Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
118 chapter six Life-CyCLe Cost AnALysis The infrastructure report of ASCE states that there are 607,308 bridges in the nation and their average age is 42 years (ASCE 2013). It is estimated that by 2028 more than $20.5 billion will be required annually to eliminate deficient bridges. Among the many factors contributing to the deterioration of existing bridges, corrosion is a critical concern because bridges are constructed with structural steel and reinforcing steel, as shown in Figure 60. In most cases it is unlikely that deteriorating bridges will be replaced with new ones and, therefore, the use of durable materials leading to sustainable structural systems is a primary interest of transportation agencies. As elaborated on in the previous sections, FRP composites have been used for bridge construction for more than two decades with significant ben- efits (e.g., noncorrosiveness). The relatively high costs of FRP composites compared with traditional construction materials often discourage bridge owners from adopting this promising technology. This is valid from a short-term standpoint; however, a different view may be generated if life-cycle costs are associated (a long-term perspective). Transportation agencies therefore may consider the entire expense to be the result of bridge construction with FRP, rather than merely taking into account FRPâs initial material costs. Bridge owners consider many options when planning highway bridges; for example, construction finance, operating strategies, maintenance and rehabilitation policies, and demolition. The life-cycle costs of bridges are defined as the entire financial resources required for the design, erection, opera- tion, maintenance, and disposal of their members. Life-cycle cost analysis is a method that examines detailed expenses incurred from technical and administrative activities. This analysis is a useful means to evaluate budgetary effectiveness on operating bridges. One of the notable benefits in life-cycle cost analysis is that transportation agencies can make a best decision in selecting bridge types accord- ing to a relationship between the expenses and long-term performance of bridges. Once a bridge is designed and constructed, expenses for maintenance and rehabilitation are virtually unavoidable until the bridge is demolished. The best decision, considering as many factors as possible, is thus required at the planning stage. ASTM E917-15 (Standard Practice for Measuring Life-Cycle Costs of Building and Building Systems) is an important reference for bridge engineers to review, although it is not directly related to bridge structures. The following are typical approaches that can be used to model life-cycle costs: â¢ Parametric model: this approach estimates costs based on the use of regression lines constructed with historical data and technical information. The statistically engaged expenses with various parameters will describe the financial background of specific bridge types (Dean 1995). â¢ Analogous model: this method compares costs between two similar products and develops an effective (or representative) cost model (Shield and Young 1991). Expertsâ opinions (e.g., DOT engineers) are a critical factor in this estimation technique. â¢ Detailed model: this is a bottom-up approach suitable for estimating various task levels. This model requires considerable time; however, detailed and accurate cost information is obtainable (Greves and Schreiber 1993; Asiedu and Gu 1998). Model prediction needs to be validated before estimating expected costs throughout a bridgeâs life span. Figure 61 summarizes a cost breakdown for bridge structures. Sensitivity analysis identifies parameters that influence the life-cycle costs of bridges more than other parameters. Ehlen (1999) assessed bridge decks made of three FRP types [i.e., Seeman composite resin infu- sion molding process (SCRIMP), pultruded plank (PP), and wood-core FRP deck (WC)] based on
119 (a) (b) (c) FIGURE 60 Deteriorated bridge members as a result of corrosion (used by permission from Yail J. Kim): (a) steel girders; (b) reinforced concrete deck and supporting steel girders; (c) steel truss elements.
