Renforcement des ponts par collage de l'armature

Résumé L'application du collage au renforcement des ponts en béton armé et béton précontraint en cas d'insuffisance de l'armature semble être, dans certains cas, très économique et utile. On a appliqué le collage à ce système de renforcement pour la reconstruction de quelques ponts en Pologne. On présente trois cas dans cet article.

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Summary Application of gluing of reinforcing steel to the surfaces of concrete structures seems to be one of the most economic and practical system of strengthening reinforced and prestressed concrete bridges. This method can be applied in many cases of insufficient reinforcing steel in reconstructed bridges. Epoxy resins ensure glued joints with sufficient strength and long term resistance. This system of strengthening has been applied to reconstruct several bridges in Poland. Three examples are described in this paper. In one of these bridges the gluing of reinforcing steel was performed in the upper surfaces of Gerber-plate bridge concrete in negative bending moment areas. The flat steel strips, well cleaned and protected against corrosion, were glued to the specially prepared surface concrete. The other repair work consisted in gluing the flat iron strips on the lower surface of the concrete bridge plate. In this case, high strength bolts were used to fasten the ends of the steel bands to the bridge slab. All the work of strengthening was performed during the winter at low temperatures, from 0 to −20°C. Equally extensive strengthening work with the aid of gluing was performed during adaptation to new loads of the old concrete viaducs in the area of Central Railway Station in Warsaw. Here the steel strips and the additional reinforcing steel were glued to the side surface of the concrete slabs. Anchoring bolts were used in all cases. This method of gluing flat steel strips to strengthen insufficiently reinforced concrete bridges is very simple and economic compared with others.

     

Strengthening of Garudchatti bridge after failure of Chauras bridge

Two continuous lattice steel truss bridges spanning 190 m with subdivided top chord members were constructed on the same design across river Alaknanda at Dugadda and Srinagar, respectively, in Uttarakhand, India. Both bridges were similar in design and geometry having middle span of 110.0 m and two end spans of 40.0 m. Garudchatti bridge at Dugadda was constructed first and opened to traffic, but excessive vibrations and lifting of end supports under live load condition were observed. Construction of Chauras bridge at Srinagar started later, but it collapsed during casting of the deck slab due to buckling of one of its top chord compression members. Failure of Chauras bridge led to the serious concerns in the minds of people and technocrats about the safety of Garudchatti bridge also, because it was constructed using the same design of Chauras bridge. Therefore, it was decided to strengthen and carry out load testing of Garudchatti bridge before reopening to the traffic.In the present work analyses of Garudchatti bridge are presented to identify structurally unsafe members for most severe live loads given in IRC:6-2010 code, and recommendations for strengthening of the critical members. Finite element space frame analyses of the bridge were carried out using STAAD Pro. v8i software to find excessively stressed members beyond their permissible stress limit. The critical compression members were strengthened by welding additional channel sections. RCC anchor blocks were constructed to restrict lifting of end supports under live load. After strengthening, load testing of the bridge was performed to ensure the safety of the bridge. The bridge is now reopened for traffic.In the past a number of bridges have collapsed during load testing. In case of any shortcoming in the design or overloading during load testing, compression members of the truss may suddenly buckle and cause collapse of the bridge. Therefore, it is not advisable to load test steel truss bridges which do not have adequate margin beyond the service load condition.     

Aluminium foam sandwiches collapse modes under static and dynamic three-point bending

Static and dynamic three-point bending tests were carried out in order to investigate the structural response (collapse modes, energy dissipation, strain rate sensitivity) of two different typologies of aluminium foam sandwich (AFS) panels, consisting of a closed-cell aluminium foam core with either two integral (Schunk) or two glued (Alulight) faces. Impact measurements were performed by a bi-pendulum testing machine designed by the authors. It was found that different collapse modes can be obtained for samples with identical nominal dimensions, depending on the support span distance and on the own AFS properties. Simplified theoretical collapse models were introduced to explain the observed experimental behaviour, showing good agreement between predicted and experimental limit loads. As far as energy dissipation is concerned, no strain rate sensitivity was found for initial impact velocity up to about 1.2 m/s.     

