Oh, I quite agree dnlv, (ASD) is most commonly used in serviceability limit analysis for deflection, vibration, clearances, etc. However, I selected strength based limits (LRFD) for the truss design and of course ASD and LRFD methods should not be mixed. Anyway, the frame analysis application...
Quite correct, hokie66, quite correct. The cap plate is a double 2x4 and the initial truss image was a composite of 3 trusses as shown below.
Also quite correct JAE, the deflections from dead load appear to only be around 1/3 of total LRFD load deflection. See table. The deflections were...
Shown below is an image of the truss that spans 4 walls. The 2 interior supports were evaluated 2 different ways. Initially the interior supports were set as pinned connections and after running an evaluation of the truss the results indicated that these supports produced horizontal forces of...
Hey rb1957
Thanks for the insight. Much appreciated.
Unfortunately, nodes 6 and 23 are not co-incident.
I wish I could add member 22-24 but that is not possible because member 23-24 defines a part of the pan ceiling.
Hey Ytyus
Excellent consideration. I had not thought that far ahead but your process is clear and quite reasonable and I will add it to the model when I get to the point of designing the bracing. Thanks for your insight.
Hey rb1957
Good points made in your last post. Just to obtain a better understanding, why do you consider the pin-pin connection creates an unreasonable reaction? Are you assuming that in field applications there is support movement thus not producing true pin-pin reaction? In the case I ran, I...
Hey rb1957
By adding a roller at the apex of the truss, rotated by 90 degrees, I was able to run the case where all supports were set to roller. I used a roller because I didn’t want to restrict any vertical node deflection. I felt there would be negligible horizontal deflection at the crest of...
Hey Koot,
On the second point, that was kind of the way I was leaning with respect to the diagonal members getting added to the truss in the field. Depending on when the member is added is an indication of the degree of lateral load it would transmit. If added right after the truss erection and...
Hey KootK, good to hear from you again.
Everything sounds good except I need a little more clarification on deflections. You had mentioned the conventional model would be one pinned end and one roller and yes that is what I had learned also. However, the deflection with that scenario is not...
The truss shown below sets on top of a 2”x4”x8’ wall with studs 16” OC; so the bottom chord is around 15’ off the ground and the truss supports are 8’ off the ground. The truss shown is one of a series of trusses set on 24” centers. The bearing wall is freestanding for 14’. Thus there are 7...
Hey KootK
Hahaha,… I’ll take that as an acknowledgement of my design creativity when faced with impossible constraints.
Yep, I get responses similar to that a lot; most problems are easily solved with traditional approaches; however, what everybody else gets to see are the difficult problems...
Hey BA
Got it. Thanks for your input, it was quite clear and I greatly appreciate it.
Hey KootK
Thanks very much for helping out.
I was trying to keep the question as simple as possible; but, perhaps I should present the entire truss for clarity sake.
Configuration for Analysis
Internal...
Correct, the plywood will extend over all nodes.
Agreed, the section, with plywood attached, will act as a single integrated unit. Under this premise I had considered evaluating this section, and all adjacent sections, as an “All Plywood Beam” under the provisions of APA Supplement 5-12 with the...
Hey Joel,
All loads are nodal loads and there are no middle-of-member loads.
All nodes are fixed joints in lieu of pinned joints; thus, transmitting moments.
Hey BA,
Yep, I am analyzing the truss structure as a frame.
Yep, it is a design problem.
Conceptually, the plywood plate will be glued...
Additional Information.
Beam 39 is just 1 beam of 18 beams which needs to be replaced. This beam was the first beam to consider when working from left to right.
On the side issue, with respect to beam 33, here are the loadings.
Beam 33
Node 2
-308 Lbs Tension; -198 Lbs Shear; -3138 In-Lbs...
Problem: Remove a 2”x4” Beam and replace with plywood.
Shown below is a section of truss I have been working on.
The problem is the spacing between the top and bottom chords is too small for a diagonal member. So I have elected to replace the diagonal member with plywood. I have the axial...
With respect to gravity induced torsion on a simple horizontal beam.
1. How does the force of gravity become eccentric to induce torsion?
2. Additionally, how significant is gravitational torsion with respect to a beams total load capacity?
Interesting that positive Y axis goes into the page instead of Z axis.
If you have a simple beam I don't understand how torsion is created in the beam from gravity. Can you explain this in a little more detail?
Can the following Generalization be made about shear force sign convention?
A shear force, when applied at one end of a beam, is considered positive if it would create an imaginary clockwise moment at the opposite end of the beam.
