Q: What are the pros and cons of post-tensioned slab against precast slab system?
A: Post-tensioned slab and precast slab are all time competitors. Their benefits might depend on the availability and skill of the builder. Some benefits of post-tensioned slab over precast slab are listed as follows:
+ Be able to construct without supporting beams.
+ Provide less structural depth
+ Be able to construct for very large span say 15m+, while it is very difficult for precast construction to operate without large crane.
+ Structure are casted continuously that the slab could be thinner.
+ It does not require much space for transporting concrete to upper floors.
+ Cost might be more effective in terms of material and labor.
Some known disadvantages of post-tensioned slab are
+ Require setting up formwork for the whole construction floor.
+ Require special method of pumping or shooting concrete.
+ Construction time might be a bit slower, but this commonly does not affect to overall project time.
+ Require larger amount of workmanship.
However, post-tensioned slab are quite more general and it does not require large equipment to install. Moreover, it depends less on outsource precast manufacturer and require less labor skill. Nowadays, post-tensioned slabs have been proven to be one of the most efficient methods for concrete building construction.
Last Updated: 11.09.2016
Q: What is shear band reinforcement?
A: Shear band is an alternative punching shear reinforcement to column-supported slab systems. The Shear band system is a high tensile and high ductility thin metal strip and differs from all existing systems. The system can be placed on top of all other reinforcement, with minimal loss of cover. Shear band brings a simple construction solution against conventional stirrup and probably easier and cheaper to manufacture than welded stud rail. Posteck Prestressing has been preparing a series of testing program of this alternative punching shear device before bring them to the actual construction projects.
Last Updated 11.09.2016
Q: What are major sources of stress loss in post-tensioned concrete design?
A: Stress losses are the reduction of tensile force in stressed tendon that affects to both compressive force and balanced load. For bonded system, this losses are not constant along tendon's length. Losses can be classified as short and long term according to elapsed time to occur:
Short term losses are due to (1) friction along length of tendon, (2) wedge seating.
Long term losses are due to (1) elastic shortening, (2) stress relaxation of tendon, (3) creep and (4) shrinkage. Restraints due to connecting stiff elements are also important, which must be considered in design of post-tensioned members.
Last Updated: 11.09.2016
Q: What is the relationship between cube and cylinder compressive strength of concrete? Why does cube strength always be greater?
A: Due to difference in geometry and hence their confinement condition are different. During testing program, almost all part of cube are subjected to lateral compressive stress formed by diagonal compression strut, while part of cylinder specimen is not subjected to lateral compression. Commonly, cube strength is 1.25 times greater than cylinder strength. While this ratio is not constant, it can be used as practical guideline.
Q: Can post-tensioned slab be used with heavy duty industrial floor?
A: Absolutely it can!
PT slab offers major advantages for industrial slab with heavy duty load over conventional RC slab or precast plank.
Major benefits are listed as following:
For more information, please contact our engineer to assist.
Last Updated: 26.06.2014