JGJ/T 92-1993 Technical specification for unbonded prestressed concrete structures JGJ/T92-93
Some standard content:
Industry Standard of the People's Republic of China
Technical Code for Unbonded Prestressed Concrete
Structures
JGJ/T 92—93
Editing Unit: China Academy of Building ResearchApproving Department: Ministry of Construction of the People's Republic of ChinaEffective Date: May 1, 19943-16—1
Notice on Issuing the Industry Standard "Technical Code for Unbonded Prestressed Concrete Structures"
Jianbiao [1993] No. 640
In accordance with the requirements of the former Ministry of Urban and Rural Construction and Environmental Protection's (88) Chengbiao No. 141 document, the "Technical Code for Unbonded Prestressed Concrete Structures" edited by the China Academy of Building Research has been reviewed and approved as an industry standard, numbered JGJ/T92—93, and will be implemented on May 1, 1994. 316—2
This standard is managed and interpreted by the China Academy of Building Research, the responsible unit for building engineering standards and technology under the Ministry of Construction, and published by the Standard and Quota Research Institute of the Ministry of Construction.
Ministry of Construction of the People's Republic of China
August 31, 1993
Main symbols
Chapter 1
Chapter 2
Materials and anchor systems
Section 1
Section 2
Section 3
Chapter 3
Concrete and steel bars
Unbonded prestressed tendons·
Anchor systems
Design and Basic Provisions for Construction Section 1 General Provisions Section 2 Fire Prevention and Corrosion Prevention Design Calculation and Construction Chapter 4 General Provisions Section 1 One-Way System Section 2 Two-Way System Chapter 5 Construction and Acceptance Section 1 tt|| Section 2 Fire Prevention and Corrosion Prevention Design Calculation and Construction Chapter 4 General Provisions Section 1 One-Way System Section 2 Two-Way System 3-16—4
3—16—4
..... 3-16—5
3—165
3—16—5
? 3—16—5
3—167
3—16-7
3--16—7
. 3--16—8
.. 3—16-8
3—16—11
…3——16--12
3——16-15
Manufacturing,
Packaging and Transportation of Unbonded Prestressed Reinforcements
3—16—15
Section 2
Laying of Unbonded Prestressed Reinforcements
and Casting of Concrete
......
Professional Quantity
3--16—16
Section 3
Tensuring of unbonded prestressed tendons3—16--17Section 4
Appendix 2
Appendix 3
Appendix 4
Appendix 5
Project acceptance
Number of unbonded prestressed tendons
Estimate...
3—16--18
3—16--18
Polar moment of inertia of failure section and calculation coefficient
α.Calculation formula.-.·
Manufacture of unbonded prestressed tendons in the head anchor system. 16.·9
Unbonded prestressed tendon tensioning
Record sheet
3-16-20
Conversion between illegal measurement units and legal measurement
Units
Appendix VI Explanation of terms used in this code
Additional explanation
3--16-20
3--16--21
3--16—21
3—16—3
MI.M2.M.-
Main symbols
Actions and effects of actions
Design value of concentrated reaction force;
Design value of bending moment;
-Principal bending moment, secondary bending moment and total bending moment in the section of the member caused by tensioning unbonded prestressed tendons; Section bending moment caused by balanced load;
Cracking moment of the normal section of a flexural member;
According to the short-term effect combination and long-term effect combination of load MM,-
calculated bending moment;
total effective prestress of unbonded prestressing tendons; shear force design value;
tensioning control stress of unbonded prestressing tendons; normal stress of concrete generated by prestressing; effective prestress of unbonded prestressing tendons;-design value of stress of unbonded prestressing tendons in the calculation of positive section bearing capacity;
prestress loss value of unbonded prestressing tendons at the corresponding stage.
Resistance and material properties
Sectional stiffness of flexural members;
-Design value of flexural bearing capacity of the member's positive section; E
-Elastic modulus of concrete;
-Elastic modulus of unbonded prestressed tendons;
E—Elastic modulus of non-prestressed steel bars;
-Design value of axial compressive strength of concrete; f
\———Compressive strength of concrete cube when prestressed; f
Design value of axial tensile strength of concrete:
-Standard value of axial tensile strength of concrete;-Design value of tensile strength of unbonded prestressed tendons; y
Jy——Design value of tensile strength of non-prestressed steel bars; fyw
-Design value of tensile strength of stirrups.
Geometric parameters
A,———Net cross-sectional area of the component;
A——Cross-sectional area of unbonded prestressed tendons; A.Cross-sectional area of non-prestressed steel bars;
A——Cross-sectional area of bent steel bars;
A—Cross-sectional area of stirrups;
)—Section width;
——Width of flat support plate;
br—Width of tension flange of T-shaped or 1-shaped section;e
Eccentricity of the center of gravity of unbonded prestressed tendons to the center of gravity of the section;316-4
Section height;
Effective height of a section:
hf——T - the height of the tension flange of a shaped or I-shaped section; hp
- the effective height from the compression edge of the beam section to the center of gravity of the unbonded prestressed tendons;
converted section moment of inertia;
converted elastic section modulus of the tension edge of the section; - the circumference at a distance of ho/2 from the periphery of the concentrated reaction area; - the height of the concrete compression zone.
