美国LRFD钢结构规范介绍(Ⅲ)
美国ANSI-AISC SSPEC-2002《钢结构建筑抗震设计规定》1
2．参考规定、规范及标准（略）
3．抗震设计一般要求
设 计 承载力 要 求和 其 他抗 震 规定 ， 如建 筑 物 抗 震 设 计 类 别、 建 筑 使 用 功 能 组 别、建筑物建设场地的地震区划和对建筑物的高度及不规则性的限制等，将在各相 关的现行建筑规范[1]~[5]中叙述。
在1997 NEHRP规范[1]（FEMA ，1997a）中，要求首先根据建筑物的使用功能 将其分为三个建筑使用功能组别（Seismic Use Groupபைடு நூலகம்。其中，第3组别为建筑物 包括重要建筑设施，第2、1组别为建筑物包括在地震时将产生较低的公共灾害的建
括考虑结构体系的超静定特点的建筑则是强制性的。
钢结构建筑抗震规定介绍（一）
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6/23/2003
冶 金工 业部 建筑 研究 总院
在ASCE 7（ASCE，2000）[2]中，根据建筑物的使用功能将其分为四种建筑用 途组别（Occupancy Group），如第4组别为包括有基本设施的建筑。然后按建筑用 途组别、建设场地的地震度等级来确定建筑物抗震性能类别（Seismic Performance Category），A 、B和C类一般适 用于建造在低至中等地震度地区的建筑物，该 规范 的抗震规定对A 、B、C三类建筑是非强制性的，但对建造在高 地震度地区的D和 E类 建筑则需强制执行。
关键词 LRFD 规范 地震荷载抗力体系 放大地震荷载 结构超强系数
1．适用范围
本规定条款适用于建筑物地震荷载抗力体系中的钢结构构件及连接节点的设计 和施工。各条款适用于现行建筑规范中分类为建筑物抗震设计类别D( 或等效于D 类) 和高于D类的建筑物的抗震设计。
本规定条款应结合AISC的钢结构建筑《荷载和抗力分项系数设计规范》(LRFD 规范)共同使用。地震荷载抗力体系中的所有构件和连接节点均应满足LRFD 规范所 规定的设计承载力要求，并应符合LRFD规范附加条款的要求。
中文版美国钢结构建筑设计规范(ANSI-AISC-360-05_)
ANSI/AISC 360-05美国国家标准钢结构建筑设计规范2005年3月9日发布本规范取代下列规范：1999年12月27日颁布的《钢结构建筑设计规范：荷载和抗力系数设计法》(LRFD)、1989年6月1日颁布的《钢结构建筑设计规范：容许应力设计法和塑性设计法》、其中包括1989年6月1日颁布的附录1《单角钢杆件的容许应力法设计规范》、2000年11月10日颁布的《单角钢杆件的荷载和抗力系数设计法设计规范》、2000年11月10日颁布的《管截面杆件的荷载和抗力系数设计法设计规范》、以及代替上述规范的所有从前使用的相关版本。
本规范由美国钢结构协会委员会（AISC）及其理事会批准发布实施。
本规范由美国钢结构协会规范委员会（AISC）审定，由美国钢结构协会董事会出版发行。
美国钢结构学会One East Wacker Drive，Suite 700芝加哥，伊利诺斯州60601-1802版权©2005美国钢结构学会拥有版权保留所有权利。
没有出版人的书面允许，不得对本书或本书的任何部分以任何形式进行复制。
本规范中所涉及到的相关信息，基本上是根据公认的工程原理和原则进行编制的，并且只提供一般通用性的相关信息内容。
虽然已经提供了这些精确的信息，但是，这些信息，在未经许可的专业工程师、设计人员或建筑工程师对其精确性、适用性和应用范围进行专业审查和验证的情况下，不得任意使用或应用于特定的具体项目中。
本规范中所包含的相关材料，并非对美国钢结构协会的部分内容进行展示或担保，或者，对其中所涉及的相关人员进行展示或担保，并且这些相关信息在适用于任何一般性的或特定的项目时，不得侵害任何相关专利权益。
任何人在侵权使用这些相关信息时，必须承担由此引起的所有相关责任。
必须注意到：在使用其它机构制订的规范和标准时，以及参照相关标准制订的其它规范和标准时，可以随时对本规范的相关内容进行修订或修改并且随后印刷发行。
本协会对未参照这些标准信息材料，以及未按照标准规定在初次出版发行时不承担由此引起的任何责任。
美国AASHTO LRFD 桥梁规范历史和目前现状
容许应力设计法 （ASD）
Qi RE/FS
Qi 荷载， RE 弹性承载力， FS 安全系数
荷载系数设计法 （LFD）
i 荷载系数，
iQi R
Qi 荷载， 强度折减系数， R 承载力
荷载和抗力系数设计法 (LRFD)
iiQ i R nR r
i 荷载修正系数， i 荷载系数， Qi 名义荷载效应， 强度折减系数，
Rn 名义承载力， Rr 乘上系数的承载力
A
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规范特点-车辆荷载
标准规范 HS20卡车
• LRFD规范使用了新的载荷HL-93,它包括HS20卡车和一个均匀分布力； • 卡车考虑冲击系数，而均布力没有冲击系数； • 连续梁桥负弯矩区域内力和桥中跨支座反力，沿桥纵向放置两辆卡车， 两车相距15m，并布置均布力，所得到的结构内力和支座反力的90%作 为最终设计荷载。
上个世纪80年代，荷载和抗力系数设计方法被越来越多国家采用， 美国标准规范已经落后于时代要求。1986年安排了一个项目研究当 前世界各个规范特点和开发新规范的可行性；
1990年，第一版《AASHTO 荷载和抗力系数桥梁设计规范》发表 （AASHTO LRFD Bridge Design Specification），共4份草稿版本
美国从1921年开始编写公路桥梁设计规范，美国州公路协会于1931 年发表了《公路桥梁标准规范》(Standard Specifications for Highway Bridges），容许应力法(Allowable Stress Design) 被运用 这规范中；
上世纪70年代，荷载系数设计方法（Load Factor Design) 被加入的 这个规范中，该规范出版以来共有17个版本，一直到2002年停止更 新；
美国结构设计规范简介
详见规范第B章节
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1. 总的设计要求（继续）
宽厚比，高厚比的要求：
截面分类: COMPபைடு நூலகம்CT;NON-COMPACT;SLENDERNESS. AISC允许局部屈曲
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2. 整体稳定设计要求
稳定设计是钢结构设计的重点 稳定设计分为整体稳定设计和构件稳定设计（有效长 度系数或计算长度系数是联系两者的桥梁）
