In order to study the durability degradation characteristics of concrete box girder under load and carbonation and chloride ion erosion, a scale model of concrete box girder was made for experimental research. According to the test results, the diffusion characteristics of chloride ions in the concrete box girder under the coupling effect of load and carbon dioxide were analyzed. By revising the calculation formula of the existing chloride ion concentration considering multiple factors, a calculation model of chloride ion concentration considering the influence of carbonation was proposed, and the test results were verified. The results show that the chloride concentration of the box girder on the same cross section is non-uniformly distributed due to the shear lag effect and the spatial structure. After considering the effect of carbonation, the difference rate of the improved model proposed in this paper is generally within 10%. Compared with the original model, the difference rate is reduced by a maximum of 19%.
Prestressed concrete girders with corrugated steel webs have received considerable attention in the past two decades due to their light self-weight and high prestressing efficiency. Most previous studies were focused on the static behavior of corrugated steel webs and simple beams with corrugated steel webs. The natural frequencies are very important characteristics when evaluating the dynamic responses of a bridge under external loads; however, very few studies have been conducted to investigate the dynamic behavior of full prestressed concrete girders or bridges with corrugated steel webs, and no simple formulas are available for estimating the natural frequencies of prestressed concrete girder bridges with corrugated steel webs. In addition, experimental work on full-scale bridges or scale bridge models is very limited. In this article, formulas for predicting the vertical bending vibration frequencies of prestressed concrete box girders with corrugated steel webs are proposed based on Hamilton’s energy variational principle. A one-tenth scale model is developed for an existing prestressed concrete box-girder bridge with corrugated steel webs. The frequencies predicted by the proposed formulas are compared to the finite element analysis results and also the experimental results from the scale bridge model. Good agreement is achieved between these results, indicating that the proposed formulas can provide a reliable and efficient tool to predict the vertical bending vibration frequencies of prestressed concrete box-girder bridges with corrugated steel webs.
To investigate the normal section strength and cracking bending moment of normal concrete–ultra-high-performance concrete (NC-UHPC) composite beams, calculation formulas were established considering the tensile strength of UHPC based on the current railway bridge design code. Using the railway T-beam as a template, prestressed NC-UHPC composite beams with different NC layer heights were built. A static bending test was performed, the pressure of the steel strand and the deflection and strain of the beam were measured, and the evolution of cracks in each beam was observed. The calculation formulas of the normal section strength and cracking bending moment of NC-UHPC composite beam were verified by the test. The results showed that the type of strain was similar to load-deflection curves with increasing load; the bending failure process of the NC-UHPC composite beam showed four obvious stages: elasticity, uniform cracking, crack development, and yield. Cracks in the beam started to appear at stage II, developed rapidly at stage III, and stopped emerging at stage IV. The calculation formulas for the normal section strength and the cracking bending moment of the NC-UHPC composite beam were in good agreement with the test values. Normal concrete with a compressive strength of 80 MPa can replace UHPC for the design of NC-UHPC composite beams.
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