The capacity of a member to resist tensile forces is implemented as a single design check. A number of modification factors may be entered to change the section properties used for checking tension. This includes the area of holes in the flange or web of the member and a correction factor to account for the distribution of forces at the ends of a member.

When checking or designing a member for tension, you need to specify any reduction in area due to boltholes or other openings within the section. If the members contain significant areas of boltholes, which need to be taken into account when determining the cross-sectional area of the section, you will need to enter the amount of cross-sectional area to be deducted to allow for these holes.  The net area of the section is the gross area minus the combined area of boltholes in the flange and web.

The reduction in area can be specified by setting the number and diameter of holes in the web or flanges or the member. Alternative, the user may override this and directly specify the height of holes across the flanges and webs of the cross section. These heights are multiplied by the thickness of the section to determine the total reduction in area of the section. The initial value for the area of boltholes is zero.

The reduced tensile capacity of members with eccentric connections is specified by clause 4.6.3 of BS5950.  Steel Designer does not use this clause but instead approximates the tensile capacity using a similar calculation to that specified by Clause 4.6.1 but which includes an extra factor to account for the reduction in area. As such that the tensile capacity is computed in Steel Designer using the expression

P_t = p_yk_tA_e

in which k_t represents an area reduction coefficient.

While this method does not directly represent the calculation of clause 4.6.3.1 it provides a simple method by which to account for the reduced tensile capacity described in this clause.  For the tensile capacity expressions of clause 4.6.3 is can be shown that minimum values of k_t are

Clause 4.6.3.1      – bolted connections  P_t = p_y(A_e-0.5a₂)  ®      kt = 0.5

– welded connections       P_t = p_y(A_g-0.3a₂)  ®      kt = 0.7

Clause 4.6.3.2      – bolted connections               P_t = p_y(A_e-0.25a₂)   ®    kt = 0.75

– welded connections       P_t = p_y(A_e-0.15a₂)  ®    kt = 0.85

while less conservative values of k_t based upon the gross area of the connected element taken as half the gross are of the section are as follows.

Clause 4.6.3.1      – bolted connections  P_t = p_y(A_e-0.5a₂)  ®      kt = 0.75

– welded connections       P_t = p_y(A_e-0.3a₂)  ®      kt = 0.85

Clause 4.6.3.2      – bolted connections               P_t = p_y(A_e-0.25a₂)   ®    kt = 0.875

– welded connections       P_t = p_y(A_e-0.15a₂)  ®    kt = 0.925

To enter the properties for tension

Ø  Select the required members in the Frame window

Ø  Choose Tension… from the Design menu

Ø  Type in the number and diameter of holes in the webs and flanges (and the total height of holes will be computed automatically) or…

Ø  Type the total height of holes in the webs and flanges directly

Ø  Choose or enter a value for the Area Reduction Coefficient (kt) if required

Ø  Click OK