Extended End-Plate Moment Connection
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常见的连接形式：
栓焊连接
Flush End-Plate Moment Connection
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常见的连接形式：
铰接连接：
端板连接
双角钢连接
刀板连接
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三、抗震相关内容简介
地震反应修正系数 （Seismic response modification coefficient） R >3
支撑框架
特殊中心支撑框架（SCBF); 普通中心支撑框架（OCBF); 偏心支撑框架(EBF); 屈曲约束支撑框架（BRBF）
钢板剪力墙（Special Plate Shear Walls)
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抗震设计的几个问题
抗震钢结构的材料 宽厚比限值, 保护区（Protected Zone) 特殊抗弯框架的一些设计概念
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P-Delta效应
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二阶弹性分析方法
一阶弯矩放大法‘B1-B2“法：
其中 GB的公式类似，但缺少B1系数： 类似B1的系数出现在：
Cm 为等效弯矩系数
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直接分析法和有效长度法
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2005版美国钢结构设计规范_部分简介_中文
2005版美国钢结构设计规范摘要美国钢结构协会成立于1921年，在1923年发行了第一版美国钢结构建筑设计规范.这本规范基于容许应力设计原则，长达十页，后来又发行了其他版本，一直到1989年的第九版本，但自从第八版本（1978）以后就没什么实质性的变化了。
极限状态设计，在美国又被称为荷载和抗力分项系数设计（LRFD），在第一版本的LRFD规范中被正式介绍，它基于超过15年的大量研究和改进，又被修改过两次，现在使用的是第三版本（1999）。
两本规范的同时存在对美国的设计人员和工业发展都带来了麻烦，AISC因此同意制定一部唯一并且标准统一的钢结构设计规范。
这部规范直到2005年8月13日才被审核通过，介绍了很多重要的概念，包括名义强度准则的使用与适当措施结合以提高可靠性的方法。
在许多其他方面的改进中，框架体系稳定性和支护设计有重大的进步，包括采用塑性准则的新设计方法。
关键词规范可靠性名义强度稳定性标准塑性连接设计组合设计论文纲要1介绍2基本设计理念2.1容许应力设计2.2荷载与阻力因素设计2.2.1强度不足和超载3 2005年AISC说明书3.1 背景3.2 格式规范3.3 基本设计要求4 新规范内容布置4.1内容概述4.2总则4.3设计要求B1 总则B3.6连接点B3.6.1简单连接B3.6.2弯矩连接4.4稳定性设计分析4.4.1稳定性设计要求4.4.2需求强度计算4.5 构件抗拉设计4.6 构件抗压设计4.7 构件抗弯设计4.8 构件抗剪设计4.9 构件组合受力设计和抗扭设计4.10 组合构件设计4.11 连接设计4.12高速钢和箱形构件连接设计5 注释6 摘要参考文献1.介绍1923版美国钢结构设计规范制定的目的是解决那个时候设计人员所面临的一系列问题。
虽然美国材料试验协会（ASTM）制定的钢材和其他材料性能标准是可用的,但仍然没有全国统一的建筑设计规范。
因此，个别州或城市有自己的要求，并且有时候设计特定的建筑甚至有多种规则可以使用，比如，那时候建造的一些桥梁必须遵守由桥梁当局制定的详细的规定，而当局又常常和杰出的设计者或制造商勾结。
美国结构设计规范简介
抗震钢结构 AISC 341
荷载规范ASCE 7简介
ASCE :American Society of Civil Engineers (美国土木工 程师学会）
ASCE 7-05 Minimum Design Loads for Building and Other Structures包括:
钢结构设计规范AISC 360
AISC American Institute of Steel Construction（美国钢 结构学会）
➢ AISC 360-05 是一本LRFD和ASD合一的规范，但本质 上是一本LRFD钢结构设计规范（13th Manual)；
➢ ASD规范是AISC于1989年出版，也是最后一本ASD钢 结构设计规范 (ASD 9th Manual)
➢ 荷载组合方式: 极限荷载组合和允许应力荷载组合 ➢ 恒荷载、楼面活荷载、洪水、风、冰、雪、雨荷载 ➢ 地震荷载（场地分类、地震谱、地震荷载计算、地
震荷载组合、抗震体系的选择，地震作用的静力、 动力分析等等）
荷载规范ASCE 7简介（接上）
荷载组合方式
Strength design：
Allowable stress design：
稳定设计方法对比
2. 整体稳定设计要求（继续）
限制条件： 二阶/一阶位移比Δ2nd / Δ1st ：The ratio of second-order drift
to first-order drift can be represented by B2。
GB50017里同样有：
直接分析法：无限制； 有效长度法：B2≤1.5； 一阶分析法： B2≤1.5；且轴压比≤0.5 注意：B2的上限为2.5
美国钢结构学会单角钢规范(英文
November 10, 2000
Supersedes the Specification for Load and Resistance Factor Design of Single-Angle Members dated December 1, 1993 Prepared by the American Institute of Steel Construction, Inc. Under the Direction of the AISC Committee on Specifications and approved by the AISC Board of Directors
When a load is transmitted by transverse weld through just one leg of the angle, Ae is the area of the connected leg and U 1.
2.
