Testing the SSL Slab Post Tension Ing System.pdf

Testing the SSL Slab Post Tensioning System

Brendan Corcoran, Consulting Engineer (retired)

Frank Filippone, formally Principal Engineer, Structural Systems Limited Synopsis This paper summarizes the componentry tests of a SSL Slab Post-tensioning System with particular reference to compliance with AS 1314:1978 and BS 4447:1991. As a result of these tests the System was certified and accepted by the UK Certification Authority for Reinforcing Steels – UKCARES. These tests were carried out in 2002 when AS 1314:1978 was the current Australian Standard. At that time it was being revised, and public comment on the first draft were under review prior to preparing the final draft. The testing was undertaken to comply with AS 1314:1978 although the number of test specimens was increased to 3, in line with international trends. In addition, testing of fixed anchorages, which were not covered by AS 1314-1978, was carried out generally with the intent of AS 1314:2004. One of the authors of this paper was the Chairman of the Standards Review Committee. These additional tests assisted the Committee revising the Standard in extending the Standard to encompass these types of anchorages. Keywords: Testing, Rectangular Stressing and Non-stressing anchors, Gripping efficiency, Strand Elongation, Bursting Reinforcement Design, Tendon Couplers. 1.0 The objective of testing The testing of a post-tensioning anchorage system is undertaken to demonstrate that the system complies with a National Standard. As the requirements of Standards can vary from country to country in several important respects it is difficult to undertake a single set of tests which satisfy two different National Standards. This paper describes the test programme of the Structural Systems Limited (SSL) Slab Post Tensioning System undertaken to show compliance with Australian and British Standards. This latter requirement resulted from their entry into the UK market at that time. The paper is divided into three parts for clarity: Part 1 deals with the Gripping Efficiency Testing of stressing anchorages, Part 2 describes anchorage Load Transfer Testing and Part 3 deals with ancillary testing of non-stressing anchorages and couplers. The test programme was designed by Frank Filippone, Principal Engineer, Structural Systems Limited to comply with both Australian and British Standards. The programme was independently witnessed by Andrew Walker of VicRoads, as nominated by the RTA, New South Wales, and Brendan Corcoran, Consulting Civil and Structural Engineer. The test program was developed to ensure compliance with:

• AS 1314:1978 - Prestressing Anchorages (current Standard under revision at time of tests) • BS 4447:1980 -The Performance of Prestressing Anchorages for Post-tensioned Construction. • AS 1311:1987 - Steel tendons for Prestressed Concrete - 7wire stress relieved strand for

tendons, (Under revision at that time). Now replaced by AS 4672.1:2007 & AS 4672.2:2007. • BS 5896:1980 - High Tensile Wire and Strand for the Prestressing of Concrete Both AS 1314 and BS 4447 require all parts of the anchorage assembly including the strand used for testing to comply. The strand diameters used in the BS 5896 are 12.9 mm and 15.7mm while AS 1311 specifies 12.7 and 15.3mm. For gripping efficiency testing either 12.7 or 12.9mm dia. can be used but the larger size required importation of a small quantity of 15.7 mm dia. strand. 2.0 The SSL Slab Post Tensioning System The Slab system stressing anchorage consists of a cast iron guide (Anchorage Casting) and a single piece anchor block. The outer face of the guide is curved to a fixed radius, which allows the strands to fan out from the tendon duct. There are three Anchorage Castings in the range, which are designed

ISBN 0 909375 78 X Concrete 07

The 23rd Biennial Conference of the Concrete Institute of Australia

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to accommodate two different strand diameters and will allow both British and Australian strand variations to be used. The anchor blocks are designed to one size of strand only. The system also includes compatible coupling block anchorages and fixed anchorages (dead end) of Bulbed and Swaged types. Details of the stressing anchorage components are given in Figures 1 – 2.

Figure 1 SSL Anchorage Casting AC 506/605

Figure 2 SSL Anchorage Block AB 506

3.0 Requirements and criteria The current range of SSL Slab System anchorage castings and anchor blocks together with coupling anchorages CA 505 and CA 506 were tested. The smallest and largest capacity non-stressing anchorages Bulbed type anchors BD 205 and BD 506 and Swaged type anchors SW 205 and SW 506 were also tested. The essential testing requirements of AS 1314 and for BS 4447 are summarised in Table 1. The principal difference is that for gripping efficiency the BS required the tendon was taken to 70% MBL prior to the test whereas AS 1314 has no similar requirement. Table 1 - Gripping Efficiency Requirements

AS 1314:1978 BS 4447:1991

Tendon shall be made up from material from a single batch of strand and must comply with AS 1311

A tendon with a quality not lower than the lowest characteristic strength specified in BS 5896:1980 shall have the following minimum performance in at least 3 consecutive tests.

The number of strands forming the tendon shall be appropriate to the anchorage under test

The actual efficiency of the anchored tendon shall not be lower than 92%. The actual efficiency of the anchored tendon shall be taken as the ratio of the failure force as measured in Clause 5 to the average ultimate tensile strength of the tendon. The actual efficiency of the anchored tendon shall not be lower than 92%.

