Bottom Flange Bearing on Steel Beam? 2

[JMHdesigns]

I have a situation where a residential framer has connected 16'-0" 2x10 SPF #2 Floor Joists @ 16" o.c. on both sides of a W10x26 A-992/50 I-Beam bearing on the W10x26 BOTTOM FLANGE ONLY. The 2x10's butt up to the I-Beams vertical web. My strucual engineering software will not calulate this unorthodox loading. I believe additional connection details will have to be made. Any advice would be greatly appreciated.

 

[Lutfi]

Before I give my response, how did you post the picture here? I have been wondering for long time if this is possible. I would appreciate your input on that.

I have few comments regarding the design:

1. How are the ends of the 2X10 connected? Are they just sitting on the flange and the OSB?

2. Why do you call this unorthodox loading? It is no different from the steel beam being loaded on the top flange?

3. Why are you using software to design on this? You can if the steel beam is simple span, run simple wl^2/8 and get the beindgi moment and check on flexure (S req'd = Mactual*12/Fb) and make sure Sx provided is larger than the S required.

4. From stability point of view, I am more concerned about the end connections of the 2X10s

Simpson strong tie makes joist hangers that work with steel wide flange beams. I suggest that you use them or at least check them out. I can think of HHB type connector. Here is a link to their web site with section and load carrying capacities:

http://www.strongtie.com/products/connectors/JB-LB-B-HB-HHB.html

Good luck

 

[MotoGP]

AMEN, "Lutfi"...

Nice post and five gold stars for the graphic...how DID you accomplish this?

 

[JMHdesigns]

Thanks for the quick response.

I am not an engineer. I came to this forum for some professional help. I am an AIBD professional member who mostly designs custom homes.

I use Strucalc 6.0 to design simple beams, rafters, etc.

Your mathematical solution is way over my head.

I am not comfortable with this type of bearing condition. Is it okay to bear on the bottom flange? I have never seen a floor joists bear on a w-beam's bottom flange like this before. The 2x10's are simply bearing on the flange with no other connection. Just like the graphic shows.

Now...as far as how to upload a graphic/image...

1st, you need an HTTP address so the forum can get the graphic/image.

2nd, once you have your image uploaded at an IP address, you type the following into the thread;

 

[JMHdesigns]

Here is an actual photograph of the situation....

 

[SlideRuleEra]

Along their length, it looks like the joists are "wedged" firmly into the beam. If this is true, blocking, probably 2x8s, between all the joists and the end walls sould keep everything stable. In other words, completely cover both sides of the steel beam web with 2x8s.

 

[UcfSE]

The only thing that comes to mind is that the top flange of the steel beam may not be considered braced at every joist location, so its unbraced length might be pretty long. I can't say if it works or not of course, but other than that I see no problems with the detail except adding some blocking like SlideRule said. A longer unbraced length isn't a problem either as long as it's been accounted for.


Nice job posting pics *thumbs up*

 

[Lutfi]

SlideRule, I agree with you and with UcfSE as well. on similar details, I used to attach a 2X nailer flat on the fop flange and bolt it with 1/2 inch diameter bolts in staggered manner.

It is perfectly acceptable to bear on the bottom or top flange and the wb as well. As long as the load is transffered to the beam. You need to keep the joist ends as close to the web as you can to reduce the eccentricity (torsion). You need to meet stability requriements as well for the steel beam (the unbreaced length) and the joists as well.

I would add some blocking between joist ends, as SlideRule stated. I cannot tell if you have any bridging between the joists along their span either. Ouch, I am not sure if that meets code. I think the top of the joists are braced by the flooring. However, the bottoms are not.

Thanks for the hint. I am sure as engineers; we can do much better sketching than writing.

Regards,


Lutfi

http://www.cdeco.com

 

[JMHdesigns]

Isn't it normally considered to load the I-Beam from it's top, transferring the loads through the web? If just the bottom flange (which is only 0.440" thick) is loaded, what is to keep the flange from separating from the web? Wouldn't the I-Beam have to be calculated with just the load applied to it's bottom flange?

 

[PSlem]

The force required to shear off the bottom flange is about 5000# per inch depending on web thickness, so not a concern here.