120 a cost classification scheme. The uncertainty of FRP materials was addressed by conducting Monte- Carlo simulations. The total life-cycle costs of the WC deck were comparable with the costs of a conventional reinforced concrete deck, whereas other FRP options resulted in higher life-cycle costs. Hastak and Haplin (2000) presented a case study to compare expenses associated with strengthening bridge columns using steel jackets and FRP-wrapping. Comparison criteria included strength benefits, weight reduction, durability, material properties, construction, aesthetics, transportability, and the ease of installation. Benefit analysis showed that FRP strengthening was 45% more effective than steel jacketing according to the proposed benefit score, whereas FRP costs were 20% higher. The overall costâbenefit ratio of FRP was 21% better than that of steel. Sahirman et al. (2003) examined initial costs for FRP decks using six bridge samples taken from West Virginia and New York. Average costs per square foot varied from $128 to $368, which were higher than those of steel-reinforced concrete decks [i.e., $40/ft2 ($430/m2) was a competitive price target]. Lee et al. (2004) conducted a cost analysis for the Watson Wash Bridge in California. The reinforced concrete girder bridge was 741 ft (226 m) long with 18 spans. Because of corrosion damage and increased traffic load, significant crack- ing and punching shear damage were noticed in the deck. FRP sheets were considered to repair this bridge, in order to recover the load-carrying capacity and to extend service life. Cost analysis was carried out to evaluate the competitiveness of FRP repair against bridge replacement. The costs of FRP repair were expected to be 23% of those of replacement. The cost analysis conducted by Phillips et al. (2005) concerned a GFRP-reinforced concrete deck for the Route 668 Bridge in Virginia, consisting of three spans with a total length of 170 ft (52 m). The installed price of GFRP bars was $6.98/ft2 ($75/m2), which was more than the prices of bare steel [$1.91/ft2 ($21/m2)] and epoxy-coated steel [$2.65/ft2 ($29/m2)]. The higher GFRP cost was anticipated to balance off with long-term rehabilitation expenses for a service life of 75 years. Berg et al. (2006) reported that a 57% cost saving was achieved with FRP-based bridge decks over traditional decks. Kostuk et al. (2006) compared the life-cycle costs of bridge decks reinforced with (1) epoxy- coated steel bars, (2) MMFX (corrosion resistant steel) bars, and (3) GFRP bars. Initial construc- tion, maintenance, and decommissioning costs were taken into consideration over a service life of 100 years. The initial construction costs of the MMFX and GFRP options were 12% and 6% higher than the cost of the epoxy-coated steel case. The MMFX and GFRP maintenance costs were, however, 101% and 24% of the epoxy-coated barâs cost. The total costs of the MMFX- and GFRP-based decks were 110% and 89% relative to the deck with epoxy-coated steel bars. Nishizaki (2009) reported the initial and maintenance costs of five bridges in Japan. The initial costs of FRP superstructure were 38% higher than those of conventional prestressed concrete superstructure. The maintenance costs of the FRP superstructure for 30, 50, and 100 years were, however, 75.5%, 76.5%, 71.3% lower than the FIGURE 61 Cost breakdown for bridge structure.
121 costs of the conventional one, respectively. The primary reasons for reducing the life-cycle costs of the FRP superstructure were low installation costs associated with the FRPâs light weight and durable performance (e.g., no corrosion). Eamon et al. (2012) studied the affordability of CFRP reinforcement in bridge construction. Two- stage, life-cycle cost analyses (deterministic and probabilistic) were conducted to estimate expenses, which resulted from various bridge types. Traffic volume was an important parameter influencing the life-cycle costs. Accordingly, the use of CFRP reinforcement for bridges subjected to high traf- fic volume showed a significant cost reduction. The bridges with I-girders prestressed with CFRP tendons exhibited better life-cycle costs than those with box girders with CFRP. Kawahara et al. (2012) evaluated the economic competitiveness of FRP decks for short-span bridges. Several cost items were taken into account, namely materials, installation labor, fuel, equip- ment rental, demolition, disposal, traffic delay, and environment. The total costs of the FRP decks were estimated to be $113/ft2 ($1,216/m2) with a 2% discount rate. Mara et al. (2014) carried out a com- prehensive cost analysis for a bridge built in 1948 in Sweden. The bridge had a deteriorated reinforced concrete deck; however, its steel girders were still in good condition. Two options were considered: (1) replacement of the bridge superstructure and (2) replacement of the existing deck with an FRP deck. The life-cycle cost analysis included initial, maintenance and repair, social, environmental, and demolition expenses. The initial costs consisted of material, manufacturing, installation, and transpor- tation components. The social and environmental aspects were based on traffic disturbance, pollutants, and carbon dioxide emissions. The disposal costs encompassed landfill and recycling fees. The FRP deck option was 45% less expensive than the replacement option. Moruza et al. (2017) calculated the costs of CFRP-prestressed concrete piles for the Nimmo Parkway Bridge in Virginia. It was expected that the CFRP-based piles would address concerns on corrosion damage that occurs in conventional steel-prestressed concrete piles in a brackish environ- ment. The bid cost of the CFRP piles [$360.71/ft ($1,183/m)] was 4.15 times more than that of the conventional piles [$87.01/ft ($285/m)]. The life-cycle analysis indicated that the costs of the CFRP piles could be as low as 71% of those of the conventional piles.