4.1.3. Limit States Design

4.1.3. Limit States Design
(See Note A-4.1.3.)
4.1.3.1. Definitions
  1. In this Subsection, the term
    1. limit states means those conditions of a building structure that result in the building ceasing to fulfill the function for which it was designed (those limit states concerning safety are called ultimate limit states (ULS) and include exceeding the load-carrying capacity, overturning, sliding and fracture; those limit states that restrict the intended use and occupancy of the building are called serviceability limit states (SLS) and include deflection, vibration, permanent deformation and local structural damage such as cracking; and those limit states that represent failure under repeated loading are called fatigue limit states),
    2. specified loads (C, D, E, H, L, P, S, T and W) means those loads defined in Article 4.1.2.1.,
    3. principal load means the specified variable load or rare load that dominates in a given load combination,
    4. companion load means a specified variable load that accompanies the principal load in a given load combination,
    5. service load means a specified load used for the evaluation of a serviceability limit state,
    6. principal-load factor means a factor applied to the principal load in a load combination to account for the variability of the load and load pattern and the analysis of its effects,
    7. companion-load factor means a factor that, when applied to a companion load in the load combination, gives the probable magnitude of a companion load acting simultaneously with the factored principal load,
    8. importance factor, I, means a factor applied in Subsections 4.1.6., 4.1.7. and 4.1.8. to obtain the specified load and take into account the consequences of failure as related to the limit state and the use and occupancy of the building,
    9. factored load means the product of a specified load and its principal-load factor or companion-load factor,
    10. effects refers to forces, moments, deformations or vibrations that occur in the structure,
    11. nominal resistance, R, of a member, connection or structure, is based on the geometry and on the specified properties of the structural materials,
    12. resistance factor, φ, means a factor applied to a specified material property or to the resistance of a member, connection or structure, and that, for the limit state under consideration, takes into account the variability of dimensions and material properties, workmanship, type of failure and uncertainty in the prediction of resistance, and
    13. factored resistance, φR, means the product of nominal resistance and the applicable resistance factor.
4.1.3.2. Strength and Stability
  1. A building and its structural components shall be designed to have sufficient strength and stability so that the factored resistance, φR, is greater than or equal to the effect of factored loads, which shall be determined in accordance with Sentence (2).
  2. Except as provided in Sentence (3), the effect of factored loads for a building or structural component shall be determined in accordance with the requirements of this Article and the following load combination cases, the applicable combination being that which results in the most critical effect:
    1. for load cases without crane loads, the load combinations listed in Table 4.1.3.2.-A, and
    2. for load cases with crane loads, the load combinations listed in Table 4.1.3.2.-B.
      (See Note A-4.1.3.2.(2).)
  3. Other load combinations that must also be considered are the principal loads acting with the companion loads taken as zero.
  4. Where the effects due to lateral earth pressure, H, restraint effects from pre-stress, P, and imposed deformation, T, affect the structural safety, they shall be taken into account in the calculations, with load factors of 1.5, 1.0 and 1.25 assigned to H, P and T respectively. (See Note A-4.1.3.2.(4).)
  5. Except as provided in Sentence 4.1.8.16.(2), the counteracting factored dead load-0.9D in load combination cases 2, 3 and 4 and 1.0D in load combination case 5 in Table 4.1.3.2.-A, and 0.9D in load combination cases 1 to 5 and 1.0D in load combination case 6 in Table 4.1.3.2.-B-shall be used when the dead load acts to resist overturning, uplift, sliding, failure due to stress reversal, and to determine anchorage requirements and the factored resistance of members. (See Note A-4.1.3.2.(5).)
  6. The principal-load factor 1.5 for live loads L in Table 4.1.3.2.-A and LXC in Table 4.1.3.2.-B may be reduced to 1.25 for liquids in tanks.
  7. The companion-load factor for live loads L in Table 4.1.3.2.-A and LXC in Table 4.1.3.2.-B shall be increased by 0.5 for storage areas, and equipment areas and service rooms referred to in Table 4.1.5.3.


    Table 4.1.3.2.-A
    Load Combinations Without Crane Loads for Ultimate Limit States
    Forming Part of Sentences 4.1.3.2.(2) and (5) to (10)

    Notes to Table 4.1.3.2.-A:
    (1) See Sentences 4.1.3.2.(2), (3) and (4).
    (2) See Sentence 4.1.3.2.(9).
    (3) See Sentence 4.1.3.2.(8).
    (4) See Sentence 4.1.3.2.(5).
    (5) See Sentence 4.1.3.2.(6).
    (6) See Article 4.1.5.5.
    (7) See Sentence 4.1.3.2.(7).
    (8) See Sentence 4.1.3.2.(10).


