Study on effectiveness of IRC Live load

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International Journal of Mechanics Structural.

ISSN 0974-312X Volume 3, Number 2 (2012), pp. 97-106

International Research Publication House

http://www.irphouse.com

Study on Effectiveness of IRC Live Load on R.C.C.

Bridge Pier

M.G. Kalyanshetti and C.V. Alkunte

Assistant Professor, Civil Engineering Department,

Walchand Institute of Technology, Solapur, IndiaP.G. Student, M.E. Civil-Structures,

Walchand Institute of Technology, Solapur, India

E-mail id: [email protected], [email protected]

Abstract

Pier is an important and most critical element of bridge structure as it acts as a

media to transfer the load from superstructure to foundation. Piers are

subjected to various forces in longitudinal and lateral direction such as windforce, water current force, seismic force etc. Realistic estimation of these

forces is required for efficient design of pier. I.R.C. codal provisions are used

for correct estimation and effect of various forces on bridge pier. Hence

separate study is required for various height of pier and span of bridge to

understand effectiveness of IRC live loads as well as to find out shape

optimization which will lead to effective selection of bridge pier. For the

above study computer programming is developed. A parametric study is

carried out for effectiveness of IRC live load for various height of pier and

span of bridge for different shape of pier. At the end effectiveness of IRC live

load for various height of pier and span of bridge for different shape of pier isstudied. The study reveals that pier designed by considering IRC class A

loading should be checked for IRC 70R wheeled loading.

Keywords: Indian Road Congress, Bridge pier, Shape of bridge pier, IS 456-

1978 (SP 16:1980), C. Language

IntroductionThe general shape and dimension of a pier depends to a large extent on the type,


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98 M.G. Kalyanshetti and C.V. Alkunte

width and span of superstructure. In the present paper piers of rectangular, square and

circular shapes are presented. Various forces acting on bridge pier and their

estimation is done as per IRC codal provisions. Some forces will act in combination

with other forces. Hence different load combinations are considered as mentioned by

IRC, to identify sever combination. After arriving at server combination, pier section

is designed by using interaction diagram given by IS 456-1978 (SP 16:1980).

Indian Road CongressThe Indian Road Congress (IRC) has formulated standard specifications and codes of

practice for road bridges with a view to establish a common procedure for the design

and construction of road bridges in India. The specifications are collectively known asthe Bridge code. Prior to the formation of the IRC bridge code ,there was no uniform

code for the whole country. Each state (or province) had its own rules about the

standard loading and stresses.

The Indian Roads Congress (IRC) Bridge code as available now consists of eight

sections as below

Section-I General features of design

Section-II Loads and stresses

Section- III Cement concrete (Plain and reinforced)

Section- IV Brick, stone and block masonry

Section V Steel road bridgesSection VI Composite construction

Section- VII Foundations and Substructures

Section-VIII Bearings

Forces Acting On Bridge Pier

Dead load of superstructure and pier itself. Live load of traffic passing over the bridge .The effect of eccentric loading due

to live load occurring on one span only need to be considered.

Impact effect Effect of wind on moving loads and on the superstructure. Longitudinal force due to tractive effort of vehicles. Longitudinal force due to braking of vehicle. Longitudinal force due to resistance in bearing. In order to reduce the net

longitudinal force in bearings, it is usual to make bearing of two spans located

on a pier to be of same type i.e. expansion or fixed bearing. Still a variation of

about 10% in frictional coefficient of sliding bearing may be assumed. Also the

resistance in two adjacent bearing would differ when live load occupies only

one of the adjacent spans.


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Study on Effectiveness of IRC Live Load on R.C.C. Bridge Pier 99

Seismic effects

Buoyancy force

Load CombinationAll above mentioned forces are to be considered and the total force on pier is

determined. But all above mentioned forces will not act at a time on pier. For

example, seismic and wind forces are not considered to act simultaneously and hence

these two need not be considered together. In this way for each probable load

combination, the total force likely to act on pier in lateral and longitudinal direction is

determined and the combination giving maximum values are to be considered for

design purpose.

As per I.R.C.-78, CL-706.1, following load combination cases are considered,

CASE-I DL+LL+ water current forces + braking forces + Temp, shrinkage

forces + buoyancy force

CASE-II CASE-I for one span dislodged condition

CASE-III CASE-I + Seismic force (Longitudinal direction)

CASE-IV CASE-I + Seismic force (Transverse direction)

CASE-V CASE-I + wind force (Longitudinal direction)

CASE-VI CASE-I + wind force (Transverse direction)

For each case , following force actions, at base of pier are to be determined,

Total Axial Load Total Force in longitudinal direction Total Force in lateral direction Total Moment in longitudinal direction Total Moment in lateral direction

While considering different load combinations, As per IRC-78, permissible

stresses are increased by 33.5% for wind combinations and 50% for seismic

combination.

