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Structural Steel Design




Structural steel design is a branch of Structural Engineering that focuses on the design of steel structures where the structural steel is used as a construction material in a variety of shapes, each having their own properties.


Pros and Cons of Structural Steel

    Pros:

  • Can be used to design high-rise buildings (skyscrapers)
  • Has a good tensile and compressive strength (equally)
  • Is a ductile material, and is, therefore, strong enough to withstand external pressures (earthquake, wind, etc.)
  • Is a recyclable material and the recycled material can be used for the construction of a new structure (has good scrap value)
  • Is a lightweight material, therefore, it can span long distance
  • Does not require formwork, unlike concrete which makes it cheaper than reinforced concrete
  • Is easily erectable which speeds up the construction process and it is easy to assemble/disassemble the structure
  • Has less repair and maintenance costs compared to concrete
  • There is a variety of connections types (welds, bolts, rivets)

    Cons:

  • Has less fire resistance compared to concrete, therefore, it needs fireproofing to resist fire damage; can melt at very high temperatures
  • Has buckling problems
  • Exact measurements have to be known before the transport and delivery of steel because the steel fabrication company does the manufacturing off-site (prefabrication)
  • Corrosion/Rusting issues therefore needs anti-rust paint
  • Requires skilled labor

Load Path is the transmission of loads from one member (Ex: Beam) to the other (Ex: Girder), where the load is transferred downward, from the roof of the structure, all the way down to the foundation.


Types of loads:

  • Dead Load (DL or D):load that is built-in, that comes with the structure itself; internal load (ex: self-weight of a beam).
  • Live Load (LL or L):load exerted by an external/foreign object that is not built-in with the structure (ex: a person standing on a floor).
  • Wind Load (W): load exerted by the wind on the structure.
  • Earthquake Load (E):load exerted by an earthquake on the structure.
  • Snow Load (S):load exerted by a snow on the structure.
  • Rain Load (R):load exerted by a rain on the structure.
  • Live load roof(Lr):load exerted by a live load on the roof.
  • Fluid Load (F):load exerted by fluids on the structure.
  • Hydrostatic/Lateral soil pressures (H):load exerted by lateral soil on the structure.
  • Self-straining force (T):self straining load.



Load combinations,Load and Resistance Factor Design(LRFD):

Ru≤ΦRn (where Ru = Ultimate,factored strength, Rn = Nominal strength and Φ= Factor of safety,FS)

  1. 1.4D
  2. 1.2D + 1.6L + 0.5(Max{Lr/S/R})
  3. 1.2D + 1.6(Max{Lr/S/R})+ (Max{L or 0.8W})
  4. 1.2D + 1.6W + L + 0.5(Max{Lr/S/R})
  5. 1.2D + 1.0E + L + 0.2S
  6. 0.9D + 1.6W
  7. 0.9D + 1.0E


Load combinations,Allowable Strength Design (ASD):

Ra≤Rn/Ω (where Ra = Allowable strength, Rn = Nominal strength and Ω=Factor of safety,FS)

  1. D + F
  2. D + H + F + L + T
  3. D + H + F + (Max{Lr/S/R})
  4. D + H + F + 0.75(L + T) + 0.75(Max{Lr/S/R})
  5. D + H + F + (Max{W/0.7E})
  6. D + H + F + 0.75(Max{W/0.7E}) + 0.75L + 0.75(Max{Lr/S/R})
  7. 0.6D + W + H
  8. 0.6D + 0.7E + H

    Worked out problems with solutions in pdf files


    ASD and LRFD


  1. How to find the factored load using LRFD method
  2. Steel Design Ex1 (factored loads)
    Figure : Steel Design example 1(Factored loads)

    SteelDesignEx1solution.pdf


    Steel Beam Design


  3. How to select the lightest beam size
  4. For the simply supported floor beam with point loads (live and dead loads) at midspan as shown below, select the lightest W-shape beam using LRFD method (factored loads). The beam is laterally braced at the supports and at midspan.

    Steel Design Ex2 (selecting the lightest beam)
    Figure : Steel Design example 2(selecting the lightest beam)

    SteelDesignEx2solution.pdf


    Column Analysis


  5. Column problem
  6. For the pinned-pinned steel column shown below, calculate:
    (a) the critical load, PCR and critical stress, FCR, and,
    (b) the available strength in axial compression,ΦPn, and
    (c) the available critical stress, ΦFCR.

    Pinned-Pinned Steel Wide Flange Column
    Figure : Pinned-Pinned Steel Wide Flange Column

    SteelDesColumnEx1solution.pdf


    Noncomposite Beam and Girder Design (Using a Floor Framing Plan)


  7. How to analyze a beam and girder in a framing plan
  8. For the floor framing plan (non-composite) shown below, design girder, G1, and beam, B1. The Dead Load including self-weight (DL) is 80 psf,and the Live Load (LL) is 110 psf.

    Floor Framing Plan
    Figure : Floor Framing Plan

    FramingPlanEx1solution.pdf

  9. How to analyze a joist
  10. Composite Floor Design
  11. Base Plate Design

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