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Search Results: 1 - 10 of 1901 matches for " PC bridge "
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预应力混凝土桥梁抗火研究综述

张岗,贺拴海,侯炜,KODUR V K
- , 2018,
Abstract: 为了促进中国桥梁工程抗火研究领域的全面发展,加快预应力混凝土桥梁的抗火研究,回顾了国内外桥梁火灾的典型事故以及发生特点,强调了油罐车火灾对桥梁结构威胁的严重性,总结了预应力混凝土桥梁的火灾特点,对其抗火研究存在的问题进行了梳理,包括其材料高温特性、高温爆裂现状,火灾下桥梁预应力的存在状态及其试验与测试方法,火灾全过程中预应力混凝土桥梁力学性能的数值模拟与仿真,预应力混凝土桥梁的耐火极限,火灾后预应力混凝土桥梁的损伤评估加固及桥梁抗火研究的工程应用。从性能退化机理与极限垮塌行为、复合单元的研发与计算机仿真技术、收敛点的获取、火灾试验方法与测试技术、损伤评估精准模型和抗火设计方法的提出,五大方面给出了预应力混凝土桥梁抗火研究亟待解决的问题和更新目标,以期对桥梁工程抗火方向的学术研究提供新的视角和基础资料。
To promote the comprehensive development of fire resistance in bridge engineering in China, and accelerate the research on fire resistance of prestressed??concrete bridges, some typical fire incidents of bridges occurring at home and abroad, as well as fire characteristics, were reviewed. The severity of oil tankers as threats to bridge structures was emphasized, and the characteristics of prestressed??concrete bridges exposed to fire were summarized. Thereafter, the status of research on the fire resistance of prestressed??concrete bridges was examined. This included the high??temperature properties of materials used for prestressed??concrete bridges, the spalling feature of prestressed concrete at elevated temperatures, the service status of prestress in concrete bridges under fire exposure conditions, a test and measurement method of prestressed concrete bridges exposed to fire, a numerical analysis and simulation method of the mechanics in prestressed??concrete bridges during fires, the fire resistance of prestressed??concrete bridges, damage evaluation and strengthening methods for prestressed??concrete bridges after fire, and engineering applications. Finally, problems based on five aspects were proposed that remain to be solved in fire??resistance research for prestressed??concrete bridges,such as performance degradation mechanism and ultimate collapse behavior, compound element development and computer simulation techniques, the point of convergence,testing techniques in fire tests and measurement methods, a precise model of damage evaluation, and a fire resistance design method. A new perspective and basic information for the academic research on the fire resistance of bridges are expected
先张法PC空心板梁桥梁底开裂成因敏感性分析
Sensitivity analysis of cracking factors for the bottom slab crack of the pre-tensioned PC hollow slab girder bridge

,
- , 2016,
Abstract: 为深入研究与探讨先张法PC空心板桥梁底的开裂成因,量化分析多种开裂因素对梁底主拉应力的影响及其敏感性,明确该类桥梁在设计、施工与运营过程中控制梁底开裂现象的侧重点,依托某3×20 m的空心板简支梁桥作为工程背景,利用MIDAS FEA中相应的旋转裂缝模型,建立了多梁与单梁有限元模型,多梁结构考虑1片边梁与2片中梁、单梁结构仅考虑中梁单板受力的情况,通过有限元仿真分析预应力钢束偏位、预应力损失、超载、混凝土强度降低、整体温差以及支座脱空等各因素对底板主拉应力的影响,并利用线性回归模型分析比较了各影响因素的开裂敏感性。研究结果表明:各影响因素对先张法PC空心板梁底开裂的敏感性由预应力损失、超载、整体温差、支座脱空、预应力钢束偏位至混凝土强度依次减小;单板受力对梁底受力更加不利,加剧了各影响因素作用下梁底裂缝的产生。所得结论可对已有先张法PC空心板梁桥的开裂分析提供参考依据。
To profoundly study the crack mechanism, quantify the influence and sensitivity of different factors on the principal tension stress of bottom beam cracks in PC hollow girders and the control of the bottom slab crack of these girders in designing, constructing and operating processes, a 3×20 m simply supported bridge was used as the background to establish the multi-beam and the single-beam finite element model by MIDAS FEA with its relevant rotating crack model. The multi-beam model considered one side girder and two middle girders, while the single-beam girder only considered the single beam bearing situation. Factors such as prestress tendon position deviation, prestress losing, overloading, concrete strength reduction, overall temperature difference and bearing separation were analyzed to check the influence on the principal tension stress and a linear regression model was used to compare the sensibility among different factors. The results show that the prestress loss factor plays the key influencing role to the principal tensile stress of bottom beam and it is also influenced by the factors of overload, overall temperature difference and bearing separation. Effects of prestress tendon position and concrete strength are not significant. The single beam bearing can lead to a bad bottom stress situation for the bottom beam which will aggravate the crack phenomenon. The comparison and conclusion can provide reference for the crack phenomenon of prestressed concrete hollow slab beam bridge
Numerical Studies on Electromagnetic Waves Properties in Metallic-Dielectric Photonic Crystal  [PDF]
Arafa H. Aly, Ehab Abdel-Rahman, Hassan S. Hanafey
Journal of Electromagnetic Analysis and Applications (JEMAA) , 2011, DOI: 10.4236/jemaa.2011.311074
Abstract: We have performed numerical analyses to investigate the propagation characteristics of a simple-one dimensional metallic-dielectric structure. Several different metals have been studied (aluminum, gold, copper, and silver). Copper gives the smallest absorption and aluminum is more absorptive. We have compared between the transmittance of these structures with different metals and the same dielectric material. Also we used these different metals with the same layer thickness, incidence angels, number of layers and the same electromagnetic waves range.
腐蚀预应力混凝土梁抗剪性能试验
Experiment on Shear Behavior of PC Beams After Prestressed Tendons Corrosion

