POINTS TO REMEMBER FOR A CIVIL ENGINEER

LABOUR REQUIREMENT FOR VARIOUS BUILDING WORKS

LABOUR REQUIREMENT FOR VARIOUS BUILDING WORKS:
The table below shows the recommended labour requirement for various civil engineering/building/construction works:

S.No.	Description of work	Unit	Labour	Recommended constant in days.	Remarks
1)	Excavation over areas (hard/dense soil),depth up to 1.5m and removal (up to one meter from edge)	M3	Mate Labour	0.06 0.62	_ _
2)	Excavation in trenches (soft/ loose soil),for foundations not exceeding 1.5m in width and for shafts, wells, cesspits and the like, not exceeding 10m3 and on plan, depth up to 1.5m and removal(up to one meter away from edge)	M3	Mate Labour	0.05 0.50	_ _
3)	Returning, filling and ramming of excavated earth in layers not exceeding 20 cm in depth, watering, well ramming and leveling, lead up to 50m	M3	Mate Labour Bhisti	0.02 0.25 0.02	_ _ _
4)	Concrete :Mixing by machine (mixer) at banker, cement concrete (with 20mm graded coarse aggregate)	M3	Labour Bhisti Mixer operator Mixer	0.50 0.10 0.07 0.07	_ _ _ _
5)	Mixer mixed cement concrete	M3	mason Labour bhisti mixer operator mixer vibrator	0.10 1.63 0.70 0.07 0.07 0.07	_ _ _ _ _ _
6)	Reinforced cement concrete in situ in foundations, footings, bases for columns, etc excluding form work and reinforcement	M3	mason Labour bhisti mixer operator mixer vibrator	0.17 2.00 0.90 0.07 0.07 0.07	The constants for items include mixing, pouring, consolidating and curing. This does not include fair finish.
7)	Reinforced cement concrete in situ in suspended floors/roofs excluding form work, and reinforcement.	M3	mason Labour bhisti mixer operator mixer vibrator	0.24 2.50 0.90 0.07 0.07 0.07	_ _ _ _ _ _
8)	Mortars :Mixing by hand, cement mortar of any mix/proportions	M3	Labour Bhisti	0.75 0.07	Labour required will be approximately same for different mix proportions.
9)	Brick work (straight walls) :Brick work in walls exceeding one brick thick, in cement / lime mortar	M3	mason Labour bhisti	0.94 1.80 0.20	The constants include labour involved in scaffolding.
10)	Brick work in walls, one brick thick, in cement/lime mortar	M2	mason Labour bhisti	0.25 0.40 0.10	The constants could be adopted for brick work with any mix or mortar.
11)	Formwork :a) fabrication and erection with all supports, struts, braces, etc, and dressing with oil as cleaning of formwork : 1) rectangular column and walls 2) suspended floors/roofs 3) sides and soffits of beam	M3 M2 M2	Carpenter Labour Carpenter Labour Carpenter Labour	0.25 0.20 0.23 0.20 0.30 0.20	_ _ _ _ _ _
12)	Reinforcement:Bar reinforcement including cutting to length, hooked ends, cranking or bending, hoisting and placing in any position, binding wire and holding firmly so as not to be disturbed while placing and ramming of concrete	Quintal	Bar bender Labour	1.00 1.00	_ _
13)	Plastering and pointing :a) 15mm thick cement plaster to ceiling including mixing of mortar. b) 15mm thick cement plaster on brick walls (exterior) including mixing of mortar c) Tuck pointing to random rubble masonry in cement mortar including mixing mortar.	M2 M2 M2	mason Labour bhisti mason Labour bhisti mason Labour bhisti	0.08 0.10 0.10 0.06 0.10 0.10 0.10 0.15 0.10	_ _ _ _ _ _ _ _ _
14)	Damping proof course :a) Laying damp proof course 40mm thick cement concrete including form work and fair finishing to edges and mixing.	M3	Mason Labour bhisti	0.10 0.10 0.01	_ _ _

Note: Bhisti means water carrier.