TENSION The tensile design strength tPn shall be the lower value obtained according to the limit states of yielding, t 0.9, Pn Fy Ag, and fracture, t 0.75, Pn FuAe. a. For members connected by bolting, the net area and effective net area shall be determined from AISC LRFD Specification Sections B1 to B3 inclusive. When the load is transmitted by longitudinal welds only or a combination of longitudinal and transverse welds through just one leg of the angle, the effective net area Ae shall be: Ae AgU (2-1)
美国钢结构规范
SECTION10COLD-FORMED STEEL DESIGNR.L.Brockenbrough,P.E.President,R.L.Brockenbrough&Associates,Inc.,Pittsburgh,PennsylvaniaThis section presents information on the design of structural members that are cold-formedto cross section shape from sheet steels.Cold-formed steel members include such productsas purlins and girts for the construction of metal buildings,studs and joists for light com-mercial and residential construction,supports for curtain wall systems,formed deck for theconstruction offloors and roofs,standing seam roof systems,and a myriad of other products.These products have enjoyed significant growth in recent years and are frequently utilizedin some shape or form in many projects today.Attributes such as strength,light weight,versatility,non-combustibility,and ease of production,make them cost effective in manyapplications.Figure10.1shows cross sections of typical products.10.1DESIGN SPECIFICATIONS AND MATERIALSCold-formed members for most application are designed in accordance with the Specificationfor the Design of Cold-Formed Steel Structural Members,American Iron and Steel Institute,Washington,DC.Generally referred to as the AISI Specification,it applies to members cold-formed to shape from carbon or low-alloy steel sheet,strip,plate,or bar,not more than1-in thick,used for load carrying purposes in buildings.With appropriate allowances,it canbe used for other applications as well.The vast majority of applications are in a thicknessrange from about0.014to0.25in.The design information presented in this section is based on the AISI Specification and its Commentary,including revisions being processed.The design equations are written indimensionless form,except as noted,so that any consistent system of units can be used.Asynopsis of key design provisions is given in this section,but reference should be made tothe complete specification and commentary for a more complete understanding.The AISI Specification lists all of the sheet and strip materials included in Table1.6(Art.1.4)as applicable steels,as well several of the plate steels included in Table1(A36,A242,A588,and A572).A283and A529plate steels are also included,as well as A500structuraltubing(Table1.7).Other steels can be used for structural members if they meet the ductilityrequirements.The basic requirement is a ratio of tensile strength to yield stress not less than1.08and a total elongation of at least10%in2in.If these requirements cannot be met,alternative criteria related to local elongation may be applicable.In addition,certain steelsthat do not meet the criteria,such as Grade80of A653or Grade E of A611,can be used10.110.2SECTION TENFIGURE10.1Typical cold-formed steel members.for multiple-web configurations(roofing,siding,decking,etc.)provided the yield stress istaken as75%of the specified minimum(or60ksi or414MPa,if less)and the tensile stressis taken as75%of the specified minimum(or62ksi or428MPa if less).Some exceptionsapply.Suitability can also be established by structural tests.10.2MANUFACTURING METHODS AND EFFECTSAs the name suggests,the cross section of a cold-formed member is achieved by a bendingoperation at room temperature,rather than the hot rolling process used for the heavier struc-tural steel shapes.The dominant cold forming process is known as roll-forming.In thisprocess,a coil of steel is fed through a series of rolls,each of which bends the sheetprogressively until thefinal shape is reached at the last roll stand.The number of roll standsmay vary from6to20,depending upon the complexity of the shape.Because the steel isfed in coil form,with successive coils weld-spliced as needed,the process can achieve speedsup to about300ft/min and is well suited for quantity production.Small quantities may beproduced on a press-brake,particularly if the shape is simple,such as an angle or channelcross section.In its simplest form,a press brake consists of a male die which presses thesteel sheet into a matching female die.In general,the cold-forming operation is beneficial in that it increases the yield strength of the material in the region of the bend.Theflat material between bends may also showan increase due to squeezing or stretching during roll forming.This increase in strength isattributable to cold working and strain aging effects as discussed in Art.1.10.The strengthincrease,which may be small for sections with few bends,can be conservatively neglected.Alternatively,subject to certain limitations,the AISI Specification includes provisions forusing a section-average design yield stress that includes the strength increase from cold-forming.Either full section tension tests,full section stub column tests,or an analyticalmethod can be employed.Important parameters include the tensile-strength-to-yield-stressCOLD-FORMED STEEL DESIGN10.3 TABLE10.1Safety Factors and Resistance Factors Adopted by the AISI SpecificationCategoryASDsafetyfactor,⍀LRFDresistancefactor,Tension members 1.670.95 Flexural members(a)Bending strengthSections with stiffened or partially stiffened compressionflanges 1.670.95 Sections with unstiffened compressionflanges 1.670.90 Laterally unbraced beams 1.670.90 Beams having oneflange through-fastened to deck or sheathing(C-or Z-sections) 1.670.90 Beams having oneflange fastened to a standing seam roof system 1.670.90 (b)Web designShear strength