后张法预应力筋伸长值在工程施工中的计算与校核

预应力筋伸长值的计算与校核是预应力张拉中的一个重要环节,对预应力工程施工具有重要的指导意义。

箍筋下料调整值法的修正

在箍筋下料长度计算众多方法中,箍筋调整值计算法精确度低,与实际相差较大。为使箍筋调整值法计算结果更加符合箍筋下料实际情况,基于现行相关规范和图集要求对其进行修正。通过对箍筋调整值法基本原理的深入分析,在原有的基础上对其公式进行修正,并与箍筋下料中心线长度计算结果进行比较,得出一种更精确、更符合工程实际的箍筋下料长度计算方法。

FRP筋无粘结预应力混凝土结构极限强度分析

FRP筋(Fiber Reinforced Plastics)是通过拉挤工艺胶合高强纤维形成,具有强度高、重量轻、耐腐蚀、无磁性等优良性能,可作为加强材用于盐害地区、海洋工程等条件严酷混凝土结构中,不仅可以解决钢筋锈蚀问题,提高结构的耐久性和使用寿命,而且还可以显著降低结构自重。提出将FRP筋应用于预应力混凝土桥梁结构最好选择无粘结预应力技术的观点,应用等效的塑性区长度来计算无粘结预应力结构FRP筋的极限应力,为结构极限强度分析提供必要技术指标。

设备安装中植筋技术的应用

结合工程实例,针对设备地脚螺栓安装过程中不易准确定位问题,采用“植筋法”克服施工难题;并介绍此工艺的工法及应用效果和适用范围,以提高设备运行的安全可靠性,降低了维修率。

后张法预应力施工伸长值的影响因素与控制方法

当前在后张法预应力张拉过程中,多采用预应力筋伸长值作为校核预应力施加效果的手段,阐述后张法预应力筋实际伸长值的测量方法;采用单因素敏感性分析法分析现行规范计算公式中各参数变化一定幅度时伸长值变化的程度,揭示伸长值对不同参数影响的敏感程度;从钢束理论伸长值计算、孔道和预应力筋安装、张拉设备及张拉操作过程四个方面分析影响伸长值的因素;对各因素在施工中控制的重要程度进行分级得出准确的预应力筋实际伸长值,以更好地校核桥梁结构的预应力施加状态,确保后张法预应力施工质量。

重视小构件的设计——植筋

本文通过对增设空调板植筋长度计算的实例，指出结构设计必须以专业规范为准，亲自核算，而不能未经核算盲目套用一些“经验”数据或引用一些非国家标准图集，以免留下安全隐患。

土层锚索浆体与筋体黏结强度的试验研究

国内外对锚杆筋体与浆体黏结强度的研究成果极少。3项工程64个土层锚索现场试验成果表明：①各锚筋与浆体极限黏结力的离散程度很大，普遍存在着孤低现象，据此反算得到的浆筋黏结强度的离散程度很大，离散程度与黏结长度无关，与锚筋数量及张拉工艺相关；②浆筋黏结强度与地层、注浆工艺及锚筋数量无关，带套管成孔、改善孔内清洁程度可明显提高；③浆体设计强度与浆筋黏结强度的对应关系无法验证，实际强度及锚筋外形对浆筋黏结强度的影响亦无法验证；④浆筋黏结强度的发挥程度随着黏结长度的增加而有所下降；⑤黏结长度3m～6m时，浆筋黏结强度标准值为0．744MPa～0．664MPa；⑥土层锚索黏结长度不宜短于8m；⑦单根锚索钢绞线数量不宜为2条。

浅谈预应力筋的伸长与校核

钢绞线预应力混凝土在桥梁工程中已普遍使用,作为质量双控指标的钢绞线张拉伸长值及锚固张拉力的计算,相应规范均已有明确规定,但在实际施工中,对预应力张拉的具体量测却存在较大差异。文章就此问题通过深圳地铁3#线高架桥施工的实践予以介绍。

Experimental study on concrete columns hybrid reinforced by steel and FRP bars under seismic loading

In order to study the dynamic behavior of hybrid reinforced concrete columns, shaking table tests of three concrete columns with equal initial stiffness were conducted.The longitudinal reinforcements include an ordinary steel bar,a steel-fiber reinforced polymer（FRP） composite bar（SFCB）, and hybrid reinforcement（steel bar and FRP bar, CH）. Test results show that the peak ground acceleration（PGA） responses of different columns are similar to each other. For an ordinary reinforced concrete（RC） column, the plastic strain of the steel bar develops rapidly after the PGA of the input ground motion reaches 100 cm / s^2, and the corresponding residual strain develops dramatically. For a SFCB column, even after the peak strain reaches 0. 015, the residual strain is below 5 × 10^- 4. For the hybrid column C-H,the residual strain of the FRP bar is similar to that of the SFCB column. In general, concrete columns with hybrid steel and FRP bar reinforcement can achieve smaller residual deformation, and the SFCB reinforced columns can be constructed in extreme environments, such as offshore bridges, due to good anti-corrosion performance.

