Imagineering the possibilities

POST TENSIONED

SLABS

CCL post - tensioned slab solutions represent continuous development throughinvolvement in building structures worldwide. CCL systems present intelligent solutionsto some of the common restrictions faced by architects, engineers and contractors:

imagineering...

• Open-plan spaces with large spans not restricted by awkward columns

• Flat slabs without drop elements that restrict the layout of partitions and services

• Thin slabs that increase plannedclearance under ceilings or reduce totalbuilding height

• Greater freedom in architectural shapesof slabs and the positioning of columns

• Slabs with fewer or no expansion joints

• Slabs with reduced, simple to fix reinforcement and less concrete to pour

• Faster stripping of shuttering allowing quicker redeployment of formwork

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CCL post-tensioned slab systems are the first choice for many architects, contractors andengineers around the world. The intelligent use of post-tensioning technology by CCL’sexperienced engineers can bring bespoke solutions to suit each unique situation.

...the possibilities.

Architectural IntelligenceCCL post-tensioned slabs can bring unique freedom overconventional building methods. This allows increased spans to beachieved reducing the need for columns within the structurethrough more efficient and stronger floor slab design.

Commercial OpportunitiesCCL post-tensioning results in thinner slabs making valuable extraceiling height between floors available as extra floors. This canproduce extra valuable rentable floor area within the same overallbuilding height.

Strong FundamentalsA CCL designed post-tensioned slab can contain less concrete(20% to 30%), minimal quantity of reinforcement and lesscomplicated re-bar shaping.

Structural ReliabilityCCL post-tensioned slabs show reduced cracking for improveddurability and lower maintenance costs. Their deflection can becontrolled by varying the amount of post-tensioning to balanceany portion of applied loads immediately after stressing.

Increasing PopularityDue to the significant benefits of CCL post-tensioned slabs fordevelopers, architects, engineers, contractors and end-users, their use is growing in popularity worldwide.

Early PlanningTo obtain maximum benefits of CCL’s post-tensioned slabs, it isrecommended for the system to be incorporated into the buildingstructure at early design stages.

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...while building confidence

UNCOVER THE TRUE POTENTIAL OF YOUR BUILDING

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Design solutions:CCL provides the complete design for a post-tensionedsolution. CCL’s design team has the experience and theexpertise, gained by working on projects around theworld, to provide you with a prompt and effectivedesign solution. We utilise state of-the-art designprograms that are continually updated to reflect thelatest international construction codes of practice.

CCL specialists are available to help structuralengineers determine the best option from an earlydesign stage through extensive value engineering inorder to meet specific requirements for each project.CCL can provide a detailed scheme with sufficientinformation for tender purposes. Upon execution, CCL’sspecialised design team will develop the design andprovide shop drawings for construction.

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“Experience and expertise,gained by working on projectsaround the world, we utilisestate of-the-art designprograms that are continuallyupdated to reflect the latestinternational constructioncodes of practice to provideyou with a prompt andeffective design solution.“

Post-tensioning is a way to overcome the naturalweakness of concrete in tension and to make better use of its strength in compression.

realising...

The principle is well perceived when holding together several books bypressing them laterally. Under such a pressure the whole row gains enough stiffness and strength to insure its integrity.

In concrete structures, this is achieved by placing high tensile steeltendons/cables in the element before casting. When the concrete reachesthe desired strength, the tendons are pulled by special hydraulic jacks andheld in tension using specially designed anchorages fixed at each end of the tendon.

This will provide compression at the edge of the structural member thatincreases the strength of the concrete for resisting tension stresses.

If tendons are appropriately curved to a certain profile, they will exert, inaddition to compression at the perimeter, a beneficial upward set of forcesthat will counteract applied loads, relieving the structure from a portion of gravity effects.

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EFFECTS OF CURVED POST-TENSIONING TENDON ON THE STRUCTURE

TENSION IN CONCRETE PRODUCES CRACKING

IN POST TENSIONED CONCRETEPRE COMPRESSION RESISTS TENSION

IN REINFORCED CONCRETE RE-BAR RESISTS TENSION

...the possibilities.

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Post Tensioning SystemsCCL provides bonded and un-bonded post-tensioning systems.Both systems can be used independently or combined to providethe optimum design solution. Selection of a system depends onthe specific requirements of each project. CCL specialists areavailable to discuss which method is best suited to particularsituations.