Numerical evaluation of shear strengthening performance of CFRP sheets/strips and sprayed epoxy coating repair systems

A numerical study is conducted to evaluate the shear strengthening performance of two repair systems: CFRP sheets/strips and a sprayed epoxy coating. Micromechanical constitutive models for the CFRP sheets/strips and sprayed FRP coating proposed by Liang et al. [Liang Z, Lee HK, Suaris W. Micromechanics-based constitutive modeling for unidirectional laminated composites. Int J Solids Struct 2006;43:5674–89] and Lee et al. [Lee HK, Avila G, Montanez C. Numerical study on retrofit and strengthening performance of sprayed fiber-reinforced polymer. Eng Struct 2005;27:1476–87] and Lee and Simunovic [Lee HK, Simunovic S. Modeling of progressive damage in aligned and randomly oriented discontinuous fiber polymer matrix composites. Composites: Part B 2000;31:77–86] in conjunction with damage models, are implemented into the finite element code ABAQUS to solve boundary value problems. Using the implemented computational model, numerical simulations of four-point bending tests on concrete beams repaired with the repair systems are conducted to quantify their strengthening abilities. The numerical tests yield load–deflection curves from which the shear strengthening performance of the repair systems is evaluated. Furthermore, the present prediction is compared with available experimental data to assess the accuracy of the proposed computational model.     

An experimental and numerical investigation on torsional strengthening of solid and box-section RC beams using CFRP laminates

The issue of maintenance and repair/upgrading of existing structures has become a major issue, particularly extending the service lifespan of bridges. Fibre reinforced polymer (FRP) has shown great promise as a state-of-the-art material in flexural and shear strengthening as external reinforcement. However, little attention has been paid to torsional strengthening in terms of both experimental and numerical research. This paper reports the experimental work in an overall investigation of torsional strengthening of solid and box-section reinforced concrete beams with externally-bonded CFRP. This was found to be a viable method of torsional strengthening. Numerical work was carried out using non-linear finite element (FE) modelling. Good agreement in terms of torque–twist behaviour, steel and CFRP reinforcement responses, and crack patterns was achieved. The unique failure modes of all the specimens were modelled correctly as well.     

FRP布加固混凝土框架子结构抗连续倒塌的精细有限元分析EI北大核心CSCD

外贴FRP布加固是一种有效提高既有建筑抗连续倒塌性能的手段,但现有FRP布加固方式存在降低结构抗震性能、加固施工不便等缺点。该文采用数值模拟方法分析了FRP布加固方式对现浇和装配式混凝土框架子结构抗连续倒塌与抗震性能的影响,并开展了优化方案研究。基于通用有限元软件LS-DYNA建立了FRP布加固混凝土框架子结构的连续倒塌精细数值模型,其中混凝土、钢筋与FRP布分别采用实体、梁与壳单元进行模拟,考虑了FRP布和钢筋的滑移、新旧混凝土界面的粘结失效和机械套筒处的钢筋截面损失。试验验证表明该方法可准确模拟试验试件的破坏模式和承载力发展。分析试验试件的不同粘贴方案结果发现:对现浇混凝土子结构,梁底与梁侧中性轴粘贴纵向FRP布并在梁端塑性铰区粘贴U形横向FRP布后,小变形下的结构倒塌抗力提升有限(最大仅2.6%)、基本不影响结构抗震性能,而对大变形下的结构倒塌抗力提升幅度可达49.5%;对于装配式混凝土子结构,在梁底、梁顶与梁侧底部外贴纵向布并在梁端塑性铰区粘贴U形横向FRP布可将小变形和大变形下的结构抗力最大提升24.2%和48.1%,使得装配式子结构在小变形下受力等同现浇结构,提升了原装配式子结构的抗震性能。对上述最优方案进一步的分析表明:保持FRP布用量不变而将塑性铰区内U形横向FRP布的分布范围和条数增加可提高大变形下的结构倒塌抗力,而不影响小变形下的加固效果。     