Parametric studyPiers are of different shape. The suitability of different shape depends on various

factors such as, height of pier, span of bridge, type of bridge etc. In the present paper

an attempt is made to understand the various live loads given by the Indian Road

Congress (IRC) for different shapes of pier with respect to different height of pier and

span of superstructure. For the study following shapes of piers are considered,

Rectangular ( d/b = 1.4)


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Square

Circular

For the given configuration, cross sectional area, intensity of wind force, intensity

of water current force required for analysis is kept constant for all type of section ie

Rectangular, Square, and Circular so as to study variation of different live load.

Above mentioned shapes are studied and the effectiveness of various live load is

studied. In the analysis following IRC live loads are considered.

IRC class AA Tracked loading. IRC class AA Wheeled loading. IRC class A Two lane loading. IRC 70R Tracked loading. IRC 70R Wheeled loading.

Data for Load Estimation on Pier

The force estimation on pier is done as per I.R.C. codal provisions. Some forces will

act in combination with other forces, Thus there are different probable load

combination, likely to act on pier. Different load combinations are considered as

mentioned by I.R.C. and for the sever combination pier section is analyzed.

Following data is assumed for Load estimation on pier,

Superstructure: Box type Girder ( Two Box) having weight 120 kN/RMT Carriage way width: 7.5 m.

The effectiveness of different IRC live load on pier w.r.t. various height as well as

various spans of superstructure are studied by parametric investigation and are

presented in the form of graph as follows,

Variation of axial force of pier w.r.t. Height of pier for different IRC live loadsas shown in Fig 1.

Variation of axial force of pier w.r.t. span of superstructure for different IRClive loads as shown in Fig 2.

Variation of longitudinal moment of pier w.r.t. span of superstructure fordifferent IRC live loads as shown in Fig 3. Variation of transverse moment of pier w.r.t. span of superstructure for different

IRC live loads as shown in Fig 4.

Variation of longitudinal moment pier w.r.t. height of pier for different IRC liveloads as shown in Fig 5.

Variation of transverse moment of pier w.r.t. height of pier for different IRC liveloads as shown in Fig 6.


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Study on Effectiveness of

Figure 1: Variation o

Live Loads

Figure 2: Variation of A

Live Loads

RC Live Load on R.C.C. Bridge Pier

f Axial Force (KN) W.R.T. Height of Pier f

ial Force W.R.T. Span of Super Structure f

101

or Various IRC

or Various IRC


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102

Figure 3: Variation of Lo

various IRC Live Load

M.G. Kalyanshetti an

ngitudinal moment (kNm) W.R.T span of su

d C.V. Alkunte

perstructure for


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Study on Effectiveness of

Figure 4: Variation of T

various IRC live Load

RC Live Load on R.C.C. Bridge Pier

ansverse moment (kNm) W.R.T span of su

103

perstructure for


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Figure 5: Variation of Longitudinal Moment (kNm) W.R.T height of pier for various

IRC Live Loads


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Study on Effectiveness of IRC Live Load on R.C.C. Bridge Pier 105

Figure 6: Variation of Transverse moment (kNm) W.R.T height of Piper for VariousIRC live Loads

ConclusionThis study is done for various height of pier and span of bridge super structure to

understand effectiveness of IRC live loads. The study is also done for various shapes

of pier to find out shape optimization. For the above study computer programming is

developed.


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Prominent conclusions are as follows.

After analysis and design of R.C.C bridge pier of Circular c/s, Rectangular c/sand Square c/s, The axial force as well as moments along both longitudinal

direction and transverse direction found to be minimum for circular c/s therefore

circular c/s found to be economical.

Axial force calculated by IRC A two lane loading gives maximum axial force,And IRC AA wheeled gives minimum axial force.

Longitudinal moment calculated by IRC A two lane gives maximum momentand IRC AA wheeled gives minimum longitudinal moment.

Transverse moment calculated by IRC 70R wheeled loading gives maximummoment along transverse direction and IRC AA wheeled gives minimum

transverse moment.

IRC:6-2000 clause number 201.1 provided provision for design of superstructure is Bridges designed for IRC class AA loading should be checked forclass A loading. Therefore it is suggested that such guideline also be require to

provide for design of pier also. As mentioned earlier IRC class A two lane gives

maximum moment along longitudinal direction where as IRC 70R wheeled

loading gives maximum moment along transverse direction therefore it is

suggested that pier designed by considering IRC class A loading should be

checked for IRC 70R wheeled loading

References

[1] D. Johnson Victor, Essentials of Bridge Engineering, Oxford and IBHPublishing company Pvt. Ltd, New Delhi.

[2] Design aids to Indian Standard Code of Practice for Plain and ReinforcedConcrete, SP -16-1980, Indian Standard Institution, New Delhi.

[3] Indian Standard Code of Practice for Plain and Reinforced Concrete, IS: 456 2000, Indian Standard Institution, New Delhi.

[4] Standard specifications and code of practice for Road Bridges, section -I, IRC-5, General features of Design, The Indian Roads Congress, New Delhi

[5] V.K. Raina (1994), Concrete Bridge Practice- Analysis, Design andEconomics, Tata McGraw Hill Publishing Company Ltd., New- Delhi.

Study on effectiveness of IRC Live load

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