羊日华,,,张旭辉,,,张建仁
- , 2018,
Abstract: 为研究预应力筋腐蚀对预应力混凝土梁抗剪性能的影响,设计制作了4片预应力混凝土梁,采用外加恒电流法对单侧弯剪区局部预应力筋进行了快速腐蚀,并对不同锈蚀程度混凝土梁进行了抗剪试验,分析了预应力筋腐蚀对梁开裂、变形、钢筋受力、破坏形态以及抗剪承载力的影响,并在试验基础上对锈蚀PC梁抗剪承载力计算方法进行了探讨。结果表明:相同剪跨比下预应力筋腐蚀对混凝土梁的破坏形态影响很小,但对构件裂缝发展影响较大,引起开裂荷载显著降低;开裂前,预应力筋腐蚀对其刚度影响较小;开裂后,腐蚀引起刚度退化较为明显;预应力筋腐蚀导致相同荷载下箍筋、纵筋应变增大,构件抗剪承载力退化;预应力筋腐蚀率为3.2%,7.9%,13.2%的混凝土梁抗剪承载力分别下降5.8%,9.1%,15.5%;考虑腐蚀预应力筋截面减小,采用《混凝土结构设计规范》(GB 50010―2010)公式对PC梁抗剪承载力计算具有较高的计算精度。
In order to study the influence of prestressed tendon corrosion on shear behavior of prestressed concrete (PC) beams, four PC beams were designed and manufactured. The prestressed tendon in the area of one-sided bending and shearing local zone was rapidly corroded by galvanostatic method, and the shear test was performed on the concrete beams with different corrosion rates of steel strands. The influence of corrosion of prestressed tendons on the cracking, deformation of steel beams, stress of reinforced bars, failure modes and shear bearing capacity were analyzed, and the calculation method of shear bearing capacity of corroded PC beams was discussed on the basis of test. The study results shows that the corrosion of prestressed tendons under the same shear-span ratio has little effect on the failure modes of concrete beams, but it has a greater impact on the development of component cracks, causing a significant reduction in cracking loads. Before cracking, the corrosion of prestressed tendon has little effect on its stiffness; after cracking, the stiffness degradation caused by corrosion is more obvious. Corrosion of prestressed tendon leads to the increased strains of stirrups and longitudinal reinforcement under the same load, it also leads to the degradation of shear capacity of components. The shear strength of concrete beam with corrosion rates of 3.2%, 7.9%, and 13.2%, respectively, decreases by 5.8%, 9.1%, and 15.5% compared to that of un-corroded beams. Considering reduction of cross??section of corroded prestressed tendons, the calculation formula for shear strength of PC beams in Code for Design of Concrete Structures (GB 50010―2010) has high accuracy
油罐车火灾下考虑混凝土高温爆裂的PC箱梁承载能力
Bearing capacity of PC box girder based on concrete spalling??under fuel tanker fire exposure