The gripping-efficiency of the anchorage calculated from the test data shall not be less than 95% of the minimum breaking load (MBL) of the tendon conforming to AS 1311

The actual efficiency of the anchored tendon shall be taken as the ratio of the failure force as measured in Clause 5 to the average ultimate tensile strength of the tendon

The test specimen subjected to static testing shall be loaded at a constant rate

The average ultimate tensile strength shall be determined from three specimens taken at random from the total length of the tendon used in the test and tested in accordance with the methods specified in BS 18 or BS 4545 as appropriate

Anchorage efficiency (Load transfer) shall not be less than 0.95%.

The percentage elongation at maximum load as measured in Clause 5 shall not be less than 1.8%

Where a range of anchorages of various capacities but of similar design form using the same size and type of tendon material, BS 4447 allows testing at both ends of a range and accepts that intermediate sizes shall be deemed to comply with the provided that at least three consecutive test results in each of two sizes comply. The details are given in Table 1. The number of specimens to be tested is not specified in AS 1314. However, as three specimens were required for BS 4447 and the draft revision of AS 1314 also required three specimens so three were tested.

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PART 1 - GRIPPING EFFICIENCY 4.0 Gripping Efficiency Test Loads AS 1311 specifies the minimum breaking forces for two grades of 12.7mm diameter strand and three grades of 15.2mm diameter strand. The specified minimum breaking forces (MBL) for the 12.7mm dia. strands are 184 and 165 kN and for the 15.2mm dia. are 261, 250 and 227 kN respectively. Hence, the minimum test load for gripping-efficiency is either 0.95% MBL or 0.92% Ultimate Tensile Strength (UTS) of the strand times the number of strands. – see Table 2.0: Table 2 - Test Loads for Gripping Efficiency

Ref. No. Tendon Size Minimum Test Load

AS 1314 (MTL) Tendon Size Minimum Test Load BS 4447

506 5 No. 15.2mm 0.95x261x5 = 1,240 kN 5 No. 15.7mm 0.92x270.4x5 = 1243.8 kN

605 6 No. 12.7mm. 0.95x184x6 = 1,049 kN 6 No. 12.9mm 0.92x205.8x6 = 1136.0 kN

406 4 No. 15.2mm. 0.95x261x4 = 992 kN 4 No. 15.7mm 0.92x270.4x4 = 995.0 kN



205 2 No. 12.7mm 0.95x184x2 = 350 kN 2 No. 12.9mm 0.92x205.8x2 = 378.7 kN

106 1 No. 15.2mm. 0.95x 261x1= 248 kN 1 No 15.7mm 0.92x270.4x1 = 248.8 kN

105 1 No. 12.7mm 0.95x184x1 = 175 kN 1 No. 12.9mm 0.92x205.8x1 = 189.3 kN 5.0 Gripping Efficiency Testing Procedure 5.1 Testing Procedure It was initially proposed to carry out testing which would comply with both Standards. It was soon apparent that this would create some difficulties. The British Standard requires that the tendon should be stressed to 0.7 times characteristic tendon strength, before undertaking gripping efficiency testing. After some initial testing a method was developed to overcome the perceived difficulties. A steel reaction frame 4.70m long with a 300t hydraulic ram jack attached to one end was used as this provided tendon test lengths well in excess of 3.0m – see Figure 3. At end ‘B’ the anchor blocks were supported during testing by a steel fabrication attached to the 300t jack and at the other end ‘A’ an array of monostrand jacks were arranged to allow the load to each strand to be individually controlled. A single pump with a manifold with individual valves was used to control the flow to each monostrand jack and monitored by separate pressure gauges calibrated with the corresponding monostrand jack. This provided a means of controlling the load and the elongation measurement of each strand.

Figure 3 - General arrangement of Test Frame Early testing using a single larger jack to apply the tendon load could not guarantee that all strands were stressed to the same load. Preliminary testing highlighted the need for the strands to be aligned so that as the strands fan out in the casting the strand and wedge were aligned axially. Where this is not achieved premature failure of one or more wires in a strand occurs prior to reaching the required test load.

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The testing commenced with the ram of the 300t jack extended 100mm and the strands threaded through the fabrication. With the wedges installed in the anchor block, a load of 50 kN was applied to each strand by the jacks at end ‘A’. The pressure in each jack was confirmed before the projecting strand behind the anchor block and the jacks at ‘A’ were marked and the initial measurements of strand length, jack extension, and the projecting strand lengths behind the 300T and the mono-ram jacks were taken. Each strand of the tendon was then stressed to 85% MBL from end ‘B’ to seat the wedges in the test anchor block. All the previous measurements were repeated. The load was then reduced to 50% MBL and the backpressure in the mono-jacks was noted and the load was increased back up to 75% MBL in each strand by increasing the pressure in the mono-strand jacks at end ‘A’. From the recorded measurements for 2 known loads for the individual strands, the strand length at zero load can be calculated. This allowed the target elongation to be calculated as the difference between the required elongation and the corrected elongation at 50% MBL Then, with the gauge pressure corresponding to 85% and 95% MBL known, the pressure in one mono-strand jack at a time was increased until 85% MBL was achieved in all of the strands. The pressure in one jack was increased continuously until the load was 95% MBL and in each jack in turn until all strands held 95% MBL. This load was held for 3 minutes before increasing to 92% of the Test Breaking Load (TBL).

