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PART8 | Strength Of Materials | Concrete
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Description: post tension
The CARES Guide to Reinforcing Steels Part 8
Punching Shear System
Earlier parts of this Guide have
described how CARES has undertaken
certification for products which have
been the subject of product standards
and, by specific reference to
properties, processes and products,
how its certification schemes provide
confidence in the compliance of
As the reinforced concrete market
develops, certain products and
systems have emerged which are
designed to provide added value to the
contractor and the end product user
through improved performance,
however that is assessed. Very often,
these new products are not covered by
a product standard but are proprietary
items designed for a specific
construction situation, Nevertheless,
users require confidence, often by
external independent verification and,
in order to deal with this, CARES has
designed a system of certification to
Part 8 of this Guide describes the
principles and practices of this system, Figure 1 Courtesy of RFA
which is called Technical Approval
by CARES.
produced by CARES and its agents, 2.1 Key differences
2.0 CARES Technical approved by experts selected from it’s
Board of Management and applied by The key differences between the
it’s assessors and nominated test CARES Technical Approvals and its
houses. All product assessment Product Certification are:
The procedure begins with a detailed
schedules include quality system
discussion between the applicant firm
requirements and the quality • Creation of bespoke tests and
and CARES, including any technical
management systems of producers are testing programme to be included
expert deemed necessary, to establish:
assessed and audited twice-yearly by within the assessment schedule.
CARES auditors’ expert in the products Such testing may be defined in a
• The extent of the product family to
and processes involved. Furthermore product standard, or alternatively
there is an evaluation of the technical designed by CARES. CARES does
• The scope of product use and its data of the producer, as applied to the try to follow the basic ethos of
intended purpose. product, which includes those standards writing in this respect,
procedures for installation and technical by the use of an expert and
• The general principles of testing
assistance. Any amendment to the balanced panel in the approval of
product production or design considered any Assessment Schedule used.
The procedure ensures that a significant to its performance is Testing may be full-scale and in-situ.
comprehensive series of tests is assessed and further tests are initiated
performed on each product in relation as required. On completion of testing • Design considerations.
to those characteristics considered the assessment report and the
important to meet its declared certificate, which includes the certificate • Safety considerations.
purpose. The product performance of approval, are approved by a group
requirements are included in an selected from the CARES Board, before • Detailed technical reporting as well
assessment schedule which is it is signed and issued. as certification.
but the most common are based on either a threaded bar and coupler. types of which CARES has already assessed and certificated.g. The load in the first bar is transmitted to the concrete by the bond between steel and concrete to the second bar. Thread/swage combination In some circumstances lapping of reinforcement is neither practicable nor cost effective and to solve this problem. which is Figure 2 Courtesy of Erico common in reinforced concrete construction.1 Mechanical Splices ■ Basic principles The basic principle of lapping. a continuous load path is . the construction industry has developed mechanically coupled splices. Some codes Figure 3 Courtesy of G-Tech restrict overlapping to areas subject to lower stresses or restrict overlapping to smaller bar diameters.0 The procedure in operation Tapered thread The following examples of product. This complexity requires design regulations for lapping and that design engineers and site engineers be familiar with these design requirements. Mechanical Splices 2. including the properties of the concrete. There is also a sleeved coupler which is bolted onto the bar.3. are used to describe the operation of the scheme in practice: 1. There are many different types of coupler. less that 32mm. a sleeved coupler which is swaged onto the bar. Since this load transference is indirect. and Parallel thread connect them with tying wire. the efficiency of this joint and therefore the lap length depends on many factors. e. Design codes typically recommend that joints in rebar are to be placed away from points of high stress and that these joints are staggered. is to lay two bars parallel to one another. overlapping for a certain designed length (lap length). or a combination of both. Punching Shear Systems 3. This product is known as a coupler and is designed to join two reinforcing bars together and transmit the load in one bar to another. By creating an end-to-end bar Figure 4 Courtesy of Dextra connection. Continuity Strips 3.
