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Strength calculation in tension and compression




 

To secure the details strength it is necessary that the stresses arising in the function process should be lesser than the limit stresses.

The safety factor is called the relation of the limit stress to the stress arising during the details work process. It is denoted by S:

 

where

It is evident that the insufficient safety factor will not ensure the construction reliability while the excessive safety factor leads to the material over-consumption and the material increase of the construction weight.

The allowable working stressis called the relation of the limit stress to the safety factor. It is denoted by

 

The strength condition of the construction details is provided by the fact that the maximum working stress does not exceed the allowable working stress:

 

 

The guide values of the allowable working stresses in tension and compression for some materials are given in table 2.1.

If stresses in tension and compression are different, they are denoted by and accordingly.

The calculation formula in tension and compression is

 


 

Tabl. 2.1.

 

Material МPа МPа
tension compression
  Grey cast iron Carbon steel constructional Alloy steel constructional Copper Brass Bronze Duraluminium Textile laminate Oak (along the grain) Laying brick Concrete   28...80 60...250   100...400 and above 30...120 70...140 60...120 80...150 30...40 9...13 up to 0,2 0,7…1   120...150     50...90 13...15 0,6...2,5 1...9

 

There are three problem types distinguished by the calculation formula form application:

1). The project calculation to determine the dangerous section dimensions by the formula

 

 

2). The checking calculation to determine the working stress and to compare with the allowable one by the formula

 

3). To determine the allowable load the formula is applied

 

 

 


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