is about $3,500 per square meter!
While this new bridge is highly promoted, a simple analysis shows that the new construction is neither efficient nor economical. For the mostly concrete structure making up about half the length of the original bridge, more steel has been used than the steel needed for the full length of the original bridge in 1936. Although transportation authorities consider the project a great achievement, this does not seem to be a reasonable evaluation. It is time our engineers consider constructive criticism, especially for projects of this magnitude, so as to encourage better and more efficient structures.
Each bridge is different because its cost and the quantity of construction materials depend on its total length, span lengths, width, structural type, location, etc. For this reason it is difficult to compare the efficiency of different bridges. Nevertheless, an objective method for comparing bridges has been developed using efficiency coefficients (Reference 3). These coefficients account for the average span length and the bridge deck area, allowing comparison of cost and material efficiency for structures with different span lengths, and can serve as a useful tool during the concept selection process.
It should be noted that the efficiency coefficient method is based on the final cost (at delivery of the bridge structure) and on the steel, concrete, and time needed for construction, but does not account for management costs during operation of the bridge. Detailed information for complete life-cycle cost of bridges including management costs, assessment of deterioration, necessary maintenance, and repair costs is provided by Bojidar Yanev in Bridge Management (Reference 4).
Unfortunately, when checking the efficiency and economy of bridges built in the country during the last 15 years, one can see that the efficiency for most is worse than the average worldwide efficiency for similar structures. Even if most new bridges cannot achieve the highest levels of efficiency, if they are at least closer to these levels that would increase the rate of improvement four to five times. The data in Efficiency and Economy for Building and Bridge Structures (Reference 3) provide a good guidance for selecting the most efficient structural system for a specific case; Table 4: Summary of Bridge Steel, Concrete and Cost Efficiency lists the efficiency margins for different bridge systems.
Using more efficient bridges will help correct the dire situation with sub-standard bridges faster; however, this approach cannot solve the problem by itself.
Fourth option — The options above show that providing necessary funding is only part of the solution. Therefore, it is critical to design and build efficient bridges. Using highly efficient economic structures is essential for more effective use of limited funding and for faster improvement of the overall poor condition of the bridge infrastructure in the country. To achieve this goal, the best solution is to allocate more money for more efficient structures.
Length of recovery period
Based on U.S. Department of Transportation data (Table 1), the current pace of improvement (0.41 percent) will require 66 years to fix sub-standard bridges if there were no additional deterioration. Even considering only a very low, 0.1 percent of yearly deterioration for the estimated 66 years, the currently non-deficient structures (of about 269,300,000 square meters) will add 269,300 square meters of new bridge area per year to the sub-standard quantity. The compound number for 66 years is an additional 17,773,800 square meters of sub-standard bridges that will also need to be replaced or retrofitted in parallel with fixing the current sub-standard bridges. So, the total quantity for fixing becomes:
current 99,809,248 m² + additional 17,773,800 m² = 117,583,048 m²
This increase would bring the length of the recovery period to 78 years at the current pace of improvement! Again, an important reminder that the funding for the recovery period considered here and in Table 2 are just for the cost of the bridges at delivery and do not include the necessary funding for regular maintenance and repair of existing structures. For the complete life-cycle cost of bridges see Yanev’s Bridge Management (Reference 4).
These 78 years needed for recovery constitute a very long and absolutely unacceptable period of time. It is obvious that shortening the recovery period will have a significant positive impact on the process.
The results of analyzing the necessary funding, total and yearly, for different target recovery periods are shown in Table 2. This time-cost analysis is based on 0.1 percent additional deterioration of bridges per year and a unit replacement/retrofitting cost of $4,200 per square meter, or an 80 percent “near high-efficiency performance.” The 100 percent high-efficiency performance unit cost is $3,500 per square meter for average bridge spans of 70 to 150 meters (Reference 3).
It is obvious that using more efficient and economical bridges will require smaller funding amounts. This means that the goal should be to design and build replacement structures at the highest possible engineering level (technically, structurally, and economically). As it cannot be expected to start building all new structures at the highest engineering level immediately, it would be more reasonable to base the estimate of unit cost at 80 percent of the highest level.
In addition to the need of using more efficient and economical bridges, we should also consider preservation of the environment. If the administration is serious about building greener, it should encourage using the minimum possible construction materials for a structure. Regardless of whether a bridge is predominantly a concrete or steel structure, the production and construction of each cubic meter of concrete or ton of steel has a significant carbon footprint. Therefore, reducing the quantities of structural materials will make a significant contribution to preservation of the environment.
