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D1.G.1 Design Operations

STAAD.Pro supports timber design per two versions of the AITC code: 1985 and 1994. The implementation of both the codes is explained below.

To access the 1994 edition, specify the commands:

CODE AITC

or

CODE AITC 1994

To access the 1984 edition, specify the commands:

CODE AITC 1984

or

CODE TIMBER

D1.G.1.1 1994 AITC Code Implementation

The salient aspects of design in accordance with the 4th edition (1994) of the Timber Construction Manual published by the American Institute of Timber Construction are:
  1. Design can be performed for two types of timber sections: dimensional timber sections (i.e., sawn lumber) and glulaminated sections.
  2. The program includes a database of dimensional timber sections with this code.

Implementation of Dimensional Lumber Properties

The database of sawn lumber sections, listed in Table 8.1 of the 1994 AITC Manual, is implemented in the program.  Some of the key aspects of this implementation are:

In the property tables in the AITC manual, one will find that, for any particular species of timber, the Modulus of Elasticity (E) and allowable stresses may vary with the cross-section size.  For example, a 2x4 Douglas Fir-Larch, Select Structural member has an E of 1900 ksi and an allowable bending stress, Fb, of 1450 psi.  A 5x5 Douglas Fir-Larch, Select Structural, Beam or Stringer member has an E of 1600 ksi and an allowable bending stress, Fb, of 1600 psi.  And a 5x5 Douglas Fir-Larch, Select Structural, Post or Timbers member has an E of 1600 ksi and an allowable bending stress, Fb, of 1750 psi. 

So, in the STAAD timber database for sawn lumber, for each species and grade of timber, the section size, or properties are associated with the Modulus of Elasticity and allowable stresses for the cross-section. When a section is assigned, its E and allowable stresses are automatically fetched along with its properties. The material properties of Southern Pine members were taken from Table 8.4 of the 1994 AITC manual.  For all other species with section sizes 2”-4” wide, the material properties have been taken from Table 8.3.  For all non-Southern Pine species with section sizes greater than 5”x5”, the material properties are obtained from Table 8.6 of the 1994 AITC Manual.

Please note that not all section sizes listed in Table 8.1 are available in every species.  Some sizes are not produced for particular species.  For example, the Aspen species only produces sizes from 2”-4” wide.  It does not produce sizes 5”x5” and larger.  This can be observed by comparing Table 8.3, where Aspen is listed as an available species, to Table 8.6, where Aspen is not listed as an available species.  Also note that although 1” wide members are listed in Table 8.1, there are no values available in the species properties tables; Table 8.4, Table 8.5, and Table 8.6.  AITC does not allow for the structural design of these small members.

D1.G.1.2 1985 AITC Code Implementation

STAAD’s Timber design module per the 1985 AITC code (Timber Construction Manual, 3rd. Edition, 1985) allows design of Glulam timber sections. It also conforms to the National Design Specification for Wood Construction and Supplement (NDS) and building codes like Uniform Building Code (UBC), Basic/National Building Code and Standard Building Code. Some of the main features of the program are:
  1. This feature is for Glulam Timber only (design of dimensional lumber are available for 1994 AITC only).
  2. Code check and design of members as per TCM - AITC.
  3. Design values for Structural Glued Laminated Timber tables are in-built into the program. The program accepts Table no., Combination and Species specifications as inputs (e.g., 1:16F-V3-SP/SP) and reads design values from in-built tables.
  4. Incorporates all the following Allowable stress modifiers:
    1. Duration of Load Factor 
    2. Size Factor
    3. Form Factor 
    4. Lateral stability of Beams and Columns 
    5. Moisture Content Factor
    6. Temperature and Curvature factors.

    The allowable stresses for bending, tension, compression, shear and Moduli of elasticities are modified accordingly.

  5. Determines slenderness for beams and columns (Short, intermediate and long) and checks for min. eccentricity, lateral stability, buckling, bending and compression, bending and tension and horizontal shear against both axes.
  6. The output results show sections provided or chosen, actual and allowable stresses, governing condition and ratios of interaction formulae and the relevant AITC clause nos. etc for each individual member.
Parent topic: D1.G. American Codes - Timber Design per AITC Code
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