Volume : 7, Issue : 10, October - 2018

Temperature Stresses Effect in Composite Girder Bridges Located at Jaipur in Rajasthan

Vishnu Sharma, Dr A. K. Dwivedi

Abstract :

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