Abstract:The difference of strain distribution, interface slip, stiffness, ultimate strength and other mechanical properties between a new type of external cable steel-concrete composite beam and ordinary steel-concrete composite beam is studied. The test results show that the rigidity and ultimate strength of the steel box-concrete composite beam with external cable increase by 54.15% and 27.72% compared with the ordinary steel box-concrete composite beam. Due to the effect of external cable, the brittle damage degree of the steel box-concrete composite beam is reduced, the strength and stiffness of the structure are increased, and the strain distribution and growth of the steel box-concrete composite beam are more reasonable. Therefore, the composite beam with external cable steel box and concrete has better mechanical properties. The experimental results show that the strain distribution of the section is nonlinear along the width direction, and the shear lag effect changes with the increase of the load, but is not constant. It is also found that the external cable stress is closely related to the maximum compressive strain of the concrete wing slab. On the basis of the experimental research, the section nonlinear analysis model and the calculation formula of the ultimate strength of the external cable-steel box-concrete composite beam are established. The calculated ultimate strength is in good agreement with the experimental results, which provides a meaningful reference and research way for the theoretical analysis and practical application of the ultimate strength of the external cable-steel box-concrete composite beam.

Abstract:Taking prestressed simply supported beam as an example, the change of prestressed beam in the process of transverse vibration is analyzed, and the differential equation of transverse bending vibration of prestressed beam is established. The modal perturbation method is used to further derive the approximate analysis method of the modal characteristics of prestressed beams, and the solution of the complex variable coefficient differential equation is transformed into the solution of linear algebraic equations, thus simplifying the calculation process effectively. Finally, the influence of prestress on the transverse vibration characteristics of the beam is discussed by an example. The results show that when the prestressed position has a large eccentricity, the prestressed position has a great influence on the natural vibration characteristics of the beam.

Abstract:According to the assumption of plane section deformation and considering the nonlinear properties of materials, the load-deflection relationship of prestressed CFRP reinforced concrete beams is calculated by the method of stepwise strain addition. The load-deflection curves of 5 prestressed CFRP reinforced concrete beams and 4 non-prestressed reinforced concrete beams are in good agreement with the experimental results. Based on the mechanical model, the nonlinear analysis of the secondary mechanical properties of the flexural members reinforced by prestressed CFRP is carried out, and the effects of the initial strain, section height and prestress on the flexural properties of the reinforced beams are studied. The results show that prestressing can effectively exert the high strength properties of carbon fiber, and the reinforcement effect of prestressed carbon fiber cloth under secondary stress is much better than that of non-prestressed carbon fiber cloth, which can effectively solve the problem of stress and strain lag under secondary stress.

Abstract:Aiming at the structural safety of large-tonnage steel cables in nuclear power plant containment, three-dimensional finite element method is used to establish a fine analysis and calculation model considering the influence of anchorage, grid reinforcement and channels, and the distribution of principal stress and transfer mechanism of concrete in anchoring area are studied. Combined with the local pressure stress distribution law of concrete in anchoring area, theoretical basis is provided for optimizing anchorage structure and reducing cost. The results show that using mesh reinforcement instead of spiral reinforcement can improve the cracking bearing capacity of specimens and effectively control the development of splitting cracks. The stress of the anchor itself is lower than the yield stress of the material during tensioning. The tensile fracture of the lower side of the anchor plate is the main type of damage that may lead to the damage of the special anchorage of the nuclear power plant containment in the process of cable tension.

Abstract:In the study of nuclear power plant containment, the analysis and calculation of prestress is a very important part. The distribution of the prestressed tendons in the containment is dense and complex, especially in the sensitive part of the gate entrance, the three-dimensional space curve shape appears, which increases the friction loss, and must be taken into account. Based on the analysis of friction and anchorage loss of prestress in CPR1000 stacked containment, a simple calculation method of the length affected by reverse friction and the curve of stress variation along the length direction of the standard section of containment, near the gate entrance and the prestress reinforcement of the containment dome are given for reference by engineering designers.

Abstract:The effective anchorage of the clip anchorage after prestressing is the ultimate embodiment of the structural quality of the post-tensioned prestressed box girder. In this paper, the reasons of anchoring failure are discussed from many aspects, such as mechanical properties of steel strand, position profile of hole, quality accuracy of anchor and tension control program. The corresponding treatment measures are put forward in order to provide guidance for the actual construction.

Abstract:In order to study the antiknock performance of the new composite anchorage structure, the field comparison test of the antiknock effect of the structure and the single anchorage structure in rock was carried out. The test results show that the critical failure load of the new composite anchorage structure cavity is 178% of that of the single anchorage structure cavity. In terms of damage degree, the single anchorage structure cavity is 2.5 times that of the new composite anchorage structure cavity. The optimization design of composite anchorage structure is a problem, and the optimization design factors include: diameter of empty hole, density of empty hole, depth of empty hole and depth of anchorage zone. The energy absorption effect of the new composite anchorage structure is very significant, and it is completely feasible to be used for anti-explosion reinforcement of rock medium caverns, and has remarkable technical and economic effects.

Abstract:3.3.3.2 Installation of arch rib system (1) The components are lifted in the precast yard by means of a four-leg lifting stool or a herringbones scraper. On the pallet, roll, drag on the light rail into gear, and then lift again, load on the 10t flat car, through the light track to the installation site, see Figure 18.