(KHBD) and AASHTO-LRFD

14 Pages·2013·2.62 MB·English

International Journalof ConcreteStructures and Materials
Vol.7, No.4,pp.319–332,December 2013
DOI 10.1007/s40069-013-0050-3
ISSN 1976-0485/ eISSN2234-1315
Comparison of Totally Prefabricated Bridge Substructure
Designed According to Korea Highway Bridge Design
(KHBD) and AASHTO-LRFD
Tae-Hoon Kim*
(Received November 10, 2012, Accepted August 8, 2013)
Abstract: Thepurposeofthisstudywastoinvestigatethedesigncomparisonoftotallyprefabricatedbridgesubstructuresystem.
Prefabricated bridge substructure systems are a relatively new and versatile alternative in substructure design that can offer
numerousbenefits.Thesystemcanreducetheworkloadataconstructionsiteandcanresultinshorterconstructionperiods.The
prefabricatedbridgesubstructuresaredesignedbythemethodsofKoreaHighwayBridgeCode(KHBD)andloadandresistance
factor design (AASHTO-LRFD). For the design,the KHBD with DB-24 and DL-24live loads is used. This study evaluatesthe
designmethodofKHBD(2005)andAASHTO-LRFD(2007)fortotallyprefabricatedbridgesubstructuresystems.Thecomputer
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 conclu-
sions and design recommendations based on the analytical findings.
Keywords: design comparison, prefabricated bridge substructure, construction periods, design method, computer program.
1. Introduction Precastingallowsforanincreaseduseofhighperformance
concrete in bridge substructures, thus improving durability.
Recently, various studies have been carried out abroad on High performance concrete may be used more consistently
the inelastic behavior and performance of precast segmental withhigherqualitycontrolinaprecastingplant.Inaddition,
bridge columns. Precast segmental construction of concrete the greater compressive strength of the high performance
bridge columns is a method in which bridge columns are concrete is utilized to reduce the handling weight and dead
segmentally prefabricated off site and erected on site typi- load of the prefabricated bridge substructure units, thus
callywithpost-tensioning(Hewes2002;Cheng2008;Wang facilitating construction (Billington and Yoon 2004; Rouse
et al. 2008; Yamashita and Sanders 2009; Dawood et al. 2004; Chou and Chen 2006; Xiao et al. 2012). However,
2012). duringthesameperiod,littleattentionhasbeengiventothe
The use of precast segmental construction for concrete design comparison of totally prefabricated bridge substruc-
bridges has increased in recent years due to the demand for ture. The design of a prefabricated bridge substructure, like
shorter construction periods and the desire for innovative most any other civil engineering project, is dependent on
designs that yield safe, economical and efficient structures. certain standards and criteria.
A shortened construction time, in turn, leads to important Inthisstudy,investigationandcomparisonsusingcodesof
safety and economic advantages when traffic disruption or practices for totally prefabricated bridge substructure in
reroutingisnecessary(Billingtonetal.2001;Ouetal.2007; Korea is done. The prefabricated bridge substructures are
Murla-Vila et al. 2012; EIGawady and Dawood 2012). designed by the methods of present design [Korea highway
bridge code (KHBD) 2005] and load and resistance factor
design(LRFD)(AASHTO2007).TheAASHTO-LRFDhas
been chosen as an alternative to KHBD in design of pre-
fabricated bridge substructure. The AASHTO Standard
ConstructionProductTechnologyResearchInstitute,
Specification has been accepted by many countries as the
SamsungConstruction&TradingCorporation,
general code by which bridges should be designed.
Seoul135-935,Korea.
The LRFD method has a number of advantages. It pro-
*CorrespondingAuthor;E-mail:
vides a more rational approachto design. Probabilitytheory
[email protected]
Copyright(cid:2)TheAuthor(s)2013.Thisarticleispublished is used to establish an acceptable margin of safety based on
withopenaccessatSpringerlink.com the variability of anticipated loads and member strength.
319
This study evaluates the present design method of KHBD the shaft is drilled, spread footings or pile cap foundations
(2005)andAASHTO-LRFD(2007)fortotallyprefabricated at the bridge site are completed, and the precast concrete
bridge substructure system. For the design, the KHBD with footing segment can be hauled to the site for erection. The
DB-24andDL-24liveloadsisused.Thedesigncomparison precast footing segment is match-cast in its vertical posi-
and nonlinear analysis of totally prefabricated bridge sub- tion. Vertical casting has many advantages: formed surfaces
structure systems are performed. 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,
2. Developed Totally Prefabricated Bridge hauled and erected in the same orientation as they were
Substructure cast.
