冷弯经济型双相不锈钢弯构件试验研究及数值分析

对冷弯经济型双相不锈钢受弯构件进行试验研究及数值分析。试件由屈服强度(σ0.2)为450MPa的经济型双相不锈钢板材冷轧成型。对方形和矩形截面空心型材试件进行绕强轴和弱轴的弯曲试验。利用取样试验得到的材料性能建立有限元模型,并利用弯曲试验结果对其进行验证。结果表明,该模型可以准确预测经济型双相不锈钢抗弯构件的性能。利用有限元模型进行了大量参数研究。利用现有的各种设计准则,如美国规范、澳大利亚/新西兰规范、欧洲规范以及直接强度法计算冷弯不锈钢的设计强度,并与经济型双相不锈钢梁的试验和数值分析结果以及可用的数据进行对比。为评估这些设计准则的可靠性,进行了可靠性分析。结果表明,现有设计准则计算经济型双相不锈钢受弯构件的设计强度时偏于保守。对美国规范、澳大利亚/新西兰规范、欧洲规范以及直接强度法进行了修正,提高了这些设计准则的精度。     

侧向扭转屈曲时冷成型钢梁的特性及设计

建筑物中越来越多地使用冷成型钢梁作为楼板的辅助及受力构件,其在没有足够侧向约束时的性能和瞬时承载力将受到侧向扭转屈曲的影响。以往对侧向扭转屈曲的研究主要针对热成型卷边钢梁,因此需要对简单支撑下相同弯曲度冷成型卷边槽钢梁的特性进行数值模拟。采用业内广泛认可的有限元分析软件ABAQUS进行建模,对不同条件下冷成型钢梁微单元的侧向扭转屈曲性能和承载力进行分析和模拟。将瞬时承载力结果与冷成型钢结构规范中当前设计准则的预测结果进行比较并对其进行适当的修正。欧洲的设计规范较为保守,而澳大利亚、新西兰和北美的设计规范则较为宽泛。基于有限元分析结果,对规范中的瞬时承载力设计公式进行修正。阐述了参数分析的细节问题,修正了当前设计规范,提出了侧向扭转屈曲时冷成型卷边槽钢梁的新设计准则。     

不锈钢板梁剪力设计建议

研究剪切作用下不锈钢板梁的性能及设计。首先,回顾了现有不锈钢板梁的设计方法(包括规范方法);然后,给出奥氏体、双相和节约型双相不锈钢板梁的34组试验数据,用于评估欧洲规范3第1.4节、欧洲规范3第1.5节及近来文献中提出的抗剪强度设计公式。比较结果表明,欧洲规范3第1.4节的设计公式偏于保守,可以通过欧洲规范3第1.5节和Estrada等人所提出的公式对结果进行修正。当然,还可以进一步修正,并基于现有试验数据,提出计算不锈钢板梁极限抗剪承载力的修正公式,且对其进行验证,以便未来适合纳入欧洲规范3第1.4节修订版。与现行欧洲规范3第1.4节不同,修正公式区分了刚性和非刚性端柱,并使剪切屈曲强度的计算值提高了10%左右。     

中美欧房屋建筑钢筋混凝土基本构件设计安全度比较

安全是建筑结构设计的重大问题,规范规定是安全性的最低要求。对中国规范、美国规范和欧洲规范中钢筋混凝土基本构件的安全度水平进行了对比分析,提出了不同规范安全度水平比较的"设计值判则"和"安全度判值"。比较结果表明,中国规范的安全度水平总体上低于美国规范和欧洲规范,平均分别低20%和10%。     

高原高寒地区钢-混凝土组合梁斜拉桥温度效应分析

对比了当前各国规范对钢-混凝土组合梁竖向温度梯度形式及温度基数取值的相关规定,其中英国规范和欧洲规范最为详尽合理。在英国规范的基础上,通过桥位处太阳辐射强度的计算结果对温度基数的取值进行修正。以青海黄南地区哇加滩黄河特大桥为背景,建立全桥有限元杆系模型,对比分析了修正的英国规范温度梯度模式和中国规范的温度梯度模式作用下主梁的应力分布,以及斜拉桥在整体温差、索梁（塔）温差、主梁竖向温度梯度和主塔顺桥向温差作用下的温度效应及各构件的温度敏感性。结果表明:在青海高原高寒地区,进行桥梁设计时采用考虑地理位置修正的英国规范主梁竖向温度梯度模式进行计算并指导设计更偏于安全;对于主桥的某些构件,温度作用已经成为仅次于恒载的第二大控制作用,所得出的全桥各构件温度敏感性分析结果可为高原高寒地区同类桥梁的设计、计算提供参考和依据。     

