AISC ASD 89

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AISC 钢结构设计手册 ASD89 版,经典的钢结构设计参考手册
STRUCTURAL STEELS PRODUCT AVAILABILITY Section A3. 1 of the Specification for Structural Steel Buildings Allowable Stress De- sign and Plastic Design,(from here on referred to as the ASD Specification), lists 16 ASTM specifications for structural steel approved for use in building construction Six of these steels are available in hot-rolled structural shapes, plates and bars Two steels, ASTM A514 and A852, are only available in plates. Table 1 shows five groups of shapes and 11 ranges of thicknesses of plates and bars available in the vari- ous minimum yield stress* and tensile strength levels afforded by the eight steels. For complete information on each steel, reference should be made to the appropriate ASTM specification. A listing of the shape sizes included in each of the five groups follows in Table 2, corresponding to the groupings given in Table A of ASTM Speci fication A6 Seven additional grades of steel, other than those covering hot-rolled shapes plates and bars, are listed in Sect. A3. 1.These steels cover pipe, cold-and hot formed tubing and cold-and hot-rolled sheet and strip For additional information on availability of structural tubing, refer to separate discussion beginning on pg. 1-91. For additional information on availability and clas- ification of structural steel plates and bars, refer to separate discussion beginning on pg.1-105 Space does not permit inclusion in the listing of shapes and plates in Part 1 of this Manual of all rolled shapes or plates of greater thickness that are occasionally used in construction. For such products, refer to the various producers'catalogs To obtain an economical structure, it is often advantageous to minimize the number of different sections. Cost per sq. ft often can be reduced by designing this way SELECTION OF THE APPROPRIATE STRUCTURAL STEEL ASTM A36 is the all-purpose carbon grade steel widely used in building and bridge construction. ASTM A529 structural carbon steel, ASTM A572 high-strength, low alloy structural steel, ASTM A242 and a588 atmospheric corrosion- resistant high strength low-alloy structural steel, ASTM A514 quenched and tempered alloy struc- tural steel plate and ASTM A852 quenched and tempered low-alloy structural steel late may each have certain advantages over astm A36 structural carbon steel, de pi pending on the application. These high-strength steels have proven economical choices where lighter members, resulting from use of higher allowable stresses, are not penalized because of instability, local buckling, defection or other similar rea- sons. They are frequently used in tension members, beams in continuous and com posite construction where deflections can be minimized, and columns having low slenderness ratios. The reduction of dead load and associated savings in shipping costs, can be significant. However, higher strength steels are not to be used indis criminately. Effective use of all steels depends on thorough cost and engineering analysis With suitable procedures and precautions, all steels listed in the AISC Specifica tion are suitable for welded fabrication ASTM A242 and A588 atmospheric corrosion-resistant, high-strength low-alloy As used in the AISC Specification, "yield stress"denotes either the specified minimum yield point (for those steels that have a yield point) or specified minimum yield strength( for those steels that do not have a yield point) AMERICAN INSTITUTE OF STEEL CONSTRUCTION steels can be used in the bare(uncoated) condition in most atmospheres. Where boldly exposed under such conditions, exposure to the normal atmosphere causes a tightly adherent oxide to form on the surface which protects the steel from further atmospheric corrosion. To achieve the benefits of the enhanced atmospheric corro sion resistance of these bare steels, it is necessary that design, detailing, fabrication erection and maintenance practices proper for such steels be observed designers should consult with the steel producers on the atmospheric corrosion-resistant prop- erties and limitations of these steels prior to use in the bare condition when either A242 or A588 steel is used in the coated condition, the coating life is typically longer than with other steels. Although A242 and a588 steels are more expensive than other high-strength, low-alloy steels, the reduction in maintenance resulting from the use of these steels usually offsets their higher initial cost ASTM A852 and A514 Types E, F,P, and Q are higher strength atmospheric corrosion-resistant steels suitable for use in the bare(uncoated) condition in most atmospheres BRITTLE FRACTURE CONSIDERATIONS IN STRUCTURAL DESIGN General Considerations As the temperature decreases, an increase is generally noted in the yield stress, ten- sile strength, modulus of elasticity and fatigue strength of structural steels In con trast, the ductility of these steels, as measured by reduction in area or by elongation decreases with decreasing temperature. Furthermore, there is a temperature below which a structural steel subjected to tensile stresses may fracture by cleavage, with little or no plastic