i applied prestressing force eventhough my moment value is same as without apply the pretension kindly clarify me(staad CE)

Please upload the .std file and provide a little more description like which member number, which load case number, which moment (My or Mz) you are expecting to change

100MCONCTOWER QUASI.STD

here i attach my std file here i need to vertical prestressing for column and my axial load and moment coming same as my load combination with and without prestress kindly help me out or u can correct my file if i did any seems wrong 

hi prashanth p

Your results seems just fine..

Taking a deeper look at the axial load (Fx) at node 16 which is part of element 398. Here is the break down:

Dead = -1859 kN

Live = -1572 kN

Wind = -209 kN

load comb 4 = LC4 = (D + L + W) = -(1859 + 1572 + 209) = -3640 kN (staad -3640.2 kN highlighted in RED)

prestress = -1500 kN

load comb 6 = (LC4 + 5) = -3640 + -1500 = -5140 kN (staad -5140.2 kN highlighted in BLUE)

Regarding the moment, in theory you should expect ZERO moment due to prestressing force because you are applying the presstressing force at the center of the element (no eccentricity). HOWEVER, because you are analyzing a hyperstatic structures and also the members are slightly inclined (due to cone-like shape of the tower). This induces some secondary moments and shear as you can see some small values shown in the results table.

Prestress at node 16 --> Fy = -0.222 kN   and Mz = -0.93 kN-m (see light blue)

hello silva its good to hear from you can u plz explain about how to calculate the prestressing force for segment-wise or whole and as well as tendon profile like example kind of problem and do reduce the moment calculation any example is highly appreciated 

hi there,

Sorry but I didn't understand your question clearly. Word of advise, please use punctuation between sentences.

Here is my tentative of answering your question:

Generally speaking, prestressing is used to offset the tensile stress in concrete structures. Therefore, the prestressing force will be determined based on the demands (load combination) and also the capacity of concrete (compression/tensile limit).

Similarly, tendon profile is often determined based on the shape of bending moment. For the same reason mentioned above.

Have you taken any prestressing design course? Your question seems to be more related to theoretical knowledge rather than how to use STAAD. I would suggest you to read some prestressing concrete textbook. Also, the internet has a ton of information. Just google it.

Good luck!

hi there,

Sorry but I didn't understand your question clearly. Word of advise, please use punctuation between sentences.

Here is my tentative of answering your question:

Generally speaking, prestressing is used to offset the tensile stress in concrete structures. Therefore, the prestressing force will be determined based on the demands (load combination) and also the capacity of concrete (compression/tensile limit).

Similarly, tendon profile is often determined based on the shape of bending moment. For the same reason mentioned above.

Have you taken any prestressing design course? Your question seems to be more related to theoretical knowledge rather than how to use STAAD. I would suggest you to read some prestressing concrete textbook. Also, the internet has a ton of information. Just google it.

Good luck!