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THE 2005 FHWA CONFERENCE
Integral Abutment and Jointless Bridges (IAJB 2005)
March 16 18, 2005
Baltimore, Maryland
Organized by: Constructed Facilities Center
College of Engineering and Mineral Resources West Virginia
University
Conference Sponsors: Federal Highway Administration USDOT
West Virginia Department of Highways - WVDOT
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TABLE OF CONTENTS
Session I: Current Practices with Design Guidelines and
Foundation Design Integral Abutment and Jointless Bridges V. Mistry
3 Integral Abutments and Jointless Bridges (IAJB) 2004 Survey
Summary R. Maruri, S.Petro 12 The In-Service Behavior of Integral
Abutment Bridges: Abutment-Pile Response R. Frosch, M. Wenning, V.
Chovichien 30 New York State Department of Transportation's
Experience with Integral Abutment Bridges A. Yannotti, S.
Alampalli, H. White 41 Integral Abutment Design and Construction:
The New England Experience D. Conboy, E. Stoothoff 50 VDOT Integral
Bridge Design Guidelines K. Weakley 61 Session II: Case Studies
Case Study: A Jointless Structure to Replace the Belt Parkway
Bridge Over Ocean Parkway S. Jayakumaran, M. Bergmann, S. Ashraf,
C. Norrish 73 Case Study Jointless Bridge Beltrami County State Aid
Highway 33 Over Mississippi River in Ten Lake Township, Minnesota
J. Wetmore, B. Peterson 84 Design and Construction of Dual
630-foot, Jointless, Three-span Continuous Multi-girder Bridges in
St. Albans, West Virginia, United States, Carrying U.S. Route 60
over the Coal River J. Perkun, K. Michael 97 Integral Abutment
Bridges with FRP Decks Case Studies V. Shekar, S. Aluri, H.
GangaRao 113
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New Mexicos Practice and Experience in Using Continuous Spans
for Jointless Bridges S. Maberry, J. Camp, J. Bowser 125 Integral
Abutment Bridges Iowa and Colorado Experience D. Liu, R. Magliola,
K. Dunker 136 Moose Creek Bridge Case Study of a prefabricated
Integral Abutment Bridge in Canada I. Husain, B. Huh, J. Low, M.
McCormick 148 Session III: Maintenance and Rehabilitation Field
Data and FEM Modeling of the Orange-Wendell Bridge C. Bonczar, S.
Brea, S. Civjan, J. DeJong, B. Crellin, D. Crovo 163 Integral
Abutment Pile Behavior and Design Field Data and FEM Studies C.
Bonczar, S. Brea, S. Civjan, J. DeJong, D. Crovo 174 Effects of
Restraint Moments in Integral Abutment Bridges M. Arockiasamy, M.
Sivakumar 185 Full-Scale Testing of an Integral Abutment Bridge S.
Hassiotis, J. Lopez, R. Bermudez 199 Analysis and Design of
Integral Abutment by LRFD Method Y. Deng, J. Farre, J. Chang, P.
Penafiel 211 Behavior of Pile Supported Integral Abutments E.
Burdette, S. Howard, E. Ingram, J. Deatherage, D. Goodpasture 222
Soil Structure Analysis of Integral Abutment Bridges P. Christou,
M. Hoit, M. McVay 233 Behavior of Two-Span Integral Bridges
Unsymmetrical About the Pier Line D. Knickerbocker, P. Basu, E.
Wasserman 244 Session IV: Construction Practices Field Study of
Integral Backwall with Elastic Inclusion E. Hoppe 257
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Plastic Design of Steel HP-Piles for Integral Abutment Bridges
P. Huckabee 270 Integral-Abutment Bridges: Geotechnical Problems
and Solutions Using Geosynthetics and Ground Improvement J. Horvath
281 P-y Curves from Pressuremeter Testing at Kings Creek Bridge, WV
Route 2, Hancock County, West Virginia W. Kutschke, B. Grajales 292
Effective Temperature and Longitudinal Movement in Integral
Abutment Bridges R. Oesterle, J. Volz 302 Transverse Movement in
Skewed Integral Abutment Bridges R. Oesterle, H. Lotfi 312
Soil-Structure Interaction of Jointless Bridges O. Kerokoski, A.
Laaksonen 323 Author Index 337
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SESSION I: CURRENT PRACTICES WITH DESIGN GUIDELINES AND
FOUNDATION DESIGN
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Integral Abutment and Jointless Bridges
Vasant C. Mistry; Federal Highway Administration; Washington, D.
C.
ABSTRACT The most frequently encountered corrosion problem
involves leaking expansion joints and seals that permit salt-laden
run-off water from the roadway surface to attack the girder ends,
bearings and supporting reinforced concrete substructures. Because
neither the materials used nor the pains taken to mitigate joint
leakage can fully resolve these problems, other options such as,
the construction of jointless bridges, the use of integral or
semi-integral abutments, and moving the joints beyond the bridges
should be sought. Since 1987, numerous States have adopted integral
abutment bridges as structures of choice when condition allow. At
least 40 States are now building some form of jointless bridges.
While superstructures with deck-end joints still predominate, the
trend appears to be moving toward integral. This paper presents
some of the important features of integral abutment and jointless
bridge design and some guidelines to achieve improved design. The
intent of this paper is to enhance the awareness among the
engineering community to use Integral Abutment and Jointless
Bridges wherever possible. WHY JOINTLESS BRIDGES?
One of the most important aspects of design, which can affect
structure life and maintenance costs, is the reduction or
elimination of roadway expansion joints and associated expansion
bearings. Unfortunately, this is too often overlooked or avoided.
Joints and bearings are expensive to buy, install, maintain and
repair and more costly to replace. The most frequently encountered
corrosion problem involves leaking expansion joints and seals that
permit salt-laden run-off water from the roadway surface to attack
the girder ends, bearings and supporting reinforced concrete
substructures. Elastomeric glands get filled with dirt, rocks and
trash, and ultimately fail to function. Many of our most costly
maintenance problems originated with leaky joints.
Bridge deck joints are subjected to continual wear and heavy
impact from repeated live loads as well as continual stages of
movement from expansion and contraction caused by temperature
changes, and or creep and shrinkage or long term movement effects
such as settlement and soil pressure. Joints are sometimes
subjected to impact loadings that can exceed their design capacity.
Retaining hardware for joints are damaged and loosened by snowplows
and the relentless pounding of heavy traffic. Broken hardware can
become a hazard to motorists,
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and liability to owners. Deck joints are routinely one of the
last items installed on a bridge and are sometimes not given the
necessary attention it deserves to ensure the desired performance.
While usually not a significant item based on cost, bridge deck
joints can have a significant impact on a bridge performance. A
wide variety of joints have been developed over the years to
accommodate a wide range of movements, and promises of long
lasting, durable, effective joints have led States to try many of
them. Some joint types perform better than others but all joints
can cause maintenance problems.
Bearings also are expensive to buy and install and more costly
to replace. Over time steel bearings tip over and seize up due to
loss of lubrication or buildup of corrosion. Elastomeric bearings
can split and rupture due to unanticipated movements or ratchet out
of position.
Because of the underlying problems of installing, maintaining
and repairing deck joints and bearings, many States have been
eliminating joints and associated bearings where possible and are
finding out that jointless bridges can perform well without the
continual maintenance issues inherent in joints. When deck joints
are not provided, the thermal movements induced in bridge
superstructures by temperature changes, creep and shrinkage must be
accommodated by other means. Typically, provisions are made for
movement at the ends of the bridge by one of two methods: integral
or semi-integral abutments, along with a joint in the pavement or
at the end of a reinforced concrete approach slab. Specific
guidelines for designing and detailing jointless bridges have not
yet been developed by AASHTO so the States have been relying on
established experience
A 1985 FHWA report on tolerable movement of highway bridges
examined 580 abutments in 314 bridges in the United States and
Canada. Over 75 percent of these abutments experienced movement,
contrary to their designers intent, typically much greater movement
vertically than horizontally. The following paragraph is from the
report.
The magnitude of the vertical movements tended to be
substantially greater
than the horizontal movements. This can be explained, in part,
by the fact that in many instances the abutments moved inward until
they became jammed against the beams or girders, which acted as
struts, thus preventing further horizontal movements. For those
sill type abutments that had no backwalls, the horizontal movements
were often substantially larger, with abutments moving inward until
the beams were, in effect, extruded out behind the abutments.
The use of expansion joints and bearings to accommodate for
thermal
movements does not avoid maintenance problems; rather, the
provision to these items can often facilitate such problems.
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In this 40-year national experience, many savings have been
realized in initial construction costs by eliminating joints and
bearings and in long-term maintenance expenses from the elimination
of joint replacement and the repair of both super and
substructures. Designers should always consider the possibilities
of minimum or no joint construction to provide the most durable and
cost-effective structure. Steel superstructure bridges up to 400
ft. long and concrete superstructure bridges up to 800 ft. long
have been build with no joints, even at the abutments.
