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 the additional demands of rebending on site), it can often appear - somewhat inexplicably - as if ‘anything goes’.
invisibleconnections.co.uk
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 and often prove wasteful in application (explained more later).
Varying the reinforcement and casing dimensions to suit, results in what we know as ‘specials’. For UK CARES approved fabricators, these simply incorporated variations help to ensure that design intent is met, whilst also making life much easier for contractors.
invisibleconnections.co.uk
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….
invisibleconnections.co.uk
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).
invisibleconnections.co.uk
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).
invisibleconnections.co.uk
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?
invisibleconnections.co.uk
Here’s what some customers say to us‌.
invisibleconnections.co.uk
‘‘We’ll just buy a pallet of ‘standards’ ....they’re cheaper.’’
invisibleconnections.co.uk
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…
invisibleconnections.co.uk
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 storeys Concrete Core ‘B’ (slip-formed) 12 storeys Creekside Wharf, Greenwich
invisibleconnections.co.uk
Core ‘A’ 22 storeys
Alphabetical key for FERBOX locations, e.g. used later in cost-analysis.
invisibleconnections.co.uk
Core ‘B’ 12 storeys Alphabetical key for FERBOX locations, e.g. used later in cost-analysis.
invisibleconnections.co.uk
Simple study to evaluate volume wastage of using ‘standards’ v made-to-length ‘specials’….
invisibleconnections.co.uk FERBOX joint length as made-to-measure (mtrs) See Note 1
Number of cases used to make FERBOX joint lengthSee Note 2
2.204 3.332 14.189 1.947 5.750 1.786 7.061 1.691 2 x 0.813 2 x 1.375 2.046 1.022 5.409 2.910 1.890 1.344 2.360 1.544 1.466 2.660 1.216
2.100 3.300 14.100 1.800 5.550 1.650 6.900 1.650 2 x 0.750 2 x 1.200 1.950 0.900 5.250 2.850 1.800 1.200 2.250 1.500 1.350 2.550 1.200
2 3 11 2 5 1 6 1 2 2 2 1 4 2 2 1 2 1 1 2 1
2 3 12 2 5 2 6 2 2 2 2 1 5 3 2 1 2 2 2 3 1
2.400 3.600 14.400 2.400 6.000 2.400 7.200 2.400 2.400 2.400 2.400 1.200 6.000 3.600 2.400 1.200 2.400 2.400 2.400 3.600 1.200
2 3 12 2 5 2 6 2 2 2 2 1 5 3 2 1 2 2 2 3 1
2.500 3.750 15.000 2.500 6.250 2.500 7.500 2.500 2.500 2.500 2.500 1.250 6.250 3.750 2.500 1.250 2.500 2.500 2.500 3.750 1.250
1 1 1 1 1 1 1 1 2 0 1 1 1 1 1 1 1 1 1 1 0
0.300 0.300 0.300 0.600 0.450 0.750 0.300 0.750 0.900 0.000 0.450 0.300 0.750 0.750 0.600 0.000 0.150 0.900 1.050 1.050 0.000
14.3% 9.1% 2.1% 33.3% 8.1% 45.5% 4.3% 45.5% 60.0% 0.0% 23.1% 33.3% 14.3% 26.3% 33.3% 0.0% 6.7% 60.0% 77.8% 41.2% 0.0%
0.400 0.450 0.900 0.700 0.700 0.850 0.600 0.850 1.000 0.100 0.550 0.350 1.000 0.900 0.700 0.050 0.250 1.000 1.150 1.200 0.050
19.0% 13.6% 6.4% 38.9% 12.6% 51.5% 8.7% 51.5% 66.7% 4.2% 28.2% 38.9% 19.0% 31.6% 38.9% 4.2% 11.1% 66.7% 85.2% 47.1% 4.2%
Total per level Total per 22 levels
66.203 1,456
63.750 1,403
54 1,188
62 1,364
74.400 1,637
62 1,364
77.500 1,705
20 440
10.650 234.300
16.7%
13.750 302.500
21.6%
Casing length (m) 1.200 Extn
Casing length (m) 1.250 Extn
If 'standards' used, then number of cuts required on site
Concrete joint length as drawn (mtrs)
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).
WASTAGE ANALYSIS: If off-the-shelf 'standards' used, then the overall metreage required, less the metreage of made-to-length 'specials' equals wastage
Core A wall 1A Core A wall 1A Core A wall 2A Core A wall 3A Core A wall 3A Core A wall 4A Core A wall 4A Core A wall 5A Core A wall 6A Core A wall 6A Core A wall 7A Core A wall 7A Core A wall 8A Core A wall 9A Core A wall 10A Core A wall 11A Core A wall 12A Core A wall 13A Core A wall 14A Core A wall 15A Core A wall 16A
FERBOX key
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).