deformation, rather than by shear, which is usually preceded by a considerable amount of plastic deformation or yielding fracture that occurs by cleavage at a nominal tensile stress below the yield stress is commonly referred to as brittle fracture. generally a brittle fracture can occur in a structural steel when there is a sufficiently adverse combination of tensile stress temperature, strain rate and geometrical discontinuity (notch) present. Other design and fabrication factors may also have an important infuence. Because of the interre- lation of these effects, the exact combination of stress, temperature, notch and other conditions that will cause brittle fracture in a given structure cannot be calculated readily. Consequently, designing against brittle fracture often consists mainly of (1) avoiding conditions that tend to cause brittle fracture and 2 selecting a steel appro priate for the application. a discussion of these factors is given in the following sec- tions. Refs. 1 through 5 cover the subject in much more detail Conditions Causing Brittle Fracture It has been established that plastic deformation can occur only in the presence of shear stresses. Shear stresses are always present in a uniaxial or biaxial state-of- stress. However, in a triaxial state-of-stress, the maximum shear stress approaches zero as the principal stresses approach a common value. Thus, under equal triaxial tensile stresses, failure occurs by cleavage rather than by shear. Consequently, triax- ial tensile stresses tend to cause brittle fracture and should be avoided. a triaxial state-of-stress can result from a uniaxial loading when notches or geometrical discon tinuities are present Shear and cleavage are used in the metallurgical sense(macroscopically) to denote different frac- ture mechanisms. Ref 2, as well as most elementary textbooks on metallurgy, discusses these mech AMERICAN INSTITUTE OF STEEL CONSTRUCTION Increased strain rates tend to increase the possibility of brittle behavior Thus structures that are loaded at fast rates are more susceptible to brittle fracture. How ever, a rapid strain rate or impact load is not a required condition for a brittle fracture Cold work, and the strain aging that normally follows, generally increases the likelihood of brittle fracture. This behavior usually is attributed to the previously mentioned reduction in ductility. The effect of cold work that occurs in cold forming operations can be minimized by selecting a generous forming radius, thus limiting the amount of strain The amount of strain that can be tolerated depends on both the steel and the application When tensile residual stresses are present, such as those resulting from welding they add to any applied tensile stress and thus the actual tensile stress in the member will be greater than the applied stress. Consequently, the likelihood of brittle frac- ture in a structure that contains high residual stresses may be minimized by a post weld heat treatment. The decision to use a post-weld heat treatment should be made with assurance the anticipated benefits are needed and will be realized and that pos- sible harmful effects can be tolerated. Many modern steels for welded construction are designed to be used in the less costly as-welded condition when possible. The soundness and mechanical proper ties of welded joints in some steels may be ad- versely affected by a post-weld heat treatment Welding may also contribute to the problem of brittle fracture by introducing notches and faws into a structure and by causing an unfavorable change in micro structure of the base metal. However, properly designed welds, care in selecting their location and the use of good welding practice, can minimize such detrimental effects. The proper electrode must be selected so that the weld metal will be as resist ant to brittle fracture as the base metal Selecting a Steel The best guide in selecting a steel appropriate for a given application is experience with existing and past structures. The A36 steel has been used successfully in a great number of applications, such as buildings, transmission towers, transportation equipment and bridges, even at the lowest atmospheric temperatures encountered in the u.s. Therefore, it appears that any of the structural steels, when designed and fabricated in an appropriate manner, could be used for similar applications with little likelihood of brittle fracture. Consequently, brittle fracture is not usually experi enced in such structures unless unusual temperature, notch and stress conditions are present. Nevertheless, it is always desirable to avoid or minimize the previously cited adverse conditions that increase the susceptibility to brittle fracture In applications where notch toughness is considered important, it usually is re quired that steels must absorb a certain amount of energy, 15 ft-lb. or higher (Charpy v-notch test), at a given temperature. The test temperature may be higher than the lowest operating temperature depending on the rate of loading, For exam ple, the toughness requirements for A709 steels are based on the loading rate for bridges LAMELLAR TEARING The information on strength and ductility presented in the previous