高强度等边角钢轴心受压局部稳定的有限元分析和设计方法研究

随着钢结构的发展,高强度热轧等边角钢在钢结构中的应用逐渐增多,如输电铁塔和大跨度桁架等。然而由于强度的提高,较多数量角钢截面的等效宽厚比超过规范的限值,不满足局部稳定的要求。我国现行规范尚未对这一问题给出明确规定。运用通用有限元软件ANSYS建立有限元模型,准确模拟构件的残余应力和几何初始缺陷,对15个高强度热轧等边角钢轴心受压构件的局部稳定受力性能进行有限元分析,并与相应的试验结果进行对比。比较结果表明,建立的有限元模型能够准确模拟几何初始缺陷和残余应力对构件局部稳定受力性能的影响,从而准确地分析计算高强度热轧等边角钢轴心受压构件的局部稳定受力性能。利用已验证的有限元模型,对高强度热轧等边角钢轴心受压构件的局部稳定受力性能进行有限元参数分析,并与美国规范和欧洲规范的设计方法进行对比。结果得到:几何初始缺陷和残余应力对于高强度热轧等边角钢轴心受压构件局部稳定承载力的影响比普通钢材受压构件小;美国钢结构设计规范能够更准确的计算Q420等边角钢轴心受压构件的局部稳定承载力。     

船舶碰撞动力响应有限元模拟

分析比较了我国《铁路桥涵设计规范》、美国AASHTO《公路桥梁设计规范》和《欧洲统一规范2.7分册》中船撞力计算公式。利用有限元软件Ls-DYNA创建不同重量、不同类型的船舶有限元模型,模拟船舶与刚性墙的正面碰撞过程,将数值模拟得到最大船撞力与各规范计算结果比较,研究表明数值模拟得到最大船撞力与美国规范和欧洲规范的计算结果相近;最大船撞力和船舶重量的开方基本呈成正比关系;相同重量而类型不同的船舶由于船艏形状不同,所得的船撞力时程曲线不同,对应最大船撞力也不相同。     

中美欧冷弯型钢结构基本构件设计安全度比较

参照《中美欧房屋建筑钢筋混凝土基本构件设计安全度比较》提出的"安全度判值ξ_d"作为不同规范安全度设置水平的可比指标,对我国冷弯型钢结构设计规范与美国和欧洲相关规范安全度设置水平进行比较了分析。对中国规范、美国规范和欧洲规范中轴心受拉、轴心受压、受弯、受剪、压弯等基本构件的强度或稳定性的安全度差异进行了计算分析,得出"中国规范的安全度水平总体上略高于欧洲规范,平均高12%,但略低于美国规范,平均低5%"的重要结果。     

矩形钢管混凝土构件抗弯性能研究

为研究厚实、非厚实和薄柔截面矩形钢管混凝土(CFST)构件的抗弯性能,提出一种有限元分析(FEA)模型。使用70组试验结果对有限元模型进行验证。有限元分析得到的复合构件极限抗弯承载力和弯矩-跨中挠度关系曲线与试验结果相符。利用有限元模型研究核心混凝土的破坏模式、外钢管典型的残余变形以及整个加载过程中组合结构的应力-应变分布。分析结果表明,组合梁中钢材和混凝土的相互作用使其产生了应力重分布,从而提高了矩形钢管混凝土梁的抗弯承载力和延性。最后,使用可靠性分析方法对欧洲规范EC 4(2004)、美国AISC(2010)和中国规范DBJ/T 13-51-2010中组合梁的现有设计公式进行了评估,结果发现,设计公式的可靠性指标较好。     

各国规范钢框架结构抗震设计方法对比研究(Ⅱ):承载力、延性与侧移要求

在对比欧洲、美国、日本和中国规范的设防目标和地震作用的基础上,对钢框架结构的设计地震力、延性、侧向刚度和强度等开展系统地对比研究。结果表明,短周期结构按欧洲、美国和中国规范计算的侧向地震力分布相同,与按日本规范计算的亦十分接近;而中、长周期结构按欧洲规范计算的侧向地震力小于按其他规范计算的,尤其是结构的顶层;尽管各国规范规定的材料和构件延性要求差别不大,美国规范针对钢框架规定的地震力折减系数大于欧洲和日本规范的,而中国规范采用了与结构形式无关的较保守的折减系数,导致按中国规范设计的钢框架侧向刚度和强度基本上均比欧洲和美国规范的大20%~150%,但由于日本规范采用的弹性反应谱远大于其他规范,折减后设计地震力也更大,使得按日本规范设计的钢框架侧向刚度和强度比中国规范的还大;总体上,按欧洲规范设计的钢框架侧向刚度和强度与按美国规范设计的结果相当。     

