6.integral bridges final report

8/11/2019 6.Integral Bridges Final Report

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1stSem M.Tech (CADS), U.B.D.T.C.E, Davangere. Page 2

Fig 1.3: Golden gate bridge, San Francisco.

1.2. CLASSIFICATION OF BRIDGES:

Bridges can be classified into various types depending upon the following factors:

1. Materials used for construction:

Under this category, bridges may be classified as timber bridges, masonry bridges, steel

bridges, reinforced cement concrete bridges, pre-stressed bridges and composite bridges.

2. Alignment:

Under this bridges can be classified as straight or skew bridges.

3. Location of bridge floor:

Under this category, bridges may be classified as deck, semi-through or through bridges.

4. Purpose:

Under this bridges can be classified as an aqueduct, viaduct, highway bridge, railway

bridge and foot bridge.

5. Nature of superstructure action:

Under this category, bridges may be classified as portal frame bridges, truss bridges,

balanced cantilever bridges, suspension bridges and integral bridges.


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6. Position of high flood level:

Under this bridges may be classified as submersible and non-submersible bridges.

7. Life:

Under this bridges may be classified as permanent and temporary bridges.

8. Span length:

Under this category, bridges can be classified as culverts (span less than 8m), minor

bridges (span between 8 to 30m), major bridges (span above 30m) and long span bridges (span

above 120m).

9. Degree of redundancy:

Under this category, bridges can be classified as determinate bridges and indeterminate

bridges.

10. Types of connection:

Under this category steel bridges can be classified as pinned connected, riveted or

welded.

Fig 1.4 A typical deck type integral abutment bridge


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CHAPTER 2

REVIEW OF LITERATURE:

P.V. Mayur Babu and N.M.Bhandari

have studied the performance of integral bridgeunder self-weight, imposed load, moving loads and thermal load and compared with simply

supported bridge. For this purpose, a 3D model of both simply supported and integral

bridge have been analyzed using RM-2004 software. In their work they have taken a three span

box girder bridge as an example having same dimension with both simply supported and integral

bridge type. Superstructure is modeled and analyzed to study the effect of dead load, moving

load and thermal load for BM, SF and deflection variations.

Pradeep Kumar T.V, D. K. Paul and Ram Kumarhave studied the performance of deck

extension integral bridges under thermal variation and seismic excitation. For this purpose, they

analyzed a 2D model of an integral bridge using SAP-2000 by considering both linear and

nonlinear behavior of soil. In their work they took an example of the deck extension integral fly

over model and analyzed the study effect of temperature and seismic loading. They conducted

linear static and time history analysis to estimate the displacement and moment capacity of the

structure under linear soil conditions.

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 joint less bridge. Where joint less bridge 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.


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CHAPTER 3

3.1. WHAT IS AN INTEGRAL BRIDGE?

Bridges constructed without any expansion joint (between spans or between spans and

abutments) and without any bearings are called integral bridges OR Integral bridges in simple

words can be defined as bridges without joints. Integral bridges are characterized by monolithic

connection between the deck and the substructure (piers and abutments). They span from

one abutment, over intermediate support to the other abutment, without any joint in the deck.

Integral bridges have been constructed all over the world including India. . Integral bridges (IB)

are designed to provide resistance to thermal movements, breaking forces, seismic forces and

winds by the stiffness of the soil abutting the end supports and the intermediate support.

In the U.S., the term integral bridge usually refers to bridges with short stub-type

abutments connected rigidly to the bridge deck without joints. This rigid connection allows the

abutment and the superstructure to act as a single structural unit. Typically, single rows of piles

provide foundation support for the abutments.

The advantages of integral construction are greater durability and lower maintenance

costs when compared with jointed bridges.

3.2. CHARACTERISTICS OF INTEGRAL BRIDGES:

The integralabutmentbridge concept is based on the theory that due to the flexibility of

the piling, thermal stresses are transferred to the substructure by way of a rigid connection

between the superstructure and substructure.


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3.3. MOTIVATION BEHIND INTEGRAL BRIDGES:

To eliminate expansion joints in the deck when earthquake forces are predominant or

when consideration like increased resistance to blasts the integral bridge concept is an

excellent option.

Less expensive.

Improved durability.

Easy to design.

3.4. WHY GO FOR INTEGRAL BRIDGES?

The

expansion joints

and bearings, by virtue of their functions are sources of weakness in

the bridge and there are many examples of distress in bridges, primarily due to

poorperformanceof these two elements.

