Reinforcement continuity strip. Why use specials?

Reinforcement continuity strip.Why use ‘specials’?

A comparison study of ‘specials’ v ‘standards’

invisibleconnections.co.uk

Introduction….

On every credible UK project, concrete reinforcement is specified (to BS4449:2005+A3:2016) and required to be CARES approved. ‘Cut and bent’ requirements are designed to a range of shape codes (BS8666:2005 refers). These shape codes are the basis for designers to define all dimensions, uniquely to the needs of the project. After careful quantification (avoiding wastage) the reinforcement is fabricated to order by CARES approved fabricators, bundled and uniquely labelled to suit, then delivered in sync with the site programme. This process is accepted and adopted as good standard practice, ensuring that design intent is satisfied, whilst meeting the practicalities of construction and the quality assurance needs of professional stakeholders.

The rationale described above also applies to threaded couplers.

However, when it comes to reinforcement continuity strip(where the reinforcement is uniquely subjected to theadditional demands of rebending on site), it can often appear- somewhat inexplicably - as if ‘anything goes’.


A structural component, not an accessory….

Using reinforcement continuity strip shouldn’t significantly compromise reinforcement design, yet it often does. UK CARES approved continuity strip manufacturers are adept at the timely fabrication of their products, to accommodate principal design and construction practicalities. Nonetheless, there is widespread use of continuity strip brought into the UK, often without any recognisable form of approval, and treated by some as if an insignificant ‘accessory’.

Such products tend to be entirely ‘standard’ in their configuration (with a‘one size fits all’ approach to anchorage, lap and casing length).They offer little to address the needs of reinforcement design andoften prove wasteful in application (explained more later).

Varying the reinforcement and casing dimensions to suit, resultsin what we know as ‘specials’. For UK CARES approved fabricators,these simply incorporated variations help to ensure that designintent is met, whilst also making life much easier for contractors.


Reinforcement design….

There is a strong argument for ‘specials’ to achieve the required reinforcement design (many compromises are made with standard units, which often don’t correctly address design requirements for anchorage, lap and concrete cover).

Clauses from EC2 provide some clues….


Providing the correct reinforcement detail….

Consider 8.3 and 8.4 (for good bond and bearing stress) and whether longitudinal reinforcement (top only) is required to link all continuity reinforcement.

Consider 5.6.4 (analysis) and 6.5 (design) strut and tie models. Continuity reinforcement anchorage should be designed to interact with main reinforcement.

Avoid this kind of partial anchorage arrangement, which could lead to cracking and reduction in stiffness. Continuity reinforcement should not be regarded as ‘stand-alone’. For most applications it should interact with main reinforcement (variable anchorage depths are easily accommodated in manufacture).


CARES. It matters.

Reinforcement continuity strips are important structural components that require performance validation.

CARES Technical Approval provides this validation through a process of structural testing, regular mechanical testing and audit. This meets the quality assurance needs of professional stakeholders and enables compliance with the National Structural Concrete Specification (NSCS).


Making the decision….

So, when specifying or procuring reinforcement continuity strip, there are three key questions.

Will you:

1. Use off-the-shelf standard units?2. Use purpose-made ‘specials’?3. Use a CARES Technically Approved system?


Here’s what some customers say to us….


‘‘We’ll just buy a pallet of ‘standards’....they’re cheaper.’’


But are they? – We’d like to challenge this popular belief.

Let’s take a look at the concrete cores of a typical London residential project…


Cost and efficiency study of reinforcement continuity strip (‘specials’ v ‘standards’)as used on a London residential project December 2016 to March 2017

Concrete Core ‘A’ (slip-formed) 22 storeysConcrete Core ‘B’ (slip-formed) 12 storeys

Creekside Wharf, Greenwich


Core ‘A’22 storeys

Alphabetical key for FERBOX locations, e.g. used laterin cost-analysis.


Core ‘B’12 storeys

Alphabeticalkey for FERBOX locations, e.g.

used later incost-analysis.


Simple study to evaluate volume wastage of using ‘standards’ v made-to-length ‘specials’….


Core ‘A’22 storeys

Note 1: The actual FERBOX joint lengths supplied were generally less than the concrete joint lengths, at the request of the customer (to provide flexibility for the slip-form mechanism).

Note 2: At the request of the customer, the individual FERBOX casing lengths were manufactured (where feasible in accommodating lap legs) to 1.200m or less (individual casing lengths of up to 2.400m are ordinarily possible).

