The clinching joints strength analysis in the aspects of changes in the forming technology and load conditions

This paper presents the strength analysis of joining by clinching for various values of parameter X of the bottom thickness. The maximum joint strength was obtained by performing lap joints, H-shaped samples and T-shaped samples strength test.For the specified value X of the bottom thickness, a test bar of clinching joints was also subjected to complex stress state until destruction. Thus, the impact of joint load direction on the maximum load capacity was determined. The effect of radial clearance between the die and the punch on the forming process, shearing and tearing was also obtained.Moreover, the paper contains an example of new sheet metal joining technology using rivets (ClinchRivet). The complex load tests results of the rivet joints were compared with those obtained for clinching.     

硫铝酸盐水泥基混凝土早强特性及其应用

修补砂浆和混凝土是我国当前工程快速施工采用最多的材料,其早强快硬特性大大缩短了工程施工周期,具有重要的工程应用价值。基于国内外研究成果,我国早强型混凝土的制备方法基本采用掺早强剂、使用特种水泥和掺高分子聚合物三种方法。本文对使用硫铝酸盐水泥制备的早强型混凝土进行了评估分析,对使用硫铝酸盐水泥配置的早强快硬混凝土在工作性、力学性能及耐久性方面进行了研究,分析了其在路面抢修方面的应用前景。     

High strength circular concrete-filled steel tubular slender beam-columns, Part I: Numerical analysis

High strength circular concrete-filled steel tubular (CFST) slender beam-columns are frequently used in high-rise composite buildings because they possess higher strength and stiffness than normal strength ones. Most nonlinear inelastic methods of analysis for circular CFST slender beam-columns have not considered the effects of high strength materials and concrete confinement that significantly increases the strength and ductility of the concrete core. As a result, these methods produce computational solutions that deviate considerably from experimental results. This paper presents a new numerical model for predicting the nonlinear inelastic behavior of high strength circular CFST slender beam-columns under axial load and bending. The numerical model developed not only accounts for confinement effects on the concrete core and circular steel tubes but also incorporates initial geometric imperfections of beam-columns. Axial load-moment-curvature relationships obtained from the fiber element analysis of column cross-sections are utilized to determine the equilibrium states in the inelastic stability analysis of slender beam-columns. Computational algorithms are developed for determining the axial load-deflection and axial load-moment interaction curves for slender beam-columns. The numerical model is implemented in a computer program, which is shown to be an efficient and accurate simulation tool that can be used to investigate the fundamental behavior of high strength circular CFST slender beam-columns. The verification and applications of the numerical model are given in a companion paper.     

高强圆钢管混凝土压弯构件(1):数值分析

由于具有比普通构件强度高、刚度大等特点,高强圆钢管混凝土压弯构件被广泛用于高层建筑中。然而,针对此类构件的大多数非线性分析方法都没有考虑高强材料属性和混凝土约束的影响,这很大程度上高估了核心混凝土的强度和韧性。因此,这些方法的求解结果与试验结果相差很大。针对高强圆钢管混凝土压弯构件的非线性性能,提出新的数值模型。该模型不仅考虑了混凝土约束对核心混凝土和钢管的影响,还考虑了压弯构件的初始几何缺陷。根据通过有限元分析求得的轴力-弯矩曲线,确定压弯构件非线性稳定分析中的平衡状态。为确定轴力-变形及轴力-弯矩曲线,提出了计算准则。在计算机程序中应用该数值模型,可研究高强圆钢管混凝土压弯构件的基本性能。在后续文章中,将验证该模型的正确性,并应用此模型。     

煤巷锚杆支护成套技术研究与实践

介绍煤巷锚杆支护技术的最新进展与研究成果。在支护理论方面,认为锚杆支护的主要作用在于控制锚固区围岩的离层、滑动、张开裂隙等扩容变形与破坏,最大限度地保持围岩完整性,避免有害变形出现;围岩地质力学测试仪器包括小孔径水压致裂地应力测量装置、围岩强度原位测量装置及钻孔窥视仪的技术特征与使用方法;论述锚杆支护动态信息设计方法的特点与设计步骤,及面向现场工程技术人员使用的支护设计软件组成与功能;分析高强度锚杆支护材料的力学性能,包括锚杆、锚固剂、W型钢带和锚索;最后,介绍井下应用实例,通过监测数据,评价支护效果。实践证明,锚杆支护是目前最适合煤巷的高效、经济的支护方式。     