Calculation coefficient and others
The angle between the bent steel bar and the bottom surface;
-Concrete tensile stress limitation coefficient;
The ratio of the elastic modulus of unbonded prestressed tendons to the elastic modulus of concrete;
Comprehensive reinforcement index;
Plastic influence coefficient of concrete in the tension zone;
-Total strain of a prestressed tendon anchor assembly when it reaches the measured ultimate tensile force;
-The number of the same arms of the steel shear frame;
Anchor efficiency coefficient measured by the static load test of the prestressed tendon anchor assembly;
The influence coefficient of the local deviation of the unbonded prestressed tendon wall (per meter) on friction;
Friction coefficient;
-Reinforcement ratio of unbonded prestressed tendons;
Ps—-Reinforcement ratio of non-prestressed tendons;
0——The influence coefficient of the combination of long-term effects of loads on the increase of deflection.
Chapter 1 General Provisions
Article 1.0.1 This code is formulated to achieve advanced technology, safety and reliability, quality assurance and economic rationality in the design and construction of unbonded prestressed concrete structures.
Article 1.0.2 This code applies to the design and construction of unbonded prestressed concrete structures used in industrial and civil buildings and general structures under normal conditions.
Note: The unbonded prestressed tendons used in this code refer to those buried in concrete members. Article 1.0.3 Unbonded prestressed concrete structures should determine reasonable design and construction plans based on building functional requirements and material supply and construction conditions, prepare construction organization designs, and make good technical disclosures. They should be constructed by professional prestressed construction teams and strictly implement quality inspection and acceptance systems.
Article 1.0.4 The design and construction of unbonded prestressed concrete structures shall comply with the requirements of this code and shall also comply with the relevant provisions of the "Concrete Structure Design Code" GBI10, "Concrete Structure Engineering Construction and Acceptance Code" GB50204, "Building Structure Load Code" GBI9, "Steel Structure Design Code" GBJ17, "Technical Code for Application of Anchors, Clamps and Connectors for Prestressed Reinforcement" JGI85 and "Anchors, Clamps and Connectors for Prestressed Reinforcement" GB/T14370 and other relevant specifications. Chapter 2 Materials and Anchorage Systems
Section 1 Concrete and Steel Bars
Article 2.1.Article 1 The concrete strength grade of unbonded prestressed concrete structure shall not be lower than C30 for slabs and C40 for beams and other components.
Article 2.1.2
The performance of steel strands or carbon steel wires used to make unbonded prestressed tendons shall comply with the provisions of the national standards "Steel Strands for Prestressed Concrete" GB5224-85 and "Steel Wires for Prestressed Concrete" GB5223-85. The main mechanical properties of commonly used steel strands and carbon steel wires shall be adopted according to Table 2.1.2.
Main mechanical properties of common steel strands and carbon steel wires Table 2.1.2
Material name Carbon steel wire
Nominal diameter
Performance index
Standard value of tensile strength (N/mm2)
Design value of tensile strength (N/mm2)
Elongation (%)
Cross-sectional area (mm2)
Nominal weight (kg/m)
Elastic modulus (N/mm2)
Steel strands
d = 15. 0(7±5)d = 12.0(74)
Article 2.1.3 Steel strands and steel wires used for unbonded prestressed tendons should not have dead bends, and must be cut off when there are dead bends. Each steel wire in the unbonded prestressed tendons should be full length, and joints are strictly prohibited. Section 2 Unbonded Prestressed Reinforcements
Article 2.2.1 The unbonded prestressed reinforcements used in this specification refer to unbonded prestressed reinforcements with a special anti-corrosion grease coating layer and an outer layer. The quality requirements shall comply with the provisions of the standards "Unbonded Prestressed Reinforcements for Steel Strands and Steel Wire Bundles" JG3006-93 and "Special Anti-corrosion Grease for Unbonded Prestressed Reinforcements" JG 3007-93.
Article 2.2.2 The outer layer material of unbonded prestressed reinforcements shall be polyethylene or polypropylene, and polyvinyl chloride is strictly prohibited. Its performance shall meet the following requirements:
, within the temperature range of -20 to +70℃, it shall not become brittle at low temperatures and have good chemical stability at high temperatures;
, it must have sufficient toughness and damage resistance;
, it shall not corrode surrounding materials (such as concrete and steel);
, it shall have good waterproof properties.
Article 2.2.3 The coating layer of unbonded prestressed tendons shall be made of special anti-corrosion grease, and its performance shall meet the following requirements: 1. In the temperature range of -20 to +70℃, it shall not flow, crack or become brittle, and have a certain toughness;
2. Good chemical stability during the service life; 3. No corrosion to surrounding materials (such as concrete, steel and outer packaging materials);
4. Impermeable, non-hygroscopic, and waterproof; 5. Good anti-corrosion performance;
6. Good lubrication performance and low friction resistance.
Section 3 Anchor System
Article 2.3.1 The anchoring performance of unbonded prestressed tendons-anchor assembly shall meet the following requirements:
1. Unbonded prestressed tendons must use Class I anchors. The static load anchoring performance of the anchor shall meet the following requirements at the same time: na ≥ 0.95
(2.3.1-1)
wherein na
Eapu=2.0%
(2.3.1-2)
The anchor efficiency coefficient measured by the static load test of the prestressed tendon anchor assembly;
The total strain of the prestressed tendon anchor assembly when it reaches the measured ultimate tensile force.