Strength design criteria for steel members at elevated temperatures

Design equations for structural steel members at elevated (fire) temperatures are evaluated through comparisons with nonlinear finite element simulations. The study includes comparative analyses of the American Institute of Steel Construction (AISC) and European Committee for Standardization (CEN) design provisions for laterally unsupported I-shaped columns, beams, and beam-columns at temperatures between ambient to 800 ^°C. The Eurocode 3 provisions are shown to predict the simulated finite element results within about 10%-20%. On the other hand, the AISC specification predicts strengths that are up to twice as large (unconservative) as the simulated results. The discrepancies are largest for members of intermediate slenderness and temperatures above 300 ^°C. Modifications to the AISC equations are proposed that provide improved accuracy with calculated strengths typically within 20%-30% of the simulated results. Limitations of the member-based assessments and future research and development needs for structural fire engineering are discussed.     

Predicting the maximum compressive beam axial force during fire considering local buckling

Local buckling in floor beams has been one of the important observations in several fire events in steel buildings such as World Trade Center Tower 7 and large-scale fire experiments such as Cardington building test in U.K. Utilizing three dimensional finite element methods for complex geometry and nonlinear behavior of such connections, local buckling of the web followed by the buckling of the lower flange is observed to occur in early stages of fire, which causes instability to the floor system, and a significant reduction in the connection strength. The observations also suggest that the maximum compression in the floor beam is limited to the buckling capacity of the web and flanges near the connection. This paper contributes to such knowledge by investigating the local buckling of floor beams for different connection types at elevated temperatures using nonlinear finite element models. Moment connections are found to be more resistant to local buckling when compared to the shear connections. The results are also compared to the AISC design equation for plate buckling under ambient and elevated temperatures. Compared to the finite element analyses of this study, it is observed that at ambient temperature the AISC curve conservatively captures the buckling capacity of webs and flanges; at higher temperatures, AISC overestimates the capacity.     

Vierendeel joints in the circular hollow sections of high strength steel subjected to brace moment and chord compressive loadings

The Vierendeel joints used in buildings and highway bridges as well as offshore platforms are investigated by both the experimental approach and finite element method. A number of full scale specimens using new high strength steel (i.e., tensile strength of 600 MPa) are tested under cyclic quasi-static loadings to understand their strengths, rotational stiffness characteristics, and failure modes. The nonlinear three-dimensional finite element models are also constructed to verify the experimental results. The present experimental results are seen to closely agree with those from finite element analysis as well as theoretical predictions such as AISC and CIDEC equations.     

A simplified approach for predicting temperatures in insulated RC members exposed to standard fire

Fire resistance of concrete structural members can be enhanced through the application of external fire insulation on the surfaces of concrete member. For evaluating fire resistance of such insulated RC members, temperatures in concrete and steel reinforcement are to be known. This paper develops a simplified approach for predicting cross-sectional temperatures in an insulated RC structural member exposed to standard fire. The approach is derived by replacing the insulation layer into an equivalent concrete thickness layer and then undertaking statistical regression analysis on temperature data of modified concrete section. The effect of critical parameters, including geometry of concrete member and insulation, thermal properties of concrete and fire insulation, and duration of fire exposure is accounted for in temperature equations. The validity of the approach is established by comparing predictions from the proposed equation with data generated from fire tests and finite element analysis. These comparisons show the proposed equation gives reasonable prediction of temperatures, within a range of ±10%, in insulated concrete members. The applicability of the proposed approach in design situations is illustrated though a numerical example. The simplicity of the proposed method makes it attractive for use in design situations and for incorporation in design manuals.     

预测火灾下钢构件温度的简单方法

为评价钢结构构件的抗火性能,需要了解构件横截面的温度。给出了一种预测火灾下有外保护层的钢构件截面温度的简单方法。利用标准火灾条件下的简化假设得到该方法,并推广到设计火灾情况。该方法适用于有保护层和没有保护层的型钢构件。将预测温度与ANSYS有限元分析结果进行比较,验证了该方法的有效性。此外,该方法的预测结果也与"最佳拟合"法的预测温度进行了比较。与试验结果、有限元计算结果和"最佳拟合"法预测结果的比较表明,所提出的简化方法能够较好地预测各种火灾下型钢构件的热梯度和温度历史。该方法简单明了,适合设计时使用。     

Experimental study on local buckling of axially compressed steel stub columns at elevated temperatures

There are few design provisions in codes and standards on local buckling of steel columns under fire conditions. To examine the local stability of steel stub columns at elevated temperatures, 12 stub columns were tested under simultaneous application of load and fire conditions. The test variables included Grade (type) of steel, buckling resistance, temperature and load levels. During fire tests, cross sectional temperatures, axial displacement, buckling deflection, and local buckling failure modes of flange and web of stub columns were recorded at various temperatures. Data from the tests is utilized to evaluate buckling resistance of flange and web both at room and elevated temperatures by applying the ultimate strain method and curve inflexion point method. Results from fire tests are utilized to validate a finite element model developed for tracing local buckling of steel columns at elevated temperatures. Results from fire tests and finite element analysis show that failure mode of columns at room and elevated temperatures follow similar pattern but the load bearing capacity of Q460 steel columns degrade much more rapidly under fire conditions than that of Q235 steel columns. Further, Eurocode 3 provisions for local buckling produce non-conservative results in certain situations.     