controlled by yielding(Condition a,Art.10.12.4) 1.50 1.00 Shear strength controlled by buckling(Condition b or c,Art.10.12.4) 1.670.90 Web crippling of single unreinforced webs 1.850.75 Web crippling of I-sections 2.000.80 Web crippling of two nested Z-sections 1.800.85 Stiffeners(a)Transverse stiffeners 2.000.85(b)Shear stiffeners 1.50/1.67 1.00/0.90 Concentrically loaded compression members 1.800.85 Combined axial load and bending(a)Tension component 1.670.95(b)Compression component 1.800.85(c)Bending component 1.670.90/0.95 Cylindrical tubular members(a)Bending 1.670.95(b)Axial compression 1.800.85 Wall studs(a)Compression 1.800.85(b)Bending 1.670.90/0.95 Diaphragm construction 2.00/3.000.50/0.65 Welded connections(a)Groove weldsTension or compression2500.90 Shear,welds 2.500.80 Shear,base metal 2.500.90 (b)Arc spot weldsShear,welds 2.500.60 Shear,connected part 2.500.50/0.60 Shear,minimum edge distance 2.500.60/0.70 Tension 2.500.60 (c)Arc seam weldsShear,welds 2.500.60 Shear,connected part 2.500.60 (d)Fillet weldsWelds 2.500.60 Connected part,longitudinal loadingWeld length/sheet thicknessϽ25 2.500.60 Weld length/sheet thicknessՆ25 2.500.55 Connected part,transverse loading 2.500.6010.4SECTION TENTABLE10.1Safety Factors and Resistance Factors Adopted by the AISI Specification(Continued)CategoryASDsafetyfactor,⍀LRFDresistancefactor,(e)Flare groove weldsWelds 2.500.60 Connected part,longitudinal loading 2.500.55 Connected part,transverse loading 2.500.55 (f)Resistance welds 2.500.65 Bolted connections(a)Minimum spacing and edge distance*When Fu /FsyՆ1.08 2.000.70When Fu /FsyϽ1.08 2.220.60(b)Tension strength on net sectionWith washers,double shear connection 2.000.65 With washers,single shear connection 2.220.55 Without washers,double or single shear 2.220.65(c)Bearing strength 2.220.55/0.70(d)Shear strength of bolts 2.400.65(e)Tensile strength of bolts 2.00/2.250.75 Screw connections 3.000.50*Fu is tensile strength and Fsyis yield stress.ratio of the virgin steel and the radius-to-thickness ratio of the bends.The forming operation may also induce residual stresses in the member but these effects are accounted for in the equations for member design.10.3NOMINAL LOADSThe nominal loads for design should be according to the applicable code or specificationunder which the structure is designed or as dictated by the conditions involved.In the absenceof a code or specification,the nominal loads should be those stipulated in the AmericanSociety of Civil Engineers Standard,Minimum Design Loads for Buildings and Other Struc-tures,ASCE7.The following loads are used for the primary load combinations in the AISISpecification:DϭDead load,which consists of the weight of the member itself,the weight of allmaterials of construction incorporated into the building which are supported by the mem-ber,including built-in partitions;and the weight of permanent equipmentEϭEarthquake loadLϭLive loads due to intended use and occupancy,including loads due to movable objectsand movable partitions and loads temporarily supported by the structure during mainte-nance.(L includes any permissible load reductions.If resistance to impact loads is takeninto account in the design,such effects should be included with the live load.)COLD-FORMED STEEL DESIGN 10.5L r ϭRoof live load S ϭSnow loadR r ϭRain load,except for ponding W ϭWind loadThe effects of other loads such as those due to ponding should be considered when signif-icant.Also,unless a roof surface is provided with sufficient slope toward points of free drainage or adequate individual drains to prevent the accumulation of rainwater,the roof system should be investigated to assure stability under ponding conditions.10.4DESIGN METHODSThe AISI Specification is structured such that nominal strength equations are given for various types of structural members such as beams and columns.For allowable stress design (ASD),the nominal strength is divided by a safety factor and compared to the required strength based on nominal loads.For Load and Resistance Factor Design (LRFD),the nominal strength is multiplied by a resistance factor and compared to the required strength based on factored loads.These procedures and pertinent load combinations to consider are set forth in the specification as follows.10.4.1ASD RequirementsASD Strength Requirements.A design satisfies the requirements of the AISI Specification when the allowable design strength of each structural component equals or exceeds the required strength,determined on the basis of the nominal loads,for all applicable load combinations.This is expressed asR ՅR /⍀(10.1)n where R ϭrequired strengthR n ϭnominal strength (specified in Chapters B through E of the Specification )⍀ϭsafety factor (see Table 10.1)R n /⍀ϭallowable design strength ASD Load Combinations.In the absence of an applicable code or specification or if the applicable code or specification does not include ASD load combinations,the structure and its components should be designed so that allowable design strengths equal or exceed the effects of the nominal loads for each of the following load combinations:1.D2.D ϩL ϩ(L r or S or R r )3.D ϩ(W or E )4.D ϩL ϩ(L r or S or R r )ϩ(W orE )Wind or Earthquake Loads for ASD.When the seismic load model specified by the applicable code or specification is limit state based,the resulting earthquake load (E )is permitted to be multiplied by 0.67.Additionally,when the specified load combinations in-clude wind or earthquake loads,the resulting forces are permitted to be multiplied by 0.75.However,no decrease in forces is permitted when designing diaphragms.10.6SECTION TENComposite Construction under ASD.For the composite construction offloors and roofs using cold-formed deck,the combined effects of the weight of the deck,the weight of thewet concrete,and construction loads(such as