- Open Access
Comparison of Totally Prefabricated Bridge Substructure Designed According to Korea Highway Bridge Design (KHBD) and AASHTO-LRFD
© The Author(s) 2013
- Received: 10 November 2012
- Accepted: 8 August 2013
- Published: 6 December 2013
The purpose of this study was to investigate the design comparison of totally prefabricated bridge substructure system. Prefabricated bridge substructure systems are a relatively new and versatile alternative in substructure design that can offer numerous benefits. The system can reduce the work load at a construction site and can result in shorter construction periods. The prefabricated bridge substructures are designed by the methods of Korea Highway Bridge Code (KHBD) and load and resistance factor design (AASHTO-LRFD). For the design, the KHBD with DB-24 and DL-24 live loads is used. This study evaluates the design method of KHBD (2005) and AASHTO-LRFD (2007) for totally prefabricated bridge substructure systems. The computer program, reinforced concrete analysis in higher evaluation system technology was used for the analysis of reinforced concrete structures. A bonded tendon element is used based on the finite element method, and can represent the interaction between the tendon and concrete of a prestressed concrete member. A joint element is used in order to predict the inelastic behaviors of segmental joints. This study documents the design comparison of totally prefabricated bridge substructure and presents conclusions and design recommendations based on the analytical findings.
- design comparison
- prefabricated bridge substructure
- construction periods
- design method
- computer program
Recently, various studies have been carried out abroad on the inelastic behavior and performance of precast segmental bridge columns. Precast segmental construction of concrete bridge columns is a method in which bridge columns are segmentally prefabricated off site and erected on site typically with post-tensioning (Hewes 2002; Cheng 2008; Wang et al. 2008; Yamashita and Sanders 2009; Dawood et al. 2012).
The use of precast segmental construction for concrete bridges has increased in recent years due to the demand for shorter construction periods and the desire for innovative designs that yield safe, economical and efficient structures. A shortened construction time, in turn, leads to important safety and economic advantages when traffic disruption or rerouting is necessary (Billington et al. 2001; Ou et al. 2007; Murla-Vila et al. 2012; EIGawady and Dawood 2012).
Precasting allows for an increased use of high performance concrete in bridge substructures, thus improving durability. High performance concrete may be used more consistently with higher quality control in a precasting plant. In addition, the greater compressive strength of the high performance concrete is utilized to reduce the handling weight and dead load of the prefabricated bridge substructure units, thus facilitating construction (Billington and Yoon 2004; Rouse 2004; Chou and Chen 2006; Xiao et al. 2012). However, during the same period, little attention has been given to the design comparison of totally prefabricated bridge substructure. The design of a prefabricated bridge substructure, like most any other civil engineering project, is dependent on certain standards and criteria.
In this study, investigation and comparisons using codes of practices for totally prefabricated bridge substructure in Korea is done. The prefabricated bridge substructures are designed by the methods of present design [Korea highway bridge code (KHBD) 2005] and load and resistance factor design (LRFD) (AASHTO 2007). The AASHTO-LRFD has been chosen as an alternative to KHBD in design of prefabricated bridge substructure. The AASHTO Standard Specification has been accepted by many countries as the general code by which bridges should be designed.
The LRFD method has a number of advantages. It provides a more rational approach to design. Probability theory is used to establish an acceptable margin of safety based on the variability of anticipated loads and member strength.
This study evaluates the present design method of KHBD (2005) and AASHTO-LRFD (2007) for totally prefabricated bridge substructure system. For the design, the KHBD with DB-24 and DL-24 live loads is used. The design comparison and nonlinear analysis of totally prefabricated bridge substructure systems are performed.
This section includes summaries of the developed totally prefabricated bridge substructure system used in the study. A full description of developed prefabricated bridge substructure is given by the authors (Kim et al. 2010a, b, submitted).
The precast concrete footing system is made up of three basic types: precast concrete footing segment, headed bars with coupler and cast-in-place footings (see Fig. 1). After the shaft is drilled, spread footings or pile cap foundations at the bridge site are completed, and the precast concrete footing segment can be hauled to the site for erection. The precast footing segment is match-cast in its vertical position. Vertical casting has many advantages: formed surfaces will make up all finally visible faces of the column; the concrete can be better consolidated around the ducts; and handling will be easier, since the segments will be stored, hauled and erected in the same orientation as they were cast.
Figure 1 also shows the design concept of the precast segmental pier cap system for moderate seismic regions. Precast pier cap systems eliminate the need for forming, reinforcement, casting, and curing of concrete on the jobsite removing the precast pier cap construction from the critical path. The precast concrete pier cap segment is match-cast in its horizontal position. Connection details are developed based primarily on constructability and economic considerations.
Diameter of cross section (mm)
Column height (mm)
Strength of materials
40 (Footing 27)
Shear connection (MPa)
7@seven-wire strands 15.2 mm (1860)/14EA
7@seven-wire strands 15.2 mm (1860)/8EA
7@seven-wire strands 15.2 mm (1860)/7EA
Prestressing force (MPa)
874.0 (Pier Cap)
832.9 (Pier Cap)
Diameter of reinforcement
D22, D29 (Transverse)
Diameter of reinforcement
D13, D16 (Horizontal)
Diameter of reinforcement
Cover thickness (mm)
In this study, author takes this prefabricated bridge substructure and tries redesign by using another method or code of practice to compare a size and cost of structure when using different code of practices. For this case, author select AASHTO-LRFD design code as our comparison code.
The design compressive strength of the concrete was 40 MPa. The yield strength of the reinforcement and tendon were 400 and 1,860 MPa, respectively. Author conducts this study by redesign existing prefabricated bridge substructure with a comparison code (AASHTO 2007) of practices.
