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Industry Standard of the Ministry of Railway
of the People’s Republic of China
GB/T 14370-2007
______________________________________________________________________
Anchorage, grip and coupler for prestressing tendons
Issued on September 11, 2007 Implemented since February 1, 2008
_______________________________________________________________________
Issued jointly by
General Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China
and
Standardization Administration of the People’s Republic of China
Preface
This Standard supersedes GB/T 14370-2000 Standard “Anchorage, grip and coupler for prestressing tendons”.
Compared with GB/T 14370-2000 Standard, this Standard mainly has the following modifications:
- The applicable range of this Standard covers “the anchorage for the stay cable may be also be used”;
- Product classification, code number and marking type are changed. The general code numbers are worked out for anchorage, grip and coupler. New marking method may avoid the function of specifying the system code numbers for the manufacturers in the engineering drawings;
Add the basic requirements for exchangeable low-stress stay cable;
The static load tests for anchorages and grips will not be divided into “anchoring first and tensioning second” system and “tensioning first and anchoring second” system and are combined into the former system, whose test equipment schematic drawings are also modified. During the static load test, when the stress exceeds 0.8 fptk, the loading rate shall be reduced. The cyclic load test and the static load test for the single prestressing tendon and anchorage assembly may have the loading rate increased up to 200MPa/min.
- The measurement, observation and requirement for the static load test are more accurate than that in the former standard.
- Supplement the method of auxiliary test.
This Standard is put forward by the former Ministry of Construction of the People’s Republic of China (now the Ministry of Housing and Urban-Rural Development of the People’s Republic of China).
This Standard is reorganized by China Academy of Building Research, the reorganizing department of engineering standards under the former Ministry of Construction.
This Standard is drafted by: China Academy of Building Research, First Highway Engineering Co., Ltd. of China Communications Construction Group, China Academy of Railway Sciences, Liuzhou OVM Machinery Co., Ltd., Liuzhou VLM Prestressing Co., Ltd., Liuzhou Qiumu Prestressing Co., Ltd., and Hangzhou Zhemao Prestressing Co., Ltd..
This Standard is mainly drafted by: Yu Bin, Pei Xiao, Tian Keping, Zhuang Junsheng, Zhu Ying, Long Yue, Lin Juzhang, Mei Shutao, and Zeng Li.
This Standard supersedes the previously published versions:
-- GB/T 14370-1993
-- GB/T 14370-2000
Anchorage, grip and coupler for prestressing tendons
1 Scope
This Standard specifies the terms, definitions, symbols, product classification, codes and designations, technical requirements, testing methods, inspection rules, marking, packaging, transportation, storage and quality guarantee period of anchorages, grips and couplers for prestressing tendons.
This Standard is applicable for anchorages, grips and couplers used in bonded, unbonded and retard-bonded prestressed concrete and the prestressed steel structures.
The use of the anchorages for stay cable may refer to this Standard.
2 Normative quote documents
The clauses in the following documents are integral parts of this Standard through the normative quotes. For the quote documents which are marked with dates, the amendment on any of the subsequent modification lists (not including the corrected contents) is not applicable for this Standard. However, this Standard encourages the relevant parties reaching the agreements according to this Standard to determine the application of the latest version of these documents. For the quote documents which are not marked with dates, their latest versions are applicable for this Standard.
GB/T 197-2003 General thread Tolerance
GB/T 1804 General tolerance Tolerances of linear and angular sizes without tolerances being noted
JG/T5011.8 Construction machinery and equipments General technical conditions of forgings
JG/T5011.9 Construction machinery and equipments General technical conditions of heat-treated parts
JG/T5011.10 Construction machinery and equipments General technical conditions of cutting and machining parts
JG/T5012 Construction machinery and equipments General technical conditions of packaging parts
3 Terms, definitions and symbols
This Standard applies the following terms, definitions and symbols.
3.1 Terms and definitions
3.1.1 Anchorage
The permanent anchoring device used in the post-tensioning structure or member, to maintain the tensile stress of the prestressing tendon and transfer it to the concrete (or steel structure).
The anchorages are classified into two types:
a) Anchorage at tensioning end: which is installed at the end of the prestressing tendon and used for tensioning;
b) Anchorage at dead end: which is installed at dead end of the prestressing tendon and is not used for tensioning.
3.1.2 Grip
The temporary anchoring device used in the pre-tensioning member construction, to maintain the tensile stress of the prestressing tendon and fix the tendon on the manufacturing table base (or equipment); the permanent anchoring device (also called clamper) used in the post-tensioning structure or member construction, to clamp the prestressing tendon on the tensioning jack or equipment.