Conclusions and recommendations
The current pace of improving the poor condition of highway bridges is not acceptable and obviously there is a need for a significant change in the approach. The analysis above clearly demonstrates the importance of designing and building highly efficient bridges if transportation authorities and engineers are seriously interested in fixing the problem with substandard bridges.
While increased funding is a question of budget priorities and economic possibility, using bridges at the highest technical level of design and construction is a question of education, knowledge, sufficient information, and selection capability — important qualities required from the transportation authorities and engineers involved in the process. Such an approach will demand a significant revision of the established methods of planning, designing, and managing the process, but there is no other option if we want to solve the deterioration of our bridge infrastructure in a reasonable timeframe.
It is necessary to select and use a target recovery period of about 15 years, and to increase the yearly funding for replacement and retrofitting of sub-standard bridges in combination with using only highly efficient and economic bridge projects. This yearly funding should be dedicated specifically for resolving the problem with sub-standard bridges. It should be recommended to increase the design and construction capacity to be able to meet the growing demand for more new/replacement bridges, for retrofitting and strengthening existing structurally deficient bridges.
Transportation authorities should approve for construction only projects with efficiency and economy within 10 to 15 percent of the highest achievements for the specific bridge type. If the new structure is a replacement of an old existing bridge, such replacement should be approved only based on analysis that the new structure is more efficient than the existing one and that strengthening/retrofitting of the existing structure is not possible or is less efficient than a complete replacement. Design (or design-build) competitions for projects with estimated costs exceeding $30 million (a four-lane, two-shoulder bridge longer than 300 meters) should be recommended.
Transportation authorities should prioritize retrofitting and strengthening existing bridges instead of replacing sub-standard structures with new ones. This will provide savings of cost, construction time, and construction materials, and should be recommended whenever technically and economically possible. Using retrofit versus complete replacement also is a greener approach as it uses fewer new materials.
Whenever possible, use efficient methods of retrofitting bridge structures, such as replacing existing concrete decks with lightweight construction decks (steel orthotropic or sandwich plate systems), or changing the static system from simple supports to continuous supports, and other rational methods (see Reference 5). Existing steel bridges are more appropriate for retrofitting and upgrading. The bridge system and construction method should also be considered because the minimum construction materials do not always deliver the most economical solution.
Transportation authorities should introduce a system that will motivate transportation departments and all their personnel, from the highest manager to the regular staff members, to strive for more efficient and economical bridges (in cost, construction time, and main structural materials); similar motivation should be introduced for general contractors awarded project construction.
The use of inefficient new structures is an enormous problem, and the first step toward resolving it is to recognize that such a problem exists and that it should be dealt with. The current poor condition of our bridges is not acceptable for American bridge engineering. American engineers, once world leaders in bridges for 150 years until the 1980s, should not accept being left behind in the development of new, more efficient structures. We should not be satisfied with middling and low levels in efficient, techno-economic constructions. To recover and to regain the highest levels will not be easy. It will require hard efforts and determination, but we have all that is necessary to succeed:
- a great tradition and experience in building excellent bridges;
- best computer software and hardware;
- high level of construction materials, production, and construction technologies;
- excellent engineering education and training;
- large pool of competent engineers; and
- traditional innovativeness and competitiveness.
With the necessary efforts and persistence, our engineers can revive the art of American bridge engineering that produced the Brooklyn Bridge, the George Washington Bridge, the Golden Gate Bridge, the original 1936 San Francisco-Oakland Bay Bridge, and the Verrazano Narrows Bridge and build great bridges once again.
Roumen V. Mladjov, P.E., S.E., has more than 52 years of experience in structural and bridge engineering and in construction management. He can be reached at firstname.lastname@example.org.
1) Total Deficient bridges U.S., 1995 to 2015, National Bridge Inventory, U.S. Department of Transportation, Federal Highway Administration.
2) Mladjov, R., Long-Span Bridges and the Art of American Bridge Engineering, presentation at SEAONC 2009 Convention, San Diego.
3) Mladjov, R., Efficiency and Economy for Building and Bridge Structures, Part I and Part II, Structure magazine, May and June 2016.
4) Yanev, B., Bridge Management, John Wiley & Sons, Inc., New Jersey, 2007.
5) Mladjov, R., Efficient Methods for Upgrading/Reinforcing Existing Old Bridges, Structure magazine, October 2015.