The anchor efficiency coefficient can be calculated as follows: Eae
np× Fapu
Fapu= f ptmApm
wherein Faru-
(2. 3.1-3)
(2.3. 1-4)
-Measured ultimate tensile force of the prestressed tendon anchor assembly;-Efficiency coefficient of the prestressed tendon, taken as 0.97;Fapu-The sum of the calculated ultimate tensile forces of each prestressed steel in the prestressed tendon anchor assembly;
The average value of the measured tensile strength of the specimens extracted from the prestressed steel;
The average value of the cross-sectional area of the specimens extracted from the prestressed steel
II. Unbonded prestressed tendons-
I. Anchor The fatigue anchorage performance of the assembly shall be tested by a fatigue performance test with an upper limit of test stress αmx of 65% of the standard tensile strength of prestressed steel, a stress amplitude of 80N/mm2, and a number of cycles of 2 million times. Note: When used in earthquake zones, the unbonded prestressed tendon-anchor assembly shall pass a cyclic load test with an upper limit of 80% of the standard tensile strength of prestressed steel, a lower limit of 40% of the standard tensile strength of prestressed steel, and a number of cycles of 50 times. Article 2.3.2 The selection of unbonded prestressed tendon anchors shall be based on the type of unbonded prestressed tendons, tensioning tonnage, and engineering use. The anchors for commonly used unbonded prestressed tendons with diameters of 15 and 12 mm single strands and 75 steel wire bundles can be selected according to Table 2.3.2. 3--16—5
Selection table of commonly used single unbonded prestressed tendon anchors Table 2.3.2
Types of unbonded prestressed tendons
Tensile end
Fixed end
Plowing anchor, welded plate clip anchor,
d=15.0(75) or d=12.0(7Φ4) clip anchor, embossed anchor
705 steel wire bundle
Upset anchor,
Clip anchor
Forged anchor plate
Note: ① Welded plate clip anchor is a clip anchor with its anchor ring welded to the bearing plate; ② Embossed anchor is suitable for use in beams, and end structural measures such as spiral reinforcement or mesh should be added;
③ Sensitive head anchor can also be used to anchor steel wire bundles with a diameter greater than 75. Article 2.3.3 The tensioning end of the clip anchor system may be constructed as follows:
, when the anchor protrudes from the concrete surface, its structure is composed of an anchor ring, a clip, a pressure plate, and spiral reinforcement (Figure 2.3.3a); 2. When the anchor is recessed into the concrete surface, its structure is composed of an anchor ring, a clip, a pressure plate, a plastic plug, spiral reinforcement, a hook screw and a nut assembly (Figure 2.3.36).
(α) Clip anchor protrudes from the concrete surface
(6) Clip anchor is recessed into the concrete surface
Figure 2.3.3 Structure of the tensioning end of the clip anchor system 1-clip; 2-anchor ring; 3-bearing plate; 4-spiral tendon; 5-unbonded prestressed tendon; 6-plastic plug; 7~-hook screw and nut Article 2.3.4 The fixed end of the clip anchor system must be buried in the concrete of the plate or beam. The following methods can be used: *. The structure of the extruded anchor consists of an extruded anchor, a bearing plate and a spiral tendon (Figure 2.3.4a). The extruded anchor should assemble the sleeve at the end of the steel strand and extrude it through special equipment to form:
, The structure of the welded plate clip anchor consists of a clip anchor, an anchor plate and a spiral tendon (Figure 2.3.46). The anchor should be pre-assembled at the end of the prestressed tendon with an open double-cylinder dry jack and a preload of 0.75 times the prestressed tendon tensioning force;
3-—16--6
3. The structure of the embossed anchor consists of an embossed end and a spiral tendon (Figure 2.3.4c). The embossed end should be made directly from the end of the steel strand by an embossing machine.
(a) Extruded anchor
(b) Welded plate clip anchor
(c) Embossed anchor
Figure 2.3.4 Fixed end structure of clip anchor system 1-clip; 2-anchor ring; 3-bearing plate; 4-spiral tendon; 5-unbonded prestressed tendon; 6-embossed end
Article 2.3.5 The clip anchor system shall comply with the following provisions: This anchor is mainly used to anchor unbonded prestressed tendons made of steel strands. When used to anchor steel wire bundles composed of 75, inclined slit clips must be used. sheet;
2. The shrinkage of the prestressed tendon at the tensioning end should not be greater than 5mm; 3. The minimum horizontal and vertical spacing of a single unbonded prestressed tendon on the end face of the member can be 60mm
Article 2.3.6 The tensioning end and fixed end of the upset anchor system can adopt the following methods:
1. The structure of the tensioning end consists of an anchor cup, a nut, a pressure plate, a plastic protective sleeve and a spiral tendon (Figure 2.3.6a);, the structure of the fixed end consists of a upset anchor plate and a spiral tendon (Figure 2.3.66).
(a) Tensioning end
(6) Fixed end
Figure 2.3.6 Structure of the head anchor system
1-anchor cup; 2-nut; 3-pressure plate; 4-spiral tendon; 5-plastic protective cover; 6-unbonded prestressed tendon; 7-forged anchor plate
Article 2.3.7 The head anchor system shall comply with the following provisions: 1. The shrinkage of the prestressed tendon at the tensioning end shall not exceed 1.0mm; 2. The length of the steel wire bundle should not exceed 25m; 3. The minimum horizontal and vertical spacing of a single unbonded prestressed tendon on the end face of the component can be 80mm.
Article 2.3.Article 8 The materials of the parts of the anchor assembly shall be adopted in accordance with the provisions of the design drawings, and shall have chemical composition and mechanical properties certificates. If there is no certificate, quality inspection shall be carried out in accordance with national standards. The materials shall not have defects such as slag inclusions and cracks.