Figure 1alsoshowsthedesignconceptoftheprecastseg-
This section includes summaries of the developed totally mentalpiercapsystemformoderateseismicregions.Precast
prefabricatedbridgesubstructuresystemusedinthestudy.A pier cap systems eliminate the need for forming, reinforce-
full description of developed prefabricated bridge substruc- ment,casting,andcuringofconcreteonthejobsiteremoving
tureisgivenbytheauthors(Kimetal.2010a,b,submitted). the precast pier cap construction from the critical path. The
Figure 1 shows the developed totally prefabricated bridge precast concrete pier cap segment is match-cast in its hori-
substructure systems. The ends of each column segment zontal position. Connection details are developed based pri-
have a shear connection to facilitate shear transfer between marilyonconstructabilityandeconomicconsiderations.
segments. Shear connection also play an important role in Recent developments, although limited in number, have
the performance of the column segments in terms of hys- shown that prefabricated bridge substructures are feasible
teretic energy dissipation and ductility. The segments are and advantageous for a wide variety of project types (see
precastwithalignedductstoallowforthethreadingofpost- Fig. 2).
tensioningstrandsthroughthecolumnoncethesegmentsare
placedinthefield.Theintroductionofpost-tensioninginthe
substructure has the potential to reduce residual displace- 3. Design Example
ments and improve joint shear performance.
The precast concrete footing system is made up of three Inthisdesignexample,theinvestigationandcomparisons
basic types: precast concrete footing segment, headed bars using codes of practices for totally prefabricated bridge
with coupler and cast-in-place footings (see Fig. 1). After substructure are studied. The mechanical properties of the
Fig.1 Developed totally prefabricated bridge substructure.
320 | InternationalJournalofConcreteStructuresandMaterials(Vol.7,No.4,December2013)
Fig.2 Details of thedesignexample bridge (Unit:mm).
design examples are listed in Table 1 and the geometric Each segmental column had 98 prestressing strands or
details are shown in Figs. 2, 3, and 4. 56 prestressing strands, respectively (see Table 1). The
In this study, author takes this prefabricated bridge sub- confinement steel was designed to ensure that the core
structureandtriesredesignbyusinganothermethodorcode concrete exhibited a sufficient ductility capacity in com-
of practice to compare a size and cost of structure when pression. It is considered appropriate to use the code
usingdifferentcodeofpractices.Forthiscase,author select provisions (KHBD 2005; AASHTO 2007) on the concrete
AASHTO-LRFD design code as our comparison code. confinement for the potential plastic hinge regions in the
The design compressive strength of the concrete was design of precast segmental columns for use in moderate
40 MPa.Theyieldstrengthofthereinforcementandtendon seismic regions.
were400and1,860 MPa,respectively.Authorconductsthis The precast segments of the design example were fabri-
study by redesign existing prefabricated bridge substructure cated. To maximize construction speed and substructure
with a comparison code (AASHTO 2007) of practices. durability, a system of match-cast segments with epoxy
Figures 5 and 6 describe the design flowchart for each joints was developed. When the substructure has been
code of practice for member design and overall design of assembled, post-tensioning strands are tensioned to a pre-
totally prefabricated bridge substructure. The scopes of determined stress level to satisfy both service and ultimate
structure element that author has compared are pier cap, limit state requirements for the totally prefabricated bridge
column and footing. substructure system (see Table 1).
InternationalJournalofConcreteStructuresandMaterials(Vol.7,No.4,December2013) | 321
Table 1 Example properties.
Item KHBD AASHTO-LRFD
Diameter of cross section (mm) 2,200 2,100
Column height (mm) 14,000
Strength ofmaterials
Concrete (MPa) 40(Footing 27)
Reinforcement (MPa) SD40 (400)
Shearconnection(MPa) STK400(235)
Tendon(MPa)
Column 7@seven-wire strands 15.2mm (1860)/14EA 7@seven-wire strands 15.2mm(1860)/8EA
Pier Cap 7@seven-wire strands15.2mm (1860)/7EA
Prestressing force (MPa) 929.0 (Column) 883.7 (Column)
874.0(Pier Cap) 832.9(Pier Cap)
Column
Diameter of reinforcement D16 (Longitudinal)
D22,D29 (Transverse)
Pier Cap
Diameter of reinforcement D13,D16 (Horizontal)
D19 (Vertical)
Footing
Diameter of reinforcement D25,D19
Cover thickness (mm) 100
Axial force 0:1f A
ck g
Fig.3 Details ofdesign example (Unit: mm).