equipment,workmen,formwork)must beconsidered.10.4.2LRFD RequirementsLRFD Strength Requirements.A design satisfies the requirements of the AISI Specificationwhen the design strength of each structural component equals or exceeds the requiredstrength determined on the basis of the nominal loads,multiplied by the appropriate loadfactors,for all applicable load combinations.This is expressed asRϽR(10.2)u nwhere Ruϭrequired strengthRnϭnominal strength(specified in chapters B through E of the Specification)ϭresistance factor(see Table10.1)R nϭdesign strengthLRFD Load Factors and Load Combinations.In the absence of an applicable code or specification,or if the applicable code or specification does not include LRFD load combi-nations and load factors,the structure and its components should be designed so that design strengths equal or exceed the effects of the factored nominal loads for each of the following combinations:1.1.4DϩL2.1.2Dϩ1.6Lϩ0.5(Lr or S or Rr)3.1.2Dϩ1.6(Lr or S or Rr)ϩ(0.5L or0.8W)4.1.2Dϩ1.3Wϩ0.5Lϩ0.5(Lr or S or Rr)5.1.2Dϩ1.5Eϩ0.5Lϩ0.2S6.0.9DϪ(1.3W or1.5E)Several exceptions apply:1.The load factor for E in combinations(5)and(6)should equal1.0when the seismic loadmodel specified by the applicable code or specification is limit state based.2.The load factor for L in combinations(3),(4),and(5)should equal1.0for garages,areasoccupied as places of public assembly,and all areas where the live load is greater than 100psf.3.For wind load on individual purlins,girts,wall panels and roof decks,multiply the loadfactor for W by0.9.4.The load factor for Lr in combination(3)should equal1.4in lieu of1.6when the rooflive load is due to the presence of workmen and materials during repair operations.Composite Construction under LRFD.For the composite construction offloors and roofs using cold-formed deck,the following additional load combination applies:1.2Dϩ1.6Cϩ1.4C(10.3)S Wwhere DSϭweight of steel deckCWϭweight of wet concreteCϭconstruction load(including equipment,workmen,and form work but excluding wet concreteCOLD-FORMED STEEL DESIGN10.7 10.5SECTION PROPERTY CALCULATIONSBecause of theflexibility of the manufacturing method and the variety of shapes that can bemanufactured,properties of cold-formed sections often must be calculated for a particularconfiguration of interest rather than relying on tables of standard values.However,propertiesof representative or typical sections are listed in the Cold-Formed Steel Design Manual,American Iron and Steel Institute,1996,Washington,DC(AISI Manual).Because the cross section of a cold-formed section is generally of a single thickness of steel,computation of section properties may be simplified by using the linear method.Withthis method,the material is considered concentrated along the centerline of the steel sheetand area elements are replaced by straight or curved line elements.Section properties arecalculated for the assembly of line elements and then multiplied by the thickness,t.Thus,the cross section area is given by AϭLϫt,where L is the total length of all line elements;the moment of inertia of the section is given by IϭIЈϫt,where IЈis the moment ofinertia determined for the line elements;and the section modulus is calculated by dividingI by the distance from the neutral axis to the extremefiber,not to the centerline of theextreme element.As subsequently discussed,it is sometimes necessary to use a reduced oreffective width rather than the full width of an element.Most sections can be divided into straight lines and circular arcs.The moments of inertia and centroid location of such elements are defined by equations from fundamental theory aspresented in Table10.2.10.6EFFECTIVE WIDTH CONCEPTThe design of cold-formed steel differs from heavier construction in that elements of mem-bers typically have large width-to-thickness(w/t)ratios and are thus subject to local buck-ling.Figure10.2illustrates local buckling in beams and columns.Flat elements in com-pression that have both edges parallel to the direction of stress stiffened by a web,flange,lip or stiffener are referred to as stiffened elements.Examples in Fig.10.2include the topflange of the channel and theflanges of the I-cross section column.To account for the effect of local buckling in design,the concept of effective width is employed for elements in compression.The background for this concept can be explainedas follows.Unlike a column,a plate does not usually attain its maximum load carrying capacity at the buckling load,but usually shows significant post buckling strength.This behavior isillustrated in Fig.10.3,where longitudinal and transverse bars represent a plate that is simplysupported along all edges.As the uniformly distributed end load is gradually increased,thelongitudinal bars are equally stressed and reach their buckling load simultaneously.However,as the longitudinal bars buckle,the transverse bars develop tension in restraining the lateraldeflection of the longitudinal bars.Thus,the longitudinal bars do not collapse when theyreach their buckling load but are able to carry additional load because of the transverserestraint.The longitudinal bars nearest the center can deflect more than the bars near theedge,and therefore,the edge bars carry higher loads after buckling than do the center bars.The post buckling behavior of a simply supported plate is similar to that of the grid model.However,the ability of a plate to resist shear strains that develop during bucklingalso contributes to its post buckling strength.Although the grid shown in Fig.10.3a buckledinto only one longitudinal half-wave,a longer plate may buckle into several waves as illus-trated in Figs.10.2and10.3b.For long plates,the half-wave length approaches the widthb.After a simply supported plate buckles,the compressive stress will vary from a maximum near the supported edges to a minimum at the mid-width of the plate as shown by line1of10.8SECTION TENTABLE10.2Moment of Inertia for Line ElementsSource:Adapted from Cold-Formed Steel Design Manual,American Iron and Steel Institute,1996,Washington,DC.COLD-FORMED STEEL DESIGN10.9FIGURE10.2Local buckling of compression elements.