Application of ALE Method on the Numerical Simulation of Reinforced Concrete Penetration

LS-DYNA program and the principle of ALE method were introduced, and the target features of the reinforced concrete penetration were analyzed by using the D material model and the ALE method. A numerical simulation has been done to show the penetration visually and veritably. The simulation results are analyzed carefully and explicitly prove their significance to the research of reinforced concrete penetration.

Flexural behaviors of FRP strengthened corroded RC beams

The flexural behavior of eight FRP （ fiber reinforced polymer） strengthened RC （reinforced concrete） beams with different steel corrosion rates are numerically studied by Ansys finite element software. The influences of the corrosion rate on crack pattern, failure mechanism, ultimate strength, ductility and deformation capacity are also analyzed. Modeling results show that the beams with low corrosion rates fail by the crushing of the concrete in the compression zone. For the beams with medium corrosion rates, the bond slip between the concrete and the longitudinal reinforcement occurs after steel yielding, and the beams finally fail by the debonding of the FRP plates. For the beams with high corrosion rates, the bond slip occurs before steel yielding, and the beams finally fail by the crushing of the concrete in the compression zone. The higher the corrosion rates of the longitudinal reinforcement, the more the carrying capacity of FRP strengthened RC beams reduces. The carrying capacity of RCB-1 （the corrosion rate is 0） is 115 kN, and the carrying capacity of RCB-7 （the corrosion rate is 20% ） is 42 kN. The deformation capacity of FRP strengthened corroded RC beams is higher than that of FRP strengthened uucorroded RC beams. The ultimate deflection of RCB-1 and RCB-7 are 20 mm and 35 nun, respectively, and the ultimate deflection of RCB-5 （the corrosion rate is 10% ） reaches 60 ilUn.

雨润国际广场裙房抗震加固设计

雨润国际广场裙房加固前为地下三层,地上五层的多层商业建筑。针对业主要求对其进行了增层和改造工作,对于改造后的建筑采用现行规范进行了整体设计和分析。并对基础加固和梁柱加固方法、植筋间距。

Analysis and application in controlling surrounding rock of support reinforced roadway in gob-side entry with fully mechanized mining

In order to optimize gob-side entry in fully-mechanized working face in moderate-thick-coal seams, we adopt a new attempt to pack roadside by pumping ordinary concrete, which is very important for the development of gob-side entry technology. The concrete has a long initial setting time and a low initial strength. So it is difficult to control the surrounding rock. In this paper, we analyze the effect of using roadside cable to reinforce supporting in gob-side entry surrounding rock controlling based on elas-tic-plastic and material mechanics knowledge. And then we propose a scheme that cable is used to reinforce roadside supporting and a single hydraulic prop is used as the temporary supporting in gob side. Using the numerical simulation software FLAC2D, we numerically simulated supporting scheme. Results of both the 2D modeling and the industrial test on No.3117 face in Jingang Mine prove that the scheme is feasible. The results show that the technology of protecting the roadway in gob-entry retained efficiently make up the deficiency of roadside packing with ordinary concrete, effectively control the roof strata and acquire a good result of retaining roadway.

Model Test and Numerical Analysis on Long-Term Mechanical Properties of Stepped Reinforced Retaining Wall

Model tests and numerical analyses of stepped reinforced retaining wall were performed to investigate the effects of rheology of backfill and creep of geogrids on the long-term performance of the structure.The geogrid tensions,soil pressures,wall deformations and foundation pressure were measured during model construction and loading.A visco-elasto-plastic model and an empirical nonlinear visco-elastic model were utilized to simulate the stresses and deformations of geogrid-reinforced earth-retaining wall under long-term loads.By comparing test data with numerical results,it is shown that the foundation pressure distribution is nonlinear,and the lateral constraint of geogrids for backfill can cause a redistribution of foundation pressure.The curve of soil pressure is outside convex at each step initially,and it is close to the distribution for the case of vertical wall subsequently.The variation trend of geogrid tensions at different heights is obtained.Moreover,the failure mechanism and development mode of potential slip surface in retaining wall are proposed.

