Abstract
Nowadays prestressed concrete (PSC) bridges have become very common, but there are still many difficulties in predicting their long-term behavior. In order to predict the long-term behavior of PSC bridges, it is possible to use very complex formulas developed by various researchers or numerical analysis through computer, but many engineers are having difficulty in using such methods. Moreover, the accuracy of the prediction result is not satisfactory compared to the effort. On the contrary, the PCI Bridge Design Manual proposes a method that can easily predict the long-term behavior using multipliers. However, this method does not take into account various construction schedules and has some assumptions that are inadequate for the current situation in various girder sections and topping thicknesses. Therefore, in this study, new long-time factors were developed by modifying the multipliers of the PCI Bridge Design Manual by a rational manner. This allows prediction of long-term behavior of bridges taking into account various construction schedules and the characteristics of modern girder sections. The prediction results of the long-term camber and deflection of PSC bridges using the proposed multipliers were compared with those using the basic PCI Bridge Design Manual, the improved PCI Bridge Design Manual, KR C-08090 (same as ACI 318-14), and numerical analysis. As a result, the newly proposed method makes possible to predict the long-term behavior at any time after casting, and the accuracy of the prediction is also improved.
Highlights
The application of prestressed concrete (PSC) bridges has been increasing due to the development of highstrength concrete, the improvement of strength and quality of prestressing (PS) steel, and the development of structural analysis technology using computer program. e long-term behavior of these PSC bridges is very important because it directly affects the serviceability and safety of the bridge
In the PCI Bridge Design Manual [18], it is assumed that the period from casting to erection is about 30–60 days, and in this period, creep and drying shrinkage, which are the main factors of the long-term behavior, will have reached about 40 to 60% of the ultimate value
The multipliers for the composite cross section are required to be modified to reflect the characteristics of the cross section used in modern PSC bridges. erefore, in this study, new modified PCI multipliers were proposed to overcome these problems. e conclusions drawn from this study are as follows: (1) e new modified PCI multipliers were proposed by using the rate of creep and shrinkage over time
Summary
The application of prestressed concrete (PSC) bridges has been increasing due to the development of highstrength concrete, the improvement of strength and quality of prestressing (PS) steel, and the development of structural analysis technology using computer program. e long-term behavior of these PSC bridges is very important because it directly affects the serviceability and safety of the bridge. E ACI 318-14 [2] merely suggests an abstract guideline that additional time-dependent deflections of PSC members can be calculated by considering the stresses of concrete and steel bars under sustained load, the creep and shrinkage effects of concrete, and the relaxation of PS steels. The long-term deflection of PSC bridges can be calculated by using the concrete creep coefficient and drying shrinkage formulas given in various standards [3,4,5] Such formulas are somewhat complicated to use in practice because they need to take into consideration various parameters including concrete mix proportion and surrounding environment. Erefore, in this study, modified PCI multipliers for longterm deflection of PSC bridges considering various construction schedules and cross sections of modern PSC bridges were proposed so that the time-dependent deformation of PSC bridges can be more and accurately predicted
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