TEMPERATURE STRESSES EFFECT IN COMPOSITE GIRDER BRIDGES LOCATED AT JAIPUR IN RAJASTHAN

Vishnu Sharma, Dr A. K. Dwivedi

Abstract


Composite bridges exposed to environment undergo varying temperatures due to diurnal and seasonal changes
in climatic or atmospheric conditions. Temperature distributions in a bridge structure depend upon various
environments, meteorological and a bridge parameter. The important environmental parameters in􀃸uencing the temperature
distributions in a bridge structure are intensity of solar radiation, daily range of ambient air temperature humidity, cloud covers, wind
speed, turbidity of atmosphere etc.
Addition to these parameters the temperature variation in bridges is also affected by other parameters and also which includes
geographic location of the bridge as governed by the latitude and altitude, geometrical parameters and materials properties of the bridge
cross sections.
The aim of the study is to construct and instrument composite bridge, b) to subject the structure to thermal loading, and c ) to correlate the
experimental temperature distributions. Theoretical procedure provides a rational method for predicting the thermal behavior of
composite-girder bridge structures and it can be applied when used with realistic temperature , pro􀃶les, material properties, and
substructure stiffness characteristics.
Bridge structures are subject to complex thermal stresses which are varying continuously with time. The magnitude of these stresses
depends upon the temperature variation within the structure and this also depends upon the geographic location and the orientation of
the bridge, climatological conditions, geometry of cross section and thermal properties of the material and the exposed surfaces. Many
bridge designers recognize that the temperature variations can produce high stresses with little guidance is given in bridge design codes
on how these stresses can be accurately calculated. The distribution of temperature throughout the cross section of a bridge structure must
be known if the resulting stresses, reactions and deformations are to be calculated. Analysis of temperature distribution throughout the
cross section of a typical bridge structure is complex as temperature varies with time and also varies from section to section. In a concrete
bridge with constant cross-sectional properties over a long length, it is assumed that the temperature is constant over the bridge length
and varies through the depth and within the width of the cross section. Therefore, the temperature 􀃶eld to be determined at any time t is
two-dimensional. In this paper, a method of analysis based on 􀃶nite elements is described to determine the time-dependent temperature
variation within the cross section of a concrete bridge of arbitrary geometry and orientation for a given geographic location and
environmental conditions. The 􀃶nite element formulation for the analysis of transient heat 􀃸ow in a two-dimensional body is treated by
various authors.
In simply supported bridge linearly or uniform varying temperatures across the depth of bridge cross section produce no stresses but the
bridge is subjected to self equilibrating stresses due to non linear temperature gradients because of the restraint of thermal expansion that
would occur between the different 􀃶bers.
In continuous bridges, stresses of continuity are developed over the supports due to restraint of induced thermal curvature which is added
to self equilibrating stresses to get the total state of thermal stresses. Non Scienti􀃶c research studies have been carried out to calculate what
should be the design of thermal gradients.
The bridge designers are adopting British Code, BS 5400; 1978, IRC :6-2000 and Indian Railway Standards, IRS-1997 have also recommended
temperature gradients to be considered in the design.
The Heat Transfer analysis is used in solving the temperature 􀃶eld distribution. The analysis process should have two steps. The 􀃶rst step is to
solve the composite girder internal temperature 􀃶eld distribution and determining boundary conditions. After calculating the
temperature 􀃶eld, effect of thermal stress study is done.
A study related to thermal stresses has been carried out with 2 D and 3 D approach which shows signi􀃶cant change in thermal stresses for
varying span length in a simply supported bridge.
A computer program on 􀃶nite element method has been developed in ANSYS to study the thermal effects in composite girder bridges.
This study is carried out to predict the temperature distribution and thermal response of a composite girder bridge located in different
parts of country in three seasons ie winter, spring, summer respectively. The country is divided into 22 zones and it was seen that many
zones computed value of thermal gradients and the observed values of the corresponding stresses differ minutely.
The numerical implementation suggested the adequacy of classifying into seven zones and attempt has been made to put thermal design
recommendations for each zone.
To do this one city from each zone has been considered as the respective representative city to predict the thermal response of a composite
girder bridge.
A detailed parametric study has been carried out to determine the thermal gradients and induce stresses in composite bridge due to
variations in environmental, geometrical and materials parameters for one location ie Jaipur, the capital of Rajasthan which can be
repeated if necessary for the other zones.
Some aspects of study include:
a) Effect of the environmental parameters i.e. ambient air temperature, wind speed and turbidity factor.
b) Effect of bridge orientation.
c) Effect of geometrical parameters eg shapes of the cross section, variation in top concrete deck thickness, steel girder web thickness and
total depth of the cross section.
d) Effect of the material parameters like wearing coat of asphalt concrete over the top deck, percentage of steel in concrete sections,
modulus of elasticity and coefficient of thermal expansion of steel and concrete.
It has been seen that non linear thermal gradients and induced stresses in a composite girder bridge are maximum when the range of daily
maximum and minimum ambient air temperature is large, the turbidity of the atmosphere is low, the surrounding wind speed is minimum
and the top deck is covered with a thicker of asphalt concrete.


Keywords


temperature difference climatological atmosphere

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References


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