sections gener ally pertains to loadings applied in the planar direction (longitudinal or transverse orientation of the steel plate or shape. It should be noted that elongation and area reduction values may well be significantly lower in the through-thickness direction than in the planar direction This inherent directionality is of small consequence in AMERICAN INSTITUTE OF STEEL CONSTRUCTION 且6 many applications, but does become important in the design and fabrication of struc- tures containing massive members with highly restrained welded joints With the increasing trend toward heavy welded-plate construction, there has been a broader recognition of occurrences of lamellar tearing in some highly re- strained joints of welded structures, especially those using thick plates and heavy structural shapes. The restraint induced by some joint designs in resisting weld de posit shrinkage can impose tensile strain sufficiently high to cause separation or tear ing on planes parallel to the rolled surface of the structural member being joined The incidence of this phenomenon can be reduced or eliminated through greater un- derstanding by designers, detailers and fabricators of (1) the inherent directionality of constructional forms of steel, (2)the high restraint developed in certain types of connections and(3) the need to adopt appropriate weld details and welding proce- dures with proper weld metal for through-thickness connections. Further, steels can be specified to be produced by special practices and/or processes to enhance through-thickness ductility and thus assist in reducing the incidence of lamellar tear ing. Steels produced by such practices are available from several producers. How- ever unless precautions are taken in both design and fabrication, lamellar tearing may still occur in thick plates and heavy shapes of such steels at restrained through thickness connections. Some guidelines in minimizing potential problems have been developed? JUMBO SHAPES AND HEAVY WELDED BUILT-UP SECTIONS Although Group 4 and 5 W-shapes, commonly referred to as jumbo shapes, gener ally are contemplated as columns or compression members their use in non-column applications has been increasing. These heavy shapes have been known to exhibit segregation and a coarse grain structure in the mid-thickness region of the flange and the web. Because these areas may have low toughness, cracking might occur as a re sult of thermal cutting or welding. Similar problems may also occur in welded built up sections. To minimize the potential of brittle failure, the current AISC ASD Specification( see Manual, Part 5) includes provisions for material toughness re quirements, methods of splicing and fabrication methods for Group 4 and 5 hot- rolled or welded built-up cross sections with an element of the cross section more than 2 in. in thickness intended for tension applications REFERENCES Brockenbrough, R L. and B G. Johnson U.s.s. Steel Design Manual 1981, U.S. Steel 2. Parker, E.R. Brittle Behavior of Engineering Structures John wiley sons, 1957, New york 3. Welding research Council Control of Steel Construction to Avoid Brittle Failure 1957. 4. Lightner, M.w. and R, w. vanderbeck Factors Involved in Brittle Fracture Regional Technical Meetings, American iron and Steel Institute, 1956 5. Rolfe, S T. and M. Barsom fracture and Fatigue Control in Structures-Applications of frac ture Mechanics Prentice-Hall, Inc., 1977, Englewood Cliffs, NJ 6. Rolfe, S T. Fracture and Fatigue Control in Steel Structures AISC Engineering Journal, Ist Qtr. 1977, New York, NY.(pg. 2) 7. American institute of Steel Construction, Inc. Commentary in Highly Restrained Welded Connections A ISC Engineering Journal, 3rd Qtr. 1973, New York, NY.(pg 61) 8. Fisher, John W. and Alan w, Pense Experience with Use of heavy w Shapes in Tension AISC Engineering Journal, 2nd @tr. 1987, Chicago, Ill.(pP 63-77) AMERICAN INSTITUTE OF STEEL CONSTRUCTION TABLE 1 Availability of Shapes, Plates and Bars According to ASTM Structural Steel Specifications Shapes Plates and Bars Mini- Fy Over OverOver Over Over Over Over OverOver ASTM mum Ten- Grou "11122”22"|45”6 Des- Yield sile ASTM A6 To to tototo tototo toto igna- Stress Stress ”11y2″24568"|0ver Type tion (ksi)I(ksi)1 2 345 Incl. Incl. Incl. Incl. Incl. Incl. Incl. Inc. Incl. Incl. 8" 325880 A36 365890° A529426085 42 A441 46 67 70 424260 alloy 6 60 60 75 6565 80 42 sIon A2424667 resistant 70 strength LoW- A58846 67 70 Quenched & 90 Tem A852470 110 Low-alloy Quenched 45人9 100 & 130 Tem ed 1010 Alloy Minimum unless a range is shown includes bar-size shapes For shapes over 426 lbs /ft, minimum of 58 ksi only applies plates only Ea Available □ Not availab|e AMERICAN INSTITUTE OF STEEL CONSTRUCTION -8 TABLE 2 Structural Shape Size Groupings for Tensile Property Classification Structural Shapes Group 1 Group 2 Group 3 Group 4 Group 5 W shapes W24×55,62W44×198,W44×248,W40×362tW36×848 W21×44to 224 285 655inc.W14×605to 57inc.W40×149toW40×277toW36×328to 730 incl W18×35to 268 incl 328 incr 798ic 71inc.W36×135toW36×230toW33×318to W16×26to 210 inc 300 inc 619 incl 57incl.