Mechanical properties of roller bent wide flange sections — Part 1: Experimental investigation

Arched roofs are built more and more with roller bent wide flange sections, serving as structural elements. Roller bent wide flange sections are manufactured from straight hot-rolled wide flange sections by a process called roller bending. The material is cold worked during forming, inducing a new distribution of mechanical properties across the section which is different compared to its original state. For the design of arches the use of original or nominal strength properties of the straight material neglects the influence of the roller bending process. This may lead to conservative or nonconservative designs. This paper presents the results of an extensive experimental investigation of the mechanical properties of roller bent wide flange sections. It comprises tensile tests and compression tests on coupons taken from roller bent sections and their straight counterparts. The results show that the roller bending process alters the mechanical properties of the material non-uniformly over the cross-section. In this paper the experimental results are presented. In a companion paper the experimental results are used to arrive at a set of equations that yields different stress-strain curves for specific zones across the roller bent steel section.     

Proposed residual stress model for roller bent steel wide flange sections

The manufacturing process of structural wide flange steel sections introduces residual stresses in the material. These stresses due to hot-rolling or welding influence the inelastic buckling response of structural steel members and need to be taken into account in the design. Based on experimental data standardized residual stress models have been proposed for inclusion in inelastic buckling analyses. By incorporating these residual stress models their effect on the resistance of beams and columns can be obtained. Residual stress models for roller bent steel sections are currently not available. Roller bent wide flange sections are manufactured by curving straight members at ambient temperature. This manufacturing technique, which is also known as roller bending, stresses the material beyond its yield stress, thereby overriding the initial residual stresses prior to bending and generating an entirely new pattern. This paper proposes a residual stress model for roller bent wide flange sections, based on earlier conducted numerical investigations which were validated by experimental research performed at Eindhoven University of Technology. The proposed residual stress model can serve as an initial state of a roller bent steel section in fully non-linear finite element analyses to accurately predict its influence on the inelastic buckling response.     

Q690高强钢疲劳损伤后力学性能试验研究

服役结构材料疲劳损伤后的残余力学性能对结构可靠性的评估有着至关重要的作用.为此,对Q690高强钢经不同疲劳损伤后的残余力学性能进行了试验研究.根据Q690高强钢在不同疲劳荷载作用下的疲劳寿命,设定了3级疲劳荷载和9组损伤振动次数,并将Q690高强钢试件在各疲劳荷载下进行不同次数的预损伤疲劳振动.然后,对这些具有不同疲劳...     

Experimental investigation of cold-formed steel material at elevated temperatures

This paper presents the mechanical properties data for cold-formed steel at elevated temperatures. The deterioration of the mechanical properties of yield strength (0.2% proof stress) and elastic modulus are the primary properties in the design and analysis of cold-formed steel structures under fire. However, values of these properties at different temperatures are not well reported. Therefore, both steady and transient tensile coupon tests were conducted at different temperatures ranged approximately from 20 to 1000 °C for obtaining the mechanical properties of cold-formed steel structural material. This study included cold-formed steel grades G550 and G450 with plate thickness of 1.0 and 1.9 mm, respectively. Curves of elastic modulus, yield strength obtained at different strain levels, ultimate strength, ultimate strain and thermal elongation versus different temperatures are plotted and compared with the results obtained from the Australian, British, European standards and the test results predicted by other researchers. A unified equation for yield strength, elastic modulus, ultimate strength and ultimate strain of cold-formed steel at elevated temperatures is proposed in this paper. A full strain range expression up to the ultimate tensile strain for the stress–strain curves of cold-formed carbon steel at elevated temperatures is also proposed in this paper. It is shown that the proposed equation accurately predicted the test results.     

AISI 316Ti (1.4571) steel—Mechanical, creep and fracture properties versus temperature

In this paper some useful, experimentally obtained, results regarding material properties of austenitic stainless steel 1.4571 are presented. Tests were performed at low and elevated temperatures. During uniaxial tests, mechanical properties such as ultimate tensile strength, 0.2% offset yield strength and short-time creep behaviour were determined. Charpy impact energy was also determined using the Charpy impact machine. Engineering stress-strain diagrams are shown at low and elevated temperatures, whereas creep curves for selected stress levels are presented at selected temperatures. Therefore, experimentally obtained data may be of importance for structure designers dealing with design of structures made of similar material and operating under similar environmental conditions.     

