Influence of chloride corrosion on the effective mechanical properties of steel reinforcement

This paper presents a methodology to develop advanced reduction factors for the effective mechanical properties of corroded steel reinforcement of reinforced concrete (RC) members. The reduction factors (mainly developed for bare steel reinforcement) reported in the literature scatter over a large range. In this regard, critical questions arise, such as the reliability and accuracy of the reduction factors of bare steel bars to evaluate residual capacity of corroded RC structure. This paper will provide answers to these questions based on reviewing past studies and the results observed from experimental inspection of corroded steel reinforcement carried out in this research. The results show using the reduction factors of bare steel bars to estimate residual capacity of corroded RC structures is not safe because they are significantly lower than the reduction that happens in real corroded RC columns.     

Life-cycle reliability assessment of reinforced concrete bridges under multiple hazards

This paper proposes a novel probabilistic methodology for estimating the life-cycle reliability of existing reinforced concrete (RC) bridges under multiple hazards. The life-cycle reliability of an RC bridge pier under seismic and airborne chloride hazards is compared to that of a bridge girder under traffic and airborne chloride hazards. When conducting a life-cycle reliability assessment of existing RC bridges, observational data from inspections can provide the corrosion level in reinforcement steel. Random variables related with the prediction of time-variant steel weight loss can be updated based on the inspection results using Sequential Monte Carlo Simulation (SMCS). This paper presents a novel procedure for identifying the hazards that most threaten the structural safety of existing RC bridges, as well as the structural components with the lowest reliability when these bridges are exposed to multiple hazards. The proposed approach, using inspection results associated with steel weight loss, provides a rational reliability assessment framework that allows comparison between the life-cycle reliabilities of bridge components under multiple hazards, helping the prioritisation of maintenance actions. The effect of the number of inspection locations on the updated reliability is considered by incorporating the spatial steel corrosion distribution. An illustrative example is provided of applying the proposed life-cyle reliability assessment to a hypothetical RC bridge under multiple hazards.     

安哥拉共和国司法大楼安全鉴定与加固设计

安哥拉共和国司法大楼在装修前需进行鉴定和加固,加固前进行了全面检测鉴定,根据鉴定结果,综合采用喷射混凝土、植筋、外包钢、粘贴碳纤维布等方法进行加固,解决了技术难题。     

螺栓灌胶节点对螺栓钢板加固钢筋混凝土连梁抗震能力影响的试验

为了提高小跨高比既有连梁的抗震性能,提出了一种新型的螺栓钢板加固法和一种新型的钢板屈曲控制装置。按照1∶2比例制作3个钢筋混凝土连梁试件,通过低周往复荷载试验研究了螺栓灌胶节点对钢板加固钢筋混凝土连梁的影响。结果表明:未采用螺栓钢板法加固的连梁呈现出脆性剪切破坏;采用螺栓钢板法进行普通高强螺栓加固的连梁,其强度和延性并没有提高;采用螺栓钢板法进行螺栓灌胶节点加固的连梁,其强度、延性和耗能能力得到大幅度提高。     

锈蚀钢筋混凝土梁抗弯承载力计算方法

目前对锈蚀钢筋混凝土梁抗弯承载力的研究主要考虑锈蚀程度的影响,忽视了构件本身参数不同对承载力退化的影响,导致不同学者提出的锈蚀钢筋与混凝土的协同工作系数差异较大。为合理评估既有锈蚀钢筋混凝土梁的剩余承载力,首先对锈后无黏结钢筋混凝土受弯构件进行模拟试验与有限元分析,系统分析严重锈蚀混凝土构件钢筋应力水平的主要影响因素,发现截面配筋指标可综合反映混凝土强度和截面配筋率对受拉钢筋应力水平的影响,并确定基于截面配筋指标的锈后无黏结混凝土梁受拉钢筋强度利用系数;对一般锈蚀钢筋混凝土梁抗弯承载力的退化机理进行深入分析,综合考虑钢筋锈蚀程度和截面配筋指标的影响,建立一般锈蚀混凝土梁钢筋强度利用系数计算公式;提出概念明确、通用性强的锈蚀钢筋混凝土梁抗弯承载力计算方法;与大量的试验结果进行对比验证,计算方法的吻合性较好。     

Segmentbrücke aus textilbewehrtem Beton: Konstruktion,Fertigung, numerische Berechnung