(a)In beams;(b)incolumns.(Source:Commentary on the Specification for the Design of Cold-Formed Steel Structural Members,American Iron and Steel Institute,Washington,DC,1996,with permission.)Fig.10.3c.As the load is increased the edge stresses will increase,but the stress in the mid-width of the plate may decrease slightly.The maximum load is reached and collapse is initiated when the edge stress reaches the yield stress—a condition indicated by line2of Fig.10.3c.The post buckling strength of a plate element can be considered by assuming that after buckling,the total load is carried by strips adjacent to the supported edges which are at a uniform stress equal to the actual maximum edge stress.These strips are indicated by the dashed lines in Fig.10.3c.The total width of the strips,which represents the effective width of the element b,is defined so that the product of b and the maximum edge stress equals the actual stresses integrated over the entire width.The effective width decreases as the applied stress increases.At maximum load,the stress on the effective width is the yield stress.Thus,an element with a small enough w/t will be able to reach the yield point and will be fully effective.Elements with larger ratios will have an effective width that is less than the full width,and that reduced width will be used in section property calculations.The behavior of elements with other edge-support conditions is generally similar to that discussed above.However,an element supported along only one edge will develop only one effective strip.Equations for calculating effective widths of elements are given in subsequent articles based on the AISI Specification.These equations are based on theoretical elastic buckling theory but modified to reflect the results of extensive physical testing.10.10SECTION TENFIGURE10.3Effective width concept.(a)Buckling of grid model;(b)buckling ofplate;(c)stress distributions.10.7MAXIMUM WIDTH-TO-THICKNESS RATIOSThe AISI Specification gives certain maximum width-to-thickness ratios that must be adhered to.For flange elements,such as in flexural members or columns,the maximum flat width-to-thickness ratio,w/t ,disregarding any intermediate stiffeners,is as follows:Stiffened compression element having one longitudinal edge connected to a web or flange element,the other stiffened by (a)a simple lip,60(b)other stiffener with I S ϽI a ,90(c)other stiffener with I S ՆI a ,90Stiffened compression element with both longitudinal edges connected to other stiffened elements,500Unstiffened compression element,60In the above,I S is the moment of inertia of the stiffener about its centroidal axis,parallel to the element to be stiffened,and I a is the moment of inertia of a stiffener adequate for the element to behave as a stiffened element.Note that,although greater ratios are permitted,stiffened compression elements with w /t Ͼ250,and unstiffened compression elements with w/t Ͼ30are likely to develop noticeable deformations at full design strength,but ability to develop required strength will be unaffected.For web elements of flexural members,the maximum web depth-to-thickness ratio,h/t ,disregarding any intermediate stiffeners,is as follows:Unreinforced webs,200Webs with qualified transverse stiffeners that include (a)bearing stiffeners only,260(b)bearing and intermediate stiffeners,30010.8EFFECTIVE WIDTHS OF STIFFENED ELEMENTS10.8.1Uniformly Compressed Stiffened ElementsThe effective width for load capacity determination depends on a slenderness factor defined as1.052wƒϭ(10.4)ͩͪΊt E͙kwhere k ϭplate buckling coefficient (4.0for stiffened elements supported by a web alongeach longitudinal edge;values for other conditions are given subsequently)ƒϭmaximum compressive stress (with no safety factor applied)E ϭModulus of elasticity (29,500ksi or 203000MPa)FIGURE 10.4Illustration of uniformly compressed stiffened element.(a )Actual element;(b )stress on effective element.(Source:Specification for the Design of Cold-Formed Steel Structural Members,Amer-ican Iron and Steel Institute,Washington,DC,1996,with permission.)For flexural members,when initial yielding is in compression,ƒϭF y ,where F y is the yield stress;when the initial yielding is in tension,ƒϭthe compressive stress determined on the basis of effective section.For compression members,ƒϭcolumn buckling stress.The effective width is as follows:when Յ0.673,b ϭw (10.5)when Ͼ0.673,b ϭw(10.6)where the reduction factor is defined asϭ(1Ϫ0.22/)/(10.7)Figure 10.4shows the location of the effective width on the cross section,with one-half located adjacent to each edge.Effective widths determined in this manner,based on maximum stresses (no safety factor)define the cross section used to calculate section properties for strength determination.How-ever,at service load levels,the effective widths will be greater because the stresses are smaller,and another set of section properties should be calculated.Therefore,to calculate effective width for deflection determination,use the above equations but in Eq.10.4,sub-stitute the compressive stress at design loads,ƒd .10.8.2Stiffened Elements with Stress GradientElements with stress gradients include webs subjected to compression from bending alone or from a combination of bending and uniform compression.For load capacity determination,the effective widths b 1and b 2illustrated in Fig.10.5must be determined.First,calculate the ratio of stressesϭƒ/ƒ(10.8)21where ƒ1and ƒ2are the stresses as shown,calculated on the basis of effective section,with no safety factor applied.In this case ƒ1is compression and treated as ϩ,while ƒ2can be either tension (Ϫ)or compression (ϩ).Next,calculate the effective width,b e ,as if the element was in uniform compression (Art.10.8.1)using ƒ1for ƒand with k determined as follows:3k ϭ4ϩ2(1Ϫ)ϩ2(1Ϫ)(10.9)Effective widths b 1and b 2are determined from the following equations:FIGURE10.5Illustration of stiffened element with stress gradient.