For the 15.2mm strand tests, after the above pressure was maintained for three minutes, the load was further increased to 95% MBL-EHT (Minimum Breaking Load–Extra High Tensile). This load was maintained for a further period of 3 minutes. The pressure was checked, and if necessary, brought back up to the required pressure and increased by a small amount. This procedure was repeated for each strand in turn until the load exceeded 95% MBL EHT for the tendon. The pressure was increased slightly above that corresponding to 95% MBL-EHT on each strand so that all strands maintained a load simultaneously in excess of 95% MBL-EHT and held for a further 3 minutes before de-stressing. The final draw-in of the wedges was then measured. 5.3 Measurements The length of the strand extending from the rear of the test anchor block at end `B’ and from the rear of the mono-strand jacks was marked and measured at initial load stage and after the final load was achieved to determine the wedge draw-in. All measurements were made by eye on marks on tapes attached to strand and steel tapes attached to the mono-jack rams. All measurements were made to the nearest half millimetre. The gauge pressure was recorded and checked at each load stage. The measurements were taken for each strand at all load stages and on completion for wedge draw-in. The testing was not continued to failure as earlier trials showed that the shock from a wire breaking resulted in a minor disruption to the loading system and delayed further testing. Furthermore, as cracking of the wedges was noted at 85% MBL, examination of the anchor blocks and wedges was considered more important than trying to achieve failure loads once the required load capacity was exceeded. TABLE 3 – Summary of Gripping Efficiency Testing of Slab Anchors

Anchor Reference Min. Gripping load = 883.5k N 5 x 12.7 mm MBL = 186kN 3 4 5

Total Load kN

% above Minimum Gripping

AB 505-1 Load - kN 190.0 192.0 192.0 193.0 189.3 956.3 108.24% Extension - mm 111.4 110.4 127.7 119.3 112.4 % Elongation 1.91% 1.89% 1.87% 2.05% 1.93%

AB 505-2 Load - kN 191.0 191.0 190.0 190.0 190.0 952.0 107.75%

Extension - mm 108.4 108.9 129.1 109.4 112.3 % Elongation 1.86% 1.87% 1.89% 1.88% 1.93%



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4 x 15.7 mm MBL = 265 kN Min. Gripping load= 1007.00 kN AB 406-1 Load - kN 253.7 255.7 255.1 252.2 1,016.7 100.96%

Extension - mm 108.0 107.2 117.6 114.1 % Elongation 1.85% 1.84% 1.88% 1.82%

AB 406-2 Load - kN 249.7 258.8 252.7 258.5 1,019.7 101.26% Extension - mm 112.4 115.7 113.2 117.7 % Elongation 1.93% 1.98% 1.81% 1.85%

AB 406-3 Load - kN 249.7 258.8 252.7 258.5 1,019.7 101.26% Extension - mm 107.3 106.8 113.2 117.7 % Elongation 1.84% 1.83% 1.84% 1.88%

5 x 15.7 mm MBL = 265 kN Min. Gripping load= 1258.75 kN

AB 506-1 Load - kN 253.8 253.6 254.8 256.0 252.7 1,270.9 100.97% Extension - mm 108.9 110.0 125.1 109.6 110.4 % Elongation 1.82% 1.84% 1.84% 1.84% 1.85%

AB 506-2 Load - kN 253.8 248.8 256.8 254.8 252.7 1,266.9 100.65% Extension - mm 111.7 110.5 124.2 111.3 112.3 % Elongation 1.87% 1.85% 1.83% 1.86% 1.88%

AB 506-3 Load - kN 251.8 250.8 252.8 254.0 252.9 1,262.3 100.28% Extension - mm 112.8 111.6 124.0 111.3 114.1 % Elongation 1.89% 1.87% 1.82% 1.86% 1.91% 5.4 Summary – Gripping-efficiency tests • These tests were carried out in accordance with the requirements of AS 1314 and BS 4447. • The three tests on each of the anchor block types AB 505, AB 506 and AB 406 were carried out

successfully. All items tested had a gripping efficiency in excess of 0.95. • By taking careful readings of load and extension at 2 stages allowed the zero length of strand to

be back calculated and the required additional extension could then be calculated. • The required elongation and load were achieved by increasing the load on each strand in a single

continuous operation. This minimised the potential for strand failure, which occurred regularly when a large number of increments of load were used.

• The angle of the strand in the anchor block must be the same as when the strand is in the anchorage casting.

• The strand used in all of these tests conformed to AS 1311 except for the use of British 15.7mm strand where required.

