Help with Structural Engineering Problem: Summation of Forces/Moments

In summary, the conversation is about finding the support reactions and internal forces in a structural problem. The participants discuss using the equations for summation of moments and forces to find the values of HA, HE, VA, and VE. There is confusion about the direction of the forces, but it is clarified that a force pointing towards a joint is in compression and a force pointing away is in tension.
  • #1
reyna12
5
0
Hi there, i hope someone can help me.

I am just unsure how to proceed with this problem.

Homework Statement



The question and diagram can be found in the attached image. I am looking for assistance on part (ii)

Homework Equations



1. Summation of Moment = 0
2. Summation of forces along x - axis = 0 ;
3. Summation of forces along y - axis = 0 ;

The Attempt at a Solution



Design Loads calculated as 142.36kN at Node C and 71.23kN at Node D using EQ (6.10)Thanks for your assistance.
 

Attachments

  • d79b817014ac8b9ebaaf23781d23d8f3.png
    d79b817014ac8b9ebaaf23781d23d8f3.png
    27.3 KB · Views: 449
Physics news on Phys.org
  • #2
Did you sum moments to find the support reactions at A and E in the horizontal direction? Is there a vertical force at E?
 
  • #3
Confused entirely in all honesty. I had attempted to but it's probably just meaningless scribbles.

+veƩM = 0 ... (HA×4)+(142.46×8)+(71.23×4) = 0
HA = -356.28kN

+ve→ƩFχ = 0 ... +(HA)+(HE)=0
HE = +356.28kN

+ve(vertical)ƩFy = 0 ... +(VA)+(VE)=0
+(VA)+(VE) = 213.69
VA = 213.69 - VE
 
  • #4
reyna12 said:
Confused entirely in all honesty.
Honesty is the best policy.
I had attempted to but it's probably just meaningless scribbles.
No-o .
+veƩM = 0 ... (HA×4)+(142.46×8)+(71.23×4) = 0
HA = -356.28kN
you mixed up the 4 with 8 and vice versa.
+ve→ƩFχ = 0 ... +(HA)+(HE)=0
HE = +356.28kN

+ve(vertical)ƩFy = 0 ... +(VA)+(VE)=0
+(VA)+(VE) = 213.69
VA = 213.69 - VE
Yes , but VE equals ? Use method of joints at E to find VE which is ?
 
  • #5
Ok i think I've figured it out?
 

Attachments

  • CAM00085.jpg
    CAM00085.jpg
    34.6 KB · Views: 426
  • #6
Yes, that looks good, but you need to convince yourself (if you haven't already) that the force is a compressive force and not a tensile force.
 
  • #7
PhanthomJay said:
Yes, that looks good, but you need to convince yourself (if you haven't already) that the force is a compressive force and not a tensile force.

That's what I'm struggling with, are you able to offer a quick explanation?
 
  • #8
reyna12 said:
That's what I'm struggling with, are you able to offer a quick explanation?
Well, OK. When you look at a free body diagram of forces acting on a joint, if the member force points toward the joint (that is, pushing toward the joint), it is in compression; if it points away from the joint (that is, pulling away from the joint), it is in tension.

The same applies if you are looking at internal forces at a cut section of a member (method of sections): if the force is pushing toward the member, it is compressive; if it is pulling away from the member, it is tensile.
 
  • Like
Likes 1 person

1. What is the difference between forces and moments in structural engineering?

Forces and moments are both important considerations in structural engineering, but they have distinct meanings. Forces are external loads or actions applied to a structure, such as weight, wind, or earthquake forces. Moments, on the other hand, refer to the tendency of a force to cause rotation around a specific point or axis. They are also known as torque. In simpler terms, forces push or pull on a structure, while moments twist or bend it.

2. How do you calculate the sum of forces and moments in a structural engineering problem?

To calculate the sum of forces, you must first identify all the external forces acting on the structure and their respective magnitudes and directions. Then, you can use vector addition to find the resultant force. To calculate the sum of moments, you must identify the point or axis around which the moments act and then use the principle of moments to sum the individual moments. This involves multiplying the magnitude of each force by its distance from the point or axis and summing the results.

3. How do you ensure that the sum of forces and moments is in equilibrium in a structural engineering problem?

In order for a structure to be stable and not collapse, the sum of forces and moments must be in equilibrium. This means that the total force acting on the structure must be zero, and the total moment must also be zero. To ensure equilibrium, you must carefully consider all external forces and moments acting on the structure and ensure that they are balanced and cancel each other out.

4. What are some common mistakes to avoid when solving a structural engineering problem involving summation of forces and moments?

One common mistake is to forget to include all external forces or moments in the calculations. It is important to carefully examine the structure and consider all possible forces and moments that may act on it. Another mistake is to use incorrect units in the calculations, which can lead to incorrect results. It is also important to double-check all calculations and ensure that they are accurate before proceeding with the design of the structure.

5. How can structural engineering software help with solving problems involving summation of forces and moments?

Structural engineering software can be a useful tool in solving problems involving summation of forces and moments. These programs can perform complex calculations quickly and accurately, saving time and reducing the likelihood of errors. They also have the ability to generate visual representations of the forces and moments acting on a structure, making it easier to analyze and understand the problem. However, it is important to use these tools with caution and always verify the results manually to ensure accuracy.

Similar threads

  • Engineering and Comp Sci Homework Help
Replies
3
Views
989
  • Engineering and Comp Sci Homework Help
Replies
2
Views
724
  • Engineering and Comp Sci Homework Help
Replies
1
Views
809
  • Engineering and Comp Sci Homework Help
Replies
1
Views
931
  • Engineering and Comp Sci Homework Help
Replies
2
Views
877
  • Engineering and Comp Sci Homework Help
Replies
2
Views
1K
  • Engineering and Comp Sci Homework Help
Replies
3
Views
1K
  • Engineering and Comp Sci Homework Help
Replies
1
Views
1K
  • Engineering and Comp Sci Homework Help
Replies
5
Views
1K
  • Engineering and Comp Sci Homework Help
Replies
5
Views
1K
Back
Top