Introduction of a Japan Concrete Institute Guideline： Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures

There are many cracked concrete structures worldwide. Although there have been numerous efforts to eliminate cracks, some cracks are very harmful and should be repaired as soon as possible. On the other hand, some cracks are almost harmless. So, a good guideline regarding how to deal with cracks in concrete structures is needed. In this guideline, the practical investigation, repair and strengthening method of cracked concrete structures is discussed. And the detecting subjects are cracks generated immediately after casting and during the service time. This guideline targets on the owners （including managers） of concrete structure and the engineers working for the maintenance of concrete structure. JCI （Japan Concrete Institute） published first version of ＂Practical Guideline for Investigation and Repair of Cracked Concrete Structures＂ in 1980, and then the fourth version titled ＂Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures--2009＂ was published. This guideline is very practical when cracks are observed in existing concrete structures, in any other countries as well as in Japan. These three authors led the establishment of this guideline.

Introduction of a JCl Guideline： Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures

There are many cracked concrete structures, although there have been numerous efforts to eliminate cracks. Some cracks are very harmful and should be repaired as soon as possible. On the other hand, the other cracks are almost harmless. So, a good guideline about how to deal with cracks in concrete structures had been needed. JCI （Japan Concrete Institute） published the first version of ＂Practical Guideline for Investigation and Repair of Cracked Concrete Structures＂ in 1980, the second version in 1987, the third version in 2003, and then the fourth version titled ＂Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures-2009＂ was published. This Guideline is very practical, when cracks are observed in existed concrete structures, in any other countries as well as in Japan.

Double linear strain distribution assumption of RC beam strengthened with external-bonded or near-surface mounted fiber reinforced plastic

Rehabilitation of existing structures with fiber reinforced plastic(FRP)has been growing in popularity because they offer superior performance in terms of resistance to corrosion and high specific stiffness.The strain coordination results of 34 reinforced concrete beams(four groups)strengthened with different methods were presented including external-bonded or near-surface mounted glass or carbon FRP or helical rib bar in order to study the strain coordination of the strengthening materials and steel rebar of RC beam.Because there is relative slipping between concrete and strengthening materials(SM),the strain of SM and steel rebar of RC beam satisfies the double linear strain distribution assumption,that is,the strain of longitudinal fiber parallel to the neutral axis of plated beam within the scope of effective height(h0)of the cross section is in direct proportion to the distance from the fiber to the neutral axis.The strain of SM and steel rebar satisfies the equation εGCH=βεsteel,where the value of β is equal to 1.1-1.3 according to the test results.

钢筋混凝土结构加固技术探析

多种结构加固技术可以用来解决钢筋混凝土结构性能无法满足正常使用要求的问题,但如何选择合适的加固方法需要认真思考。基于不同加固方法的工作原理对各种结构加固技术的优缺点、适用范围和技术要点进行了详细分析,并提出了根据工程需要选择合适加固技术的方法。结果表明:对使用空间要求高的结构应采用置换混凝土法等增加截面较小的加固方法;腐蚀环境下宜采用增大截面法等耐受性好的加固方法;地基承载力富余小的情况下宜采用粘贴纤维法等增加自重小的加固方法;需要复原的临时加固工程可采用增设支点法等具有可逆性的加固方法。

高层建筑剪力墙置换加固技术研究

以某18层钢筋混凝土剪力墙结构建筑为研究背景,分析因剪力墙、柱节点核心区混凝土强度低于设计标准,导致结构抗震性能和承载能力不足而进行的加固设计以及施工技术的研究,为同类加固工程项目提供参考。

某学校公寓砖混结构的鉴定与加固

介绍了既有砖混结构建筑物的抗震鉴定方法,以某学校公寓砖混结构为研究对象,对其进行结构安全性鉴定和抗震鉴定,就相应问题选择合理的加固方法,同时对钢筋混凝土面层加固法和钢筋网聚合物砂浆面层加固法进行对比计算和有限元分析,结果表明钢筋混凝土面层加固法能更有效地提升砖砌体结构的各方面承载力。

