Computation of Secondary Moments in Prestressed Concrete Structures

The consideration and computation of secondary moments are important in the design analysis of continuous prestressed concrete structures. Such moments are secondary in nature but not in magnitude. Based on a comprehensive review of available methods of computing secondary moments such as equivalent load method, an alternative methodology of computing secondary moments is developed in this study. The proposed method discretizes an indeterminate structure into individual structural elements with end constrains. The concept of secondary moments under constraints is introduced in discrete structural elements. And they are computed as the function of primary moments in the structure. Secondary moments in the structure are then computed by applying basic principles in structural mechanics. The computing procedure is shown to be simple, prompt and accurate. The advantages of the proposed method over other existing methods are discussed and illustrated through numerical examples. In addition, the proposed computing method can be readily integrated into existing finite element codes of structural modeling and design. The application of the proposed method in practical design practice is demonstrated through a design case with complex tendon geometry.