Rapid prediction of deflections in multi-span continuous composite bridges using neural networks

This paper proposes closed form expressions for the rapid prediction of deflections in steel-concrete composite bridges of large number of spans subjected to service load. The proposed expressions take into account shear lag effect, flexibility of shear connectors and cracking in concrete slabs. Three separate neural networks have been developed for right exterior span, left exterior span and interior spans. The closed form expressions have been obtained from the neural networks developed in the study. The training, validating and testing data sets for the neural networks are generated using finite element software ABAQUS. The proposed expressions have been validated for number of bridges and the errors are found to be small for practical purposes. Sensitivity studies have been carried out using the proposed expressions to evaluate the suitability of input parameters. The use of the proposed expressions requires a computational effort that is fraction of that required for the finite element analysis, therefore, can be used for rapid prediction of deflection for everyday design.     

Neural networks for prediction of deflection in composite bridges

Neural networks have been developed for prediction of deflections, at service load, in steel-concrete composite bridges incorporating flexibility of shear connectors, shear lag effect and cracking in concrete slabs. Three neural networks have been presented to cover simply supported bridges, two span continuous bridges and three span continuous bridges. The use of the neural networks requires a computational effort almost equal to that required for the simple beam analysis (neglecting flexibility of shear connectors, shear lag effect and cracking of concrete). The training and testing data for neural networks are generated using finite element software ABAQUS. The neural networks have been validated for number of bridges and the errors are found to be small. Closed form solutions are also proposed based on the developed neural networks. The networks/ closed form solutions can be used for rapid prediction of deflection for everyday design.     

基于神经网络的组合桥挠度分析

基于神经网络,对剪切连接、剪滞效应、混凝土板裂缝不同情况下的型钢-混凝土组合桥正常使用状态下的挠度进行分析。建立3种神经网络,分别针对简支桥、两跨连续桥及三跨连续桥。神经网络的计算量几乎等同于忽略剪切连接、剪滞效应、混凝土板裂缝不同的简支梁分析。采用有限元分析软件ABAQUS,生成神经网络的训练和试验数据。神经网络对很多桥梁都有效,分析结果误差很小。基于改进的神经网络,给出封闭解。神经网络和封闭解可用于设计中的快速挠度分析。     

冻融循环后再生粗骨料混凝土梁受弯性能试验研究

为了研究冻融循环对再生粗骨料混凝土梁受弯性能的影响,首先通过冻融循环试验研究不同冻融循环次数对再生粗骨料混凝土质量损失率、立方体抗压强度和相对动态弹性模量的影响;然后对经历不同冻融循环次数（0、25、50、75）的再生粗骨料混凝土梁进行受弯性能试验,研究了试件的破坏形态、开裂荷载和极限荷载、混凝土和钢筋应变、跨中挠度等。结果表明：冻融循环次数由0增加到25次时,再生混凝土的质量呈增加趋势,冻融循环超过25次后,再生混凝土的质量呈不断减小的趋势;抗压强度和相对动态弹性模量随着冻融循环次数的增加而减小;再生混凝土梁的开裂荷载和极限荷载随冻融循环次数的增加而减小;再生混凝土梁的极限挠度随冻融循环次数的增加呈现出不断减小的趋势。     

Control of time-dependent effects in steel-concrete composite frames

Studies are presented for the control of time-dependent effects of creep and shrinkage in steel-concrete composite frames with pre-cast concrete slab for both shored and un-shored constructions. A developed hybrid procedure has been used for carrying out the studies. The procedure accounts for creep, shrinkage and progressive cracking in concrete slab panels. Two frames, a single storey and a five storey frame are considered. It is shown that, for both the types of constructions, shored and un-shored, the increase in bending moments and mid-span deflections can be controlled to a significant degree, without putting constraints on design parameters, by simply delaying the time of mobilization of composite action between the pre-cast concrete slab panels and the steel section. It is also found that though there is insignificant effect of type of construction on bending moments, the percentage change in mid-span deflection due to creep and shrinkage is significantly higher for shored construction.     

Long-term deflection of cracked composite beams with nonlinear partial shear interaction — A study using neural networks

A new study of the short- and long-term deflections of simply-supported composite beams using finite element analysis and artificial neural networks (ANNs) is presented. In this study, two ANN models are developed and trained using the results of a finite element model developed by the authors in a companion paper. The finite element model accounted for the nonlinear load–slip relationship of shear connectors as well as the creep, shrinkage, and cracking of concrete slabs. The effects of creep and shrinkage of the concrete slab are considered only for non-cracked concrete. A large database representing a wide range of different design parameters was constructed for the purpose of training and verifying the two ANN models. It was found that the two ANN models were capable of predicting deflections of composite beams not used as part of the training process. The ANN models were then used to evaluate the effects of non-geometric design variables on the short- and long-term deflections of simply-supported composite beams. Finally, the short- and long-term deflections computed based on the approaches given in the AISC specification and Eurocode 4 were assessed using the results of the finite element model. It was found that the AISC approach underestimates short-term deflections and overestimate long-term deflections when compared with the results of the finite element method.     