ImplementationDuring construction, CCL supplies all materials necessary for posttensioning tendons and will supervise or perform installation workas required. After casting, CCL’s specialised site team can performspecialist stressing and grouting operations to complete yourbuilding project.

Types of SlabsThe CCL post-tensioned slab systems can be integrated into any type of slab: flat slab, ribbed slab and coffered or waffle slabs.The slab may include drop caps, drop panels or band beams to produce optimal configurations.

SOLID FLAT SLAB SOLID FLAT SLABWITH DROP PANELS

BANDED FLAT SLAB

RIBBED SLAB BANDED COFFERED FLAT SLAB

BEAM AND SLAB

COFFERED SLABWITH SOLID PANELS

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structural design...

Post-tensioning tendons are virtually replacedin the slab by the set of forces they exert onit: compression along the slab perimeter,upward forces in the field and downwardforces over the supports.

Several elastic methods of analysis can beused to determine stresses in slabs undergravity loads and equivalent post-tensioningactions such as the Equivalent Frame Method(EFM) and the Finite Element Method (FEM).Stresses and deflections resulting from theelastic analysis are checked under ServiceLimit State (SLS) against allowable valuesimposed by the adopted code of practice.

Critical sections are checked under UltimateLimit State (ULS) and where a lack ofresistance occurs; it is compensated bylocalised additional ordinary reinforcement.The punching shear is checked and if thecorresponding resistance is not sufficient, it iscatered for by additional reinforcement, shearstuds or increased concrete thickness(drop caps).

When an analysis is satisfactorily completed,structural detailing is carried out to show theslab’s layout and dimensions, tendons’distribution and profiles, details of ordinaryreinforcement, jacking forces andcorresponding elongations in tendons dueto stressing.

Typical Tendon Layout

FINITE ELEMENT MESHING

STRESS DISTRIBUTION

2 WAY BANDED 1 WAY BANDED1 WAY DISTRIBUTED

2 WAY DISTRIBUTED

The following table gives span/depth ratios for a variety of section types of multi-spanfloors. The table can be used to determine slab thickness for given span and loads.

typical span to depth ratios...

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Table reproduced from Technical Report 43 ‘Post-tensioned concrete floors’ with kind permission of The Concrete Society. For further information please contact CCL.

Section Type Total Imposed Load (kN/m2)

Span/Depth Ratio for 6m ≤ L ≤ 13m

1. SOLID FLAT SLAB2.55.0

10.0

403630

2. SOLID FLAT SLABWITH DROP PANELS

2.55.0

10.0

444035

3. BANDED FLAT SLAB

2.55.0

10.0

Slab454035

Beam252218

4. COFFERED FLAT SLAB

2.55.0

10.0

252320

5. COFFERED FLAT SLAB WITH SOLID PANELS

2.55.0

10.0

282623

6. COFFERED SLAB WITH BAND BEAM

2.55.0

10.0

282623

7. RIBBED SLAB2.55.0

10.0

302724

8. ONE WAY SLAB WITH NARROW BEAM

2.55.0

10.0

Slab423834

Beam181613

CCL’s un-bonded single strand tendon system is quick to install; tendons can be easilydeflected to avoid openings and to cope with irregular slab shapes. The system hasreduced friction losses and increased eccentricity. It requires no grouting.

mono strand unbonded systems...

Single low relaxation PC 7-wire strands of 13mm or 15mm diameterare coated with permanent corrosion-inhibiting grease and encased inHigh Density Polyethylene (HDPE) sheathing, continuously extrudedover the entire strand length to form a single strand tendon.

Tendons are laid in the slab according to specific profiles beforepouring concrete.

The grease reduces friction and the sheathing allows for free relativemovement of the strand with respect to the surrounding concreteduring stressing. Both grease and sheathing provide long-termcorrosion protection to the steel.

The strands are individually anchored at both ends to CCL un-bonded monostrand anchorages that are embedded in theconcrete to transfer compression to the slab after stressing.

Plastic re-usable fittings facilitate the fixing of live anchorages to theside shutters. Pocket formers are used to provide access for stressingat the edge of the slab.

Stressing is performed using CCL special hydraulic jacks.