AISI 316Ti (1.4571) steel—Mechanical,creep and fracture properties versus temperature

In this paper some useful, experimentally obtained, results regarding material properties of austenitic stainless steel 1.4571 are presented. Tests were performed at low and elevated temperatures. During uniaxial tests, mechanical properties such as ultimate tensile strength, 0.2% offset yield strength and short-time creep behaviour were determined. Charpy impact energy was also determined using the Charpy impact machine. Engineering stress-strain diagrams are shown at low and elevated temperatures, whereas creep curves for selected stress levels are presented at selected temperatures. Therefore, experimentally obtained data may be of importance for structure designers dealing with design of structures made of similar material and operating under similar environmental conditions.     

方钢管混凝土柱与钢梁连接的拉伸试验研究

本文通过对带内隔板的十字形连接节点的拉伸试验,研究了方钢管混凝土柱与钢梁连接的结构性能。借助于在柱翼缘、梁翼缘和内隔板上的应变测量,分析了连接区域的应力传递机制。基于屈服线理论,并考虑连接区域的应变性能,提出了方钢管混凝土柱与钢梁连接的承载力方程,可供制订规范和工程设计参考     

高温后新Ⅲ级钢筋力学性能的试验研究

通过对37组共111根(?)16和(?)12新Ⅲ级钢筋高温后的力学性能试验,研究了经历不同受火温度和受火恒温时间 后的屈服强度、极限强度、弹性模量、延伸率和受拉应力-应变关系等力学性能的变化规律。试验表明。新Ⅲ级钢筋在经历 高温作用后,其屈服强度、极限强度和弹性模量在400℃以前变化不大,之后随所经历温度的升高而逐渐下降,降幅一般在 15％左右,实测的受拉应力-应变关系曲线,仍然出现明显的屈服台阶和强化段。根据试验结果,本文建议了高温后新Ⅲ 级钢筋屈服强度、极限强度、弹性模量、延伸率和受拉应力.应变全曲线计算公式。本文研究成果可作为火灾后混凝土结 构的损伤评估和非线性有限元全过程分析的依据。     

Finite element simulations of residual stresses in roller bent wide flange sections

Curved structural wide flange steel sections are frequently used in buildings or bridges. These sections are usually curved at ambient temperatures with a roller bending machine. This process alters the residual stress distribution, which may affect the elasto-plastic buckling behavior of arches. This paper presents a numerical modeling technique to estimate residual stresses in curved wide flange sections manufactured by the pyramid roller bending process. The technique incorporates material non-linearity, geometrical non-linearity and contact modeling. Numerically obtained residual stresses are compared to experimental results and good agreement was found for the top flange. Only moderate agreement was observed for the web but very good coherence was realized for the bottom flange. It is concluded that a finite element analysis can be used to estimate residual stresses in roller bent wide flange sections.     

Experimental investigation of residual stresses in roller bent wide flange steel sections

Residual stresses in straight hot rolled wide flange sections are well documented and have been investigated in the recent past. However, to the knowledge of the authors, residual stress measurements have not been published on roller bent wide flange sections. Straight sections are curved into roller bent ones at ambient temperatures by means of the roller bending process. Since roller bent sections underwent severe plastic deformation during the forming process, the well-known residual stress patterns from hot rolling may not be appropriate for the roller bent steel. Roller bent sections can be applied in halls, roofings and bridges, thereby acting as structural arches and it is important that a realistic residual stress pattern is implemented when assessing their load carrying capacity. An experimental program has been carried out to investigate the residual stresses in roller bent wide flange sections bent about the strong axis. Residual stresses were measured with the sectioning method. The experimental technique was investigated with respect to possible temperature influence and repeatability of the measurements. Experimental values revealed that the residual stress pattern and magnitude in roller bent sections is different when compared to their straight counterparts.     