4. Results and Analysis method uses a nonlinear finite element analysis program
[Reinforced concrete analysis in higher evaluation system
4.1 Computational Platform for Totally technology (RCAHEST)] developed by the authors (Kim
Prefabricated Bridge Substructure et al. 2007, 2008, 2010a, b, submitted).
An evaluation method for the performance of totally pre- The structural element library, RCAHEST, is built around
fabricated bridge substructure is proposed. The proposed the finite element analysis program shell named FEAP,
322 | InternationalJournalofConcreteStructuresandMaterials(Vol.7,No.4,December2013)
Fig.4 Details ofdesign example (Unit: mm).
developedbyTaylor(2000).Theelementsdevelopedforthe considers the bond characteristics, and the model is a
nonlinear finite element analyses of reinforced concrete bilinear model. For prestressing tendons that do not have a
bridge columns are a reinforced concrete plane stress ele- definite yield point, a multilinear approximation may be
ment and an interface element (Kim et al. 2007, 2008). required. In this study, the trilinear model has been used for
Accompanying the present study, the authors attempted to the stress–strain relationship of the prestressing tendon. The
implement a bonded tendon element and a modified joint transverse reinforcements confine the compressed concrete
element for the segmental joints with a shear connection inthecoreregionandinhibitthebucklingofthelongitudinal
(Kim et al. 2010a, b, submitted). reinforcingbars.Inaddition,thereinforcementsimprovethe
The nonlinear material model for the reinforced and pre- ductility capacity of the unconfined concrete. This study
stressed concrete (PSC) comprises models for concrete and adopted the model proposed by Mander et al. (1988) for
models for the reinforcing bars and tendons. Models for normal strength concrete of below 30 MPa and adopted the
concretemaybedividedintomodelsforuncrackedconcrete modelproposedbySunandSakino(2000)forhighstrength
andforcrackedconcrete.Forcrackedconcrete,threemodels concrete of above 40 MPa. An analytical model was pro-
describe the behavior of concrete in the direction normal to posedforconfinedintermediatestrengthconcretefrom30to
thecrackplane,inthedirectionofthecrackplane,andinthe 40 MPa (Kim et al. 2008). The model incorporates all rel-
sheardirectionatthecrackplane,respectively.Thebasicand evant parameters of confinement with a smooth transition
widely-known model adopted for crack representation is from 30 to 40 MPa.
based on the non-orthogonal fixed-crack method of the Details of the nonlinear material model used have been
smearedcrackconcept(MaekawaandPimanmas2001).The provided by the authors in previous research (Kim et al.
post-yieldconstitutivelawforthereinforcingbarinconcrete 2007, 2008, 2010a, b, submitted).
InternationalJournalofConcreteStructuresandMaterials(Vol.7,No.4,December2013) | 323
SUB PIER CAP SUB COLUMN SUB FOOTING
Spread Footing
MAIN Section Assumption Section Assumption
Thickness Check
Section Force Calculation Section Force Calculation No
Overturning Check
Yes
Tendon Layout Moment Magnification
PIER CAP
No
Sliding Check
No Allowable Stress in Tendon Layout
Yes
Tendon Check
No Bearing Capacity
Yes
Allowable Stress in Check
No
No Member Allowable Tendon Check
COLUMN Yes
Stress Check
Yes
Member Force Estimation
Yes
No Member Allowable
No Flexural Strength Stress Check
Check No Flextural Strength
Yes
Check
Yes
No Flexural Strength
FOOTING Yes
No Shear Strength Check
Check No Shear Strength
Yes
Check
Yes Determination of
Confinement Reinforcement Yes
No Torsional Strength
Check No
Crack Check
STOP No Shear Strength
Yes
Check
Yes
Shear Key Check
Yes
Block Shear Key
Shear Resistant
Check
Connecting Structure Check
RETURN
END
RETURN RETURN
END
END END
Fig.5 Design flowchart for totally prefabricated bridge substructure (KHBD).
SUB PIER CAP SUB COLUMN SUB FOOTING
Spread Footing
MAIN Section Assumption Section Assumption
Thickness Check
Section Force Calculation Section Force Calculation No Eccentricity Limit
Check
Yes
Tendon Layout Moment Magnification
PIER CAP
No
Sliding Check
No Tendon Stress Limit Tendon Layout
Yes
Check
No Bearing Capacity
Yes
No Tendon Stress Limit Check
No Service Limit State Check
COLUMN Yes
Check
Yes
Member Force Estimation
Yes
No Service Limit State
No Flexural Strength Check
Limit State Check No Flextural Strength
Yes
Limit State Check
Yes
No Flexural Strength
FOOTING Yes
No Shear Strength Limit Limit State Check
State Check No Shear Strength Limit
Yes
State Check
Yes Determination of
Confinement Reinforcement Yes
No Torsional Strength
Limit State Check No
Crack Check
STOP No Shear Strength Limit
Yes
State Check
Yes
Shear Key Check
Yes
Block Shear Key
Shear Resistant
Check
Connecting Structure Check
RETURN
END
RETURN RETURN
END
END END
Fig.6 Design flowchartfor totally prefabricated bridgesubstructure (AASHTO-LRFD).