 

[Lutfi]

JMHdesign,

This is why I said above that you need to consider torsion. In ideal situations, the load would be applied directly through the shear center as you have drawn. However, in real life that is not possible all the time. Even if steel beams frame into the W10X26 webs, they still have eccentricities that would cause torsion (or biaxial bending). Most engineers ignore these moments if they are too small. However, they can creep up on you can be cause significant stress increases. In my practice I avoid torsion as much as I can by preventing it.

Regarding your question about what keeps the flange from separating from the web, well good observation. You need to consider your loads and make sure this does not happen. The code dictates how much stress you are allowed on steel beam and they leave enough margins that is called safety factor.

The flange to web zone will see the following loads/stresses:

1. Direct vertical shear
2. flexural stress due to bending moment from 2X10 bending moment
3. Torsional stress if one side exerts higher load than the other side

You need to combine the effects of the above stresses and determine there maximum stress in the zone/area.

This application is not unique to your situations. I have designed many overhead cranes and monorails. The trolley wheels travel on the beam flanges and load them in identical manner as yours are loaded. You need to keep the actual stresses at or below the code allowable stresses. As n engineer, I have made judgment call in the past where I exceeded the allowable stress by as much as 10%. I did that based on the following:

1. My computed loads are based on theoretical maximum loads.
2. I had knowledge in real life that the probability of reaching/achieving these maximum loads is highly unlikely.

Now I like to comments about your use of software:

1. Be careful using software. You need to understand how it works, its accuracy and most impotently you need to know the governing codes. You also need to be able to interpret the input and output parameters. I can give you simple example regarding unbraced length of the members that you have in your example (steel and 2X10). What did you use? On the 2X10 did you use repetitive member use? When modeling the W10X26, did you load it uniformly or place the 2X10 end reactions as point loads? Did you assume that the W10X26 full length was unsupported? All of these assumptions and conditions will give you various results.

I hope since you stated that you are no an engineer that you do not offer your cal cautions for real life use!

Regards


Lutfi

http://www.cdeco.com

 

[haynewp]

I would look around the room to find the minimum bearing length the joists have onto the beam flange. Some joists may be shorter than others (1" etc), you may only have about 2" of bearing at most anyway. Expect the joists to shrink a little too. I would calculate the required bearing for wood compression, it shouldn't be that much for this case. Then compare this to the lengths you actually have.

It just looks cheap, I think a lot of people would notice when inspecting the house to purchase. I would suggest to the framer not to do it again.

 

[TTK]

I don't want to rain on an otherwise pleasant post but....

I do have concerns about AIBD professionals straying too far beyond their abilities into the proper realm of structural engineers. I have no problem with building designers using the very prescriptive residential building codes to properly size simple beam elements using the span tables.

Using structural design software to go beyond these span tables without the proper engineering background is dangerous to say the least, and when done for commercial purposes likely violates local laws.

I will let others form their own opinion, but you may want to check out the following website and click on the "engineering" heading:

http://www.jmhdesigns.org

 

[JMHdesigns]

TTK,

Out of all design professions, I respect the PE the most. I have never and will never claim to have more experience than I have. My web site under "engineering" clearly states that I work with local PE's who will seal my drawings when required.

In fact, I have been in the roof and floor truss industry since 1980 using Alpine engineering software, Mitek engineering software, and many others. I am well aware of building code requirements and design loads.

Calculating simple PLF and Point loads are well inside my experience and comfort zone. Using structural engineering software such as Strucalc is certainly within my understanding of simple load calcs.

I do not design commercial projects. Too many headaches for me!

I appreciate your concerns and again, I hold all PE's at the highest level of my respect.

By the way, this thread in particular indicates that I did not “stray too far” from my design knowledge and capabilities. Of course, that is my opinion...

 

[JAE]

TTK - in a lot of states, a PE is not required for residential projects under a certain sf threshold - such as 5000 sf. This is just to respond to the legal issue you raise, of course.

