Flexural performances of prestressed high strength concrete piles reinforced with hybrid GFRP and steel bars

Abstract

This study developed prestressed high-strength concrete (PHC) piles reinforced with high-strength materials (glass fiber-reinforced polymer (GFRP) bars) for flexural performance enhancement. Flexural strengths and behaviors of PHC piles reinforced with hybrid GFRP and steel bars were experimentally investigated, respectively. Large-scale specimens with total lengths of 12,000?mm and diameters of 600?mm were constructed and tested under bending, accompanied by evaluation of effects of non-prestressed reinforcement type and longitudinal reinforcement ratio. J-factors were calculated to evaluate deformability of all the specimens. PHC piles reinforced with GFRP bars were demonstrated to have much higher flexural capacity than those reinforced with steel bars. Moreover, strains at the midspans of cross sections of all the specimens basically conformed to the assumption of plane section. Failure of PHC piles reinforced with GFRP bars was attributable to gradual concrete crushing, while that of PHC piles reinforced with steel bars resulted from steel yielding. Results of this study were expected to provide theoretical basis for wide engineering applications of PHC piles reinforced with hybrid GFRP bars and steel bars in marine structures.     

氯离子侵蚀对钢筋混凝土构件抗力影响的研究

氯化物是钢筋混凝土结构在使用寿命期内可能遇到的一种最危险的侵蚀介质,混凝土中钢筋表面的氯离子浓度超过一定的限值,钢筋就可能会发生锈蚀,锈蚀的钢筋会导致混凝土构件的承载力下降.通过分析国内外研究者所做的大量工作,讨论了氯离子侵入引起的锈蚀钢筋混凝土构件的抗力计算方法,为氯化物环境条件下混凝土结构的耐久性评估提供参考.     

沿海砼结构耐久性问题研究现状与对策

混凝土耐久性能不良引起的适用性、安全性问题以及由此引发的环境、能源、经济问题在全球范围内已引起广泛的关注.而沿海城市经济的飞速发展和大规模的开发海洋资源使得混凝土结构面临严峻的海洋环境的挑战.因此,了解沿海混凝土结构耐久性问题的研究现状与对策具有十分重要的现实意义.综合分析了沿海砼结构性能退化的原因及解决办法并在此基础上指出进一步研究的可能方向.     

Analytical Crack Model for 2-D Reinforced Concrete Structures

A two-dimensional smeared crack model for reinforced concrete members is presented. Special emphasis is placed on the bond between concrete and reinforcement as the main factor influencing tension stiffening in cracked reinforced concrete. With the derived tangential stress-strain equations for concrete in the direction perpendicular to the cracks, the constitutive relationship for cracked reinforced concrete is established. Experimental specimens have been analyzed with the analytical model, and the analytical and experimental results are found to be in good agreement.     

碳纤维布加固技术

碳纤维布是纤维增强塑料的一种,作为新型加固材料,克服了传统加固方法的诸多不足,可用于各种结构加固,具有良好的应用前景．     

电化学修复过程氢致钢筋塑性降低的影响与控制试验研究

电化学修复技术是提升既有钢筋混凝土结构耐久性重要方法,能有效除去有害氯离子,延长结构使用寿命。采用电化学修复技术对钢筋混凝土结构进行耐久性修复时,作为阴极的钢筋会发生析氢反应,当钢筋表面的氢浓度达到临界值时,钢筋的塑性会降低,并发展成裂纹,导致钢筋出现氢脆现象。开展了不同电化学参数的电化学修复试验,并采用物理方法和力学方法进行了氢致塑性降低的影响分析。结果表明氢致塑性降低与电流密度、应力水平均相关;当清楚工程构件的受力状态时,可采用合适的电流密度对构件进行电化学修复,控制塑性损失程度在工程的可接受范围内,以达到钢筋氢脆控制的目的。     

Chemical degradation characteristics of reinforced concrete reefs in South Korea

The chemical degradation characteristics of reinforced concrete reefs, which had been fully immersed in Tongyeong waters of South Korea for 18–25 years, were studied. In order to investigate the marine environmental impact on the concrete reefs, environmental factors, for example pH, have been observed between 1997 and 2002. Then, four reinforced concrete reefs recovered from different sites in Tongyeong waters were nondestructively tested. Finally, those test results were analyzed to determine the chemical deterioration. Based on the test results, it is shown that the reinforced concrete reefs have sound chemical properties and their originally estimated service life is secure enough for a further service period in water depths of 28–32 m. A concrete cover depth of 40 mm is recommended for the design of reinforced concrete reefs to achieve safety in marine environments and special events occurring during installation and construction.     