PART 2 - ANCHORAGE-EFFICIENCY (LOAD TRANSFER) 6.0 Comparison between AS 1314 and BS 4447 Test Load requirements Both AS 1314 and BS 4447 specify that the anchorage castings be cast in concrete prisms when testing for load transfer using BS 4447 terminology. The Australian Standard AS 1314 requires that a concrete test prism shall support a load greater than 95% of the MBL of the tendon for which the anchorage is designed, while BS 4447 requires that the force transferred to the concrete, without failure, shall be not less than 1.1fpu (1.1 MBL). Therefore, BS 4447 determined the maximum test loads to be applied. This larger BS load precludes the use of normal stressing equipment or strand. As a result the Load Transfer testing was carried out at the Noel Murray Structures Laboratory, Monash University, Melbourne, Victoria. 6.1 Test Specimen Where a system can accommodate different tendon sizes the local zone (bursting) reinforcement was designed to resist the maximum tendon jacking force times the maximum number of the largest diameter strands that the anchorage can accommodate and not the maximum specified test load in the Standards. Concrete Test prism design would normally be sized in accordance with the generally adopted dimensions which have a ratio of a1 /a ratio of 0.6. However, when the prisms were sized to have an a1/a and b1/b equal to 0.6 the resulting prisms were considered to be too slender and impractical namely 130mm deep for both AB 506/605 and AB 406/505 and 112mm deep for AB 206/205. These depths were not considered to be representative of good practice and would be unsuitable for testing

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for reasons of occupation health and safety. So test specimens with a depth that would normally be used in a slab were selected. Three depths of slab were adopted - 200mm, 180mm and 150mm for the three sizes of anchors. These depths gave values of a1/a, which were not 0.6 as recommended by BS 4447. The prism sizes are shown in Table 4.

Table 4 - Dimensions of Test Prisms Prism Type Anchor Type Width ‘a’ Depth ‘B’ Length

L1 – L3 AB 506/605 600 200 1200 M1 – M3 AB 406/505 500 180 1000 S1 – S3 AB 206/205 350 150 700

Figure 4 Reinforcement details of for L- Series Prisms

6.2 Concrete A standard structural concrete Grade 40 mix with 14mm crushed basalt, being supplied to a large Melbourne project, was chosen on the basis of the pre-mix concrete supplier’s QA records. To allow the gain in concrete strength to be monitored, a set of 12 No. 100 x 200 cylinders was cast from this concrete in February 2002. These were demoulded after 24 hours and stored under hessian and polythene in the open and were tested daily from 1 to 9 days. One pair was tested each day to determine the rate of gain in strength. The test prisms were cast on 18 April 2002 and to allow the strength to be tested on a daily basis for 8 days, 12 No. 100mm dia. test cylinders were cast. These were demoulded after 24 hours and stored outside under wet hessian and polythene under similar conditions to the prisms. Four cylinders were stored under standard conditions in accordance with AS 1012 and tested at 7 and 28 days. From this trial it was hoped to predict the gain in strength of the prisms and allow a date for casting to be set so that the prism would have the design strength when access to the testing facilities at the Noel Murray Structures Laboratory at Monash University was available. 6.3 Prisms The decision to provide a rectangular spiral was adopted as testing of different arrangements of reinforcement by Professor John Breen’s team at the University of Texas, Austin, Texas (1), indicated that spiral reinforcement is very efficient and in recent times this form of reinforcement has become a popular construction detail. The detail of the large test prism reinforcement is shown in Figure 4. The other prisms are similar in reinforcement layout. The ‘as-cast’ dimensions of each prism were checked at the time of testing. The prism concrete was vibrated and finished with a steel trowel before being covered with hessian and polythene. They were stripped after 48 hours and were continuously moist cured until they were taken to Monash University for testing. 6.4 Maximum Test Loads The design load of an anchored tendon is the product of the jacking load of the strand times the number of strands. The SSL slab system being tested is designed to accommodate different arrangements of tendon and tendon sizes. The anchorage casting AB 605/506 will accommodate 5

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No. 15.7mm, 6 No. 12.9mm British strands, 5 No. 15.2mm or 6 No. 12.7mm Australian strands. The maximum loads required to satisfy both Standards is given in the Table 5.

Table 5 - Maximum Test Loads for Load Transfer AS 1314 BS 4447 Anchorage

Type Tendon Size

Test Load kN

Tendon Size

Test Load kN

AB 506/605 5/15.2 1240.00 5/15.7 1457.50 AB 506/605 6/12.7 1048.00 6/12.9 1227.60

AB 406/505 4/15.2 992.00 4/15.7 1166.00 AB 406/505 5/12.7 874.00 5/12.9 1023.00

AB 206/205 2/15.2 496.00 2/15.7 583.00 AB 206/205 2/12.7 350.00 2/12.9 409.20

Notes: MBL 15.2mm dia. = 261kN: SCBL 15.7mm dia. = 265kN MBL 12.7mm dia. = 184kN: SCBL 12.9mm dia. = 186kN SCBL = Specified Characteristic Breaking Load (BS 5896) 6.5 Design of anti-bursting reinforcement The characteristic strength of the anchored tendon is the product of the characteristic strength of the strand times the number of strands anchored. BS 8100 allows tendons to be initially stressed to 0.75 times the characteristic strength of the tendon but may be increased to 0.80 while AS 3600 allows tendons to be stressed to 0.85 times the characteristic strength of the tendon. AS 3600 governed the design of the local zone reinforcement used in this test series. The loads adopted for the design of the local zone reinforcement are those in bold type below.

