Question

2. Explain the differences between a Wide Flange Member and a Standard American-I shape: Remember the term ‘beefy’ as a hint.

3. Why might built up members be more economical than long span members?

4. List 3 factors that should be considered for erecting steel?

5. If beams are not being used for the roof structure, name and describe at least one other popular type of steel/ metal construction.

Answer 1

Ans 2:

The picture below illustrates the general visual difference between the two types of steel beams.

General Difference:

• H beam has thicker centre web than I beam (which means it is stronger than I beam).
• H beam is heavier than I beam (which means it takes more force than I beam).
• H beams is used when span up to 100 m when I beam is used when span up to 10 to 30m.
• The difference between both H-beams and I-beams is in the flange/web ratio.
• The I beam is lighter than the H-beam, which means a H-beam is not always ideal.
• An I-beam is made by rolling or milling steel which means the I-beam is often limited by the capacity or size of the milling equipment. H beams are usually welded as per requirement which makes them more economical.
• In case of H beams the width of the flange would be equal to or more than the height of the cross section. In the case of I section, the height of the cross section would be higher than the width of the flange.

Major Difference:

• H beams are preffered for structural applications requiring long span beams, where the design is governed by Shear. I beams are used when desig involves high Bending Moments.
• H beams have symmetrical/equal bending capacities about both major and minor axis. This makes them more preferable choice for columns when compared to I beams which have higher bending moment capacity about major axis.
• Steel I-beams ensure a structure’s integrity with relentless strength and support. The immense power of I beams reduces the need to include numerous support structures, saving time and money, as well as making the structure more stable.  

Ans 3:

Built up members are used over long span traditional members because of the following reasons:

• Using Built up mebers project wise requirements can be fulfilled. Each unique project may have varying nature and magnitude of loads and force developed on a members specially for long spans. Built up members can be fabricated as required. Whereas, using long span members of typical rolled sections can be uneconimical.
• Built up members ensure proper and higher material (steel) utilisation because themember thickness and sizes can be customized and the member can be made economical. Long span members are available prefabricated and hence their sectional properties cannot be altered thus making them less economicalfor long span.
• For Eg: Plate girders are designed to resist the applied actions using proportions that ensure low self-weight and high load resistance. For efficient design it is common to use a relatively deep girder to minimise flange area for a given applied moment. A deep girder also provides a deep web whose area may be minimised by reducing its thickness to the minimum required to carry the applied shear. Such a deep web may be quite slender (a high web depth to thickness ratio) and may be susceptible to shear and local buckling.

Ans 4:

Design factors to consider in relation to Steel Erection are:

• Repetition and standardisation: repetition of the same structural components and common/standard details for connections
• Achievable tolerances: if ‘tight’ tolerances are specified i.e. more restrictive, then special controls will be needed and possibly specially engineered detail.
• Frame type: the primary choice is between braced frames and continuous frames
• Floor systems: for multi-storey frames, the choice of floor system will affect the erection sequence as it determines the stability of the part-erected structure.

Ans 5:

Channel sections can be used as an alternative for Beams for steel construction.

The channel section or C- section consists two equal flanges connected to web at both ends. Channel sections are extensively used in steel framed structures.

  

They are available in various sizes ranging from 100 mm x 45 mm to 400mm x 100 mm.

The advantage that Channel sections offer is that they have good BM resistance and also offer a clean and flat surface on the outside of the web to which connections of treads are easily and conveniently made.