张岗,侯章伟,宋超杰,贺拴海,李源
- , 2018,
Abstract: 针对油罐车火灾对预应力混凝土桥梁的破坏过程,选取桥梁工程建设中应用较为广泛的预应力混凝土(PC)箱梁为研究对象,建立油罐车火灾下预应力混凝土箱梁桥混凝土高温爆裂的“三级指标”,并设定了相应油罐车火灾下混凝土的爆裂场景,采用单元生死技术模拟混凝土高温爆裂特征,分析考虑混凝土高温爆裂的预应力混凝土箱梁截面温度场的完整分布形态,计算混凝土不同高温爆裂指标下的预应力混凝土箱梁极限承载能力,拟合并建立计算公式。研究结果表明:截面关键点的温度曲线呈三阶段上升趋势;爆裂导致混凝土截面的温度在传导过程中产生突变,温度分布以爆裂后截面形态分层递进;混凝土的高温爆裂使钢束、钢筋的强度显著下降;混凝土的爆裂深度越大,正截面抗弯承载能力下降越快;混凝土发生重度爆裂,延火时间180 min时,箱梁跨中截面的抗弯承载能力从未爆裂时的60.73%降至14.87%,箱梁??L??/4截面(??L??为跨径)的抗弯承载能力从未爆裂时的64.37%降至19.37%;混凝土高温爆裂不同深度下预应力混凝土箱梁桥抗弯承载能力衰变呈现多阶段特征。混凝土爆裂对预应力混凝土箱梁的截面温度分布和抗弯承载能力影响显著,提出的考虑爆裂的承载能力计算公式简单实用。
Aiming at the damage characteristics of prestressed concrete bridge caused by oil tanker fire, a prestressed concrete (PC) box girder, which is widely applied in bridge construction, was selected as the research object, and a three??grade index of concrete spalling at elevated temperature was proposed. The concrete spalling conditions under hydrocarbon fire scenarios were defined, and the birth??death element technique was applied to simulate the concrete spalling. The complete distribution profile of the cross??sectional temperature within the PC box girder considering concrete spalling was analyzed. The ultimate flexural capacity of the PC box girder under different spalling indices was calculated, and the calculation formula was proposed. The results show that the temperature curve of key points in the cross section has a three??stage rise. The concrete spalling can lead to a sudden change of cross??sectional temperature, and the temperature shows a layer distribution toward the inside of the cross section after concrete spalling. The strength of the prestressed strand and reinforcement decreased significantly as a result of concrete spalling. With a larger depth of concrete spalling, the flexural capacity decreased with a faster step. When severe spalling of concrete occurred at 180 min, the flexural capacity of a PC box girder at midspan decreased from 60.73% to 14.87%, and the flexural capacity of the PC box girder at ??L??/4 section (??L?? is the span) decreased from 64.37% to 19.37%. Flexural capacity demonstrated a multistage descent at different depths of concrete spalling. Concrete spalling has a significant effect on the flexural capacity and temperature distribution of PC box girders. The proposed formula considering concrete spalling is simple and practical, and it can be used to evaluate the fire resistance of the PC box girder. 4 tabs, 10 figs, 26 refs.?
A New Type of Bridge, Mobilebridge? to Super-Quickly Recover a Bridge  [PDF]
Ichiro Ario, Yuki Chikahiro
World Journal of Engineering and Technology (WJET) , 2015, DOI: 10.4236/wjet.2015.33C025
Abstract:

Many natural disasters cause not only critical situations for facilities and resident’s residents’ life, but also significant damage to economy. It is obvious that quick rescue action must be undertaken and that there are many problems due to the occurrence of secondary disasters at rescue worksite. Basing Based on the previous study of deployable structures and the concept of the multi-folding micro-structures, we propose a new type of foldable bridge in form of scissor structure called the Mobile-bridge?. In this paper, we discuss the vehicle passing test performed on the real-scale Mobile-bridge in order to evaluate its mechanical characteristics and application limits. Moreover, we verified the compatibility between the result of calculations and experiments by means of theoretical modelling. The results show that it is sufficient to treat the load as equivalent nodal forces applied at the joints without including the stiffness of the deck.

