Joist/beam live, dead, dynamic loads question

[Pico]

I understand that a basic structure, like a deck or a house, is designed according to the following:
1. Dead load - the weight of the structure itself
2. Live load - the "users" of a structure, the people and furniture on a deck for instance
3. Joist deflection - Expressed as a ratio, and as I understand it, either 1/360 or 1/480 is typically used. Meaning a 30 foot span (360 inch) would result in a 1 inch deflection. Under what loads is this deflection calculated?

Are dynamic loads usually engineered in structures like our mythical deck? I guess this would be wind and earthquakes? What else is considered a "dynamic load"?  Snow?

What load safety factors are used to design stuff like this? I know bridges usually use a safety factor of 2 or 3, and utility category aircraft have a safety factor of 1.5. Is there a safety factor computed when designing our example deck, or is the live load computation fairly close to the ultimate strength of the deck/structure?

What about joist shear strength? All I have ever heard discussed is deflection, but surely the shear forces at the ends of the joists must be considered?

By the way, I'm not trying to design anything, just curious

[conohawk]

Funny you should be asking these questions.  I also want to learn more about this topic.    Googling didn't really provide satisfactory hits, so I did a book search.

This arrived from Amazon, yesterday:

     Basic Lumber Engineering for Builders

http://www.amazon.com/exec/obidos/tg/detail/-/1572180420/002-1087877-1364859?%5Fencoding=UTF8&v=glance

I can tell you that, from my brief scan of the text, your questions are answered.

Also, a Windows (16 bit) program is included that will calculate basic beam and column loading.  Works on Windows 95, not sure about Windows 98.  

[John Raabe]

I have this book and have installed the program on an XP system. It is valuable for calculating beams, joists and posts for estimation purposes.

It is designed for a much earlier Windows environment so you need to be a bit more nerdy to find things like the shortcut to start the program.

All of these calculations are for static loads - downward. Snow loads are static loads but of shorter term duration.

Dynamic loads are wind and earthquake - sidewards or upward. These require more sophisticated engineering and and involve things like racking resistance and shear panels.

This is why houses designed in areas where such things are possible can be required to have a local engineering review.

Most plan checkers will have a program like the one above to check beams and joists. They will not be able to do the lateral loading calculations and will refer you to an engineer unless the home is designed to meet the prescriptive wall bracing requirements.

[Daddymem]

If you want to explore these subject further, they are called Statics and Dynamics in engineering terms.  Statics deals with things standing still, Dynamics deals with things moving.  Sometimes they are combined and called Mechanics of materials.  Basically these subjects are like what is studied in physics 101 on steroids.  Trust me when I say things can get really complicated.  Here are some tools that you can play around with:
http://www.engapplets.vt.edu/
 

[conohawk]

I have this book and have installed the program on an XP system. It is valuable for calculating beams, joists and posts for estimation purposes...

An updated version of the software is available here:

http://www.northbridgesoftware.com/wbs.html


Price is $125.00.

Basic Mode:


"Professional" Mode:

[conohawk]

...Here are some tools that you can play around with:
http://www.engapplets.vt.edu/

I appreciate their making the Java source code available, too.
Thanks for the link.

[Ryan B]

This also might be of interest
Engineering for Beginners Parts 1-5
Around page 14 - early January posts

http://countryplans.com/cgi-bin/yabb/YaBB.cgi?board=01;action=messageindex;start=260

Ryan B

[Pico]

Thanks for the replies.  In addition to the book mentioned, I found this one at the local Barnes&Noble, and it seems quite good:
http://www.amazon.com/exec/obidos/tg/detail/-/0963226886/ref=wl_it_dp/002-1610779-5688800?%5Fencoding=UTF8&coliid=I36WQ36DC5J0A6&v=glance&colid=2SAKT2H0PE8FR

[John Raabe]

Just ordered this. I'll post a report. JLC generally does a very good job on such projects.

PS - Also ordered Malcolm Gladwell's "Blink" - got tired of waiting for the library to buy it.