水电站常态砼施工技术

结合实例对水电站中常态砼的工艺、技术等进行总结,希望能对类似的工程进行保质保量的施工有借鉴意义.     

磨细矿渣混凝土性能初步研究

运用试验分析方法,通过对不同掺量磨细矿渣的混凝土性能在室内进行有关试验,依据试验结果分析温度和不同掺量对磨细矿渣的混凝土的活性指数、强度的影响,并进一步探讨了磨细矿渣的混凝土的收缩性能、抗渗性能和防腐蚀的性能。     

Construction Stage Analysis on Replacement of Closure Segment in Prestressed Concrete Cable-stayed Bridges

To deal with failure of wet joint between a closure segment and its neighboring segments of main girder in an existing prestressed concrete cable-stayed bridge, the technology on replacement of closure segment was presented. In order to analyze structural characteristics of this technology, its technical approaches and construction key points were introduced. Then a FEM model for a typical prestressed concrete cable-stayed bridge was established, and a construction stage analysis method was given in detail, including establishing a structural basement calculation model for replacement of closure segment and simulating its construction procedures. Based upon calculation results, variations of some structural state parameters with construction stages, such as deck deflection of main girder, longitudinal horizontal displacement at the top of pylons, cable forces, were analyzed. The results showed, this method could reflect actual change process of structural state and existing inspected results of cable-stayed bridge, and FEM results could well meet with construction monitoring results during replacement of closure segment. Thus variations of structural characteristics with construction stages could actually be revealed. This method could provide references for design and construction control of replacement of closure segment in existing prestressed concrete cable-stayed bridges.     

Chloride Transport in Splitting Cracked Concrete at Marine Tidal Zone

The chloride ion transport in concretes with different size of splitting cracks at marine tidal zone is investigated. The splitting crack widths of concrete are about 003 mm, 005 mm, 010 mm, 015 mm and 030 mm. The cracked concrete and sound concrete are placed at marine tidal zone for 30 d, and the chloride ion content in crack zone and perimeter zone of concrete, chloride ion penetration depth and steel bar corrosion area are quantitatively determined. It is shown that splitting crack will be recovered when the concrete is unloaded in split test. And the splitting crack width of concrete should be characterized by the value of displacement sensor when the concrete is unloaded in split test. The chloride ion content of cracked concrete decreases with increased depth, and then gets to remain steady from 10 mm to the inner. The relationship between chloride ion content and crack width in the steady zone can be regressed as the exponential function and the linear function for the crack zone and the perimeter zone of concrete, respectively. Due to away from the crack zone, the influence of splitting crack width on accelerated chloride ion ingression in the perimeter zone is less than that in the crack zone. When the splitting crack width is more than 005 mm, the chloride ion penetration depth in crack plane and in vertical crack plane of concrete is 50 mm and 20 mm, respectively. And the steel corrosion area enlarges with the increasing crack width. And the chloride diffusion coefficient of cracked concrete is closely related to the resistance capacity to chloride penetration of concrete, crack density (matrix width, crack width), and chloride binding capacity of concrete. When the crack density of concrete is less than 70, the chloride diffusion coefficient of cracked concrete increases with decreased crack density linearly. The chloride penetration will accelerate near the crack zone. And the raised splitting crack width will lead to its influence area in concrete increased quickly.     

Experimental Analysis on Bending Capacity of Unbonded Prestressed Concrete Beams with HRBF500 Steel Bars

The bending capacity tests on ten simple supported beams were conducted to investigate the damage characteristics, prestress increment, beading capacity and displacement ductility of unbounded prestressed concrete beams with HRBF500 steel bars. The results show that the HRBF500 steel bars has yielded before the limit state. The concrete in compression zone crushes upon the broken of the beams, which shows a sudden damage mode. The measured ultimate stress increments of unbounded tendons are in linear relationship with the comprehensive reinforcement ratio index, while the values of the ultimate stress increments are obviously higher than those values specified in the code GB50010-2010, and the average ratio of predicted values to testing values is about 0.35. The mid span deflection upon yielding of the beams is large, while the displacement ductility is bad and the average value of the displacement ductility ratio is 1.67. The displacement ductility ratio decreases with the increases of the comprehensive reinforcement ratio index. Based on the experimental results, the proposed calculation formula of ultimate stress increments of unbounded tendons was established, and it is in good agreement with the experimental results when the testing value is less than 450 MPa.     