Plastic caps filled with corrosion-inhibiting grease seal the strand endafter stressing and cropping.

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cclstressing.com

un-bonded installation...

“Post-tensioning - placing hightensile steel tendons/cables in

the structure before casting - isthe way to overcome the natural

weakness of concrete and toinsure its integrity.”

un-bonded installation...

• Grease coated and plastic sheathed strands are cut to therequired length and fitted with dead end anchorages whereapplicable

• The slab formwork is laid

• The position of the live end anchorages is marked on the sideshutters

• The live end anchorages are fitted to the side shutters

• The bottom layer of reinforcement is laid (whereapplicable)

• Tendons are laid and profiled on the chairs to the correct design profile

• The top reinforcement is fixed over the supports

• Concrete is poured and vibrated with care in order not to damage the tendons

• The side shuttering is removed in preparation for stressing

• The wedges are installed and the ends of the strands are marked for elongation measurement

• The concrete strength is confirmed by crushing of cylinder (or cube) samples from the same pour

• The calibrated CCL stressing equipment is assembled and set to the required force

• CCL trained specialists stress the tendons according to therequired stressing sequence and check the elongation

• Tendon tails are cut with CCL strand croppers or cutting discs

• The bottom formwork is stripped

• Tendon ends are capped and stressing pockets are filled withnon-shrink grout/mortar

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CCL bonded systems incorporate groups of 2, 3, 4, 5 or 6 strands contained within a tendon in a flat duct anchored at each end by CCL Flat Anchorages. This allows the tendons to bepositioned close to the surface to obtain maximum eccentricity within the slab.

multi-strand bonded flat slab systems...

The tendons are laid in the slab according to specific profilesbefore pouring concrete. Ducts allow for free relativemovement of the strand with respect to the surroundingconcrete during stressing.

After the strands are locked within the anchorage by thewedge, they are individually stressed with CCL hydraulic jacks.

The ducts are then filled with a cement-based grout to fullybond the strands to the concrete through the duct wall and allalong the length of the tendon.

The grout creates an alkaline environment around the steelfor permanent corrosion protection.

The strands are attached at one end to a CCL flat anchorage,and can be left exposed at the other end and embedded inthe concrete through enough length that ensures theiranchoring by bonding.

CCL’s bonded system requires a reduced amount of ordinaryreinforcement as bonding allows the strands to reach higherstrength at ultimate state.

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bonded installation...

• The slab formwork is laid

• Live anchorage positions are marked to side shutters

• Live anchorages are fixed to side shutters

• The bottom layer of reinforcement is fixed (whereapplicable)

• Ducts are laid out by connecting and sealing standardduct lengths

• The appropriate number of strands are pushed throughthe ducts and cut to required length; bonded dead endsare formed where required

• Grout vents are installed and ducts are set upon chairs tothe correct design profile

• The top reinforcement is fixed over supports (whereapplicable)

• Concrete is then poured with proper vibration, with caretaken not to damage the tendons

• Side shutters are removed

• Anchor heads and wedges are threaded onto the ends ofthe tendon

• Tendon tails are marked for elongation measurement

• Concrete strength is confirmed on samples taken fromthe same pour

• The calibrated CCL stressing equipment isassembled and set to the required force

• CCL trained specialists stress the tendons according torequired stressing sequence and check the elongation

• Stressing tails are cut and stressing pockets are filledwith non-shrink grout/mortar

• Formwork is stripped

• CCL trained specialists use CCL approved groutmixers/pumps to grout and seal the tendons

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Imagineering the possibilities.

Global QualityCCL operates globally, with a network of sister companies andpartners to ensure a close proximity to projects worldwide. Ourindependence, extensive know-how, attention to detail, honestyand service make CCL the preferred choice on projects that matter.

CCL Stressing Systems Ltd is an ISO registered company andour systems comply with the requirements of the latest FIP"Recommendations for acceptance of post-tensioning systems",ETAG 013, BS-EN13391:2004 and AASHTO.

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CCL was established in 1935 to provide cutting edge engineering

solutions. Since then, the company has grown and diversified

whilst adhering to these original goals.

Each day, CCL’s products and services are used in prestigious

building and civil engineering structures throughout the world.

CCL is committed to offer high quality, innovative

engineering solutions and outstanding service.

www.cclstressing.com