The impact on the total project cost and quality is best
illustrated by the figure shown on the right. As is seen, the
decisions made at the design stage account for over 80 percent of
the influence on both cost (first and life-cycle) and quality
(service life performance) of the structure. Decisions made in the
initial stages of design establish a program that is difficult and
costly to change once detailed design or construction begins.
The following quote is very appropriate for bridge
engineering:
Quality is never an accident. It is always the result of high
intention, sincere effort, intelligent direction, and skillful
execution. It represents the wise choice of many alternatives. This
is especially true when the Engineer begins the task of planning,
designing and detailing a bridge structure. The variables are many,
each of which has a different, first and life cycle, cost factor.
The question to be asked continuously through the entire process is
what value is added if minimum cost is not selected? Another
question to be asked is what futures should be incorporated in the
structure to reduce the first and life cycle cost and enhance the
quality? Most of the variables are controlled by the designer.
These decisions influence the cost and quality of the project; for
better or for worse! WHAT IS AN INTEGRAL ABUTMENT BRIDGE?
Integral abutment bridges are designed without any expansion
joints in the bridge deck as shown by the figures on the right.
They are generally designed with the stiffness and flexibilities
spread throughout the structure/soil system so that all supports
accommodate the thermal and braking
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loads. They are single or multiple span bridges having their
superstructure cast integrally with their substructure. Generally,
these bridges include capped pile stub abutments. Piers for
integral abutment bridges may be constructed either integrally with
or independently of the superstructure. Semi-integral bridges are
defined as single or multiple span continuous bridges with rigid,
non-integral foundations and movement systems primarily composed of
integral end diaphragms, compressible backfill, and movable
bearings in a horizontal joint at the superstructure-abutment
interface. WHY INTEGRAL ABUTMENTS?
As stated earlier, integral abutment and jointless bridges cost
less to construct
and require less maintenance then equivalent bridges with
expansion joints. In addition to reducing first costs and future
maintenance costs, integral abutments also provide for additional
efficiencies in the overall structure design. Integral abutment
bridges have numerous attributes and few limitations. Some of the
more important attributes are summarized below. Simple Design-
Where abutments and piers of a continuous bridges are each
supported by a single row of piles attached to the superstructures,
or where self-supporting piers are separated from the
superstructure by movable bearings, an integral bridge may, for
analysis and design purposes, be considered a continuous frame with
a single horizontal member and two or more vertical members.
Jointless construction - Jointless construction is the primary
attribute of the integral abutment bridges. The advantages of
jointless construction are numerous as has been stated earlier.
Resistance to pressure - The jointless construction of integral
bridges distributes longitudinal pavement pressures over a total
superstructure area substantially greater than that of the approach
pavement cross-section. Rapid construction - Only one row of
vertical piles is used, meaning fewer piles. The back wall can be
cast simultaneously. Fewer parts are required. Expansion joints and
bearings are not needed. The normal delays and the costs associated
with bearings and joints installation, adjustment, and anchorages
are eliminated.
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Ease in constructing embankments - Most of the embankment is
done by large earth moving and compaction equipment requiring only
little use of hand operated compaction equipment. No cofferdams -
Integral abutments are generally built with capped pile piers or
drilled shaft piers that do not require cofferdams. Vertical piles
(no battered piles) - At abutment a single row of vertical piles is
used. Simple forms - Since pier and abutment pile caps are usually
of simple rectangle shape they require simple forms. Few
construction joints are required in the integral abutment bridges,
which results in rapid construction. Reduced removal of existing
elements - Integral abutment bridges can be built around the
existing foundations without requiring the complete removal of
existing substructures. Simple beam seats - Preparation of load
surface for beam seat can be simplified or eliminated in integral
bridge construction. Greater end span ratio ranges - Integral
abutment bridges are more resistant to uplift. The integral
abutment weight acts as a counterweight. Thus, a smaller end span
to interior span ratio can be used without providing for expensive
hold-downs to expansion bearings. Simplified widening and
replacement - Integral bridges with straight capped-pile
substructures are convenient to widen and easy to replace. Their
piling can be recapped and reused, or if necessary, they can be
withdrawn or left in place. There are no expansion joints to match
and no difficult temperature setting to make. The integral abutment
bridge acts as a whole unit. Lower construction costs and future
maintenance costs. Improved ride quality - Smooth jointless
construction improves vehicular riding quality and diminishes
vehicular impact stress levels. Design efficiency - Design
efficiencies are achieved in substructure design. Longitudinal and
transverse loads acting upon the superstructure may be distributed
over more number of supports.
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For example, the longitudinal load distribution for the bent
supporting a two span bridge is reduced 67 percent when abutments
are made integral instead of expansion. Depending upon the type of
bearings planned for expansion abutments, transverse loadings on
the same bent can be reduced by 67 percent as well. Added
redundancy and capacity for catastrophic events - Integral
abutments provide added redundancy and capacity for catastrophic
events. Joints introduce a potential collapse mechanism into the
overall bridge structure. Integral abutments eliminate the most
common cause of damage to bridges in seismic events, loss of girder
support. Integral abutments have consistently performed well in
actual seismic events and significantly reduced or avoided problems
such as back wall and bearing damage, associated with seat type
jointed abutments. Jointless design is preferable for highly
seismic regions. Improve Load distribution - Loads are given
broader distribution through the continuous and full-depth end
diaphragm. Enhance protection for weathering steel girders
Tolerance problems are reduced or eliminated - The close tolerances
required with expansion bearings and joints are eliminated or
reduced with the use of integral abutments. RECOMMENDED BEST
PRACTICES
The following best practices are believed to contain the key
elements to ensure quality improvements in designing and
constructing Integral Abutment and Jointless Bridges. Develop
design criteria or office practices for designing integral
abutment
and jointless bridges. In extending the remaining service lives
of existing bridges, develop
criteria for evaluating and retrofitting bridges with joints to
integral or semi-integral structures.
Establish an annual workshop between joint specialists of
various State to
exchange information in the areas of design, construction and
maintenance of joints and jointless bridges since there is
continuing innovation and changing technology. This will help
leverage the expertise of limited manpower in all the States and
allow more effective communication of What works and what does
not.
The decision to install an approach slab should be made by the
Bridges
and Structures Office, with consultation from the Geotechnical
group.
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The decision should be based upon long-term performance and life
cycle costs, rather than just first costs to the project.
Standardize practice of using sleeper slabs at the end of all
approach slabs.
An irregular crack and pavement settlement typically develops at
the interface of the approach slab and the approach pavement.
Develop a method to control and seal this cracking, and if not
already provided, develop a method to channel the water coming
through this crack away from the pavement without allowing material
to be washed away.
RECOMMENDED DESIGN DETAILS FOR INTEGRAL ABUTMENTS Use embankment
and stub-type abutments. Use single row of flexible piles and
orient piles for weak axis bending. Use steel piles for maximum
ductility and durability. Embed piles at least two pile sizes into
the pile cap to achieve pile fixedly
to abutment. Provide abutment stem wide enough to allow for some
misalignment of
piles. Provide an earth bench near superstructure to minimize
abutment depth
and wingwall lengths. Provide minimum penetration of abutment
into embankment. Make wingwalls as small as practicable to minimize
the amount of
structure and earth that have to move with the abutment during
thermal expansion of the deck.
For shallow superstructures, use cantilevered turn-back
wingwalls (parallel to center line of roadway) instead of
transverse wingwalls.
Provide loose backfill beneath cantilevered wingwalls. Provide
well-drained granular backfill to accommodate the imposed
expansion and contraction. Provide under-drains under and around
abutment and around wingwalls. Encase stringers completely by
end-diaphragm concrete. Paint ends of girders. Caulk interface
between beam and backwall. Provide holes in steel beam-ends to
thread through longitudinal abutment
reinforcement. Provide temporary support bolts anchored into the
pile cap to support
beams in lieu of cast bridge seats. Tie approach slabs to
abutments with hinge type reinforcing. Use generous shrinkage
reinforcement in the deck slab above the
abutment. Pile length should not be less than 10 ft. to provide
sufficient flexibility. Provide prebored holes to a depth of 10
feet for piles if necessary for
dense and/or cohesive soils to allow for flexing as the
superstructure translates.
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Provide pavement joints to allow bridge cyclic movements and
pavement growth.
Focus on entire bridge and not just its abutments. Provide
symmetry on integral bridges to minimize potential longitudinal
forces on piers and to equalize longitudinal pressure on
abutments. Provide two layers of polyethylene sheets or a fabric
under the approach
slab to minimize friction against horizontal movement. Limit use
of integral abutment to bridges with skew less than 30 degree
to
minimize the magnitude and lateral eccentricity of potential
longitudinal forces.
SUMMARY
There are many advantages to jointless bridges as many are
performing well in service. There are long-term benefits to
adopting integral bridge design concepts and therefore there should
be greater use of integral bridge construction. Due to limited
funding sources for bridge maintenance, it is desirable to
establish strategies for eliminating joints as much as possible and
converting/retrofitting bridges with troublesome joints to
jointless design.