3.1.3 Coupler
Device used to connect the prestressing tendons.
3.1.4 Prestressing steel
General name of steel wires, steel strands or steel reinforcements used in various prestressing structures.
3.1.5 Prestressing tendon
The single or stranded prestressed steel wires, strands or reinforcements used in the prestressing structure to build up the prestress.
3.1.6 Prestressing tendon-anchorage assembly
The load bearing unit assembled by single or stranded prestressing tendons and the anchorages installed at the ends.
3.1.7 Prestressing tendon-grip assembly
The load bearing unit assembled by single or stranded prestressing tendons and the grips installed at the ends.
3.1.8 Prestressing tendon-coupler assembly
The load bearing unit assembled by single or stranded prestressing tendons and the couplers.
3.1.9 Anchorage zone
The local zone of the structure which can support the anchorage load and transfer it to the structure.
3.1.10 Tension length
Clearance between anchorage and grip or coupler at both ends of the prestressing tendon, during the anchorage, grip and coupler test.
3.1.11 Ultimate tensile force of tendon-anchorage assembly
The maximum tensile force of the prestressing tendon-anchorage assembly during the static load test.
3.1.12 Ultimate tensile force of tendon-grip assembly
The maximum tensile force of the prestressing tendon-grip assembly during the static load test.
3.1.13 Efficiency factor of prestressing tendon
The factor considering the non-uniform tensile stress of the prestressing tendon due to the influence of prestressing steel quantity, test equipment and initial stress adjustment.
3.1.14 Draw-in
The retraction due to relative displacement and partial plastic deformation between the parts of the anchorage, and between anchorage and prestressing tendon during the anchoring process of prestressing tendon.
3.2 Symbols
Apk----- Characteristic (or nominal) section area of one test piece of prestressing steel;
Ap----- Characteristic (or nominal) section area of each test piece of prestressing steel in prestressing tendon-anchorage and -grip assembly;
fptk----- Standard tensile strength of prestressing steel;
fpm----- Measured average ultimate tensile force of prestressing steel used in the test (calculated with the area of Apk);
Fpm----- Actual average ultimate tensile force of prestressing tendon, calculated with the average value of the measured breaking load of prestressing steel test pieces;
Fapu ---- Measured ultimate tensile force of prestressing tendon-anchorage assembly;
Fgpu ---- Measured ultimate tensile force of prestressing tendon-grip assembly;
εapu --- Total strain of prestressing tendon when the prestressing tendon-anchorage assembly reaches the measured ultimate tension;
ηa ---- Anchorage efficiency factor measured in the static load test of prestressing tendon-anchorage assembly;
ηg ---- Grip efficiency factor measured in the static load test of prestressing tendon-grip assembly;
ηp ---- Efficiency factor of prestressing tendon.
4 Product classification, codes and designations
4.1 Product classification
Anchorages, grips and couplers may be classified into wedge type (single hole and multi-hole wedge-type anchorage), supporting type (pier head anchorage, nut anchorage etc.), conical plug type (conical steel anchorage etc.) and gripping type (extrusion-type anchorage, bulb anchorage etc.) according to their different anchoring methods.
4.2 Codes
The general codes of anchorages, grips or couplers may be expressed with the first pinyin letter of their respective Chinese words, that is, M (for anchorage), J (for grip), or L (for coupler). The anchoring methods are classified with the codes as shown in Table 1.
Table 1 Codes of anchorages, grips and couplers
Type code Anchorage Grip Coupler
Wedge type Round style YJM YJJ YJL
Flattened style BJM
Supporting type Pier head style DTM DTJ DTL
Nut style LMM LMJ LML
Conical plug type Steel style GZM - -
Cold casting style LZM - -
Hot casting style RZM - -
Gripping type Extrusion style JYM JYJ JYL
Embossing style YHM - -
Remarks: The codes of the couplers are given by the anchoring method at the end of the lengthening section.
4.3 Designations
The designation of anchorage, grip or coupler consists of three parts, that is, product code, prestressing steel diameter and prestressing steel quantity (with the system code of the manufacturer indicated when necessary):
企业体系代号(需要时标注) system code of the manufacturer (indicated when necessary)
预应力钢材根数 prestressing steel quantity
预应力钢材直径(mm) prestressing steel diameter
锚具、夹具或连接器代号 code of anchorage, grip or coupler
For example:
a) Round wedge-type anchorage to anchor 12 steel strands with the diameter of 15.2mm for the use of prestressed concrete, should be designated as “YJM 15-12”;
b) Extrusion-type anchorage with prestressing tendon made of 12 steel strands with the diameter of 12.7mm, for the use of anchoring at the dead end, should be designated as “JYM13-12”, and the system code of the manufacturer may be added when necessary;
c) Coupler used to connect 12 steel strands with the diameter of 15.2mm with the extrusion method should be designated as “JYL15-12”.