Mode-I fracture and durability of FRP-concrete bonded interfaces

In this study, a work-of-fracture method using a three-point bend beam （3PBB） specimen, which is commonly used to determine the fracture energy of concrete, was adapted to evaluate the mode-I fracture and durability of fiber-reinforced polymer （FRP） composite-concrete bonded interfaces. Interface fracture properties were evaluated with established data reduction procedures. The proposed test method is primarily for use in evaluating the effects of freeze-thaw （F-T） and wet-dry （W-D） cycles that are the accelerated aging protocols on the mode-I fracture of carbon FRP-concrete bonded interfaces. The results of the mode-I fracture tests of F-T and W-D cycle-conditioned specimens show that both the critical load and fracture energy decrease as the number of cycles increases, and their degradation pattern has a nearly linear relationship with the number of cycles. However, compared with the effect of the F-T cycles, the critical load and fracture energy degrade at a slower rate with W-D cycles, which suggests that F-T cyclic conditioning causes more deterioration of carbon fiber-reinforced polymer （CFRP）-concrete bonded interface. After 50 and 100 conditioning cycles, scaling of concrete was observed in all the specimens subjected to F-T cycles, but not in those subjected to W-D cycles. The examination of interface fracture surfaces along the bonded interfaces with varying numbers of F-T and W-D conditioning cycles shows that （1） cohesive failure of CFRP composites is not observed in all fractured surfaces; （2） for the control specimens that have not been exposed to any conditioning cycles, the majority of interface failure is a result of cohesive fracture of concrete （peeling of concrete from the concrete substrate）, which means that the cracks mostly propagate within the concrete; and （3） as the number of F-T or W-D conditioning cycles increases, adhesive failure along the interface begins to emerge and gradually increases. It is thus concluded that the fracture properties （i.e., the critical load and fracture energy） of the bonded interface are controlled primarily by the concrete cohesive fracture before conditioning and by the adhesive interface fracture after many cycles of F-T or W-D conditioning. As demonstrated in this study, a test method using 3PBB specimens combined with a fictitious crack model and experimental conditioning protocols for durability can be used as an effective qualification method to test new hybrid material interface bonds and to evaluate durability-related effects on the interfaces.

Structural Retrofitting of Old Illyria Hote

Illyria hotel （formerly Bozhur） was built during the sixties in the heart of the actual Kosovo＇s capital Prishtina, according to former old Yugoslav standards in a Modernist architectural style. It represents a massive structural system with brick walls up to 54 cm thick and ＂avramenko＂ type reinforced concrete floors. The investor＇s aim was to add another two floors on the top of the existing ones and to build two level underground parking floors, a health spa centre, whilst at the vicinity of the existing building （the northern side） to erect a new 17 story-high brand new hotel and administration building. The retrofitting of the structure as well as construction of the new structure has been done in full accordance with the new structural Eurocodes＇ recommendations. 3D FEM （finite element method） modeling was used for the analysis and design, using ETABS v 9.5 nonlinear and ARSAP 2010 （Autodesk Robot Structural Analysis Professional 2010）. Response spectrum design according to EC 8,3.2.2.4 has been used for seismic analysis and design with a reference peak ground acceleration on type A ground Of AgR = 0.25 g.

3种加锚方式下2种碳纤维布加固钢筋砼梁抗剪承载力计算的比较

按照《碳纤维片材加固混凝土结构技术规程》与《混凝土结构加固设计规范》分别对胶锚或钢板锚、环形箍及自锁式、加织物压条一般式3种U形箍加锚方式加固后的梁斜截面承载力进行计算。结果发现,2种计算方式得出胶锚或钢板锚加锚方式的承载力增加值差异最小,加织物压条一般式的差异最大。2个工程抗剪加固应用算例的验证结果与计算结果一致。由此可知,在相同加固要求条件下,采用胶锚或钢板锚加锚方式的加固成本最低。