The National Bridge Inventory database notes that eighty percent
of the bridges in the United States have a total length of 180-ft.
or less. These bridges are well within the limit of total length
for integral abutment and jointless bridges. Where jointless
bridges are not feasible, installation of bridge deck joints should
be done with greater care and closer tolerances than normal bridge
construction to achieve good performance. Since 1987, numerous
States have adopted integral abutment bridges as structures of
choice when conditions allow. At least 40 States are now building
integral and/or semi-integral abutment type of bridges. Preference
range from Washington State and Nebraska, where 80-90 percent of
structures are semi-integral; to California and Ohio, which prefer
integral, but use mix, depending upon the application; to
Tennessee, which builds a mix of both integral and semi-integral,
but builds integral wherever possible.
While superstructures with deck-end joints still predominate,
the trend appears
to be moving toward integral. Although no general agreement
regarding a maximum safe-length for integral abutment and jointless
bridges exists among the state DOTs, the study has shown that
design practices followed by the most DOTs are conservative and
longer jointless bridges could be constructed.
There are several activities underway that will affect the way
States are
designing jointless bridges in the future. These include a joint
AASHTO/NCHRP task force responsible for initiating and drafting
AASHTO design guide specifications and synthesis report on current
practices for integral and semi-integral abutment bridges,
FHWA-sponsored research study on Jointless
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Bridges, update of LRFD specs to address jointless bridge design
issues, and future workshops. An excellent reference document on
current issues regarding jointless bridges is the FHWA Region 3
Workshop manual on Integral Abutment Bridges, November 1996.
Continuity and elimination of joints, besides providing a more
maintenance
free durable structure, can lead the way to more innovative and
aesthetically pleasing solutions to bridge design. As bridge
designers we should never take the easy way out, but consider the
needs of our customer, the motoring public first. Providing a joint
free and maintenance free bridge should be our ultimate goal. The
best joint is no joint. REFERENCES 1. Wasserman, Edward P. And
Walker, John H., Integral Abutments for Steel Bridges, October
1996. 2. Burk, Martin P., Jr., An Introduction to the Design and
Construction of Integral Bridges,
FHWA, West Virginia DOT and West Virginia University, Workshop
on Integral Bridges, November 13-15, 1996.
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Integral Abutments and Jointless Bridges (IAJB) 2004 Survey
Summary
Rodolfo F. Maruri, P.E.1 and Samer H. Petro, P.E.2
ABSTRACT
Integral Abutment and Jointless Bridges (IAJB) have been used
for decades and the criteria for using them and detailing has
varied from state to state. The main advantage of IAJB is the
elimination of joints, which after they start leaking, account for
70% of the deterioration that occurs at the end of girders, piers
and abutment seats. FHWA promotes the usage of Integral Abutment
and Jointless bridges, where appropriate, as one method of building
bridges that will last 75-100 years with minimal maintenance.
In 1995 and 1996, Federal Highway Administration (FHWA) in
conjunction
with the Constructed Facilities Center (CFC) at West Virginia
University (WVU) conducted a survey and workshop about Integral
Abutment Bridges [1]. In 2004, another survey [2] was developed by
FHWA and the CFC at WVU, using similar questions as the 1995 survey
and incorporating additional questions, to obtain a status of usage
and design for Integral Abutments and Jointless bridges. The survey
was distributed by AASHTO subcommittee on Bridge and Structures to
all 50 states Department of Transportation (DOT), District of
Columbia DOT, Puerto Rico Highway and Transportation Authority and
Federal Lands Highways Division (referred to as states in the
paper).
This paper summarizes the responses received to date from the
states. The
survey was divided into different topic areas which included
General Issues, Design and Details, Foundation, Abutment/Backfill,
Approach Slabs, Retrofit (Jointed to Jointless), and Other Issues.
Integral Abutments, as defined in the survey and in this paper,
refers to the monolithic construction of the abutment with the deck
in order to eliminate the joints at the end of the bridge. This
includes the use of Full, Semi Integral Abutments and Deck
Extensions. Jointless bridges refers to the elimination of joints
at the piers through the usage of integral pier caps, continuous
spans and continuous for live load construction.
The purpose of the survey was to obtain a snapshot about the
usage of integral
abutments and jointless bridges from the states, their policy,
their design criteria and other issues. The results of the survey
are presented in this paper and will be used to disseminate
information between states and help FHWA encourage the usage of
IAJB.
1 Rodolfo F. Maruri, P.E., Federal Highway Administration,
Richmond, Virginia. 2 Samer H. Petro, P.E., Gannett Fleming, Inc.,
Morgantown, West Virginia.
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INTRODUCTION
Integral abutments and jointless bridges (IAJB), when properly
designed and constructed, perform better than bridges with
expansion joints because they minimize maintenance, extend service
life of bridge components including bearings, abutment and pier
seats, paint system and superstructure. Although integral abutments
have been designed and constructed successfully for decades, the
design and analysis of these structures have relied primarily on a
fragmented body of technical references, and design and
construction details have varied from state to state.
The Federal Highway Administration (FHWA) in conjunction with
the
Constructed Facilities Center (CFC) of West Virginia University
(WVU) conducted a survey of integral abutment design and
construction as part of a three-day workshop on integral abutment
and jointless bridges scheduled for March 16-18, 2005 in Baltimore,
Maryland. The IAJB 2004 survey was sent to all 50 States Department
of Transportation (DOT), DC DOT, Puerto Rico Highway and
Transportation Authority and the Federal Lands Highway Division
(referred to as states in the paper). The survey was conducted with
the intention that bridge designers and owners will use the
information to promote usage and design practices for integral
abutment and jointless bridges.
The IAJB 2004 survey include questions about the number of
integral
abutments designed, built and in service, the criteria used for
design and construction, including maximum span lengths, total
length, skews and curvature and problems experienced with integral
abutment bridges. In addition, the survey questioned the states
about their design considerations such as thermal movement, passive
earth pressure, approach slabs, foundation and pile design and
retrofitting of non-integral abutments to integral abutments.
For consistency in the terminology used, the survey defined and
provided a
sketch of full integral abutments, semi integral abutments, and
deck extensions. Full Integral Abutment was described as a capped
pile stub type abutment with or without a hinge between
superstructure and foundation cap, semi-integral abutment was
described as a rigid, non-integral foundation with movement system
primarily composed of internal end diaphragms and movable bearings
in a horizontal joint at the superstructure-abutment interface and
a deck extensions was described as extension the deck over the top
of the backwall and place joint behind the abutment backwall to
prevent deterioration of the end of superstructure beams [2].
Of the fifty-three (53) states surveyed, thirty-nine (39) states
(74%) responded (Figure 1). In addition, other states indicated
that they will submit the responses to the survey in the
future.
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Figure 1: States that Responded to the IAJB 2004 Survey
According to the responses, there are approximately 13000 integral
abutment
(IA) bridges, of which approximately 9000 are full integral
abutment bridges, approximately 4000 are semi-integral abutment
bridges and approximately 3900 deck extension bridges in-service
(Table 1). The increase in the number of integral abutments from
the numbers reported in the 1995 survey [1] can be attributed to
the acceptability of the benefits of integral abutments,
familiarity with design and construction issues and a larger sample
of responding states (39 respondents in 2004 versus 18 in 1995).
The numbers reported are approximate since the National Bridge
Inventory (NBI) data, which is kept by all the states with
information about their bridges, does not differentiate between the
different types of abutments and most states do not have other
methods for maintaining an inventory bridges and/or integral
abutments.
The following sections in the paper, discuss the survey answers,
analysis and
compilation of answers and conclusions based on responses
provided.
GENERAL ISSUES This section of the survey questioned the states
about their use of integral
abutments since the last workshop [1], the number of integral
abutment bridges in service, the states policy for design of
jointless bridge construction and the criteria used for integral
abutments and jointless bridges. A breakdown of integral bridges
designed and built since 1995 and the total number of in-service
integral abutment bridges is shown in Table 1.
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Table 1: Number of IAJB Designed and Built Since 1995 and
In-Service
DESIGNED since 1995 BUILT
since 1995 IN SERVICE
(TOTAL) Integral Abutment ~ 7000 ~ 8900 ~ 13000
Full Integral ~ 5700 ~ 6400 ~ 9000 Semi Integral ~ 1600 ~ 1600 ~
4000
Deck Extension ~ 1100 ~ 1100 ~ 3900
The survey responses indicate an increase in the number of
integral abutments
of over 200% in the last 10 years. As in 1995, Tennessee
continues to have over 2000 integral abutments bridges, but
Missouri reports having 4000 integral abutment bridges, which
represent the largest amount of integral bridges. An increase in
the number of integral abutments, since 1995, is most evident in
the northern states where Illinois, Iowa, Kansas and Washington all
reported having over 1000 in-service. In addition, Michigan,
Minnesota, New Hampshire, North Dakota, South Dakota, Oregon,
Wyoming and Wisconsin, reported having between 100-500 integral
abutment bridges in-service. Unlike the northern states, the
southern states like Florida, Alabama and Texas do not use integral
abutment and reported having one or less bridges with integral
abutments.
