Calculating ultimate tendon stress in externally prestressed continuous concrete beams using simplified formulas

This paper presents a brief review of equations proposed for calculating the increase in stress in external prestressing tendons at the ultimate stage. The validity of these equations to calculate the ultimate stress of external tendons in continuous beams was checked. Then, a simple method to calculate the stress in external tendons for continuous beams with or without symmetrical loading from the deformation of the strengthened member is presented and discussed. The steps of this method are simple and can be used at any stage of loading. Experimental results of 37 beams obtained from the published literature were used to check the accuracy of the proposed method. Several factors such as tendon type, internal and external prestressing forces, loading type, the presence of non-prestressed steel, tendon eccentricity/depth ratio, span/depth ratio, beam type, concrete strength, deviators number and deviator location were covered. The comparison between the actual and the calculated results showed good agreement.