建筑工程中钢混梁装配后力学性能分析

为了保障高层建筑的安全性,在施工中广泛应用大跨度的钢混梁结构。为准确分析钢混梁的力学性能,构建一种内剖面分析模型。在这种模型下,梁结构中的混凝土材料等效转化为钢材料,对其进行受力和变形分析,得到有关弯矩、挠度等力学性能指标的分析结果。采用ANSYS软件对高层建筑中的大跨度钢混梁进行有限元建模,并对装配后承受载荷及对应变形进行分析。结果表明:增加钢纤维的掺杂浓度,可以有效提高钢混梁结构承受变形的能力,使高层建筑安全性更高。

沉井顶板钢混梁板组合结构抗弯性能试验研究

依据沉井工程实际,设计并制作了两种地下沉井顶板钢混梁板组合结构的模型试件,根据钢骨架与混凝土板之间是否设置抗剪连接件,将两个模型试件分为梁板点焊连接的无抗剪模型以及梁板整体浇筑的有抗剪模型。通过对两个试件进行三点弯单轴静力加载试验,得到组合结构的抗弯承载力,并绘制出其跨中荷载-挠度曲线和荷载-应变曲线,分析二者破坏特征。通过对比试验可知:设置抗剪连接件可有效提高结构的整体性以及抗弯承载能力,并推迟混凝土板裂缝的开裂时间,减缓裂缝发展趋势;通过降低截面高度能提高组合结构的整体稳定性,并增加工作空间利用率。

高速公路钢混梁施工关键技术

为了提升钢结构桥梁质量,推动钢结构桥梁建设的现代化进程,交通运输部发布的《关于推进公路钢结构桥梁建设的指导意见》中,提出了钢箱梁、钢桁梁、钢混组合梁等高速公路钢混梁施工建设中的关键技术,这些技术环节对于提升公路桥梁品质,推动高速公路建设转型升级具有积极的作用。文章以某高速公路钢混梁施工为背景,对其关键技术中的钢梁制作、剪力钉施工、桥面板施工技术、湿接缝施工、支座安装控制要素等方面展开论述,为推动高速公路钢混梁施工项目技术的未来发展模式指明道路。

高速公路钢混组合梁专项施工技术探究

为提高我国钢桥工程的质量,促进我国钢桥工程的现代化,在《关于推进公路钢结构桥梁建设的指导意见》中,提出了钢箱梁、钢桁梁、钢混组合梁、钢桁梁、钢混组合梁等工程技术,对提高公路桥梁品质、推动高速公路建设转型升级具有积极的作用。本文结合一条高速公路钢混梁施工实例,就钢梁制作、剪力钉施工、桥面板施工、湿接缝施工、支座安装控制因素等几个关键技术进行了探讨,为今后高速公路钢混梁施工技术的发展方向指明了方向。

中小跨径多梁式钢混组合梁桥稳定性评估

传统的钢混组合梁桥稳定性评估方法受到材料非线性的影响,面对多梁式结构时,该方法存在较大的响应差异。为此,提出中小跨径多梁式钢混组合梁桥稳定性评估。在车辆正常行驶的情况下,从影响梁体构造的因素中确定梁桥稳定性影响因素,并将其作为评估指标,在遵守指标体系建立规则的前提下,建立评估指标体系,根据评估指标的状态和体系层次划分等级,实现梁桥稳定性评估。实验表明:设计的中小跨径多梁式钢混组合梁桥稳定性评估方法在不同的工况条件下,响应差异较小。

Fatigue behavior of crane beam strengthened with CFRP

In order to study the fatigue behavior of the damaged reinforced concrete （RC） beams strengthened by carbon fiber reinforced polymer （CFRP） laminate, three T-shaped beams strengthened by CFRP and one contrasting beam are tested under fatigue loading, with the parameters of different modes of strengthening and different fatigue load levels considered. The main results obtained from the tests are： the width of the crack decreases 50. 2% to 66%, and the development of the crack is limited; the stress of steel decreases 24. 1% to 28. 2%, and the stiffness increases 14.9% to 16. 1% after being strengthened. Based on the technical specification for strengthening concrete structures with CFRP and the conclusions from the tests, a calculating scheme of the flexure stiffness is given, which can be used for reference in engineering design. Finally, some suggestions are given for design in fatigue strengthening.

