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ТЕХНИЧЕСКИЕ НАУКИ
UDC 624.071
Mavlonov Ravshanbek Abdujabborovich, Ergasheva Nazokat Erkinboevna
Assistants of department of "Construction of buildings and structures" Namangan Engineering Pedagogical Institute, Namangan city, Uzbekistan ravshanbek.mavlonov@gmail.com
STRENGTHENING REINFORCED CONCRETE MEMBERS
Annotation
Nowadays, repairing and strengthening of damaged reinforced-concrete buildings has become an important issue. There are many different kinds of repairing and strengthening methods. Reinforced jacketing, carbon fiber and reparation with steel plates are the ones that are used the most.
Key words
Reinforced concrete members, strengthening methods, section enlargement, reinforced jacketing
Over the years, engineers have used different methods and techniques to retrofit existing structures by providing external confining stresses. For the past few years, the concept of jacketing has been investigated to provide such forces. Externally applied jackets have been used as a reinforcement to contain concrete for different reasons. Engineers have used traditional materials such as wood, steel, and concrete to confine and improve the structural behavior of concrete members.
Steel jacketing has been proven to be an effective technique to enhance the seismic performance of old bridge columns. The steel jacket is manufactured in two shell pieces and welded in the field around the construction. However, this method requires difficult welding work and, in a long term, the potential problem of corrosion remains unsolved.
Section enlargement is the best methods used in retrofitting concrete members. Enlargement is the placement of reinforced concrete jacket around the existing structural member to achieve the desired section properties and performance.
When it comes to reinforced-concrete structures, certain parts or the entire building can be strengthened due to disability, damage or regulation changes. This strengthening process can be done by increasing structure rigidity through adding bearing elements and bearing system or increasing the rigidity and strength of insufficient components in the structure.
The strengthening of reinforced concrete members is a task that should be carried out by a structural engineer according to calculations. Here only a few suggestions are included to illustrate the ways in which the strengthening could be done.
1. Reinforced concrete columns can best be strengthened by jacketing, and by providing additional cage of longitudinal and lateral tie reinforcement around the columns and casting a concrete ring, Fig 1, the desired strength and ductility can thus be built-up.
Fig. 1. Jacketing a concrete column
1 - existing column section; 2- added section; 3 - new longitudinal bars; 4 - new tie bars. 2. Jacketing a reinforced concrete beam can also be done in the above manner. For holding the stirrup in this case, holes will have to be drilled through the slab, Fig 2.
3
3 \
a b C
Fig. 2. Increasing the section and reinforcement of existing beams 1 - old concrete; 2- new concrete; 3 - holes for passing stirrup; 4 - chip old surface; 5 - groove in slab; 6 -
groove for new stirrup.
3. Similar technique could tie used for strengthening reinforced concrete shear walls.
4. Inadequate sections of reinforced concrete column and beams can also be strengthened by removing the cover to old steel, welding new steel to old steel and replacing the cover. In all cases of adding new concrete to old concrete, the original surface should be roughened, groves made in the appropriate direction for providing shear transfer. The ends of the additional steel are to be anchored in the adjacent beams or columns as the case may be.
5. Reinforced concrete beams can also be strengthened by applying prestress to it so that opposite moments are caused to those applied. The wires will run on both sides of the web outside and anchored against the end of the beam through a steel plate.
Fig. 3. Column enlargement
Jacketing of columns with the new longitudinal reinforcement passing through the slab has several advantages. As was mentioned earlier, a major advantage is that the lateral load capacity of buildings strengthened using column jacketing can be reasonably uniformly distributed throughout the structure of the building, thereby avoiding the concentrations of lateral load resistance which occurs when only a few shear walls are added. Hence, major strengthening of foundations can be avoided. In addition, because there are no major changes in the original geometry of building with this technique, the original function of the building can be maintained. However there are some disadvantages associated with the column jacketing technique. They are: in some cases the presence of beams may require most of the new longitudinal bars in the jacket to be bundled into the corners of the jacket, because of the presence of the existing column it is difficult to provide cross ties for new longitudinal bars which are not at the corners of the jacket, and because of the lack of guidelines, this type of jacketing of columns is based mostly on
engineering judgment. Experimental and analytical investigations are needed to provide information on the strength, ductility and seismic performance of reinforced concrete columns repaired and the strengthened with new longitudinal reinforcement placed through the floor structure.
References:
1. С.Э.Абдурахмонов, Р.А.Мавлонов. Трещины в железобетонных изделиях при изготовлении их в нестационарном климате. Материалы сборника международной НПК «Наука и образование: проблемы и перспективы». 13 март 2014 г./Уфа: Ч.1/отв. Ред. А.А.Сукиасян. - Уфа: РИЦ БашГУ, 2014. - С. 197-198.
2. Р.А.Мавлонов, И.А.Ортиков. Cold weather masonry construction. Материалы сборника международной НПК «Перспективы развития науки». 20 март 2014г./ Уфа: отв. Ред. А.А.Сукиасян. - Уфа: РИЦ БашГУ, 2014. - С. 49-51.
3. Р.А.Мавлонов, И.А.Ортиков. Sound-insulating materials. Материалы сборника международной НПК «Актуальные проблемы научной мысли». 24 апреля 2014г./ Уфа: Ч.2/отв. Ред. А.А.Сукиасян. - Уфа: РИЦ БашГУ, 2014. - С. 31-33.
4. Reinforced Concrete Designer's Handbook, 10th edition.//Charles E. Reynolds, James C. Steedman. UK,
1999
© R.A.Mavlonov, N.E.Ergasheva, 2015
УДК 691.16
Аюпов Дамир Алиевич
канд. техн. наук, ст. преп. КГАСУ г. Казань, РФ E-mail: ayupov_damir@rambler.ru Мурафа Асия Владимировна канд. техн. наук, доцент КГАСУ г. Казань, РФ E-mail: makarov@kgasu.ru Харитонов Виталий Александрович студент КГАСУ г. Казань, РФ E-mail: vitaliiharitonov@mail.ru
ВЛИЯНИЕ ДЕВУЛКАНИЗАТОВ РЕЗИНЫ НА РЕОЛОГИЧЕСКИЕ СВОЙСТВА БИТУМА
Изменение свойств битума при модификации их полимерами обусловлено заметным воздействием последних на структуру вяжущего.
Для оценки поведения битума при эксплуатации в случае длительно действующих нагрузок следует уделять внимание его реологическим характеристикам, так как они крайне важны для технологического процесса - от них зависят условия и качество перемешивания смеси [1, с. 12].
Асфальтены в битуме выполняют функцию дисперсной фазы, вызывая отклонения от линейности при течении. При воздействии малых нагрузок наблюдается медленное необратимое течение материала, соответствующее высоким значениям вязкости, то есть процесс ползучести. При воздействии значительных нагрузок, в особенности, если они действуют продолжительное время, структура материала может быть нарушена (например, возникает плоскость сдвига), что приводит к резкому снижению вязкости. Битум может проявлять как ньютоновское, так и неньютоновское поведение в зависимости от условий загружения. Так, при малых напряжениях вязкость не зависит от величины действующей нагрузки (ньютоновское поведение). При больших нагрузках проявляется зависимость вязкости от условий загружения (неньютоновское поведение).
