This article provides an overview of the procedures that must be followed when designing steel beams. Basic steps must be followed to complete the construction. These steps can be grouped into six main topics in accordance with BS 5950.
To carry out the project correctly, the following steps can be followed in the following order.
- Section classification
- Shear capacity
- Bending ability
- Torsional buckling bending
- Detour
- Bridge storage
- Bridge buckling
Section classification
The classification is based on the section aspect ratio.
Based on b/t and d/t profiles, flange and web are divided into plastic, compact, semi-compact and thin profile categories. Click here to learn more about section classification.
The first step in steel beam design is to classify the cross section. No construction can be carried out without beam classification.
Shear capacity
P against = 0.6P j A against
P against >F against
Where
P against – Design shear strength
F against – Design shear force
Av is the shear area and is calculated in accordance with BS 5950. For rolled I and H profiles and U profiles, the load is parallel to the web
The against =tD
Bending ability
The bending capacity equation is selected in the design of steel beams based on the shear force in the section.
There are different equations for low shear (F versus ≤0.6P versus ) and high shear (F versus ≥0.6P versus ).
To avoid irreversible deformations under service loads, the value of Mc must be limited to 1.5P. j Z general and up to 1.2P j Z in the case of a beam or console supported on one side.
Low shear (F versus ≤0.6P versus )
| Section classification | Moment capacity |
| Class 1 – Plastic Class 2 – Compact |
M C =P j S |
| Class 3 – Semi-compact | M C =P j Z or M C =P j S ef |
| Class 4 – Slim | M C =P j Z ef |
Where,
S – Plastic section module
S ef – Effective plasticity modulus
Z – section modulus – elastic
Z ef – Effective elastic modulus
High shear force (F versus ≥0.6P versus )
| Section classification | Moment capacity |
| Class 1 – Plastic Class 2 – Compact |
M C =P j (S – ρS against ) |
| Class 3 – Semi-compact | M C =P j (Z –ρS against /1.5) or M C =P j (page ef –ρS against ) |
| Class 4 – Slim | M C =P j (Z ef –ρS against /1.5) |
Based on the section classification and after checking the low and high shear conditions, the flexural capacity can be evaluated.
For more information about the remaining checks to be carried out, click on the relevant checklist item above.
Torsional buckling bending
The beam must be checked for torsional buckling along its span and according to the arrangement of the internal supports. The Torsional Buckling Bending article could be used for theoretical and practical examples.
The design of steel beams must include a flexural and torsional buckling design. It should not be avoided for any reason.
Detour
The beam must be checked for vertical deflection, taking into account the loads acting on the beam. Table 8 of BS 5950:2000 presents the limits to be considered in the project.
Deflection due to design loads can be calculated manually or derived from analysis. For example, the maximum deflection of a simply supported beam loaded with a uniformly distributed load can be derived from the following equation.
δ = 5W t M 4 / (384EI)
Similarly, the stress-related defect can be calculated based on data or literature analysis.
Deflection control must be carried out when designing the steel beam to ensure that excessive deflection does not occur.
The Wikipedia article distraction (technology) specifies the methods for calculating deflections.
Bridge storage
The load capacity of the web is checked to ensure that it can withstand the vertical loads acting on it. If the project requires it, reinforcements are provided to improve the stiffness of the web.
Web load capacity, P man
P head = (b 1 + nk) tP Yes
Where
b 1 – The storage length must be calculated based on the location
n = (2 + 0.6b t /k), but ≤ 5 at the end of the element and all other cases n = 5
k = T+ r – for rolled profiles I and H and
k = T – for welded profiles
r = root radius from cross-section table
t = web thickness
P Yes = web design strength
For further clarification, a worked example can be used.
Bridge buckling
The rotation of the flange in relation to the web and the lateral movement between the flanges are due to buckling of the web. Depending on the distance to the center of the load, there are different equations to calculate the load capacity of the core.
Core capacity (Px) when the distance to the load or reaction to the near end is equal to or greater than 0.7d; (at t ≥ 0.7d)
P X = 25εt P heads /√( ( b 1 + nk) d)
When a t <0.7 days
P
In this case, the flange is not protected against rotation
P xr = 0.7dP face / L E
As explained in this article, all tests must be carried out in steel beam design. To learn more about the applicability of these equations, you can consult the worked examples on this website.