As illustrated in Figure 2, fifty-one percent (51%) of the
responding states
indicated that they designed and built over 50 integral abutment
(IA) bridges since 1995, of which 21% built 101-500 integral
abutment bridges, 5% built 501-1000 integral abutment bridges and
5% built over 1000 integral abutment bridges.
3%
8%
10%
23%
18%
5% 5%
3%
18%
10%
8%
21%
5% 5%
15%
21%
0%
10%
20%
None 1 - 10 11 - 20 21 - 50 51 - 100 101 - 500 501 - 1000 Over
1000
NUMBER OF BRIDGES DESIGNED USING INTEGRAL ABUTMENTS (RANGE)
PER
CEN
T O
F ST
ATE
S
Integral Abutment (Designed)
Integral Abutment (Built)
Figure 2: Percent of States that reported designing and building
Integral Abutments within
the range specified (since 1995).
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Analysis of responses shows a similar distribution with the
in-service integral abutments bridges as in Figure 2. For
in-service integral abutment bridges, fifty-nine percent (59%) of
the responding states indicated having over 50 integral abutment
bridges in-service, of which 31% have 101-500 integral abutment
bridges, 3% have 501-1000 integral abutment bridges, and 15% have
over 1000 integral abutment bridges. The 2004 survey revealed that
approximately 85% of the states (about 33 states) constructed
integral abutment bridges equally with either simple spans or
multiple spans.
The responses to General Question 4, regarding the states
criteria for using
integral abutments, show that a majority of the states do not
limit the maximum span within the bridge, but do limit the total
length of the bridge and the skew of the bridge. Table 2 summarizes
the criteria range provided by the states for prestressed concrete
girder and steel bridges for maximum span, total length of bridge,
maximum skew of bridge and maximum curvature.
Table 2: Range of Design Criteria Used For Selection of Integral
Abutments.
PRESTRESSED CONCRETE GIRDERS
RANGE
STEEL GIRDERS RANGE
MAXIMUM SPAN MAXIMUM SPAN Full Integral 60 200 Full Integral 65
- 300 Semi Integral 90 200 Semi Integral 65 - 200 Deck extensions
90 200 Deck extensions 80 - 200 Integral Piers 120 200 Integral
Piers 100 - 300 TOTAL LENGTH TOTAL LENGTH Full Integral 150 1175
Full Integral 150 - 650 Semi Integral 90 3280 Semi Integral 90 -
500 Deck extensions 200 750 Deck extensions 200 - 450 Integral
Piers 300 400 Integral Piers 150 - 1000 MAXIMUM SKEW MAXIMUM SKEW
Full Integral 15 70 Full Integral 15 - 70 Semi Integral 20 45 Semi
Integral 30 - 40 Deck extensions 20 45 Deck extensions 20 - 45
Integral Piers 15 80 Integral Piers 15-No Limit MAXIMUM
CURVATURE
MAXIMUM CURVATURE
Full Integral 0 10 Full Integral 0 - 10 Semi Integral 0 10 Semi
Integral 0 - 10 Deck extensions 0 10 Deck extensions 0 - 10
Integral Piers 3 - No Limit Integral Piers 0 - No Limit
-
17
Based on the experience of many states, their comments and their
established design criteria, it can be concluded that a majority of
new bridges could be built using integral abutments. Colorado, Iowa
and Tennessee indicated that they built the majority of their new
bridges using integral abutments.
The utilization of integral abutments with curved bridges is not
widely
accepted based on survey responses. Four states reported that
they allow the use of curved girder bridges with integral abutments
and three (3) more allow the construction of curved bridges with
straight girders and integral abutments. An alternative mentioned
to account the forces in curved bridges and/or long bridges is the
use of integral abutments with an expansion joint elsewhere on the
bridge.
The IAJB 2004 survey shows that although progress has been made
in the construction of integral abutments since 1995, there is
still a lot of variability in the usage and criteria used for
selection of integral abutments. The non-uniformity of selection
criteria for integral abutments indicates that this is an area
where standardization is warranted.
DESIGN AND DETAILS This section of the IAJB 2004 survey
questioned the states regarding their changes to the design
procedures or details, future plans for jointless bridges, policy
regarding the use of integral abutments, forces and loads used to
design integral abutments and other design issues. The following
presents the questions asked in the survey and their respective
responses. Question 1 in this section asked whether the design
procedures or details changed since August of 1995 with regard to
loads, substructure design, backfill, approach slabs and jointless
retrofit of bridges. The survey results indicated that less than
25% of the states that responded changed their design procedures
regarding primary and secondary loads, substructure design,
abutment/backfill and approach slab since 1995. However, this
percentage increased with regard to changing the details associated
with the same issues of integral abutments. The largest change
occurred in the details for foundation/substructures and approach
slabs (38% and 36% respectively). Figure 3 illustrates the
percentage of states that responded in each of the issues noted.
Some of the changes reported in the survey include Iowa specifying
a 10-foot prebored hole filled with bentonite for each pile (8-foot
prebored hole used prior to 2002), Virginias accountability of
lateral forces on skewed integral abutment bridges, and
Connecticuts incorporation of approach slabs in all bridges to
minimize bump/settlement problems at the bridge/approach fill
interface. In addition to these detailing changes, several states
noted that they have changed their design to incorporate the Load
Factor Design (LFD) specifications and/or the Load and Resistance
Factor Design (LRFD) specifications.
-
18
24% 23%
21%
15%
18%
8%
10%
13%
36%
28%
36%
13%
0%
10%
20%
30%
40%
Primary LoadConsiderations
Secondary LoadConsiderations
Substructure/foundation Abutment/Backfill Approach Slab
Jointless retrofit
PER
CEN
T O
F ST
ATE
S
DESIGN PROCEDURES
DETAILS
Figure 3: Percent of States that Reported Changing their Design
Procedures and Details since 1995.
Design and Details Question 2 and 3 asked about the states
future plans for jointless bridge construction, including the
future use of integral abutments, continuous spans, retrofit of
existing bridges, and policy about elimination of joints. The
survey revealed that over ninety percent (90%) of the states have a
policy to eliminate as many joints as possible and construct
jointless simple and continuous span bridges whenever possible.
However, only 77% indicated that they will design integral (fully
and semi) abutments whenever possible and 79% noted that they will
design bridges as jointless whenever they meet the design criteria
for jointless bridges (Figure 4). The difference in the percentages
between eliminating as many joints as possible (92%) and using
integral abutments whenever possible (77%) can be attributed to
states that do not extensively use chemicals for deicing of bridges
in the winter and therefore do not have a policy of incorporating
integral abutments in their bridge design (Figure 5). Noteworthy
comments included Oregons comment about problems with multiple-span
jointless bridges; Arizonas comment about having problems with
integral abutment approach slabs which is the reason Arizona does
not use integral abutments anymore; Vermont noting that they do not
use integral abutment extensively because of scourability issues;
and Washington State noting that they preferred using semi-integral
type abutments because they are more economical since it avoids the
transfer of seismic forces into the substructure
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19
79%
92%
54%
90%
77%
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Design integral (fully andsemi) abutments whenever
possible.
Design bridges as jointlesswhenever they meet the
design criteria for jointlessbridges.
Eliminate as many deck jointsas possible.
Retrofit existing bridges andeliminate deck joints where
possible
Design (jointless) simple andcontinuous span bridges
PER
CEN
T O
F ST
ATE
S
Figure 4: Percent of States that Answered with Regard to Their
FUTURE Plans for
Jointless Bridge Construction.
Figure 5: Future Plans for IAJB Design and Construction
-
20
Design and Details Question 4 dealt with the forces, including
passive and active earth pressure, temperature, creep, shrinkage,
settlement, additional loads due to skew layout, additional forces
due to curvature and other forces that states account for in the
design of integral abutments. The survey revealed that 72% of the
states account for temperature related forces (Figure 6). In
addition, states also noted that they account for temperature
(temperature gradient, thermal expansion and contraction in
longitudinal and transverse direction) in their design (Design and
Details Question 5), but the procedure for accounting for the
thermal expansion and contraction varied widely.
The survey results also indicate that 59% of the states surveyed
accounted for passive earth pressures, but only 21% of the states
allow for curved bridges with integral abutments and account for
the additional forces due to the curvature of the bridge (Figure
6).
Noteworthy comments about design of integral abutments include
Illinois practice to designed only for vertical loads, North
Dakotas practice to use 1000 lb/ft2 to account for various loads
(passive pressure, thermal, creep and shrinkage loads) and Iowas
use of the a simple, fixed-head pile model which does not consider
passive or active pressure and is based on research conducted by
Greimann and Abendroth at Iowa State University during the
1980s.
59%
33%
44%41%
21%
15%
72%
28%
0%
10%
20%
30%
40%
50%
60%
70%
Passive EarthPressure
Temperature. Creep Shrinkage Settlement Additional forcesdue to
skew
Additional forcesdue to curvature
Other. Describebelow in
commentssection.
PER
CEN
T O
F ST
ATE
S
Figure 6: Percent of States That Account for the Forces Listed
in the Design of Integral
Abutments. Thirty-three percent (33%) of the responding states
account for creep effects when designing integral abutment bridges
(Design and Details Question 4 and 6), while Georgia, Illinois,
Iowa and other states indicated that they do not account for creep
movements.
