1. Design of Reinforced Concrete to
BS8810
Durability & Fire Resistance
of Elements
Section -6
2. Other Serviceability Requirements
• Durability
• Resistance to fire
• Fatigue (moving loads or machines)-reduced
working stresses
• Thermal Insulation –use of light weight
aggregates
• Sound Insulation
3.
4. Definition
“Durability is the ability of a Material or Structure
to withstand its design service conditions for its
design life without significant deterioration.”
5. Factors Affecting Durability
• Quality of Concrete
▫ Permeability of concrete
• Degree of protection to Reinforcement
• Chemical Composition
• External Environment
7. Factors Affecting Durability
• Alkaline resistant of concrete is good but very
susceptible to attack by acids.
• Concrete is also attacked by salts like calcium chloride
and soluble sulphates.
• Chloride has solvent effect of concrete and causing
corrosion of concrete when available in concentrated
solution.
• Suphates cause internal expansion of concrete resulting
cracking and strength loss, even with small quantities.
8. Factors Affecting Durability
• Physical attacks caused by abrasion or attrition
or alternate wetting and drying should also be
considered.
• Alternative freezing and thawing may also
results physical attack.
9. How to achieve durability
• Quality concrete: dense, well compacted and less
permeable concrete.
▫ Reduce porosity by low w/c ration constituent
▫ Good curing (better hydration)
▫ Selection of less alkali reacting aggregates
▫ Cement content
▫ Compaction
• Adequate cover to reinforcements
10. Specification for Durability
• Mix proportions (w/c ratio, minimum cement
content)
• Strength ( grade of concrete): the easiest way of
specifying for durability is strength
• Performance criteria (water absorption, air
permeability): the best way of specifying for
durability is to specify performance criteria.
13. Fire Resistance
• Need to consider the fire resistance of the individual
member depending on the usage of the structure.
• Three condition must be examined
▫ Effects on structural strength
▫ Flame penetration resistance
▫ Heat transmission properties
Walls & slabs
14. Fire Resistance
• Concrete starts loosing its strength a t about 200oC and post
cooled strength loss occurs after 300oC
• Steel starts loosing its strength at about 200oC. However post
cooled strength is not reduced too much but ductility may be
affected.
• Concrete cover provide thermal barrier to steel
reinforcements
• The aim therefore is to provide a sound protection to steel
delaying temperature rise at reinforcements by adequate
sectional dimension and cover.
15. Fire Resistance
• The presence of plaster, screed and other non- combustible
finishes assists the cover in protecting the reinforcement.
• Generally fire resistance of an element or combination of
elements are determined by;
▫ Using tabulated data (BS8110)
▫ Testing the element in actual condition.
▫ Fire engineering calculations (ex: expansion may cause extra
loads on structures).
16. Design to resist fire
• BS 8110 gives tabulated values of minimum dimension and
nominal cover for various type of concrete members to
withstand fire for a specified period of time.
• Table 3.4 for cover and Fig 3.2 for sectional dimensions.
• In table 3.4 & Fig 3.2
▫ Duration (0.5hrs to 4hrs) is selected based on exit time from
the building.
▫ Cover values depending 1) duration of fire resistance 2)
element type and element connectivity.
▫ Minimum dimensions depend on 1) element type 2) duration of
fire resistance
19. Design to resist fire
• For columns; degree of exposure is important while for wall
% of reinforcement steel is important.
• Cover for fire resistance is not a function of strength.
• Fore cover >40mm; precaution against spalling shall be
taken as per Cl 4.1.7.of BS8110: prt2.
▫ Apply fire resistance paints.
▫ Provide fire barrier.
▫ Use of lightweight aggregates.
