Question

Question 5 a- Calculate the Duration and Total Cost of executing an underground RC tank that requires 800 m3 of concrete. The material cost is 1000 LE/m3. While the crew produces 60 m3/day: the number of laborers required are & carpenters at a wage 20 LE/hour and 3 laborers at a wage of 15 LE/hour. Assume an efficiency rate between (0.78 -0.93) and 8 working hours/day. b- If the Owner would like to reduce the activity duration to 10 days. Calculate the new cost based on an overtime rate of 1.5 the normal rate and a productivity of 0.9 the normal productivity.

Answer 1

1] Given -

a) Material cost for producing concrete = 1000 LE/$m^3$

b) Concrete Produced per day by crew = 60 $m^3$

c) Number of carpenters required = 8

d) Number of Laborers Required = 3

e) Wages of Carpenter = 20 LE/hour

f) Wages of Laborer = 15 LE/hour

g) Number of working hours per day = 8

h) Overtime rate = 1.5 x Normal time rate

i) New productivity on overtime day = 0.9 times the normal time day productivity

2] To Find -

a) Total cost and Total Duration for executing an underground RC tank work that requires 800 $m^3$ of concrete.

b) The new cost of the owner want to reduce the activity duration to 10 days

3] Solution -

A)

i)

Let us assume an efficiency rate of 0.83.

So, the concrete produced per day by crew = (0.83 x 60) $m^3$ /day

As the concrete to be done is 800 $m^3$

800 Therefore, the total number of days required = = 0.83 X 60 60 = 16 days

ii)

Total Cost = Material Cost + Manpower Cost

$\textup{Material cost per }m^3 \textup{ of concrete}= 1000\textup{ LE}$

Material Cost = Material Cost per mx 800 = 1000 x 800 = 800000 LE

As the total duration is 16 days and wages of Carpenter are 20 LE/hour and 15 LE/hour with 8 working hours per day.

$\begin{aligned}\textup{Cost for carpenter}&=\textup{Number of carpenters}\times \textup{Number of working hour}\times \textup{Wage per hour} \times \textup{Total duration}\\\textup{ }&=8\times 8\times 20\times 16=\textbf{20480\textup{ LE}}\end{aligned}$

$\begin{aligned}\textup{Cost for laborer}&=\textup{Number of laborers}\times \textup{Number of working hour}\times \textup{Wage per hour} \times \textup{Total duration}\\\textup{ }&=3\times 8\times 15\times 16=\textbf{5760\textup{ LE}}\end{aligned}$

$\begin{aligned}\textup{Manpower cost}&=\textup{Cost for carpenter}+\textup{Cost of Laborer}\\\textup{ }&=20480+5760\\\textup{ }&=\textbf{26240\textup{ LE}}\end{aligned}$

$\begin{aligned}\therefore \textup{Total Cost}&=\textup{Material Cost}+\textup{Manpower Cost}\\\textup{ }&=800000+26240\\&=\textbf{826240\textup{ LE}}\end{aligned}$

Thus the total duration of concreting is 16 days and total cost of concreting is 826240 LE

B]

To complete the activity in 10 days the working hours of workers needs to be increased to match the new per day requirement of concrete production

$\textup{New per day concrete production}=\frac{800}{10\times 0.83}=96.4m^3$

For 60$m^3$ the working hours was 8 per day, so for 96.4$m^3$ with reduced productivity to 0.9,

$\textup{The working hours per day for 96.4}m^3=\frac{96.4\times 8}{60\times 0.9}=14.28\approx 14\textup{ hours per day}$

Thus a total of 10 days will require 14 hours per day of working hours, this will change the manpower cost but the material cost will remain same, the new manpower cost with 1.5 times the old rates is as below

$\begin{aligned}\textup{New cost for carpenter}&=\textup{Number of carpenters}\times \textup{Number of working hour}\times \textup{Wage per hour} \times \textup{Total duration}\\\textup{ }&=8\times 14\times (20\times 1.5)\times 10=\textbf{33600\textup{ LE}}\end{aligned}$

$\begin{aligned}\textup{New cost for laborer}&=\textup{Number of laborers}\times \textup{Number of working hour}\times \textup{Wage per hour} \times \textup{Total duration}\\\textup{ }&=3\times 14\times (15\times 1.5)\times 10=\textbf{9450\textup{ LE}}\end{aligned}$

$\begin{aligned}\textup{New Manpower cost}&=\textup{New Cost for carpenter}+\textup{New Cost of Laborer}\\\textup{ }&=33600+9450\\\textup{ }&=\textbf{43050\textup{ LE}}\end{aligned}$

$\begin{aligned}\therefore \textup{Total New Cost for completion in 10 days}&=\textup{Material Cost}+\textup{New Manpower Cost}\\\textup{ }&=800000+43050\\&=\textbf{843050\textup{ LE}}\end{aligned}$

Thus for the total duration 10 days and total cost of concreting is 843050 LE