Strain coordination of quasi-plane-hypothesis for reinforced concrete beam strengthened by epoxy-bonded glass fiber reinforced plastic plate

The testing of thirteen reinforeed concrete （RC） beams strengthened by epoxy-bonded glass fiber reinforced plastic plate （GFRP） shows that the RC beam and the GFRP plate with epoxy bonding on it can work fairly well in coordination to eaeh other. But there is relative slipping between RC beam and GFRP plate. And the strain of GFRP and steel rebar of RC beam satisfies the quasi-plane-hypothesis, that is, the strain of longitudinal fiher that parallels 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 GFRP and steel rebar satisfies the equation： εGFRP=Kεsteel.

Long term behavior of self-compacting reinforced concrete beams

Tests were carried out on 8 self-compacting reinforced concrete(SCC) beams and 4 normal reinforced concrete beams. The effects of mode of consolidation,load level,reinforcing ratio and structural type on long term behavior of SCC were investigated. Under the same environmental conditions,the shrinkage-time curve of self-compacting concrete beam is very similar to that of normal concrete beam. For both self-compacting reinforced concrete beams and normal reinforced concrete beams,the rate of shrinkage at early stages is higher,the shrinkage strain at 2 months is about 60% of the maximum value at one year. The shrinkage strain of self-compacting reinforced concrete beam after one year is about 450×10-6. Creep deflection of self-compacting reinforced concrete beam decreases as the tensile reinforcing ratio increases. The deflection creep coefficient of self-compacting reinforced concrete beam after one and a half year is about 1.6,which is very close to that of normal reinforced concrete beams cast with vibration. Extra cautions considering shrinkage and creep behavior are not needed for the use of SCC in engineering practices.

Influence of Repeated Variable Load on Long-Term Behavior of Concrete Elements

The objective of this paper is to study the influence of repeated variable action on long-term behavior of concrete structural elements using quasi-permanent combination of actions, for the assessment of long-term effects （e.g., effects due to creep and shrinkage in concrete structures）, as it is proposed in Eurocodes. Extensive experimental program and analytical research using model B3 and AAEM （age adjusted effective modulus） method was performed in order to define quasi-permanent factor ψ2, for two specific loading histories. These loading histories were consist of long-term permanent action ＂G＂ and repeated variable action ＂Q＂. The variable load was applied in cycles of loading/unloading for 24 h and 48 h in period of 400 days appropriately for one series of concrete elements. 24 reinforced concrete beams, dimensions 150 mm × 280 mm × 3,000 mm, were tested. Twelve beams were made of concrete class C30/37 and 12 of concrete class C60/75.

Comparison on construction of strut-and-tie models for reinforced concrete deep beams

With consideration of the differences between concrete and steel,three solutions using genetic evolutionary structural optimization algorithm were presented to automatically develop optimal strut-and-tie model for deep beams.In the finite element analysis of the first method,the concrete and steel rebar are modeled by a plane element and a bar element,respectively.In the second method,the concrete and steel are assigned to two different plane elements,whereas in the third method only one kind of plane element is used with no consideration of the differences of the two materials.A simply supported beam under two point loads was presented as an example to verify the validity of the three proposed methods.The results indicates that all the three methods can generate optimal strut-and-tie models and the third algorithm has powerful capability in searching more optimal results with less computational effort.The effectiveness of the proposed algorithm III has also been demonstrated by other two examples.