Article 2.3.9 The quality inspection and acceptance of the unbonded prestressed tendon anchor system shall comply with the provisions of the current national standards "Technical Specifications for the Application of Anchors, Clamps and Connectors for Prestressed Reinforcements" JGJ85 and "Anchors, Clamps and Connectors for Prestressed Reinforcements" GB/T14370. Chapter 3 Basic Provisions for Design and Construction
Section 1 General Provisions
Article 3.1.1 The crack control of unbonded prestressed concrete components shall comply with the following provisions:
Grade 1: Unbonded prestressed concrete components that are strictly required not to crack. When calculated according to the combination of short-term effects of loads, the tensile edge concrete of the component should not produce tensile stress;
Grade 2: Bending components that are generally required not to crack. When calculating according to the combination of short-term load effects, the tensile stress generated by the tensile edge concrete of the member should not exceed αcsf, and αc is not greater than 0.6. When calculating according to the combination of long-term load effects, the tensile stress generated by the tensile edge concrete of the member should not exceed αclyf, and acu is not greater than 0.25. Here, αcts is the tensile stress limit coefficient under the combination of short-term load effects, αct is the tensile stress limit coefficient under the combination of long-term load effects, is the plastic influence coefficient of concrete in the tensile zone, and f is the standard value of concrete tensile strength. Generally, for axial tension members that are not required to crack, when calculating according to the combination of long-term load effects, the concrete of the member should not generate tensile stress; when calculating according to the combination of short-term load effects, the concrete of the member is allowed to generate tensile stress, but the tensile stress should not exceed 0.3fk. Note: When there is engineering experience, the anti-cracking design requirements for unbonded prestressed concrete beams controlled by secondary cracks can be appropriately relaxed. In unbonded prestressed concrete members, non-Article 3. 1.2
prestressed steel bars should preferably use ribbed steel bars. When the diameter of the steel bar is less than 10mm, hot-rolled smooth steel bars can also be used. Article 3.1.3 When the length of the unbonded prestressed steel bar exceeds 25m, it is advisable to tension it at both ends; when the length of the steel bar exceeds 50m, it is advisable to tension it in sections and anchor it.
Article 3.1.4 For unbonded prestressed concrete one-way multi-span continuous beams and slabs, the unbonded prestressed steel bars should be anchored in sections or additional intermediate anchorage points should be added during the design, and the provisions of Article 4.2.1 of this Code on the reinforcement quantity of non-prestressed steel bars should be met.
Article 3.1.5 For unbonded prestressed concrete structures that directly bear dynamic loads and require fatigue verification, their fatigue strength and structure should be determined through special test studies.
Section 2 Fire and Corrosion Prevention
Article 3.2.1 To meet the requirements of different fire resistance levels, the minimum thickness of the concrete protective layer of unbonded prestressed tendons shall comply with the provisions of Table 3.2.1-1 and Table 3.2.1-2.
Minimum thickness of concrete protective layer for slabs (mm) Table 3.2.1-1
Constraints
Constraints
Fire resistance limit (h)
Minimum thickness of concrete protective layer for beams (mm)3
Table 3.2.1-2
Fire resistance limit
Take special measures
Note: ① When the width is between 200 and 300 mm, the concrete protective layer can take the interpolated value in Table 3.2.1-2;
② If the static fire level is high, when the foam concrete protective layer thickness cannot meet the requirements listed in the table, fireproof aggregate should be used. 。
3-16—7
The fire resistance limit of the anchorage area shall not be lower than the fire resistance limit of the structure itself. Article 3.2.2Www.bzxZ.net
The corrosion of unbonded prestressed tendons by chlorides shall be strictly prevented. In concrete construction, admixtures containing chloride ions shall not be used; post-cast concrete or mortar in the anchorage area shall not contain chlorides. Article 3.2.4 The outer covering materials shall be connected, sealed and waterproof over the entire length of the prestressed tendons and at the connection between the anchor and the connecting sleeve. Article 3.2.5 After the unbonded prestressed tendons are tensioned, the anchorage area shall be protected in a timely manner. For the swaged head anchor, first use an oil gun to inject sufficient anti-corrosion grease into the connecting sleeve through the anchor cup oil filling hole (until the grease overflows from the other oil filling hole), then fill the anchor cup tightly with anti-corrosion grease and cover it tightly with a plastic or metal cap (Figure 3.2.5α), and then apply waterproof coating on the surface of the anchor and the pressure plate; for the clip anchor, first cut off the excess length of the exposed unbonded prestressed tendons, and then apply waterproof coating on the surface of the anchor and the pressure plate (Figure 3.2.56).
(a) Protection of head paving
(5) Protection of central piece misalignment
Figure 3.2.5 Protection measures for anchorage area
1—Apply adhesive; 2—Apply waterproof coating; 3—Post-cast concrete; 4—Plastic or metal cap
Article 3.2.6 The anchorage area of unbonded prestressed tendons treated in accordance with the provisions of Article 3.2.5 shall be sealed with post-cast expansive concrete or low shrinkage waterproof mortar or epoxy mortar. Before pouring the mortar, an epoxy resin adhesive shall be applied to the inner wall of the notch. The anchorage area may also be closed with a post-cast external reinforced concrete ring beam. The external ring beam shall not protrude beyond the outer wall surface.
For areas where concrete or mortar coating cannot be used, all anchors of unbonded prestressed tendons should be coated with the same anti-corrosion grease as the unbonded prestressed tendon coating 3--16—8
layers, and all anchors should be sealed with protective covers with reliable anti-corrosion and fire-proof properties.