国产Q690高强钢高温下力学性能试验研究

通过国产Q690高强钢的稳态试验研究,得到20~800℃下钢材的试验现象、应力-应变关系曲线、力学性能参数,并将所得试验结果与相关规范和已有研究进行比较。研究发现：随温度升高,试验后钢材表面及断口形貌区别明显,应力-应变关系曲线的初始线弹性段缩短、极限应力对应应变减小、下降段趋于平缓;弹性模量、屈服强度和抗拉强度等力学性能指标随温度升高而降低;而断后伸长率在200~500℃时相较于常温值有小幅度下降,600℃后明显增加;当温度低于500℃时,不同名义屈服强度折减系数之间存在较大差异。目前已有研究建议的钢材高温力学性能模型并不适用于Q690高强钢,通过试验结果拟合得到了高温下Q690钢力学性能模型,以期用于Q690钢材的钢结构抗火安全评估与设计。     

考虑应变时效影响的Q460C高强钢力学性能试验研究

为深入研究应变时效对Q460C高强钢基本力学性能影响,建立考虑应变时效影响Q460C高强钢应力-应变本构关系曲线,对经应变时效影响的Q460C高强钢进行了试验研究,分析了Q460C高强钢经应变时效后基本力学性能指标,采用修正Ramberg-Osgood模型对试验结果进行拟合。结果表明:Q460C钢经预应变后具有显著的应变硬化现象,屈服强度得到大幅提高,极限应变和断裂应变显著降低,屈强比接近1.0,结构发生脆性断裂的可能性增加; Q460C钢经时效后产生时效硬化现象,试件在各时效之间应力-应变曲线差别较小,经时效硬化后钢材的硬化程度低于应变硬化; 采用修正的Ramberg-Osgood模型能够较为准确地拟合经预应变及时效影响后高强钢的应力-应变曲线,拟合结果与试验结果具有较好的一致性; 研究内容可为相关工程应用和理论分析提供参考。     

高温下及高温后1770级ф~P5低松弛预应力钢丝力学性能试验研究

鉴于预应力钢丝高温下及高温后的力学性能是开展预应力结构抗火设计及进行火灾后预应力结构损伤评估与修复的重要依据,对16个1770级P5低松弛预应力钢丝试件进行了高温下拉伸试验,14个钢丝试件进行了高温后拉伸试验。试验表明,随着温度升高,高温下钢丝应力-应变关系曲线形状趋于平缓,钢丝的强度、弹性模量等力学指标不断退化;对于高温后钢丝,温度历程低于300℃时,钢丝力学性能变化不明显;高于300℃时,随温度历程的升高,钢丝应力-应变关系曲线逐渐软化,钢丝各项力学指标逐渐退化。应用粘弹性力学理论,得到了去除加载速率影响的高温下钢丝应力-应变关系曲线,得到了钢丝各项力学指标在高温下及高温后的退化规律,建立了高温下及高温后的钢丝应力-应变曲线方程。为开展预应力结构抗火性能分析及火灾后损伤评估提供了基础性素材。     

Q460高强钢单调与反复加载性能试验研究

通过对Q460高强钢进行单向拉伸与反复加载下材料性能试验，得到了各试件单调拉伸和反复加载下的应力-应变关系曲线，以及反复加载下的骨架曲线，并将试验结果与文献研究结果进行了对比。试验结果表明：单向拉伸材性试验中，11 mm厚Q460C高强钢板的平均断后伸长率为23.7%，屈强比为0.847； 21 mm厚钢板的平均断后伸长率为30.4%，屈强比为0.792；Q460钢的循环硬化程度比Q345钢明显减弱，主要原因是随着钢材强度的提高，钢材的屈强比增大，钢材的应变强化效应减小。根据钢材反复加载的滞回曲线，提出了Q460高强钢材的应力 应变滞回模型，用该模型计算得到的关系曲线与试验曲线对比，两者吻合较好。     

选择性激光熔融增材制造不锈钢力学性能研究进展及统计分析

在简要介绍金属增材制造技术分类的基础上,对选择性激光熔融(SLM)技术的研究进展进行梳理,以SLM制品的力学性能及其主要影响因素为重点进行综述.通过SLM技术制备了48个316L不锈钢试样,通过单轴拉伸试验获得了弹性模量、屈服强度、抗拉强度、延伸率和泊松比等基本力学性能数据.采用SPSS软件分析了力学性能试验数据的分布...     

