I-Beam spanning conditions

[Striker]

After reading the scathing done in previous posts I am not sure I want to ask this question. There are some differences however in their posts and mine. This design will ultimately be approved and sealed by a PE, but, as many of you may know, a person does not want to have the PE giving you a call (or your boss for that matter) and telling you that you must have bumped your head if you think that is going to work! This way they will both think I am "The Man" for being able to get it right the first time.

Well enough rambling..... here is what I need

I am in need of adequately sizing a steel I-Beam for a spanning condition. The details are as follows:

Clear span = 21'-4"
Distributed Load = 40# LL 10# DL
Midpoint Point Load = 10# LL 5# DL
Single Loading 8' span

This is for a 7'-9" x 22'-6" porch on a second floor that will be attached to a house along the 22'-6" length on one side and be supported by (2) - 8x8 posts on either end on the other 22'-6" side. The point load is a single post at midspan supporting the center of a shed roof.

After giving it some thought and performing some basic mathematical calculations, preliminarily I suspect the beam will need to be a W10X16 or W8X24, but I am prepared to go up to a W12X21 if needed.

So please....no flaming.... I am just trying to get an idea from someone who may have either the tables, knowledge or program needed to either verify my calculations are correct

OR .....

Tell me I have bumped my head if I think that is going to work!

TIA

K

 

[burtonli]

the most important is whether you need to consider the stability in lateral direction or not.

 

[Striker]

No need to consider lateral stability, the porch is continuous on either end of the beam and there is enough horizontal bracing with sheathing and supporting structure that it does not present a problem.

 

[mrbridge]

I won't do your calcs for you, but I will offer some suggestions.
First, calculate the applied moments using the AISC beam diagrams and then determine the required section modulus Sx=M/fb. Look through the Sx table in the AISC ASD manual until you find the next highest value for Sx in bold. The bold values are the most economical sections.
Second, you say W8x24, W10x19(?), and W12x19(?) work. All have have similar properties. Since steel is bought by the pound, you would use the lightest section possible if height is not a problem. The best choice would be the W12x19.
Finally, I have a hard time believing that the roof support dead load is 5#. Please check the tributary area of the column.

 

[Striker]

Well, I finally just spec'd a W10X26 and said the heck with it... I was held to a max of 12" clearance for the beam so I decided to use the 10" instead.

To reflect upon your notes..

The 5# DL and 10# LL for the roof section at the midspan point load was to identify the presumed PSF load. The actual point load is around 1.2k

Anyway the point it moot since it has been reviewed and sealed by an engineer.

Thanks anyway..