Determination of Defect Factors for a Road Bridge Made of Prestressed Concrete

The paper concerns determination of defect factors for a road bridge made of prestressed concrete. Cracking and permanent deformations of the continuous triple-span road bridge made of prestressed concrete were reported by road administration. Inspection of the bridge was carried out. Bridge design and erection documentation were researched. Hypotheses concerning defect factors were put forward. Parametric analysis of the bridge was carried out. The analysis showed that the cause of observed defects was faulty design of prestressing, namely: underestimation of prestressing force losses, underestimation of the influence of concrete shrinkage, and inappropriate tendon layout which introduced rapid changes to prestressing force. The general conclusions are: (a) symmetric prestressing of continuous main girders should be applied in zones where sagging and hogging bending moments occur in turns, (b) long prestressing tendons should be applied with care due to substantial prestressing force losses that may occur, (c) anchoring numerous tendons at the same cross-section should be avoided since it results in rapid variation of prestressing force, (d) variations of structure deformations due to prestressing should be recorded and checked against the predicted ones.