Building structures and structural design
Building structures and structural design
This domain tests whether you can apply limit-state design to reinforced concrete, steel, timber and masonry structures under Mongolia’s loads: heavy snow, wind, seismic action and severe frost. You must distinguish ultimate limit state (ULS) from serviceability limit state (SLS) and use the correct load factors.
Core rules
- Design for ULS with factored loads (strength, stability, fatigue) and check SLS for deflection, crack width and vibration.
- Characteristic loads are multiplied by partial factors; a common gravity combination is 1.2G + 1.6Q. Seismic combinations use reduced live load and include seismic action.
- Mongolia is seismically active; design must follow national seismic zoning and ductility detailing, not just gravity loads.
- Reinforced concrete: cover, anchorage, lap length and shear reinforcement control brittle failure modes.
- Steel: check section class, buckling and connection resistance. Timber: moisture content and decay protection.
Worked example A 4.0 m simply supported one-way slab has dead load 4.5 kN/m² (including self-weight) and live load 2.0 kN/m². Factored line load per metre width: w = 1.2×4.5 + 1.6×2.0 = 5.4 + 3.2 = 8.6 kN/m. Maximum moment M = wL²/8 = 8.6×4.0²/8 = 17.2 kN·m per metre width. Compare this with the design moment resistance of the chosen reinforcement; then check deflection and crack width at SLS using unfactored loads.
Traps that cost marks
- Using service loads for a strength check, or factored loads for deflection.
- Omitting snow or seismic combinations because they are not the largest gravity case.
- Confusing characteristic strength with design strength (forgetting the material partial factor).
- Forgetting that a slab’s self-weight is part of the dead load.