Behavior and Flexural Prediction of Special Cementitious Bonding Material for Fiber Reinforced Strengthening Systems

Strengthening of RC structures with externally bonded FRP （fiber reinforced polymers） has become an important challenge in civil engineering. Epoxy is the main bonding agent used so far, but in the case of a fire, it is subjected to complete loss of his bonding capabilities. Mineral based composites strengthening systems consist of FRPs and a cementitious bonding agent which form a repair or strengthening system that is more compatible with the concrete substrata, and roved its efficiency. The current research introduces the use of a special cementitious material ＂Grancrete＂ as a bonding agent. Test results of 32 T-section RC beams strengthened with various FRG （fiber reinforced Grancrete） strengthening systems are presented. The results demonstrated that most of the specimens were likely to fail by debonding of the FRP from the concrete either at the ends or at intermediate flexural cracks. This paper presents an in-depth study aimed at the development of a better understanding of debonding failures in RC beams strengthened with externally bonded FRP systems. Different analytical models, published in the literature for plate end debonding, are reviewed and compared to test results. The results also demonstrated that when using U-wraps, the specimens were likely to fail by FRP sheet rupture.

The Continuum Analytical Method of Steel Frame- Reinforced Concrete Shear Wall Mixed Structure

The inter-story drift stiffness considered the semirigidity of beam and column joints connection, and P-Delta second order effect of steel frame parts in the mixed structure is presented in the paper. After considering on the influence of semirigidity between steel beams and steel columns, second order effect of beam-column members for steel frame and structural second order effect, the traditional continuum analytial method used in RC shear-frames wall structure is developed to steel frames-reinforced concrete shear wall mixed structure subject to horizontal load in this paper. A continuum approach, which is suitable for analyzing steel frames-reinforced concrete shear wall mixed structure subject to horizontal load, is presented. The method is relatively simple and more practical. It will be referred to structural design for steel frames-reinforced concrete shear wall mixed structure.

Strengthening of Concrete Box Girder Bridges under Close-in Detonations

The response of a bridge superstructure under blast loading might depend largely on the extent of the local damage experienced due to close-in explosion threats. This paper investigates the local and structural response of box girder bridge decks strengthened using CFRP （carbon fiber reinforced polymers） under close-in detonations. Due to the lack of experimental research on this topic, the study is conducted using the explicit finite element computer program LS-DY-NA. The numerical study will be verified using the results of strengthened reinforced concrete slabs under field detonations. The blast load was assumed to be detonated above the bridge deck. The key parameters investigated are the charge size, and the strengthening location on the deck. This paper will present the results of this investigation and provides recommendations for predicting the local damage level based on the CFRP strengthening design under blast threat.

Distribution of Reinforcement in Tensile Flanges of Concrete T-shape Continuous Beam

In this paper the analysis of tensile stress distribution in flexural continuous T- beam has been presented. The observed damages in carrying deck of RC bridge over the Wieprz River in Baranow indicate that over pillar zones are not protected enough. The results of numerical analysis have shown that tensile stress in T- section beam appears not only in a web but in flanges as well. Thus reinforcing bars should be distributed within the whole effective width. This fact is mentioned in building codes, for example, in Eurocode 2： ＂Design of concrete structures＂, both in part 1.1 ＂General rules and rules for building＂ and in part 2 ＂Reinforced and prestressed concrete bridges＂, but there are not detailed rules how to place the bars in flanges of T-section.

Structural Behavior of Repaired Reinforced Concrete Beams with Glued Steel Plate and Carbon Fiber

This paper investigates the strength and deformation characteristics of reinforced normal and high-strength concrete rectangular beams which failed in shear and repaired by external bonding of carbon fiber and steel plate. Five simply supported reinforced concrete beams with shear reinforcement are tested, three of which are made with NSC （normal-strength concrete） and the other two with HSC （high-strength concrete）. The span of the simply supported beams is 0.9 m with 100 mm wide by 200 mm deep cross section. All five beams are tested under four-point bending. Careful repair process is adopted and proved successful. The aim is to restore or increase shear strength of these beams and to monitor their post-repair load-deflection behavior. The effect of concrete compressive strength on the behavior and strength of beams before and after repair is also investigated. Shear cracks patterns and their evolution are observed and discussed.