考虑收缩徐变影响的两跨钢-混凝土连续组合梁长期性能预测方法

为量化混凝土翼板收缩徐变对多跨钢-混凝土连续组合梁长期性能的影响,提出相应的预测方法,基于现有两跨连续组合梁长期试验结果对典型的组合梁设计方法进行适用性评述; 在此基础上,基于龄期调整的有效模量法并考虑混凝土的收缩徐变、开裂及组合梁界面相对滑移的综合影响,提出两跨连续组合梁长期中支座弯矩与跨中挠度的计算公式,并采用长期试验结果验证预测方法的可靠性; 进一步对比不同混凝土翼板类型(收缩徐变分布模型)对组合梁长期性能的影响。结果表明:采用龄期调整的有效模量法模拟混凝土徐变特征,考虑收缩产生的附加弯矩,采用折减刚度考虑混凝土开裂与界面滑移的影响,提出的两跨连续组合梁长期性能计算公式,可有效预测组合梁长期中支座弯矩分布与跨中挠度,计算结果与试验结果最大相差25.3%; 混凝土的收缩变形对组合梁长期性能影响显著,当不考虑混凝土收缩变形时,组合梁中支座弯矩与跨中挠度仅分别为试验值的41.1%和60.6%; 组合梁长期性能设计时,应根据楼板类型采用不同的收缩徐变模型,针对钢筋混凝土楼板采用均匀收缩、均匀徐变模型,针对组合楼板采用非均匀收缩、非均匀徐变模型。     

非线性局部剪力交互作用下的开裂组合梁长期变形神经网络研究

结合有限元分析和人工神经网络,提出一种新的思路,研究简支组合梁的短期和长期变形。本文建立两个神经网络模型,采用相关论文中有限元模型的结果进行样本训练。有限元模型考虑了抗剪连接件的非线性荷载-滑移关系,以及蠕变、收缩和混凝土板的裂缝。而对没开裂的混凝土只考虑了蠕变、收缩的影响。为训练及验证两个神经网络模型,建立了一个包括不同设计参数的大数据库。研究发现,两个神经网络模型均能预测组合梁的变形。因此,神经网络模型可用以评估非几何设计参数对简支组合梁的短、长期变形影响。最后,根据AISC规范和欧洲规范4方法计算简支组合梁的短、长期变形,并与有限元模型结果进行比较。结果表明,与有限元方法相比,AISC方法低估了短期变形而高估了长期变形。     

Effect of creep and shrinkage in reinforced concrete frame–shear wall system with high beam stiffness

The behaviour of frames and frame–shear wall systems with regard to creep and shrinkage with high beam stiffness has been largely unexplored until recently since no procedure has been available. For low beam stiffness the most widely used procedure available in literature for determining creep and shrinkage effects in reinforced concrete building frames and frame–shear wall systems designated herein as approximate procedure, AP has been recommended for buildings having flexible slab systems and with a limited number of storeys. Recently an accurate procedure termed Consistent Procedure (CP) has been developed which is applicable to low as well as high beam stiffness and requires no restriction on number of storeys. In this paper, using CP, studies are reported for frame–shear wall systems with high beam stiffness. The effect of introduction of shear walls on load transfer among vertical members considering creep and shrinkage is studied. It is shown that the presence of shear wall alters significantly the load transfer among vertical members. It is also shown that whereas differential vertical deflections between adjacent vertical members are small owing to high stiffness of beams, the load transfer between them can be significant. Copyright © 2003 John Wiley & Sons, Ltd.     

煤矸石混凝土梁受剪性能试验研究

为研究煤矸石混凝土梁受剪性能,对9个煤矸石混凝土梁和1个普通混凝土对照梁进行了受剪试验,分析了煤矸石混凝土梁斜截面破坏形态、开裂荷载和受剪承载力。结果表明:煤矸石混凝土梁和普通混凝土梁受剪破坏形态相似;在同一荷载等级下,煤矸石混凝土梁试件跨中挠度随煤矸石取代率的增加而增大,而达到各试件极限荷载时其挠度值相差不大;斜向开裂荷载随煤矸石取代率的增加而减小,煤矸石混凝土梁较普通混凝土梁降低了19.6%～31.5%;受剪承载力随煤矸石取代率的增加也有降低趋势,煤矸石混凝土梁较普通混凝土梁降低了8.9%～24.0%;此外,剪跨比和配箍率对煤矸石混凝土梁受剪性能的影响与普通混凝土梁相似,受剪承载力随剪跨比的增加而减小,随配箍率的增加而增加;煤矸石混凝土梁受剪承载力计算可采用GB 50010—2010《混凝土结构设计规范》中公式,且计算结果有一定的安全储备。     