Structural performance and economics of tall high strength RC buildings in seismic regions

For a multitude of economic and societal considerations, high rise structures are on the increase. This in turn promotes the use of high strength materials to reduce column size and construction times. Whereas design guidance and engineering understanding of high strength RC structures under static loading is well‐developed, little work has been undertaken on the economics of whole buildings and their performance under earthquake loading. In this paper, 10 buildings of 24 stories are designed and detailed according to modern seismic codes. The buildings are all nominally equivalent, using a stiffness equivalence criterion and its derivatives. The cost of construction is compared in terms of steel, concrete and formwork. The static inelastic response of the buildings is also assessed, followed by a full nonlinear dynamic analysis of all buildings using three earthquake records at the design acceleration and twice the design value. Comprehensive assessment of the static and dynamic results is undertaken. It is concluded that the cost increase is mainly due to the steel, whilst significant member reductions may be availed of by using high strength concrete. The behaviour of high strength concrete structures is not inferior to that of normal strength materials. Indeed, it is observed that lower levels of overstrength can be achieved in high strength materials than in their normal strength counterparts, mainly due to the over‐reinforcement of the latter to resist vertical forces. Recommendations on the use of equivalent cracked stiffness for period calculation in design, and also effective periods for use in displacement‐based design, are given. Copyright © 1999 John Wiley & Sons, Ltd.     

节理的剪切强度准则和剪切分量Ⅰ：剪切强度准则

节理的峰值剪切强度受表面三维形貌和材料力学属性的影响,已有的文献着重阐述形貌参数的重要性。总结分析了材料的抗拉强度对节理剪切力学性质的影响。采用最大可能接触面积比、最大视倾角、视倾角分布参数描述节理沿剪切方向的三维形貌特征,用双曲线函数描述不同法向应力下的剪胀角,提出新的剪切强度准则,计算值与试验值保持了较好的一致性。采用其中28组岩石节理的直剪试验数据对新准则与JRC-JCS准则进行了比较,结果表明JRC-JCS准则的计算值与试验值相比差异更大。新准则采用的形貌参通过由形貌测试确定,避免了主观因素对形貌参数取值的影响,可用用于估算岩石节理的峰值剪切强度。     

线性和非线性的统一强度理论

统一性,即将以前相互没有联系的概念、方法、理论、现象等统一起来,这是一个科学理论美的重要特点之一。统一强度理论是一种新的序列化的理论,它不仅建立起各种线性破坏准则的相互联系,并且产生一系列新的准则。单剪强度理论、双剪强度理论和介于单剪强度理论与双剪强度理论之间的一系列线性准则均为它的特例。但是,它没有将Huber-von Mises准则等非线性准则统一起来,而只能线性逼近它们。根据一个新的力学模型,提出一个普遍形式的统一强度理论,它不仅将单剪强度理论和双剪强度理论的线性准则统一起来,并且将八面体剪应力理论的非线性准则统一起来,从而建立起各种强度理论之间的相互联系,并将最常用的各种强度理论统一于一体,形成一个线性和非线性准则统一的普遍形式的强度理论,可以适用于更多的材料。     

Experimental evaluation of geosynthetics as reinforcement for shotcrete

One of the commonly used stabilization systems for rock tunnels is shotcrete. This fine aggregate mortar is usually reinforced for improving its tensile and shear strength. In deep tunnels, its capacity to absorb energy has been recently considered for design purposes, as large displacements of the wall are expected. Two of the most used materials of reinforcement are steel welded-wire mesh and fibers (steel or polypropylene) in the shotcrete mix. This study presents the results and discussion of an experimental test program conducted to obtain the load-deformation curves of reinforced shotcrete, according to ASTM C 1550, using geosynthetics grids and geotextiles as alternative reinforcement materials. In addition, plain shotcrete and steel welded-wire mesh reinforced shotcrete specimens are also considered in the experimental program as benchmark cases. The experimental results are analyzed in terms of maximum strength and toughness. Results show that the use of geosynthetics as a reinforcement material is a promising alternative to obtain shotcrete with energy absorption capacity comparable with the most common reinforcement materials used.     

