| A series of experimental and analytical research of the concrete thin-walled box girder have been investigated in this paper. These include the flexural behaviors of reinforced concrete and externally prestressed concrete box girders as well as torsional behaviors of steel fiber reinforced high-strength concrete box girder. The main achievements are as follows:(1) The shear lag phenomenon has been confirmed based on the experimental study of flexural behavior of reinforced concrete box girder, which include the elastic behaviors of cantilever, continuous girder and simply-supported girder under uniform loads or concentrated loads, and behavior of simply-supported girder at breakage stage under concentrated loads, while strain distribution along height at rib is agree with the basic assume, i.e. Plane section before deforming remain plane. The experimental value of equivalent calculating coefficient of flange width has been obtained at elastic stage. Some valuable conclusions have been made by comparing with calculating value according to the code (JTG D62-2004): the calculated value according to the code prone to safe in root segment of cantilever, middle support section and middle span section of continuous girder; the experimental value agreed with well the calculated value. The breakage experimental results disclosed the full process law of equivalent calculated coefficient of compressed flange width at middle span section, and confirmed fine flexible behavior and ductility of reinforced concrete thin-walled box girder.(2) Considering particular characteristics of the concrete thin-walled box girder, if suitable element models and material constitutive laws is chose, the ANSYS program may simulate the fully flexural experimental process of the concrete thin-walled box girder. The analysis result is well agree with the experimental result. The section relative pressing height ζ and the maximum strain on the pressing flange εc have been considered as the main factors in determining the variation of equivalent calculated coefficient of compressed flange width in the middle span. And great deals of parameters have been analyzed. Based on the analyze values, the calculated formulae has been proposed about equivalent calculated coefficient of flange width at the middle span of simply-supported concrete thin-walled box girder in elastic state and carrying capacity limit state.(3) According to the conclusions of the equivalent calculated coefficient of flange width of simply-supported concrete thin-walled box girder, the fully process analysis of the equivalent I-shaped section girder has been conducted. The comparison shows a good agreement between the analytical results and the test ones of the box girders. Meantime, combined the flexural carrying capacity ultimate state characteristic of concrete thin-walled box girder, when the strain of longitudinal steel at tensile region firstly arrives at 0.01, the ultimate flexural capacity calculated formula and designed formula of concrete thin-walled box girder has been obtained. At normal service ultimate state, the crack and deformation of concrete thin-walled box girder were calculated according to corresponding code, without considering the equivalent calculated coefficient of flange width.( 4 ) The experimental study and analysis of the externally prestressed high-strength concrete thin-walled box girder showed that: The prestress loss may be calculated by the last code (JTG D62-2004) formula according to post-tensioned prestressed concrete structure, and calculated results agree with test ones. The external prestress increment mainly lies on the whole deformation of the members and the section eccentricity of the external prestressed tendons, also the calculated formulae before or behind cracks has been deduced. The experimental values of the limit stress increment of external prestressed tendons agree well with the value calculated by the Canada code (A23.3-94), while may be safe when calculated by the Chinese code (JGJ/T92-93).(5) A fully test on external prestressed concrete thin-walled box girder has been performed. The experiment and analysis values exposed that: strain distribution along height at rib in middle span is also agree with the basic assume, i.e. Plane section before deforming remain plane, and the shear lag phenomena has also been showed. The laws of equivalent calculated coefficient of flange width resembles with that of reinforced concrete box girder. The action of external prestressing prolonged elastic state range and reduced the vary rapidity of equivalent calculated coefficient of flange width after concrete cracking, but it hardly influenced the equivalent calculated coefficient of flange width in elastic state and carrying Capacity limit state. The ultimate flexural capacity calculated formula and designed formula of reinforced concrete thin-walled box girder may also be applicable for the external prestressed concrete thin-walled box girder.(6) At normal service limit state, the deflection of external prestressed thin-walled reinforced concrete box girder can be calculated according to prestressed... |
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