For special products or new products whose characteristics are necessary to be explained, the text description or drawings may be provided for accurate expression.
5 Requirements
5.1 Use requirements
The anchorages, grips and couplers shall have reliable anchorage property, sufficient load bearing capacity and good applicability, to ensure full use of the strength of prestressing tendon and realize the prestress tensioning operation in a safe way.
5.2 Material requirements
The materials for the products shall meet with the design requirement and shall have the qualification and quality certificates for the mechanical properties and chemical compositions. The acceptance tests shall be carried out on the materials before they are delivered into the plant.
5.3 Requirements of manufacturing processes
5.3.1 The mechanical processing of the parts shall comply with relevant regulations in JG/T 5011.10 Standard.
5.3.2 The unspecified accuracy class of the threads shall be not lower than 7H/8g in GB/T197 Standard. The threads with special requirements shall be treated according to the design drawings.
5.3.3 The tolerance level without individual tolerance indication shall comply with the relevant regulations in GB/T1804 Standard.
5.3.4 The forging of the part blanks shall comply with the regulations of JG/T5011.8 Standard. The forgings shall not have the defects of forging crack, over-burning, folding or partial big and coarse crystal particles.
5.3.5 The heat treatment processing of the parts shall be carried out according to the product design drawings, and shall also comply with relevant regulations in JG/T5011.9 Standard. There should be no cracks, over-burning or carbon depletion. The heat treatment process and equipments shall ensure the compliance with the requirements for the working surface of the parts, the hardness of core, and the metallurgical structure, as well as the uniform and consistent product quality.
5.4 Requirements of appearance, sizes and hardness
5.4.1 Appearance, sizes and hardness shall comply with the design drawings. None of the products shall have any crack.
5.4.2 The hardness for the surface and core of the product parts and their allowable hardness tolerances shall comply with the design drawings.
5.5 Basic property requirements of anchorage
5.5.1 Static load anchoring properties
The compliance of static load anchoring properties is judged by the anchorage efficiency factor ηa measured in the static load test of prestressing tendon-anchorage assembly and total strain εapu for the tension length of the assembly at the measured ultimate tension.
Anchorage efficiency factor ηa is calculated according to Equation (1):
ηa = Fapu/(ηp•Fpm)………………………………………………………..(1)
Where,
The value of ηp is: when the quantity of prestressing steel in the prestressing tendon-anchorage assembly is 1 to 5 pieces, ηp =1; when the quantity is 6 to 12 pieces, ηp = 0.99; when the quantity is 13 to 19 pieces, ηp = 0.98; and when the quantity is more than 20 pieces, ηp = 0.97.
The static load anchoring property of the anchorages shall meet with the following two requirements at the same time:
ηa≥0.95, εapu≥2.0%
The breaking mode of the prestressing tendon-anchorage assembly shall be the breakage of prestressing tendons (breakage of one by one or many at the time). The anchorage parts shall not have too much deformation or even result in the fracturing, and the anchoring reliability shall be determined according to the requirements of Clause 6.2.5.
5.5.2 Fatigue load properties
In addition to meeting with the requirement of static load anchoring properties, the prestressing tendon-anchorage assembly shall also meet with the requirement of fatigue load tests with two million cycles.
When the anchored prestressing tendons are steel wires, steel strands or heat-treated steel reinforcement, the upper limit of the test stress shall be 65% of fptk, standard tensile strength of prestressing steel, and the amplitude of fatigue stress shall be no less than 80MPa. If required for the projects, the upper limit of test stress and the amplitude of fatigue load may be separately determined.
When the anchored prestressing tendons are the prestressing steel with obvious yield plateau, the upper limit of the test stress shall be 80% of fptk, standard tensile strength of prestressing steel, and the amplitude of fatigue stress shall be properly 80MPa.
After two million times of cycling load, the anchor parts shall not suffer fatigue breakage. The section of the fatigue breakage of prestressing tendons due to anchorage clamping shall be no more than 5% of total section area of test pieces.
