An Analytical Investiagtion on Deflections of Pratt Pattern Bridge Truss Posttensioned With External Tendons
Ravindra P M1, Nagaraja P S2

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 04, 2013. | Revised Manuscript Received on December 17, 2013. | Manuscript published on December 20, 2013. | PP: 23-28 | Volume-2, Issue-1, December 2013. | Retrieval Number: A0378122113/2013©BEIESP
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Abstract: Majority of the existing steel truss bridges all over the world are very old and more than 80 % of them inventoried in the United States are structurally deficient and/or functional obsolete. There is a need to strengthen these bridges in order to fulfill the present and future loading and traffic requirements. Posttensioning is one of the potential techniques to enhance the performance of these old steel bridges, as it creates redundancy in the structure and also, it is a simple, easy and economical method. In the present analytical study, determinate Pratt pattern of truss is posttensioned with external tendon layouts located below the bottom chord and their effectiveness in reducing deflection is studied. Stiffness matrix for truss member and twodrape tendon are formulated. Posttensioned Truss analysis is carried out in three stages: in first stage, for dead loads, in the second stage for dead loads and posttensioning loads and further in the last stage for other loads. The final deflections are obtained by superimposing the results of second and the third stage. External posttensioning reduced deflection and the reduction is more with the increase in distance between the bottom chord and the tendon. When compared to internal posttensioning along the bottom chord, external posttensioning is more effective in reducing deflections.
Keywords: Bridges, Posttensioning, tendon, stiffness, chord, deflections, redundancy.