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American Wood Council

Can carriage bolts be designed per the National Design Specification (NDS) for Wood Construction?

Carriage bolts (now known as round head bolts) do not conform to ANSI/ASME B18.2.1 Square and Hex Bolts and Screws, so the installation provisions in 2015 NDS (2012 NDS do not apply. Also, carriage bolt dimensions do not comply with the dimensions in ANSI/ASME B18.2.1, therefore, NDS tabulated values do not apply. However, the use of carriage bolts is permissible in accordance with 2015 NDS (2012 NDS provided that characteristics of the carriage bolt are accounted for in connection design and installation. These characteristics include carriage bolt material, bending yield strength (Fyb), diameter, and the potential presence of a square neck under the head in lateral calculations and installation instructions. ASME B18.5-2012 Round Head Bolts provides standard dimensions as shown in Tables 1 and 2 respectively for round head and round head square neck bolts.

Plate Washer Diagram

Plate Washer Diagram

Tables 1 and 2 reprinted from ASME B18.5-2012 Round Head Bolts (Inch Series), by permission of The American Society of Mechanical Engineers. All rights reserved.

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