-
21
As expected, the majority of the states responded that they use
computer software to design integral abutment bridges (78%).
However, the program and/or method used varied widely. Several
states, including California, Illinois and North Dakota indicated
that they use hand calculations and charts, while other states
noted that they have developed their own in-house spreadsheet,
using Excel and MathCAD, to design integral abutment bridges.
Structural programs and finite element software like STAAD, STRUDL,
and RISA are used by Pennsylvania, Rhode Island and North Carolina
to design integral abutments while Tennessee, New Hampshire,
Virginia and New Jersey use COM624P and/or L-pile for pile design.
FOUNDATIONS The monolithic construction of the deck with integral
abutment (backwall) requires special design for the backwall and
supporting piles of integral abutments and jointless bridges. The
design of the foundation for integral abutments needs to account
for the expansion and contraction of the bridge due to thermal
movement. The resulting soil pressures due to thermal expansion and
restraining effects due to jointless construction of the bridge
have been recognized as the controlling load for design of integral
abutments and piles. Designing and detailing of integral abutments
to handle these forces is critical for the proper performance of
integral abutments. The 2004 IAJB survey questions where chosen to
obtain an understanding about how states are designing foundations
for integral abutments, including criteria used to select
foundation type, type of pile, orientation of pile, pile design
considerations, pressure used in the design of integral abutments
and special details utilized to reduce the pressures at the
integral abutment. The survey responses (Foundation, Questions 1
and 2) indicate that full-integral abutment with steel bearing
piles is the most commonly type of integral abutments (~ 70%).
However, several states noted that they are currently designing
and/or creating standards for semi-integral abutments. The comments
provided indicated that semi-integral abutments are commonly used
with the uncharacteristic designs that incorporate larger skews,
higher abutment walls and unique soil conditions. Washington State
noted they preferred using semi-integral abutments because they are
more economical since they avoid transferring seismic forces into
the substructure. New Hampshire indicated that they use deck
extensions extensively since the foundation design is not an issue.
The use of deck extensions is predominant in the northeast region
(New Hampshire, New York, Connecticut and Maine) as is evident in
the large number of in-service deck extensions in this region.
-
22
Nevada and Hawaii indicated that in addition to steel bearing
piles (H piles and pipe piles), friction piles and spread footings,
they are using drilled shafts for foundations of integral
abutments. Noteworthy, even though steel bearing piles were the
most common type of pile used for integral abutments, there was no
consensus on the typical orientation of the pile (Foundation,
Question 4). Thirty three percent (33%) of the responding states
orient the piles with the strong axis parallel to the centerline of
bearing, 46% orient the piles with the weak axis parallel to the
centerline of bearing, 8% (3 states) leave it to the discretion of
the Engineer and the remaining 13% did not provide a comment or
noted that the question was not applicable because of their use of
symmetric piles (Figure 7). The non-uniformity of pile orientation
seems to indicate that this is an area where further
standardization is warranted.
33%
46%
8%
13%
0%
10%
20%
30%
40%
50%
Strong Axis Parallel to CL ofBearings
Weak Axis Parallel to CL ofBearings
Designer's Option Not Applicable (Symmetric Pile)or No Answer
Provided
ORIENTATION OF PILES
PER
CEN
T O
F ST
ATE
S
Figure 7: Typical Pile Orientation Use for FULL Integral
Abutments Responses to Foundation Question 3 indicate that a number
of states have developed office practices that allow designers to
detail integral abutments without doing complicated analysis. These
states use the office practices in conjunction with geotechnical
recommendations based on soil parameters to decide the type of
foundation used. Based on the comments provided, there is no
evidence of problems relating to the type of foundation used for
integral abutments. The use of MSE wall has increased dramatically
over the years and as such the use of integral abutments where the
MSE walls serves as a component of the integral abutments has
increased correspondingly. Foundations-Question 5, questioned about
the states policy regarding the combination of integral
-
23
abutments and MSE walls. Based on the survey responses, the
preferred detail is to offset the MSE wall from the integral
abutment and footing between two (2) feet to five (5) feet.
According to comments, the offset provides space for construction
of MSE wall and offsetting of MSE straps around abutment piles. In
addition to offsetting of the integral abutment behind the MSE
wall, several states noted that they have special requirements for
the placement of piles in the MSE backfill including the use of
sleeves filled with sand. The detailing of MSE abutments with
integral abutments is inconsistent based on the responses received
and is another area where guidelines based on all available
research would be beneficial to states that are currently using
this type of construction and/or plan to use it. The soil pressure
used for the design of integral abutments and its piles has been
the subject of controversy and much research. The survey,
Foundation-Question 6, shows that there is still no consistent
design method used with regard to soil pressures. The majority of
the respondents indicated that they use passive pressure (33%)
and/or a combination of passive and active pressures (18%). Active
pressures, however, is used by a minority of respondents (8%) and
other combination of pressure and/or methods was used by 26% of the
states responding (Figure 8). The survey was not specific enough to
make any conclusions about the variability of pressures used in the
design of integral abutments.
18%
8%
26%
33%
0%
10%
20%
30%
Combination Active Pressure Passive Pressure Other PRESSURE USED
FOR DESIGN
PER
CEN
T O
F ST
ATE
S
Figure 8: Typical Soil Pressures Used for Design of
Substructure
-
24
The limits or capacities used for piles provide another
opportunity for standardization. Based on the comments provided
(Foundation-Questions 7, 8 and 9), states use AASHTO in combination
with statewide practices that limit lateral deflection of pile,
computer programs and other methods to determine the capacity of
piles. The pile capacity is based on the axial capacity of the pile
(using 0.25*fy as stipulated in AASHTO Standard Specification,
section 4.5.7.3 or other) [41% of states], or a combination of
axial/bending capacity based on beam-column analysis and frame
analysis [51% of states]. In addition to accounting for bending due
to expansion/contraction of superstructure, 26% of the states also
account for the bending due to superstructure rotation in the
horizontal plane (skew bridges) (Figure 9).
41%
51%
26%
0%
10%
20%
30%
40%
50%
Axial Forces (No Bending) Bending Forces Due
toExpansion/Contraction of Superstructure
Bending Forces Due to SuperstructureRotation in the Horizontal
Plane (skew
bridges)
TYPE OF FORCE USED TO DETERMINE CAPACITY OF PILE
PER
CEN
T O
F ST
ATE
S
Figures 9: Forces Used to Determine Capacity of Piles for
Integral Abutments.
ABUTMENT/BACKFILL
The handling of the backfill behind the integral abutments can
have a significant effect on the performance of integral abutments
and as a result has been discussed and researched over the past
decades. A review of the answers and comments provided in the IAJB
2004 survey (Abutment/Backfill Question 1 and 2), show that most
states require the fill behind the integral abutment to be
compacted (69%) as compared to 15% for uncompacted fills.
Interestingly, in addition to using compacted fills there are a
number of states that require the use of expanded polystyrene
(EPS), other compressible materials behind abutment, lightweight
fills and additional inspection during construction in order to
reduce
-
25
and/or control the earth pressures exerted on integral abutments
during expansion cycles (Figure 10). The other survey questions in
this section inquire about whether the states specify the minimum
length of approach fill required behind the integral abutment
(Abutment/Backfill - Question 3) and whether the states limit the
maximum height of integral abutments (Abutment/Backfill Question
4). In both questions, the analysis of the responses indicated that
the states specified the length of approach fills and/or limited
the height of the integral abutments 31% of the time, but the
majority of the states did not limit or specified these parameters.
The comments for Abutment/Backfill Question 4 inferred that the
limit for the height applied only to the full integral abutment.
Washington State indicated that they have used a 30-foot high
semi-integral abutment.
13%10% 10%8%8%
13%
69%
0%
10%
20%
30%
40%
50%
60%
70%
Require compactedbackfill
Requireuncompacted backfill
Use ExpandedPolystyrene (EPS)
Use othercompressible
material behindabutment.
Use Lightweight fill Require additionalinspection during
construction
Other. Describe incomments section
below.
PER
CEN
T O
F ST
ATE
S
Figure 10: Percent that Responded to Listed Requirement for
Approach Backfill.
APPROACH SLABS
Some of the most common problems associated with integral
abutments are the settlement and the cracking of approach slabs.
Fortunately, these problems do not cause a significant disruption
of traffic or a decrease of the service life of the bridge. The
questions in this section were designed to find out the design
procedure and details used for approach slabs (Approach Slabs
Questions 1 and 2), the problems experienced with approach slabs
(Approach Slabs Question 3) and the criteria about the usage of
approach slabs behind integral abutments (Approach Slabs Question
4).
-
26
The comments provided in Approach Slabs - Questions 1 and 2,
indicate that there is no consistency in the detailing of approach
slabs. Thirty-one percent (31%) of respondents indicated that they
use a sleeper pad at the end of approach slab, 26% indicated that
they float the slab on the approach fills and 30% indicated that
they do both. Many states indicated that they have or are using
corbels on the abutment backwall for the support of the approach
slab, while other states indicated that they use reinforcing
projecting from the abutment backwall to tie the approach slab to
the abutment backwall, and other states are using a combination.
