Prediction of rotation capacity of wide flange beams using neural networks

This study proposes Neural Networks (NN) as a new approach for the estimation and explicit formulation of available rotation capacity of wide flange beams. Rotation capacity is an important phenomenon which determines the plastic behaviour of steel structures. Thus the database for the NN training is directly based on extensive experimental results from literature. The results of the NN approach are compared with numerical results obtained by a specialized computer. Available rotation capacity is also introduced in a closed form solution based on the proposed NN model. The proposed NN method is seen to be more accurate than numerical results, practical and fast compared to FE models.     

A new formulation for web crippling strength of cold-formed steel sheeting using genetic programming

This study presents Genetic programming (GP) as a new tool for the formulation of web crippling strength of cold-formed steel decks for various loading cases. There is no well established analytical solution of the problem due to complex plastic behaviour. The objective of this study is to provide an alternative robust formulation to related design codes and to verify the robustness of GP for the formulation of such structural engineering problems. The training and testing patterns of the proposed GP formulation are based on well established experimental results from the literature. The GP based formulation results are compared with experimental results and current design codes and found to be more accurate.     

Analytical prediction of available rotation capacity of cold-formed rectangular and square hollow section beams

In this paper, a soft-computing based study aimed to estimate the available rotation capacity of cold-formed rectangular and square hollow section (RHS-SHS) steel beams is described and novel mathematical models based on neural network (NN) and genetic expression programming (GEP) are proposed. In order to develop the proposed formulations, a wide experimental database obtained from available studies in the literature has been considered. The data used in the NN and GEP models are arranged in a format of eight input parameters covering both geometrical and mechanical properties such as width, depth and wall thickness of cross section, inside corner radius, yield stress, ratio of modulus of elasticity to hardening modulus, ratio of the strain under initial hardening to yield strain and shear length. The accuracy of the proposed formulations is verified against the experimental data and the rates of efficiency and performance are compared with those provided by analytical semi-empirical formulation developed by some of the Authors in a previous study. The proposed prediction models proved that the NN and GEP methods have strong potential for predicting available rotation capacity of cold-formed RHS-SHS steel beams.     

Prediction of available rotation capacity and ductility of wide-flange beams: Part 2: Applications

Exploiting the capabilities of the DUCTROT-M computer program, a comparison between cross-section ductility classes, recommended in codes, and member ductility classes, proposed in technical literature, is performed, showing very important differences. A numerical analysis was carried out examining the main influencing factors such as collapse modes, fabrication details (welding, hot-rolling, connection details), material properties, geometrical beam dimensions and type of action. Because the out-of-plane mechanism produces very high ductility degradation during a cycling earthquake, the first purpose of the study is to determine the measures to eliminate this mechanism mode. For the welded beams, geometrical proportion of the flange and web thickness is the key, while for hot-rolled beams, the constructional detailing of the joint. The contribution of the junction between flange and web that increases the rotation capacity was revealed. Consequently, rolled and welded sections possess different available ductility, but this effect does not reflected to the current Eurocodes     

Prediction of available rotation capacity and ductility of wide-flange beams: Part 1: DUCTROT-M computer program

This paper is a development of the [1], presenting the new improvements in determining the rotation capacity of wide-flange beams. It deals with the available rotation capacity of steel beams, using the local plastic mechanism methodology. For these purposes, a more advanced software was elaborated at the “Politehnica” University of Timisoara, namely DUCTROT-M, substituting the old DUCTROT-96 computer program presented in [1]. The new version considers two different forms the in-plane and out-of-plane plastic mechanisms, as well as the application of gradient or quasi-constant moments. A CD-ROM containing the free DUCTROT-M computer program can be finding in Appendix of [2] or free on the site [3]. Thus, the present paper is focused on the phenomenological aspects of the utilized plastic collapse mechanisms, while the companion paper [41] is devoted to applications in design practice exploiting the new capabilities of the aforementioned current software version.     

Cross-sectional flexural capacity of cold-formed laterally-restrained steel rectangular hollow flange beams

This paper presents the results of a comprehensive experimental-numerical study aimed at determining the flexural performance of cold-formed laterally-restrained steel rectangular hollow flange beams (RHFBs). Two RHFBs of different dimensions were considered as representative of typical secondary beams in small steel-framed houses. Results of the experimental study that consisted of (i) material characterisation and (ii) tests on full-scale specimens are thoroughly presented. Moreover, a numerical work was performed in order to develop a model able to reproduce the experimental outcomes and used to expand the available findings over a wider slenderness range through parametric studies.     