Carbon-FRCM materials for structural upgrade of masonry arch road bridges

Background/PurposeNumerous bridges of the Italian arterial road network were designed for live loads significantly lower than those produced by the current vehicular traffic. Many of them are masonry arch bridges whose load carrying capacity should be assessed for defining the necessary strengthening interventions. In the present paper the design criteria for strengthening masonry bridges with carbon fiber reinforced cementitious matrix (C-FRCM) materials are presented with reference to a masonry arch road bridge built right after the second world war.MethodsThe structure is analyzed both in its original and in its strengthened configuration following the approach of the collapse mechanisms. The considered approach allows to capture the strengthening effect of the C-FRCM material in terms of modification of the collapse mechanism and increase of the load collapse multiplier. Two different configurations of C-FRCM strengthening material applied at the extrados have been considered. In the first configuration the ends of the C-FRCM material are anchored at the vaults imposts, while in the second configuration they are not anchored at the imposts.ResultsTo obtain load collapse multipliers greater than one three layers of C-FRCM strengthening material have to be applied at the extrados of all the three vaults in the case of end anchored strengthened material, while in the case of unanchored strengthening material four layers of C-FRCM strengthening material have to be applied at the extrados of all the three vaults.ConclusionThe performed analyses show a lack of load carrying capacity of about 60% with respect to the load carrying capacity required by current codes. This lack can be filled up adopting the considered strengthening technique.     

RC two-way slabs strengthened with CFRP strips: experimental study and a limit analysis approach

This paper deals with strengthening of reinforced concrete (RC) two-way slabs with carbon fibre reinforced plastic (CFRP) strips bonded to the tensile face. The first part deals with an experimental study. The fibre reinforced plastics (FRP) strengthened slab test presents a failure mode with debonding of the external FRP strips from the slab. The second part deals with a limit analysis modelling. The strengthened slab is designed as a three-layered plate. A simplified laminated plate model is used to describe the behaviour of three-layered plate supported in four sides, which is subjected to a load in the centre. The upper bound theorem of limit analysis is used to approximate the ultimate load capacity and identify the different collapse mechanisms. Experimental results are compared with theoretical predictions.     

基于动态可靠度和经济优化相结合的服役桥梁维修加固风险决策

服役桥梁的维修加固需要综合考虑安全和经济的问题,基于服役桥梁的动态可靠度,以后续服役期内收益期望值最大或损失期望值最小为目标函数,对服役桥梁的维修加固决策进行了探讨,利用实际检测数据修正抗力模型,对一座服役期为35年的钢筋混凝土梁桥动态可靠度进行了计算,同时,比较分析了汽车荷载等级的提高和采用不同维护加固措施对后续服役期内动态可靠度的影响。该方法结合工程实际,把失效损失与失效风险相结合,对桥梁结构的维修加固决策有一定的指导作用。     

Seismic performance of post-mainshock FRP/steel repaired RC bridge columns subjected to aftershocks

This study compares the performances of three types of repair jackets on mainshock (MS) earthquake-damaged RC bridge columns subjected to aftershock (AS) attacks. These repair jackets include fiber reinforced polymers (FRP), thick steel, and thin steel wrapped with prestressing strands. Results obtained from incremental dynamic time history analyses on refined numerical finite element bridge models were utilized to evaluate the efficacy of different repair jackets application on the post-MS collapse safety of RC bridges subjected to AS attacks of various intensities. Numerical results indicated that the three repair jackets can effectively improve the bridge collapse capacity by approximately 20% under severe MS-severe AS even though they cannot restore the initial stiffness of damaged columns. Repair jackets for the severe MS-damaged columns were ineffective under moderate AS events and thus not required. Steel repair jackets exhibited higher energy dissipation under MS–AS sequences than FRP jackets. In the case of FRP jackets, bidirectional fiber wraps are recommended for plastic hinge confinement of MS-damaged bridge columns subjected to aftershocks.     

Performance updating of concrete bridges using proactive health monitoring methods

Uncertainties associated with modelling of deteriorating bridges strongly affect management decisions, such as inspection, maintenance and repair actions. These uncertainties can be reduced by the effective use of health monitoring systems, through which information regarding in situ performance can be incorporated in the management of bridges.The objectives of this paper are twofold; first, an improved chloride induced deterioration model for concrete bridges is proposed that can quantify degradation in performance soon after chlorides are deposited on the bridge, rather than when initiation of corrosion at the reinforcement level takes place. As a result, the implications of introducing proactive health monitoring can be assessed using probabilistic durability criteria. Thus, the second objective of the paper is to present a methodology for performance updating of deteriorating concrete bridges fitted with a proactive health monitoring system.This methodology is illustrated via a simple example of a typical bridge element, such as a beam or a part of a slab. The results highlight the benefits from introducing ‘smart’ technology in managing bridges subject to deterioration, and quantify the reduction in uncertainties and their subsequent effect on predictions of future bridge performance.     