Elastic rigidity of composite beams with full width slab openings

Openings often exist in the concrete slab of composite floors due to the functional requirements of structures. The strength and rigidity of steel-concrete composite beams are reduced by openings. Based on three tests of steel-concrete composite beams with full openings in the concrete flange, the elastic rigidity of composite beams is analyzed. Finite element analysis (FEA) considering the slip effect between the steel and concrete is conducted to simulate the composite beams with full openings in the concrete slab, and the results show that the FEA method is reliable. The analytical calculation method for the deflection of composite beams with full openings in the concrete slab is also proposed, and the results are verified by tests. The predicted deflections using the analytical method and FEA method both agree well with the test results. It is further verified that openings near the supports have insignificant effects on the deflection at the mid-span and this effect can be thus ignored. The simplified method to calculate the rigidity reduction factor is developed by a regression analysis. The analytical method and FEA method can be used for the serviceability limit state design of steel-concrete composite beams with full openings in the concrete flange.     

凹槽销栓型竹-混凝土组合梁的受弯性能

文章将混凝土与竹材组合,提出一种新型凹槽销栓型竹-混凝土组合结构,为研究凹槽销栓型竹-混凝土组合梁的受弯力学性能,对5组组合梁和1组对比竹梁进行四点弯曲试验,试验参数包括连接件间距及其数量,试验主要测试试验荷载、跨中挠度、竹梁与混凝土翼缘的应变以及竹梁与混凝土翼缘的界面相对滑移。试验结果表明,凹槽销栓型竹-混凝土组合梁的破坏模式表现为两种:第Ⅰ类以混凝土翼缘斜向剪切破坏为控制,脆性特征明显,发生于连接件间距较密时;第Ⅱ类是以凹槽混凝土剪压破坏为控制,发生于连接件间距较疏时,连接件的凹槽内混凝土破损严重,破坏之前有明显的预兆。相对于对比竹梁,组合梁在各级荷载下的跨中位移大幅降低,截面刚度得到大幅度的提高,与对比竹梁相比,组合梁的承载力提高了1.23～1.61倍,对应跨中挠度为L/250和L/300时的荷载P_L/250和P_L/300平均提高了3.81倍和3.95倍,在正常使用荷载下,凹槽销栓型竹-混凝土组合梁的组合系数为0.86～0.98,组合截面的混凝土和竹材两种材料呈现良好的整体工作状态,凹槽销栓型连接件表现出刚性连接件的特征,具有较高的组合...     

考虑滑移效应的简支钢-混凝土组合梁挠度计算

采用栓钉等柔性抗剪连接件的钢-混凝土组合梁交界面上存在相对滑移变形,增大了组合梁的挠度。论文研究了冷弯薄壁U型钢-混凝土组合梁的滑移性能,推导了滑移量的计算公式,建立了考虑滑移效应的钢-混凝土组合梁在均布荷载作用下的挠度计算公式。分析表明：滑移效应对组合梁挠度影响不能忽略。     

Steel cantilever strength by inelastic lateral buckling

Methods used for the design of steel beams supported at both ends are not well suited for the design of cantilevers against lateral buckling. The end restraints are very different for cantilevers, and the maximum displacements and twist rotations take place at the free ends, instead of near mid-span. Consequently, their buckling modes are very different to those of supported beams. The methods of allowing for the effects of the moment distribution on the elastic and inelastic buckling of supported beams use a mean of the moment distribution, which is weighted to allow for the maximum deformations being near mid-span. These methods are clearly inappropriate for cantilevers whose deformations are greatest at the free ends.Lateral buckling design methods for cantilevers are modifications of the methods for supported beams, but are of doubtful accuracy, and may be over conservative. In some cases there is little or no design guidance.This paper summarizes information on the effects of the moment distribution and load height on the elastic buckling of cantilevers which can be used in the method of design by buckling analysis. It then extends a method of designing supported beams by inelastic buckling analysis to allow for the effects of the moment distribution on the inelastic buckling of cantilevers. This extended method is then used to provide improved design methods for cantilevers which are consistent with those for simply supported beams. A worked example is summarized.     