1.200 Extn 1.250 Extn 1.200 % 1.250 %Core A wall 1A 2.204 2.100 2 2 2.400 2 2.500 1 0.300 14.3% 0.400 19.0%

Core A wall 1A 3.332 3.300 3 3 3.600 3 3.750 1 0.300 9.1% 0.450 13.6%

Core A wall 2A 14.189 14.100 11 12 14.400 12 15.000 1 0.300 2.1% 0.900 6.4%

Core A wall 3A 1.947 1.800 2 2 2.400 2 2.500 1 0.600 33.3% 0.700 38.9%

Core A wall 3A 5.750 5.550 5 5 6.000 5 6.250 1 0.450 8.1% 0.700 12.6%

Core A wall 4A 1.786 1.650 1 2 2.400 2 2.500 1 0.750 45.5% 0.850 51.5%

Core A wall 4A 7.061 6.900 6 6 7.200 6 7.500 1 0.300 4.3% 0.600 8.7%

Core A wall 5A 1.691 1.650 1 2 2.400 2 2.500 1 0.750 45.5% 0.850 51.5%

Core A wall 6A 2 x 0.813 2 x 0.750 2 2 2.400 2 2.500 2 0.900 60.0% 1.000 66.7%

Core A wall 6A 2 x 1.375 2 x 1.200 2 2 2.400 2 2.500 0 0.000 0.0% 0.100 4.2%

Core A wall 7A 2.046 1.950 2 2 2.400 2 2.500 1 0.450 23.1% 0.550 28.2%

Core A wall 7A 1.022 0.900 1 1 1.200 1 1.250 1 0.300 33.3% 0.350 38.9%

Core A wall 8A 5.409 5.250 4 5 6.000 5 6.250 1 0.750 14.3% 1.000 19.0%

Core A wall 9A 2.910 2.850 2 3 3.600 3 3.750 1 0.750 26.3% 0.900 31.6%

Core A wall 10A 1.890 1.800 2 2 2.400 2 2.500 1 0.600 33.3% 0.700 38.9%

Core A wall 11A 1.344 1.200 1 1 1.200 1 1.250 1 0.000 0.0% 0.050 4.2%

Core A wall 12A 2.360 2.250 2 2 2.400 2 2.500 1 0.150 6.7% 0.250 11.1%

Core A wall 13A 1.544 1.500 1 2 2.400 2 2.500 1 0.900 60.0% 1.000 66.7%

Core A wall 14A 1.466 1.350 1 2 2.400 2 2.500 1 1.050 77.8% 1.150 85.2%

Core A wall 15A 2.660 2.550 2 3 3.600 3 3.750 1 1.050 41.2% 1.200 47.1%

Core A wall 16A 1.216 1.200 1 1 1.200 1 1.250 0 0.000 0.0% 0.050 4.2%

66.203 63.750 54 62 74.400 62 77.500 20 10.650 13.750

1,456 1,403 1,188 1,364 1,637 1,364 1,705 440 234.300 302.500

Total per level16.7% 21.6%

Total per 22 levels

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If off-the-shelf 'standards' used, then

number and length required (results

are shown for 1.200m or 1.250m

casing lengths, being representative of

common market options)

If 's

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WASTAGE ANALYSIS: If off-the-shelf

'standards' used, then the overall

metreage required, less the metreage

of made-to-length 'specials' equals

wastage

Casing length (m) Casing length (m) Wastage (m) Wastage (m)


Core ‘B’12 storeys

Note 1: The actual FERBOX joint lengths supplied were generally less than the concrete joint lengths, at the request of the customer (to provide flexibility for the slip-form mechanism).

Note 2: At the request of the customer, the individual FERBOX casing lengths were manufactured (where feasible in accommodating lap legs) to 1.200m or less (individual casing lengths of up to 2.400m are ordinarily possible).