(a)Actual element;(b)stress on ef-fective element varying from compression to tension;(c)stress on effective element with non-uniform com-pression.(Source:Specification for the Design of Cold-Formed Steel Structural Members,American Iron and Steel Institute,Washington,DC,1996,with permission.)bϭb/(3Ϫ)(10.10)1ebϭb/2(10.11)2eThe sum of b1and b2must not exceed the width of the compression portion of the webcalculated on the basis of effective section.Effective width for deflection determination is calculated in the same manner except that stresses are calculated at service load levels based on the effective section at that load.FIGURE 10.6Illustration of uniformly compressed unstiffened element.(a )Actual element;(b )stress on effective element.(Source:Specification for the Design of Cold-Formed Steel Structural Members,American Iron and Steel Institute,Washington,DC,1996,with permission.)10.9EFFECTIVE WIDTHS OF UNSTIFFENED ELEMENTS10.9.1Uniformly Compressed Unstiffened ElementsThe effective widths for uniformly compressed unstiffened elements are calculated in the same manner as for stiffened elements (Art.10.8.1),except that k in Eq.10.4is taken as 0.43.Figure 10.6illustrates the location of the effective width on the cross section.10.9.2Unstiffened Elements and Edge Stiffeners with Stress GradientThe effective width for unstiffened elements (including edge stiffeners)with a stress gradient is calculated in the same manner as for uniformly loaded stiffened elements (Art.10.9.1)except that (1)k in Eq.10.4is taken as 0.43,and (2)the stress ƒ3is taken as the maximum compressive stress in the element.Figure 10.7shows the location of ƒ3and the effective width for an edge stiffener consisting of an inclined lip.(Such lips are more structurally efficient when bent at 90Њ,but inclined lips allow nesting of certain sections.)10.10EFFECTIVE WIDTHS OF UNIFORMLY COMPRESSED ELEMENTS WITH EDGE STIFFENERA commonly encountered condition is a flange with one edge stiffened by a web,the other by an edge stiffener (Fig.10.7).To determine its effective width for load capacity determi-nation,one of three cases must be considered.The case selection depends on the relation between the flange flat width-to-thickness ratio,w/t ,and the parameter S defined asS ϭ1.28͙E /ƒ(10.12)For each case an equation will be given for determining I a ,the moment of inertia required for a stiffener adequate so that the flange element behaves as a stiffened element,I S is the moment of inertia of the full section of the stiffener about its centroidal axis,parallel to the element to be stiffened.A ЈS is the effective area of a stiffener of any shape,calculated by methods previously discussed.The reduced area of the stiffener to be used in section property calculations is termed A S and its relation to A ЈS is given for each case.Note that for edge stiffeners,the rounded corner between the stiffener and the flange is not considered as part of the stiffener in calculations.The following additional definitions for a simple lip stiffener illustrated in Fig.10.7apply.The effective width d S Јis that of the stiffener calculated ac-cording to Arts.10.9.1and 10.9.2.The reduced effective width to be used in section propertyFIGURE 10.7Illustration of element with edge stiffener.(a )Actual element;(b )stress on effective element and stiffener.(Source:Specification for the Design of Cold-Formed Steel Structural Members,American Iron and Steel Institute,Washington,DC 1996,with permission.)calculations is termed d S and its relation to d S Јis given for each case.For the inclined stiffener of flat depth d at an angle as shown in Fig.10.7,32I ϭ(d t sin )/12(10.13)S A Јϭd Јt(10.14)S S Limit d /t to 14.Case I:w /t ՅS /3For this condition,the flange element is fully effective without an edge stiffener so b ϭw ,I a ϭ0,d S ϭd S Ј,A S ϭA ЈS .Case II:S /3Ͻw /t ϽS43I ϭ399t {[(w /t )/S ]Ϫ͙k /4}(10.15)a u where k u ϭ0.43.The effective width b is calculated according to Art.10.8.1using the following k :。
美国冷弯薄壁型钢规范(图)
简介美国冷弯薄壁型钢规范全面升级在美国钢框架联盟(Steel Framing Alliance)网站下单2个多月后，今天公司终于收到了刚刚升级完成的全套北美冷弯薄壁型钢结构设计规范（(North American Standard for Cold-formed Steel Framing 2007Edition).之前据说这次升级幅度很大，反映了最近几年北美冷弯薄壁型钢结构界的最新研究成果，下班回家后大致翻了一下，果然动作很大。
先简要摘录如下：一是有更新又有新增；这是再原有基础上更新的标准:•AISI S200-07: North American Standard for Cold-Formed Steel Framing – General Provisions •AISI S211-07: North American Standard for Cold-Formed Steel Framing – Wall Stud Design •AISI S212-07: North American Standard for Cold-Formed Steel Framing – Header Design •AISI S213-07: North American Standard for Cold-Formed Steel Framing – Lateral Design •AISI S214-07: North American Standard for Cold-Formed Steel Framing – Truss Design •AISI S230-07: Standard for Cold-Formed Steel Framing –Prescriptive Method for One and Two Family Dwellings以下是这次新增的标准:•AISI S201-07: North American Standard for Cold-Formed Steel Framing – Product Data •AISI S210-07: North American Standard for Cold-Formed Steel Framing – Floor and Roof System Design二是这次将加拿大和墨西哥规范一起统一了起来，真正形成了北美标准；三是内容进行了很大的更新，特别是Lateral Design分册，有了很大的扩充；四是发现North American Specification and Commentary fo the Design of Cold-Formed Steel Structural Members 2007 Edition先于North American Standard for Cold-Formed Steel Framing 标准发布了。
中美两国钢结构抗震设计对比分析
中美两国钢结构抗震设计对比分析钢结构建筑应用日益广泛，在设计时仍需考虑地震作用，就中国和美国在钢结构抗震设计方面的不同进行了对比分析。
标签：钢结构；抗震设计；中国和美国doi：10.19311/ki.16723198.2016.12.0941美国钢结构抗震设计的发展1923年，美国钢结构协会制定了第一个钢结构设计规范，该规范是以容许应力为基本原则的设计法，经过多次修改，在1961年，其格式与内容基本上形成了固定模式。