独塔部分斜拉桥顺桥向地面运动作用下的易损性分析
Seismic fragility analysis on extra-dosed PC bridge with single-tower under the motion of longitudinal bridge direction

吴少峰,上官萍,姜绍飞
福州大学学报(自然科学版) , 2017, DOI: 10.7631/issn.1000-2243.2017.02.159
Abstract: 以墩塔梁固结的独塔预应力混凝土部分斜拉桥为对象,采用动力增量法和数据统计分析研究该类桥梁的地震易损性,确定顺桥向地面运动作用下结构构件的易损部位及损伤破坏概率. 采用理论易损性分析方法,选取地面峰值加速度作为地震输入强度指标,并以放大系数为基础选取地震输入;以位移延性比、强度与变形、相对位移、索力为指标分别定义了各构件的损伤状态;根据各构件的损伤概率,拟合建立了各构件及全桥的易损性曲线. 结果表明,在顺桥向地面运动作用下,中墩和支座为最易损构件;边墩、主梁均会发生不同程度的损伤;斜拉索、桥塔、桩基安全储备较高.
The PC cable-stayed bridge with a single tower rigidly connected with the girder was selected as the object of the research. The dynamic increment method and data statistical analysis method were used to study the seismic vulnerability for bridge of this kind. The vulnerable elements and the corresponding damage probability were ensured under the ground motion in longitudinal bridge direction. The peak acceleration of ground motion was chosen as the intensity index input of the earthquake records with the use of vulnerability analysis theory and earthquake input was selected by the amplification coefficient. Damage status for each component was defined with the index of displacement ductility ratio,strength and deformation,relative displacement and the cable force. The vulnerability curve for the component and the whole bridge were established based on the damage probability. Results shows that the middle pier and the bearing were the most vulnerable part under the ground motion in longitudinal bridge direction,the side pier and the girder showed a damage at different degree and the cables,bridge tower and the piles showed a high safety storage
Identification of Bridge Movement Mechanisms  [PDF]
Matthew T. Yarnold
Engineering (ENG) , 2014, DOI: 10.4236/eng.2014.69059
Abstract:

Bridge behavior is highly dependent upon the movement mechanisms present throughout the structure. These mechanisms (e.g. bearing, joints, etc.) have a substantial impact on the long-term durability and potential safety of the structure. A major distinguisher between the varieties of movement systems is their operating timescale. In some cases, they function rapidly, within fractions of a second, and in other cases gradually over days, months or even years. However, in nearly all cases, the lifecycle of the movement system is shorter than that of the bridge assuring the need for future intervention. Breakdown of a movement system can produce unintended forces/deformations that progressively degrade the structure. Identification and tracking of movement mechanisms proactively address long-term durability by helping to avoid these unintended consequences. A general framework for characterization of these mechanisms was developed. This framework was applied to an operating bridge that includes several critical mechanisms operating over different timescales. As a result of this and other studies, recommendations are provided for identification of bridge movement systems.

 

Sixth Scale Model Studies of Masonry Arch Rib Behaviour at Different Eccentricities  [PDF]
Abbagana Mohammed, T. G. Hughes
Open Journal of Civil Engineering (OJCE) , 2018, DOI: 10.4236/ojce.2018.84038
Abstract: This paper reports a validation study involving sixth scale masonry model to replicate prototype tests carried out on five unit high masonry prisms. In order to test the applicability of small masonry models to real life problems, an investigation into masonry behaviour relevant to the serviceability requirement of masonry arch bridges was chosen as prototype test to validate the small scale masonry tests. Only representative masonry specimens were considered in the study; this corresponded to parts of an arch ring in a complete masonry arch. Two mortar designations; designation iv and designation v were used. These weak mortars tend to conform better to existing old structures. Loads were applied at four eccentricities of 0, 5, 9, and 14 mm from the centre of the specimens. This corresponds to e/d ratios of 0, 0.14, 0.25, and 0.39, where e is the eccentricity of the load and d the length of the transverse section of the specimens. The result shows that validation study corresponds with prototype study for low eccentricities; therefore, strength enhancement is seen over the concentric compressive strength. However, this does not apply at higher eccentricities as specimens were noticed to fail by elastic instability characterised by tension debonding of the top mortar joint.
A New Design for Anterior Fixed Partial Denture, Combining Facial Porcelain and Lingual Metal; PTU Type II
A. Pahlevan
Journal of Dentistry of Tehran University of Medical Sciences , 2005,
Abstract: A new design for replacing a missing anterior tooth is described. In this article, a lingually fixed partial denture, its advantages, disadvantages, indication and contraindications have been explained. The ability of this design to replace a single missing central or lateral incisor is discussed.
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