Post-yield response of cold-cambered wide flange steel beams

The post-yield response of steel beams is important in steel fabrication particularly for setting cambers. A commonly used cambering process known as “cold cambering” consists of bending the girder about its strong axis using single or dual symmetrically applied concentrated loads. This paper recasts available solutions for wide flange steel beams relating loads to permanent deformation in parametric form to determine the effect of cross-sectional geometry and load position on its post-yield response. Sensitivity analyses were then conducted to identify appropriate values of these key parameters and their impact on alternative cambering set-ups. This allows optimization of the cold cambering operation for single- and dual-load systems. The analysis shows that dual-load systems offer significant benefits over single-load systems as they develop the required camber profile at smaller loads without overstraining the steel section. The best results are obtained if the spacing between the two loads is kept within one-third to one-quarter of the span.     

Moment resistance and rotation capacity of semi-rigid composite connections with precast hollowcore slabs

Semi-rigid composite connections with precast hollowcore slabs are a newly developed technique with few applications in current construction practice. The research on the structural behaviour of this new type of connection is limited, with no existing method available to predict its important characteristics such as moment and rotation capacities. In this paper, based on the parametric studies of the three-dimensional finite element model and full-scale tests, analytical methods to calculate the moment and rotation capacity of this type of composite joint are proposed. A comparison between the proposed calculation method and the full-scale test results was made, and good agreement was obtained.     

A new formulation for longitudinally stiffened webs subjected to patch loading

This study proposes a new formulation for patch loading longitudinally stiffened webs using genetic programming (GP) for the first time in the literature. The database for the GP formulation is based on extensive experimental results from the literature. The results of the GP based formulation are compared with existing models and design codes. The results indicate that the proposed GP formulation performs quite well compared to existing models and design codes.     

Genetic programming-based formulation for distortional buckling stress of cold-formed steel members

The main purpose of the research is to develop formulations for estimating the Elastic distortional buckling stress (EDBS) of cold-formed steel member under compressive loading using Genetic programming (GP) which has not been applied so far. The required data used for the training and testing is collected from the literature. Two GP-based formulations are proposed to predict the elastic distortional buckling of cold formed steel C sections. The results of proposed GP formulations are compared with experimental and analytical results of different researchers and methods and found to be accurate. The results obtained from the formulas have shown that GP is a promising technique for predicting EDBS of cold-formed steel C sections.     

Dual-phase steel re-bars for high-ductile r.c. structures, Part 2: Rotational capacity of beams

The article presents an application of an innovative type of reinforcing bars, made by dual-phase (DP) steel, for the design of high-ductile r.c. structures in seismic areas.

In particular a comparison of the capacity, in terms of ductility, of r.c. structural elements reinforced using dual-phase (DP) steel bars with that of identical structures reinforced with the traditional Tempcore steel bars, currently used in practice, has been carried out.

To this purpose an analytical procedure enabling the calculation of the plastic rotational capacity of r.c. beams has been set up, obtaining the bending moment–curvature law through an expressly developed model in order to reproduce “tension-stiffening” phenomenon.     

基于拉压杆模型的FRP-混凝土组合梁受剪承载力研究

为分析FRP-混凝土组合梁的斜截面受剪承载力,在拉压杆模型的基础上,建立了考虑FRP板与混凝土界面发生黏结滑移的FRP-混凝土组合梁拉压杆受剪承载力模型。该模型中,将配置在受拉区的FRP板简化为拉杆,而将变形非协调区的混凝土简化为压杆。为反映FRP与混凝土界面之间的黏结,建立了拉压杆节点区的破坏准则--界面剪应力达到最大黏结剪应力。为验证建立模型的有效性,对已有的试验梁进行了受剪承载力和斜裂缝开裂角度的计算分析。计算结果表明,建立的受剪承载力模型可以有效地预测组合梁的受剪承载力和斜裂缝开裂角度,与试验值吻合较好。     

