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 Tendon Layout Tendons can have the following type of arrangement on plan Distributed - distributed (common in MIddle east and Australia) Tendons in the x and y directions are distributed over the length of the slab with a spacing not exceeding 1.5m. The issue with this arrangement is the tendon will be like a basket wieve and it’s difficult to know which one goes up and which one goes down. Banded - distributed (common in US) This will have the same distributed tendon as part 1 but one direction will be banded (usually grouped in a width 1-1.2m). No max spacing requirements for banded tendons Very easy to install as all the banded will be install first then the distributed Banded - banded Not very common Note: the horizontal spacing between tendons doesn’t affect the structures a lot, the most important thing is the tendon profiles (measured vertically) Economy of PT system PT slabs will commonly have up-to 30% less thickness, and complet...

 Myth associated with PT we cannot make an opening in PT slab, this is actually a false statement, a PT slab can be modified with proper calculations and expertise. We have made as big as 4m x5m opening in a PT slab which was required for sky light or escalators we need to do restressing periodically: this is also one of the things I hear about PT, but this is wrong. The strands are cut flush with the concrete surface and can not be restressed even if we wanted to. There is no requirements for restressing as we have low relaxation strands and a very good wedge anchor system PT slab can not crack: even though PT slabs are designed to be crack free at service load (at least based on ACI, some codes like EC allow for a certain degree of crack), cracks can be witnessed in PT slabs. This can attribute to one of the two 1. If the actual load exceeds the service load momentary 2. Surface cracks, which are very common No one can claim to have a crack free concrete by definition, we w...

  Definition of terms Strand: is the high tension cable (typically more than 4 times the strength of rebar) Tendon: agroup of strands (can be one for unbonded but it’s multiple strands inside a duct for bonded system) Duct: a galvanized or HDPE that separates the concrete from the strand Issues associated with PT Restrain to shortening: this needs a special consideration for pouring sequence and connection detailing Relaxation of strand: this can be avoided with a use of low relaxation strands Design of Post tension members The design of post tension elements needs a sound engineering knowledge and field skill, the amount of force applied to a single strand with a diameter of 12.7mm is about 15Ton (this is more than the weight of 7 Toyota Corollas). One can imagine how dangerous it can get if either the design or site execution are not properly done. That’s why all countries (at least the countries I am aware of) requires a specialized contractor who can do...

 Bonded PT Stress transfer is through bond (require cement grouting) strain compatibility between strand and concrete Very common in Australia, Middle East, and Europe Unbonded PT stress transfer is through anchorage no grouting required no strain compatibility strand and concrete moves independently Very common in North America Mono strand system strands in tendon are stressed separately usually 1, 3 or 5 strands per tendon Used in slabs or beams Multi strand system strands in a tendon are stressed at the same time (16, 19, as much as 37 strands per tendon) Used in bridges, and in buildings (transfer beams) PT structures are used in slab on grade (for houses in expansive soil) Mat foundation (raft) parking structures flat plate bridges (Girder type, cable stay, suspension) silos water tanks walls (currently becoming common for shear walls in seismic areas)

Prestressed Concrete part 2  Benefit of prestressing system some benefits of using a Prestress system over RC are  Longer floor spans and cantilevers As much as 70% saving in reinforcement Thinner slab thickness (as much as 1/3 less than that of RC) High architectural freedom (freedom in column layout, need not to be aligned, can deviate as much as you want to) Removal of form-work in 4 to 5 days after casting bigger floor to floor clear span (this will decrease the cost of facade) very less deflection and crack complete flat plate (no beam required) Decrease structural weight which interns decrease column, wall, and foundation sizes. Decrease the amount of reinforcement required in column & shear walls due to earthquake load, as the seismic weight of the whole structure is decreased. The most common form of prestressing is the post tensioning system. This system can further be classified in to two groups based on type of strand used, and method of stress...

 PRE-STRESSED CONCRETE PART 1 Pre-stressing is a way of counteracting the effect of external loads on structure by imposing a state of stresses contrary to the load effects Pre-stressing has two parts Pre-Tensioning Usually straight or harped profiles, mostly used in the precast industry some example would be hollow core slabs, precast beams, Girder beams Post Tensioning Any type of profile, can be precast or cast in place The only basic difference between pre-tensioning and post tensioning is the state of the structural element while the stressing activities are done. In pretension the stressing is applied prior to concreting while in post tensioning the stressing is applied after the concrete is poured and hardened Further, Post Tensioning is divided in to bonded and unbonded systems; we will get in to this in later days. Pre-stressing a concrete element has two effect axial and transversal based on the tendon profile and anchorage selected. We can have...

 How much quantity of steel required for 1m3 concrete? Quantity of steel in concrete depending on type of structure and load of structure. For Foundation  :- 0.5 to 0.8 % steel are required Let we take minimum 0.5 % of steel is required on 1 m3 concrete Then quantity of steel. = (0.5/100)×1× 7850 = 39.25 kg 7850 = density of steel If we take maximum 0.8% steel is required Then quantity of steel is = (0.8/100)× 7850 = 62.8 kg 2.  For column  :- 0.8 – 6 % of steel required For minimum 0.8 %. = (0.8/100)×7850 = 62.8 kg For maximum 6% = (6/100)× 7850 = 471 kg 3.  For Beam  :- 1- 2 % For minimum 1% = (1/100) ×7850 = 78.5 kg For maximum 2 % = (2/100) × 7850 = 157 kg 4.  Slab and lintel  :- 0.7 – 1.0 % For minimum :- (0.7/100)× 7850 = 54.95 kg For maximum 1% :- (1/100)× 7850 = 78.5 kg Overall we assume Average 2.5 % of steel  required in 1 m3 concrete work Then = (2.5/100) × 1 ×7850 = 196.25 kg Approx 200 kg steel 1m3 =...

 Calculate the quantity of cement , sand and brick in one meter cubic volume  Given  - Mortar ration = 6:1 = 7 - mortar thickness = 10mm=0.01m - density of cement = 1440 Solution   brick of 1 m³  - volume of brick = length X width x                       thickness ( without mortar)  - volume of brick = L x W x T  - volume of brick = 0.19 x 0.09 x 0.09  - volume of brick = 0.001539 m³  With mortar  Volume of brick add 0.01m in the three dimensions  (0.19+0.01) x (0.09+0.01) x (0.09+0.01) = 0.2m x 0.10m x 0.10m Now let’s compute the volume  - volume of brick = L x W x T - volume of brick = 0.2m x 0.1m x 0.1m  - volume of brick = 0.002 m³  - Number of brick 1m³ = 1/ 0.002 =      #500 of brick 🧱  ➪ Volume of mortar  = 1 - ( 500x0.001539) .... Dry  VOLUME   Thus; 1 is total meter cube of volume        ...

What are the Advantages and disadvantages of prestressed concrete? Advantages of Prestressed Concrete: 1. Prestressed concrete members are free from cracks and the resistance to the effect of impact, shock and stresses are higher than RCC structures. 2. Longevity of prestressed structure is greater than RCC structure because the reinforcement stays unaffected from outer agencies. 3. The high compressive strength of concrete and high tensile strength of steel are used for prestressin that makes it more economical. 4. Smaller sections can be used for longer span by reducing the section of members. 5. Prestressed members are lighter in weight and easily transportable. 6. It requires a smaller amount of construction materials. 7. The shear resistance of members can be increased by using curved tendons. 8. Prestressing also reduces the diagonal tension in concrete. Disadvantages Of Prestressed Concrete: 1. The main disadvantage of prestressing is that it requires some special equipment like...