>Walter D. Graves wrote in message ...>>This demands correction.>>>>AlTrussGuy wrote in message <7td38d$es0$ >...>>>Built up beam, is this 3 - 2 X 12's spruce, pine, doug fir?>>>>>>LVL, Glue Lam, Steel question (from the steel capitol of the south)>>>>Not necessarily. If it did we would not use steel for anything.>Mr. Graves, Wood products can and do replace steel in Residential>aplications. The products have the consistancey, that framing lumber lack,>these products must be sizes.>>>>> The first thing a beam must do is carry it's own weight, the steel>will>>>sag under it's own weight if not sized for the span.>>>>So will any other material>Mr. Graves you attack a statement that said. a beam must carry , it doesn't>say steel beam, our wood, states beam (any beam)
If you are looking for more details, kindly visit i joist beam.
AlTrussGuy wrote in message <7ti83k$fg1$ >...
The statement says and I quote "the steel will sag under it's own weight if
not sized for the span". My statement is correct. So will any material if
not properly sized for the load.
>>
>
>>> Disadvantages, CUTTING, WELDING, HANDELING (back hoe knocks down
>>>basement walls), WEIGHT, STEEL SNAPS UNDERLOAD
>>
>>Not true. Steel deforms and is a very ductile material. It will undergo
>>significant strain before failure.
>Mr. Gray explain shear , as it applies to over loaded beams, please
>steel being ductile has what to do with my statement?
Steel does not "snap" under load. It strains significantly even before
going into a plastic state. From there it starts plastic deformation
(permanent) along with strain hardening. ASTM A36 steel (a very common
steel for I beams) has a yield strength of 36ksi. Minimum elongation at
yield is 20%. That is pretty doggone ductile. A brittle material
(non-ductile) would fail suddenly with little to no indication of overload.
Steel will yield significantly before this happens. My name is Mr. Graves,
however, since you asked for some information on shear, I will provide.
Since shear is not a normal failure mode for steel I beams (it is more
common in timber member), I fail to see what shear has to do with this
thread. A timber member overloaded in shear will tend to fail rapidly. In
actuality, timber fails by cascading splits down the center of the beam
starting at the high shear point, which reduces moment carrying capacity to
vitually nothing and down it comes. It is very sudden if a shear failure
occurs. The reason for this failure mechanism is timber is not an
isoptropic material. The strength along the grain is much less then accross
the grain. However, using simple strength of materials concepts it can be
shown that the maximum shear will be at the center of the beam and will go
both against and with the grain in equal magnitude (a small element at the
center of the beam must be in rotational equilibrium, this mandates the
shear along the grain to equal the shear across the grain). Thus, shear
impacts timbers weakest feature (splitting along the grain). After a split
occurs, the strength is significantly reduced and a second split rapidly
develops. Typically the split will start at the high shear point and result
in a failure at the nearest knot, connection, or notch. Steel on the other
hand is isoptropic. Shear failures are hard to produce in steel (web
crippling or web buckling usually occur first. In fires, steel beams do not
nornally fail in shear. They fail due to a bending moment. Columns fail
due to buckling (which is a bending phenomenon associated with pdelta
effects after a minute deflection or destablization). Steel is shear is far
superior to timber performance. In bending it is at least equal. It has a
far superior strength to weight ratio.
I would like to know what your structural engineering credentials are. I am
a registered Professional Engineer, I majored in structural engineering
summa cum laude from the Ohio State Univeristy. I have designed several
structures, both timber and steel and am well versed on both the AISC codes
(steel) and NDS codes (timber). Of course, like any good civil engineer, I
also am well versed in ACI codes and pavement design.
>>
>>> , (Wood sags)
>The nature of wood fiber is IMHO much more likly to move, give, change
>shape, show signs of overloaded long before steel , The steel will handle
>much more ? so when steel being more brittle does give up , wouldn't it
>follow that these reactions would be more damaging.
Not true. Steel beams will show signs and has, depending on the grade of
steel selected, more elongation before catostrophic failure. This includes
tension members. In tension timber will provide almost no warning before
failure. Steel will elongate quite a bit, but you may still not see it in
time (example is the Hyatt Regency walkway disaster). However, we are
talking beams. That steel will handle much more per unit weight is a fact.
It has an extremely high strength to weight ratio. However, it used to cost
so much more than timber that one used timber primarily for economics, not
structural reasons. Steel is not a brittle material. Cast iron is, but not
steel. Wood is forgiving, but that is not because it is a superior
material, quite the contrary, it is because we have to use a large factor of
safety when working with it due to its non-homogeneous nature (knots,
splits, checks, etc).
>>
>>Yes. It also will deform permanently under continous load (develop a
>>memory) and when unloaded will not return to its original state. Steel
>will
>>return to its original state provided you have not exceeded the yield
>point.
>>A properly designed steel beam will be operating below its yeild point if
>>either Allowable Stress Design or Load Resistance Factored Design is used
>to
>>size the beam.
>
>So will the wood under the same conditions.
Not true. Timber develops a memory if subjected to a sustained load. It is
an unusual creep strain whose mechanism is not yet fully understood, but has
been computed and added to the design guidance. Try reading the NDS.
>Residential loading does not
>require, steel for many, many, application.
True. Almost most residential construction in the US and Canada uses
timber. If I built a house today it would use mostly timber. I might have
a steel member here or there, but timber is still economically more
attractive (barely) and you don't have to be an iron worker to work with it.
>Stress design, uniform load,
>point loads, side loading, top loading, cantilevers, Mr. Graves your attack
>on wood products seems un called for these product work and are being used
>every day.
