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TR.20.1 Assigning Properties from Steel Tables

The following commands are used for specifying section properties from built-in steel table(s). The section type specification is followed by additional specifications as needed.

General Format

type-spec  . table-name additional-spec 

Where:

ParameterDescription
type-spec
  = { ST | RA | D | LD | SD | T | CM | TC | BC | TB | FR }
Table 1. Type-specs for various profile types
type-spec Description Diagram
ST single section from the standard built-in tables
RA single angle with reverse Y-Z axes (refer to G.4.2 Local Coordinate System)
D

double profile. In the case of channels, back-to-back

The spacing between shapes is provided using the SP additional specification.



LD double angle with long legs back-to-back
SD double angle with short legs back-to-back
T tee section cut from I shaped section
CM composite section, available for I shaped sections
TC section with top cover plate
BC section with bottom cover plate
TB

section with both top and bottom cover plate

top plate dimensions are described using WP and TH parameter values and bottom plate dimensions are described using BW and BT parameter values

FR

front-to-front (i.e., toe-to-toe) channels.

Note: Spacing between the channels must be provided using the SP option mentioned in the additional spec specification described below.
SA double angle in a star arrangement (heel to heel)
table-name Table section name like W8X18, C15X33 etc. 

The documentation on steel design per individual country codes contains information regarding their steel section specification also.  For details on specifying sections from the American steel tables, refer to D1.A.4 Built-in Steel Section Library.

additional-spec
  = * {SP f1 | WP f2 | TH f3 | WT f4 | DT f5 | OD f6 | ID f7 | CT f8 | FC f9 | CW f10 | CD f11 | BW f12 | BT f13 }
Table 2. Additional specifications for steel sections
Variable Description
SP f1 Either:
  • Spacing between double angles, double channels, or double wide-flange sections (i.e., D, LD, SD, or FR). The default spacing is 0.0.
  • Rib height for composite sections
WP f2 Width of top cover plate for I shaped sections with cover plate.
TH f3 Thickness of plates or tubes (top plate for I shaped sections)
WT f4 Width of tube.
DT f5 Depth of tube.
OD f6 Outer diameter of pipe.
ID f7 Inside diameter of pipe.
CT f8 Concrete thickness of the concrete for composite sections.
FC f9 Compressive strength of concrete for composite sections.
CW f10 Concrete width for composite sections.
CD f11 Concrete density for composite sections (default is 150 pounds per cubic ft.)
BW f12 With of bottom cover plate for I shaped sections with cover plates
BT f13 Thickness of cover plates for I shaped sections with cover

Refer to G.6.2 Built-In Steel Section Libraries for more information.

Examples

UNIT  …
MEMBER PROPERTIES
1  TO  5  TABLE  ST  W8X31
9  10  TABLE  LD  L40304  SP  0.25
12  TO  15  PRISMATIC  AX  10.0  IZ  1520.0
17  18  TA  ST  PIPE  OD  2.5  ID  1.75
20  TO  25  TA  ST  TUBE  DT  12.  WT  8.  TH  0.5
27  29  32  TO  40  42  PR  AX  5.  IZ  400.  IY  33. -
IX  0.2  YD  9.  ZD  3.
43  TO  47  UPT  1  W10X49
50  51  UPT  2  L40404
52  TO  55  ASSIGN  COLUMN
56 TA TC W12X26 WP 4.0 TH 0.3
57 TA CM W14X34 CT 5.0 FC 3.0
See TR.20.6 Examples of Member Property Specification for additional details on this example.

Notes

All values f1 - f9 must be supplied in current units.

Some important points to note in the case of the composite section are:

  1. The CM parameter can be assigned to I-shaped sections only. A CM (composite) section is one obtained by considering a portion of a concrete slab to act in unison with the I shaped steel section. FC is the strength or grade of concrete used in the slab. In the USA, FC is called the specified compressive strength of concrete. Typical values of FC range between 2.0 and 5.0 ksi, and 20 to 50 Mpa.
  2. The width of the concrete slab (CW) (if not entered) is assumed to be the width of the top flange of the steel section + 16 times the thickness of the slab.
  3. In order to calculate the section properties of the cross-section, the modular ratio is calculated assuming that:
    • Es = Modulus of elasticity of steel = 29,000 ksi.
    • Ec = Modulus of elasticity of concrete = 1,802.5√(Fc) ksi

    Where Fc (in ksi) is defined earlier.

Some other general notes on this subject of member property designations are:
  1. The T parameter stands for a T-shaped section obtained by cutting an I-shaped section at exactly its mid height level along the web. Hence, the area of a T shape is exactly half the area of the corresponding I shape. The depth of a T shape is half the depth of the I shape it was cut from.

    What we refer to as I shaped sections are sections which look like the English alphabet I. The American Wide Flange, the British UB and UC sections, Japanese H sections, etc., all fall under this category. Consequently, the 'T' shape cut from a Japanese H shape is one obtained by cutting the H shape at exactly its mid-height level of the web.

    Not all I shaped sections have a corresponding T. This may be inferred by going through the section libraries of individual countries and organizations. In such cases, if a user were to specify such a T section, the program will terminate with the message that the section does not exist.

  2. Steel Cover plates also can be added only to I shaped sections. Thus, the TC, BC, and TB are not applicable to any shape other than an I shape.