Post-tensioned concrete forms one of the most of import mixtures that form the footing of most structural technology plants. Extant literature has been dedicated to the survey of post-tensioned concrete. In this paper we analyse the assorted signifiers and types post-tensioned concrete and the ideal mix ratio that consequence in the most lasting post-tensioned concrete. Our major purpose is to better the public presentation of post-tensioned concrete constructions through the usage of optimum design in footings of stuff and form. This paper starts with the basic definition and debut to the construct of post-tensioned concrete constructions. It so proceeds to the survey of relevant literature that concerns post-tensioned concrete constructions with a peculiar focal point to ache modeling. This is so followed with a recommendation on the best design parametric quantities and conditions for the production of the highest quality/best pre-tensioned concrete construction. A decision is so drawn from the prescribed recommendations.
The procedure of planing a structural edifice system involves a careful choice and design by both applied scientists and designers and a proper apprehension of stuffs that are used. The appropriate use of constructions such as post-tensioned concrete coupled with their possible the effects on the lastingness and stableness of the whole construction to be built is one of the most of import constructs for the interior decorators. A proper analysis and assembly of the concrete constructions coupled with high quality stuffs that can supply a unique, robust construction consequences to unprecedented superior combination of stuff for better lastingness, sound control and standard fire safety that is extremely required in the modern-day edifice market. A consideration of the the current building market and planetary economic sciences highlights the demand to pay great attending to factors such as the building cost, material supply procedure and the averagely reduced floor-to-floor heights.The factors combined with the deficiency of proper developer funding mechanisms leads contractors to choose concrete as the more cost effectual stuff to utilize in building over steel ( Olson and Smith,1997 ) .
Technological promotion is one of the chief drivers for the go oning addition in the usage of post-tensioned concrete systems ( Crigler,2007 ) . This is because the usage of engineering has continually expanded the bounds of lastingness of constructions that are designed and developed utilizing station tensioned concrete.
How post-tensioned concrete work
It is overriding to understand what post-tensioned concrete is composed of and how it achieves its on the job status. Concrete in itself is really strong under compaction and weak in footings of its tensile belongingss ; steel on the other manus is really strong in tenseness while comparatively weak in compaction. However, the bordering members in all building structures must defy the assorted tonss through a combined action of both compressive and tensile forces. Assorted signifiers of concrete framing are reinforced with steel in order to better their burden bearing capablenesss. The development of post-tensioned concrete was hence to do up for concrete ‘s structural failing under tenseness through the infliction of a for good compressive burden on its chief structural members. This type of concrete agreement is made up if highly lasting steel sinews with increased strength. This agreement in concurrence with several reenforcing steel bars are so embedded and so firmly anchored in the solid concrete. After the concrete has attained equal strength, a procedure which occurs in approximately 3 or 4 yearss from the minute of arrangement, the steel sinews are the suitably tensioned through the infliction of a compressive force on the concrete construction. Subsequently on, sinews remain would stressed all through the life of the construction thereby bring forthing a counterbalancing tenseness for future tonss. The sinews together with the usual rebar reinforcing allows the s the applied scientist to come up with a shallower design for the structural members which posses an increased burden capacities with a characteristically little warp under burden.
Fig1.The lading action of post-tensioned concrete
Benefits of Post-Tensioned Concrete
Post-tensioned constructions provides several advantages. Among these advantages are reduced dead burden coupled with member deepness due to the reduced sum concrete that is needed. The other advantage is the better control of warp with a far greater cleft control. Capabilities. The better cleft control leads to improved lastingness which is an added virtue. Apart from these virtues, post-tensioning gives room for increased span to depth ratios. A fact that has the consequence of take downing the edifice highs and therefore taking to a decrease of both the warming and chilling volume of the edifices. The overall accomplishment is a lessening in the facade country of whole the construction.
For several developers and proprietors of immense commercial edifices, the virtues of post-tensioning brand it the preferable reinforcing system. As apparent from Scott Greenhaus, president of VSL when he said “ aˆ¦Since the slab thickness is reduced, a developer constructing a high rise construction can easy add more floors without increasing the overall edifice heightaˆ¦.Over the class of the edifice ‘s life, this can stand for significantly increase leasing gross for the proprietor. ”
The traditional strengthened concrete edifice with had a bipartisan slabs required more concrete in its assembly which resulted in more weight. Its less heavy option, the post-tensioned slabs requires less concrete in order to accomplish the same public presentation criterions. This therefore creates a construction which has fewer shear walls while possessing smaller columns and of class lower foundation tonss. The overall construction is hence consequences more lasting, efficient and possesses longer clear spans.
