# Steel rules of thumb

• To: <seaint(--nospam--at)seaint.org>
• Subject: Steel rules of thumb
• From: "Jason Kilgore" <jkilgore(--nospam--at)leok.com>
• Date: Wed, 27 Feb 2002 15:52:37 -0600
```Here are a couple of formulas I use to find required Ix and Sx of a
simply-supported uniformly loaded beam during preliminary calculations (it
uses ASD to find Sx, but it's easy for preliminary work, even for LRFD
designers - just substitue Zx).

Ix = wll * (L^3) * Delta / 15466
Zx/Sx = wtl * (L^2) / 20

For a typical floor load with max deflection = L/360 the first equation can
be shortened to:
Ix = wll * (L^3) / 43

wll = live uniform load in kips/ft.
wtl = total uniform load in kips/ft.
L = beam length in ft.
Delta = max deflection as a function of length (i.e. for max defl. = L/360,
Delta = 360)

Assumptions:
Fy = 50 ksi
E = 29,000 ksi
ASD at 60% stress

Example: Beam supporting masonry (max deflection = L/600), wtl = wll =
2.0klf, L = 25 ft.

Ix = 2.0*(25^3)*600/15466 = 1213 in^4 --- W24x55 <= Controls
Sx = 2.0*(25^2)/20 = 62.5 in^3  --- W16x40
Zx = 62.5 in^3  --- W18X35

-----
Jason Kilgore
Leigh & O'Kane, L.L.C.
(816) 444-3144
jkilgore(--nospam--at)leok.com

-----Original Message-----
Sent: Wednesday, February 27, 2002 3:03 PM
To: seaint(--nospam--at)seaint.org
Subject: Steel rules of thumb

>From: Daryl Richardson
>Subject: Re: Steel rules of thumb
>To: seaint(--nospam--at)seaint.org

>Charlie,

>	Here's a rule of thumb that's very handy for >quick
and dirty
>calculations for beam deflection.

>	Delta(max) = M*L^2/(10*E*I)

Daryl,
I've derived the same equation--it's very handy.  With
moment in foot-kips, span in feet, and deflection in
inches, and for a steel beam (E = 29,000 ksi), it ends
up:

Delta = M * L^2 / 161 I

A few more:

Working stress design of E70 fillet welds, allowable
load = 0.928 kips/inch per 1/16 inch of weld size
(e.g. a 3/16 fillet is 3 x 0.928 kips/inch).

Working stress concrete design (OK, all you new guys,
flame away): As = M / 1.76 d    (M in ft-k, d in
inches), or, far more accurately (good for

Per foot width,
As = ((M, ft-k)^1.04) x 11.84/(Fs (ksi) x d (inches))

(Charlie, don't put this one in MSC)

TKDA
St. Paul, Minnesota

__________________________________________________
Do You Yahoo!?
Yahoo! Greetings - Send FREE e-cards for every occasion!
http://greetings.yahoo.com

******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
*
*   This email was sent to you via Structural Engineers
*   Association of Southern California (SEAOSC) server. To
*   subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
*   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you
*   send to the list is public domain and may be re-posted
*   site at: http://www.seaint.org
******* ****** ****** ****** ******* ****** ****** ********

******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
*
*   This email was sent to you via Structural Engineers
*   Association of Southern California (SEAOSC) server. To
*   subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
*   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you
*   send to the list is public domain and may be re-posted