Numerical Simulation on Whole Construction Process of High-Rise CFST Structures

The time-changing analysis model for concrete filled steel tubes was established based on the time-changing concrete model of CEB-FIP MC90, in which the interaction between steel tube and concrete core was considered by the restraint conditions of master and slave nodes. The numerical simulation method was developed for analyzing the whole construction process of high-rise CFST structures. A real structure was taken as numerical example, in which the influence of concrete creep and shrinkage as well as construction process was considered. The results of numerical simulation are compared with those obtained from on-site monitoring. It is shown that the concrete creep and shrinkage as well as construction process have big influence on high-rise CFST structures, which should be taken into account in designs and constructions.     

Experiment and FEM Analysis on the Joint of Inserted Steel Beam

A new composite structure which is composed of steel beam and concrete girder is introduced in fuel electric plant construction. With different height of concrete girders with or without anchor bar, two scale models from an actual project were designed and tested. It is shown that the maximum restraining moment of ends of steel beams is approximately 60kN*m; influence of anchor bar is little; the one with 600mm high concrete beam is damaged by shear, and the others steel beam is damaged by bending failure. Finite element models were built for supplementary analysis, and the result indicates that critical value of the height of concrete beam of different failure modes is 700mm; stiffness of shear key and thickness of floor have great influence on the structure; size of anchor bar has little influence; and width of the end of the steel beam has certain influence.     

Dynamic Finite Element Model Updating of Prestressed Concrete Continuous Girder Bridge Based on Real-Coded Accelerating Genetic Algorithm

The dynamic finite element model (FEM) of a prestressed concrete continuous girder bridge (PCCGB), named Zhangjiagang river main bridge, was established and updated based on the results of field ambient modal testing using real-coded accelerating genetic algorithm (RAGA), which objective function was defined based on frequency index and correlation coefficient index for evaluating the updated FEM. The dynamic FEM of the bridge was updated based on seven experimental modal parameters. The prediction ability of the updated FEM were evaluated based on three experimental modal parameters. The updated results and prediction ability of updated FEMs indicated that they can reflect adequately the dynamic characteristics of actual PCCGB by using the above objective function and RAGA.     

Experimental Analysis of Extension Length of Shape Steel in SRC-RC Transfer Column

Seismic performance of SRC-RC transfer column was analyzed based on experiment of 12 specimens of transfer columns and 1 RC specimen under low cyclic reversed loading, which mainly focused on the extension length of shape steel. Analysis and comparison on skeleton curves of specimens was carried out. Analysis was completed for ductility, bearing capacity, energy dissipation capacity and degeneration ratio of strength. Displacement ductility changes with the increase of extension length of shape steel, enhancing at first, then reducing, and reaching peak value when extension length is close to three fifths of column height. Extension length of shape steel has little effect on bearing capacity. Energy dissipation capacity of transfer columns has relationship with many factors. Three fifths of column height is rational for extension length of shape steel, and specimens have not only advanced performance of energy dissipation but also good stability of stiffness and strength in this condition. The bond performance between concrete and shape steel decreases with the increment of extension length of shape steel, and hence stability of strength decreases.     

A Modified Chloride Ion Diffusion Model in Concrete

Based on the analysis of influencing factors chloride ion diffusion in concrete and the simplified model induced by Fick's second law, a chloride ion diffusion model was established, in which , the influences of water-cement ratio, humidity, time, temperature, chloride ion binding capacity of concrete and freeze-thaw cycle are taken into consideration. The Validity of the new model is verified through the comparison of results between the proposed model and the existing analytic /numerical model. Compared with the analytic model, the proposed model can consider the seasonal change of humidity and temperature,and the time-variant effect of freeze-thaw cycle.Compared with the numerical model, the computational efficiency of the proposed model is higher.