住宅现浇钢筋混凝土楼板裂缝成因及防治

在建筑工程中,现浇钢筋混凝土楼板出现裂缝的情况较多,这已成为影响住宅工程质量的一大通病。对其产生裂缝的原因进行了分析,并结合工程实际,就预防和综合治理提出了较全面的对策。     

基于广义扩散方程海工混凝土结构耐久寿命概率评估方法

针对国内现有的氯离子侵蚀寿命预测模型存在的问题,提出了基于广义扩散方程(GDF)的海洋环境下混凝土结构耐久寿命预测的概率方法.以某海上混凝土工程原位取粉测试及室内快速试验为手段,获得不同环境分区的时变模型参数统计值.采用随机抽样方法,实现结构各部位混凝土使用寿命的概率预测.通过对模型参数的敏感性分析讨论了该模型的优点.最后,提出了周期性检测,不断更新模型参数的动态寿命评估思路.     

A Method for Reinforcing the Ground Adjacent to the Footing Using Micropiles

The in-situ application of micropiles has gradually increased in limited spaces of downtown areas because the micropile has various advantages, such as low vibration and noise and compact machine size. In this study, model tests were carried out to understand the reinforcement effect induced by the mechanical interaction between the micropile and soil. The micropiles were installed in the soil adjacent to footings. Factors such as reinforced range (W) with piles, spacing (S) between piles, the installed angle (θ) of piles, and pile length (L) were considered variables in the tests. The reinforced angle (θ) was a more critical factor than the others for restraining the settlement and increasing soil stiffness in the model test results. The reinforcement effect rapidly increased around the reinforced range (W) of 2B (B: the width of a footing), the reinforced angle (θ) of 45 ～ 75°, and the pile length (L) of 3B. Based on the results of the experimental analyses, the purpose of this study is to improve the reinforcement efficiency of micropiles by recommending the most effective pattern and design method for installing them.     

Stress Variation Model of Bond Stress-Slip Relationship Between Steel Bar and Concrete

Based on the experimental data, a stress variation model of the bond stress-slip relationship between steel bar and concrete is established. The characteristic of the model is that the boundary conditions are satisfied very well; the effects of the material properties, the concrete cover, the crack spacing and the distance from the cracked cross section are considered. Good agreement between measured and calculated bond stress-slip relationship is found. This model is useful for the study of the stiffness, deformation and crack width of reinforced concrete members, and for the nonlinear analysis of reinforced concrete structures by the finite element method.     

Local joint flexibility of CHS X-joints reinforced with collar plates in jacket structures subjected to axial load

This paper aims to investigate the local joint flexibility (LJF) of tubular X-joints with collar plates subjected to axial load. A total number of 136 FE models were generated and analyzed to investigate the effect of collar plate size and joint geometry (η, τ_c, β, γ, and τ) on the local joint flexibility factor (f_LJF). Also, the weld profiles and the contact between the chord wall and the collar plates were modeled in the numerical simulations. Results showed that the increase of the collar plate thickness and length results in the decrease of the f_LJF. Despite the difference between the f_LJF of unreinforced and collar plate reinforced X-joints, there has not been any study on the f_LJF of the X-joints reinforced with collar plate. Also, there is no design equation for determining the f_LJF of the collar plate reinforced X-joints. Thus, the results of the parametric study were used to develop a design formula, to determine the f_LJF of X-joints reinforced with collar plates under axial load.     

Experimental study on the unconfined compressive strength of carbon fiber reinforced clay soil

To study the effect and mechanism of carbon fiber reinforced clay, a series of unconfined compression tests for clay reinforced with carbon fiber have been performed under the conditions of controlled water content and dry density. The carbon fiber is mixed into soil with the quality percentage of 0.01, 0.02, 0.03, 0.05, 0.1, 0.15, 0.25, 0.35, and 0.5%, then a certain quality of water was added in the soil to achieve the optimum soil water content. Ten groups of samples were tested by the unconfined compression experiment. The results showed that the incorporation of carbon fiber elements can effectively improve the unconfined compressive strength and brittle failure mode of soil. The soil is strengthened at the beginning and then weakened with the increased incorporation of carbon fiber, the effect is especially significant when the mix percentage becomes 0.1%. The interaction at the interface between carbon fiber surface and soil matrix is analyzed by using scanning electron microscopy (SEM). It is found that the enhancement mechanisms of carbon fiber reinforced soil are one-dimensional reinforcement of a single carbon fiber thread and three-dimensional reinforcement caused by fiber network respectively.     