FACTORS AFFECTING CONCRETE CUBE & CYLINDER STRENGTH RATIO

The relation between compressive strength of concrete cube and cylinder is complex. The various factors including inherent variations in concrete quality and comparison between cube and cylinder strength affects the strength ratio.
Factors affecting Concrete Cube and Cylinder Strength Ratios are:
1. Concrete cube and cylinder casting, curing and testing procedures
2. Geometry of the specimen
3. Level of strength
4. Direction of loading and machine characteristics
5. Grading of aggregates
1. Effects of concrete cube / cylinder casting, curing and testing procedures:
The method of casting and capping of cube and cylinder affects the strength ratios of both. The use of rigid and non-rigid moulds affects their strength. Also the method of capping these moulds affects the strength as out of plane surface also influences their strength ratio.
Proper curing and testing procedure is necessary to associate a proper relation between concrete cube and cylinder compressive strength ratios, otherwise the ratio obtained will be misleading.
2. Effects of geometry of specimen
Geometric factors such as volume of concrete, shape of concrete and h/d ratio (height to lateral dimension) of specimen affects the concrete cube and cylinder strength ratio. The following figure shows the effect of height/diameter ratio to concrete strength ratio.


3. Effect of concrete strength level
Nominal strength of concrete has been shown to affect the concrete cube and cylinder strength ratio. Research by Evans indicates that this ratio decreases with increasing concrete strength. Cylinder to cube strength ratio ranges from 0.77 to 0.96 depending on concrete strength level.
4. Direction of loading and machine characteristics
Concrete cubes may be loaded in the direction perpendicular to casting while cylinders are always loaded in the direction of casting. Since these concrete cubes and cylinders are casted in multiple layers, their strength will differ based on direction of loading.

5. Grading of aggregates
Grading of aggregates in concrete affects the strength of any structure or specimen. The effect of compression test on concrete specimens are large due to relative size of aggregate particles to specimen dimensions. Most standards sets limits for the ratio of diameter or size of specimen to maximum nominal size of aggregates. Typically this allowable minimum is around 3 to 4.

EFFECT OF ENTRAINED AIR ON CONCRETE STRENGTH

Compressive strength and workability are two important aspects of concrete. Compressive strength of concrete is inversely proportional to workability of concrete. When workability of concrete increases, its compressive strength decreases. To achieve the required compressive strength of concrete, its workability is limited. But workability cannot be decreased beyond certain limit so that concrete can be effectively placed and compacted at site.
To maintain the desired compressive strength and workability of concrete together, generally in the case of higher strength concrete, admixtures are used. Air entraining agent is one such concrete admixture to increase the workability without affecting much reduction in compressive strength.
But use of concrete admixture in concrete shall be considered in mix design so that desired compressive strength is achieved with required amount of admixture and workability.

Fig: Air Entrained Concrete

In general, the compressive strength of concrete is reduced by use of air entrained admixture. The amount of reduction in strength depends on many factors such as mix proportions, type and grading of concrete, cement and actual air-entraining agent.
Normal reduction in strength of concrete by use of air-entrained admixtures varies from 3 to 7%. This variation of strength shall be considered in the mix design of concrete. Suitably, trial mix designs should be done to find exact variation of strength with the use of this admixture and suitable corrections should be done in mix design to ensure desired strength.
Typically it may be assumed that a loss of 5% in compressive strength of concrete occurs due to each 1% by volume of entrained air in the concrete mix.
In order to estimate water-cement ratio required for an air entrained concrete, an allowance for strength reduction is incorporated in the mix design and higher target mean strength is assumed.
The appropriate higher target mean strength for an air entrained mix is given by:

Where fc = specified characteristic strength
M = the margin
a = percentage by volume of entrained air.

Chenab Bridge, India

Shear Force & Bending Moment Diagram

Scaffolding Safety Checklist...!!!