in which a steel sleeve is attached to both bar ends by applying radial pressure to the bar/coupler assembly and resulting in a pressure sealed splice. to suite the taper thread of the • TA1-A. CARES also assesses how technique. the tensile strength requirement is using a set of dies and a threading based on the actual yield strength machine. to assessment is driven by design 540Mpa for grade B500B and code/specification requirements.10mm @ 0.15 and < Re. the following applications properties are assessed for all sizes Tapered thread under approval. act x 1. (Based on use of Only B500C grade reinforcement is The ends of the rebar are sawn square BS4449 reinforcement grades): permitted for nuclear applications and and a tapered thread is cut onto the bar. R class couplers assessment. . which should be calibrated for strength/yield strength) and The effective strain across the splice the purpose. easy and inexpensive to test. shall be < strain in the control bar that the bars are easily and correctly The minimum UTS = Re x (Rm/Re) = +40%. wrench. centred in the coupler. As detailed above. CARES has formulated Permanent set < 0. A benefit of this system is yield strength.65 fy three different assessment schedules in tension and compression for EC2 There are a number of proprietary for mechanical splices. are connected by means of a high performance threaded stud. the effective diameter of the may be used without the need for a reinforcement fabricators produce and threaded bar is equal to the bar diameter fatigue assessment. (Figure 2). Furthermore. To overcome this. various claims of performance and management system. The tensile strength requirements UTS > load required to produce 2% The coupler is assembled using a torque are based on the Ratio (tensile strain in reinforcing bar. ■ Types of mechanical coupler As a result. subject to a cold soak (-7°C) or low cycle fatigue (100 cycles. the CARES approach for grade 460B reinforcement.10mm @ 0. thereby creating the conditions for failures within the bar and not the coupled joint. between Parallel thread Permanent set < 0. a range of endurance levels. with full system of assessment of both for BS8110. D and increased to a predetermined diameter. including practical benefits. Using this fatigue assessment. as approved by CARES. D class may be used in bridges but Finally. Continuity strip Swaged or thread/swage combination Swaging of a coupler. apply mechanical splices. or “upset”.6 fy. is less common in today’s market. reduced.6fy. After cutting square. thus ensuring a full strength joint. This ensures ease of reinforcement and 575MPa for Additionally some of the samples are installation. The most common of mechanical splice and bar traceability • TA1-C for use in nuclear these. by cold forging. for use with Highway and is coupler. This may be due to a very slow installation rate. provided by the coupler manufacturer. which are swaged onto the bar ends. In addition to a and tension and optional compression splicing systems that are sold. based on the above and are 497MPa mechanical splice is relatively quick. failure must be by bar break. for use with BS8110 and EC2 independent of the condition and quality Claims of performance between the The tensile strength requirements are of the concrete. 5% and 90% fy). are: and installer qualification. such that the core diameter of the bar is There are two fatigue classes. 575MPa for grade B500C. act x 1. the ends of the bar Fatigue = Fatigue testing in air using For “Type A” couplers the mode of are enlarged.created from one bar to another that is ■ CARES assessment • TA1-B. R. The threading machine is usually Structures > Re. grade B500C. mechanical splices have been developed which employ a combination of swaging and parallel threading to ensure a full strength joint with flexibility of assembly. Sleeves. the different types are wide and varied. and whilst outside the direct A parallel thread is then either cut or requires the designer to undertake a remit of the Technical Approval rolled onto the enlarged end.35.10mm @ 0. The coupler is a assembled using a torque wrench (Figure 3). Figure 5 Courtesy of Ancon (Figure 4). and the opportunity for cross-threading is 540Mpa for grade B500B Permanent set < 0.