324 | InternationalJournalofConcreteStructuresandMaterials(Vol.7,No.4,December2013)
Table2 Comparison for different code.
Item KHBD AASHTO-LRFD Percentof difference (%)
Concrete (M3) 208.1 204.9 1.6
Tendon(tonf) 2.288 1.610 42.1
Reinforcement (tonf) 22.999 22.743 1.1
Fig.7 Load-moment interaction diagram: aKHBD; and bAASHTO-LRFD.
4.2 Results amount of tendon area if author applies AASHTO-LRFD
In this section, author tries to compare two codes of Code.
practice KHBD (2005) and AASHTO-LRFD (2007) for Author can conclude that by applying AASHTO-LRFD
totally prefabricated bridge substructure. code for prefabricated bridge substructure design it’s more
Table 2 shows the value of require quantity for usage of savethanKHBDintermofKoreasituation.Authorcansave
differentcodes. Basedontheresultandanalysis,authorcan cost.Thiscaseoccurredbecausethewindloadcombinations
see that cost for using different code is decrease in term of inAASHTO-LRFDisconsidertosmallcomparetoKHBD.
InternationalJournalofConcreteStructuresandMaterials(Vol.7,No.4,December2013) | 325
(a)
[email protected]
seven-wire strands
100
2200 1100
H29
650 450
650 450
D = 2200 Unit: mm
(b)
8-node RC element 96
6-node Joint element 32
6-node Interface element 4
n-node Bonded
5
prestressing bar element
Fig.8 Finite element mesh for design example: a transformation of a circular column to an idealized equivalent rectangular
column;and bfinite elementmesh for analysis.
The wind load combination shows a 30 % benefit using procedure suggested here should lead to a conservative yet
AASHTO-LRFDversusKHBDandcollisionloadswerenot economically attractive design.
included.
The P–M interaction diagram for prefabricated bridge 4.3 Analysis
substructure in the previous section is shown in Fig. 7. The A three-dimensional finite element analysis is tedious and
column strength is generally checked by comparing the expensive, and requires a high number of elements to
appliedaxialloadandthetotalmomentwiththeaxialforce- achieve a good accuracy. Therefore, two-dimensional eight-
moment capacity of the column section. Therefore, the noded smeared elements are used to model the design
strength analysis of the column section may be essential to examples. Figure 8 shows the finite element discretization
the practical design of precast segmental PSC bridge col- and the boundary conditions for two-dimensional plane
umns. Load–moment interaction diagrams presented here stress nonlinear analyses of the prefabricated bridge sub-
have been developed based on the KHBD (2005) and structure. The joints between the precast segments with a
AASHTO-LRFD (2010) code provisions for fully pre- shear connection were modeled using modified six-noded
stressed concrete compression members. For the normal joint elements. The interface elements between the precast
strengthcolumns,theanalyses provideconservativecolumn concrete footing segment and the cast-in-place footings
strengths compared with the design results. The design enhance the modeling of the effects of localized
326 | InternationalJournalofConcreteStructuresandMaterials(Vol.7,No.4,December2013)
(a) of cyclic behavior, the simulation captures the hysteretic
4000
loops.Theself-centeringcharacteristicoftheprecastsystem
isevidencedbythepinchedhysteresisloopsneartheorigin.
The design examples also exhibited ductile behavior under
2000
cyclicloading.Ultimateductilitycapacitycanbedetermined
as 6.3 and 5.7, with a safe design limit of 5.0, providing 26
N)
k and 14 % reserve of displacement capacity. Figure 9 also
ad( 0 shows the design shear strength of the prefabricated bridge
o
L substructures. The design shear strength obtained from the
design code (KHBD 2005; AASHTO 2007) is conservative
-2000
for the design example.
Analysis Figure 10showsthefailurepatternofexampleKHBDand
Designshearstrength
(KHBD) example AASHTO-LRFD. Damage was concentrated only
-4000
at the column-footing joint. The calculated failure sequence
-800 -400 0 400 800
was similar. The final failure was due to the crushing of
Displacement(mm)
concrete, followed by the yielding of the tendons.