5.5.3 Cyclic load properties
For the anchorages in the structures with the requirement for earthquake resistance, the prestressing tendon-anchorage assembly shall meet with the requirement of cyclic load tests for 50 times.
When the anchored prestressing tendons are steel wires, steel strands or heat-treated steel reinforcement, the upper limit of the test stress shall be 80% of standard tensile strength of prestressing steel, fptk, and the lower limit shall be 40% of standard tensile strength of prestressing steel, fptk.
When the anchored prestressing tendons are the prestressing steel with obvious yield plateau, the upper limit of the test stress shall be 90% of standard tensile strength of prestressing steel, fptk, and the lower limit shall be 40% of standard tensile strength of prestressing steel, fptk.
After 50 times of cyclic load tests, the prestressing tendons shall not break at the clamping zone of the anchorages.
5.5.4 Auxiliary property requirements
This test shall be carried out on newly developed anchorage. And this test may be carried out on some or all items of the products for type inspection. Then the construction tensile force shall be amended properly according to the comparison of the measured average draw-in and friction loss at the anchoring end with the values in the design specifications.
5.5.4.1 Measurement of anchorage draw-in
When the tensile stress of prestressing tendon reaches 0.8 fptk, the prestressing tendon shall be released. Then measure the draw-in amount (in mm) of prestressing tendon during the anchoring. Average the measured values.
5.5.4.2 Measurement of friction loss at the anchoring end
From the clamper of tensioning jack to the bell-shaped shrinking end of base plate, the prestressing tendon has one or two folds. During tensioning, this will result in prestress friction loss and reduce the self-anchoring function. Measure and average the prestress loss (calculated with the percentage of tensile stress) when the tensile force reaches 0.8 fptk.
5.5.4.3 Requirements for tensioning and anchoring process
To prove the workability and applicability of the anchorage in the prestress construction, the tensioning and anchoring process test shall be carried out on complete set of equipments and instruments for the prestress tensioning and anchoring system.
5.5.5 Other property requirements
5.5.5.1 The anchorage shall meet with the requirements of prestressing tendon in graded tensioning and supplementary tensioning.
5.5.5.2 It is suitable to design the grouting holes or air discharge holes in the anchorages necessary for hole grouting or their accessories. The positions and diameters of the grouting holes shall comply with the requirements of the grouting process, and the grouting holes shall be designed with the structure to connect the grouting pipes.
5.5.5.3 The anchorage used for exchangeable low-stress stay cable shall be designed with the exchangeable and anti-loosening structure.
5.5.5.4 The anchorages shall be designed with the anti-corrosion measures and meet with the requirement of durability for the engineering construction.
5.6 Basic property requirements of grips
5.6.1 The static load anchoring properties shall be determined by the grip efficiency factor ηg measured in the static load test of prestressing tendon-grip assembly, in Equation (2):
ηg = Fgpu/Fpm………………………………………………………..(2)
Where,
The static load anchoring property of grips shall meet with the requirement of ηg≥0.92.
5.6.2 When the prestressing tendon-grip assembly reaches the measured ultimate tensile force, this should result from the breakage of prestressing tendon, instead of the breakage of grips. All parts of the grips shall have the quality to be reused. The grips shall have reliable self-anchoring property, good anchorage loosening property and reuse property. During the use of grips, the safety of operators shall be ensured.
5.7 Basic property requirements of couplers
During the pre-tensioning and post-tensioning construction, the couplers which will be permanently left in concrete structure or member after being prestressed shall comply with the property requirements of anchorages; and the couplers which will be released and disassembled after being tensioned shall comply with the requirements of grips.
5.8 Quality document requirements
The manufacturers shall provide the complete design documents, product qualification documents of raw materials, manufacturing batch no. records and property inspection records with traceability for the anchorages, grips, couplers and the load bearing components in the anchorage zone.
6 Testing methods
6.1 General regulations
5.1.1 The prestressing tendon-anchorage, grip or coupler assembly used in the tests is composed of product parts and prestressing tendons. The parts used in the tests shall be the qualified products after visual inspection and hardness test. Before the test of the assembly, the greasy dirt shall be removed from the anchorage parts (minimal amount of oil film permissible), and it is not allowed to add any media influencing the anchoring properties on the anchorage parts. Various steel materials for the prestressing tendons in the assembly shall be parallel to each other with the same length and uniform initial stress, and their tension length shall be equal to or more than 3m.