1986年，AISC规范委员会提出了以概率理论为基础编写的荷载和抗力分项系数钢结构设计规范，简称LRFD。
以概率理论为基础编写的ASCE/SEI 7—05，作为美国各种设计理论依据，后该理论被不断修改与改进。
美国工程结构抗震设计大体上分为三种，国家标准、协会标准以及地方标准。
发展过程大致经过初创、发展、统一几个阶段。
1925年，出现了第一个建筑结构抗震设计规范UBC，紧接着又出现了NBC，SBC。
美国的抗震目标是把地震伤害降到最小化，即那些专门为人民提供生命安全、财产安全保障的设施，要按照他们的作用进行改造，加强它们的防震性能，使它们在震后也能正常的运行工作。
该抗震目标把抗震强度分为两个等级，即“设计地震”和“最大考虑地震”。
“最大考虑地震”是指五十年的超越概率为百分之二的地震；“设计地震”的加速度是“最大强度地震”的三分之二。
2中国抗震设计规范中国抗震规范提出的抗震目标为三水准，即“小震不坏，中震可修，大震不倒”。
第一水准是指，当某地区所受到的地震强度伤害低于该地区所预防的强度时，遇到这种地震，震后可以不用修复，继续正常使用；第二水准是指，当某地区所受到的地震强度伤害等于该地区所预防的地震强度时，建筑物可能会受到小的或局部损伤，只需进行简单的修理甚至不用修理，就可以继续使用；第三水准是指，当某地区遇到的地震强度远大于他所预防的强度时，不会导致房屋坍塌或危及到人的生命财产安全。
其中，小震五十年的超越概率为63.2%；中震是指五十年的超越概率为10%，相当于美国的“设计地震”等级；大震是指五十年的超越概率为2%到3%，相当于美国的“最大考虑地震”等级。
美国钢结构建筑设计规范(ANSI-AISC-360-05)
关于钢结构建筑设计规范的条文说明（本条文说明不是《钢结构建筑设计规范》（ANSI/AISC 360-05）的一部分，而只是为该规范使用人员提供相关信息。
）序言本设计规范旨在提供完善的标准设计之用。
本条文说明是为该规范使用人员提供规范条文的编制背景、文献出处等信息帮助，以进一步加深使用人员对规范条文的基础来源、公式推导和使用限制的了解。
本设计规范和条文说明旨在供具有杰出工程能力的专业设计员使用。
术语表本条文说明使用的下列术语不包含在设计规范的词汇表中。
在本条文说明文本中首次出现的术语使用了斜体。
准线图。
用于决定某些柱体计算长度系数K的列线图解。
双轴弯曲。
某一构件在两垂直轴同时弯曲。
脆性断裂。
在没有或是只有轻微柔性变形的情况下突然断裂。
柱体弧线。
表达砥柱强度和直径长度比之间关系的弧线。
临界负荷。
根据理论稳定性分析，一根笔直的构件在压力下可能弯曲，也可能保持笔直状态时的负荷；或者一根梁在压力下可能弯曲，平截面发生扭曲或者其平截面状态时的负荷。
循环负荷。
重复地使用可以让结构体变得脆弱的额外负荷。
位移残损索引。
用于测量由内部位移引起的潜性损坏的参变量。
有效惯性矩。
构件横截面的惯性矩在该横截面发生部分逆性化的情况下（通常是在内应力和外加应力共同作用下），仍然保持其弹性。
同理，基于局部歪曲构件的有效宽度的惯性矩。
同理，用于设计部分组合构件的惯性矩。
有效劲度。
通过构件横截面有效惯性矩计算而得的构件劲度。
疲劳界限。
不计载荷循环次数，不发生疲劳断裂的压力范围。
一阶逆性分析。
基于刚逆性行为假设的结构分析，而未变形结构体的平衡条件便是基于此分析而归纳出来的——换言之，平衡是在结构体和压力等于或是低于屈服应力条件下实现的。
柔性连接。
连接中，允许构件末端简支梁的一部分发生旋转，而非全部。
挠曲。
受压构件同时发生弯曲和扭转而没有横截面变形的弯曲状态。
非弹性作用。
移除促生作用力后，材料变形仍然不消退的现象。
非弹性强度。
当材料充分达到屈服应力时，结构体或是构件所具有的强度。
2005版美国钢结构设计规范
2005版美国钢结构设计规范摘要美国钢结构协会成立于1921年，在1923年发行了第一版美国钢结构建筑设计规范.这本规范基于容许应力设计原则，长达十页，后来又发行了其他版本，一直到1989年的第九版本，但自从第八版本（1978）以后就没什么实质性的变化了。
极限状态设计，在美国又被称为荷载和抗力分项系数设计（LRFD），在第一版本的LRFD规范中被正式介绍，它基于超过15年的大量研究和改进，又被修改过两次，现在使用的是第三版本（1999）。
两本规范的同时存在对美国的设计人员和工业发展都带来了麻烦，AISC因此同意制定一部唯一并且标准统一的钢结构设计规范。
这部规范直到2005年8月13日才被审核通过，介绍了很多重要的概念，包括名义强度准则的使用与适当措施结合以提高可靠性的方法。
在许多其他方面的改进中，框架体系稳定性和支护设计有重大的进步，包括采用塑性准则的新设计方法。
关键词规范可靠性名义强度稳定性标准塑性连接设计组合设计论文纲要1.介绍2.基本设计理念容许应力设计荷载与阻力因素设计2.2.1强度不足和超载3. 2005年AISC说明书3.1 背景3.2 格式规范3.3 基本设计要求4 新规范内容布置4.1内容概述4.2总则4.3设计要求B1 总则B3.6连接点B3.6.1简单连接B3.6.2弯矩连接4.4稳定性设计分析4.4.1稳定性设计要求4.4.2需求强度计算4.5 构件抗拉设计4.6 构件抗压设计4.7 构件抗弯设计4.8 构件抗剪设计4.9 构件组合受力设计和抗扭设计4.10 组合构件设计4.11 连接设计4.12高速钢和箱形构件连接设计5 注释6 摘要参考文献1.介绍1923版美国钢结构设计规范制定的目的是解决那个时候设计人员所面临的一系列问题。
虽然美国材料试验协会（ASTM）制定的钢材和其他材料性能标准是可用的,但仍然没有全国统一的建筑设计规范。
因此，个别州或城市有自己的要求，并且有时候设计特定的建筑甚至有多种规则可以使用，比如，那时候建造的一些桥梁必须遵守由桥梁当局制定的详细的规定，而当局又常常和杰出的设计者或制造商勾结。
钢结构设计外文翻译参考文献
钢结构设计外文翻译参考文献(文档含中英文对照即英文原文和中文翻译)使用高级分析法的钢框架创新设计1．导言在美国，钢结构设计方法包括允许应力设计法(ASD)，塑性设计法(PD)和荷载阻力系数设计法(LRFD)。
在允许应力设计中，应力计算基于一阶弹性分析，而几何非线性影响则隐含在细部设计方程中。
在塑性设计中，结构分析中使用的是一阶塑性铰分析。
塑性设计使整个结构体系的弹性力重新分配。
尽管几何非线性和逐步高产效应并不在塑性设计之中，但它们近似细部设计方程。
在荷载和阻力系数设计中，含放大系数的一阶弹性分析或单纯的二阶弹性分析被用于几何非线性分析，而梁柱的极限强度隐藏在互动设计方程。
所有三个设计方法需要独立进行检查，包括系数K计算。
在下面，对荷载抗力系数设计法的特点进行了简要介绍。
结构系统内的内力及稳定性和它的构件是相关的，但目前美国钢结构协会（AISC）的荷载抗力系数规范把这种分开来处理的。
在目前的实际应用中，结构体系和它构件的相互影响反映在有效长度这一因素上。
这一点在社会科学研究技术备忘录第五录摘录中有描述。
尽管结构最大内力和构件最大内力是相互依存的（但不一定共存），应当承认，严格考虑这种相互依存关系，很多结构是不实际的。
与此同时，众所周知当遇到复杂框架设计中试图在柱设计时自动弥补整个结构的不稳定（例如通过调整柱的有效长度）是很困难的。
因此，社会科学研究委员会建议在实际设计中，这两方面应单独考虑单独构件的稳定性和结构的基础及结构整体稳定性。
图28.1就是这种方法的间接分析和设计方法。
在目前的美国钢结构协会荷载抗力系数规范中，分析结构体系的方法是一阶弹性分析或二阶弹性分析。
在使用一阶弹性分析时，考虑到二阶效果，一阶力矩都是由B1,B2系数放大。
在规范中，所有细部都是从结构体系中独立出来，他们通过细部内力曲线和规范给出的那些隐含二阶效应，非弹性，残余应力和挠度的相互作用设计的。
理论解答和实验性数据的拟合曲线得到了柱曲线和梁曲线，同时Kanchanalai发现的所谓“精确”塑性区解决方案的拟合曲线确定了梁柱相互作用方程。
美国国家标准建筑钢结构规范中轴心受压柱、受弯和压弯构件的稳定设计
CH EN Ji
( Colleg e o f Civ il Engineering , Xican U niver sit y of A rchitect ur e & T echnolog y, X ican 710055, China) CHEN Ji: chenji- jichen@ 163. com
Keywords: flexura-l torsional buckling; effective r adius of gy ration; resistance factor; residual str ess; plate gir der; w eb plastification factor
不安全, 按照 AN SI/ A IS C 360 - 05 的规定, 此时 式( 5) 中
的等效弯矩系数 可偏于 安全 地用 Bb = 1. 0, 而在 式( 6) 中 只需将其中的根号项取为 1. 0 即可。验 算梁整体 稳定的
公式为:
第3期
美国国家标准建筑钢结构规范中轴心受压柱、受弯和压弯构件的稳定设计
M cr =
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M cr =
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( 6)
在塑性阶段, 式( 5) 中梁侧向长度的限值为:
1. 25M max 2. 5M max + 3M A + 4M B +
美国钢结构学会钢结构规范全文AISC-LRFD中文译稿
受压穹作用的腹板
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当拉力仅通过横向焊缝传递
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属于八1 5 0 建筑钢结构抗震规程中定义的பைடு நூலகம்风 险地震性能类的建筑物的抗震设计，应与该规程相 — 致。^ 1 5 0 钢结构建筑抗震规定中没有覆盖的抗 震设计应与本规范相一致。
1 . 4 . 1 荷载、荷载分项系数及荷载组合
常用的荷载及荷载组合有： 0 ：结构构件和结构上的永久部件的重量引起
的恒荷载 乙:使用及移动设备引起的活荷载
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美国AASHTO LRFD 桥梁规范历史和目前现状
小结（2）
自从2007年10月，美国所有联邦政府资助的桥梁项目必 须使用 LRFD 设计规范;
（1）标准规范设计荷载横向分布系数比LRFD大； （2）标准规范中斜桥斜度和跨径的影响没有考虑； （3）LRFD规范中，斜桥斜度越大，荷载分布系数越小； （4）LRFD规范中，跨径越大，荷载分布系数越小。
设计案例-背景
Gowanus 高速公路 拓宽改造工程
位于：美国纽约城 建于：1941年， 60年代拓宽 总长：约10公里 车道：双向4车道->双向6车道 车流量：约20万次/日 上部结构：钢混叠合梁，大部 分桥跨采用简支梁形式，部分 路段采用双层结构 下部结构：钢结构桥墩
在结构设计中，由于涉及到不同时期的结构，不同的分析方法被运用。
新匝道包括桥面板，钢混叠合梁，支座，立柱和下部基础，使用 LRFD 设计方法，而旧钢桥桥台则使用 ASD 法复核其承载力，对于在旧高架上 的新叠合梁设计采用 LFD。
考虑到地震对新，旧桥的影响，开发了三维有限元模型，要求新桥设计 能符合抗震要求，对旧桥部分，提供抗震加固方案。
规范开发背景-目标
开发一套反映当前美国最新科技水平，在国际桥梁设 计界接近或者达到领先地位的规范；
规范尽可能具有广泛性，应包括新的结构形式，分析 方法和承载力模型；
考虑到使用规范的人员和组织的广泛性，规范要求可 读和易用；
要使用规范语言而不是使用教科书式语言编写规范； 鼓励在桥梁设计中使用多学科方法，特别是在水力学
美国钢结构焊接规范宣贯
4.2.1 免除评定的适用范围
WPS的免除评定应定义为免除本规范第4章（WPS的评定）所要 求的WPS的评定试验。 ①所有免除评定合格的WPS （焊接工艺规程）必须形成书面文件； ②WPS必须符合第3章（WPS的免除评定）的所有条款； ③工程师有权要求证实免除评定合格的接头是否适用于工程； ④按免除评定合格的WPS实施焊接工作的焊工、自动焊工和定位 焊工的资格一定要按照第4章（WPS的评定）C部分的要求进行评 定，这种人员资格的评定是不能免除的。 GB50661-2011缺③、 ④两条。
焊工和焊机操作工资格评定的焊缝类型 1 非管材连接的CJP坡口焊缝 2 非管材连接的PJP坡口焊缝 3 管材连接的CJP坡口焊缝 4 管材连接的PJP坡口焊缝 35 管材和非管材连接的角焊缝 6 管材和非管材连接的塞焊和曹焊缝
试焊 验工 方和 法焊 和机 合操 格作 准工 则资
格 评 定 的
• 试验方法为： 目检、宏观腐 蚀试验、 无损 检测、角焊缝 破断试验和弯 曲试验。
深度和宽度超过焊缝面宽度的焊道示意图
在进行WPS免除评定时，每一条焊道的焊缝金属横截面，无论 是深度还是最大宽度，均应严禁超过焊道表面的宽度。
4.2.6 焊后热处理的免除评定
焊后热处理应免除评定的条件是: 1、母材规定的最低屈服强度不得超过345MPa； 2、母材严禁淬火和回火、淬火和自回火、控扎 控冷或使用冷作用来达到更高的力学性能； 3、没有对母材、热影响区或焊缝金属的缺口韧 性有更高的要求； 4、应有数据证实在焊后热处理条件下焊缝金属 应有足够的强度和塑性； 5、焊后热处理的实施应符合相关规定。