国产超高强钢Q890高温力学性能试验

通过稳态拉伸试验法对国产超高强钢Q890在不同火灾高温条件下的力学性能进行了试验研究,得到高温下钢材的力学性能参数、应力-应变关系曲线和试验现象,并将所得试验结果与钢结构抗火设计规范及相关超高强钢研究文献中高温材料模型结果进行比较。分别采用多项式模型和钢材高温通用材料模型对试验结果进行数值拟合,建立高温下Q890钢力学性能参数的材料模型。结果表明:不同温度条件下的Q890钢试件在试验后有明显不同的外观特征,相应的应力-应变关系曲线基本形状差异较大;当受热温度低于500 ℃时,弹性模量和强度随温度升高逐步减小,断后伸长率变化不大;超过500 ℃后,弹性模量和强度下降速率明显加快,断后伸长率急剧增大;所建立的模型为研究Q890钢结构抗火性能及其计算方法提供理论基础。     

The effect of elevated temperatures on corroded and uncorroded reinforcement embedded in mortar

In this study, the alterations at the reinforcement steels embedded in corroded and not corroded reinforcement mortar specimens after high temperatures were investigated. These reinforced mortar specimens with 3 cm and 5 cm covers were first exposed to 20, 100, 200, 300, 500 and 800 °C temperatures. Subsequently, to determine the mechanical properties tensile tests were applied on the steels taken out of these mortar specimens. With the tensile tests performed stress–strain curves of the steel bars exposed to several temperatures were obtained. Besides, yield and ultimate strengths of the steel bars were also determined. It is obtained that, high temperatures affected the mechanical properties of reinforcement steel considerably negatively. Results of the study have shown that the larger the covers are the better the steel bars are protected against high temperatures.     

High Temperature Mechanical Properties of High Strength Structural Steels Q550, Q690 and Q890

This paper reports the results of an experimental study on high temperature mechanical properties of high strength structural steel produced in accordance with Chinese materials standards. Steady-state tensile coupon tests were carried out on specimens made of China grade steels of Q550, Q690 and Q890. Nine elevated temperature levels up to 800°C were considered. The elastic modulus, yield strength, ultimate strength and ultimate strain were derived from the measured stress–strain curves. A model was developed to predict the high temperature properties of these steels using an approach developed by the National Institute of Standards and Technology and by calibrating the model parameters to the test data. The test results are compared to other tests on high strength steels reported in literature. The test results are also compared to predictions of high temperature properties from various building codes and other standards. The study found that steel grade has significant effect on the reduction factors. The difference between the reduction factors of elastic modulus for Q690 and Q550 was 30% at 600°C. In this study, reduction factor is defined as the ratio of the high temperature property to the corresponding room temperature property. The study also found that the material models in current codes are not applicable to the investigated high strength steels.     

预应力高强钢丝绳抗弯加固钢筋混凝土梁的理论分析

预应力高强钢丝绳加固是一种新型高效加固方法(简称P-SWR加固技术)。首先对试验用钢丝绳抗拉强度、拉伸极限应变和松弛等力学性能进行试验研究;然后给出预应力高强钢丝绳加固后混凝土梁开裂荷载、最大承载力计算方法;结合预应力高强钢丝绳加固混凝土梁的荷载-挠度关系曲线,分析了预应力度、配筋率、钢丝绳与混凝土黏结性能等各种参数对P-SWR加固梁截面短期刚度的影响,提出了相应的计算公式;基于高强钢丝绳抗弯加固对混凝土梁裂缝平均间距和钢筋应力影响的分析,建议了计算P-SWR加固后混凝土梁最大裂缝宽度的修正规范方法、名义拉应力方法和实用简化方法。建议的各计算方法简单,与相应试验值的比较表明具有较高的精度,可用于P-SWR抗弯加固混凝土结构的理论分析和简化设计。     

箍筋约束轻骨料混凝土轴心受压应力-应变曲线研究

为研究轻骨料混凝土轴心受压应力-应变曲线,考虑箍筋约束效率的影响,以有效侧向约束应力与非约束轻骨料混凝土强度之比为参数,建立了适用于轻骨料混凝土的峰值应力、峰值应变和下降段代表点计算模型,给出了轴心受压应力-应变曲线峰值点时箍筋实际应力计算方法;根据箍筋约束轻骨料混凝土应力-应变曲线的特点,基于箍筋强度和混凝土强度,通...