热轧钢筋强度取值和分项系数的校准

通过对大量HRB400钢筋屈服强度检测数据的统计分析,结合之前关于热轧钢筋检测数据的统计结果,对热轧钢筋强度特征值取值和材料强度分项系数的取值进行探讨。     

HPB235钢筋强度标准值及其分项系数的校准

通过对HPB235钢筋强度的检验数据进行统计分析得到:该品种钢筋屈服强度的变异系数约为0.09,规范关于该品种钢筋强度标准值的取值可能比较合适;钢筋混凝土受拉构件的钢筋材料强度分项系数可能偏低,宜进行调整.     

小直径冷轧螺纹钢筋的生产与应用

在建筑工程混凝土施工和混凝土预制构件的生产中,需要使用大量小直径钢筋。目前,国内生产的钢材中,小直径钢筋只有表面光滑的热轧钢筋和冷拔低碳钢筋。热轧光圆钢筋不仅强度较低,而且与混凝土的握裹力也差。因此在混凝土构件中应用耗钢量较大。冷拔底碳钢筋与热轧钢筋相比,强度上虽有较大的提高,但由于表面光滑,钢筋与混凝土之间的握裹力差,在构件受力后,钢筋与混凝土之间容易产生滑移。特别使用在     

400MPa热轧钢筋渐成"新宠"

为推动建筑材料科技进步 ,适应建筑业对新材料的需求 ,扭转落后被动局面 ,国家冶金局开发研制了微合金40 0 MPa热轧钢筋。不同地区的工程实践表明 ,40 0 MPa热轧钢筋的强度高且性能稳定 ,今后将成为现浇混凝土结构的主导钢筋。目前 40 0 MPa热轧钢筋的生产技术已经成熟 ,生产规模已经具备。与此同时 ,《建筑设计规程》、《建筑设计指南》、《建筑构件手册》等都在积极修订中 ,预计今年可陆续完成。40 0 MPa热轧钢筋系通过微合金化 (加入金属钒等 )和穿水工艺来提高钢筋强度、改善综合性能。这种钢筋的优点体现在四大指标上 :在强度方面 …     

既有建筑结构安全性鉴定中分项系数的调整研究

在既有建筑结构鉴定中直接采用设计公式简单通用,但基于可靠指标调整分项系数的鉴定方法更为合理,既能充分利用既有建筑的实际现状,又能避免潜在的不定性风险。为此,基于可靠指标对构件承载力分项系数分解算法进行比较,阐述抗力分项系数、材料强度分项系数的调整方法,并通过工程算例验证其用于既有建筑结构鉴定的可行性。通过研究比较可知：直接分解法简单明了,当构件承载力变异系数在0.11～0.15,可靠指标在3.5～5之间取值时,直接分解法和间接分解法等效;对于既有建筑结构,按调整抗力分项系数、材料强度分项系数的方法进行鉴定具有可行性,尤其是采用调整材料强度分项系数的鉴定方法,在检测批合理划分、检测数据可靠的情况下,既可以充分利用既有建筑的实测材料强度或材料强度分项系数的可靠指标裕度,又能满足标准规定的目标可靠指标要求。     

双钢筋混凝土梁的受弯试验及裂缝计算

双钢筋系由两根纵向平行的纵筋与之垂直的短横筋按一定间距焊接组成梯格型骨架,采用双钢筋技术,可以改善钢筋混凝土的粘结作用,从而改善钢筋混凝土受弯构件的裂缝分布,减小裂缝宽度,使裂缝开展呈现细而密的特征。然而,目前使用的双钢筋类型主要是由冷拔低碳钢丝或冷轧钢筋制成的双钢筋,这些双钢筋大多用于小跨度的单向板、过梁、楼梯等构件中,而采用大直径热轧带肋三级钢筋制成的双钢筋混凝土构件国内外尚未见有报道。为了充分发挥双钢筋的技术优势,拓宽双钢筋技术的使用范围,对热轧带肋三级钢筋焊制的双钢筋构件作了较全面的分析研究,重点研究了双钢筋受弯构件的裂缝及变形计算,对双钢筋构件的裂缝特征作了较完整的理论分析。通过试验观察和理论分析,并针对热轧带肋三级钢筋制成的双钢筋混凝土构件,提出了裂缝计算的建议公式。并与普通构件对比进行技术经济分析,可取得良好的经济效益。     

