# Area calculations & what about 12.5m? [closed]

The shown girder is made from plain stone concrete and four 25 mm diameter steel wires. Including the weight of steel wires, determine self weight of the girder if its length is 12.5 m. Neglect the volume of concrete displaced by steel wires

My answer, area of concrete = ((150*1200)+ 4((200*100)+(0.5*100*150))-(4*pi*(12.5)^2))*(1×10^-3)^2=70.44m^2

area of steel = (4*pi*(12.5)^2))*(1×10^-3)^2 = 1.963×10^-3m^2

W = [(70.44×22.6)+(1.96×10^-3×77.3)] = 1.59×10^3KN/m

## closed as off-topic by perror, 0xec, Igor Skochinsky♦Feb 25 '17 at 18:06

• This question does not appear to be about reverse engineering within the scope defined in the help center.
If this question can be reworded to fit the rules in the help center, please edit the question.

• Have you thought about asking this question on the mathematics SE site? – julian Feb 25 '17 at 1:49
• I'm voting to close this question as off-topic because this is a question of areas and weight calculations related to Mathematics. – 0xec Feb 25 '17 at 5:09
• Well this question has nothing to do with reverse engineering i assume this is your homework question so here are some hints split the shape into basics so it is 3 rectangles and 4 triangles compute the area multiply the ares by length gives you volume muliply the volume by density to get msss and answer it on your own – blabb Feb 25 '17 at 14:48
• But What about asking for it's length which is 12.5m while actually it is 12m? – Just Believe Feb 25 '17 at 17:00
• This question it's not about Reverse Engineering. – Igor Skochinsky Feb 25 '17 at 18:06

## 1 Answer

This is not a question of reverse engineering, but anyway this is how you can proceed.

Divide the cross-section into 5 parts - 3 rectangles and 2 trapezoids.

Area of rectangle and trapezoids can be calculated with their respective formulae. Multiply by the length (12.5m) to get the volume. The product of volume and density would give the mass.

Similarly, you can calculate the mass for the 4 steel wires.