Analysis Of Creep Effect On Reinforced Concrete (RC) High Piers

Large amounts of high pier in long span prestressed concrete (PC) continous bridges or continous rigid bridges were built at the Southwestern mountain districts with complex geological conditions, and the difference of height of piers is sometimes obviously. Creep of concerete is intrinsic characteristic of material which will increase the vertical displacement of the pier and cause redistribution of stresses between concrete and steel in sections during the construction, and not only the creep secondary internal forces but the different values of vertical displacement in neighbor range high piers will be generated. In the meanwhile, creep will impact on the horizontal displacement in top of piers and the stresses in bottom section of piers. So it has theoretical significance and engineering value to study the effect of creep on reinforced concrete (RC) high piers.Combining with the construction process of continuous rigid bridge, creep effect of reinforced concrete pier in the various stages is analyzed. Combining with T-B equation in the pier construction stage and starting from the internal force balance equation of sections, the expression formula of vertical displacement in the top of the pier is summarized. During the cantilever construction of the superstructure, for the construction of the continuous rigid frame bridge is symmetrical, the effect of the construction process on the pier acts an axial force imposed on the pier and no moment. The method of vertical displacement of the pier in the cantilever construction stage can refer to the calculation expression of vertical displacement of the construction phase of the pier. After the closure of the superstructure, for convenience of analysis, the pier was regarded as an cantilever beam, and then the effect superstructure acted on the pier was treated as external loads. the time-dependent stress of bottom section was calculated with the use of T-B equation and the time-dependent horizontal displacement in the top of the pier was obtained by quadratic integral of sectional curvatural. As the secondary interior force and additional moment change with time, the creep effects also become time-dependent. In order to calculate the creep effect caused by secondary interior force and additional moment, reduction coefficient was introduced to consider the influence of ignoring creep effects middle time span produced on subsequent time span, whose idea was come from the introduction of aging coefficient in T-B equation. The horizontal displacement and vertical displacement in the top of the piers and the stresses of bottom sections at any time was calculated finally.Finally, all the deduced formula are developed by Fortran Language, which are used to calculate the vertical displacement of the pier of yu jin bridge in Guangzhou before the system conversion,as well as the horizontal displacement and the section stresses after the system conversion. Comparison between the results given by presented methods and given by software midas/civil show that the results given by presented methods are reasonable and effective.