Creep & Shrinkage Analysis of Two Span Continuous Prefelx beam Moon Gu Kim
ABSTRACT These days in Korea, the bridges using preflex beam have been constructed because of height limitation. Due to crack in such bridges, two major difficulties encounter while construction and use. This problems can be raised because the longterm behaviors of preflex beam are usually neglected while designing. The major drawbacks of steel composite structures are loss of prestress because steel restrains deformation of concrete. Especially in the preflex beam, stress loss by creep and shrinkage is big due to a lot of compression forces induced at the initial time and high steel ratio on the cross section. Furthermore, preflex beam systems constructed in Korea are simple beam type, which is facing maintenance problems at the expansion joints and supports. Therefore the continuity of preflex beam is highly demanded. However, if the continuity of preflex beam is done, the behavior of structure becomes complex due to secondary effects and increment of construction steps. It is difficult to consider at the all construction steps, so to solve these problems simplified works and parameter study about longterm behaviors are necessary. In this study, the analysis method was proposed and experimental works were performed to prepare design criteria about longterm behavior of 2 span continuous preflex beam. In the analytical studies, the phased analysis method was proposed using AEMM(Ageadjusted Effective Modulus Method). This analysis method was verified by experiment and three dimensional finite element method using the commercial program DIANA. Experimental works were performed for 70days using vibration wires on the 2span continuous preflex beam model. The results of experiment estimated initial effects of creep and shrinkage, and verified the proposed analysis method. And then using the analysis method verified by experiment and F.E.M, parameter study was performed in order to estimate the degree of effects of each variable. Finally, throughout these procedures the criteria of longterm behavior analysis of 2 span continuous preflex beam were proposed.
Key Word Creep, Shrinkage, 2 Span Continuous Preflex Beam, AEMM(Ageadjusted Effective Modulus Method)