Segmental Textile Reinrorced Concrete Bridge Design, Manufacturing and Numerical Simulation Concrete provides a brought variety of construction and design possibilities. The low tensile capacity of concrete is taken by reinforcement of steel, short fibres or textile fabrics. Textile reinforced concrete (TRC) is a high performance composite in which technical textiles made of high performance fibers are embedded in a fine‐grained concrete matrix. Because of the corrosion resistance of the textile materials, thick concrete covers as known in ordinary reinforced concrete are no longer needed. Slender new concrete elements extend concrete application to completely new fields and gives architects and engineers more design possibilities. Design, reinforcement concept, production, approval tests, and numerical simulations considering uncertain data are demonstrated for the first bridge made of textile reinforced concrete. It is shown that application of this new, sophisticated composite material is already possible, although more research is needed.     

混杂纤维自密实混凝土梁受弯性能的试验研究

在纤维自密实混凝土工作性试验的基础上,对7组无筋混杂纤维自密实混凝土梁和5组混杂纤维增强低配筋率的钢筋自密实混凝土梁受弯性能进行试验研究,并分析纤维类型和纤维长径比对梁的开裂荷载、屈服荷载、极限荷载以及弯曲韧性的影响。结果表明:梁的弯曲韧性随着纤维长径比的增加而增加,混杂纤维混凝土梁的弯曲韧性优于钢纤维,两种纤维协同作用时具有很好的正混杂效应;与最小配筋率的钢筋混凝土梁相比,纤维的掺入明显地改善了梁的屈服荷载和极限荷载,掺有(40+4)kg/m3混杂纤维并按最小配筋率配筋的梁的极限荷载与仅按1.5倍最小配筋率配筋的梁相当。     

竹筋混凝土楼板的结构性能检验及评估

上世纪50年代末、60年代初,我国由于大量缺乏钢铁,不少建筑物用竹筋代替钢筋作为受力筋,制作小跨度混凝土构件,节省了不少钢材。目前,这批建筑物使用至今已近50a,接近钢筋混凝土结构的正常使用年限,因此,必须对这部分竹筋混凝土建筑物的结构性能进行重新检验和评估。以某高级中学教学楼为例,较详细介绍了竹筋混凝土结构性能检验方案的确定、检验数据的处理以及竹筋混凝土结构的性能评估等,以期对国内同类建筑物的性能检验与评估提供参考。     

Experimental flexural behavior of SMA-FRP reinforced concrete beam

The most critical drawback in currently used steel reinforcement in reinforced concrete (RC) structures is susceptibility to accumulation of plastic deformation under excessive loads. Many concrete structures due to damaged (yielded) steel reinforcement have undergone costly repairs and replacements. This research presents a new type of shape memory alloy (SMA)-based composite reinforcement with ability to withstand high elongation while exhibiting pseudo-elastic behavior. In this study, small diameter SMA wires are embedded in thermoset resin matrix with or without additional glass fibers to develop composite reinforcement. Manufacturing technique of new proposed composite is validated using microscopy images. The proposed SMA-FRP composite square rebars are first fabricated and then embedded in small scale concrete T-beam. 3-point bending test is conducted on manufactured RC beam using a cyclic displacement controlled regime until failure. It is found that the SMA-FRP composite reinforcement is able to enhance the performance of concrete member by providing re-centering and crack closing capability.     

叠合法加固混凝土结构的适用性和工程实例

既有混凝土结构的加固改造方法很多,如叠合法、粘钢法、粘贴碳纤维方法等。通过具体的工程加固实例,对比分析各种方法的适用性,以其为类似工程提供参考。     

钢筋加劲T形截面钢管混凝土柱抗震性能试验研究

制作4根钢筋加劲的T形截面钢管混凝土柱、1根非加劲T形截面钢管混凝土柱和1根T形截面钢筋混凝土柱试件,对其进行低周往复水平荷载作用下的滞回性能试验,研究其破坏模式和滞回性能,分析钢筋加劲肋的作用机理以及钢管对混凝土的约束作用。结果表明：相比T形截面钢筋混凝土柱,T形截面钢管混凝土柱破坏程度有明显减轻,刚度、承载力以及耗能性能均有明显提高;钢筋加劲肋能有效限制钢板局部屈曲和阴角处钢管与混凝土脱离,保证钢管和混凝土共同工作,对拉钢筋加劲肋相对锯齿形钢筋加劲肋的效果更加显著;含钢率较高的钢管混凝土柱承载力更高,耗能能力更好;轴压比从0.2增加到0.4时,钢筋加劲的T形截面钢管混凝土柱的承载力增大,延性降低。     