Chapter 4 Design Calculation and Construction
Section 1 General Provisions
Article 4.1.1 For general civil buildings, the thickness of unbonded prestressed concrete one-way slab should be 1/40~1/45 of the span; the thickness of the two-way slab of the slab-column system should be 1/401/45 of the long side dimension of the column grid; the thickness of the two-way slab with flat support plate (measured from the center of the column to each direction, the extension length of the flat support plate should not be less than 1/6 of the slab span, and the thickness of the flat support plate should be greater than 1.5 times the slab thickness) should be 1/45~1/50 of the long side dimension of the column grid; the rib height (including the panel thickness) of the dense rib slab should be 1/30~1/35 of the long side dimension of the column grid; the main beam height should be 1/15~1/20 of the span length; the secondary beam height should be 1/20~1/25 of the span length.
Article 4.1.2 When the load balance method is used to estimate unbonded prestressed tendons, for general civil buildings, the balanced load value can be the standard value of the dead load or the standard value of the dead load plus no more than 50% of the standard value of the live load. When the column grid size is unequal in each direction, the balanced load value can take different values in each direction. The number of unbonded prestressed tendons can be estimated according to the method in Appendix 1. The internal forces and deformations caused by the prestress on the structure can be calculated using the equivalent load method.
Article 4.1.3 The effective prestress α of the unbonded prestressed tendons shall be calculated according to the following formula:
Where αon
Ope=aon
Unbonded prestressed tendon tensioning control stress; the nth item prestress loss value.
The prestress loss value includes the following five items:
1. Deformation of the anchor at the tensioning end and shrinkage of the unbonded prestressed tendons α; 2. Friction of the unbonded prestressed tendons ai2; 3. Stress relaxation of the unbonded prestressed tendons a14; 4. Shrinkage and creep of concrete a15;
5. When batch tensioning is adopted, the elastic compression loss of concrete caused by the unbonded prestressed tendons in the last batch of tensioning.
The total loss value of the unbonded prestressed tendons should not be less than 80N/mm2. Article 4.1.4 The prestress loss aur (N/mm2) of the unbonded prestressed straight tendons due to the deformation of the anchor and the shrinkage of the unbonded prestressed tendons can be calculated according to the following formula:
-deformation of the anchor at the tensioning end and the shrinkage value of the unbonded prestressed tendons (mm). When the swaged anchor is used, a is 1mm; when the clip anchor is used, a is 5mm;
- the distance between the tensioning end and the anchorage end (mm); - the elastic modulus of the unbonded prestressed tendon (N/mm2). Article 4.1.5 The prestress loss value oi of the unbonded prestressed curved tendons or broken line tendons due to the deformation of the anchor and the shrinkage of the unbonded prestressed tendons shall be determined based on the condition that the deformation value of the unbonded prestressed tendons within the reverse friction influence length 1 between the unbonded prestressed curved tendons or broken line tendons and the wall is equal to the deformation of the anchor and the shrinkage value of the unbonded prestressed tendons. The reverse friction coefficient can be taken according to the value in Table 4.1.6 of this code. Parabolic unbonded prestressed tendons can be considered approximately as circular arc curves. When the corresponding central angle 6 is not greater than 60° (Figure 4.1.51), the prestress loss value can be calculated according to the following formula: dn = 2gomlt
芒+)(1-
(4.1.5-1)
The reverse friction influence length (m) is calculated according to the following formula: αE
It= ~/ 1000m(μ/r + k)
(4. 1.5-2)
where cm is the tension control stress of the unbonded prestressed tendon; r is the radius of curvature of the unbonded prestressed tendon (m); the friction coefficient between the unbonded prestressed tendon and the wall is taken according to Table 4.1.6 of this Code;
considers the influence coefficient of the local deviation of the unbonded prestressed tendon wall (per meter) on the friction;
-the distance from the tensioning end to the calculated section (m), and shall comply with the provisions of ≤.
, when the unbonded prestressed tendon is a straight line at the end, its initial length is lo, and then it is composed of two circular arc curves (Figure 4.1.5-2). When the central angle 6 corresponding to each circular arc is not greater than 60°, its prestress loss a can be calculated according to the following formula:
When r≤:
0/ =2i1(11-l0)+2i2(f- [1) (4.1.5-3)When ≤:
on=2i(l -)+2iz(l:-lt)
(4.1.5-4)
When ≤≤;
dl=2i2(lt)
(4.1.5-5)
The reverse friction influence length (m) is calculated according to the following formula: aE.
tr=1000i2
In the formula, i
+3(4.1.5-6)
The slope of the stress in the unbonded prestressed tendons in the first arc curve is approximately a linear change. The calculation formula is: ra
The slope of the stress in the unbonded prestressed tendons in the second arc curve is approximately a linear change. The calculation formula is: i2=n(+length)
In the formula, AB
The stress of the unbonded prestressed tendons at points A and B. 3. When the anchorage loss of the broken line unbonded prestressed tendons disappears outside the inflection point (Figure 4.1.5-3), the prestress loss can be calculated according to the following formula:
When ≤:
on =2i1(l1 - )+2afi +2i2(lf- l1)(4.1.5-7)
At that time:
Tensoring end
(α)Curve prestressed tendon
Symmetric axis
(b)Distribution diagram after the first batch of prestress loss\4.1.5-1Loss caused by anchor deformation and prestress
Symmetric axis
Tensoring end
(a) Prestressed tendon contour
（6）Distribution diagram after the first batch of prestress loss4.1.5-2Loss caused by anchor deformation and prestress
Symmetric axis
Tensoring end
(a) Prestressed tendon contour
（6）Distribution diagram after the first batch of prestress loss4.1.5-2Loss caused by anchor deformation and prestress
Symmetric axis
Tensoring end
(6)The situation outside the inflection point of the curveon=2i2(lf- α)
(4.1.5-8)
The reverse friction influence length (m) is calculated according to the following formula: E+20+3(4.1.5-9)
lf=N1000i2
1= dn(1 - kt1),μr0
where i
-the slope of the approximate linear change of stress in the prestressed tendons of the first broken line segment. Calculation formula:
ii=gonk
the slope of the approximate linear change of stress in the prestressed tendons of the second broken line segment. Calculation formula:
i2 = acn(1 - ncl1)(1 - pμ0)x:t.