Based on the responses received, it is evident that the detailing
of approach slabs, including the connection to the abutment
backwall and the interface between the approach slab and approach
fills is an area where standardization and guidelines would be
beneficial. Review of comments provided for Approach Slabs Question
3, indicates that approach slab settlement, cracking, and bump at
the interface between the approach slab and approach fill are the
major problems with approach slabs. The answers and comments
provided with this question are consistent with the answers
provided in Other Issues Question 1 (Figure 11). In order to
mitigate some of the problems with approach slabs, several states
are using buried approach slabs and/or select fills under the
approach slab while other states have filled voids under approach
slab with grout, resurfaced approach slabs with asphalt, and/or
used an overlay. Surprisingly, a state noted that the reasons they
do not use integral abutment bridges anymore are because of the
bump formed at the end of the approach slab and settlement problems
under approach slabs due to poor drainage.
RETROFIT Retrofit of jointed decks to jointless decks has been
increasing as the condition of the decks deteriorates and a
complete deck replacement is needed. Forty-nine percent (49%) of
the respondents indicated that they have a policy to retrofit
existing bridges whenever possible. Virginia has used a poor-man
continuity detail, obtained from Utah DOT, for complete and partial
re-decking projects with great success. For re-decking projects,
Virginia has found that the main cost of using a continuous deck
with simple spans is the need to retrofit the existing bearings. As
the age of the bridges in the United States continues to increase
and concrete decks need to be replaced to improve rideability and
the condition rating of the decks, consideration should be given to
retrofitting existing simple span to continuous (jointless) deck.
Based on the responses in the survey, this is an area where further
guidelines would be beneficial to those states that have not yet
established a retrofit policy.
-
27
Conversion of non-integral abutment bridges to integral or
semi-integral abutment bridges is not widely used and only 39% of
the responding states indicated that they have a policy to
investigate its feasibility. New Mexico notes that this is very
common retrofit and that the selection of bearings is critical;
Missouri notes that they consider retrofitting only on short spans
and small skew; Virginia notes that they try to incorporate this
retrofit with major superstructure replacement projects; and South
Dakota notes that they incorporate this type of retrofit with a
major renovation such as a deck replacement or if there are severe
problems at the abutment.
OTHER ISSUES The last section of the survey inquired about the
problems states are having with integral abutments (Other Issues
Question 1), special details/design procedure for bearing in
integral abutments (Other Issues Question 2) and list of recent
research in the area of integral/jointless bridges (Other Issues
Question 3). Details and design procedure for bearings and recent
research in the area of integral/jointless bridges will be provided
during the IAJB 2005 Conference. A summary of the problems reported
with Other Issues Question 1 is shown in Figure 11. The compilation
of Other Issues Question 2 revealed that 36% of the states use the
same procedure for design of integral abutment bearings as for
regular abutment bearings, 13% design the bearings based on thermal
movements and 38% use other methods to design and detail the
bearings of integral abutments.
15%
26%
10%
8%
3%
46%
28%
0%
10%
20%
30%
40%
50%
Cracking of integralabut. backwall
Cracking of deck atintegral abutment
Cracking of approachslabs
Cracking of wingwall Detailing Detrimental rotationof integral
abutment
backwall
Setlement ofapproach slabs
PER
CEN
T O
F ST
ATE
S
Figure 11: Problems Experienced with Integral Abutments.
-
28
CONCLUSIONS / RECOMMENDATIONS The IAJB 2004 survey revealed that
design practices and details vary greatly from state to state. For
example, maximum span limits, curvature and skew effects, thermal
movement limits and creep effects are just a few criteria that
differ considerably between states according to the surveys
received. Therefore, the papers authors believe that
standardization and/or guidelines are warranted. The cost
associated with proper maintenance of joints, subsequent
deterioration of bridge components when joints do not perform
satisfactorily and FHWAs goal to built bridges with 75-100 years
service life with minimal maintenance, are some of the reasons that
the authors consider that integral abutment and jointless bridges
should be the construction of choice, whenever feasible. Based on
the compilation of the surveys, the following conclusions and
recommendations are made:
1. Develop guidelines that incorporate the research done in the
area of integral abutments. These guidelines should include
problems experienced by other states, as well as design guidelines
and examples. Examples of areas identified in the 2004 IAJB survey
where non-uniformity in design and detailing are apparent
include,
a. Criteria used for selection of integral abutments. b. Forces
and pressures used to design integral abutment and integral
abutment piles. c. Orientation of integral abutment piles. d.
Design of integral abutments with curved bridges. e. Detailing of
approach slab at bridge interface and approach fill
interface.
2. Promote the issuance of a national policy for the use of
integral abutments, especially in states that indicated that they
do not have a policy regarding the future use of integral
abutments.
3. Develop guidelines and/or additional information to increase
the use of continuous jointless and/or continuous decks with simple
span superstructures, whenever appropriate.
4. Develop guidance and/or additional information on the use of
deck extensions to eliminate joints at abutments. These guidelines
should incorporate criteria on when to use them, problems
experienced by other states, and design guidelines.
5. Develop guidelines and/or additional information for
detailing of integral abutments around MSE walls.
-
29
6. Develop guidelines and/or additional information for handling
of backfill behind integral abutments.
7. Develop guidelines and/or additional information for
detailing of approach slabs to minimize cracking and mitigate
problems at the approach slab and roadway fill interface.
8. Develop guidelines and/or additional information for the
retrofitting of existing bridges to eliminate joints at piers and
abutments.
9. Create a new survey incorporating comments given in the IAJB
2004 Survey and clarifying areas which were unclear according to
submitters.
10. Re-issuance as a Technical Advisory by Federal Highway
Administration and/or policy guidelines for Integral Abutments.
These recommendations and conclusions presented within this
paper are the opinions of the authors, based on the IAJB 2004
survey, and are not necessarily endorsed by Federal Highway
Administration. However, a goal of the conference is for the CFC at
WVU to provide recommendations to Federal Highway Administration
for its consideration and issuance as a Technical Advisory and/or
policy guideline. ACKNOWLEDGEMENT
The authors would like to thank all the individuals who
completed the survey and returned it to the CFC at WVU. Their work
is the basis for the survey summary and this paper. In addition, we
would like to acknowledge the support of Malcolm T. Kerley,
chairman of AASHTO sub-committee on Structures and Bridges, for
sending the IAJB 2004 survey to all the states Bridge Engineers.
REFERENCES 1. GangaRao, H., Thippeswamy, H., Dickson, B. Franco,
J., 1996. Survey and Design of
Integral Abutment Bridges, Constructed Facilities Center at West
Virginia University, Morgantown, West Virginia.
2. Maruri, R., Petro, S., GangaRao, H., 2004. IAJB 2004 Survey,
Federal Highway
Administration and Constructed Facilities Center at West
Virginia University, Morgantown, West Virginia.
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30
The In-Service Behavior of Integral Abutment Bridges:
Abutment-Pile Response
Robert J. Frosch, Purdue University
Michael Wenning, American Consulting, Inc. Voraniti Chovichien,
Thai Engineering Consultants Co, Inc.
ABSTRACT
Integral bridges have been used for many years across many
regions of the country. However, empirical guidelines have often
limited their use. While removal of limits imposed by these
guidelines may be warranted, there are many questions regarding the
behavior of these structures that remain unanswered. In particular,
the interaction of the abutment, pile and soil remains uncertain.
In Indiana, the decision to explore extension of the limits has
resulted in a study to ascertain the in-service behavior of
integral abutment bridges. Through several field instrumentations,
new light is being shed on the behavior and performance of these
bridges. The behavior of integral abutment bridges is concentrated
in the response of the abutment-pile-soil system. Therefore, this
response is the focus of this paper. INTRODUCTION
The Indiana Department of Transportation (INDOT) has used
empirical limits for integral bridge construction. These limits are
similar to those used by many departments; namely bridges less than
300 ft in total length with skews no greater than 30 degrees [1].
Like most departments, INDOT has observed many advantages to this
type of construction and wishes to increase these limits. Among the
leading advantages are simpler construction and reduced
maintenance.
Many unanswered questions, however, have kept INDOT from opening
the
limits on these designs. Among them are: How far can empirical
details be stretched without additional analysis? Should H-piles be
oriented in their strong or weak axis for best results? What
methods of design should be proscribed when bridges fall
outside
the empirical limits? What components of the bridge require
additional design? How much does the mass of the bridge buffer the
daily temperature
changes? Does the bridge skew enter into the design and if so
how?
-
31
In May 1998, the Indiana Department of Transportation made a
decision that is likely to change the course of bridge design in
the state. They authorized the design of a jointless bridge 302 m
(990 ft) long, over 3 times longer than any previously built in
Indiana. This decision began a series of events that resulted in a
research study at Purdue University [2,3]. While the overall goal
of the Purdue research study was to provide answers to the various
questions, the first phase of research was directed towards
providing an understanding of the in-service behavior of these
bridges.