(b)
4000 The purpose of this section is also to investigate the
seismic performance of totally prefabricated bridge sub-
structure when subjected to impulsive near fault ground
motions. Figure 11 shows the acceleration record of input
2000
ground motions, which was used for this dynamic analysis.
N) The peak ground acceleration (PGA) value for artificial
k
d( 0 earthquakeis0.391 gandthedurationis15.9 s.PGAvalues
a for input load start from 0.0627 g and gradually increase to
o
L
thefailurePGAby*0.1 g.Aprocedurewasappliedtothe
totally prefabricated bridge substructures by incrementally
-2000
increasing the earthquake amplitudes by multiplying the
Analysis
Designshearstrength acceleration time history by a scalar factor. The loading
(AASHTO-LRFD)
protocol used included the effects of impulsive near fault
-4000
-800 -400 0 400 800 ground motions. For the numerical analysis, the author
Displacement(mm) recommended using 3 % critical damping.
The solution to the seismic response of prefabricated
Fig.9 Load–displacement relationship for design example:
bridgesubstructurewasobtainedbynumericalintegrationof
a KHBD; andbAASHTO-LRFD.
thenonlinearequationsofmotionusingtheHilber–Hughes–
Taylor (HHT) algorithm (Hilber et al. 1977; Hughes 1987).
discontinuous deformation. The bonded post-tensioning The HHT method is adopted in the present implementation
tendons were modeled with two-noded truss elements that forthesolutionofthedynamicequilibriumequations.Inthe
were attached at their end nodes to the concrete element present study, ‘Rayleigh damping’ is also used, which is a
nodes at the anchorage locations. linear combination of the mass and stiffness matrices. The
Figure 8 also shows a method for transforming a circular mainadvantageofusingRayleighdampingisthatitleadsto
section into rectangular strips when using plane stress ele- a banded damping matrix that has the same structure as the
ments. For rectangular sections, equivalent strips are calcu- stiffness matrix (Taylor 2000).
lated.Aftertheinternalforcesarecalculated,theequilibrium Figures 12, 13, and 14 show the comparison of the
is checked. In this transformation of a circular section to a responsetimehistoryobtainedbyanalysis.Thevaluesgiven
rectangular section, a section with minimum error was by design examples were similar. Consequently, the com-
selected through iterative calculations concerning the puted overall response to seismic motions can give efficient
momentof inertiafor the sectional and area of concrete and data for examining the required seismic performances.
reinforcements,toensurethatthebehaviorwassimilartothe The relationship between maximum shear force and dis-
actual behavior of the segmental bridge columns with cir- placement is obtained as shown in Fig. 15. The relative
cular sections. The prefabricated bridge substructures were magnitudes of these residual displacements sustained by
performed under a 0:1f A constant compressive axial load such a self-centering system are minimal compared to those
ck g
to simulate the gravity load from bridge superstructures. expected from a conventional reinforced concrete system.
The lateral load–lateral displacement response for design The analytical solution has good agreement in linear
examples are shown in Fig. 9. The proposed analytical behavior region as well as in nonlinear behavior region.
model predicts the load–displacement relationship of pre- An analytical evaluation was developed to assess damage
fabricated bridge substructure with flexure failure. In terms states and performance levels of solid reinforced concrete
InternationalJournalofConcreteStructuresandMaterials(Vol.7,No.4,December2013) | 327
Fig.10 Failure patternfor design example:a KHBD; andbAASHTO-LRFD.
bridge columns (Kim et al. 2007). Explicit descriptions of may be expected to sustain severe damage requiring partial
the different performance levels are defined to employ spe- orcompletereplacementofthecolumn.Thisframeworkhas
cific engineering criteria. Table 3 provides an example of been formulated in various documents on performance-
such descriptions that might be associated with the three based design of bridge and building structures (ATC 1996;
performance levels.For the‘‘fullyoperational’’ performance FEMA 1997).
level, the column is designed to remain almost undamaged, The proposed method predicts damage state and perfor-
and repair is not required. For the ‘‘delayed operational’’ mance level for design examples as shown in Fig. 16. The
performance level, the column is expected to sustain some used damage index shows a reasonable gradual progression
damagethatimpairsitsfulluseandthatmightrequirerepair. of damage throughout the load history. These damage indi-
Finally, for the ‘‘stability’’ performance level, the column ces were derived from a parametric study using finite
328 | InternationalJournalofConcreteStructuresandMaterials(Vol.7,No.4,December2013)