Effect of External Posttensioning on Member Forces of Determinate Pratt Pattern Bridge Truss
Ravindra P. M.1, Nagaraja P. S .2

1Ravindra P M, Associate Professor, Department of Civil Engineering, Bangalore Institute of technology, K R Road, V V Puram, Bangalore- 560 004, Karnataka, INDIA
2Nagaraja P S, Associate Professor, Faculty of Engineering-Civil, UVCE, Jnanabharathi, Bangalore University, Bangalore- 560 056, Karnataka, INDIA

Manuscript received on December 11, 2013. | Revised Manuscript received on December 15, 2013. | Manuscript published on December 25, 2013. | PP:31-35 | Volume-2 Issue-2, December 2013. | Retrieval Number: B0611122213/2013©BEIESP

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© The Authors. Published By: Blue Eyes Intelligence Engineering and Sciences Publication (BEIESP). This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)

Abstract: Transportation on land is the most common one among all the modes of transportation: may be on roads or railways. In India and abroad bridges have been built along roadways and railways in order to make the transportation system more efficient and economical. Some of them are steel truss bridges and majority of which are very old and have been designed as per the codal standards existing at the time of their construction. Problems with these truss bridges are that, they are deteriorated to such extents which are not able to resist the loads for which they are originally designed and/or they may not be able to match with the current loading and traffic requirements. Hence there is a need to strengthen these existing truss bridges. The method to be adopted for strengthening should be cheap and economical with minimum disturbance to the existing traffic. Even though there are different methods of strengthening of bridges, one of the best methods is the posttensioning by high tension steel tendons. In the present analytical investigation, only the truss portion of the steel truss bridge is undertaken for strengthening. Pratt pattern of the truss is considered as it is one of the commonly used trusses. In order to know the effect of posttensioning on member forces, the truss is externally posttensioned with twodrape tendon layout which is placed below the bottom chord. Stiffness matrix for two-drape tendon is developed and MATLAB computer programs are generated for the posttensioned truss analysis. From the results obtained after analysis, significant reduction in member forces is noticed and the reduction in member forces increases with the increase in the vertical distance between the bottom chord and tendon. If the truss is internally posttensioned by keeping tendon along the bottom chord, there will be reduction of forces only in the bottom chord members; whereas in external posttensioning, there is reduction in almost all the members of the truss and the percentage reduction is also more when compared to that due to internal posttensioning. Hence, to reduce the member forces external posttensioning is more efficient than internal posttensioning.
Keywords: Bridges, Chord, Posttensioning, Pratt, Tendon, Truss, Two-Drape