David, I see there are a lot of design factors too consider- with
major ones to not get sued or get hurt Will try to keep that in
mind when applying theory to practice

Those pdf links are great! Thanks a lot.

Ross

On Sep 28, 5:53 pm, "David Merrill" wrote:
I trust that you will come to appreciate that credible structural analysis
consists of rather a lot more than plugging numbers into formulas and hoping
for the best.

For example:

- Measuring, calculating, guesstimating the loads and the uncertainty
thereof.

- Determining the interaction effect of multiple, simultaneous loads.

- Determining whether loads are constant (static) or fluctuating, and if
the latter,
characterizing that fluctuation numerically.

- Considering less obvious sources of loading (e.g. earthquake, snow
loads, steady
wind loads, wind gusts flowing fluid loads, people clambering on your
baby).

- Determining whether a 2D analysis is adequate to describe a 3D
situation
(or when nothing short of a valid finite element computer analysis is
required or
when the situation is so complicated that an established empirical
approach (e.g.
lugs)or outright experimental load testing of a prototype is called
for).

- Determining how loads distribute themselves among redundant structural
elements
(such as multiple fasteners).

- Determining all the possible modes of structural failure and which is
the critical one
(e.g. excessive deflection, non-linear deflection, permanent
deformation,
tension/compression/shear failures, ductile rupture, brittle fracture,
fatigue
cracking, stress-corrosion cracking, hydrogen embrittlement, creep,
elastic buckling,
elastic/plastic buckling, plastic buckling, delamination).

- Locating the appropriate properties for the material in the condition
pertaining to its
planned use (e.g. Tensile yield strength, in the direction of the
grain, of Southern
yellow pine, air dried, at a moisture content in equilibrium with its
worst-case
planned environment).

- Statistical variability and possible directionality of material
properties.

- Environmental degradation of material properties over time (e.g. wood
decay, sunlight
and atmospheric effects on PVC).

- Materials that behave as composites (e.g. concrete slabs with rebar).

- Estimating the effects of material imperfections (e.g. holes, knots,
notches, changes
in section thickness, corrosion penetration) and whether this is
relevant to the
critical failure mode.

- Understanding how joints and support points affect stress distributions
(and whether
that's relevant to the critical failure mode).

- Understanding the assumptions and simplification inherent in the
derivation of strength
formulas (even the most sophisticated analyses contain simplifying
assumptions, such
as, for example, linear material behavior) and recognizing situations
in which these
assumptions are simply not tenable.

- Considering how serious are the possible consequences of a structural
failure.

- Are there liability issues associated with structural failure (anbody
but you going
to go near it) ?

- Knowing when established codes or standards should be (or must be)
applied (e.g.
residential/commercial building codes, AISC structural steel design
codes, timber
design codes).

- Considering all the things that I forgot to mention in the absence of a
specific
design problem.

- Given all of the above, determining the appropriate factor of safety to
apply
Note: The appropriate FS arrived at logically by an engineer is often
much greater
than one the layman might choose and feel to be adequate.

All that said, some references a

Roark, Formulas for Stress and Strain

Baumeister & Marks, Standard Handbook for Mechanical Engineers

AISC Manual of Steel Construction (ASD)

http://www.fpl.fs.fed.us/documnts/fp.../fplgtr113.htm

http://trs.nis.nasa.gov/perl/search?...%2Freportno%2F...
%2Feditors=&authors%2Feditors_srchtype=ALL&year=&_ satisfyall=ALL&_order=byti
tle&_action_search=Search

http://www.knovel.com/knovel2/Toc.jsp?BookID=589

http://www.efunda.com/materials/mate.../materials.cfm

http://www.matweb.com/index.asp?ckck=1

http://www.knovel.com/knovel2/Toc.jsp?BookID=754

David Merrill

"djenyc" wrote in message

ups.com...

Hi, I'm doing some hobby level wood and metal fabrication projects
around house - shelving, boat cradle/ boat lift / trailer implements/
carts / work tables/ bike racks etc. I'm mostly using scrap material
that I happened to come buy...

I'm not a mechanical engineer, and have no idea what load/deflection
ratings are for different materials. I've been using 2x4, steel
tubbing, angle iron ... just found 20 ft of 2" pipe another day ...
Currently, when I'm designing stuff, I just rely on limited prior
experience and eye measure. Some things turn out to be overbuilt and
sometimes things fail under load (hopefully it's not critical and I
get a chance at redesign ). For example, I built a manual forklift
last week and it crumbled while testing/lifting my dad - now I know
where to strengthen it , but is where a better way?

Would it be worthwhile to look up load ratings of common materials
like steel pipe and 2x4? Where would I find such information? Or are
this calculations so complicated, that I'd be better off continuing
with what I'm doing?

snip...

Are there any good books for home-workshop design /plans making? -
just basic practical stuff that can be readily applied, not looking
for Mechanical Engineering intro course

Thanks a lot

Ross