SRC和RC柱耐火性能和抗火设计的若干问题探讨

扼要介绍了影响型钢混凝土SRC和RC钢筋混凝土柱耐火极限的可能因素主要有截面尺寸、构件长细比、火灾荷载比、截面配筋率、截面含钢率、荷载偏心率、截面高宽比、钢材和混凝土强度等的几何参数、物理参数和荷载参数等对SRC和RC构件.构件耐火极限的影响规律,探讨了SRC和RC柱耐火性能和抗火设计中的若干问题。     

钢筋混凝土梁底托梁换柱加固补强施工技术

结合具体工程,介绍了钢筋混凝土大梁底托梁换柱加固补强方法的应用,并重点阐述了该方法的施工要点,为今后类似构件的拆除加固施工提供了有益经验。     

钢筋网复合砂浆加固受弯足尺RC梁二次受力试验研究

本文对钢筋网复合砂浆加固的受弯足尺混凝土梁二次受力进行了试验研究。试验包括10根用钢筋网复合砂浆加固的加固试验梁和4根未加固的对比试验梁。试验梁采用三面U形加固形式,量测了试验梁的挠度,钢筋、混凝土及复合砂浆应变等。通过改变加固钢筋的直径、数量及强度等级,研究了本加固法对二次受力的RC梁的极限承载力,破坏形态,截面刚度及裂缝分布等的影响。试验结果表明,钢筋网复合砂浆薄层加固是一种有效的加固方法,能够显著地提高钢筋混凝土梁的抗弯承载力、截面刚度以及抗裂性能;另外,当梁底加固纵筋的配筋率超过“界限配筋率时”,加固梁可能发生脆性的剥离破坏。     

纤维增强混凝土剪力墙抗震性能试验研究与理论分析

为根本改善混凝土基体的脆性,提高混凝土剪力墙的抗震性能和损伤容限,设计制作6个局部纤维增强混凝土（FRC）剪力墙试件,在试件变形关键部位采用FRC替代普通混凝土,并考虑高轴压比下剪力墙受压钢筋屈曲和受拉纵筋应力集中的问题,在塑性铰区纵向钢筋上设置钢套管,以改善受力钢筋的稳定性和变形性能。通过对悬臂剪力墙试件的拟静力试验,研究此类剪力墙的破坏现象、受力机理和滞回特性,探讨轴压比、FRC区高度、纵筋强度和钢套管长度等因素对墙体变形能力及耗能能力的影响。研究表明,与普通混凝土剪力墙试件相比,塑性铰区采用FRC的剪力墙试件具有较高的损伤容限和变形能力;提高钢筋强度和延性以及在纵筋上设置钢套管,对其抗震性能和耗能能力均具有明显的改善作用。     

Computer-aided oxygen transport model of mass and energy simulation for corrosion of reinforced steel

The paper includes automated modeling and experimental verification of corrosion in reinforced concrete construction under the effect of varying oxygen concentration. Various construction corrosion cells with different concrete compositions under four different environmental conditions (air dry, submerged, 95% R.H and alternate wetting-drying) have been investigated under controlled laboratory conditions. Using the results (half-cell potential and gravimetric corrosion mass loss) of these laboratory tests and an automated computer-aided simulation model based on mass and energy transfer through the porous construction media for the corrosion process, it was possible to predict, maintain and manage the influence of oxygen concentration on the corrosion rate of the reinforcement in concrete construction under various defined conditions satisfactorily. The variation in oxygen concentration available for corrosion reaction has been taken into account simulating the actual construction field conditions such as by varying concrete cover depth, relative humidity, water-cement ratio, etc. The modeling task has been incorporated by the use of an automated computer based construction durability model ‘DuCOM’ developed by our construction research group at The University of Tokyo as a finite element computational approach for the effect of oxygen on corrosion in relation to W/C, concrete cover, chloride concentration and various environmental humidity construction conditions. This paper is of interest to a broad readership for those interested in automation in reinforced concrete construction involving durability design & engineering related to corrosion of steel in concrete, corrosion resistant construction technology, corrosion maintenance & management. The scope of this paper encompasses various stages of the corrosion in construction life cycle from initial planning and design, through construction of steel reinforced concrete facility, its operation and maintenance, to the estimation of demolishing due to limiting oxygen controlled corrosion damage. This paper contains novel investigations involving computer-aided durability design, corrosion modeling under varying oxygen, classification and standardization of corrosion product data. The paper incorporates mass and energy process simulation models and graphics for the effect of oxygen on corrosion and its automated inspection as well as management. This comprehensive automated modeling and experimental investigation involving variety of materials and environmental variables will help in profound understanding, maintenance and management of oxygen controlled corrosion reaction in RC construction and will provide significant future research prospects in the field of oxygen limiting automated corrosion modeling of RC construction.     

