Serviceability limit state is related to the criteria governing normal use. Serviceability limit state is limit state beyond which the service criteria specified below, are no longer met:
- a) Deflection limit,
Table 5 Partial Safety Factor for Materials,
(Clause 5.4.1)
| SI No. | Definition | Partial Safety Factor | |
|---|---|---|---|
| i) | Resistance, governed by yielding, Ymo | 1.10 | |
| ii) | Resistance of member to buckling, Ymo | 1.10 | |
| iii) | Resistance, governed by ultimate stress, Ym1 | 1.25 | |
| iv) | Resistance of connection: | Shop Fabrications | Field Fabrications |
| a) Bolts-Friction Type, Ymf | 1.25 | 1.25 | |
| b) Bolts-Bearing Type, Ymb | 1.25 | 1.25 | |
| c) Rivets, Ymr | 1.25 | 1.25 | |
| d) Welds, Ymw | 1.25 | 1.50 | |
- b) Vibration limit,
- c) Durability consideration, and
- d) Fire resistance.
Unless specified otherwise, partial safety factor for loads, , of value equal to unity shall be used for all loads leading to serviceability limit states to check the adequacy of the structure under serviceability limit states.
5.6.1 Deflection
The deflection under serviceability loads of a building
or a building component should not impair the strength of the structure or components or cause damage to finishings. Deflections are to be checked for the most adverse but realistic combination of service loads and their arrangement, by elastic analysis, using a load factor of 1.0. Table 6 gives recommended limits of deflections for certain structural members and systems. Circumstances may arise where greater or lesser values would be more appropriate depending upon the nature of material in element to be supported (vulnerable to cracking or not) and intended use of the structure, as required by client.
| Type of Building | Deflection | Design Load | Member | Supporting | Maximum Deflection |
|---|---|---|---|---|---|
| (1) | (2) | (3) | (4) | (5) | (6) |
| Industrial Buildings | Vertical | Live load/ Wind load | Purlins and Girts | Elastic cladding | Span/150 |
| Brittle cladding | Span/180 | ||||
| Live load | Simple span | Elastic cladding | Span/240 | ||
| Brittle cladding | Span/300 | ||||
| Live load | Cantilever span | Elastic cladding | Span/120 | ||
| Brittle cladding | Span/150 | ||||
| Live load/ Wind load | Rafter supporting | Profiled Metal Sheeting | Span/180 | ||
| Plastered Sheeting | Span/240 | ||||
| Crane load (Manual operation) | Gantry | Crane | Span/500 | ||
| Crane load (Electric operation up to 50 t) | Gantry | Crane | Span/750 | ||
| Crane load (Electric operation over 50 t) | Gantry | Crane | Span/1000 | ||
| Lateral | No cranes | Column | Elastic cladding | Height/150 | |
| Masonry/Brittle cladding | Height/240 | ||||
| Crane (absolute) | Span/400 | ||||
| Crane + wind | Gantry (lateral) | Relative displacement between rails supporting crane | 10 mm | ||
| Crane + wind | Column/frame | Gantry (Elastic cladding; pendent operated) | Height/200 | ||
| Gantry (Brittle cladding; cab operated) | Height/400 | ||||
| Other Buildings | Vertical | Live load | Floor and Roof | Elements not susceptible to cracking | Span/300 |
| Elements susceptible to cracking | Span/360 | ||||
| Live load | Cantilever | Elements not susceptible to cracking | Span/150 | ||
| Elements susceptible to cracking | Span/180 | ||||
| Lateral | Wind | Building | Elastic cladding | Height/300 | |
| Brittle cladding | Height/500 | ||||
| Wind | Inter storey drift | — | Storey height/300 |
5.6.1.1
Where the deflection due to the combination of dead load and live load is likely to be excessive, consideration should be given to pre-camber the beams, trusses and girders. The value of desired camber shall be specified in design drawing. Generally, for spans greater than 25 m, a camber approximately equal to the deflection due to dead loads plus half the live load may be used. The deflection of a member shall be calculated without considering the impact factor or dynamic effect of the loads on deflection. Roofs, which are very flexible, shall be designed to withstand any additional load that is likely to occur as a result of ponding of water or accumulation of snow or ice.
5.6.2 Vibration
Suitable provisions in the design shall be made for the dynamic effects of live loads, impact loads and vibration due to machinery operating loads. In severe cases possibility of resonance, fatigue or unacceptable vibrations shall be investigated. Unusually flexible structures (generally the height to effective width of lateral load resistance system exceeding 5:1) shall be investigated for lateral vibration under dynamic wind loads. Structures subjected to large number of cycles of loading shall be designed against fatigue failure, as specified in Section 13. Floor vibration effect shall be considered using specialist literature (see Annex C).
5.6.3 Durability
Factors that affect the durability of the buildings, under conditions relevant to their intended life, are listed below:
- a) Environment,
- b) Degree of exposure,
- c) Shape of the member and the structural detail,
- d) Protective measure, and
- e) Ease of maintenanc
5.6.3.1
The durability of steel structures shall be ensured by following recommendations in Section 15. Specialist literature may be referred to for more detailed and additional information in design for durability.
5.6.4 Fire Resistance
Fire resistance of a steel member is a function of its mass, its geometry, the actions to which it is subjected, its structural support condition, fire protection measures adopted and the fire to which it is exposed. Design provisions to resist fire are briefly discussed in Section 16. Specialist literature may be referred to for more detailed information in design of fire resistance of steel structures.