1.200 Extn 1.250 Extn 1.200 % 1.250 %Core B wall 1B 6.827 6.750 5 6 7.200 6 7.500 1 0.450 6.7% 0.750 11.1%

Core B wall 2B 3.305 3.150 3 3 3.600 3 3.750 1 0.450 14.3% 0.600 19.0%

Core B wall 2B 3.929 3.750 3 4 4.800 3 3.750 0 1.050 28.0% 0.000 0.0%

Core B wall 3B 7.627 7.500 7 7 8.400 6 7.500 1 0.900 12.0% 0.000 0.0%

Core B wall 4B 3.735 3.600 3 3 3.600 3 3.750 0 0.000 0.0% 0.150 4.2%

Core B wall 4B 2.280 2.100 2 2 2.400 2 2.500 1 0.300 14.3% 0.400 19.0%

Core B wall 5B 5.459 5.400 5 5 6.000 5 6.250 1 0.600 11.1% 0.850 15.7%

Core B wall 6B 3.176 3.000 2 3 3.600 3 3.750 1 0.600 20.0% 0.750 25.0%

Core B wall 7B 4.600 4.500 4 4 4.800 4 5.000 1 0.300 6.7% 0.500 11.1%

Core B wall 8B 2.376 2.250 2 2 2.400 2 2.500 1 0.150 6.7% 0.250 11.1%

Core B wall 9B 0.899 0.900 1 1 1.200 1 1.250 1 0.300 33.3% 0.350 38.9%

Core B wall 10B 2.009 1.950 1 2 2.400 2 2.500 1 0.450 23.1% 0.550 28.2%

Core B wall 11B 1.450 1.350 1 2 2.400 2 2.500 1 1.050 77.8% 1.150 85.2%

Core B wall 12B 2.676 2.550 2 3 3.600 3 3.750 1 1.050 41.2% 1.200 47.1%

Core B wall 13B 0.888 0.900 1 1 1.200 1 1.250 1 0.300 33.3% 0.350 38.9%

48.636 49.650 42 48 57.600 46 57.500 13 7.950 7.850

584 596 504 576 691 552 690 156 95.400 94.200

Stru

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join

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as m

ade-

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(mtr

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1

Nu

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ses

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ake

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BO

X jo

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See

No

te 2

If off-the-shelf 'standards' used, then

number and length required (results

are shown for 1.200m or 1.250m

casing lengths, being representative of

common market options)

Total per level16.0% 15.8%

Total per 12 levels

If 's

tan

dar

ds'

use

d,

then

nu

mb

er o

f cu

ts

req

uir

ed o

n s

ite

WASTAGE ANALYSIS: If off-the-shelf

'standards' used, then the overall

metreage required, less the metreage

of made-to-length 'specials' equals

wastage

Casing length (m) Casing length (m) Wastage (m) Wastage (m)


Wastage impact analysed across both cores….

+397m(20%) wasted

if using 'standards'

1,998mIf using FERBOXmade-to-length

'specials'

Up to 397m 'standards' material wastage(at nom £12.50 per mtr, but could be much more)

Labour to cut and seal 'standard' cases(596 cuts x 3 mins/£1 each @ £20 hour)

Sub-total costPLUS VARIABLE ‘UNSEEN’ ADDITIONAL COSTS

Cost of waste disposalCost to drill and resin-fix rebar (where applicable)

Cost of remedial couplers (where applicable)Cost of project delay

REAL UNACCOUNTED COST OF USING ‘STANDARDS’

£4,959

£596

£5,555

£,££££,££££,££££,£££

>>£5,555


For good reasons, over 90% of FERBOX reinforcement continuity strip is made-to-measure, which has many efficiency advantages for concrete frame construction. Here's our top 10….

FERBOX reinforcement continuity strip….the difference is that ‘specials are our standard’


1. It removes the labour and associated costs of cutting and re-sealing cases (also compromising lap-lengths, which are cut short).

A

C

B

result!


2. There are no material losses (on a typical project, we estimate that 20% of 'standard' cases and reinforcement are wasted).


3. Wastage transfer and disposal is eliminated, saving cost whilst protecting the environment.


4. By having correctly sized casing lengths, the un-planned and expensive cost of remedial couplers, drilling and resin-fixing rebar are eliminated.


5. There's no need to run power and power-tools, improving efficiency.


6. Health and safety conditions are improved by removing the use of power-tools.


….by simply varying ‘H’, ‘L’ & ‘W’ to suit

7. The specified reinforcement design can normally be met (achieving correct anchorage, lap and concrete cover)....


8. In congested site working conditions, installation is de-hassled by transferring avoidable operations off-site, into factory controlled conditions.


9. Deliveries can be scheduled on a just-in-time basis, minimising site storage requirements and making the location-labelled FERBOX 'easy to find‘.

WALL 12A CORE A

15 BARS 1 of 22.250 m Ref: 129575-1A


10. Product performance requirements are met….

All FERBOX manufacture is endorsed by CARES Technical Approval, helping you to meet requirements of the National Structural Concrete Specification (NSCS).


….and last but not least, a customer’s view….

The customer used in our project example chose to useFERBOX ‘specials’ and the project manager had this to say….

‘‘We hadn’t typically gone the ‘specials’ route before. But, by investing a little up-front time to schedule our FERBOX requirements, we gained a smooth supply and installation process - without wastage or complication - and exceeded the programme demands of our slip-formed cores.’’

Adrian Paul, Project ManagerO’Keefe Construction (Greenwich) Ltd

Invisible Connections Ltd

Unit 6│Thame Forty│Jane Morbey RoadThame│Oxfordshire│OX9 3RR

+44 (0)1844 266000sales@invisibleconnections.co.ukwww.invisibleconnections.co.uk

Documents

Reinforcement continuity strip. Why use specials?