Table 6 - Test Prism Design Forces for design of local zone reinforcement

AS 1314 BS 8100 Anchorage -efficiency Tendon Design Force - kN Tendon Design Force - kN

AB 506/605 5/15.2 1109.25 5/15.7 1060.00 AB 506/605 6/12.7 938.40 6/12.9 892.80 AB 406/505 4/15.2 887.40 4/15.7 848.00 AB 406/505 5/12.7 782.00 5/12.9 744.00 AB 206/205 2/15.2 443.70 2/15.7 424.00 AB 206/205 2/12.7 312.80 2/12.9 297.60

Figure 5 - BS 4447 diagram showing location of bursting reinforcement

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6.6 Design of anti-bursting reinforcement – BS 4447 The peak stress is given by f max = αP/A c

where P = A ps A c = Area of specimen less the area of the opening in the anchorage fct = 0.8 ξ ytfc BS 4447 is quite specific in specifying how the amount of steel reinforcement is calculated. The greater amount of steel given by the following two conditions is required :

Normal working condition: As = Pβ/fs{1-( 0.85ξ fcyt Ac/αP)2} Ultimate condition: As = Puβ/fy where As = Total area of bursting reinforcement. Ac = Cross-sectional area of test specimen less area of duct.

P = Design applied loading taken as the maximum permissible tendon force applied during stressing normally not exceeding 0.8f pu A ps. fcyt = Tensile strength of concrete which shall be taken as 4.0 ± 0.8 MPa for cube

strength in the range 50 ± 10 MPa. PU = 1.1fpu Aps Aps = Area of prestressing tendons

6.7 Design of anti-bursting reinforcement - BS 8110 BS 8100 gives tabular relationship between the bursting force and the prestressing force at jacking (Po). The ratio of Fbst to Po depends on the ratio a1/a or b1/b. Fbst divided by the design steel stress of 200 MPa gives the area of steel reinforcement. 6.8 Design of local reinforcement The value of the concrete tensile strength fcyt was taken as 0.6√f’c as recommended by AS 3600 where at the time of testing we required f’c = 32 MPa. BS 4447 requires that the local steel reinforcement be provided where the bearing stress exceeds the allowable concrete tensile stress - see figure 5. BS 4447 gives values for α, β and ξ only for a1/a = 0.6. These coefficients were derived from the research work of Zielinski and Rowe - C&CA Research Reports 9(2) and 13(3). From a plot of the original values it appears by linear equations in terms of a1/a or b1/b can be used without significant loss of accuracy - see figure 6.

Figure 6 Design Chart for values of a1/a or b1/b.

The following linear equations can be used to evaluate the coefficients for ratios of a1/a, which fall outside 0.6 as recommended by BS 4447.

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α = - 0.767(a1/a) + 0.940 ….…..(6.1) β = 0.20 (a1/a) + 0.10 ………(6.2) ξ = 0.467 (a1/a) +1.14 ………(6.3) The value of the concrete tensile strength fcyt was taken as 0.6√f’c as recommended by AS 3600 where at the time of test we required f’c = 32 MPa. BS 4447 requires that the local steel reinforcement be provided where the bearing stress exceeds the allowable concrete tensile stress see figure 5. 6.9 Design of local zone reinforcement - AS 3600 (AS 5100) AS 3600 provides a formula to allow the calculation of the transverse tensile force T, where T shall be taken as: T = 0.25 P (1- kr) where

P = the maximum force occurring at the anchorage during jacking (0.85 MBL) kr = the ratio of the depth or breadth of an anchorage bearing plate to the corresponding

depth, or breadth, of the symmetrical prism (a1/a or b1/b). The area of local zone reinforcement is determined by dividing the tensile force T by 150 MPa. Note AS 5800 uses 0.33P not 0.25P but allows a stress of 200 MPa which give identical results for Ast. Table 7 Properties of Prisms and Anchorages

Anchor N Fu Pu Fu Pu a1 a b1 b a1/a b1/a b

kN kN kN kN mm mm mm mm

AB 506/605 5 261 1305 265 1325 262 600 78 200 0.44 0.39

AB 406/505 4 261 1044 265 1060 220 500 78 180 0.43 0.43

AB 206/205 2 261 522 265 530 135 350 67 150 0.45 0.45

Table 8 - Reinforcement Design to AS 3600

Fs Fysp Fbst Abst No. Fbst Abst No. Anchor MPa MPa kN mm^2 of bars kN mm^2 of bars

a1/a 150 500 156.22 1041 7 AB 506/605 b1/b 161.96 1128 7

a1/a 150 500 124.24 828 5 AB 406/505 b1/b 127.62 851 5

a1/a 150 500 68.14 454 3 AB 206/205 b1/b 62.32 415 3 Note: that b1/b is the more critical ratio requiring greater amount of reinforcement.