|W33×118tW33×201tW30×292to W14×22to 152 incl 291 incl 581 incl 53inc.W30×90tow30×235tW27×281to W12×14to 211 inc 261 inc 539 incl 58 inc W27×84tow27×194toW24×250to W10×12to 178 inc 258in 492 incl 45inc.W24×68toW24×176oW21x248t W8×10to 162 inch 229 incl 402 inci 48inc.W21×62toW21×166tow18×211t W6×9to 147 inci 223 incl 311 incl 25ic.W18×76toW18×158toW14×233to W5×16,19 13 incl 92 incl 550inc!. W16×67toW14×145toW12×210to W4×13 100 incl 211 incl 336 inch W14×61toW12×120to 132 inc 190 incl W12×65to 106 inc W10×49to 112 inch W8×58,67 M Shapes to 37.7 ib, /ft s Shapes to 35 b /ft Inc HP Shapes to 102 lb /ft over 102 I, /ft American to 20.7 lb /ftover 20.7 Standard incl Channels(C) iscelianeous to 28.5 lb/ft over 28.5 Channels(MC) Incl. 1b./ ft Angles(L) to v in incl. over v2 to 3y Structural in. incl ar-sIze Notes: Structural tees from W, M and S shapes fall into the same group as the structural shape from hich they are cut Group 4 and group 5 shapes are generally contemplated for application as columns or com- pression components. When used in other applications ( e.g., trusses)and when thermal ci ting or welding is required, special material specification and fabrication procedures apply to minimize the possibility of cracking. (See Part 5, Specification Sects. A3. 1, J1.7,J1.8, J2. 7, and M2.2 and corresponding Commentary sections. AMERICAN INSTITUTE OF STEEL CONSTRUCTION DIMENSIONS AND PROPERTIES W Shapes M Shapes S Shapes HP Shapes American Standard Channels(C Miscellaneous Channels(MC) Angles(L) STRUCTURAL SHAPES DESIGNATIONS DIMENSIONS AND PROPERTIES The hot rolled shapes shown in Part 1 of this Manual are published in astm specifi cation A6/A6M, Standard Specification for General Requirements for Rolled steel Plates, Shapes, Sheet Piling, And Bars For Structural Use W shapes have essentially parallel flange surfaces. The profile of a w shape of a given nominal depth and weight available from different producers is essentially the same except for the size of fillets between the web and flange HP bearing pile shapes have essentially parallel fange surfaces and equal web and flange thicknesses. The profile of an HP shape of a given nominal depth and weight available from different producers is essentially the same American Standard beams(S)and American Standard channels(c) have a slope of approximately 163/3%(2 in 12 in. )on their inner flange surfaces. The profiles of S and C shapes of a given nominal depth and weight available from different pro ducers are essentially the same The letter M designates shapes that cannot be classified as W, HP or S shapes Similarly, MC designates channels that cannot be classified as C shapes. Because many of the M and Mc shapes are only available from a limited number of produc- ers, or are infrequently rolled, their availability should be checked prior to specifying these shapes. They have various slopes on their inner fange surfaces, dimensions for which may be obtained from the respective producing mills ann The flange thickness given in the tables for S, M, c and Mc shapes is the average fange thickness In calculating the theoretical weights, properties and dimensions of the rolled shapes listed in Part 1 of this Manual, fillets and roundings have been included for all shapes except angles. The properties of these rolled shapes are based on the smallest theoretical size fillets produced; dimensions for detailing are based on the largest theoretical size fillets produced. These properties and dimensions are either exact or slightly conservative for all producers who offer them Equal leg and unequal leg angle(L) shapes of the same nominal size available from different producers have profiles which are essentially the same, except for the size of fillet between the legs and the shape of the ends of the legs. The k distance given in the tables for each angle is based on the largest theoretical size fillet avail able. Availability of certain angles is subject to rolling accumulation and geographi- cal location, and should be checked with material suppliers AMERICAN INSTITUTE OF STEEL CONSTRUCTION K,k W SHAPES Dimensions br Web Flange Distance DesigArea Depth Thickness w Width Thickness TkK nation A d in In. In. In.In W46104my|4104与11121-242 22465843.31489407871nde191114161138%121 985804214210709%丰1841112201%丰382% W40×3296420014060190zh11033 298876399139%0830=17830157511%13%131场 26738133739107505%126012%45鱼13342%豆 241713906190210%1771017%12601%3424 X2216481386213890719左 70141065多3%32 19256538203810710%171Q|0.830|33%32联 W40×65192014362笑97021680635403%33%49461 59314042994317901%11690160232304343434642 53141560423442%16106101651011621290 又480414014181414146011636016%126402%34=2 6128043441%134011162401624002%33%311 3971601409541 22011612016612012%133%3%17 96210601051401201%16020161201023%31 3249531401640在100115905451810丰13%131 27180439840g91158515/60%317 213090×41501042dB 2563338981390650%615:7501512201/4312619 19584386713B%|0650%丰多1575015108513%421% W40X18353213681391060%丰%18011122132G 16749135943% 618101d1025133241%6 149481862038060%丰H:8101H10801%d3%2%12 For application refer to notes in table 2 hEavier shapes in this series are available from some producers Shapes in shaded rows are not available from domestic producers AMERICAN INSTITUTE OF STEEL CONSTRUCTION

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