Application of electro-mechanical impedance sensing technique for online monitoring of strength development in concrete using smart PZT patches

Electro-mechanical impedance (EMI) sensing technique utilizing smart piezoelectric materials has emerged as a potential tool for the implementation of an online monitoring system for structural health monitoring. Many nondestructive methods for strength gain monitoring seem to have limited capabilities in monitoring of the strength gain in a continuous manner. In this study, the feasibility of the EMI sensing technique for the online strength gain monitoring of early-age concrete is investigated. The experimental study is conducted on the piezoelectric patch instrumented concrete specimen. It is found that the EMI signature is very sensitive to the strength gain in early age concrete.     

堆石料状态相关三维多重机制边界面模型

堆石料的应力应变特性与材料的密度、压力等状态密切相关。针对堆石料的变形与强度非线性,在临界状态和边界面弹塑性理论框架内,建立了一个堆石料状态相关三维多重机制边界面模型。模型将复杂的宏观变形行为分解为一个宏观体应变机制和一系列空间分布的相互独立虚拟微观剪切机制。每个微观剪切机制包含3个方向的微观剪应力–应变关系和微观应力–剪胀关系。引入一个与密度、压力相关的状态参数,用以统一描述不同状态下堆石料的变形和强度特性。模型包含12个参数,多数具有明确的物理意义。对2种堆石料三轴压缩试验结果进行模拟计算,模型模拟值与试验结果吻合良好,说明模型能够较合理地预测堆石料的应力应变特性。     

纳米SiO2在不同分散条件下对水泥基材料微观结构、性能的影响

采用手工搅拌、高速研磨搅拌以及高速研磨搅拌加超声波震荡这3种方法对纳米SiO2进行分散处理,研究了不同处理方式下纳米SiO2对水泥浆体性能的影响.用扫描电镜(SEM)观测了浆体微观结构,并采用紫外-可见分光光度法测定了在不同分散方法下纳米SiO2的分散程度.结果表明,采用后2种方法处理的纳米SiO2分散程度更高,可大幅提高水泥砂浆的抗压、抗折强度,使砂浆水化产物结构均匀,更密实.     

客运专线隧道工程喷射混凝土施工质量控制的研究

喷射混凝土是隧道工程复合支护普遍采用的结构材料,具有施工速度快、支护及时、施工安全,以及支护质量好、强度高、密实、防水性能好等特点;为了更好地满足客运专线隧道工程的技术要求,该文对喷射混凝土的原材料、配合比设计及施工的质量控制进行了深入探讨,为今后客运专线隧道工程喷射混凝土的施工提供了较完善的技术支撑。     

Parameter optimization on compressive strength of steel fiber reinforced high strength concrete

This paper illustrates parameter optimization of compressive strength of steel fiber reinforced high strength concrete (SFRHSC) by statistical design and analysis of experiments. Among several factors affecting the compressive strength, five parameters that maximize all of the responses have been chosen as the most important ones as age of testing, binder type, binder amount, curing type and steel fiber volume fraction. Taguchi analysis techniques have been used to evaluate L₂₇ (3¹³) Taguchi’s orthogonal array experimental design results. Signal to noise ratio transformation and ANOVA have been applied to the results of experiments in Taguchi analysis. The confirmation runs were conducted for the optimal parameter level combination, which is obtained from the results of the above methodologies. The maximum compressive strength has been observed as around 124 MPa. By using the optimal parameter level combination, the direct tensile strength and flexural strength tests have been conducted. The mean values at the age of 28 days are obtained as 7.5 MPa and 13 MPa respectively. In this study, it is clearly demonstrated that all main factors except steel fiber significantly contribute to the compressive strength of steel fiber reinforced high strength concrete, yet age and binder type are the most significant contributors.     