纤维布粘包钢板抗弯加固钢筋混凝土梁探索性试验

纤维布和钢板是钢筋混凝土梁外贴片材抗弯加固法的常用材料,基于2种片材的材料特性,提出了以纤维布粘包钢板(FESP)为复合板的外贴加固法。首先,为改善复合板与混凝土梁之间的粘结效果,混凝土表面处理方式以开槽代替凿毛;其次,采用玄武岩纤维布包钢复合板对钢筋混凝土梁进行抗弯加固,通过7个试件的静力加载试验,明确了开槽外贴FESP加固法的施工工艺;最后,探讨了钢板厚度、复合板长度以及施工工艺对加固梁受力性能的影响。研究结果表明:混凝土梁开槽粘贴新型复合板加固后,极限性能得到显著提高;当钢板较薄时,随着FESP加长,剥离发生的位置由端部转移到中部,承载力和延性得到改善;在FESP较长的试件中,复合板两端始终与梁粘结良好,尽管出现了中部剥离,荷载仍可继续增加,直至接近理论上限时混凝土被压碎;当复合板较长的加固梁中钢板厚度加倍时,试件抗弯刚度增大,但因较早发生了端部剥离破坏,导致承载力和延性反而下降;当复合板完全相同时,未用修补胶抹面的试件在钢板屈服前便已过早发生端部剥离,反映板下全面涂胶打底的重要性。

HFMRPC加固不同高宽比砌体窗间墙抗震性能试验研究

目前广大农村地区拥有大量不符合抗震要求的砌体结构房屋,因此,针对老旧砌体结构房屋进行加固是一门值得研究的课题。为了研究混杂纤维改良活性粉末混凝土(HFMRPC)加固不同高宽比砌体窗间墙的抗震性能,对1面作为对照组的未加固砌体墙和3面不同高宽比的面层加固砌体墙进行了低周往复荷载试验。对比分析了4面墙体的破坏模式、滞回曲线和骨架曲线等抗震性能指标。试验结果表明:HFMRPC面层加固能够有效提高墙体的承载能力,峰值荷载提高约42%;HFMRPC面层对砌体窗间墙具有良好的约束作用,能够有效提升墙体的延性,延性系数提升约199%;HFMRPC面层加固后墙体耗能能力显著提升,累积耗能约提升98%;高宽比是影响墙体破坏模式的重要因素,随着高宽比的减小,砌体墙的承载能力提高,试件的破坏模式趋向于脆性破坏,相反随着高宽比的增大,砌体墙的耗能能力提高,试件趋向于延性破坏。根据试验结果进行了墙体抗剪、抗弯承载力计算分析,并提出了适用于HFMRPC面层加固的抗剪承载力计算公式,可为实际工程应用提供理论基础。

CFRP护套加固的低强钢筋混凝土柱数值建模研究

为了研究低强混凝土配筋柱在碳纤维增强聚合物(CFRP)加固后的受压行为,使用ABAQUS软件对低抗压强度的钢筋混凝土柱进行数值模拟及参数分析,采用三维实体单元和三维桁架单元分别对混凝土柱及钢筋进行建模,采用混凝土损伤塑性模型考虑基体压缩和拉伸的损伤。结果表明:相比配筋柱,采用3 mm CFRP护套加固的低强钢筋混凝土柱的承载力提高34%。对于不同基体强度的混凝土配筋柱,CFRP护套存在最优加固厚度。

老旧砌体结构抗震加固研究综述

该文总结老旧砌体(砖混)结构现状,以及加固老旧砌体(砖混)结构的必要性和可行性。目前加固老旧砌体(砖混)结构技术已经有了相对成熟的技术,该文将目前已经应用于工程实践中的技术进行总结。随着市场和政策的需求,该行业对新型加固材料和新型加固技术进行研究,该文也对这些新技术进行归纳总结。对于具体老旧砌体(砖混)结构的抗震加固,需要根据实际工程情况选择相应的抗震加固技术和施工方法,该文也对此进行讨论。