SR 249 OVER US 12 THE FIRST BRIDGE The SR 249 Bridge is designed
to carry traffic over US 12 and nine railroad
tracks into the Port of Indiana at the northernmost part of the
state. The ten-span bridge has a 13-degree skew and a total length
of 990 ft (302 m). Individual spans ranged from 87 to 115 ft (26.4
to 35.0 m). The intent of this project was to build a bridge using
standard construction materials and details and monitor it to
evaluate the assumptions that were made in design.
Due to the size of the bridge, alternate plans were produced for
both a steel
girder and prestressed bulb-tee option. The continuous,
composite prestressed bulb-tee option received the low bid and was
constructed. The four girders were 5 ft deep, made of
semi-lightweight concrete (130 pcf) and spaced at 10 ft-4 in. (3.15
m) on the 38ft-4 in. (11.7 m) wide bridge.
The girders sat on elastomeric bearing pads that were designed
to deflect with
the anticipated temperature change. Per INDOT detailing
standards, the diaphragm encapsulating the ends of the beams over
the piers were cast the full width of the bridge seat, or 50 inches
in this case. The bottom of the diaphragm rested on a layer of
polystyrene that was intended to allow the superstructure to expand
or contract without locking up at the piers. A keyway is provided
to restrain the superstructure from excessive movement.
The design of the end bent presumed that the bridge length would
expand and
contract with annual temperature variations. For this region,
AASHTO temperature ranges of 45 and 60 degrees from construction
temperatures were used for the concrete and steel options,
respectively. This amounted to 1.6 in. and 2.3 in. of anticipated
movement in each direction.
Once the movement was computed, a model was set up to calculate
the
resisting force of the soil. Soil borings at the site revealed
that the bridge would be founded on seams of peat and marl that
extended about 45 ft below ground line. The geotechnical report
advised against adding any weight to the existing spill slopes due
to large anticipated settlements. As a result, the approaches for
the bridge had to be constructed of expanded polystyrene fill. This
created a situation that pulled the project out of its standard
construction methods
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32
Sub-Base
PrestressedBulb TeeGirder
HP14x89
Expanded Polystyrene
Fill
Approach Slab Deck
17
Retaining Wall
18Min. 18
Anchor Plateand Beam Seat
Sleeper Slab
Ground Level
Sub-Base
PrestressedBulb TeeGirder
HP14x89
Expanded Polystyrene
Fill
Approach Slab Deck
17
Retaining Wall
18Min. 18
Anchor Plateand Beam Seat
Sleeper Slab
Ground Level
category. The piles supporting the end bents would have to be
designed as free standing for the first 19.68 ft. The computer
program COM624P was used to model the spring coefficients for the
various soil layers. The anticipated deflection at the pile head
was inputted to obtain the maximum moment and point of fixity for
the pile. The point of fixity was assumed to be the second location
where the deflection diagram crossed the zero point. The portion of
the pile extending into the cap was covered with polystyrene to
obtain a pinned connection. Piles were then designed as columns
with a height from the point of fixity to the bottom of the end
bent.
Steel encased concrete (shell) piles, 14 in. diameter, would
have been the first
choice of support for these soil conditions. However, when an
analysis was performed, the thickness of the piles would have been
excessive. Larger diameters were investigated but the same
thickness was always required. Since the stiffness of the pile
increases the force required to move it the predetermined distance,
the moment increased linearly with the pile section modulus. It was
determined that the shape of the pile would have to change to
obtain a better ratio.
H piles were then investigated in both strong and weak axis
orientation.
Ultimately a strong axis orientation was used to avoid the
possibility of local flange buckling. A schematic of the end bent
detail is provided in Figure 1.
Figure 1: SR 249 End Bent Detail
The bridge was instrumented with a combination of strain, tilt,
crack and temperature meters. In addition to this bridge, INDOT has
continued to build and instrument others to measure the response of
other types of bridges, piles, skews and soil conditions.
FIELD STUDIES
Overall, four bridges in Indiana have been instrumented to
observe the in-service behavior of integral abutment bridges as
well as the behavior of the piles
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33
supporting these structures. These bridges range in length from
150 to 990 ft providing a spectrum of behavioral data [2,3].
While the SR 249 Bridge provided excellent information regarding
the
behavior of a relatively long integral structure, this structure
was not typical in regards to the design of the end bent.
Therefore, several other bridges including the SR18 over
Mississinewa River Bridge (Figure 2) were also selected for
instrumentation. There are several reasons that the SR18 Bridge in
particular was selected.
1. The bridge was designed and constructed according to typical
integral
abutment details. 2. The bridge exceeded the length limitation
of INDOT and could provide
much needed data regarding bridge length. 3. The skew of the
structure was small. Therefore the research could focus
on the effects of bridge length.
Figure 2: SR18 over Mississinewa River Bridge
To better understand the soil-pile-abutment-system, the
five-span, continuous
prestressed, concrete bulb-tee integral bridge was instrumented.
This bridge is located east of the city of Marion in Grant County,
Indiana on the westbound lanes of State Road 18 crossing the
Mississinewa River. The total bridge length is 367 ft with a skew
angle of 8.
To evaluate the abutment movement, tiltmeters and convergence
meters were
provided on the end bents (Bents 1 and 6). The convergence meter
was oriented horizontally and operated perpendicular to the
abutment. This meter measured the relative displacement between the
end bent and the reference pile to determine the longitudinal
abutment movement. The locations of the convergence meters,
tiltmeters and pile strain gages are shown in Figure 3.
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34
Tiltmeter
10
8 Slab
R/C Bridge Approach Slab
Prestressed Conc. Bulb-T Beam
End Bent Backfill
3-3
Strain Gages
1-3
14 CFT pile
Convergence Meter
Reference Pile
3
Drain
Ground Level
Strain GageTiltmeter
10
8 Slab
R/C Bridge Approach Slab
Prestressed Conc. Bulb-T Beam
End Bent Backfill
3-3
Strain Gages
1-3
14 CFT pile
Convergence Meter
Reference Pile
3
Drain
Ground Level
Strain Gage
Centerline ofAbutment
1-3
Parallel toRoadway
8
5 sp
aces
at 4
=20
Abutment
PilePlan
Elevation
N
90
GroundLevel
Strain GageCenterline ofAbutment
1-3
Parallel toRoadway
8
5 sp
aces
at 4
=20
Abutment
PilePlan
Elevation
N
90
GroundLevel
Centerline ofAbutment
1-3
Parallel toRoadway
8
5 sp
aces
at 4
=20
Abutment
PilePlan
Elevation
N
90
GroundLevel
Strain Gage
Strain gages were installed on piles, not only at ground level
but also along the length of Pile 6 of the western bent (Figure 4)
to evaluate the in-service, soil-structure response and to
determine the response of the entire pile rather than only at the
base of the abutment. All strain gages except the ones at ground
level were installed prior to pile driving to provide the strain
profile along the length of the pile enabling investigation of
overall pile behavior. The strain gages at ground level were
installed after driving. These gages on Pile 6 allow calculation of
pile bending down the length of the pile and estimate of the
deflected shape. Strain gages on the south face were installed to
provide redundancy, locate the neutral axis, and evaluate
out-of-plane movement of the pile.
Figure 3: End Bent Instrumentation (SR18)
Figure 4: Strain Gages along the Pile Length (SR18)
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35
-100
102030405060708090
100110120
06/0
1/03
07/0
1/03
07/3
1/03
08/3
0/03
09/2
9/03
10/2
9/03
11/2
8/03
12/2
8/03
01/2
7/04
02/2
6/04
03/2
7/04
04/2
6/04
Air
Tem
pera
ture
(F)
Construction Day
Hottest Day
Coldest Day
Construction Temperature
DeckGirder
-100
102030405060708090
100110120
06/0
1/03
07/0
1/03
07/3
1/03
08/3
0/03
09/2
9/03
10/2
9/03
11/2
8/03
12/2
8/03
01/2
7/04
02/2
6/04
03/2
7/04
04/2
6/04
Air
Tem
pera
ture
(F)
Construction Day
Hottest Day
Coldest Day
Construction Temperature
DeckGirder
ABUTMENT BEHAVIOR
The temperature on the SR18 Bridge was measured by temperature
gages located on a girder and in the deck as shown in Figure 5. The
temperature measured by both gages was almost identical; however,
the response of the deck was slightly slower than that of the
girder.
Figure 5: Air Temperature
The rotation of the abutment was measured by tiltmeters located
on the east and west faces of the end bents (Bents 1 and 6). The
rotations of the abutments were filtered by taking the average of
the data recorded between the time interval four hours before and
four hours after the desired measurement time. The filtered
rotations of both bents are plotted in Figure 6. The results
indicate that both bents translated and hardly rotated. The date of
deck casting is noted as the construction day. This day is
significant in that it signifies the time at which the structure
became integrally connected.
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36
-0.2
-0.1
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
06/0
1/03
07/0
1/03
07/3
1/03
08/3
0/03
09/2
9/03
10/2
9/03
11/2
8/03
12/2
8/03
01/2
7/04
02/2
6/04
03/2
7/04
04/2
6/04
Long
itudi
nal M
ovem
ent (
in.)