Each segmental column had 98 prestressing strands or 56 prestressing strands, respectively (see Table 1). The confinement steel was designed to ensure that the core concrete exhibited a sufficient ductility capacity in compression. It is considered appropriate to use the code provisions (KHBD 2005; AASHTO 2007) on the concrete confinement for the potential plastic hinge regions in the design of precast segmental columns for use in moderate seismic regions.
The precast segments of the design example were fabricated. To maximize construction speed and substructure durability, a system of match-cast segments with epoxy joints was developed. When the substructure has been assembled, post-tensioning strands are tensioned to a predetermined stress level to satisfy both service and ultimate limit state requirements for the totally prefabricated bridge substructure system (see Table 1).
4.1 Computational Platform for Totally Prefabricated Bridge Substructure
An evaluation method for the performance of totally prefabricated bridge substructure is proposed. The proposed method uses a nonlinear finite element analysis program [Reinforced concrete analysis in higher evaluation system technology (RCAHEST)] developed by the authors (Kim et al. 2007, 2008, 2010a, b, submitted).
The structural element library, RCAHEST, is built around the finite element analysis program shell named FEAP, developed by Taylor (2000). The elements developed for the nonlinear finite element analyses of reinforced concrete bridge columns are a reinforced concrete plane stress element and an interface element (Kim et al. 2007, 2008). Accompanying the present study, the authors attempted to implement a bonded tendon element and a modified joint element for the segmental joints with a shear connection (Kim et al. 2010a, b, submitted).
The nonlinear material model for the reinforced and prestressed concrete (PSC) comprises models for concrete and models for the reinforcing bars and tendons. Models for concrete may be divided into models for uncracked concrete and for cracked concrete. For cracked concrete, three models describe the behavior of concrete in the direction normal to the crack plane, in the direction of the crack plane, and in the shear direction at the crack plane, respectively. The basic and widely-known model adopted for crack representation is based on the non-orthogonal fixed-crack method of the smeared crack concept (Maekawa and Pimanmas 2001). The post-yield constitutive law for the reinforcing bar in concrete considers the bond characteristics, and the model is a bilinear model. For prestressing tendons that do not have a definite yield point, a multilinear approximation may be required. In this study, the trilinear model has been used for the stress–strain relationship of the prestressing tendon. The transverse reinforcements confine the compressed concrete in the core region and inhibit the buckling of the longitudinal reinforcing bars. In addition, the reinforcements improve the ductility capacity of the unconfined concrete. This study adopted the model proposed by Mander et al. (1988) for normal strength concrete of below 30 MPa and adopted the model proposed by Sun and Sakino (2000) for high strength concrete of above 40 MPa. An analytical model was proposed for confined intermediate strength concrete from 30 to 40 MPa (Kim et al. 2008). The model incorporates all relevant parameters of confinement with a smooth transition from 30 to 40 MPa.
Comparison for different code.
Percent of difference (%)
Author can conclude that by applying AASHTO-LRFD code for prefabricated bridge substructure design it’s more save than KHBD in term of Korea situation. Author can save cost. This case occurred because the wind load combinations in AASHTO-LRFD is consider to small compare to KHBD. The wind load combination shows a 30 % benefit using AASHTO-LRFD versus KHBD and collision loads were not included.
Figure 8 also shows a method for transforming a circular section into rectangular strips when using plane stress elements. For rectangular sections, equivalent strips are calculated. After the internal forces are calculated, the equilibrium is checked. In this transformation of a circular section to a rectangular section, a section with minimum error was selected through iterative calculations concerning the moment of inertia for the sectional and area of concrete and reinforcements, to ensure that the behavior was similar to the actual behavior of the segmental bridge columns with circular sections. The prefabricated bridge substructures were performed under a constant compressive axial load to simulate the gravity load from bridge superstructures.
The solution to the seismic response of prefabricated bridge substructure was obtained by numerical integration of the nonlinear equations of motion using the Hilber–Hughes–Taylor (HHT) algorithm (Hilber et al. 1977; Hughes 1987). The HHT method is adopted in the present implementation for the solution of the dynamic equilibrium equations. In the present study, ‘Rayleigh damping’ is also used, which is a linear combination of the mass and stiffness matrices. The main advantage of using Rayleigh damping is that it leads to a banded damping matrix that has the same structure as the stiffness matrix (Taylor 2000).
Description of performance levels (Kim et al. 2007).
Limited epoxy injection
Epoxy injection concrete patching
Open cracks concrete spalling
Replacement of damaged section
Bar buckling/fracture core crushing
Failure criterion and damage index (Kim et al. 2007).
Type of failure
Failure criterion ( or )
Damage index ( or )
Compressive and shear
As noted in the results of design comparison, as much as 9 % smaller costs for prefabricated bridge substructure are possible using AASHTO-LRFD versus KHBD. This case occurred because the wind load combinations in AASHTO-LRFD is consider to small compare to KHBD. The load combination shows a 30 % benefit using AASHTO-LRFD versus KHBD and collision loads were not included.
The proposed constitutive model and numerical analysis describe with acceptable accuracy the inelastic behavior of the totally prefabricated bridge substructure when subjected to earthquake conditions. This method may be used for the seismic analysis and design of prefabricated bridge substructure system.
The use of load–moment interaction diagrams as a design aid should provide a quick and economical solution for the design of totally prefabricated bridge substructure when a complete computer solution is not available.
The importance of identifying and evaluating the adequacy of simulation methods is an important and necessary step in applying performance-based assessment techniques for assessing new, enhanced performance systems such as the self-centering system herein under consideration.
Additional parametric research is needed to refine and confirm design details, especially for actual detailing employed in the field.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited.
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