Recently, a main concern in bridge engineering had been the rehabilitation and reconstruction of deteriorated bridge members. Accelerated bridge

construction (ABC) can overcome the shortcomings of traditional construction methods, which are typically labor-intensive and time-consuming.

ABC can minimize disruption to public communities and save indirect costs

associated with detouring traff c. Concrete members prefabricated in factory are often utilized in ABC, where the connections of prefabricated concrete members have been extensively studied in recent years

As alternatives to

prefabricated concrete members, bridge superstructures entirely made of

advanced composites or f ber-reinforced polymer (FRP) are also potential

solutions to ABC, due to the following advantages of the materials:

• Light weight – FRP superstructures weigh about 25% or less of a conventional reinforced concrete superstructure. Therefore, FRP composites reduce the dead load of a superstructure signif cantly. Reduction of dead

load can increase the rating factor when capacity rating of a bridge is

performed. Since capacity rating of a bridge is proportional to the rating

factor, the load carrying capacity of a superstructure reconstructed or

rehabilitated with FRP composites may be re-rated to its original design

load.

• Durability – Corrosion of steel reinforcement in concrete is the leading

cause of deterioration of conventional concrete superstructures. Steel

reinforcement is susceptible to oxidation when exposed to deicing salt

and other chlorides. Compared to conventional materials, FRP composites provide high resistance to corrosion. Therefore, less maintenance

may be required for FRP superstructures.

• Rapid Installation – Factory fabrication and modular construction

of FRP superstructures allows rapid installation on construction sites.

Installation of FRP superstructures in bridges with high traffc volume

can substantially reduce the construction time of superstructures to half

when compared to the labor-intensive and time-consuming construction process of a conventional cast-in-place concrete superstructure. As

a result, disruption to communities, and indirect costs associated with

detouring traff c, can be minimized by FRP superstructures.

• High Specifc Stiffness/Strength – Advanced composites offer the advantages of high stiffness-to-weight ratios (specif c stiffness) and strengthto-weight ratios (specif c strength) when compared to conventional construction materials. Therefore, they can provide good combinations of

strength/stiffness and weight for bridge superstructures.

• Lower Life-cycle Cost – A life-cycle cost usually consists of an initial

construction cost and maintenance cost. Since FRP superstructures are

expected to have good long-term durability and require little maintenance, they can be more cost-effective in service life than bridge superstructures with reinforced concrete** Structural analysis and design **

When designing all-composite bridge superstructures, designers can tailor

FRP materials and structural conf gurations of superstructures to meet

design requirements. As an example, the design of a two-lane FRP superstructure is discussed in this section. The FRP superstructure is now in

service in South Korea, and has a sandwich construction (Ji et al., 2010).

Corrugated cores are sandwiched between top facing and bottom facing.

The sandwich construction in this study can reduce weight and provide

signifcant stiffness in the selected direction. The discussion in this section includes design requirements, material selection, preliminary design

based on design requirements, and detailed design of the cross-section.

** Design requirements **

The design of FRP superstructures is stiffness-oriented (Federal Highway

Administration, 2011). Although no offcial specifcations are available for

the deﬂ ection limit of FRP superstructures, general design guidelines for

conventional bridge superstructures are provided by the AASHTO LRFD

Bridge Design Specif cations (AASHTO, 2010). The AASHTO’s requirement for the stiffness of bridge superstructures with conventional materials is that the maximum deﬂ ection due to vehicular live loads should not

exceed 1/800 of the bridge span length.

The criterion above was used to design the FRP superstructure in this

chapter. The FRP superstructure in this chapter was expected to be in service in South Korea. As a result, the design vehicular live load in this study

6.1 DB-24 truck load and tire contact areas.

was consistent with Ministry of Construction and Transportation (MOCT)

(2000a). As for the strength requirements, the maximum strain under service

load should be limited to 20% of the ultimate strain. Laminate failure prediction was based on the f rst-ply failure criterion.

For a simply-supported bridge with span less than 44 m, the standard

design truck load DB-24 produces higher moment and deﬂ ection than the

design lane load (MOCT, 2000a). A DB-24 truck load is approximately

1.3 times heavier than the HS-20 truck load specif ed in AASHTO LRFD

Bridge Design Specif cations (2010). One standard design truck load DB-24

with tire contact areas, as shown in Fig. 6.1 (MOCT, 2000b), was assumed to

be the design live load. The weight of a DB-24 truck is 423 kN.

** Materials and lamina design **

Superstructures with FRP composites including the one in this study can

be characterized at three levels: the lamina level (a single ply), the laminate

level (multiple plies), and the structural level (Altenbach et al., 2004). This

section focuses on the materials and lamina design. The design at the latter

two levels will be addressed in the following sections.

The primary constituents of FRP composites are f bers and resin matrices.

In FRP bridge superstructures, glass f bers are mainly used as fber reinforcement, and polyester or vinyl ester is the most widely used resin matrix.

Their combinations can be the most cost-effective in current practice. In this

study, E-glass f bers and vinyl ester resin were chosen as the main constituents for the all-FRP superstructure for ABC. Their material properties are

given in Table 6.1 (Ji et al., 2010).

**Properties of constituent materials **

Table 6.1 Properties of constituent materials

Material E (GPa) G (GPa) υ ρ (kN/m3)

E-glass fiber 72.4 27.6 0.22 25.4

Vinyl ester resin 3.91 1.38 0.37 12.4

E is the Young’s modulus; G is the shear modulus; υ is the Poisson’s ratios; ρ is

the density.

To design a superstructure with FRP composites, it is necessary to know

the mechanical properties of a single ply or a lamina made of fber reinforcement and resin matrix. The properties of a lamina with unidirectional

fbers can be predicted from properties of f bers and resin matrix according to micro-mechanics models based on several simple rules of mixtures.

Most calculations about the properties of a unidirectional lamina depend on

the volume fraction of f bers and resin matrix. The f ber and matrix volume

fractions, Vf and Vm, respectively, for a unidirectional lamina based on their

weight fractions and densities are calculated in Equation

where w

f and wm are the weight fractions of f bers and resin matrix, ρf and ρm

are the densities of f bers and resin matrix.

The mechanical properties of a unidirectional lamina with known fber

and matrix properties and their volume fractions can be calculated by simple rules of mixtures as shown in Equations

where η0 is the eff ciency factor of f bers – for unidirectional fbers, η0 is

equal to 1.0; Ef and Em are the Young’s moduli of f bers and resin matrix,

respectively; Gf and Gm are the shear moduli of f bers and resin

matrix, respectively, and; υf and υm are the Poisson’s ratios of f bers and resin

matrix, respectively.