土木工程文章英译汉To give you some insight into the design cycle,an e
土木工程文章英译汉
To give you some insight into the design cycle,an extremely simple member will be dealt with first..That member is a prismatic bar with a force,P,acting along its longitudinal axis in the direction such that it tends to elongate the bar.Such a force is referred to as an axial tensile load,and we can readily imagine it trying to pull the fibers apart and to cause failure on a transverse plane.It is safe to assume that all fibers of the bar,in regions remote from the point of application of the load ,are being pulled apart with the same load intensity.With this assumption,the load intensity or stress is uniform on a transverse plane and is given by
= (4-1)
When P is in Newtons and A is in square metres,stress,,is in Newtons per square metre ( N/rn2 ) ,which is by definition Pascals( Pa).
For a given axial load and given dimensions,the stress can be calculated from( 4-1 ) and compared with the stress that can be safely carried by the material ...The safe stress,known as the design stress or allowable stress,is determined by tests performed on material made to the same specifications as the part being considered.A safety factor,frequently imposed by a legally established code,is applied to the strength,as determined by tests,to give the allowable stress.
The allowable stress,,give by
= (4-2)
where is the stress at which the material fails( failure to be defined later) and n is the safety factor.
Before approving trial dimensions,the designer makes certain that the design is safe by determining that the inequality
≥
or
≥ (4-3)
is satisfied.The inequality is usually more convenient in the form
≥ (4-4)
It might at first seem that the designer would always dimension the cross section that the stress would exactly equal the allowable stress.However,it may be very costly to produce .parts that have nonstandard sizes,so it is usually more economical to waste some material by selecting the next larger standard size above that required by the allowable stress.Departure from standard sizes is justified in cases where the penalty for excess weight is very severe,as in aircraft or space-ship design.
中间读不出来的符号可以省略不译