For the test pieces of single-steel-strand assembly and the test pieces for mechanical property test of parent materials of steel strands, the tension length excluding the clamping position shall be equal to or more than 0.8m. And for the test pieces of the other assembly of single prestressing tendon and parent materials, the minimum length may be determined according to the test equipments and relevant standards.
For the assembly with prestressing steel not bending at the clamping position of the anchorage (when all anchor bar holes are vertical to the bottom of anchor plate), all pieces of prestressing steel are tensioned parallel to each other, where there should be no contact point preventing the tensioning or creating friction at the side (refer to Drawing 1); when there is some turning angle between the clamping position of the prestressing steel and the axial line of the test piece (such as, anchor bar hole is oblique to the bottom of the anchor plate or the coupler with the extrusion head installed in an oblique position), there should be designed with the turn restraining steel ring, which shall not have slide friction with prestressing steel when the test piece is tensioned.
6.1.2 The prestressing tendons used in the tests shall have good homogeneity, and may be supplied by the anchorage manufacturer or the test organization together with the quality certificate of the prestressing tendons. The diameter tolerance of the chosen prestressing tendons shall be within the designed matching range of the tested anchorages, grips or couplers. For the prestressing tendons used in the tests, the mechanical property tests of parent materials shall be carried out at first with at least six test pieces in the typical positions according to the sampling standard, and the test results shall comply with the regulation of the current national standards (the supplier and buyer may also negotiate and determine the relevant standards in other countries). The grade of the measured average tensile strength of prestressing tendons fpm in the relevant steel standards shall be the same as the design grade of the tested anchorages, grips and couplers. The prestressing tendons exceeding this design grade shall not be used. The qualified anchorages after the test with the prestressing tendon of some intermediate strength grade may be used with the prestressing tendons at the same or low grade in practical construction, not applicable for those at higher grades. The damaged prestressing tendons shall not be used in the tests of the assembly.
6.1.3 The force measuring system in the test shall have its uncertainty no more than 2%. The instruments measuring the total strain shall have the uncertainty no more than 0.2%. The strain gauge indicator shall have the uncertainty no more than 0.1%.
6.2 Static load test
6.2.1 The static load test shall be carried out on the prestressing tendon-anchorage or grip assembly as shown in Drawing 1. The static load test shall be carried out on the prestressing tendon-coupler assembly as shown in Drawing 2. When the prestressing tendon (No. 11 in Drawing) in the connected section is pre-tightened during the installation, the spacers may be added under the tested coupler (No. 7 in Drawing) in a halved way and shall be disassembled whenever proper after the loading. The supporting conditions (supporting means, position and area etc.) of anchorages, grips and couplers shall be consistent with the practical conditions in the construction.
6.2.2 Before the loading, the measuring instruments shall be installed and commissioned till with normal and accurate operation. The initial stress of the prestressing tendons shall be commissioned to be uniform, which may be 5%-10% of the standard tensile strength fptk of the prestressing tendon. And the instrument for the measurement of total strain εapu shall have the standard measuring distance of at least 1 m. If εapu is calculated with the measurement of the piston extension ΔL of the loaded jack, the flexible contraction and gap compression of the load-bearing support table as well as the measured draw-in of the tested anchorage, grip or coupler shall be deducted from the calculation. The calculated length of the prestressing tendon shall be the distance between the clamping points at both ends for the anchorage (grip or coupler).
Unit: mm
1 ----Test anchorage or grip at the tensioning end
2 ---- Loading jack
3 ---- Load bearing support table
4 ---- Prestressing tendon
5 ---- Device to measure total strain
6 ---- Load sensor
7 ---- Test anchorage or grip at the dead end
Drawing 1 The schematic drawing of static load test device for the prestressing tendon-anchorage (grip) assembly
Unit: mm
1 ----Test anchorage or grip at the tensioning end
2 ---- Loading jack
3 ---- Load bearing support table
4 ----- Prestressing tendon at the extended section
5 ----- Device to measure total strain
6 ----- Restraining steel ring
7 ----- Test coupler
8 ----- Auxiliary load bearing cylinder or through jack
9 ----- Load sensor
10 ---- Test anchorage at the dead end
11 ----- Prestressing tendon at the connected section
Drawing 2 The schematic drawing of static load test device for the prestressing tendon-coupler assembly
6.2.3 The standard loading procedures are: the load is applied with four grades of 20%, 40%, 60% and 80% of fptk, the standard tensile strength of the prestressing tendon, at the rate of about 100MPa/min. When the applied load reaches 80%, this load should be maintained for 60 minutes. Then the load is applied at the rate lower than 100MPa/min till the maximum value of Fapu when the test piece is completely damaged. During the test, the measurement and inspection shall be carried out according to Clause 6.2.5 of this Standard. For the test pieces which are required to comply only with the “Qualification level” standard, the test may be stopped when ηa, εapu and ηg meet with the requirements of Clause 3.5.1 or 5.6.1 in this Standard.
