اسمحو لي اليوم بفتح باب مناقشة موضوع (minimum precompression in PT Members) , هو بصراحة موضوع طويل و متشعب.
Minimum prestess as it appers in ACI code and other morden codes serves as a guide in selection of prestessing and reinforcement, it is not required to checks for serviceability limit stat or ultimate limit state or initial condition.
The ACI code provision for a minimum avarage precompression in PT slabs serves the means by the code gurantees a minimum amount of reinforcement, other major codes do so by stipulating specific values for minimum reinforcement as opposed to minimum precompression.
the minimum reinforcement in slabs can be atchevied by providing prestress steel or a combination between prestess steel and reinforcement.
It is not the level of precompression that gurantees the serviceability and safety of slab.
The ACI Codes and other moderate codes assume the minimum value of preciompression is sufficient if the total area of prestressed and non-prestressed reinforcement in each design section satisfies the shrinkage and temperature requirments, for example in ACI the reinforcement ratio for each design section shall not be less than (0.0018) for grade 60.
and the punching shear design at column slab junction recognizes the absense and level of avarage precompression over the column region.
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