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ASME BTH-1-2008 pdf download

ASME BTH-1-2008 pdf download.Design of Below-the-Hook Lifting Devices.
1-1 PURPOSE This Standard sets forth design criteria for ASME B30.20 below-the-hook lifting devices. This Standard serves as a guide to designers, manufacturers, purchasers, and users of below-the-hook lifting devices. Commentary: This Standard has been developed in response to the need to provide clarification of the intent of ASME B30.20 with respect to the structural design of below-the-hook lifting devices. Since the origi- nal publication of ASME B30.20 in 1986, users have requested interpretations of the construction (structural design) requirements stated therein. The level of detail required to provide adequate answers to the questions submitted extends beyond that which can be covered by interpretations of a B30 safety standard. 1-2 SCOPE This Standard provides minimum structural and mechanical design and electrical component selection criteria for ASME B30.20 below-the-hook lifting devices. The provisions in this Standard apply to the design or modification of below-the-hook lifting devices. Com- pliance with requirements and criteria that may be unique to specialized industries and environments is outside of the scope of this Standard. Lifting devices designed to this Standard shall comply with ASME B30.20, Below-the-Hook Lifting Devices. ASME B30.20 includes provisions that apply to the marking, construction, installation, inspection, testing, maintenance, and operation of below-the-hook lifting devices. Commentary: ASME BTH-1 addresses only design requirements. As such, this Standard should be used in conjunction with ASME B30.20, which addresses safety requirements. ASME BTH-1 does not replace ASME B30.20. The design criteria set forth are minimum requirements that may be increased at the discretion of the lifting device manufacturer or a qualified person. 1 1-3 NEW AND EXISTING DEVICES The effective date of this Standard shall be one year after its date of issuance. Lifting devices manufactured after the effective date shall conform to the requirements of this Standard. When a lifter is being modified, its design shall be reviewed relative to this Standard, and the need to meet this Standard shall be evaluated by the manufacturer or a qualified person. Commentary: It is not the intent of this Standard to require retrofitting of existing lifting devices. 1-4 GENERAL REQUIREMENTS 1-4.1 Design Responsibility Lifting devices shall be designed by, or under the direct supervision of, a qualified person. Commentary: Although always implied, this provi- sion now explicitly states that the design of below-the- hook lifting devices is the responsibility of a qualified person. This requirement has been established in recog- nition of the impact that the performance of a lifting device has on workplace safety, the complexity of the design process, and the level of knowledge and training required to competently design lifting devices. 1-4.2 Units of Measure A dual unit format is used. Values are given in U.S. Customary units as the primary units followed by the International System of Units (SI) in parentheses as the secondary units. The values stated in U.S. Customary units are to be regarded as the standard. The SI units in the text have been directly (softly) converted from U.S. Customary units. Commentary: The requirements of this Standard are presented wherever possible in a manner that is dimensionally independent, thus allowing application of these requirements using either U.S. Customary units  (USCU) or International System of Units (SI). U.S. Customary units are the primary units used in this Standard. 1-4.3 Design Criteria All below-the-hook lifting devices shall be designed for specified rated loads, load geometry, Design Category (see section 2-2), and Service Class (see section 2-3). Resolution of loads into forces and stress values affecting structural members, mechanical compo- nents, and connections shall be performed by an accepted analysis method. Commentary: The original ASME B30.20 structural design requirements defined a lifting device only in terms of its rated load. Later editions established fatigue life requirements by reference to ANSI/AWS D1 4.1. ASME BTH-1 now defines the design requirements of a lifter in terms of the rated load, the Design Category, and the Service Class to better match the design of the lifter to its intended service. An extended discussion of the basis of the Design Categories and Service Classes can be found in Chapters 2 and 3 Commentaries. 1-4.4 Analysis Methods The allowable stresses and stress ranges defined in this Standard are based on the assumption of analysis by classical strength of material methods (models), although other analysis methods may be used. The anal- ysis techniques and models used by the qualified person shall accurately represent the loads, material properties, and device geometry; stress values resulting from the analysis shall be of suitable form to permit correlation with the allowable stresses defined in this Standard. Commentary: The allowable stresses defined in Chapters 3 and 4 have been developed based on the presumption that the actual stresses due to the design loads will be computed using classical methods. Such methods effectively compute average stresses acting on a structural or mechanical element. Consideration of the effects of stress concentrations is not normally required when determining the static strength of a lifter component (see Commentary for para. 3-5.2). However, the effects of stress concentra- tions are most important when determining fatigue life. Lifting devices often are constructed with discontinuities or geometric stress concentrations, such as pin and bolt holes, notches, inside corners, and shaft keyways that act as initiation sites for fatigue cracks. Analysis of a lifting device with discontinuities using linear finite element analysis will typically show peak stresses that indicate failure, where failure is defined as the point at which the applied load reaches the loss of function load (or limit state) of the part or device under consideration. This is particularly true when evaluating 2 static strength. While the use of such methods is not prohibited, modeling of the device and interpretation of the results demands suitable expertise to assure the requirements of this Standard are met without creating unnecessarily conservative limits for static strength and fatigue life. 1-4.5 Material The design provisions of this Standard are based on the use ofcarbon, high strengthlow-alloy, or heattreated constructional alloy steel for structural members and many mechanical components. Other materials may be used, provided the margins of safety and fatigue life are equal to or greater than those required by this Standard. All ferrous and nonferrous metal used in the fabrica- tion oflifting device structural members and mechanical components shall be identified by an industry-wide or written proprietary specification. Commentary: The design provisions in Chapters 3 and 4 are based on practices and research for design using carbon, high-strength low-alloy, and heat-treated constructional alloy steels. Some of the equations pre- sented are empirical and may not be directly applicable to use with other materials. Both ferrous and nonferrous materials, including the constructional steels, may be used in the mechanical components described in Chapter 4. Industry-wide specifications are those from organiza- tions such as ASTM International (ASTM), the American Iron and Steel Institute (AISI), and the Society of Automotive Engineers (SAE). A proprietary specification is one developed by an individual manufacturer. 1-4.6 Welding All welding designs and procedures, except for the design strength of welds, shall be in accordance with the requirements of ANSI/AWS D14.1. The design strength ofwelds shall be as defined in para. 3-3.4. When conflicts exist between ANSI/AWS D14.1 and this Standard, the requirements of this Standard shall govern. Commentary: ANSI/AWS D1 4.1 is cited as the basis for weld design and welding procedures. This requirement is in agreement with CMAA #70 and those established by ASME B30.20. The allowable stresses for welds are modified in this Standard to provide the higher design factors deemed necessary for lifting devices.

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