Ductlity is clearly the and shear loading. ready for splicing the main reinforcement of the consequent pour. providing Straighten bars with a rebate and key for the subsequent rebending tool pour of the adjoining member. as successful testing is also performed as part of re-bending of reinforcing steel is a the CARES assessment. Using a specially designed tool (Figure 7). traditionally formed size and supplier is appropriately construction joints. equivalent. Traditional methods for forming construction joints on site can require the site bending and re-bending of reinforcing steel. After The CARES Technical Approval covers bending and straightening. matter of steel suitability. These tests key property here and. CARES construction joints formed with undertake mechanical testing to ensure these systems are comparable to Figure 7 Courtesy of Ancon that steel of each process route. This certification is defined ■ Basic principles in Appendix 8 of its Steel for the Reinforcement of Concrete Scheme. the carrier case lid is removed to reveal the connection legs (starter bars) folded inside the casing (Figure 6). whilst of course demonstrate that the flexural ensuring that all steel used meets the strength and shear strength of requirements of BS4449. Figure 8 Courtesy of Ancon ■ CARES assessment selected by the continuity strip producer prior to its use. bend parameters and workmanship. tensile property requirements of Figure 6 Courtesy of RFA bending of reinforcement protruding BS4449. the unit is fixed to the shutter and cast into Peel off outer face the front face of the wall or floor. Regular independent Bending tool assessment process. pre- bent and housed in a purpose-designed carrier casing (Figure 5). The typical reinforcement continuity system consists of reinforcement. as well as the approval of (TA2) individuals who operate this in situ equipment. such as scabbling at the joint. On-site. which can adversely Continuity Strip affect the material properties. steel Ready for use the use of these systems in accordance must be shown to comply with the with EC2. The casing remains embedded in the wall or floor. eliminating the need for traditional preparation.2 Reinforcement particular to the type of coupler in continuity system Continuity Strip question. these legs are bent out by the contractor. This is therefore a reinforcement must not have any fundamental consideration in the surface rupture. Any site-bending or re. Parts 2 Full scale in-situ structural testing is and 3 of this Guide explain the varying also performed to evaluate the properties of reinforcing process routes performance of construction joints and properties relating to steel sold into under combinations of high flexural the market today. After the formwork is struck. in operation Reinforcement continuity systems are designed to maintain continuity across construction joints in concrete structures in a time saving and cost effective manner.The CARES Guide to Reinforcing Steels Part 8 It covers the use of equipment 3. Also after bending and from concrete is a matter for the straightening twice. the Engineer’s approval. . type.
usually with used by the applicant manufacturer. reinforcement and the stud heads determine their total elongation at and ribs on the shaft provide maximum force in accordance with • An evaluation of the technical data of anchorage and bond with the BS4449 and must comply with the the manufacturer. This is subject to the scrutiny of CARES in order to ensure that it is within its area of defined expertise and that full support for assessment requirements are available.0 The CARES Scheme scope of use that has been assessed and that the stud heads remain and approved. Any amendment to the its spacing. All product assessment schedules include quality system requirements and include 3. approved by experts selected from it’s Board of Management and applied by its auditors and nominated test Figure 9 Courtesy of RFA houses. requirements both for the product Product Requirements itself and for its application. its specific application and the scope of certification are fully understood. performance characteristics to determine their tensile strength in Traditionally shear link reinforcement considered important to meet its accordance with BS4449 and must is used to resist punching shear declared purpose. ■ Basic principles • The formulation of a comprehensive A concentrated load on a slab causes Product testing: testing programme giving full high punching shearing stresses on consideration to each of those a Tensile strength: The studs are tested the section around the load. The slabs/columns must tests are initiated as required if ■ CARES assessment achieve the necessary punching shear CARES approval is to be maintained. The tensile load must management systems of producers a