Size effect of confined concrete subjected to axial compression

In order to investigate the size effect and other effects on the stress-strain relationship of confined concrete, 42 specimens with different sizes and section shapes were placed under axial compression loading. Effects of key parameters such as size of specimens, tie configuration, transverse reinforcement ratio, and concrete cover were studied. The results show that for specimens with the same configuration and the same volumetric ratio of the transverse reinforcement, along with the increasing specimen size, the peak stress, peak strain and deformation of the post-peak show a down trend, however, the volumetric ratio of the transverse reinforcement is lowered, the decreasing of the peak stress is accelerated, but the decreasing of the deformation is slow down. For specimens with the same volumetric ratio but different configurations of transverse reinforcement, though the transverse reinforcement configuration becomes more complicated, the peak stress of the large size specimen does not improve more than that of the small size. However, the deformation occurs before the stress declines to 85% of peak stress, and the improvement with the grid pattern tie configuration is much greater due to size effect.

预应力构件在施工过程中受力性能的检测评定

通过对某工程项目进行施工过程的监测,得出预应力筋的摩擦系数、锚具变形和钢筋内缩值等,明确了施工过程的各项数据指标,为保证工程质量提供了科学依据。

预应力混凝土结构施工异常问题的分析及解决和预防措施

在预应力混凝土结构预应力施工过程中常会遇见一些异常现象,针对预应力施工过程常出现的预应力筋伸长值不符、夹片开裂、力筋滑丝断丝等几个异常问题进行了分析。

Coupling model for calculating prestress loss caused by relaxation loss,shrinkage,and creep of concrete

The calculation model for the relaxation loss of concrete mentioned in the Code for Design of Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts(JTG D62—2004) was modified according to experimental data. Time-varying relaxation loss was considered in the new model. Moreover, prestressed reinforcement with varying lengths(caused by the shrinkage and creep of concrete) might influence the final values and the time-varying function of the forecast relaxation loss. Hence, the effects of concrete shrinkage and creep were considered when calculating prestress loss, which reflected the coupling relation between these effects and relaxation loss in concrete. Hence, the forecast relaxation loss of prestressed reinforcement under the effects of different initial stress levels at any time point can be calculated using the modified model. To simplify the calculation, the integral expression of the model can be changed into an algebraic equation. The accuracy of the result is related to the division of the periods within the ending time of deriving the final value of the relaxation loss of prestressed reinforcement. When the time division is reasonable, result accuracy is high. The modified model works excellently according to the comparison of the test results. The calculation result of the modified model mainly reflects the prestress loss values of prestressed reinforcement at each time point, which confirms that adopting the finding in practical applications is reasonable.

Numerical Analysis of Dynamic Behavior of RC Slabs Under Blast Loading

In order to reduce economic and life losses due to terrorism or accidental explosion threats, reinforced concrete （RC） slabs of buildings need to he designed or retrofitted to resist blast loading. In this paper the dynamic behavior of RC slabs under blast loading and its influencing factors are studied. The numerical model of an RC slab subjected to blast loading is established using the explicit dynamic analysis software. Both the strain rate effect and the damage accumulation are taken into account in the material model. The dynamic responses of the RC slab subjected to blast loading are analyzed, and the influence of concrete strength, thickness and reinforcement ratio on the behavior of the RC slab under blast loading is numerically investigated. Based on the numerical results, some principles for blast-resistant design and retrofitting are proposed to improve the behavior of the RC slab subjected to blast loading.

Test and Numerical Analysis on Performance of Reinforced Concrete Segment in Subway Tunnel

To investigate the mechanical behavior of segmental lining, a three-dimensional numerical analysis and test using three actual segments were used to analyze the effects of axial force and reinforcement ratio on the failure mechanism and ultimate bearing capacity of segmental lining. Both numerical and test results confirmed that the cracking load, yield and ultimate load were strongly influenced by axial force, and it was also proved that the yield and ultimate load would increase with the increase of reinforcement ratio, but the cracking load was almost not affected. The cracking load, yield and ultimate load are about 28.7%, 500% and 460% larger due to the effect of axial force respectively. The comparison between numerical calculation and test results showed that the finite element analysis resuits were in good agreement with the test results.