Verformungsbezogene mittragende Breite niedriger Verbundträger

Effective width due to deflections of composite girders with shallow height. Due to the high slenderness of composite girders with shallow height their deflection behaviour is of great importance. In many cases the cross sectional dimensions are determined by the limitation of the deflections. In contrary to high composite beams the deflection behaviour of these girders is influenced especially by the bending state and cracking behaviour of the concrete slab. Among others the deflection or the stiffness of the composite girders depend on the effective width of the slab. This article reports on investigations of the deflection behaviour and the effective width of shallow composite girders taking into account the bending state and the cracking of the concrete slab. At first it is shown that for the calculation of stresses a different value of the effective width has to be taken into account than for the calculation of deflections. On basis of extensive experimental, analytical and numerical investigations the influences on the effective width are analysed. A wide‐ranging parametric study leads to the development of an approach of the effective width for the calculation of deflections and a proposal for a quasi‐elastic calculation of the deflections of shallow composite girders. At this it turns out that the effective width due to deflections is influenced above all by the bending state of the concrete slab, its cracking behaviour, its ratio width to length, the ratio of the individual stiffness components of the composite cross section and the load level. On basis of the proposed approach for the calculation of the effective width the deflections of shallow composite girders can be determined realistically. This leads to a more economic design of composite shallow girders than until now.     

Die Methode der effektiven Spannungen zur einfachen Berechnung der Kriechverformung von Stahlbetonträgern

The method of effective stresses for simple calculation of creep deflections of reinforced concrete girders A method for simple calculations of deflections of reinforced concrete beams is taken on and enhanced. It is shown how the results of computer analysis on the basis of linear‐elastic material behaviour can replace the integration of the curvature distribution by hand to evaluate the deflection. For a systematic evaluation of deflections of reinforced concrete beams with regard to creep effects, parameters of major influence are identified and first evaluations are presented.     

由钢筋混凝土剪力墙和钢管混凝土框架组成的高层组合结构抗震性能研究

建筑结构中,由钢管混凝土柱和钢梁组成的组合框架得到广泛应用。在中国,组合框架结构常与钢筋混凝土剪力墙组合构成高层建筑结构。然而,对这种结构抗震性能的研究却很少。对2个由组合框架和钢筋混凝土剪力墙组成的30层建筑模型进行振动台试验,组合框架分别采用钢管混凝土圆柱和方柱;分别选用了加速度峰值为0.2g,0.4g,0.6g及0.8g的Taft波,ElCentro波和天津波。结果表明:地震作用下组合框架能很好地与核心混凝土剪力墙结构共同工作,2个模型均表现出了很好的抗震性能。     

非弹性侧向屈曲的悬臂钢梁强度

两端支承钢梁的设计方法不适用于抗侧向屈曲的悬臂梁。悬臂梁与两端支承梁的约束不同,其最大位移和转角发生在自由端,而不是在跨中附近。因此,它们的屈曲模态不一样。这些方法考虑了弯矩分配法对两端支承梁弹性及非弹性屈曲的影响,但不适用于悬臂梁。悬臂梁的侧向屈曲设计法是对端支承梁设计法的修正,但其精度不高,有时过于保守,某些情况下,不能用于设计。使用弯矩分配法进行结构的屈曲分析,总结了该方法对悬臂梁弹性屈曲的影响。改进两端支撑梁的非弹性屈曲设计方法,使其能考虑弯矩分配法对悬臂梁非弹性屈曲的影响。改进的方法与简支梁的设计法是一致的。以某工程为实例,演示了此方法的应用。     

基于地震塑性损伤的混凝土框架结构分析模型研究

采用经典塑性和连续损伤模型,确定了塑性变形的演化法则,发展了一种基于抗震损伤的混凝土框架结构分析模型。运用两端具有塑性铰的梁模型模拟框架结构的梁柱。算例表明,该模型的损伤指数可以确定结构各单元和整体在地震时的性能及结构极限荷载,具有可靠的精度。     

Thermal and structural response of two-storey two-bay composite steel frames under furnace loading

The collapse of the World Trade Center Towers and other recent fires in tall buildings has motivated this study to understand the performance of structural frames under fire loading. Three two-storey, two-bay composite steel frames were constructed and subjected to dead loads by applying weight blocks, and to thermal load by placing the frame in a furnace. The furnace was specially designed to allow for controlled heating of the structural elements that formed the four compartments of the test frame. This paper describes the experimental results of furnace test conducted on the three full-scale composite frames. The three tests differed from each other in the number and location of compartments that were heated by the furnace. For each test, the structural elements were subjected to a heating-up phase followed by a cooling-down phase. The furnace temperatures and the steel and concrete temperatures recorded during the test are presented. The thermally induced horizontal displacements of the columns and vertical deflections of the composite beams are discussed. Observations on local buckling of the steel beam, cracking of the concrete slab and failure of the beam-to-column connections are tabulated. Experimental results of the three tests are compared with each other by studying the complete deformation process of the test frames over time. Results indicate that the deformation process of the test frames was highly dependent on the number and location of compartments that were subjected to thermal loading.