Bending of Beams

  • Thread starter dvep
  • Start date
  • #1
43
0

Homework Statement



Calculate the reaction forces at B and D

See attached jpeg.

The Attempt at a Solution



sum of vertical forces

By + Dy = 7 + (9*5)

Do I then solve for the moment about D or A or B?

for moment about D i have: -Dy -7 -(9*5)+9By+(12*2)=0

is this correct, please explain to me the process of and how I should go about these problems

Any advice is appreciated, thankyou.
 

Attachments

  • fig.jpg
    fig.jpg
    13.5 KB · Views: 358
Last edited:

Answers and Replies

  • #2
SteamKing
Staff Emeritus
Science Advisor
Homework Helper
12,798
1,670
The moment equation you have written is incorrect. For example, what is the moment of the 7 kN force about D? Remember, the sign of the moment is important. The moment of the distributed load is also incorrect. I don't know why you are multiplying the applied moment of 12 kNm by 2.
 
  • #3
43
0
The moment equation you have written is incorrect. For example, what is the moment of the 7 kN force about D? Remember, the sign of the moment is important. The moment of the distributed load is also incorrect. I don't know why you are multiplying the applied moment of 12 kNm by 2.

When the moment is clockwise to the left of the point it is positive?

moment about D:

9By +12 - (9*5*2.5) -(7*4) = 0

Is that correct now?
 
  • #4
SteamKing
Staff Emeritus
Science Advisor
Homework Helper
12,798
1,670
On the moment of the distributed load, remember the center of the load must be taken about point D. Check your moment arm.
 
  • #5
43
0
On the moment of the distributed load, remember the center of the load must be taken about point D. Check your moment arm.


9By +12 - (9*5*6.5) -(7*4) = 0

By= 34.28

I'm am still a bit unclear on the moments when they are positive and negative, is what I said before correct, when they are to the left of the point and clockwise , they are positive?
 
  • #6
SteamKing
Staff Emeritus
Science Advisor
Homework Helper
12,798
1,670
The convention chosen doesn't matter, as long as it is consistently applied. I use the convention where the horizontal direction is positive to the right, vertical is positive upward, and the counterclockwise moment about the origin is positive. This is a right-hand system, and it is used later on in other areas of physics.
 

Related Threads on Bending of Beams

  • Last Post
Replies
8
Views
11K
  • Last Post
Replies
6
Views
3K
Replies
8
Views
2K
Replies
0
Views
3K
Replies
2
Views
4K
Replies
0
Views
2K
Replies
3
Views
1K
Replies
5
Views
2K
Replies
1
Views
164
  • Last Post
Replies
1
Views
7K
Top