Of course, and so is steel. I don't attack timber. I design with it as
well. I do counter attributing advantages and disadvantages to steel that
are not accurate. Steel is a good material and so is timber. Steel's major
drawback in residential construction is still cost (with the exception of
light gage metal studs which are now very close to wood studs in cost
including installation). As an engineer, my selection of material is based
on structural requirements (sustaining the loads), architectural
considerations (will it fit and how will it look), economics (what is the
most bang for the buck), and life safety code (what kind of fire rating do I
need). Thus in some applications I use timber, some use steel, and some use
concrete. However, steel is a very versatile material and is not brittle.
It is more difficult for the average homeowner to deal with when it comes to
installation and modifications. Most homeowners can swing a hammer, but
very few can use a welder.
>>
>>
>>>Steel is as
>>>good as the poorest weakest weld.
>>
>>And timber is as good as its weakest connection. Timber also is subject
to
>>weakened areas due to rot, knots, splits, checks, termites, etc
>Steel rust, bust, bends, corrodes, and flakes.
rust--yes but not when used within the building envelope. At least not in
any significant amount.
busts--not if designed properly
bends--not if designed properly
corrodes--corrosion on steel is rust so answer is the same
flakes--flaking is rust so answer is the same
>please roll out your purfect
>construction material.
There is none. All have good points and bad. You will note that I did not
disagree with some of the drawbacks you attributed to steel. I do take
exception to calling it a brittle material. Structural steels are not
brittle. Or saying that connections make steel a bad material. In any
material, connections are almost always your weakest link and the MOST
common location for a failure.
>excuse me, steel will remain prestine under the
>conditions which cause problems with wood.
Maybe in heaven steel will remain prestine, but not here. It is pretty much
safe from termites, but steel will often outlive timber in hostile
environments with the noted exception of salt air. The salt will
dramatically increase the corrosion rate.
>>
>>>condensation (wet dripping) attaching wood
>No responce to condesation dripping from steel and the problems associated
>which mixed medi............
Condensation will not be a problem unless the member is used as a portion of
the building envelope. Even then, proper vapor barriers and insulation
prevent this problem. Attaching wood to steel is not a problem. I have
done it in several times.
>
>>>to steel (Joist, hangers) expansion rate, wood moves steel doesn't (as
>>fast)
>>
>>If you did it right, you attached a nailer to the steel and the wood to
the
>>nailer. This will almost eliminate squeaks.
>Mr. Graves please explain this attachment, is the wood bolted to the flange
>for a drop girder. should the wood be attached to the web on each side, so
>the joist can be cut to fit, and the top flange be scabbed over to support
>decking. The bait to almost eliminate squeaks will be passed,
Want more information on door skin plywood? Feel free to contact us.
The nailer is attached to the flange using a Hilti drill or powder actuated
fasteners. (Yes, you can blow a fastener into ASTM A36 steel. I have seen
it done many many times.) You may need to go out and watch some structural
steel go up some time. Take close notes on how non structural members are
tied in. You will learn a great deal. Fastening timber to steel is not
difficult. However, Joe homeowner does not own the equipment for it. Some
carpenters do. Most iron workers do.
>>
>>>floor squeeks. alittle time I'm sure there are more other than fire.
>>>BUILDER COST DEPENDS ON WHERE THE STEEL COMES FROM. His labor cost is
more
>>>to install steel period.
>
>No comment, I will assume that this statement is correct in your eyes then.
Yes.
>>>
>>>YOU WANT 2 COLUMNS, tell me about your house and I'll size the
>>LVL..........
>>>I joist must be sized also, based on span, load, deflection, and spacing.
>>
>>Unless you are an engineer and licensed to practice in his state, you may
>be making a very bad move.
>That is true, the product selection question should be handled through
>education,
>
> How familiar are you with the theory behind the
>>charts?
>I am very familiar with the theory behind the charts.
>
> How do you know when the charts are applicable or not? Unless you
>>are familiar with the theory and constraints of the design guides or model
>>building codes, you really are not qualified for using them to design
with.
>>Otherwise you could easily be applying a formula or using a chart that is
>>not valid for the situation.
>
>YOU ARE ABSOLUTLY CORRECT, which is why I said, " tell me about your
house",
>while I offer to help sovle a product selection question, you as a PE have
>made severial confussing statements. The home owner would not hire a PE to
>size the products, the PE will not expose himself to select new materials.
Says who? I am a PE and I use new materials. I research them first, but I
do use them when they make sense.
>The construction industry continues to old tried and true methods.
This is primarily driven by the labor market. A new material generally
requires different skills to install and these skills may not be available
in the market. As the labor market changes so do materials. Engineers are
not opposed to new materials, however, emerging new materials usually are
not economically attractive. Try convincing an owner he/she should spend an
extra 10-20% to use this new product when an existing product can meet there
need. A very difficult sale. If you are designing a turn key project, then
you will lose the bid.
>The
>manufacturies carry product insurance for years until new PE's can replace
>the old ones.
Are we talking steel, timber, and concrete? These are not new. Moving back
and forth between steel and timber is not new. Nor is the current moving
back and forth between steel and concrete in commercial construction new.
It is simply driven by economics. Insurance really has nothing to do with
these moves. An example of emerging construction materials is the
introduction of plastics into the construction as structural members.
Introductions of plastics as structural members is occuring slowly. Again,
this is not necessarily due to insurance. My insurance company does not
review my design work nor do they forbid me to use "new" technology. I have
concerns on plastics mostly based on engineering principles (effects of UV,
flame spread, toxic gasses when burning), that make me leary of using it
until I feel confortable as an engineer that I will not put someone in harms
way. I don't even consider my "insurance" or "liability" in that decision.
I could not sleep at night if I knowingly put someone in harms way. They
trust me to design a safe structure for them and I have made a commitment to
do just that. My decisions are based on protecting the interests of my
client, especially when it comes to life safety.
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