Experimental Research on Shear Behavior of Reinforced Concrete Composite Beams Under Uniformly Distributed Load

An experimental program was carried out to study the shear behavior of the reinforced con-crete composite beam(RCCB)subjected to two-phase uniformly distributed load.A total of 12 reinforcedconcrete composite beams were tested:10 of them were the RCCB subjected to two-phase uniformly dis-tributed load,the other 2 were the comparative reinforced concrete beams cast at the same time as theRCCB subjected to one-phase uniformly distributed load.The interface of precast unit and recast concretewas natural and rough.The test range of the main composite factors:the ratio of precast section depth tocomposite section depth was from 0.35 to 0.65,the ratio of first-phase load moment to precast section ulti-mate bearing moment was from 0.25 to 0.65.Based on the test results,the stresses of the longitudinal rein-forcements and stirrups,the load-bearing properties of the interface,the crack state and the failure charac-teristics of the RCCB under uniformly distributed load are discussed.The effects of the stirrups,the     

A New Type Anticorrosion Coating for Ocean Reinforced Concrete Structures

—Corrosion of reinforced concrete structures is a serious problem in ocean engineering.As anorientation of study anticorrosion coating technique is developed and widely applied.but many problemsneed to be solved.LSW-2 type anticorrosion coating for maritime reinforced concrete structures is charac-terized by sea water resistance.salt fog resistance.moisture and heat resistance as well as impermeabilityto chlorions.The new type coating can be applied to wet concrete surface by conventional constructiontechnique.It is a breakthrough in solving the above- mentioned problem.The paper mainly introduces thetest results.the property indices.coating procedure.construction technique and economic benefit ofthe coating.     

Evaluation of Bearing Capacity for Multi-Layered Clay Deposits with Geosynthetic Reinforcement using Discrete Element Method

A stability analysis of reinforced foundation soil is presented in this paper. A method based on the discrete element method (DEM) is suggested for calculating the bearing capacity on strip footings over multilayer soils reinforced with a horizontal layer of geosynthetics. The proposed method can estimate the ultimate bearing capacity and the distribution of tensile force developed in the geosynthetics of the footing system by Winkler springs to account for the compatibility between soil blocks and tensile elements to consider the tensile behavior between soil and geosynthetics. For footings on various multilayer soils with or without reinforcement of geosynthetics, the results of the method were compared to the field test results as well as to those obtained by various methods proposed by other researchers.     

Shearing response of geotextile-reinforced calcareous soils using monotonic triaxial tests

Abstract

Different types of geosynthetic reinforcements have been widely used for improving shear strength of soil materials in recent decades. In this study, two different calcareous soils reinforced by geotextile layers were evaluated by monotonic compression triaxial tests. The calcareous soils were obtained from Hormuz Island and Boushehr Port located in the north coast of the Persian Gulf. Different reconstituted samples were prepared at dense conditions with and without geotextile layers and consolidated under different effective confining pressures ranging from 100 to 600?kPa. Different layers of reinforcements including one, two and three geotextile layers were placed in the reinforced samples and sheared under drained condition. The results show that confining pressure has a significant effect on the efficiency of reinforcements. Evidently, increasing the reinforcement layers decreased the particle breakage of the calcareous soils used in this study.     

玻璃钢渔船总纵弯曲的实船试验研究

本文通过实船试验研究玻璃钢渔船的总纵弯曲,以求得玻璃钢渔船应变和挠度随载荷的变化特性,从而了解玻璃钢渔船的总纵强度。     

非稳定性砼裂缝的处理

裂缝渗漏是引起钢筋混凝土破坏的原因之一,而非稳定性裂缝更因其不稳定性而难于处理。结合实例,介绍了一种针对非稳定性裂缝的堵漏施工方法。     

Prediction of Load Carrying Capacity of Corroded Reinforced Concrete Beam

A novel method for prediction of the load carrying capacity of a corroded reinforced concrete beam (CRCB) is presented in the paper. Nine reinforced concrete beams, which had been working in an aggressive environment for more than 10 years, were tested in the laboratory. Comprehensive tests, including flexural test, strength test for corroded concrete and rusty rebar, and pullout test for bond strength between concrete and rebar, were condueted. The flexural test results of CRCBs reveal that the distribution of surface cracks on the beams shows a fractal behavior. The relationship between the fractal dimensions and mechanical properties of CRCBs is then studied. A prediction model based on artificial neural network (ANN) is established by the use of the fractal dimension as the corrosion index, together with the basic intbrmation of the beam. The validity of the prediction model is demonstrated through the experimental data, and satisfactory resuits are achieved.