双钢筋混凝土梁裂缝计算的试验研究

双钢筋是一种经济、安全可靠的结构形式,在钢筋混凝土结构中值得大力推广,可为国家节约大量钢材,是企业创造更好经济效益的理想途径。本文对热轧带肋Ⅲ级钢筋焊制的双钢筋构件作了较全面的分析研究,重点研究了双钢筋受弯构件的裂缝及变形计算,对双钢筋构件的裂缝特征作了较完整的理论分析。通过实验观察和理论分析,并针对热轧带肋Ⅲ级钢筋制成的双钢筋混凝土构件,提出了裂缝计算的建议公式。     

Q460GJ钢轴压构件可靠度分析

建筑结构用钢板是我国研发的高性能钢材,其综合性能优于同等级低合金高强度结构钢,并已在众多大型工程项目中得到应用,Q460GJ钢轴压构件计算模式不确定性统计参数和设计指标亟待研究。基于8个焊接箱形截面和14个焊接H形截面轴压构件的整体稳定承载力试验结果,获得了Q460GJ钢轴压构件计算模式不确定性统计参数。结合已有的Q460GJ钢材料性能不确定性和几何特征不确定性研究成果,通过进一步统计分析,获得了两种截面Q460GJ钢轴压构件的抗力不确定性统计参数。采用可靠度方法提出Q460GJ钢轴压构件抗力分项系数,并分析了其变化规律。考虑现行规范关于抗力分项系数取值的延续性,建议沿用Q345GJ钢的抗力分项系数1.059作为Q460GJ钢轴压构件抗力分项系数,对应的设计强度指标取435 MPa。最后对建议抗力分项系数进行了可靠性校核,结果表明该抗力分项系数满足可靠性要求。     

台山EPR核电站钢筋施工管理

台山EPR核电站核岛土建施工中钢筋分项工程量巨大,涉及各种结构构件。通过采取合理的施工顺序和绑扎方法,依据合理的技术要求等一系列措施,对钢筋分项进行总体施工管理,以保证钢筋分项的工程质量和施工进度。     

锈蚀混凝土压弯构件性能的有限元分析

研究了钢筋锈蚀影响下偏心受压构件力学性能和工作机理的变化规律。使用名义屈服强度描述钢筋锈蚀对有效截面积和屈服强度的影响,使用粘结强度降低系数描述粘结强度降低的影响。分别按照大偏压和小偏压的情况,使用有限元方法,建立了锈蚀钢筋混凝土压弯构件的分离式模型,得到了压弯构件承载力、延性、钢筋混凝土共同工作性能等的变化规律。     

高强度角钢轴心受压构件稳定设计方法研究

Q420和Q460高强度热轧等边角钢在钢结构中的应用逐渐增多,由于强度提高,部分角钢截面的宽厚比超过规范限值,不满足局部稳定性的要求。GB 50017—2003《钢结构设计规范》对于这一问题并没有给出相应的计算方法和设计规定。结合DL/T 5154—2002《架空送电线路杆塔结构设计技术规定》和美国ANSI/ASCE 10—97《输电铁塔设计导则》的相关规定,研究Q420和Q460高强度热轧等边角钢轴心受压构件稳定承载力的设计计算方法,分析了上述规范中对于高强度角钢轴心受压构件稳定设计方法的合理性,为相关设计提供了参考。     

The development of the direct strength method for welded steel members with buckling interactions

The direct strength method (DSM) has been adopted by the NAS (2004) and AS/NZS 4600 (2005) for the design of cold-formed steel members. The method can be successfully applied to the design of welded and hot-rolled sections. This paper reviews the development of the DSM for welded steel structural members. The design strength formulae for welded section columns and beams for the DSM are provided based on the tests performed on welded H-section, C-section, circular and rectangular hollow section columns fabricated from steel plates whose nominal yield stress is 235 MPa or 315 MPa. The comparison between the design strength of welded sections predicted by the DSM and that estimated by existing specifications is provided. This paper verifies that the DSM which adopts the nominal axial strength and flexural strength in the AISC (2010) or EC3 (2004) can properly predict the ultimate strength of welded section columns and beams.     

