Profile Weights in US Imperial Environment

Why does Tekla output different weights than calculated from traditional (AISC tabulated) Weight per unit length values?

AISC's Steel Construction Manual provides different profile dimensions and weight calculations for design purposes, detailing, estimating, and ordering. This causes confusion with the weight values output in the US Imperial environment drawings and reports.

There is approximately a 7% greater weight when calculating using the traditional AISC weight per unit length method than those output by default in Tekla Structures.

By default, Tekla Structures calculates the weight based on the object's cross sectional area and length in the model. These values are based on AISC's Steel Construction Manual detailing values.

The traditional calculation method used by fabricators for estimating and ordering is based off the weight per unit length in AISC's Steel Construction Manual and the length of a member.

Default Tekla Structures Weight Calculation

For parts with cross-sections defined in the profile catalog, the WEIGHT (same as WEIGHT_GROSS) is calculated as the product of:

• The modeled object's VOLUME
  • The cross section area in the profile catalog (CROSS_SECTION_AREA). This value is listed on the Analysis tab of the profile in the Profile catalog
  • The modeled length (LENGTH)
• The profile density (PROFILE_DENSITY) of the material specified. This value is found in the material catalog under the profile weight.

For example, a HSS8x8x1/4 of A500-GR.B material has the following values:

• Cross Section Area = (Ain) 7.10 in²  or (A_ft) 0.0493056 ft²
• A500 has the Density = (D_ft) 490.06 lbs/ft³ or 490.06 lbs/ 1728 in³ = (D_in) .283599 lbs / in³
• (V)olume = (L) x (A)

The WEIGHT calculation for a (L)20 foot (240 inch) long HSS8x8x1/4 is:

(L) 20'-0" × (A_ft) 0.0493056 ft² = (V_ft) .986112 ft³ * (D_ft) 490.06 lbs/ft³  = 483.25 lbs

or

(L) 240" × (A_in)  7.10in² = (V_in) 1704 in^{3 *} (D_in) 0.283599 lbf/in³  =  483.25 lbs

Traditional Weight per Unit Length (in AISC Manual) Calculation

The traditional calculation method used by fabricators is the product of the weight per unit length of a shape (in AISC's Steel Construction Manual) and the length of a member.

A fabricator would calculate the weight of a HSS8x8x1/4 (see values above) as:

20'-0" × 25.82 lbf/ft = 516.4 lbf

How to force Tekla to output fabricator traditional (weight per unit length) values?

Tekla Structures' reports and templates use the cross section area, length, and density product method because it is more accurate to the real life weight of these members.

However, if you desire to use the traditional method, then you will need to either:

1. Change the weight fields in your reports/templates
2. Modify the Profile density for rectangular tube (HSS) materials

Back to top

Change the weight fields in your reports/templates

Tip:

T he value field Data type (red), Meaning (blue), and Unit (green) must be set up correctly (as shown in the images).

All profiles

To have all profiles to use the traditional weight per unit length method, GetValue("WEIGHT") would need to be replaced GetValue("PROFILE_WEIGHT") in all existing value fields and their formulas.

Image

Only Rectangular tube (HSS) profiles

To only have Rectangular tube (HSS) profiles use the traditional weight per unit length method, all existing value fields and their formulas must use a formula similar to:

if GetValue("PROFILE_TYPE") == "M" then
GetValue("PROFILE_WEIGHT")
else
GetValue("WEIGHT")
endif

Image

Back to top

Modify the Profile density for rectangular tube (HSS) materials

Open up the material catalog and find the material for Rectangular (including Square) tubes and change the Profile density value from 490.06 lbf/ft³ to 526.10 lbf/ft³.

Image