×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Help with Unit Load Method for Gable Frame

Help with Unit Load Method for Gable Frame

(OP)
Hi guys,

Back again!

I am attempting to solve a pinned support gable frame using the unit load method.

I am using BeamGuru software, but I want to check the results to esure the program is working properly.

I have replaced the pinned supporta at A with a roller and it looks like this:

The height to eaves is 8 metres, the height to the apex is 9.58 metres. The frame is 30 metres long and the roof is at an angle of 6 degrees.

I have been using Octave to perform the integrations:

CODE -->

syms x E I
% Real structure
Mxr1 = (196.787*cosd(6) - 0.587*sind(6)).*x - 13.14.*x.^2/2 % left rafter
Mxr2 = (197.413*cosd(6) + 0.587*sind(6) - 1.174*sind(6)).*x + 9.392 - 13.14.*x.^2/2; % Right rafter
Mxc2 = -1.174*x  % right-hand column

% Virtual structure
mxr1 = -sind(6)*x + 8   % Left rafter
mxr2 = sind(6)*x + 8    % Right rafter
mxc2 = -x               % Right-hand column

% Integrations over excah member length for real and virtual structures
Ix1 = 1/(E*I)*int(Mxr1*mxr1,15.083,0)
Ix2 = 1/(E*I)*int(Mxr2*mxr2,15.083,0)
Ix3 = 1/(E*I)*int(Mxc2*mxc2,8,0)
ix1 = 1/(E*I)*int(mxr1.^2,15.083,0)
ix2 = 1/(E*I)*int(mxr2.^2,15.083,0)
ix3 = 1/(E*I)*int(mxc2.^2,8,0)

% calculate the horizontal reaction at A
HA = (Ix1+Ix2+Ix3)/(ix1+ix2+ix3) 

For HA, from these calculations I am getting 111.90 kN. The software is giving me 98.6 kN. So, Im a bit off. I think I could be getting mixed up with signs, but I have checked and checked, and cannot see why I am getting the incorrect result.

Many Thanks!

Replies continue below

RE: Help with Unit Load Method for Gable Frame

in your virtual model, should "8" be "8.79" (the average of the roof heights) ? ... 10% difference ??

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

RE: Help with Unit Load Method for Gable Frame

(OP)
I have always understood it that you take the moment at the start of the section, which is 8 kNm.

If you do this you get:

-sin(6)*x - 8

So, the moment at the end of the member (the apex) is:

-0.105*15.083 - 8 = -9.58 kNm ---> this is the moment at the apex.

RE: Help with Unit Load Method for Gable Frame

no, your moment is from the center of effort of the force ... you're replacing the distributed force with a point load, through the center of the distributed force, yes?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

RE: Help with Unit Load Method for Gable Frame

(OP)
-sin(6)*x - 8 is the general equation for the moment along the member. Plug in any x value and you will get the moment at that particular point.

RE: Help with Unit Load Method for Gable Frame

ok, what is "mxr1" ? sind(6)*x is the height about the lower edge, so "+8" is the height about ground. ok, but why "-" of the left and "+" on the right ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

RE: Help with Unit Load Method for Gable Frame

If you just want to check your program, you could use Kleinlogel Rigid Frame Formulas (see below).

RE: Help with Unit Load Method for Gable Frame

(OP)
Hi BAretired,

Thing is my frame has equivalent horizontal forces applied to it. Not just vertical loads.

RE: Help with Unit Load Method for Gable Frame

(OP)
Its okay now guys, I have sussed it. I wasn't including the virtual loads on the left-hand column. Because for the real structure the loads were zero for the left-hand column, it escaped me that there were indeed loads for the virtual.

RE: Help with Unit Load Method for Gable Frame

good on you for figuring it out. thx for closing the thread.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

(OP)
Thanks rb1957.

RE: Help with Unit Load Method for Gable Frame

Quote (Tygra 1983)

Hi BAretired,

Thing is my frame has equivalent horizontal forces applied to it. Not just vertical loads.
Gre

I too am pleased that you were able to resolve the problem on your own Tygra, but for those who may believe that Kleinlogel Rigid Frame Formulas deal exclusively with vertical loads, please be aware that the tables deal with any type of load, including horizontal loads. There are several pages associated with Frame 89, which I did not post.

Prior to the computer age, structural engineers regarded Kleinlogel as the go-to reference for rigid frame design.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!