Tangent moduli of hot-rolled I-shaped axial members considering various residual stress distributions

This paper presents an equation for the effective tangent moduli for steel axial members of hot-rolled I-shaped section subjected to various residual stress distributions. Because of the existence of residual stresses, the cross section yields gradually even when the member is subjected to uniform axial stresses. In the elasto-plastic stage, the structural response can be easily traced using rational tangent modulus of the member. In this study, the equations for rational tangent moduli for hot-rolled I-shaped steel members in the elasto-plastic stage were derived based on the general principle of force-equilibrium. For practical purpose, the equations for the tangent modulus were presented for conventional patterns of the residual stress distribution of hot-rolled I-shaped steel members. Through a series of material nonlinear analyses for steel axial members modeled by shell elements, the derived equations were numerically verified, and the presented equations were compared with the CRC tangent modulus equation, the most frequently used equation so far. The comparative study shows that the presented equations are extremely effective for accurately analyzing elasto-plastic behavior of the axially loaded members in a simple manner without using complex shell element models.     

Comparison of component method with experimental tests for flush end-plate connections using hot-rolled perwaja steel sections

A component method has been introduced by Steel Construction Institute to predict the moment resistance of partial strength connection. The design philosophy is taken directly from Eurocode 3 with strength checks on bolts, welds, and steel which have been modified to comply with BS 5950-1:2000. The accuracy of the method however needs to be validated with the experimental tests especially for hot-rolled sections other than typical British Section (BS). Six experimental tests on beam-to-column connections have been carried out for Flush End-Plate (FEP) connections consisting of variable parameters such as thickness of end-plate, size and number of bolts, size of columns, and beams. The tests were set-up using local hot-rolled steel sections known as Perwaja Section (PS) for beams and columns instead of typical British Section (BS). The strength of materials for end-plate, column and beam sections were tested for tensile strength and used in predicting the moment resistance for component method. The moment versus rotation of the test results were plotted and compared with the moment resistance derived from component method. The study concluded that the moment resistance of the tested flush end-plate connections was higher than the predicted moment resistance from component method which showed good agreement between the two moments. The study also concluded that the tested FEP connections met the requirements and criteria of partial strength connections.     

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.     

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。     

热轧H型钢组合柱轴压承载性能研究

热轧H型钢组合柱是由热轧H型钢与钢板焊接拼合而成,并在内部灌注混凝土形成钢-混凝土组合截面构件。为研究热轧H型钢组合柱的轴压承载性能,完成了3个热扎H型钢组合短柱轴压试验,得到了试件在轴压荷载下的破坏形态、荷载-位移关系曲线和荷载-应变关系曲线等。建立了经试验验证的精细化有限元模型,并以钢材强度、混凝土强度和长细比为关键参数进行分析。研究结果表明:热轧H型钢组合柱的延性很好,但是试件端部H型钢外伸翼缘由于约束较弱,所以轴压荷载作用下先行屈曲;试件截面中部腹板拼接焊缝处钢板的宽厚比较大,易出现局部稳定问题;采用的有限元模型可准确模拟试件在轴压荷载下的破坏形态、荷载-位移关系等。在混凝土强度等级C20~C90、钢材强度等级Q235~Q420范围内,基于试验和有限元分析结果,提出钢-混凝土组合构件的轴压短柱承载力和中长柱的稳定承载力计算公式,公式计算结果与试验值及有限元分析值吻合较好。     

热轧高强度钢压杆的承载能力分析

现行钢结构设计规范的一些规定不利于充分发挥高强度钢压杆的潜力。热轧型钢的残余应力和钢材的强度等级无关,因而它对高强度钢压杆的不利效应低于Q235钢。本文基于这一认知进行了承载力分析,提出了改进稳定系数取值的两种方案,可使高强度钢压杆设计得更为合理。     

Residual stresses in cold-rolled profiles

Structural steel members obtained by cold-forming have become more and more popular in steel construction. They allow for lightening the weight and thus provide appreciable savings over conventional hot-rolled sections.Cold-forming leads to changes in the main structural characteristics of the virgin material. Among them the increase of the yield strength due to strain-hardening and of the ultimate strength due to strain-ageing and the birth of residual stresses which play an important role in the behaviour of the profiles under compression loads.The aim of the paper is to propose a theoretical method for predicting residual stresses due to cold-rolling. The numerical results obtained lead to a better knowledge of the characteristics of the cold-rolling (elastic spring-back, effect of the ratio of the thickness versus the radius of the corner, distribution and size of the residual stresses with respect to the dimensions of the profiles).