Civil engineering - QUICK REVISION

Important Notes for Civil Engineering exam

As per IS 456:2000 Clause 17.4:

• The points from which cores are to be taken and the number of cores required shall be at the discretion of the engineer - in - charge and shall be representative of the whole of concrete concerned.

• In no case, however, shall fewer than three cores be tested.

• Cores shall be prepared and tested as described in IS 516.

• IS 456 : 2000 states that the concrete in the member represented by a core test shall be considered acceptable, if the average equivalent cube strength of core is equal to at least 85% of the cube strength of the grade of concrete specified, but no individual core has a strength less than 75%.

The effective length of groove weld:

As per IS: 800-2007, Clause 10.5.4.2 

• The effective length of butt weld or groove weld shall be taken as the length of the continuous full-size butt weld, but not less than four times the size of the weld or minimum of 40 mm.

• Maximum clear spacing between the effective length of the weld:

• For the welds in compression zone = Minimum of 12 × Thickness of the weld or 200 mm

• For the welds in tension zone = Minimum of 16 × Thickness of the weld or 200 mm

Classification of sections

• IS 800:2007, classified the cross sections into four classes depending upon the material yield strength and width to thickness ratio of the individual components within the cross section and loading arrangement.

The basic characteristics of these four classes are given below:

Plastic or Class I section:   

• 1. It has the capacity to develop plastic hinge and collapse mechanism.
• 2. They are fully effective in pure compression and capable to reaching the full plastic moment in bending and hence, used in plastic design.

Compact or Class 2 Section:

• 1. It has the capacity to form plastic hinge but does not have capacity to develop collapse mechanism because of local buckling.
• 2. They have lower deformation capacity but also fully effective in pure compression and are capable of reaching their full plastic moment in bending.

Semi- Compact or Class 3 Section:

• 1. It has capacity to develop yield moment only and local buckling is liable to prevent the development of the plastic moment resistance.
• 2. They are also fully effective in pure compression but local buckling prevents the attainment of the full plastic moment in bending.  Bending moment resistance in these cross-sections is limited to yield moment only.

Slender or Class 4 Section:

• 1. These section fails before reaching the yield stress i.e. local buckling will occur even before the attainment of the yield stress in extreme fiber.
• 2. An effective cross-section is defined based on the width to thickness ratio of the individual plate elements and this is used to determine the resistance of cross-section.

Among all these sections Plastic, Compact and semi-compact can be used as compression member but slender section cannot be used as compression member because member fails by buckling before reaching its yield strength.

Split tensile strength test of stone:

Three cylindrical test pieces of diameter not less than 50 mm and the ratio of diameter to height 1 : 2 are used to determine the tensile strength of the stone in each saturated and dry condition. Each test piece to be tested is sandwiched in between 2 steel plates of width 25 mm, thickness 10 mm and length equal to the length of test piece. The load is applied without shock and increase continuously at a uniform rate until the specimen splits and no greater load is sustained. The maximum load applied to the specimen is recorded. The average of 3 results separately for each condition should be reported as split tensile strength of the sample. In case any test piece gives a value of as much as 15% below the average.

In tensile strength test of stone,

•  diameter to height ratio is 1 : 2
• lets take
• diameter of sample is 50 mm
• diameter to height ratio = 1 : 2
• than height of cylindrical sample is 100 mm

Which of the following is NOT a coagulant?

• Ferrous sulphate
• Sodium aluminate
• Sodium sulphate - answer
• Ferric chloride

Type of milestone color code for Highways

The various type of milestone color code being used in India for highways are specified in below tabulated form:

• Type of Highway         Milestone Color Code

• National Highway         Yellow & White Strip

• State Highway         Green & White Strips

• City or Main District Roads Blue or Black & White strips

• Village Roads                 Orange & White strips