The other advantage is related to their public presentation in caustic environments where encapsulated bonded systems offer a much better design advantages that consequences in to salvaging related to life cycle.. This is due to the fact that the sum of mild steel used is minimized, particularly at the upper portion of slab. There is besides less steel to be corroded in instance the concrete gets cracked or spalled. This is of extreme of import in assorted parking garages in which a important sum of care costs are incurred to mend that are related to the spalling of concrete that occur due to the corroded rebar.A
Another virtue of bonded post-tensioning is the congenital ability to supply equal opposition to progressive prostration. This is really of import in the event of localized blast burden. Bonded post-tensioning systems give flexibleness in footings of leting easy future alterations to the construction are needed. This gives room for better and efficient restructuring and reconfiguration of the whole construction
Both the bonded together with the boundless systems can be combined within given construction. The overall consequence is the accomplishment of.perfect and lasting design.An illustration of how bonded and unbonded systems were utilised together for the accomplishment of better economic sciences, design efficiency and building demands is the W Victory Hotel & A ; Residences located in Dallas, Texas. The edifice ‘s concrete frame construction included a mixture of both monostrand and unbonded post-tensioning systems coupled with bonded and multistrand post-tensioning concrete systems. In the building, the unbonded post-tensioned systems were utilized at the typical degrees. However the bonded post-tensioning systems were used and implemented in the girders ‘s transportation on three degrees so as to give optimum cleft and warp control ; elements that are paramount for transportation of the girders necessary for transporting the tonss from the architecturally multi-story construction. The bonded post-tensioning systems were besides utilized in the exterior applications that were susceptible to corrosion onslaught.
Post-tensioning undergone a batch of development and betterments over the last 50 old ages, this has the consequence of bettering and giving rise to the current methods that now serve as the most important characteristic in the major building industry.
Lastingness of post-tensioned concrete
Several surveies have been devoted to the survey of the lastingness of tensioned concrete. As an illustration we can indicate out the assorted legion and extended surveies that were carried out by the U.S Army Corps of Engineers who conducted assorted exposure trial with the purpose of proving the effects of tides on the post-tensioned concrete structures.The trial was carries out in a tidal flat in chief ( Treat island ) .The consequences was desirable since all the trial specimens exhibited good qualities since they had no indicant of a impairment in their service integrity.The fact tha at that place has been no indicant of a impairment in post-tensioned concrete construction under exposure to a decennary long period of cyclic freeze conditions and chlorides is in title a great public presentation ( Freyermuth,1991 )
Another study that was compiled by the NCHRP in 1989 gave the consequence of exposing post-tensioned concrete beams to a twelvemonth long trial of corrosion protection ( Perenchio et al 1989 ) . In the trial, really terrible and extremely accelerated corrosion trials were carried out on legion corrosion protection systems. Perenchio discovered that canals that were coated with epoxy gave the best public presentation of corrosion resistance.It is deserving observing that the North American post-tensioned concrete industry is made up of constructions that have a different post-tensioned construction criterions. These criterions require the post-tensioned concrete construction to hold a bare anchorage and must be made up of galvanized steel canals which bear canal taped articulations. The prepressing strands must be bare and the grout must be cementitious and be adequately protected.
A more comprehensive analysis of the lastingness of the post-tensioned concrete was subsequently carried at the University of Texas at Autin.This was concentrated on the methods of bettering the lastingness of the criterion span decks by agencies of a transversal prestressing system ( Poston et al,1997 ) .The happening were that the usage of grouted and galvanized canals resulted in better and adequately protected sinews that lie between the assorted anchorage points. It was besides found that thin concrete screens provided adequate protection against corrosion. In fact it was recommended by the writers that complete encapsulation of the post-tensioning concrete constituents be provided for effectivity in increasing the structural lastingness of the constituent. The University of Texas experiment besides highlighted the negative function that the snap of the concrete has on the corrosion rate of the component/structure.The consequence of snap of concrete was found to be more terrible on the mild support in the system of slabs. The incursion of chloride ions was besides found out to be reduced or instead hampered wherever the clefts had a restriction in footings of their breadth.
Subsequently on, it was found out that the following are bound to be achieved on the post-tensioned concrete systems.
The trial have revealed that for assorted signifiers of external sinew systems, there exists an unsure degree of protection that can be observed on the grout whenever there is a via media of the grout.The 2nd observation is that the installing of plastic canal system in the internal sinews has the consequence of extinguishing the jobs associated with secondary lastingness such as staining and spalling.
The trials have revealed that steel canals are capable of supplying a comprehensive and long term protection against corrosion. Finally, the trial revealed that the usage of assorted signifiers of fluidizing alloies together with pozzolans aid in the betterment of the grouting operations and the overall consequence of increasing the protection of the grout ‘s value.
Post-tensioned concrete has been utilized for over than 40 old ages in the United States in a broad Texas Ranger of building undertakings ( Crigler,2007 ) .. Initially employed in the building of Bridgess its applications have by now increased far beyond the building of Bridgess and now encapsulated the edifice of armored combat vehicles, offices condos, hotels, parking garages, pavings, assorted signifiers of masonry, lasting seismal walls, household places among many other applications. The fact that post-tensioning can be efficaciously combined with other structural stuffs coupled with he fact that it has employed in the strengthening of steel, reenforcing of concrete, applied in masonry and the strengthening of other lumber constructions, together with the sweetening and extension of the basic capabilities of precast, pre-tensioned constructions, the techniques of use will of all time increase.