Bent 6 Center
Bent 1 Center
Bent 6 SE
Inward
Outward
Construction Day
Hottest Day Coldest Day
-0.2
-0.1
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
06/0
1/03
07/0
1/03
07/3
1/03
08/3
0/03
09/2
9/03
10/2
9/03
11/2
8/03
12/2
8/03
01/2
7/04
02/2
6/04
03/2
7/04
04/2
6/04
Long
itudi
nal M
ovem
ent (
in.)
Bent 6 Center
Bent 1 Center
Bent 6 SE
Inward
Outward
Construction Day
Hottest Day Coldest Day
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
06/0
1/03
07/0
1/03
07/3
1/03
08/3
0/03
09/2
9/03
10/2
9/03
11/2
8/03
12/2
8/03
01/2
7/04
02/2
6/04
03/2
7/04
04/2
6/04
Rot
atio
n (d
egre
es)
Average Bent 1
Average Bent 6
Construction Day
Hottest Day Coldest Day
Bent 1
Bent 6 -1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
06/0
1/03
07/0
1/03
07/3
1/03
08/3
0/03
09/2
9/03
10/2
9/03
11/2
8/03
12/2
8/03
01/2
7/04
02/2
6/04
03/2
7/04
04/2
6/04
Rot
atio
n (d
egre
es)
Average Bent 1
Average Bent 6
Construction Day
Hottest Day Coldest Day
Bent 1
Bent 6
Figure 6: Abutment Rotation The movements of the abutments were
measured by convergence meters, and
the displacements are plotted in Figure 7. The data was zeroed
immediately prior to casting. These results indicate that the
abutment movement corresponds well with temperature. For instance,
as the temperature decreases (contraction phase), both abutments
move toward each other as anticipated. Furthermore, the
displacements were essentially identical indicating symmetrical
behavior.
Figure 7: Abutment Displacement
-
37
The measured movement of Bent 1 was compared to the thermal
movement calculated according to Equation 1 as shown in Figure 8.
It can be seen that the calculated abutment movements are greater
than the measured values. This difference is most likely due to
backfill restraint, pile resistance and friction from the approach
slab.
L = (T)L (1)
where: = thermal coefficient of concrete, taken as 6.0x10-6
/F;
T = temperature change L = half of the total span length, 367
ft/2 = 183.5 ft.
-0.2
-0.1
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
06/0
1/03
07/0
1/03
07/3
1/03
08/3
0/03
09/2
9/03
10/2
9/03
11/2
8/03
12/2
8/03
01/2
7/04
02/2
6/04
03/2
7/04
04/2
6/04
Lon
gitu
dina
l Mov
emen
t (in
.)
Bent 1 Center
Inward
Outward
Construction Day
Hottest Day
Coldest Day
Calculated
-0.2
-0.1
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
06/0
1/03
07/0
1/03
07/3
1/03
08/3
0/03
09/2
9/03
10/2
9/03
11/2
8/03
12/2
8/03
01/2
7/04
02/2
6/04
03/2
7/04
04/2
6/04
Lon
gitu
dina
l Mov
emen
t (in
.)
Bent 1 Center
Inward
Outward
Construction Day
Hottest Day
Coldest Day
Calculated
Figure 8: Calculated vs. Measured Movements
PILE BEHAVIOR
Stresses and strains along the pile length over various
temperature change ranges, T, were determined by grouping the
strain according to the temperature range (Figure 9). The average
strains of each temperature range were calculated. The increment of
the temperature change range is 10 F 5% except for T equal to 0 F.
At T = 0 F, the range considered was from -1 to 1 F. It is noted
that the construction temperature was considered as 60 F, and all
temperature changes are referenced from this temperature.
-
38
Figure 9: Pile Stresses with Depth
Deflections along the pile depth were computed by integrating
the moment of the area under the curvature diagram considering the
deflection measured at the pile top as measured by the convergence
meter located at the center of the eastern bent. The deflected
shape of Pile 6 over various temperature change ranges was
estimated as shown in Figure 10. The estimated deflected shapes
correspond very well to the temperature change, T. Double curvature
bending occurs with the inflection point located between a depth of
4 and 8 ft. It should be noted that the deflection at the bottom of
the pile was not directly measured. This value was assumed for
calculation of the displacement shape and was considered
reasonable.
Figure 10: Pile Displacement with Depth
-
39
SUMMARY AND CONCLUSIONS
Based on the field study, the following conclusions have been
reached.
1. The abutment responds to temperature changes, and its
movement can be estimated conservatively using the theoretical
thermal expansion/contraction of the superstructure, L = (T)L. The
actual displacement is expected to be slightly less due to backfill
restraint, pile resistance and approach slab friction.
2. The abutment primarily translates or slides longitudinally in
response to
thermal expansion and contraction of the bridge. Only minor
rotations of the abutment occur and for analysis purposes can be
ignored.
3. Piles integrally connected with the abutment bend in double
curvature.
Lateral displacements in the soil correspond directly with
temperature changes. Measures to eliminate the integral
abutment-pile connection can be used such as in the SR249 structure
to provide for a pinned connection. This connection eliminated the
double curvature response.
4. For satisfactory bridge performance, the structure must be
detailed and
constructed properly. a. Piles must be constructed and oriented
as designed. b. Intermediate piers should be designed to
accommodate lateral
displacement or the connection must be detailed to minimize
lateral force transfer. If the piers are not designed for the
lateral displacement, locking of the superstructure to the
intermediate piers must be prevented through isolation.
The overall goal of the research program was to provide answers
to questions
that have limited the design of integral abutment bridges. While
the scope of this paper is limited to the measured response, two
additional phases of research have been conducted including an
analytical and laboratory experimental study. The comprehensive
view provided through these three phases of research has provided
answers to most of the questions originally posed. An ongoing study
is completing the investigation into bridge skew. While all three
phases of research have been essential to providing answers, the
measured in-service response was indispensable for not only the
calibration of analytical models, but for a true understanding of
behavior.
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40
REFERENCES
1. Indiana Department of Transportation. 1992. Bridge Design
Memorandum #233 Revised, Inter-Department Communication,
Indianapolis, IN, 5 pp.
2. Durbin, K.O. 2001. Investigation of the Behavior of an
Integral Abutment Bridge, Masters Thesis, Purdue University, West
Lafayette, IN, 2001, 138 pp.
3. Chovichien, V. 2004. The Behavior and Design of Piles for
Integral Abutment Bridges, Doctoral Dissertation, Purdue
University, West Lafayette, IN, 489 pp.
ACKNOWLEDGEMENTS
The authors would like to gratefully acknowledge the Indiana
Department of Transportation. Funding for the research program
conducted by Purdue University was provided through the Joint
Transportation Research Program (JTRP) through Project No.
SPR-2393. Thanks are also extended to Katrinna Durbin and David
Fedroff for their contributions to this research study.
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41
New York State Department of Transportation's Experience with
Integral Abutment Bridges
Arthur P. Yannotti, P.E. New York State, Department of
Transportation
Sreenivas Alampalli, PhD, P.E. New York State Department of
Transportation Harry L. White 2nd, P.E. New York State Department
of Transportation
ABSTRACT The New York State Department of Transportation
(NYSDOT) has been using integral abutment bridges since the late
1970's. Since that time, the design methodology and details have
been modified several times to improve performance. Semi-Integral
abutments were introduced in 1998. Approximately 450 integral and
semi-integral abutment bridges have been constructed in New York
and thus far, their in-service performance has been excellent. They
are the preferred abutment type for NYSDOT. This paper examines the
evolution of the design and construction practices and explains the
reasons for the modifications. HISTORY
Traditionally, bridges in New York were constructed with a joint
in the deck slab at abutments to accommodate thermal movements. By
the 1970's, multiple span bridges were commonly designed as
continuous spans, thus eliminating the deck joints over the piers.
Deck joints were of a number of types, including various types of
neoprene seals, finger joints and open trough systems. However, all
types were prone to leak and allow water containing road salt to
drain onto the underlying superstructure beams, bearings, abutment
backwalls and bridge seats.
In order to eliminate the "leaking joint" problem, the first
integral
abutment bridges constructed by NYSDOT were built in the late
1970's. These were typically single span steel bridges with a span
length under 100 feet. A single row of steel H piles with the
strong axis parallel to the girders was used so that bending
occurred about the weak axis. The steel piles were extended into a
short abutment stem. The steel girders were erected on the steel
piles and attached to them by welding to a cap plate that was
welded to the top of the piles. The girders and piles were then
encased in concrete as the deck slab was placed creating an
integral type abutment. Design assumptions included equal
distribution of the vertical load to the piles. Bending moments in
the piles were ignored, and the abutments and wingwalls were
designed for full passive earth pressure. A section of an early
typical integral abutment with a steel superstructure is shown in
Figure 1.
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42
Figure 1. Early Steel Superstructure Integral Abutment
Superstructures with adjacent prestressed concrete box beams are
commonly used in New York. Early attempts were made in the 1980's
to adapt integral a