Flexural behavior of FRP-HSC-steel composite beams

This paper reports on an experimental study on the flexural behavior of fiber reinforced polymer (FRP)-high-strength concrete (HSC)-steel composite beams. Seven double-skin tubular beam (DSTBs) and a concrete-filled FRP tube (CFFT) with an internal steel I-beam were tested as simply supported beams in four-point bending. The main parameters of the experimental study included the cross-sectional shapes of inner steel reinforcement and external FRP tube, concrete strength, presence (or absence) of concrete filling inside the steel tube, and effects of the use of mechanical connectors on the inner steel tube. The results indicate that DSTBs are capable of developing very high inelastic flexural deformations. However, the results also indicate that slip between the concrete and the steel tube of the DSTB can be relatively large, unless the bond between concrete and steel tube is enhanced through the use of mechanical connectors. The results of the beam tests illustrate that the flexural behavior of DSTBs is influenced significantly by the diameter and thickness of the inner steel tube. Concrete-filling the inner steel tube and increasing the concrete strength increase the flexural capacity of DSTBs without affecting their overall ductility. Furthermore, the shape of the inner steel tube influences both the flexural capacity of DSTBs and the occurrence of slippage between the concrete and the inner steel tube. It is shown that the bond slip between the concrete and inner steel tube can be prevented through the use of mechanical connectors. These results are presented together with a discussion on the influence of the main parameters on the flexural behavior of DSTBs.     

锈蚀钢筋混凝土梁抗弯承载力计算方法

基于锈蚀钢筋混凝土梁内钢筋与混凝土间黏结强度随锈蚀量的变化,对锈蚀梁的抗弯承载力进行了研究.当钢筋锈蚀量较小时,锈蚀梁内钢筋与混凝土间黏结强度随锈蚀量变化不大,锈蚀梁的力学性能同未锈蚀梁,可运用传统的梁理论计算锈蚀梁的抗弯承载力;但随着钢筋锈蚀量的增加,钢筋与混凝土间黏结强度发生退化,锈蚀梁的力学性能介于黏结完好梁与无...     

Genetic programming based formulation for fresh and hardened properties of self-compacting concrete containing pulverised fuel ash

Self-compacting concrete (SCC) flows into place and around obstructions under its own weight to fill the formwork completely and self-compact without any segregation and blocking. Elimination of the need for compaction leads to better quality concrete and substantial improvement of working conditions. This investigation aimed to show possible applicability of genetic programming (GP) to model and formulate the fresh and hardened properties of self-compacting concrete (SCC) containing pulverised fuel ash (PFA) based on experimental data. Twenty-six mixes were made with 0.38 to 0.72 water-to-binder ratio (W/B), 183–317 kg/m³ of cement content, 29–261 kg/m³ of PFA, and 0 to 1% of superplasticizer, by mass of powder. Parameters of SCC mixes modelled by genetic programming were the slump flow, JRing combined to the Orimet, JRing combined to cone, and the compressive strength at 7, 28 and 90 days. GP is constructed of training and testing data using the experimental results obtained in this study. The results of genetic programming models are compared with experimental results and are found to be quite accurate. GP has showed a strong potential as a feasible tool for modelling the fresh properties and the compressive strength of SCC containing PFA and produced analytical prediction of these properties as a function as the mix ingredients. Results showed that the GP model thus developed is not only capable of accurately predicting the slump flow, JRing combined to the Orimet, JRing combined to cone, and the compressive strength used in the training process, but it can also effectively predict the above properties for new mixes designed within the practical range with the variation of mix ingredients.     

悬伸梁和双跨连续梁的整体稳定承载力试验研究

为了研究悬伸梁和双跨连续梁在集中荷载作用下的整体稳定性能,对两种单轴对称截面形式(上翼缘加强、下翼缘加强)、两种悬伸长度(1200mm、1600mm)共计5根悬伸梁,以及一种单轴对称截面形式(上翼缘加强)、三种相邻跨度之比(1∶0.48、1∶0.64、1∶1)共3根双跨连续梁进行了试验研究。在进行破坏试验前,对悬伸梁进行了三种荷载作用位置的弹性试验,对连续梁进行了三种加载比例的弹性试验,并利用Southwell法确定了临界荷载。试验研究结果表明:当最大弯矩出现在悬伸梁的简支跨且上翼缘受压时,上翼缘加强构件稳定承载力明显高于同尺寸的下翼缘加强构件;悬伸长度为1600mm的构件承载力明显高于悬伸长度为1200mm的构件承载力;荷载作用在简支梁段跨中时构件稳定承载力最低,荷载作用点离中间支座越近构件稳定承载力越高。双跨连续梁中,在等比例加载时,相邻跨度之比越大,构件稳定承载力越高。此外,对试验进行了有限元模拟,计算结果与试验结果吻合良好。     