prefabricated solution that is be applied via the head and the mode both initially and periodically by CARES relatively easy to install (figure 9). assessment report and Technical a Mechanical testing of the studs to Approval report are produced. as applied to the concrete. the shaft b Elongation at maximum force: This assessment is based on the of each stud provides the shear The studs must be tested to requirements of ISO9001:2008. designed in product production or design accordance with the manufactures considered significant to its guidance and subject to punching performance is assessed and further shear loads. . sub-contracting production and testing ribbed reinforcing steel. EC2 enables the calculation requirements of BS4449 Table 10. This includes any Shear studs are fabricated from the head. the CARES Technical Approval as proof that the approval is current system and design and detailing Scheme uses many of the same and valid. • The formulation of an assessment schedule by CARES and its agents. comply with the tensile properties of however shear studs connected to BS4449 for the specified grade of • An assessment of the quality rails are a popular alternative. slab/column samples. product. hot forged enlarged ends. in must be accompanied by a specific b Structural testing in concrete that it does not deal with standardised CARES Technical Approval certificate to verify that the producers stud products. both of ensure that the stud’s tensile which detail the product scope and properties comply with BS4449 4. capacity and the mode of failure must CARES assessment comprises: • On completion of testing an be ductile and flexural in nature. including those procedures of area punching shear reinforcement for installation and technical required and also gives guidance on c Structural testing: reinforced concrete assistance.3 Punching Shear guidance provide adequate consideration of the design Systems (TA7) punching shear resistance. The Technical Approval procedure ensures the following: • That the product. It is important to note attached under full tensile load. of failure must be by ductile failure of auditors’ expert in the products and the shaft and not by detachment of processes involved. offering reinforcement. Whilst being different in nature to the that the Technical approval report CARES Product Certification scheme.The CARES Guide to Reinforcing Steels Part 8 principles as they are described in Punching Shear System in situ Part 1 of this Guide.
2. CARES Guide to Reinforcing Steel • The product is installed and used as e-mail: general@ukcares. 21 Pembroke Road.Part 1-1: General rules for buildings.0 References CARES Technical Approval Document 1 BRITISH STANDARDS INSTITUTION. 5. appendices 6 and 10. its limitations.com URL: www. All CARES Technical Approvals are 9001:2008 Important conditions in relation to the published in PDF format on CARES’ “Quality Management Systems- validity of the approval to be website: www. 3. Code of Figure 10 Technical Approval Report and Certificate practice for design and construction”. The Product Certification from that assessed.ukcares. in effect.com Steel. BRITISH STANDARDS INSTITUTION. Tel: 01732 450000 Fax: 01732 455917 7. BS EN ISO therefore. The Welding of Reinforcing detailed in the report website: www. coil and decoiled product - Specification. BS EN 1992-1-1: 2004 Eurocode 2 Design of concrete structures.ukcares. BS 8110:Part 1:1997 “Structural use of concrete. UK CARES Pembroke House. BRITISH STANDARDS conditions of use of the product and INSTITUTION. UK CARES “Steel for the 5. BS 4449: 2005 Steel for the reinforcement of concrete – Weldable reinforcing steel . Scheme” Edition 3 September The Technical Approval Report is an Figure 10 shows a CARES Technical 1999. recognised include: UK CARES • The product design and 6. • The materials and method on manufacture remain unchanged. important document for the end Approval Certificate alongside its product user in that it defines the associated Certificate of Approval.Bar.0 The Technical Approval Report be read in conjunction with the relevant Reinforcement of Concrete CARES Certificate of Approval.com Part 6. Kent TN13 1XR Phone: +44(0)1732 450000 Fax: +44(0)1732 455917 E-mail: general@ukcares. please send an e-mail to the address above P8/REV1/2011/AARON . BRITISH STANDARDS INSTITUTION. The Technical Approval Report must 4. Sevenoaks.The CARES Guide to Reinforcing Steels Part 8 6. Sevenoaks Scheme for Steel for the Kent TN13 1XR Reinforcement of Concrete.com Copyright UK CARES © This guide is available in pdf format. If you wish to receive a pdf copy and receive future updates. CARES Guide to Reinforcing Steel Pembroke House specification remain unchanged 21 Pembroke Road Part 1.UKCARES.com Requirements”.
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