6.2.4 When the testing machine or the load bearing support table is used to test the static load of the prestressing tendon-anchorage assembly, the load may be applied at higher rate, but not more than 200MPa/min. When the stress reaches 0.8 fptk, the holding time of the load may be shortened, but not less than 10 minutes. When the stress exceeds 0.8 fptk, the load shall be applied at the rate not higher than 100MPa/min.
6.2.5 The items to observed and measured in the tests and the requirements for the test results are as follows (Drawing 3),
a) Choose some typical prestressing tendons. During the application of the load at the first four grades on the prestressing tendon, the relative displacements Δa are measured with anchorage, grip or coupler respectively grade by grade. The relative displacement Δa shall be proportional to the increment of tensile stress of the prestressing tendon. If Δa is not proportional to the increment of tensile stress of the prestressing tendon, inspection shall be made on the anchoring efficiency loss or slide of the prestressing steel.
b) Choose some typical parts for the anchorage (grip or coupler). During the application of the load at the first four grades on the prestressing tendon, the relative displacements Δb are measured grade by grade respectively. The relative displacement Δb shall be proportional to the increment of tensile stress of prestressing tendon. If Δb is not proportional to the increment of tensile stress of prestressing tendon, inspection shall be made on the plastic deformation of the relevant parts.
c) When the stress of the prestressing tendon reaches 0.8 fptk, Δa and Δb shall be stable during the holding time of 60 minutes. If they cannot be stable but continue increasing during the holding time of 60 minutes, it shows that the prestressing tendon has lost its reliable anchoring capacity.
d) When the test piece reaches the maximum tensile force, it is required to take record of Fapu (or Fgpu), the ultimate tensile strength and εapu, total strain for the total tension length of the prestressing tendon. The measured value shall meet with the regulations of Clause 5.5.1 or 5.6.1 of this Standard.
e) When the stress of the prestressing tendon reaches 0.8 fptk, the crack or breakage of the wedge of the wedge-type anchorage is not allowed. Fine crack and longitudinal breakage is allowed when the regulations of Clause 5.5.1 or 5.6.1 of this Standard are complied with. The horizontal or oblique crack or breakage is not allowed. The crack or breakage of the wedge is normal due to the shock from the intense breakage of some strands or the whole tendon for the prestressing tendon. When the tensile force of the prestressing tendon reaches the ultimate breaking strength, it is not allowed that too much plastic deformation happens in the anchor plate and conical anchor hole, and that there is obvious deflection for the residual deformation in the center of the anchor plate. If Δb increases at the double rate than that when the stress of prestressing tendon is 0.8 fptk, it shows that it has lost its reliable anchoring capacity.
f) When the breakage of the prestressing tendon happens before complying with the regulations of Clause 5.5.1 or 5.6.1 of this Standard, and if the prestressing tendon is broken by pulling due to the butt welding joint or damage of prestressing steel, this test piece will be rejected and a new test piece will be made for the retest. It is normal that gripping-type anchorage loses its gripping capacity after it complies with the requirements of ηa≥0.95, εapu≥2.0% during the static load test.
(a) (b)
(a) After pre-tensioning of the prestressing tendon and before anchoring
(b) After the anchoring and during the loading
Drawing 3 Displacement of the parts for the prestressing tendon (or grip, coupler) during the test
6.2.6 The consecutive static load tests shall be carried out on three assemblies, with all test results recorded. Based on these test results, the following calculation, analysis and evaluation are made: calculate ηa, efficiency factor of anchorage (or coupler), according to Equation (1) of this Standard; calculate ηg, efficiency factor of grip, according to Equation (2) of this Standard; make evaluation according to Chapter 5 and Clause 6.2.5 of this Standard; and draw the conclusion for the compliance of the test results. All the three test results, instead of their averaged value, shall comply with the regulations of this Standard. The test organization shall submit the complete test report to the inspection authority.
6.3 Fatigue test
6.3.1 Fatigue test for the prestressing tendon-anchorage or coupler assembly shall be carried out on the fatigue testing machine. When the fatigue testing machine does not have sufficient capacity, less prestressing steel may be installed on the anchor plate, according to the rule of typical test results, or the test assembly may be made by the anchorage with smaller specification in the relevant series, but the quantity of the prestressing tendons shall be not fewer than 1/10 of actual quantity. To ensure the inspection result is representative, both the straight and curved prestressing tendons shall be included in the assembly during the test.