钢筋混凝土结构加固方法分析

累积损伤、材料老化以及各种灾害将导致混凝土结构抗力衰减,安全性降低。本文基于钢筋混凝土结构加固原理,对钢筋混凝土结构加固方法进行了研究,从加固技术特点、适用范围及构造要求3个方面,详细分析了增大截面加固法、粘贴纤维复合材料加固法及粘贴钢板加固法。结果表明:粘贴纤维复合材料加固法加固效果高强高效,施工最便捷,宜优先选用。

某中学教学楼砖混结构抗震加固设计研究

主要介绍昆明某中学教学楼的结构抗震加固设计,本工程采用主体结构脱缝与连缝两种方案进行结构对比,发现将原有主体结构缝连接后,可以有效提高墙体的抗震承载能力,并可以有效控制主体结构的扭转效应;采用高延性混凝土加固承重墙体方案,不但可以有效减轻基础受荷,提高整体结构的抗震承载力,还可以大幅度节省施工周期;主体结构楼板采用预制板,只采用角钢增加搭接长度,不能完全提高结构的整体性,本文提出一种新型的加固预制板的节点做法,不但有效提高了预制板受力的整体性,还充分保证了主体结构的安全性。

探讨地下室外墙混凝土结构温度效应及裂缝控制措施

地下室外墙混凝土结构出现裂缝的主要原因是温度效应,文中以某大型综合建筑工程为例,分析了有限元模型的建立,从板的变化、侧墙的变化、地基水平阻力的变化、混凝土结构裂缝的分布情况四方面对其温度效应进行详细分析,并以原料、设计和施工为基础提出了具体的裂缝控制措施,以期为类似项目提供参考。

装配式钢结构住宅的设计研究和实践

相较于装配式混凝土结构住宅体系,钢结构住宅体系的工业化程度更高,抗震性能更优,空间更加灵活,材料更加绿色环保,更符合高品质住宅发展的要求。位于上海市浦东新区的某住宅4号楼项目,主体结构采用钢框架+支撑结构体系,外围护结构则采用预制夹心保温混凝土外墙,为尽量减少预制混凝土结构对主体钢结构的影响,采用点支承和外挂式的连接方式,通过合理化设计和精细化计算确保结构的安全,同时通过采取有效的措施解决了建筑防水等问题,为钢结构住宅的推广提供了一定的参考价值。

多层砌体结构底层承重墙托换加固设计及施工

随着人们对生活、工作环境要求的不断提高,以及城市更新工作的推进,已有项目改建日趋增多。本文结合南方某六层砖混办公楼底层改造实践案例,阐述了三种托换方案及对应的关键施工技术,并从设计、施工角度进行了比选,可供其他类似改造工程设计施工项目参考。

某砖混结构建筑阳台漏雨原因及处理措施分析

90年代的老旧楼房,很大一部分是砖混结构形式的建筑,建筑材料的热胀冷缩系数不同,导致自然沉降不同,加之施工质量差、监督管理部门监管不到位等,砖混结构楼房外檐墙面开裂成为该形式建筑的一个通病。墙面开裂问题会影响建筑物的美观性,严重危害建筑结构的稳定性。因此,文章基于某砖混结构形式的单体建筑阳台的漏雨情况,分析此类建筑外延阳台漏雨的原因,并提出了相应的解决办法。

混凝土粘钢补强用结构胶的耐久性研究

钢筋混凝土构件外部粘钢加固补强所使用的环氧树脂类结构胶 ,在室内常温环境条件下粘结强度具有较长期的稳定性。而在长期浸水或冻融条件下 ,粘结强度虽然仍能超过C40 以下混凝土基材的强度 ,但结构胶强度 ,尤其是结构胶与钢板的界面粘结强度发生了明显的劣化 ,90d就下降近 70 %。因此 ,混凝土构件粘钢补强只能在室内常温环境条件下使用。