F

Fig 3.1

Metallic bearings destroyed during earthquake

Girder shifted in the longitudinal direction with loss of seating during shaking


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Fig 3.2Surajbari new bridge super structure shifted in the

transverse direction

Fig 3.3 Suraj Bari new bridge expansion joint damaged due to excessive movement


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CHAPTER 4

4.1. TYPES OF INTEGRAL BRIDGES:

4.1.1 Full integral bridge:

In full integral bridge/ integral abutment bridge the superstructure and abutments are cast

monolithically by concrete or steel. This is the most efficient design in most situations and every

effort should be made to achieve full integral construction as shown in figure.

Fig 4.1Single span Integral Abutment Bridge or Full Integral Bridge

4.1.2. Semi integral bridge:

Semi-integral bridges are having continuous superstructure supported by abutments,

which are structurally separated as shown in figure, the key advantage of these bridges is

superstructure behavior is independent of the foundation type. A small gap is provided between

the integral back wall and the substructure to allow it to move freely in the longitudinal direction.

The concept of semi-integral bridges is being adapted at places where rigid abutments are

necessary. The role of semi-integral bridges becomes important when there is a need of long

span integral bridges.


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Fig 4.2 Semi Integral - Abutment Bridge.

4.1.3. Deck extension integral bridge:

In deck extension integral bridges, the deck slab is extended from the end piers and taken

over the traditional back wall and into adjoining approach pavement. In India, the integralbridges are built with the expansion joints near abutment face.

These bridges can also be classified into deck extension integral bridges. In this the main

beams or slab is not cast into a concrete end diaphragm. India has also adopted this type of

design for flyovers.

Fig 4.3 Deck Extension Integral Bridge.

The use of an integral abutment eliminates the need for deck joints and expansion

bearings. The absence of joints and bearings significantly reduces costs during construction.

More significantly, maintenance costs are also reduced since deck joints, which allow water to

leak onto substructure elements and accelerate deterioration, are not needed. In addition, future

widening or bridge replacement becomes easier, since the simple design of the integral abutment


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leads itself to simple structural modification. Integral bridges are alternatively referred to as

integral abutment bridges, joint less bridges, integral bent bridges and rigid-frame bridges.

Semi-integral or integral back wall bridges typically have sliding bearings, but no

expansion joints. Expansion joints and bearings have traditionally been used to accommodate the

seasonal thermal expansion and contraction of bridge decks, typically in the order of tens of

millimeters. A survey of approximately 200 concrete highway bridges in the U K, carried out for

the Department of Transport, however, revealed that expansion joints are a serious source of

costly and disruptive maintenance work.

Although the integral bridge concept has proven to be economical in initial construction

for a wide range of span lengths, as well as technically successful in eliminating expansion

joint/bearing problems, it is susceptible to different problems that turn out to be geotechnical in

nature. These are potentially due to a complex soil structure interaction mechanism involving

relative movement between the bridge abutments and adjacent retained soil. Because this

movement is the result of natural, seasonal thermal variations, it is inherent in all integral

bridges.

The effective temperature is the temperature that governs the overall longitudinal movement of

the bridge superstructure. Change in effective bridge temperature causes the deck to expand and

contract. This is the most important effect governing the design of integral bridges.

Fig 4.4


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4.2. INTEGRALABUTMENT:

The integral abutment is defined as abutment, which is

connected

to the bridge

deck without any movement joint for expansion or contraction of

the deck.

4.3. NEED FOR INTEGRAL ABUTMENTS:

1. Simple Design

2.Joint less construction

3.Resistance to pressure

4.Rapid construction

5.Ease in constructing embankments

6.Vertical piles (no battered piles)

7.Simple forms

8.Few construction joints

9.Reduced removal of existing elements

10.Simple beam seats

11.Simplified widening and replacement

12.Lowerconstruction costsand future maintenance costs

13.Improved ride quality

14. It Design efficiency.

Fig 4.5 K L international Airport Curved Bridge


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CHAPTER 5

5.1. SUGGESTED GUIDELINES FOR DESIGNING INTEGRAL BRIDGES:

As temperature changes daily and seasonally, the lengths of integral bridges increase and

decrease, pushing the abutment against the approach fill and pulling it away. As a result the

bridge superstructure, the abutment, the approach fill, the foundation piles and the foundation

soil are all subjected to cyclic loading, and understanding their interactions is important for

effective design and satisfactory performance of integral bridges. The main concept of these

integral bridges is to shift the location of the thermal expansion joints from within the bridge to

the end of approach slab. This shift of location of the joint results in shifting the associated

problems dealing with expansion joints from a structural engineer to the geotechnical engineer.