3—46-—9
Tensile mite-
(α) Broken line prestressed tendons
(6) Distribution after the first batch of prestress loss
Figure 4.1.5-3 Anchorage loss disappears outside the inflection point Article 4.1.6 The prestress loss a2 (N/mm2) caused by the friction between the unbonded prestressed tendons and the wall (Figure 4.1.6) can be calculated according to the following formula:
(4.1.6-1)
When r+g is not greater than 0.2, a2 can be calculated according to the following approximate formula 012 (xx + μ0)aon
(4.1.6-2)
--the length of the curve from the tensioning end to the calculated section (m), also in the formula—
can be approximated as the projection length of the curve on the longitudinal axis; 9---the sum of the angles of the tangents of the curve part from the tensioning end to the calculated section (rad).
Tensioning end
Calculated section
Figure 4.1.6 Calculation of prestress friction loss
The friction coefficient of unbonded prestressed tendons is shown in Table 4.1.6. Friction coefficient of unbonded prestressed tendons
Types of unbonded prestressed tendons
745 carbon steel wire
$15 steel strand
Article 4.1.7 The prestress loss α14 (N/mm2) caused by stress relaxation of unbonded prestressed tendons can be calculated according to the following formula: Sgm -0.18)acom
014 = (0. 36 No.
When tensioning once, take ±=1; when over-tensioning, take =0.9. 3-16-—10
The tensioning procedure using the over-tensioning method shall comply with the requirements of Article 5.3.4 of this code. When αcm/fpk is less than or equal to 0.5, the stress relaxation loss value of the unbonded prestressed tendons shall be taken as zero. Article 4.1.8 The prestress loss ais (N/mm2) caused by concrete shrinkage and creep can be calculated according to the following formula: 25+220
Where po
Normal compressive stress of concrete at the combined force point of unbonded prestressed tendons in the tension zone;
-compressive strength of concrete cube when prestressing is applied;
-reinforcement ratio, the ratio of the sum of the cross-sectional areas of unbonded prestressed tendons and non-prestressed steel bars in the tension zone to the net cross-sectional area of the member. For symmetrically arranged prestressed steel bars and non-prestressed steel bars For components with stress reinforcement, the reinforcement ratio shall be calculated based on half of the cross-sectional area of the reinforcement.
When calculating the normal compressive stress α of concrete at the resultant point of unbonded prestressed tendons, the prestress loss value shall only consider the sum of the loss before concrete prestressing (the first batch) and 12; the value shall not be greater than 0.5f. When calculating the normal stress α of concrete, the influence of deadweight can be considered according to the manufacturing conditions of the component.
For structures in a high humidity environment, the a15 value calculated according to the formula in this article can be reduced by 50%; for structures in a dry environment, the ats value should be increased by 20%~30%.
Article 4.1.9, when unbonded prestressed tendons are tensioned in batches, the influence of the elastic compression (or elongation) of the concrete caused by the later batch of tensioned tendons on the earlier batch of tensioned tendons shall be considered, and the tensioning stress value αcm of the earlier batch of tensioned tendons shall be increased (or decreased) by αEOpd. Here, αE is the ratio of the elastic modulus of the unbonded prestressed tendons to the elastic modulus of concrete, and α is the normal stress of concrete generated by the subsequent batch of tensioned tendons at the center of gravity of the previous batch of tensioned tendons. For unbonded prestressed flat plates, in order to consider the influence of the elastic compression of concrete generated by the subsequent batch of tensioned tendons on the previous batch of tensioned tendons, the tension stress value α can be increased by 0.5αEOpeo
Article 4.1.10 Average prestress refers to the average prestress established on the total cross-sectional area of concrete after deducting all prestress losses. For unbonded prestressed concrete flat plates, the average prestress of concrete should not be less than 1.0N/mm2, nor should it be greater than 3.5N/mm2. Note: ① If the prestress is applied only to meet the allowable deflection of the component, it is not subject to the minimum value of the average prestress;
② When the tensioning length is short, the concrete strength grade is high or special measures are taken, the maximum average prestress limit can be appropriately increased. Article 4.1.11 For flexural members using carbon tangled steel wire or steel strand as unbonded prestressed tendons, the design stress value of the unbonded prestressed tendons under the ultimate bearing capacity state shall be calculated according to the following formula: For members with a span-to-height ratio of 1/h less than or equal to 35 and βo less than or equal to 0.45:
ge + (500 - 770Po)
(4.1.11-1)
βo = βp + β. =
fombhp+ fombhp
wherein βo is the comprehensive reinforcement index;
(4.1.11-2)
pe is the effective prestress in the unbonded prestressed tendons after deducting all prestress losses.