受火冷却后钢筋混凝土梁斜截面抗剪承载力分析

研究受火冷却后钢筋混凝土梁抗剪承载力的计算方法,从材料性能和抗剪传力机理两个方面分析了受火冷却后钢筋混凝土梁抗剪承载力下降的原因。建议了受火冷却后钢筋混凝土梁抗剪承载力计算公式。根据受火冷却后钢筋混凝土梁试验结果对集中荷载作用下抗剪承载力折减系数的取值进行了分析,参考试验值建议了适当的抗剪承载力折减系数,计算值具有一定的安全储备,可满足工程要求。还需要进一步研究钢筋混凝土梁抗剪承载力折减系数的取值。     

基于拉-压杆模型的框架结构平移托换梁受剪承载力研究

在16个框架结构平移托换节点试验研究基础上,根据托换梁的裂缝开展规律及破坏特点,并结合有限元分析结果,将托换梁的荷载等效为两点集中荷载,建立托换梁的拉-压杆模型。针对托换梁剪跨比较小的情况,在斜压杆的主压应力中考虑拉杆传来的应力分量。依据Kupfer-Gerstle的双向拉压应力关系考虑混凝土的软化效应,推导了托换梁的受剪承载力计算式,并与试验结果进行了对比。结果表明：不考虑拉杆分量的拉压杆模型的计算结果与试验值的相对误差均值为38.9%,考虑拉杆应力分量的拉-压杆模型的计算结果与试验值的相对误差均值为26.9%。     

钢筋UHPC梁正截面抗弯承载力计算方法

超高性能混凝土(ultra-high-performance concrete,UHPC)是一种高强、高韧性和高耐久性的新型水泥基复合材料,具有广阔的应用前景。由于UHPC内的钢纤维能有效控制裂缝开展并提高UHPC的抗拉强度,因此,UHPC构件抗弯承载力分析时,一般计入截面受拉区UHPC的抗拉作用,但对于如何考虑受拉区UHPC的抗弯贡献,国内外相关研究结果间存在较大分歧,因此值得进一步研究。首先,编制钢筋UHPC梁正截面抗弯承载力分析程序,分析不同设计参数对截面受拉区UHPC抗弯贡献的影响。结果表明:配筋率、梁高、钢纤维长度、截面形状和预应力水平是影响受拉区UHPC抗弯贡献的主要参数。基于参数分析结果的回归分析,提出截面受拉区UHPC的均匀分布应力折减系数k的计算公式;通过引入受拉翼缘面积折减系数k_f,考虑不同截面形状的影响。在此基础上,提出不同弯曲破坏模式下钢筋UHPC梁抗弯承载力的简化计算方法,并以国内外115根钢筋UHPC梁抗弯承载力试验结果验证所提方法的适用性。     

Section moment capacity tests of LiteSteel beams

The LiteSteel beam (LSB) is a new cold-formed hollow flange channel section developed by OneSteel Australian Tube Mills using their patented dual electric resistance welding and automated continuous roll-forming process. It has a unique geometry consisting of torsionally rigid rectangular hollow flanges and a relatively slender web. In addition to this unique geometry, the LSB sections also have unique characteristics relating to their stress–strain curves, residual stresses, initial geometric imperfections and hollow flanges that are not encountered in conventional hot-rolled and cold-formed steel channel sections. An experimental study including 20 section moment capacity tests was therefore conducted to investigate the behaviour and strength of LSB flexural members. The presence of inelastic reserve bending capacity in these beams was investigated in detail although the current design rules generally limit the section moment capacities of cold-formed steel members to their first yield moments. The ultimate moment capacities from the tests were compared with the section moment capacities predicted by the current cold-formed and hot-rolled steel design standards. It was found that compact and non-compact LSB sections have greater moment capacities than their first yield moments. The current cold-formed steel design standards were found to be conservative in predicting the section moment capacities of compact and non-compact LSB sections, while the hot-rolled steel design standards were able to better predict them. This paper has shown that suitable modifications are needed to the current design rules to allow the inclusion of available inelastic bending capacities of LSBs in design.