Seismic based strengthening of steel and RC telecommunication poles based on fem analysis

This study describes a numerical projection of pre- and post-retrofitted conditions of telecommunication poles subjected to seismic hazards. The absence of explicit guidelines for the rehabilitation of existing poles motivated the investigation of the effectiveness of steel jacketing for the retrofitting of self-supporting steel and reinforced concrete (RC) telecommunication poles. Effects of mast flexibility, variable damping on dynamic response, and significance of period on base shear amplification were investigated. The overall effectiveness of retrofitting against base excitation was assessed for RC and steel poles through the application of modal analyses and response spectrum approach based on a set of strong motion accelerograms recorded during the 1994 Northridge earthquake. Based on a serviceability approach, the analysis of results shows effectiveness of the steel jacketing in increasing load carrying capacity of the poles by enabling stress redistribution.     

Utilisation of electrical resistance method for the evaluation of the state of steel reinforcement in concrete and the rate of its corrosion

In this paper, the applications of an electrical resistance method for monitoring of the state of steel reinforcement in concrete and its rate have been described. The following possibilities of the method were shown: an estimation of quantitative data on corroding steel reinforcement, including the values of a cross-sectional decrease, the depth of the corroded layer, the mass loss of steel material due to corrosion; the possibility of the mathematical modelling of the dependence of the rate of steel reinforcement on important factors like ambient relative humidity, concentration of chloride in embedding concrete and others; and obtaining quantitative data on corroding steel reinforcement by means of a potentiodynamic method through the results of the electrical resistance method and the related mathematical relationship.     

Effects of strain hardening of reinforcement on flexural strength and ductility of reinforced concrete columns

In the evaluation of flexural strength of reinforced concrete (RC) columns, the elastic–perfectly plastic constitutive model is generally used for steel reinforcement, which ignores the strain hardening effect. While some engineers believe that the flexural strength so obtained is on the safe side, others are concerned that underestimation of member strength could lead to inaccurate prediction of overall structural behaviour especially under extreme events. In any case, better understanding of the possible over‐strength and its effects on flexural ductility and failure mechanism is necessary. In this paper, the effects of strain hardening of reinforcement on the flexural strength and ductility of reinforced normal‐ and high‐strength concrete columns are studied based on rigorous full‐range moment–curvature analysis. The study has identified if and how various parameters affect the strain hardening effect, which include axial load ratio, concrete strength, confining stress, reinforcement ratio and the tensile‐strength‐to‐yield‐stress ratio of steel. The effects of strain hardening can be quite significant for RC columns under relatively low axial load and relatively high confining stress. Copyright © 2009 John Wiley & Sons, Ltd.     

无腹筋锈蚀钢筋混凝土梁承载能力的计算

锈蚀钢筋混凝土梁的承载力不仅与纵向钢筋的截面损失有关 ,而且和钢筋与混凝土之间的粘结强度的降低、混凝土保护层中出现的纵向锈胀裂缝有关。本文先考虑了由于钢筋的截面损失引起的钢筋混凝土梁的抗弯承载力的降低 ;再在梁 拱共同作用抵抗剪力的机制上 ,计算了无腹筋锈蚀钢筋混凝土梁的抗剪承载力 ,进而得到了无腹筋锈蚀钢筋混凝土梁的承载力及其相应的破坏模式。对一实例的计算结果表明 ,当混凝土保护层出现纵向锈胀裂缝后 ,钢筋与混凝土之间的极限粘结强度相应降低 ,梁的破坏模式由受弯破坏转向受剪破坏 ,承载能力有较大的降低。同时 ,锚固区的粘结强度的降低 ,导致梁也可能发生粘结锚固破坏。