Design of axial/torque joint made by electromagnetic forming

Recently, weight reduction of vehicles has been of great interest, and consequently, the use of low-density materials in the automotive industry is increasing every year. However, the substitution of one material for another is not simple work. Simple substitution of material cannot achieve stiffness and strength, so that the structure of the automobile should be redesigned totally. Spaceframe is rapidly being adopted as a body structure for accommodating lightness, stiffness and strength requirement. In spaceframe manufacturing, it is often required to join tubular parts with different cross sectional shapes and different materials. But there are few suitable methods for satisfying these requirements, so that much interest has been focused on testing suitable joining methods. Joining by electromagnetic forming (EMF) can be useful method in constructing spaceframe. It offers some advantages compared with the conventional joining method such as welding. In this paper, joining by EMF was investigated as a pre-study for application to an automotive spaceframe. Finite element simulations and strength tests were performed to analyze the influence of geometric parameters on the joint strength. Based on these results, axial joint and torque joint were designed and guidelines for designing EMF joint were established.     

Investigation of fibre reinforced mud brick as a building material

Most of the buildings in the rural areas are made out of limestone, low quality traditional concrete brick and adobe. But these materials do not have sufficiently high compressive strengths. In the present research, an earthquake-resistant material with high compressive strength has been sought. To this end, the mechanical properties of certain combinations of fibrous waste materials and some stabilisers were investigated thoroughly and some concrete conclusions were drawn. It was concluded that the interface layers of fibrous materials increased the compressive strength and a certain geometrical shape of these layer materials gave the best results. The mix proposed satisfies the minimum compressive strength requirements of ASTM and Turkish Standards.     

对焊接高强度钢材箱型构件中残余应力的评估

关于残余应力在低碳型钢中的大小和分布之前已经进行了很多研究,然而,对于高强度型钢中残余应力的测定研究甚少。高强钢和低碳钢在应力-应变曲线及高温材料特性上的差异是研究高强度焊接型钢残余应力的必要研究方面。在当前研究中,采用以厚11mm的Q460钢板焊接而成、不同的3个箱型柱做试验。切条法和钻孔法都可用于测量。最终将可看到测定的残余应力在3个箱型柱中的分布状况及其相应的简易残余应力分布图。与低碳钢的残余应力图相比较,可以发现,由高强度钢板焊接而成的箱型柱有较低的残余应力比。同时也对采用不同测定方法(切条法、钻孔法)所造成的差异进行了比较。     

The assessment of residual stresses in welded high strength steel box sections

Much work on the investigation of the magnitude and distribution of residual stresses in mild carbon steel sections have been made previously. However, limited efforts have been put on residual stress measurements of high strength steel sections. The differences of stress–strain curves and high-temperature material properties between the high strength steel and mild carbon steel demands a necessary study of the residual stresses in high strength steel welded sections. In the present study, three box columns fabricated from Q460 steel plates of 11 mm in thickness with different details were used for the examination. Both sectioning and hole-drilling methods are adopted for the measurement. The measured residual stress distributions of three different box sections are presented, and the corresponding simplified residual stress pattern is proposed. By comparing with the residual stress patterns for mild carbon steel, it is found that the box section fabricated from HSS plates has the lower compressive residual stress ratio. The differences in the measurement by using sectioning and hole-drilling methods are also compared.     

基于BP神经网络的堆肥物料抗剪强度预测模型

针对目前传统方式采集堆肥物料抗剪强度数据过程中环境恶劣、数据采集困难、试验误差大等问题,提出一种基于BP神经网络的抗剪强度预测模型。通过现场试验得到堆肥物料抗剪强度和堆体高度、温度、含水率、密度等参数共39组有效数据,以其中35组作为训练样本,其余4组用于评价模型的预测性能。结果表明,该模型预测值与实测值的平均误差为11. 35%,基于BP神经网络的抗剪强度预测模型具有较高的预测精度,为抗剪强度的预测提供了一种新方法。