锈蚀RC桥梁弯曲抗力时变概率模型与试验研究

在退化RC结构的时变性能评估、剩余寿命预测以及维修加固决策分析中,其抗力模型的建立至关重要。钢筋锈蚀导致钢筋的屈服强度降低、改变钢筋力学行为和影响钢筋与混凝土之间的粘结行为。钢筋腐蚀损失量影响钢筋的失效模式,即从延性破坏到脆性破坏变化。该文发展了退化RC 桥梁的概率抗力时变模型,可以定量考虑腐蚀对钢筋力学行为、倒塌机理和粘结性能的影响。建立退化结构的抗力概率模型可以抓住退化结构的退化机理、点蚀分布、结构尺寸参数、粘结行为、腐蚀扩展、钢筋失效模式和计算模型的随机性和变异性。RC 梁的加速腐蚀试验和旧桥的破坏性试验验证了该文模型的正确性和可靠性。     

预后验决策分析用于优化混凝土桥梁检修规划

桥梁检修规划是基于桥梁可靠度退化模型、检查修理的技术和费用模型之上的一种决策方法,其目的是确定在什么时间对桥梁进行检查、修理,采用什么样的检查和修理技术最为经济。桥梁修理保证在桥梁设计使用期间内桥梁的可靠度不低于规定的限值,修理决策依据桥梁承载力退化模型和荷载模型;桥梁检查是为了进一步获得桥梁承载力和荷载的信息,从而使得修理决策依据的信息越来越充分。将预后验决策方法应用于桥梁的检修规划,确立了一种桥梁检修的规划方法。     

Characterisation of a Selection of AC and DC Resistance Bridges for Standard Platinum Resistance Thermometry

Accurate resistance bridges are used to measure the ratio between the resistance of standard platinum resistance thermometers and a reference (standard) resistor at the level of microkelvin in temperature terms and as such play a critical role in the realisation and dissemination of the ITS-90. For AC bridges, the ratio test unit has been available for some time, and for both AC and DC bridges, the increasing availability of resistance bridge calibrators based on combinatorial calibration has increased the ease with which the accuracy and linearity of resistance bridges may be determined, under conditions which provide a realistic representation of the actual measurement set-up. In this study, the performance of 14 resistance bridges, which were available for testing at NPL, consisting of a range of manufacturers and types, has been evaluated and expressed in terms of the standard deviation of the bridge errors over a given range of ratios, namely s. In general, the bridges are found to comply with the manufacturers’ specifications. The uncertainty of s has also been determined using Monte Carlo techniques and is found to be of the order of 10 % of s for most bridge types.     

混凝土空间板柱结构震致落层倒塌的试验研究

开展了2个具有薄弱层的3层混凝土空间板柱结构模型的地震模拟振动台试验,采用加速度峰值逐级加大的El-Centro (NS) 波作为输入激励,直至薄弱层发生落层倒塌。量测了倒塌前、倒塌后模型各层的水平加速度响应,以及倒塌碰撞引发的薄弱层及其下层楼板的竖向加速度响应。模型M-2相比于模型M-1额外施加了附加配重。试验结果表明:1) 随着地震损伤程度的增加,模型的扭转效应有所增大;2) 倒塌前模型M-1和模型M-2的基本频率仅比初始值分别降低8.9%和4.7%,采用频率改变幅度进行结构倒塌预警可能是不现实的;3) 倒塌碰撞导致模型各层的水平加速度出现短时剧烈波动,波动期间模型M-1和模型M-2各层的绝对加速度最大值介于5g~10g之间,分别为倒塌前各层绝对加速度最大值的5倍~20倍和10倍~50倍;4) 倒塌碰撞引发的楼板竖向加速度高达30g~40g。     