Table 9 - Reinforcement to BS 4447

BS 8110:1991 BS 4447:1981

Anchor F’c As Fs Fysp Fbst Abst No. As-Ser As- Ult

Ratio

MPa mm^2 MPa MPa kN mm^2 of bars mm^2 mm^2 a1/a 35 80 200 460 200.34 1002 6 429.6 1163.2

AB 506/605 b1/b 35 80 200 460 215.18 1076 7 463.0 555.5 a1/a 35 80 200 460 161.97 810 5 403.4 471.5 AB 406/505 b1/b 35 80 200 460 161.12 806 5 401.8 451.2 a1/a 32 80 200 460 78.44 392 2 154.4 240.8 AB 206/205 b1/b 32 80 200 460 78.86 394 2 156.0 240.0

The reinforcement from each method is given in Tables 8 and 9. The bold numbers in Table 7 were adopted using a rectangular spiral for bursting reinforcement as testing by Breen. This allows the bursting steel to be located accurately and is more practical for thin sections. A 10mm diameter steel reinforcing wire (Grade 500) was used and the number of loops of the spiral chosen satisfied AS 3600. The BS 4447 allowance for the tensile strength of concrete was included and the middle of the first half turn was taken as the start of the reinforcement to ensure good anchorage of the spiral was achieved.

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7.0 Testing at Monash University 7.1 Test Arrangement The testing at Monash University was undertaken using a 5000 kN Amsler testing machine. It is a twin column machine with an under-floor hydraulic jack. The rate of loading was manually operated and the results recorded by computer. 7.2 Testing Sequence The testing was carried out on 22-26 April 2002 in the Noel Murray Structures testing laboratory at Monash University. The S prisms containing the smallest casting AC 206/205 were tested on 22 April 2002 as they had the lowest concrete strength requirement. The M prisms containing the casting AC 406/505 were tested on 23 April 2002 and the L prisms containing the casting AB 506/605 was tested on 24 April 2002. For each anchorage casting type, four prisms had been cast but only three were tested. The fourth was a back up in case of a premature failure of one of the prisms. As this did not eventuate and it was decided to test the fourth M prism on 26 April 2002 to investigate the effect if any of the increase in concrete strength with time on the prisms. 7.3 Test procedure The prism was levelled and plumbed so that the axis of the prism was vertical on the load trolley. Then the trolley was moved under the testing machine and a specially machined anchor block was placed concentrically on the curved face of prism casting. The load was applied at a constant rate and held for a short period at each stage 2-3 minutes to allow the prism to be inspected for cracks and for the extent of the cracking to be marked on the prism. The load continued to be increased in stages until the design load capacity was achieved. With three prisms to be tested only the first two were taken to 0.95 MBL and the load was then increased to 1.1fpu. Only the final test prism of each group was taken to failure. 7.4 Type S Prism Tests The maximum test load for the type S prisms was 583 kN. Prisms S1 and S2 withstood this load without significant cracking. Prism S3 was taken to 583 kN and then the loading increased at the same rate until no further increase in load could be achieved. The crack pattern at failure was not very different from that of prism S2. The failure load was 680 kN. The concrete strength was 35 MPa. The maximum crack width was less than 0.1mm for loads up to 583 kN. 7.5 Type M Prism Tests The maximum load for the type M prisms was 1166 kN. Prisms M1 and M2 withstood this load without significant cracking. Prism M3 was taken to failure. The failure load was 1250 kN. The concrete strength was 39.5 MPa. The maximum crack width at 1166 kN was 0.15mm. Prism M4 was tested 3 days later when the concrete strength was 45.5 MPa. The failure load was 1260 kN thus a 15% increase in concrete strength only produced 0.8% increase in failure load.

Figure 7 Crack pattern at failure for prism L1, Load = 1655kN

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7.6 Type L Prism Tests The maximum load for the type L prisms was 1458 kN. The prisms were tested in the reverse order, Prism L3 and L2 withstood a load of 1458 kN with crack widths less than 0.1mm. Prism L1 had a failure load of 1655 kN and similar crack pattern. The concrete strength was 42.0 MPa. MONASH UNIVERSITY ENGINEERING LABORATORY TESTING MACHINE – 5000 kN Amsler

L Series Casting AC 605/AC 506 Percentage of

Anchorage suitable for tendons to: Concrete = 42.0 MPa AS 1314 BS 5896 a) AS 1311 6/12.7(184 kN) = 1104 kN uts

5/15.2(250 kN) = 1250 kN uts L1 1655 kN 129.04% 113.6% 5/15.2(261 kN) = 1305 kN uts

L2 1458 kN 113.68% 110.00%

b) BS 5896 6/12.9 (186kN) = 1116 kN uts

5/15.7(265 kN) = 1325 kN uts L3 1458 kN 113.68% 110.00%

M Series Casting AC 505/AC 406 Percentage of

Anchorage suitable for tendons to: Concrete = 45.5 MPa AS 1314 BS 5896 a) AS 1311 5/12.7(184 kN) = 920 kN uts

