Why is helical reinforcement sometimes designed instead of normal links.

There is no mechanical property in which the columns of circular cross section with spiral reinforcement lag behind their counterparts rectangular ones. Their implementation in the areas of negligible seismic hazard is possible to achieve a reduction of the cross section due to significantly improved strength due concrete confinement stemming from the presence of spiral reinforcement. In earthquake zones, they exhibit their superiority thanks to their increased ductility. It is well-known the case of columns of Olive View Hospital which made history in the San Fernando earthquake of 1971 [1]. Some of the reasons that the columns in question account deprived, at least in our country, the spread they should be entitled to are constructional, e.g. the problem of their formwork or the construction of the spiral reinforcement. But today with the proliferation of one-use paper formwork and the possible standardization of metallic spirals, construction barriers are lifted and perhaps the only ones left from the obstacles is the lack of knowledge of the benefits and the momentum of the past that is certainly in favor of rectangular section columns.

Regulatory requirements. Pitch: Helical reinforcement shall be of regular formation with the turns of the helix spaced evenly and its ends shall be anchored properly by providing one and a half extra turns of the spiral bar. The pitch of helical reinforcement shall be the least of the following:

1. the least lateral dimension of the compression members;

2. sixteen times the smallest diameter of the longitudinal reinforcement bar to be tied;

3. 300 mm for all cases except where an increased load on the column is allowed for on the strength of the helical reinforcement. In such cases only, the maximum pitch shall be the lesser of 75 mm and one-sixth of the core diameter of the column, and the minimum pitch shall be the lesser of 25 mm and three times the diameter of the steel bar forming the helix [2].

Diameter: The diameter of the helical reinforcement shall be not less than one-fourth of the diameter of the largest longitudinal bar, and in no case less than 6 mm [2].

A modern problem that its treatment is associated with the use of spiral reinforcement is the applications of high strength concrete (HSC), i.e. improved concrete strength greater than the maximum specified quality (C50) [3]. More precisely, according to the literature, high strength concretes are characterized those possessing strength above 80 MPa. But it is known that as concrete strength increases the more brittle concrete becomes, respectively steel loses its ductility increased when its yield strength increases. In the concrete case, “drugs” are two: (a) Confinement using spiral reinforcement and (b) Adding fibers to the concrete (fiber concrete) uniformly distributed and randomly dispersed throughout its mass. Fig. 1 shows a gradual lifting of the brittleness of concrete by incorporating therein various percentages of steel fibers. Also Fig. 2 shows a further reduction of brittleness by applying varying degrees of confinement using spiral reinforcement. It is also observed in the latter case that while brittleness is reduced, concrete material strength significantly increases [4].

Finally, the primacy of circular cross-section columns with spiral reinforcement is not limited to the compressive axial stress state, but extends to other stress states, too, like bending and punching shear. This is due to the fact that the adverse effects of inclined seismic stress, which causes a significant reduction of the mechanical properties of seismic structural elements, such as strength, stiffness and energy absorption capacity, do not occur to circular columns. This advantage of columns of circular cross-section over the corresponding square ones covers the small difference in flexural strength (≈ 10%) observed between the two types of columns when they do not differ in: the longitudinal reinforcement, confinement reinforcement, core crosssectional area, qualities of materials and axial loading (see Fig. 3) [4].

 

Fig. 1: Improvement of downward branch of concrete stress-strain diagram σ-ε by incorporating metal fibers in its mass

 

Fig. 2: Additional improvement in the mechanical behavior of fiber-reinforced concrete by confinement with the use of spiral reinforcement

Fig. 3: Strength comparison of columns with square section and circular cross-section for two cases of concrete quality

 

Conclusion

Spiral columns are cylindrical columns with a continuous helical bar wrapping around the column. The spiral acts to provide support in the transverse direction and prevent the column from barreling. The amount of reinforcement is required to provide additional load-carrying capacity greater than or equal to that attributed from the shell as to compensate for the strength lost when the shell spalls off. With further thickening of the spiral rebar, the axially loaded concrete becomes the weakest link in the system and the strength contribution from the additional rebar does not take effect until the column has failed axially. At that point, the additional strength from spiral comes into play and prevents catastrophic failure, instead giving rise to a much slower ductile failure.

Научный руководитель – М.А. Ращупкина, канд. тех. наук, СибАДИ; Т.Г. Галкина, канд. филологич. наук, доцент кафедры «Иностранные языки» СибАДИ, Омск.

 

Библиографический список

 

1. Bertero, V.V., Bresler, B., Selna, S.G., Chopra, A.K., Koretsky, A.V., «Design implications of damage observed in the Olive View Medical Center buildings», Proceedings of the 5th World Conference on Earthquake Engineering, Rome, Italy, 1974.

2. Module Compression Members. Definitions, Classifications, Guidelines and Assumptions, Version 2 CE IIT, Kharagpur.

3. European Committee for Standardization, «EN 1992-1.1:2004, Eurocode 2: Design of concrete structures - Part 1.1: General rules and rules for buildings (Incorporating corrigendum January 2008)», Brussels, Belgium, 2004.

4. Ioannis A. Tegos, Theodoros A. Chrysanidis, «International Journal of Research in Engineering and Technology», Aristotle University of Thessaloniki, Greece, 2014.

 

 

УДК 85

студент Ковтун Ю.А.

Сибирская государственная автомобильно-дорожная академия (СибАДИ), Омск

Abstract. In Germany decided to follow all kinds of regulations, laws, instructions, including the rules of national etiquette. The Germans have a reputation for the nation with good character. Inherent honesty and efficiency. Having considered, business etiquette, we can conclude that Germans are very punctual, punctilious, economical people.

Аннотация. В Германии принято чётко следовать всевозможным предписаниям, законам, инструкциям, в том числе и правилам национального этикета. Немцы пользуются репутацией нации с хорошим характером. Им присущи честность и деловитость. Рассмотрев, деловой этикет, можно сделать вывод о том, что немцы очень пунктуальный, педантичный, экономичный народ.

Keywords: people, features, economy, etiquette.

Ключевые слова: жители, черты, экономность, этикет.

 

ДЕЛОВОЙ ЭТИКЕТ В ГЕРМАНИИ