Structural member
Core ‘A’ 22 storeys
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)
Wastage (m) 1.200 %
Wastage (m) 1.250 %
6.827 3.305 3.929 7.627 3.735 2.280 5.459 3.176 4.600 2.376 0.899 2.009 1.450 2.676 0.888
6.750 3.150 3.750 7.500 3.600 2.100 5.400 3.000 4.500 2.250 0.900 1.950 1.350 2.550 0.900
5 3 3 7 3 2 5 2 4 2 1 1 1 2 1
6 3 4 7 3 2 5 3 4 2 1 2 2 3 1
7.200 3.600 4.800 8.400 3.600 2.400 6.000 3.600 4.800 2.400 1.200 2.400 2.400 3.600 1.200
6 3 3 6 3 2 5 3 4 2 1 2 2 3 1
7.500 3.750 3.750 7.500 3.750 2.500 6.250 3.750 5.000 2.500 1.250 2.500 2.500 3.750 1.250
1 1 0 1 0 1 1 1 1 1 1 1 1 1 1
0.450 0.450 1.050 0.900 0.000 0.300 0.600 0.600 0.300 0.150 0.300 0.450 1.050 1.050 0.300
6.7% 14.3% 28.0% 12.0% 0.0% 14.3% 11.1% 20.0% 6.7% 6.7% 33.3% 23.1% 77.8% 41.2% 33.3%
0.750 0.600 0.000 0.000 0.150 0.400 0.850 0.750 0.500 0.250 0.350 0.550 1.150 1.200 0.350
11.1% 19.0% 0.0% 0.0% 4.2% 19.0% 15.7% 25.0% 11.1% 11.1% 38.9% 28.2% 85.2% 47.1% 38.9%
48.636 584
49.650 596
42 504
48 576
57.600 691
46 552
57.500 690
13 156
7.950 95.400
16.0%
7.850 94.200
15.8%
Casing length (m) 1.200 Extn
Casing length (m) 1.250 Extn
If 'standards' used, then number of cuts required on site
Number of cases used to make FERBOX joint lengthSee Note 2
Total per level Total per 12 levels
WASTAGE ANALYSIS: If off-the-shelf 'standards' used, then the overall metreage required, less the metreage of made-to-length 'specials' equals wastage
FERBOX joint length as made-to-measure (mtrs) See Note 1
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).
Core B wall 1B Core B wall 2B Core B wall 2B Core B wall 3B Core B wall 4B Core B wall 4B Core B wall 5B Core B wall 6B Core B wall 7B Core B wall 8B Core B wall 9B Core B wall 10B Core B wall 11B Core B wall 12B Core B wall 13B
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)
Concrete joint length as drawn (mtrs)
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).
FERBOX key
Core ‘B’ 12 storeys
Structural member
invisibleconnections.co.uk
Wastage (m) 1.200 %
Wastage (m) 1.250 %
invisibleconnections.co.uk
Wastage impact analysed across both cores…. +397m (20%) wasted if using 'standards'
1,998m If using FERBOX made-to-length 'specials'
Up to 397m 'standards' material wastage £4,959 (at nom £12.50 per mtr, but could be much more) Labour to cut and seal 'standard' cases £596 (596 cuts x 3 mins/£1 each @ £20 hour) Sub-total cost £5,555 PLUS VARIABLE ‘UNSEEN’ ADDITIONAL COSTS Cost of waste disposal £,£££ Cost to drill and resin-fix rebar (where applicable) £,£££ Cost of remedial couplers (where applicable) £,£££ Cost of project delay £,£££ REAL UNACCOUNTED COST OF USING ‘STANDARDS’ >>£5,555
invisibleconnections.co.uk
FERBOX reinforcement continuity strip…. the difference is that ‘specials are our standard’
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….
invisibleconnections.co.uk
1. It removes the labour and associated costs of cutting and re-sealing cases (also compromising lap-lengths, which are cut short). A
result!
B
C
invisibleconnections.co.uk
2. There are no material losses (on a typical project, we estimate that 20% of 'standard' cases and reinforcement are wasted).
invisibleconnections.co.uk
3. Wastage transfer and disposal is eliminated, saving cost whilst protecting the environment.
invisibleconnections.co.uk
4. By having correctly sized casing lengths, the unplanned and expensive cost of remedial couplers, drilling and resin-fixing rebar are eliminated.
invisibleconnections.co.uk
5. There's no need to run power and power-tools, improving efficiency.
invisibleconnections.co.uk
6. Health and safety conditions are improved by removing the use of power-tools.
invisibleconnections.co.uk
7. The specified reinforcement design can normally be met (achieving correct anchorage, lap and concrete cover)....
….by simply varying ‘H’, ‘L’ & ‘W’ to suit
invisibleconnections.co.uk
8. In congested site working conditions, installation is de-hassled by transferring avoidable operations off-site, into factory controlled conditions.
invisibleconnections.co.uk
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 2.250 m
1 of 2 Ref: 129575-1A
invisibleconnections.co.uk
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).
invisibleconnections.co.uk
….and last but not least, a customer’s view…. The customer used in our project example chose to use FERBOX ‘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 Manager O’Keefe Construction (Greenwich) Ltd
Invisible Connections Ltd
Unit 6│Thame Forty│Jane Morbey Road Thame│Oxfordshire│OX9 3RR +44 (0)1844 266000 sales@invisibleconnections.co.uk www.invisibleconnections.co.uk