4/15.2(250 kN) = 1000 kN uts M1 1166 kN 116.9% 110.00%

4/15.2(261 kN) = 1044 kN uts

M2 1168 kN 116.9% 110.00%

b) BS 5896 5/12.9(186 kN) = 930 kN uts

4/15.7(265 kN) = 1060 kN uts M3 1250 kN 119.73% 117.92% M4 1260 kN 120.69% 118.87

S Series Casting AC 205/AC 206 Percentage of

Anchorage suitable for following tendons to: Concrete = 35 MPa AS 1314 BS 5896 a) AS 1311 2/12.7(184 kN) = 368 kN uts

2/15.2(250 kN) = 500 kN uts S1 583 kN 117.56% 110.00%

2/15.2(261 kN) = 522 kN uts

S2 583 kN 117.56% 110.00%

b) BS 5896 2/12.9(186 kN) = 372 kN uts

2/15.7(265 kN) = 530 kN uts S3 680 kN 123.19% 128.30%

NOTE: The figures in bold type are failure loads PART 3 - NON-STRESSING ANCHORAGES 8.0 AS 1314 Requirements Non-stressing anchorages are commonly used in building structures where access for stressing is only available to one end of the tendon and use either swages or t the individual wires of the strand are upset to form a bulb anchor. Neither AS 1314:1987 nor BS 4447:1980 has requirements for testing of non-stressing anchorages. However, as a non-stressing anchorage performs a similar task to a stressing anchorage, a limited number of non-stressing anchorages at either end of the system size range were tested for anchorage-efficiency. 8.1 Prism Design Marti(4) proposed a design method for the design of local zone reinforcement for “dead-end” anchorages. However, Australian practice is to provide the same reinforcement as for a stressing anchorage. Three prisms with 5/15.2mm dia strand and three prisms with 2/12.7mm dia. strand were cast with bulb anchors. One additional prism of each size was cast with swages in place of the bulb anchors. Approximately, 6.0m of strand extending beyond the prism to allow the same arrangement of mono-jacks to be used. Typical detail of the prisms with 5 bulbs is shown in figure 8. Contrary to recommendation of FIP Commissions on Prestressing Materials (5) the anti-bursting reinforcement was placed close to the anchors and not at the entry to the duct.

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Figure 8 - Reinforcement layout for non-stressing prisms

8.2 Prism Manufacture The prism sizes chosen were the same as those adopted for the testing at Monash University and the same concrete mix was used. 8.3 Test Arrangement The tests were carried out at SSL’s yard in South Melbourne using the same test frame used for the gripping-efficiency testing of the anchor blocks. A thick steel plate was located at end ’A’ end of the frame to ensure uniform bearing for the prism. The projecting strand was threaded through the bearing plate at end ‘A’ and passed through the test frame to end ‘B’ where mono-jacks were located. The same test procedure as used for the stressing anchorage Gripping-efficiency testing was followed. When the load in each strand reached 95% MBL, the prism was inspected for cracks. The load was held for 10 minutes and the pressure in the jacks checked and where necessary brought back up to the required load. After a further inspection the load was increased above 95% MBL in all strands and the load held for at least 3 minutes, after which the load was released. The results are summarised in Table 11. 8.4 Summary - Anchorage-efficiency tests of Non-stressing Anchorages All of the non-stressing anchorages had a gripping efficiency greater than 0.95.without any cracking. The location of a normal stressing anchorage spiral located over the transmission zone provided greater strength and precluded any cracking of the prism at loads of 95% MBL. Table 11 - Results of Non-stressing anchorages Gripping Tests

Anchor Reference 1 2 3 4 5

5 x 15.7 mm MBL(eht) - 261 kN Min. Gripping load= 247.95 kN BD 506-1 Load - kN 250.0 249.5 250.8 250.1 250.7 BD 506-2 250.0 251.8 250.9 250.8 250.7 BD 506-3 250.0 249.9 250.5 250.1 252.7 SD 506-4 250.0 249.9 250.8 252.0 252.7

2x12.7mm MBL(eht) - 194.8 kN Min. Gripping load= 174.80 kN BD 205-1 180.3 180.3 BD 205-2 176.2 175.5 BD 205-3 176.2 175.5 SD 206-4 176.2 175.5

1x15.7 mm MBL(eht) - 261 kN Min. Gripping load= 247.95 kN BA 106-1 249.7 BA 106-2 249.0 BA 106-3 249.4

1x12.7mm MBL(eht) - 189.6 kN Min. Gripping load= 174.8 kN BA 105-1 183.2 BA 105-2 183.2 BA 105-3 183.2