6.3.2 The load is applied at the rate of about 100MPa/min on the test piece till the upper limit of the test stress. After the stress amplitude is adjusted to the required value, start recording the number of cycles.
6.3.3 Choose the pulse frequency for the fatigue testing machine with the rate of no more than 500 times per minute.
6.4 Cyclic load test
The cyclic load test for the prestressing tendon-anchorage or coupler assembly may be carried out on the testing machine or the support table at the loading rate of 100MPa/min--200MPa/min till the upper limit of the test stress. After this, the test piece is unloaded to the lower limit of the test stress. This is the first cycle. Then the load increases from the lower limit to the upper limit and then to the lower limit. This is the second cycle. Repeat 50 cycles like this.
The prestressing tendon-anchorage or coupler assembly passing the fatigue test without any damage may be used in this test.
6.5 Inspection of appearance, sizes and hardness
6.5.1 The product appearance may be inspected visually, and the crack may be inspected with the magnifying glass with or without scale.
6.5.2 The product sizes shall be inspected with scale ruler, vernier caliper, screw micrometer and plug gauge and ring gauge according to the general mechanical manufacturing methods.
6.5.3 The hardness inspection shall be carried out with the hardness tester selected according to the classification of the hardness values specified in the design drawings of the product parts.
6.6 Auxiliary test
6.6.1 Anchorage draw-in test
This test may be carried out with single piece or small prestressing tendon coupled with the anchorage for times of tensioning or releasing on the prestressing hole of the support base or member 5m-10m long. Then measure the draw-in (in mm) of the anchorage wedge. The tensile stress shall be 0.8 fptk of prestressing tendon. The pressure sensor is used to measure the tensile strength difference of the prestressing tendon before and after being anchored. It may also be calculated to obtain the draw-in. There shall be at least 3 test pieces for this test, with the measurement values averaged as the final test result.
6.6.2 Friction loss test at the anchorage end
This test is used to measure the prestress loss from the place under the tensioning jack tool anchorage to the shrinking end of the bell-shaped bearing plate. It includes the friction loss of the prestressing tendon in the anchorage and the tensile force loss due to twice folding in the bell-shaped base plate.
This test may be carried out on the simulated concrete test piece or tension support table. The anchor base plates and spiral reinforcements shall be completely installed. The tensile force shall be taken as 0.8 fptk• Ap of prestressing tendon. The tensile stress difference of the anchorage and anchor base plate measured with the sensors at both sides is the friction loss at the anchorage end, usually calculated as the percentage of the tensile force. The test pieces of three specifications may be chosen for this test from the list of the anchorage specifications. There shall be at least three pieces for this test, with the average value as the test result.
6.6.3 Tensioning and anchoring process test
Simulated concrete blocks shall be specifically designed as the test platform according to the structure arrangement of prestressing, tensioning and anchoring system. The concrete blocks shall include various curved and straight holes, bell-shaped base plates or anchor plates integrated with the base plates. And various plastic embedded parts shall be embedded into the concrete. The tensioning devices of this system are used to carry out the operations of tensioning at different levels, times of tensioning and releasing. The maximum tensile force is 0.8 fptk• Ap.
The tensioning and anchoring process test shall prove that:
a) The prestressing system shall be possible for the tensioning at different levels or temporary anchoring due to the reverse stroke of the tensioning device;
b) After times of tensioning and anchoring, the stress on the prestressing tendons of the same strand is also uniform;
c) In case of the trouble during the tensioning, there will be the measure to completely release the prestressing tendons;
d) The single anchorage integrated with the base plate has the structure for the free alignment of the prestressing tendon in the conical wedge hole, as well as the reliability of anchoring without top pressing.
7 Inspection rules
7.1 Classification of inspections
The inspection for the anchorages, grips and couplers is classified into plant inspection and type inspection.
7.1.1 The plant inspection is the inspection made by the manufacturer on the product quality control in the plant before each delivery out of the plant.
7.1.2 Type inspection is the inspection on the complete property control of the product. Type inspection shall be made under either of the following conditions:
a) For the type approval of the new or old product from the trial manufacturing during the period of plant transfer production;
b) After the normal production starts and when product structure, material and process encounter big changes possible to affect the product properties;
c) Such test is required once every two to three (2-3) years regularly or after some production capacity is achieved during the normal production;
d) At production recovery after the discontinued production for two years;
e) When plant inspection result has big difference from the last type inspection result;
f) When the national or provincial supervision authority requires the type inspection.
