decompression

huangyhg

decompression
eurocode 2 speaks of decompression with regards to prestressed concrete design.
can anyone explain to me what decompression means. many thanks
decompression refers to the loss of compression stress in a prestressed concrete   
i am particularly refering to pargraph 3 of section 7.2 in eurocode 2:
. . . under severe exposure conditions when decompression is required, the design proces tends to be dominated by the serviceability requirements of cracking, rather than by ultimate strength as in reinforce concrete.
hope you can explain further in conjucntion with the above.
thanks
with prestressing you are compressing the concrete around the tendon.  you can think of the concrete going from zero stress to an effective (after losses) compressive prestress.  decompression is simply the loss of that compression (or prestress) due to an increase in the load on a   
barblaze,
in ec2, decompression is the point at which the stress in the concrete is 0. in other words, the tendon cannot be in the tension zone under the loading nominated in the code for the particular cracking condition you are investigating.