The model must have at least one framed opening.

Use dimension lumber (or LVL beams if needed). Note that 1-1/2" thick boards may be modeled as 1/16" thick bass, balsa or cardboard.

Structure: Obey the laws of statics, based on the approximate "rules of thumb" tabulated below. Follow standard framing methods for walls, floors, and roofs as shown in class, in the text, and in other references on reserve in the Fine Arts Library.

Model Requirements:

• Size: approximately 20' in each direction, but may vary with each individual design.

• Scale: 1/2" = 1'-0"

• Include a cardboard foundation wall (8" thick) to serve as the base for your model

• To reduce the amount of "framing lumber" used in the model, walls, floors, and roofs may be shown as solid surfaces (chipboard) that are cut away strategically to reveal the wood framing at critical intersections, framed openings, and other important or typical conditions.

  Consider also the need to "look inside" the model when deciding which surfaces are solid and which have the framing exposed.

References

• Text book: Allen, Fundamentals of Building Construction,
• Allen, Architectural Detailing NA2718 A42
• Architectural Graphic Standards, latest edition (permanent reserve), shows generic sections and misc. details (see contents and index).

• Ching, Building Construction Illustrated TH146 C53 1991;
• Huntington, Building Construction +TH145H95 1987;
• Thallon, Graphic Guide to Frame Construction TH1101 T48x 1991

Computing beam and column sizes

• Beams: Compute the approximate required section modulus, S, using this equation:

  required S = 0.086 x (tributary area in sq. ft.) x (span in feet)

  Find a beam or joist with at least the required S using the charts below. Note that this accounts approximately for bending stress, but leaves out consideration of shear and deflection. For this reason, it should not be used for an actual design, but only for a first approximation. Numbers are based on Spruce-Pine-Fir, No. 2 or better; or LVL beams with unadjusted F_b = 2800 psi.

  Adjusted S for S-P-F dimension lumber, No. 2 or better Number of 2x pieces 1 2 3 2x4 4.59 9.18 13.77 2x6 9.83 19.66 29.49 2x8 15.77 31.54 47.31 2x10 23.53 47.06 70.59 2x12 31.64 63.28 94.92 Equivalent adjusted S for LVL beams Depth Width 1-3/4" 3-1/2" 5-1/4" 5-1/2" 32 63 94 7-1/4" 50 101 151 9-1/2" 75 151 226 11-7/8" 102 203 305 14" 178 357 535 16" 228 456 684 18" 282 565 848	Examples: 1: Simple joist: required S = 0.086 x (tributary area) x (span) required S = 0.086 (14 x 1.33) (14) = 22.42 use 2x10 with adjusted S = 23.53.
  	2: Cantilever beam: required S = 0.086 x (tributary area) x (span) note: use tributary area over "span" area only, not cantilevered part required S = 0.086 (12 x 16) (16) = 264 note: dimension lumber not strong enough; use 5-1/4" X 11-7/8" LVL with equivalent adjusted S = 305.

• Columns and walls: Use 2x6 studs, 16" on center (o.c.) for walls; use 2-2x6 or 3-2x6 "built up" sections for columns, even if the columns are hidden within walls. Note that columns are needed wherever concentrated loads (from beams or girders) need to be supported.

• Floors and roofs: Space joists and rafters 16" o.c. Compute typical sizes using methods shown above.

last updated: 13 Sept. 2002

Copyright 2002 J. Ochshorn. All rights reserved. Republishing material on this web site, whether in print or on another web site, in whole or in part, is not permitted without advance permission of the author.