Characteristic Strength of Materials

Characteristic Strength of Materials Characteristic Load or ultimate load

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Learn : Characteristic Strength of Materials :Characteristic Strength of Concrete, Characteristic Strength of Steel. and Characteristic Load or ultimate load


CHARACTERISTIC VALUES  (REFER CLAUSE 36, IS CODE)

Characteristic Strength of Materials

The characteristic strength is based on the statistical analysis of the test results because there are variations in the strength of the material used. In order to simplify the analysis, it may be assumed that the variation in strength follows a normal distribution curve which is symmetric about the mean value as shown below in Fig. 3.1.

Characteristic Strength of Materials :Characteristic Strength of Concrete, Characteristic Strength of Steel. and Characteristic Load
Characteristic Strength of Materials

Therefore, characteristic strength = Mean strength – k S

where S is the standard deviation, k=1.64, corresponding to 5% probability

    \[\therefore                f_{ck}=f_{m} - 1.64 S\]

 Characteristic Strength of Concrete

The term characteristic strength means that value of strength of material below which not more than 5% of the test results are expected to fall. It is denoted by fck is N/mm2. The value of fck for different grades of concrete are specified by IS code 456:2000 and given in Table 1.1

TABLE 1.1. Grades of Concrete, Characteristic Strength of Concrete

Group Designation Characteristic Compressive Strength, fck (N/mm2)
Ordinary

Concrete

M10

M15

M20

10

15

20

Standard

Concrete

M25

M30

M35

M40

M45

M50

M55

25

30

35

40

45

50

55

High Strength Concrete M60

M65

M70

M75

M80

60

65

70

75

80

 

Characteristic Strength of Steel

The characteristic strength of steel is taken as the minimum yield stress or 0.2 percent proof stress specified by various Indian standards. In the case of mild steel it is taken as equal to minimum yield strength and is the case of HYSD bars it is taken as equal to 0.2 percent proof stress the values of characteristic strength of various types of steel are given in Table 1.9

TABLE 1.9.

S.No. Type of Reinforcement Sub-Type Relevant Indian Standard
1. Mild steel plain bar (a) Cold worked mild steel bars

(b) Hot rolled mild steel bars

IS 432-1996 (Part-I)

IS 1139-1966 (Part-II)

2. High yield strength

deformed bars (Tor steel)

(a) Cold worked deformed bars

(i) Grade Fe 415

(ii) Grade Fe 500

(b) Hot rolled deformed bars

IS 1786-1979

 

 

IS 1139-1966 (Part-II)

3. Hard drawn steel wire fabric Wire mesh IS 1566-1967
4. Rolled steel members Angles, T-sections Joists,

Channels etc.

IS 226:1975
5. (i)     Thermo-mechanically treated bars (TMT)

(ii)    Corrosion resistant steel (CRS) bars

Latest in use deformed bars

Characteristic Load or ultimate load

The characteristic load is the ultimate load that is liable to come on structure during its lifetime. For simplicity, the variation in the loading is also assumed to follow a normal distribution cure, the characteristic load or ultimate load  is given as

Characteristic load or ultimate load = Mean load + 1.64 S

    \[W_{u}=W_{m} + 1.64 S\]

Characteristic load is that value of load which has a 95 percent probability of not being exceeded during the life time of the structure. In absence of any data, loads given in various standards shall be assumed as the characteristic loads. The following standards may be used for this purpose.

IS 875 (Part 1) – for dead loads

IS 875 (Part 2) – for imposed loads

IS 875 (Part 3) – for wind loads

IS 875 (Part 4) – for snow loads

IS 1893 (Part 1) – for earthquake loads

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Characteristic Strength of Materials Characteristic Load or ultimate load
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Characteristic Strength of Materials Characteristic Load or ultimate load
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