Fundamentally these problems are due to complex soil-structure interaction mechanism

involving relative movement between the bridge and its adjacent retained soil.

The widespread interest in the integral bridge concept is however dampened to a a certain

extent due to the absence of any specific IRC code / guidelines on the design and detailing

issues.

5.2. PLANNING CONSIDERATIONS:

It is important to ensure that the feasibility of IB concept for any project is established in the

early planning stage. Every site is not necessarily suitable for this type of structure and hence use

of this concept in situations where it is not suitable, should be avoided. The following factors

would influence the feasibility of adopting integral type of structure.

Length of the Structure:The longest bridge built in one continuous deck without

joints, except at the abutments, is the Kingsport Bridge in Tennessee (USA), which is 850

m long. In India, the maximum length of IB built so far is 150 m long. In India, the length

of the structure is limited to 150 m, until further studies and research is conducted on the

subject due to the absence of specific guidelines and codes.


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Climatic Condition: The IBs are sensitive to daily and seasonal changes in

temperature and moisture. Lesser the variation in temperature, lesser will be the force

induced on the structure. It may be hence noted that southern and eastern regions of our

country are more suitable for adoption this concept than the northern region.

Seismic Zone:In high seismic zone (i.e. zone IV and V), IBs should not be preferred

as they perform better under earthquake loads. The multiple degree of redundancy in the

structure helps to minimize the risk of failure.

Geometry of

the Structure:A complex geometry creates problems in the design of

IBs. Irregular structures i.e. where there are abrupt or unusual changes in the mass,

stiffness or geometry along the span should therefore be avoided. Preferably abutment

heights on either side shall be the same. A difference in abutment height will cause

unbalanced lateral loads resulting in sideway, which should be considered while

designing. This procedure is quite complex process which should be avoided.

Along with the above mentioned considerations, the following some of the planning

characteristics are also considered:

Complexity in Analysis and Design

Type of Superstructure

Type of Abutments

Type of Foundations and Sub-Soil Conditions.


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Fig 5.1 K L international Airport Curved Bridge

5.2 Fly over using integral bridge concept for Delhi metro length 115m


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Fig 5.3 Delhi Metro

5.3 ADVANTAGES OF INTEGRAL BRIDGES OVER CONVENTIONAL

BRIDGES:

1. Simplified details for construction.

2. Reduced life cycle cost and long term maintenance.

3. Improved design efficiency Improved riding quality.

4. Added redundancy with improved seismicperformanceEase in constructing

embankments.

5. Elimination of water leakage on critical structural elements.

6. Lesser tolerance restriction due to elimination of bearings andexpansion joints.

7. Faster construction.

8. Simplified widening and replacement detail Useful for strengthening of existing bridges.


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5.4 DISADVANTAGES OF INTEGRAL BRIDGES:

1. Design of Continuous Spans:The design and detail are much simplified with the

help of computer programs and design aids, the extra effort of designing continuous

spans can be minimized.

2. Joints off the Bridge: Cycle control joints, joints which facilitate longitudinal

cycling of bridges and approach slabs are provided between approach slabs and approach

pavement. For the shortest bridges, the usual pavement expansion joint is sufficient. For

longer bridges, however, specially designed cycle control joints are devised and

provided.

3.

Pile Loading: One primary concern expressed about the construction of integral

bridges with pile supported flexible abutments is the uncertainty about abutment pile

flexural stresses. However, for typical two and three span bridges, the amount of thermal

movement is less than an inch. Consequently, these stresses are generally ignored. For

longer bridges, actual bridge performance has shown that high pile flexural stresses do

not adversely affect bridge performance.

4. Buoyancy and Uplift: Care must be exercised when using integral bridges for

stream crossings because most deck type integral bridges are buoyant. Consequently, for

those bridges with superstructures which become submerged, air vents are provided

through the top of beam webs, and anchorage to piers are considered. For multiple span

bridges with short end spans, deck slab concrete for the end-spans are placed first to

prevent end-span uplift during deck slab placement.

5. Embankments:Since integral bridges receive significant support from embankments,

such bridges are built only in conjunction with stable, well consolidated embankments.