    Table 4.1.3.2.-B
    Load Combinations With Crane Loads for Ultimate Limit States
    Forming Part of Sentences 4.1.3.2.(2), (5) to (8), and (10)

    Notes to Table 4.1.3.2.-B:
    (1) See Sentences 4.1.3.2.(2), (3) and (4).
    (2) See Sentence 4.1.3.2.(8).
    (3) See Sentence 4.1.3.2.(5).
    (4) See Article 4.1.5.5.
    (5) See Sentence 4.1.3.2.(6).
    (6) See Sentence 4.1.3.2.(7).
    (7) Side thrust due to cranes need not be combined with full wind load.
    (8) See Sentence 4.1.3.2.(10).

  8. Except as provided in Sentence (9), the load factor 1.25 for dead load, D, for soil, superimposed earth, plants and trees given in Tables 4.1.3.2.-A and 4.1.3.2.-B shall be increased to 1.5, except that when the soil depth exceeds 1.2 m, the factor may be reduced to 1 + 0.6/hs but not less than 1.25, where hs is the depth of soil in metres supported by the structure.
  9. A principal-load factor of 1.5 shall be applied to the weight of saturated soil used in load combination case 1 of Table 4.1.3.2.-A.
  10. Earthquake load, E, in load combination cases 5 of Table 4.1.3.2.-A and 6 of Table 4.1.3.2.-B includes horizontal earth pressure due to earthquake determined in accordance with Sentence 4.1.8.16.(7).
  11. Provision shall be made to ensure adequate stability of the structure as a whole and adequate lateral, torsional and local stability of all structural parts.
  12. Sway effects produced by vertical loads acting on the structure in its displaced configuration shall be taken into account in the design of buildings and their structural members.
4.1.3.3. Fatigue
  1. A building and its structural components, including connections, shall be checked for fatigue failure under the effect of cyclical loads, as required in the standards listed in Section 4.3. (See Note A-4.1.3.3.(1).)
  2. Where vibration effects, such as resonance and fatigue resulting from machinery and equipment, are likely to be significant, a dynamic analysis shall be carried out. (See Note A-4.1.3.3.(2).)
4.1.3.4. Serviceability
  1. A building and its structural components shall be checked for serviceability limit states as defined in Clause 4.1.3.1.(1)(a) under the effect of service loads for serviceability criteria specified or recommended in Articles 4.1.3.5. and 4.1.3.6. and in the standards listed in Section 4.3. (See Note A-4.1.3.4.(1).)
4.1.3.5. Deflection
  1. In proportioning structural members to limit serviceability problems resulting from deflections, consideration shall be given to
    1. the intended use of the building or member,
    2. limiting damage to non-structural members made of materials whose physical properties are known at the time of design,
    3. limiting damage to the structure itself, and
    4. creep, shrinkage, temperature changes and pre-stress.
      (See Note A-4.1.3.5.(1).)
  2. The lateral deflection of buildings due to service wind and gravity loads shall be checked to ensure that structural elements and non-structural elements whose nature is known at the time the structural design is carried out will not be damaged.
  3. Except as provided in Sentence (4), the total drift per storey under service wind and gravity loads shall not exceed 1/500 of the storey height unless other drift limits are specified in the design standards referenced in Section 4.3. (See Note A-4.1.3.5.(3).)
  4. The deflection limits required in Sentence (3) do not apply to industrial buildings or sheds if experience has proven that greater movement will have no significant adverse effects on the strength and function of the building.
  5. The building structure shall be designed for lateral deflection due to E, in accordance with Article 4.1.8.13.
4.1.3.6. Vibration
  1. Floor systems susceptible to vibration shall be designed so that vibrations will have no significant adverse effects on the intended occupancy of the building. (See Note A-4.1.3.6.(1).)
  2. Where the fundamental vibration frequency of a structural system supporting an assembly occupancy used for rhythmic activities, such as dancing, concerts, jumping exercises or gymnastics, is less than 6 Hz, the effects of resonance shall be investigated by means of a dynamic analysis. (See Note A-4.1.3.6.(2).)
  3. A building susceptible to lateral vibration under wind load shall be designed in accordance with Article 4.1.7.1. so that the vibrations will have no significant adverse effects on the intended use and occupancy of the building. (See Note A-4.1.3.6.(3).)

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