Application of fire-resistant steel to beam-to-column moment connections at elevated temperatures

This paper presents a new method of using fire-resistant steel to improve the fire-resistance of beam-to-column moment connections in steel structures. Two full-scale beam-to-column moment connection specimens were tested at elevated temperatures according to the standard ISO-834 fire to verify the feasibility of the proposed method. In addition, a detailed 3-D finite element model was developed to simulate the structural behavior of the column-tree moment connection specimens in fire. The fire test results show that the proposed method can effectively extend the fire endurance time, reduce structural deformation, and raise the critical temperature to failure for the beam-to-column moment connections. The numerical results obtained from the 3-D finite element analyses for the two specimens successfully simulated the fire test results.     

Macroscopic FE model for tracing the fire response of reinforced concrete structures

A macroscopic finite element model for tracing the fire response of reinforced concrete (RC) structural members is presented. The model accounts for critical factors that are to be considered for performance-based fire resistance assessment of RC structural members. Fire induced spalling, various strain components, high temperature material properties, restraint effects, different fire scenarios and failure criteria are incorporated in the model. The validity of the numerical model is established by comparing the predictions from the computer program with results from full-scale fire resistance tests. Case studies are conducted to demonstrate the use of the computer program for tracing the response of RC members under standard and design fire exposures. Through the results of the case studies, it is shown that the fire scenario has a significant effect on the fire resistance of RC columns and beams. It is also shown that macroscopic finite element models are capable of predicting the fire response of RC structural members with an adequate accuracy for practical applications.     

Numerical simulation of concrete encased steel composite columns

This paper investigates the behaviour of pin-ended axially loaded concrete encased steel composite columns. A nonlinear 3-D finite element model was developed to analyse the inelastic behaviour of steel, concrete, longitudinal and transverse reinforcement bars as well as the effect of concrete confinement of the concrete encased steel composite columns. The interface between the steel section and concrete, the longitudinal and transverse reinforcement bars, and the reinforcement bars and concrete were also considered that allowed the bond behaviour to be modeled and the different components to retain their profile during the deformation of the column. Furthermore, the initial overall (out-of-straightness) geometric imperfection was carefully incorporated in the model. The finite element model has been validated against published experimental results. The main objective of the study was to understand the structural response and modes of failure of the columns and to assess the composite column strengths against current design codes. The study covered slender, non-slender, stub and long concrete encased steel composite columns. The concrete strengths varied from normal to high strength (20-110 MPa). The steel section yield stresses also varied from normal to high strength (275-690 MPa). Furthermore, the variables that influence the composite column behaviour and strength comprising different slenderness ratios, concrete strength and steel yield stress were investigated in a parametric study. It is shown that the increase in structural steel strength has a small effect on the composite column strength for the columns having higher relative slenderness ratios due to the flexural buckling failure mode. The composite column strengths obtained from the finite element analysis were compared with the design strengths calculated using the American Institute for Steel Construction AISC and Eurocode 4 for composite columns. Generally, it is shown that the EC 4 accurately predicted the design strength for the concrete encased steel composite columns having a concrete cylinder strength of 30 MPa and structural steel yield stresses of 275 and 460 MPa, which are in the limits of the code, which otherwise, was generally conservative. The AISC predictions were quite conservative for all the concrete encased steel composite columns.     

Behavior of plate-to-circular hollow section joints of 600 MPa high-strength steel

While the recent high demand for high rise buildings has led to the development of high-performance and high-strength steels, the requirements for structural-performance steel for such buildings have been raised as engineers recognized the potential wreak damage that an earthquake could cause on a tall building. Many studies on high-strength steels have explored such requirements, but appropriate design equations are needed for the case of hollow structural section (HSS) due to the design equations that limit the maximum yield stress up to 360MPa in the design codes (AISC, 2011; KBC, 2009). This study investigated the behavior of 600MPa plate-to-circular hollow section joints subjected to applied moment and shear force by experiment and finite element analysis (FEA), and the results are compared with current design equations. The nominal strength of AISC (2005) (or KBC (2009)) overestimated the tested strength in the range between 105% and 137%. It is found that the nominal strength equation of AISC (2011) is reasonably revised in comparison to those of other design codes.