Mullions Section properties 1

[sutki1]

Hi All,

I am working on a project with aluminum mulions. How does one get the section properties of the mullions. What is the typical way?
Especially if you need the torsional constant.

Thank you,

 

[UcfSE]

Mechanics of Materials.

 

[par060]

Typically the mullion manufacturer will supply you with all the section properties of the individual parts they supply...usually all you have to do is ask

 

[RARWOOD]

In the early 80's when I worked in Texas, certified calculatins were required for curtain wall. At that time I performed a lot of calculations on aluminum mullions.

Normally what would happen is that the supplier would provided me with the mullion profile and the shop drawings. I would then use mechanics of materials ( Parallel Axis Theorem ), to determine the centroid, moment of inertia and the section modulas.

Today with CAD and other programs the manufacturers may already have that information as par060 indicated. However in the early 80's I would just do a hand sketch of the individual elements of the mullion calculate their properties and determine the properties of the total section.

In most cases to get the mullion to check, I had to included every small part of the mullion.

 

[sutki1]

I can calculate the radius of gyrationa and Moment of inertia and area using MASSPROP in AutoCad. The new code uses the value J, Torsional constant. How do I get that?

 

[DaveVikingPE]

What is the shape of the mullion?

Are you doing a complex blast analysis on windows and window frames?

 

[UcfSE]

Calculating section properties is basic structural engineering. You need to find a book and study a little. Timoshenko and Gere have a good mechanics of materials text, and Boresi and Schmidt have a good advanced text.

 

[apsix]

As said above it's all basic engineering which I expect would be covered by most, if not all, structural engineering degree courses.
A google could well find the required information for you, it's what I use if I don't have the relevant books with me. Of course, verifying the accuracy from 2 different sources is always a good idea when using the internet.

 

[pba]

Agreed - Section properties are covered by most degree level texts.

The extruders do usually have basic section properties all worked out. The trick is to speak to the right person as the extruders or the system manfacturers are not likely to have the right background to understand your requirements.

Also get confirmation on the alloy used as we have encountered so very strange metal being used for basic extrusions.

 

[sutki1]

Hello All,

Thanks for your replies.
I guess phrased my question incorrectly.
I know how to calculate the properties of a section. What I am looking for is an efficient and quick way to calculate J. The mullion sections are highly complex (

http://www.vistawall.com./details/fastnav/fastnav_frames.htm

u can download from this website) as RARSWC wrote one has to included every small part of the mullion. I am dealing with a variety of sections.
It is time consuming and inefficient to hand calc the J(torsional constant). A worksheet wont work as each section is unique.

I am not doing Blast analysis, however I have to include windload. The new code has included the J in one of the equations to get the allowable stress.
The values of area, moment of inertia, radius of gyration can be calculated for these complex sections in matter of seconds usinf AutoCad, it is the J, "torsional constant" I am have problems with.

THe manufactures donot have the values for J, they can provide with the Ix and Iy which is easier to calcuate using AutoCad
What I really am looking for is a program that calculates J for non conventioananl sections, or if AUtoCad has a LISP developed that covers J.

 

[RARWOOD]

sutki1

I pulled out several of my college text books including one called "Advanced Strength and Applied Elasticity". When I saw all the intergral symbols I started getting a headache.

I now understand how complex of a problem that you are trying to solve.

From your experience it is clear that you understand that most of the time if you just consider the most simple shape of the mullion the wind stress will never check. I wonder if the samething would be ture if you base the J constant on the main elements.

I wonder if you would have more luck posting your question on a mechanical forum which is part of this website. I go to the mechanical forum once in a while and have learned quiet a bit. I think mechanical engineers deal with the properties of more complex shapes on a regular basis. After all for us structural engineers in you need the J constant of a wide flange you just look in the steel book.

 

[haynewp]

It's not that hard to get J. I just did it for an angle section and verified it with CFS.

http://www.rsgsoftware.com/

Don't confuse J with polar moment of inertia.

 

[par060]

It has been awhile since I have done mullion design but I believe in the Aluminum design manual from the Aluminum Association (2000) there is a section that gives an approximation for J that can be used......see section 3.4.14 of the comentary