safety factors
safety factors
(OP)
how many safety factors does an engineered problem include? by the time the calculation is done what really is the safety factor. from the material properties that the manufacture uses to provide a piece of wood at some safety factor to the last 1.5 factor at he end.





RE: safety factors
I guess we always assume that we accurately analyze it no matter whether we use an approximate or refined method. The engineer should be aware of this but I know of no code provision that gives any direction in this regard.
RE: safety factors
RE: safety factors
Wood is a strange beast as it is not a manufactured material in the engineering sense like steel and concrete are. In this respect, it is similar to soils.
Wood is also generally "graded" by visual means. This leads to (I would suspect) greater inherent uncertainty in the strength and performance properties of each member.
There is a code for designing with wood - the AFPA/AWC NDS. You should refer to this code and commentary to answer specific questions regarding methods of calculation for structural resistance to loads for wood elements.
The various structural design codes seek to provide a standard way of evaluating the resistance of structural elements to specified loading conditions. Additionally, each code may permit the use of differing (although similar) approaches, such as Allowable Stress Design (ASD) or Load and Resistance Factor Design (LRFD). Additionally, they present formulae for the evaluation of member capacity that are tractable using hand calculation methods, rather than using overly complicated computer-only relations that yield an "exact" answer.
Each design approach views the interaction of loads, load combinations, material properties, inherent errors in the analysis and resistances slightly differently. I suspect that there are good introductions available on the internet that describe the subtleties of each design approach and compare them with each other. I suggest that you spend some time to review this literature and come back with questions.
Jeff
RE: safety factors
RE: safety factors
Never, but never question engineer's judgement