What does post-tensioning do?
When a concrete slab is stressed by the post-tensioning method, it means the steel is being tensioned and the concrete is being compressed. Compression is a force that squeezes or crushes, and tension is a force that pulls something apart. As a building material, concrete is very strong in compression but relatively weak in tension. Steel is very strong in tension. Putting a concrete slab into compression and the steel into tension before any substantial service loads are applied, puts both building materials into their strongest states. The result is a stiffer concrete slab that actively is compressed and has more capacity to resist tensile forces.
When a concrete floor slab is subjected to forces, it flexes and bends. These forces are a result of gravity pulling down on the slab while additional weight is applied to the top of the slab. The bending and flexing create high tensile forces that can cause the concrete floor slab to crack. This is where the use of reinforcing becomes important. Because steel has a high capacity to resist tensile forces, it can be embedded in the concrete at the tension zones - the areas that tensile failures could occur - allowing the tensile forces to be handled by the reinforcing steel.
Adding post-tensioned reinforcement instead of rebar alone combines the action of reinforcing the tension zones with the advantages of compressing the concrete slab. Now optimum efficiency is obtained because the post-tensioned reinforcement is located in the tension zones, the concrete is compressed, and the post-tensioned reinforcement is creating an uplift force in the middle of the spans where it is needed the most.
Read, listen to the pronunciation and memorize the active vocabulary to the text:
Active Vocabulary
1. post-tensioning напряжение стальной арматуры и сжатие бетона после его заливки
2. pre-stressed предварительно напряженный
3. to retain сохранять, удерживать
4. flexibility гибкость
5. cast-in-place с отливкой на месте
6. to elevate поднимать, повышать
7. internal внутренний
8. counteract противодействовать
9. service load полезная нагрузка
10. jobsite стройплощадка
11. tendon элемент напрягаемой арматуры; арматурный пучок
12. formwork опалубка для бетона
13. to squeeze сжимать, сдавливать
14. substantial существенный, значительный
15. tensile force растягивающая сила, сила растяжения
16. to subject подвергать
17. to bend изгибать(ся)
18. to crack трескаться, раскалывать(ся)
19. to embed внедрять, вставлять, врезать; to embed in concrete - забетонировать
20. slab плита
21. advantage преимущество, благоприятное положение
22. span диапазон, интервал, промежуток
TEST I
Decide whether these statements are true or false:
1. a). When the steel is tensioned before concrete placement, the process is called pre-tensioning.
b). When the steel is tensioned before concrete placement, internal forces are applied to it.
c). When the steel is tensioned before concrete placement, the concrete is subject to compression.
2. a). The internal forces are applied by tensioning high-strength steel, which can be done before the concrete is placed.
b). The internal forces are applied by tensioning high-strength steel, which can be done after the concrete is placed.
c). The internal forces are applied by tensioning high-strength steel, which can be done either before or after the concrete is placed.
3. a). Because pre-tensioning requires specially designed casting beds, it is used extensively in bridges, elevated slabs, residential foundations, etc.
b). Because pre-tensioning requires specially designed casting beds, the cast-in-place method of building concrete structures is employed.
c). Because pre-tensioning requires specially designed casting beds, it is used generally in the precast manufacturing process.
4. a). Post-tensioning is done onsite by introducing internalforces (or stress) into a concrete.
b). Post-tensioning is done onsite by installing post-tensioning tendons within the concrete formwork.
c). Post-tensioning is done onsite by tensioning high-strength steel.
5. a). When a concrete floor slab is subjectedto forces, it flexes and bends.
b). When a concrete floor slab is subjectedto forces, the building materials are put into their strongest states.
c). When a concrete floor slab is subjectedto forces, it can cause its cracking.
TEST II
Match words in columns A and B (synonym match):
A B
1. to enable a). to bring b). to allow
c). to join d). to guess
2. application a). gravity b). joist
c). framing d). use
3. to conceive a). to devise b). to mean
c). to establish d). to reduce
4. extensively a). usually b). typically
c). broadly d). realistically
5. placement a). allocation b). axis
c). accumulation d). delineation
6. to squeeze a). to cost b). to reduce
c). to compress d). to involve
7. apart a). however b). piecemeal
c). notwithstanding d). also
8. to describe a). to surround b). to accomplish
c). to qualify d). to depict
9. to handle a). to brace b). to include
c). to hold d). to install
10. to obtain a). to achieve b). to point
c). to enclose d). to suspend
TEST III
Select the best possible answer out of the choices from the list to the statements (multiple choice):
1. The bending and flexing create high tensile forces that can … .
a. create an uplift force in the middle of the spans.
b.cause the concrete floor slab to squeezeor crush.
c. cause the concrete floor slab to crack.
d. counteract with the external loads.
2.When a concrete slab is stressed by the post-tensioning method, … .
a. the internal forces are applied by tensioning high-strength steel.
b.it means the steel is being tensioned and the concrete is being compressed.
c. this is where the use of reinforcing becomes important.
d.the external loads are applied when the structure is put into use.
3. Putting a concrete slab into compression and the steel into tension before any substantial service loads are applied … .
a. can cause the concrete floor slab to crack.
b. requires installing post-tensioning tendons within the concrete formwork.
c. results in gravity pulling down on the slab.
d. puts both building materials into their strongest states.
4. The term pre-stressing is used to describe the process of … .
a. installing rebar within the concrete formwork.
b. counteracting of all types of loads applied when the structure is put into use.
c.introducing internalforces into a concrete element during the construction process in order to counteract the external loads.
d. putting a concrete slab into compression and the steel into tension before any service loads are applied.
5.Because steel has a high capacity to resist tensile forces, … .
a. is widely used in bridges, parking structures, residential or commercial buildings, etc.
b.optimum efficiency can be obtained.
c. it can be embedded in the concrete at the tension zones.
d. it creates an uplift force in the middle of the spans.
TEST IV