Consequently, integral bridge embankments are constructed first to ensure that


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embankments and sub foundation soils are consolidated and stabilized before the flexible

pier and abutment piles are driven.

6. Other Considerations:Integral bridges should be restricted to sites where not less

than 10 or preferably more than 15 feet of overburden is present (to ensure pile

flexibility and effective pile end-bearing), to sites where appreciable settlement is remote

(these bridges cannot easily be adjusted to compensate for large settlements), to sites

where skews of 30 degrees or less are appropriate, and to uncrowned sites where

embankments and extra spans can be added to avoid the use of wall-type abutments.

Fig 5.4 Dankuni-Palsit Flyover:

It is situated at the Durgapur Expressway. The deck is RC solid slab type integral with the twin piers. The bridge is a

joint less bridge without any expansion joint over intermediate piers without any bearings


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CHAPTER 6

COMPARISON OF INTEGRAL VS CONVENTIONAL BRIDGES:

1. Reduced Substructure Costs:

Abutments are composite structures. Whereas single Span jointed bridges with wall-type

abutments are designed to support embankments (Fig.6a), continuous multiple span integral

bridges on the other hand are built compositely with embankments and are supported by them

(Fig. 6b). In the first case, expensive wall-type abutments and abutment foundations are needed

to support embankments. In the second, cost savings are realized because integral bridges receive

much of their longitudinal and lateral support from embankments.

Fig 6: Different bridge types: a) single span with wall type abutments.

b) Multiple spans with stub-type abutments.

2. No Bearings and Joints:

Integral bridges can be built without bearings and deck joints. This will not only save

initial costs but also reduce maintenance efforts. This is an important benefit because presently

available deck joint sealing devices have such short effective service lives.


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3. Simplified Construction:

The simple characteristics of integral bridges make for rapid and economical

construction. For example, there is no need to construct cofferdams, excavation of footings is

made, backfill is placed, cofferdams is removed, bridge seats are prepared, bearings are placed,

back walls, and deck joints. Instead, integral construction generally results in just four concrete

placement days. After the embankments, piles, and pile caps have been placed and deck stringers

are erected, deck slabs, continuity connections, and approach slabs are followed in rapid

succession.

4. Minimized Deterioration:

The most obvious reason why integral bridges have become so popular, especially withtransportation departments located in and above the Snow Belt, is their outstanding resistance to

deicing chemical corrosion and deterioration. Since these bridges do not have movable deck

joints at abutments, deck drainage contaminated by deicing chemicals cannot penetrate bridge

deck slabs and adversely affect the primary bridge members.

5. Simplified Bridge Replacement:

While using multiple span integral bridges to replace single span structures with wall-

type abutments, the great adaptability of integral bridges allows them to span across existing

foundations, thus avoiding the need to remove them. Since small bridges are usually replaced in

50-year cycles, use of integral bridges with their simple pile foundations will considerably

simplify future bridge replacements.


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CHAPTER 7

CONCLUSION:

Integral bridges have become increasingly popular over recent years. Problems and costs

associated with failed expansion joints in conventional bridges not only make integral bridges a

cost-effective option but also means they have longer life spans than their counterparts.

The growing importance of integral bridges has highlighted the need for more

information and guidance to assist in improving bridge design.

The smooth, uninterrupted deck of the integral bridge is aesthetically pleasing, and it

improves vehicular riding quality. As temperature changes daily and seasonally, the lengths of

integral bridges increase and decrease, pushing the abutment against the approach fill and pulling

it away. As a result the bridge superstructure, the abutment, the approach fill, the foundation

piles and the foundation soil are all subjected to cyclic loading, and understanding their

interactions is important for effective design and satisfactory performance of integral bridges.


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REFERENCES

Alok Bhowmick, Design and construction of integral bridges - An innovative concept,

The Indian Concrete Journal, July 2003, Vol. 77, No 7, pp 1163-1174.

Alok Bhowmick, 2003, Design and construction of integral bridges- An innovative

concept, The Indian Concrete Journal, 77(7), pp 2235.

S.Ponnuswamy Bridge Engineering, Second edition, published by Tata Mc Graw Hill

publishing, 1986

The department for regional development Northern IrelandTheDesign of Integral

Bridges

Vasant C. Mistry1 Integral abutment and jointless bridgesStructural Engineer, Federal

Highway Administration, Washington, DC

6.integral bridges final report

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