I've seen this detail on a number of houses before, nothing new here. The two big issues, in my mind are:

1. The wood is not directly connected to the wide flange so there is the potential for the joist to pull off the beam. This could be caused by foundation movement at the other end of the wood joist, or by seismic events. A strap across the top of the joists would be preferred....but I notice that the floor sheathing above has already been placed....perhaps this sheathing takes care of this concern.

2. Blocking between the joists are a good idea to keep the bottom of the joist from working sideways.

 

[TTK]

JMH,

From your website it looks as though you have built a respectable business designing custom residential homes and I applaud you for that.

It is also encouraging to see that you took the time and effort to get AIBD certification, which far too few building designers have.

I don't doubt your knowledge of the building codes, you have 20+ years in the manufactured truss industry, and you are obviously proficient in several software programs. In addition, you probably have more practical design knowledge of residential structures than most newly licensed structural engineers.

Having said all of the above, I also believe that there is an appropriate place in every structure (residential or commercial) to draw the line between where a designer should stop and a structural engineer should start. This line should not vary depending on the personal preference or astuteness of a local building code official, and should be respected by all professions involved in the design and construction of structures.

As I said an my earlier post, I have no problem with building designers using the span tables out of the residential building codes to properly size simple joists, headers or other common beam elements that are covered in these prescriptive codes. That is exactly why these tables exist.

I do believe there are several components of residential structures that should be designed and sealed by a licensed structural engineer. A few that come to mind are:

1. All truss systems (floor or roof). Manufactured systems are typically sealed by the manufacturer, but site-built trusses should be designed and sealed by a licensed structural engineer.

2. Slender (i.e. steel) beam or column elements.

3. Special connection details that are not specifically addressed in the building code.

4. Site specific design elements (i.e. special high wind or seismic design zones)


Your website has a good explanation of the services that licensed surveyors should provide for site plans and I would expect the same treatment for structural engineers. Instead of showing images of sample engineering stamps, why not provide a description of the licensed individuals that you contract with to complete specialty structural designs?

Using the phrase “JMH Designs has registered professional engineering associates…” has probably crossed the line in advertising your company as an engineering organization. I don’t know the corporate licensing laws in Maryland, but this would cause a problem for you in my area of the country.

And it is not really necessary for you to promote your business this way. You have a great residential design business and you should easily be able to affiliate your company with a reputable engineering organization. This approach may cost you a portion of your current design fees on occasion but it could also open up a whole new market sector for you by building a relationship with a structural engineer who is qualified to do much more than just simple truss of steel beam designs. How about cable supported structures, post tensioned structural elements, cantilevered beams or complex frame systems?

One last comment on your original post is the lateral stability of steel beam in question. IMHO, I would like to see this detail improved by adding positive connection to the beam and full height blocking to better brace the top compression flange.

Best wishes for a safe and pleasant holiday season, and for a successful business in 2005.

Regards,

Tom Kendrick, P.E. (CT, NH, ME)

 

[UcfSE]

Though I agree with TTK in principle, I don't really see a problem specific to JMH's question about the detail. I dare say that many track and custom homes, even here in high-wind hurricane regions, are "designed" and signed and sealed by architects with less structural background and knowledge than this man appears to have. Worse than that there are plenty of "plan stampers" out there who will sign anything. I do think it's good that he recognizes his limitations and asks for help with something beyond those, whether it's advice from us or from his own engineer(s). JAE has a very good point that professional engineers aren't required for most residential applications. As long as the numbers work out for the beam with the proper design assumptions, it doesn't appear that anyone here thinks the detail is a poor one, and just made some suggestions to help him out. Other than little details mentioned by myself and by others, looking at this doesn't through up any red flags, so to speak.

 

[jheidt2543]

Regarding the beam/joist detail, as long as there is a positive connection between the steel beam and wood joist I see no problems with the detail itself. I've see and used bottom flange loading many times to save on headroom. This detail is VERY prevalent in the precast concrete industry where flat plank are set on the bottom flange.

I do question the fact that there is no bridging shown in the photos for the wood joist, it is surely required on a 16' span. The use of Simpson connectors or solid blocking between the joist at the flange bearing should be required. I detail I like better is to thru bolt a plank on each side of the beam, then use regular joist hangers to attach the joist to the beam.