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9.0 COUPLING ANCHORAGES 9.1 AS 1314 Requirements AS 1314:1978 specifies gripping-efficiency testing for coupling anchorages. Coupling anchorages are used with normal anchorage castings cast into the edge of the slab. The tendons are stressed in the normal manner through the anchorage. Strands with swaged ends are then located on the coupling anchorage and inserted into a normal duct sealed and encased in a sheet metal cover prior to casting the concrete. Only the five strand-coupling anchor was tested. The arrangement of 5 strands with 3 on one side and 2 on the other creates an out of balance force when tested in an exposed situation. This situation does not occur when the anchorage is located in a concrete slab. Two coupling anchorages CB 506 and CB 505 were tested using the same testing frame as previously. 9.2 Test Arrangement A new anchorage support frame was designed to provide lateral restraint to counteract the out-of-balance force causing the coupling anchorage to rotate when tested in air. A fabrication was designed to match the end of a five strand casting AC 506/605 and machined tapered plugs of identical size to the projecting first stage strand wedges were provided to ensure that the same conditions of internal stress were attained in the coupling anchorage. The central tapered plug was provided with a locating pin to ensure that the coupling anchorage was located axisymetrically to the frame. The fabrication had four 20mm dia. bolts which provided the necessary resistance to the out of balance force which could be adjusted to maintain the coupling anchorage normal to the axis of the tendon, only two of which were in contact with the coupling anchorage. The fabrication was located at the ‘A’ end of the test frame and the strands were tested using the same test frame. The tapered plugs were inserted and located centrally on the curved face of the fabrication. The swaged strand was then threaded through a bearing plate at end ‘A’. The swaged ends were located on the coupling anchorage lugs after the strand was passed through the test frame to end ‘B’ where mono-jacks were located. Each strand was inserted into a mono-strand jack. 9.3 Test Procedure The test arrangement was similar to that used in the earlier gripping-efficiency tests described previously and the same test frame was used.

Table 10 - Summary of Coupler Testing 5 x 15.7 mm MBL – 250 kN Min. Gripping load=247.95kN

CA 506-1 Load/ strand 247.0 237.5 237.5 248.4 237.5

5x12.7mm MBL = 184kN Min. Gripping load=174.8 kN CA 505-1 Load/ strand 176.1 177.2 176.8 178.0 178.2

9.4 Summary - Gripping-efficiency tests of Coupling Anchorages The testing of the coupling anchorages was carried out in accordance with the requirements of AS 1314, had a gripping-efficiency greater than 0.95 and supported their test loads without any distortion or distress. Both coupling anchorages were subjected to loads which would be generated by stressed tendons in both directions as the reaction of the tapered plugs against the test frame was equal and opposite to that in the strands. Thus the coupling anchorage was loaded in both directions simultaneously.

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10.0 SUMMARY The design and testing of prestressing anchorages both live and fixed can be tested satisfactorily provided that the anti bursting reinforcement is correctly designed and located making the appropriate allowance for concrete tensile strength generally in accordance with the recommendations of BS 4447. The SSL Slab System was accepted by UKCARES for use in the UK. The expressions given in the paper for α, β and ξ allow the BS 4447 design method and location of bursting reinforcement any rectangular anchorage to be used with confidence. Prior testing of similarly cured concrete cylinders allows the testing at the required concrete strength. Gripping efficiency testing should be carried out on a tendon length greater than 3.0 m to achieve accurate elongation readings. Taking all readings at two loads allows the strand length at ‘zero’ extension to be calculated. By careful measurement it is possible to make the correct allowance for wedge draw-in and then the load to achieve the required elongation can be calculated. It is essential always to measure the actual elongation to confirm the calculations and to be sure that you have satisfied the Standard. Constant increase to force in a strand will assist in achieving required elongations and avoid premature breakage of strand, which is common with slow incremental application of force. It is essential to ensure that the strand and wedges are aligned axially in the anchor block, as any misalignment of the wedges and strand will reduce the failure load. For fixed anchorages, tests showed conclusively that the provision of bursting reinforcement identical to that required for the stressing anchorage, located in the transmission zone close to the end of the tendon prevents cracking and ensures full load capacity is achieved. Coupling anchorages can be tested for gripping efficiency in air in a similar manner normal gripping efficiency testing provided that attention is given to controlling any out balance forces. ACKNOWLEDGEMENT The authors thank the Directors of Structural Systems Limited for permission to publish this paper and their support during the period that the testing took place. REFERENCES

1. Roberts-Wollmann, C.L. and Breen, J.E. Design and test specifications for local anchorage zones. ACI Structural Journal, Vol. 97, No.6, Nov.-Dec. 2000, pp 867-875.

2. Zielinski, J. and Rowe, R.E. An investigation of the stress distribution in the anchorage zones

of post-tensioned concrete members. London. Cement and Concrete Association, September 1960. pp 32. Research Report No. 9.

3. Zielinski, J. and Rowe, R.E. The stress distribution associated with groups of anchorages in

post-tensioned concrete members. London. Cement and Concrete Association, October 1962. pp 40. Research Report No. 13.

4. Marti, P., and Rogowsky, D.M. Detailing for post-tensioning. Bern, Switzerland. VSL

International, April 1991, pp 50. VSL Report Series No. 3.

5. Fédération Internationale de la Précontrainte (FIP) - FIP Recommendations for Acceptance of Post-tensioning Systems, June 1992.

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Documents

Testing the SSL Slab Post Tension Ing System.pdf