Effect Of Tensioning Method On Internal Forces And Its Design In Multi-story Prestressed Concrete Framed Columns

Prestressed concrete structures are widely used in civil engineering in China. Among them the prestressed concrete frame gradually becomes an important structural type due to its advantages in large spans, overall integrity, and excellent performance in cracking control, as well as comprehensive economic efficiency.However, when implementing the prestressed techniques for large span frame structure, some issues still remain to be unsolved and unclear in the design and construction process. For example, the construction of prestressed concrete structures is different from that of reinforcement concrete structures. It not only asks for higher requirements in technology, but also has more close relationships to design and construction, as different assumptions in design and construction method may cause different internal forces.The design of prestressed concrete frame based on the current method does not consider that the structural types and bearing load vary with the construction process. The designed internal forces value deviate from the real value resulting from that analytical model is different from practical construction method. On this point, some researches were undertaken by comparing the so called "Cast-in-place and Prestressed Story-by-Story" construction method adopted in multi-storied prestressed concrete frame structure with the popular method of "Prestressed after Completion of Construction".Based on theories of structural mechanics and analysis of analytical results, discussion was made to effect of different tensioning construction methods on the comprehensive and designed bending moment in the frame columns. Analytical and computational results show that the effect is much significant. The discrepancy between the comprehensive moment derived from the measured value is relevant with such factors as the number of spans, location of sections, and linear stiffness ratio of beam to column. Compared with the results derived from internal forces based on the current designed method, the influence of "Cast-in-place and Prestressed Story-by-Story" to the bending moment of frame columns is more favorable, so the current methods are adopted to design the frame columns.