2. For components with a span-to-height ratio of 1/h greater than 35 and β less than or equal to 0.45:
0,= e+(250- 3803o)
(4.1.11-3)
の, should not be less than the effective prestress αre of the unbonded prestressed tendons, nor should it be greater than the design value of the tensile strength of the unbonded prestressed steel foy. Article 4.1.12 For over-determined structures calculated elastically, the influence of the secondary internal forces generated by the unbonded prestressed tendons in the structural section should be considered in the design. The secondary bending moment M2 and the main bending moment M, can be determined according to the following formulas respectively;
The secondary bending moment is calculated according to the following formula:
M2 - M,- M
(4. 1.12-1)
Where M,-Total bending moment, the bending moment caused by the equivalent load of prestressing on the structural section;
Primary bending moment, the bending moment caused by the deformation of the statically indeterminate structure due to the constraint caused by the main bending moment of prestressing M2—
. The main bending moment is calculated according to the following formula:
Mi- Npeep
Where Npe
(4.1.12-2)
Npe=peAp
(4.1.12-3)
-Total effective prestressing in unbonded prestressing tendons; Eccentricity of the center of gravity of unbonded prestressing tendons to the center of gravity of the section.
When performing crack resistance verification and normal section bearing capacity calculation, the influence of secondary bending moment on the section bending moment value should be considered. The influence of secondary bending moment on the bearing capacity of the positive section can be calculated according to the following provisions;
The bending bearing capacity of the negative bending moment section is calculated according to the following formula: IMI-iM2≤M.
(4.1.12-4)
The bending bearing capacity of the positive bending moment section is calculated according to the following formula: IMI+[M2]≤Mu
(4.1.12-5)
Where M--the design value of the bending moment on the structural section (excluding the prestressing effect);
The design value of the bending bearing capacity of the positive section of the member. Note: Formula (4.1.12-4) is applicable to the case where the difference between the absolute value of the total bending moment M and the main bending moment M1 is greater than zero;
Formula (4.1.12-5) is applicable to the case where the difference between the absolute value of the total bending moment M and the main bending moment M1 is less than zero.
Article 4.1.13 In the local compression area of the anchor head in the unbonded prestressed concrete member, the local compressive bearing capacity shall be verified. In the local compression calculation of the anchor, the longitudinal force shall be calculated by taking the larger value of 1.2gcm and 0.8fpk, where k is the standard value of the tensile strength of the unbonded prestressed tendons. Article 4.1.14 The deformation of the unbonded prestressed concrete bending member under the combined action of the short-term effect of the load can be calculated by the structural mechanics method based on the short-term stiffness B of the member. For members without cracks, the short-term stiffness B can be determined according to the following formula: B, = 0.85Elo
Where Io-
-converted section moment of inertia.
Article 4.1.15 When the short-term effect of load is combined and the influence of the long-term effect of load is considered, the long-term stiffness B of the bending member can be calculated as follows:
B= M(o-)+MB
Wherein M—
The moment value under the combined action of the long-term effect of load; the moment value under the combined action of the short-term effect of load; M.
The deflection increase influence coefficient, take 2.0.
Article 4.1.16 In order to reduce the adverse effects of columns and walls on the prestressing effect of beams and slabs, the following measures are taken: 1. Arrange the lateral force resisting members near the fixed point of the structural displacement center; use relatively slender flexible columns; or configure additional steel bars in the columns to bear the additional bending moment caused by the constraint effect; 2. When the length of the slab exceeds 50m, the structure can be divided into sections by post-cast strips or temporary construction joints. However, the prestressed tendons and non-prestressed steel bars should still pass through continuously;
3. Design the nodes between the beam and the supporting column as sliding bearings that can produce unconstrained sliding during the tensioning process. Section 2 One-way System
Article 4.2.1 The configuration of non-prestressed steel bars in the tension zone of unbonded prestressed concrete flexural members shall comply with the following provisions: 1. The cross-sectional area A of non-prestressed steel bars in one-way plates. It should be calculated according to the following formula:
Ag≥0.002bh
Where b
-section width;
(4.2.1-1)
section height.
And the diameter of non-prestressed steel bars should not be less than 8mm, and the spacing between them should not be greater than 200mm
2. The minimum cross-sectional area A of non-prestressed steel bars configured in the tension zone of the beam. The following provisions shall be met:
Asf,+Apop
A, = 0.0036h
(4. 2. 1-2)
(4.2.1-3)
The larger of the above two calculation results shall be taken. The diameter of the steel bar shall not be less than 14mm.
According to the requirements of formula (4.2.1-1)(4.2.1-3), the non-prestressed steel bars shall be evenly distributed in the tension zone of the beam and close to the tension edge. The length of the non-prestressed steel bars shall meet the requirements of the anchorage length or extension length of the relevant specifications.
Article 4.2.2
The design value of the bending bearing capacity of the positive section of unbonded prestressed concrete flexural members shall meet the following requirements: 3—16—-11
Mu≥Mer
(4.2.2-1)
Mcr=(α: + yft)Wo
(4.2.2-2)
Wherein, Mu——the design value of the bending bearing capacity of the positive section of the member; M.——the cracking moment value of the positive section of the member.
Article 4.2.3 The shear bearing capacity of the inclined section of unbonded prestressed concrete flexural members can be calculated according to the formula of the relevant provisions of Chapter 4, Section 2 of the "Code for Design of Concrete Structures" GBJ1089, but the stress design value of the unbonded prestressed bent tendons should be the effective prestress value. Article 4.2.4 The maximum spacing of unbonded prestressed tendons can be 6 times the thickness of the plate, and should not be greater than 1.0m.
