Un nmero en parntesis indica el ao de ltima re-aprobacin. Una psilon en superndice indica un cambio editorial desde la ltima revisin o re-aprobacin. Alcance 1. Las unidades pulgada-libra y las unidades del SI no son necesariamente equivalentes. En el texto de esta especificacin y cuando sea pertinente, las unidades del SI se encuentran en parntesis. Documentos de Referencia 2.
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Practice ASTM A provides guidance on safeguarding against warpage and distortion for optimum hot-dip galvanizing and shall be complied with in both design and fabrication.
The primary recommendations within ASTM A for bridge design are as follows: Avoid Susceptible Thin Sheet Steels Steel invariably contains internal stresses induced at the mill from rolling operations used to bring structures, plate, and sheet to the final thickness. Oftentimes sheet or plate can be returned to a flattened state using a jig or by weighing the product down on a flat surface during the cool-down. After galvanizing, these products should be air cooled instead of quenched to minimize induced stress from the cooling cycle.
Where excessive cold working or tight bend radii cannot be avoided, the product should be stress relieved per the guidelines provided within ASTM A, Section 6. Optimize Welding Before Hot-Dip Galvanizing Welding results in significant residual stress in small areas of an assembly due to the extreme temperature differences experienced. All efforts should be made to keep the stresses in the construction as low as possible right from the beginning to enable the steel to absorb the internal stresses completely.
The overall amount of welding can be minimized by using bolted connections or performing assembly after hot-dip galvanizing. Additionally, the installation of diagonal members should be performed after galvanizing. Where welding before galvanizing cannot be avoided, the internal stresses in the connections can be minimized by avoiding joint designs or weld lengths which are greater than statically required, and by placing welds near to and symmetrically around the neutral axis - aligning welds so that shrinkage and opposing forces are balanced rather than all pulling in the same direction.
Furthermore, cylindrical structures are less likely to warp or distort than rectangular or elliptical ones. Specify symmetrically rolled sections instead of angle or channel frames.
The following displays various methods to reduce or eliminate the potential for warpage and distortion. Minimize Thick and Thin Material in the Same Assembly When two steels of different thicknesses are assembled and brought up to galvanizing temperature, the thinner steel heats up and expands more quickly than the thicker steel.
Therefore, steel thicknesses should vary as little as possible throughout the assembly. Wherever possible, galvanize thick and thin portions separately and join them after galvanizing.
ASTM A384 PDF
Nikosho Inch pounds and SI units are not necessarily exact equivalents. I the f frame has to be dipped one half at a time, it will be better to have the sheets galvanized, rolled flat after galvanizing, and assembled to the galvanized frame by the use of aluminum alloy or galvanized rivets. This will prevent the rusting of the surfaces which are so connected that molten zinc cannot circulate through the crevices to galvanize the contacting surfaces. This abstract is a brief summary of the referenced standard. Referenced Documents purchase separately The documents listed below are referenced within the subject standard but are not provided as part of the standard.
ASTM A384 Recommendations