合龙段底板分层破坏抗裂设计方法研究

针对悬浇预应力混凝土箱梁桥合龙段底板在合龙索张拉过程中经常发生分层破坏的现象,介绍了混凝土多种破坏准则,并从理论上指出最大拉应力准则不适用于箱梁桥合龙段的底板抗裂设计,而应该采用双向应力状态下的混凝土强度破坏准则。选取多座典型破坏桥梁与未发生破坏桥梁为研究对象,建立了桥梁结构的三维实体有限元模型,得出合龙段底板预应力管道之间的竖向应力与纵向应力,进而利用不同混凝土破坏准则分别对典型桥梁的应力状态及安全性做了预测,并与桥梁实测结果进行了对比,证明了理论分析的正确性。研究结论可为同类桥梁的抗裂设计提供参考。     

Bond behaviour of CFRP reinforcement for torsional strengthening of solid and box-section RC beams

The economic and time constraints in the repair or upgrading of existing infrastructure have become a major issue, particularly extending the service lifespan of bridges. Fibre reinforced polymer (FRP) has shown great promise as a state-of-the-art material in flexural and shear strengthening as external reinforcement. However, little attention has been paid to torsional strengthening in terms of both experimental and numerical research. This paper focuses on the bond-behaviour of externally bonded CFRP in an overall investigation of torsional strengthening of solid and box-section reinforced concrete beams. Significant levels of debonding prior to failure by CFRP rupture were measured in experiments with photogrammetry. Numerical work was carried out using non-linear finite element (FE) modelling. Good agreement in terms of torque-twist behaviour, steel and CFRP reinforcement responses, and crack patterns was achieved. The addition of a bond-slip model between the CFRP reinforcement and concrete meant that the debonding mechanisms prior to and unique failure modes of all the specimens were modelled correctly as well.     

管道修复用涤纶-苎麻复合机织物性能试验

针对传统管道内衬修复材料施工中易出现内壁塌陷等问题,结合目前快速发展的绿色纤维复合材料,提出在涤纶机织物内衬材料中加入苎麻纱线,制作涤纶-苎麻复合机织物材料来提高树脂对管道修复用内衬机织物的浸透性能,增强内衬材料和管壁的粘结性能。以纤维外观、抽拔实验后纤维断面形貌的电镜观察,并通过树脂与织物接触角的测试、粘结实验,综合分析了涤-麻复合机织物的树脂浸透性,同时对涤纶-苎麻复合机织物力学性能进行测试来保障内衬复合材料满足强度的要求。实验结果表明,采用上述涤-麻复合织造的方法,可以显著提高树脂的浸透性能,有利于携带更多的树脂粘结剂提高树脂与管壁的粘结性,减少塌陷发生的可能性。同时加入麻复合的机织物,拉伸顶破性能都满足高压燃气管道的修复要求。     

不等跨布置RC空间梁-板结构竖向倒塌能力数值研究

为研究不等跨布置下RC空间梁-板结构抗连续倒塌能力，利用有限元软件ABAQUS建立在关键柱失效下空间框架结构精细化模型，通过Pushdown分析方法对试验子结构进行数值模拟。分析关键柱失效位置、梁板参数、楼板的损伤性能以及梁端截面内力对倒塌能力的影响。分析结果显示:内柱失效工况下楼板能提供承载力的40%~50%，边柱失效工况下楼板能提供20%~30%的承载力，角柱失效工况下楼板能提供15%~25%的承载力；梁跨度越大，柱失效后结构承载力越低，等跨设计的结构较不等跨设计受力存在“滞后性”，且横向约束对无板结构承载力基本上没有影响；梁板参数对提高结构承载力以及延性有重要影响；小变形下楼板损伤性能可以反映楼板的屈服模式，从而可推测楼板裂缝分布；最后提出了不等跨布置下考虑楼板影响的承载力计算公式。     

Experiments on curved sandwich panels under blast loading

In this paper curved sandwich panels with two aluminium face sheets and an aluminium foam core under air blast loadings were investigated experimentally. Specimens with two values of radius of curvature and different core/face sheet configurations were tested for three blast intensities. All the four edges of the panels were fully clamped. The experiments were carried out by a four-cable ballistic pendulum with corresponding sensors. Impulse acting on the front face of the assembly, deflection history at the centre of back face sheet, and strain history at some characteristic points on the back face were obtained. Then the deformation/failure modes of specimens were classified and analysed systematically. The experimental data show that the initial curvature of a curved sandwich panel may change the deformation/collapse mode with an extended range for bending dominated deformation, which suggests that the performance of the sandwich shell structures may exceed that of both their equivalent solid counterpart and a flat sandwich plate.