The type inspection for technical and quality appraisal shall be held by the quality inspection institution specified by the government, and various tests for new product development and product quality control shall be carried out by the manufacturers themselves.
7.2 Inspection items
The items for plant inspection and type inspection shall comply with the regulations in Table 2.
Table 2 Product inspection items
Type of anchorage, grip and coupler Plant inspection items Type inspection items
Anchorages and couplers permanently embedded in the concrete structure or the couplers in the member Appearance, hardness, static load test Appearance, hardness, static load test, fatigue test, cyclic load test, auxiliary test
Grips and the couplers which should be released and dissembled after being tensioned Appearance, hardness, static load test Appearance, hardness, static load test
7.3 Batching and sampling
7.3.1 During the plant inspection, the number for each batch of the anchorages refers to the number of the anchorages once manufactured with same specification, same batch of raw material, and same process. In each sampling batch, the sampling quantity shall not exceed 2000 pieces (sets). 5%-10% pieces are sampled for appearance inspection. 3%-5% pieces are sampled for hardness inspection of the products with hardness requirement according to the amount in each furnace with heat treatment. After the qualification of the appearance inspection and hardness inspection, the static load test shall be carried out on the complete-set products of the anchorages, grips or couplers from the qualified products at the sampling rate of 3 samples per manufacturing batch.
7.3.2 For the type inspection of the anchorages and couplers permanently kept in the concrete structure or member, three assembly samples should be taken for each of fatigue test, cyclic load test and auxiliary test in addition to the sampling specified in 7.3.1 of this Standard.
7.3.3 During the continuous mass production, the plant inspection may be carried out on the monthly basis. The sampling amount for the appearance inspection shall be at least 5% of the monthly production capacity. For the parts with the hardness requirement, the sampling quantity for the hardness test shall be at least 3% of the monthly production capacity. The sampling amount for the static load test shall be at least 3 assemblies of the same specification every two months. If the quality results of the above inspections are unstable, more samples should be taken.
7.4 Judgment of inspection results
Appearance inspection: The outline size and appearance quality of the test pieces shall comply with the requirements of the design drawings. None of the samples should have any crack. If any, the products of the whole batch shall be inspected one by one.
Hardness inspection: In this inspection, the quality of the samples shall be judged and judged according to the surface position and hardness range specified in the drawings. If there is one unqualified sample, the parts of double quantity shall be sampled for retest. If there is still one unqualified sample during the retest, the parts of the whole batch shall be inspected one by one. Only the qualified parts can be used.
Anchor plate strength test, static load test, fatigue test and cyclic load test: If the tested samples comply with the technical requirements in Chapter 5, these parts of this batch shall be judged as qualified; if there is one unqualified sample, these parts of this batch shall be judged as unqualified, but it is allowed to make the retest with the test pieces of double quantity, and if all test pieces are qualified, then this batch may be judged as qualified; and if there is still one unqualified piece, the whole batch shall be judged as unqualified.
Auxiliary test: This test is used to measure the parameters and inspect the process equipments, instead of being taken as the judgment standard for product qualification.
8 Marking, packaging, transportation and storage
8.1 Marking
Anchorages, grips and couplers shall be provided with the manufacturer names, product types, manufacturing dates or product manufacturing batch No.. And there shall be the identification codes for the anchorage parts hard to be distinguished (such as, wedge).
8.2 Packaging
Anchorages, grips and couplers shall be packaged in the cases complying with the regulations of JG/T 5012 Standard before delivery. There should be packing list in each packaging case. With each delivery, there should be provided product certificate and product instruction.
Product certificate shall include the following contents:
a) Type and specification;
b) Applicable prestressing steel type, specification and strength grade;
c) Product batch No.;
d) Manufacturing date;
e) Qualification document sealed with the company stamp of the manufacturer;
f) Manufacturer name and address.
The product instruction shall specify the use process as well as the matching requirements for the prestressing steel. The recommended accessories (such as, bell-shaped base plate, spiral reinforcement etc.) shall be provided with the test evidence or practical evidence in the production instruction.
8.3 Transportation and storage
During the transportation and storage, the anchorages, grips and couplers shall be properly protected from rust, contamination, mechanical damage and storage in the open. The temporary protective measures shall not affect the effect of installation operation or the implementation of permanent antirust measures.
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