Load Types and Combinations

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Structural framing needs to be designed for loads that fulfill client’s performance requirements, to transfer loads stably through proper load paths, and to fulfill code requirements for spans and headroom heights for the specific type of usage.

Vertical loads

  1. Live loads based on the specific type of use
  2. Superimposed dead loads (floor finishes, non-structural partitions, ceilings, and services)
  3. Fixed equipment loads
  4. Soil self-weight
  5. Dead load or self-weight of the structure

Horizontal Loads

  1. Lateral wind loads that should be distributed at center of mass
  2. Soil, surcharge, and water loads
  3. Notional horizontal loading (loading that are used for structural stability of column and walls)
  4. Seismic loads

Some loads that affect the internal stresses of the structural members are not considered in design calculations include temperature, expansion, shrinkage, contraction, inertial, and support movement forces.

Load Combinations
LC1: 1.4DL + 1.6LL
LC2: 1.4DL + 1.4WL
LC3: 1.2DL + 1.2Ll + 1.2WL

DL = Dead Load
LL = Live Load
WL = Wind Load

Note: Superimposed dead loads (SDL) should have the same factor of safety as that of dead loads.

Typical Loads

These loads are often used for scheme design purposes. It should be noted that these loads are preliminary estimates and should not be used for actual design. These loads are only for reference to check preliminary sizes of members required to support the loads.

Superimposed Dead Load
Floor finish (screed) 50mm                               1.2 kPa
Floor finish (screed) 50mm                              2.0 kPa
Raised floor                                                           0.5 kPa
False ceiling                                                           0.5 kPa
Ceiling and Services                                            0.5 kPa
Partitions                                                                 1.0 kPa (minimum)
External walling:
Curtain wall
Cavity walls made out of masonry
Steel wall framing
Windows0.5 kPa
3.5 kPa
0.5 kPa
0.5 kPa
Roofing:
Bituman roofing
Concrete tiles0.3 kPa
0.5 kPa
External:
Paving
Asphalt for insulation
Metal outer covering1 kPa
0.5 kPa
0.5 kPa

Live Load
Office3 kPa
Classroom3 kPa
Corridors5 kPa
Wind uplift for metal decks1 kPa

Wind Loads

Wind load values are based on the height of the structure, in which design wind pressures with respect to height about site or ground level can be obtained. Values are also dependent on the shape of the building, in which shape factors can be obtained. Wind forces are derived with the following equation obtained from the Code of Practice on Wind Effects in Hong Kong 2004. Wind load cases that govern critical load combinations include tall and slender structures and roof slabs with long spans.
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​Source: Code of Practice on Wind Effects in Hong Kong 2004
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​Source: Code of Practice on Wind Effects in Hong Kong 2004
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​Source: Code of Practice on Wind Effects in Hong Kong 2004

Soil Loads
Active soil pressures are generally used for soil load calculations. 
Active pressures are applied loads induced by the soil onto the contained environment. Passive pressures are forces induced by the soil's resistance to applied loads. Passive pressures are generally not conservative for calculations. This is because there will be a worst case scenarios if the soil mass is removed or when an empty space develops between the wall and the soil due to hydration. There will be no passive resistance due to lack of forces induced by soil resistance and there will only be passive resistance until the wall moves towards and is in direct contact with the soil for the soil to resist the wall mass. Constants used to determine soil pressures include the angle of repose and soil/wall friction.

Soil load calculations are often calculated for soil pressure induced onto retaining walls and basement walls. Here are some typical loads used:

Uniform surchage load = 10 kPa
Soil load = 20 kPa using dead load factors

Hydrostatic water pressure should also be designed for, assuming it acts onto ⅓ height of the wall. However, full hydrostatic head will be used for soils with high water table.

Propped retaining wall     Ko = 0.7
Overconsolidated clays   Ko = 1.5
Overconsolidated sands  Ko = 1.0

Other pressures

Pressures that need to be considered when constructing retaining walls, basement walls or any other substructures include the following.

  1. Earth pressure
  2. Water pressure (accounting for extreme flood conditions, buoyancy where groundwater is taken the full basement depth)
  3. Surcharge from adjacent structures
 Fluid Loads
Fluid loads should be calculated by using the static pressure of liquid and its effect on its containment (pressure = density x height of fluid in the contained environment).
Common uses include water tanks and basement walls.
 
Vehicle Loads
Vehicle loads should be incorporated into the structure’s design, when the structure consist of parking lots, ramps, highways, loading bays at industrial buildings, bridges, and any other structure that has vehicles moving on it. Not only do self-weight of the vehicles should be included in the design, vehicle impact loads should be included, as well as, the design of kerbs and rails and other protective and preventative measures for vehicle impact.
Normally, 2.5 kPa should be used for uniformly distributed loads for a car parking area and 5 kpa  should be used for uniformly distributed loads for a commercial vehicle area.

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