Article 4.2.5 In the main beam, secondary beam and multi-ribbed slab, support reinforcement for unbonded prestressed tendons must be arranged. For bundled prestressed tendons composed of 24 unbonded prestressed tendons, the diameter of the support reinforcement should not be less than 10mm, and the spacing should not be greater than 1.0m; for bundled prestressed tendons composed of 5 or more unbonded prestressed tendons, the diameter should not be less than 12mm, and the spacing should not be greater than 1.2m; the spacing of the support reinforcement used to support a single unbonded prestressed tendon in the slab should not be greater than 2.0m. The support reinforcement should be Grade 1 steel.
Section 3
Two-way system
Article 4.3.1 The calculation of the two-way slab of the unbonded prestressed slab-column system shall be carried out in the longitudinal and transverse directions of the slab. The internal force calculation of the rectangular column grid unbonded prestressed concrete slab and multi-ribbed slab under vertical load can be carried out according to the equivalent frame method; the beam width of the equivalent beam can be taken as the sum of the half spans on both sides of the column. For grid beam slabs, slabs with special column grids, and slabs that bear large concentrated loads and large openings, the finite element method and other methods can be used for calculation.
Article 4.3.2 When calculating the internal forces of rectangular column grid unbonded prestressed concrete flat plates and multi-ribbed slabs according to the equivalent frame method under the action of lateral forces, the slab width of the equivalent beam shall comply with the provisions of Article 4.3.3. The internal forces generated by the lateral force shall be combined on the main beam of the column slab or multi-ribbed slab.
Article 4.3.3 Under the action of lateral forces, the calculated width of the equivalent frame beam shall be the smaller value of the calculation results of the following formulas: by=（1++ba）
武中b,——
Y-axis calculated width of the equivalent frame beam;
lxl,—calculated span of the equivalent beam;
bd—effective width of the flat support plate.
(4.3.3-1)
(4.3.3-2)
Article 4.3.4 For solid two-way slabs of equal thickness, the minimum cross-sectional area and distribution of non-prestressed longitudinal reinforcement shall comply with the following provisions: 1. Non-prestressed longitudinal reinforcement in the negative bending moment zone. In the negative bending moment zone of the column side, the cross-sectional area of non-prestressed reinforcement in each direction shall comply with the following provisions:
(4.3.4-1)
A,=≥0.00075hl
The span of the slab parallel to the direction of the calculated longitudinal reinforcement; where {-
3--1612
h--the thickness of the slab.
The non-prestressed longitudinal reinforcement determined by the above formula shall be distributed within the slab width range of 1.5h from the column side. At least 4 steel bars with a diameter of not less than 16mm shall be set in each direction. The spacing between non-prestressed longitudinal reinforcements should not be greater than 300mm, and the length of the extension from the column side should be at least 1/6 of the clear span on each side of the support. When considering the role of non-prestressed longitudinal reinforcement in the bearing capacity calculation, its extension length should be determined by calculation and should comply with the provisions of the relevant specifications on the anchorage length.
2. Non-prestressed longitudinal reinforcement in the positive moment zone. The cross-sectional area of the non-prestressed longitudinal reinforcement in each direction of the positive moment zone shall comply with the following provisions:
(4.3.4-2)
As≥0.0015bh
When tensile stress is not allowed in the tension zone under the normal service limit state, the cross-sectional area of the non-prestressed longitudinal reinforcement in each direction of the two-way slab shall be calculated according to the following formula:
A s≥0.001bh
(4.3.4-3)
And the diameter of the steel bar should not be less than 6mm, and the spacing should not be greater than 200mm.
Non-prestressed longitudinal steel bars should be evenly distributed in the tensile zone of the slab and should be arranged close to the tensile edge. When considering the role of non-prestressed longitudinal steel bars in the bearing capacity calculation, their length should comply with the provisions of the relevant specifications for anchorage length.
Third, at the edges and corners of the slab, a blind ring beam or reinforced concrete edge beam should be set. The diameter of the longitudinal steel bar of the blind ring beam should not be less than 12mm, and should not be less than 4; the diameter of the stirrups should not be less than 6mm, and the spacing should not be greater than 250mm.
Article 4.3.5 The type and structural design of the cast-in-place slab-column node shall meet the following requirements:
I. Unbonded prestressed bars and non-prestressed longitudinal steel bars configured in accordance with Article 4.3.4 shall pass through the slab-column node orthogonally. There shall be no less than 2 unbonded prestressed bars passing through the column in each direction. 2. If the punching bearing capacity of the slab-column joint needs to be enhanced, the following methods can be used:
1. Partially thicken the thickness of the slab near the slab-column joint (Figure 4.35a) or add a column cap.
2. A hidden beam can be used to pass through the column section and arranged in the slab. The hidden beam is composed of shear stirrups and longitudinal steel bars (Figure 4.3.56). At this time, the upper steel bars should not be less than the non-prestressed longitudinal steel bars required for the column upper slab within the width of the hidden beam, and the diameter should not be less than 16mm; the diameter of the lower steel bars should not be less than 16mm.
3. When a steel shear frame is welded from steel sections that are perpendicular to each other and pass through the column section, such as I-beams and channel steels (Figure 4.3.5c), the design should be carried out in accordance with Article 4.3.8.
Article 4.3.6 The punching bearing capacity of the unbonded prestressed concrete slab without stirrups and bent steel bars under the action of concentrated reaction force can be calculated according to the following formula:
Tip: This standard content only shows part of the intercepted content of the complete standard. If you need the complete standard, please go to the top to download the complete standard document for free.