WO2019242366A1 - 粘结退化影响下pc构件抗弯承载力计算方法 - Google Patents

粘结退化影响下pc构件抗弯承载力计算方法 Download PDF

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WO2019242366A1
WO2019242366A1 PCT/CN2019/079890 CN2019079890W WO2019242366A1 WO 2019242366 A1 WO2019242366 A1 WO 2019242366A1 CN 2019079890 W CN2019079890 W CN 2019079890W WO 2019242366 A1 WO2019242366 A1 WO 2019242366A1
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concrete
force
formula
steel strand
corroded
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PCT/CN2019/079890
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English (en)
French (fr)
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王磊
戴理朝
张旭辉
张建仁
马亚飞
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长沙理工大学
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Priority to KR1020197031496A priority Critical patent/KR102291531B1/ko
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/38—Concrete; Lime; Mortar; Gypsum; Bricks; Ceramics; Glass
    • G01N33/383—Concrete or cement
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F30/00—Computer-aided design [CAD]
    • G06F30/10—Geometric CAD
    • G06F30/13—Architectural design, e.g. computer-aided architectural design [CAAD] related to design of buildings, bridges, landscapes, production plants or roads
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F17/00—Digital computing or data processing equipment or methods, specially adapted for specific functions
    • G06F17/10—Complex mathematical operations
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F30/00—Computer-aided design [CAD]
    • G06F30/20—Design optimisation, verification or simulation
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F2119/00—Details relating to the type or aim of the analysis or the optimisation
    • G06F2119/06—Power analysis or power optimisation

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  • the invention relates to the technical field of calculation methods of bearing capacity, and in particular to a calculation method of bending bearing capacity of PC components under the influence of adhesion degradation.
  • Prestressed concrete has been widely used in bridge engineering because of its large spanning ability and good durability.
  • failures of PC bridges have occurred from time to time, and the safety of existing bridges has caused widespread concern.
  • Corrosion of steel strands is one of the main factors that cause the bearing capacity of existing PC beams to deteriorate.
  • rust will cause the cross-sectional area of steel strands to decrease, material degradation, concrete cracking and bond strength degradation.
  • the occurrence of load cracks will also affect the magnitude of the bending bearing capacity. These factors will cause the bending capacity of the existing PC beam to decrease. How to evaluate the residual bending capacity of a corroded PC beam is a prerequisite to ensure its normal use and safety.
  • the present invention proposes a method for calculating the flexural bearing capacity of PC components under the influence of adhesion degradation.
  • the advantage of this method is that it can comprehensively consider the reduction of cross-sectional area of steel strands caused by corrosion, material degradation, concrete cracking, and bonding Influence of factors such as degradation and load cracks.
  • the purpose of the present invention is to provide a method for calculating the bending bearing capacity of PC components under the influence of adhesion degradation, so as to effectively solve the above technical problems.
  • Calculation method for flexural bearing capacity of PC components under the influence of adhesion degradation includes the following steps:
  • the component determines the value of the geometric parameters, use the thick-walled thin-tube theory to simulate the rust expansion and cracking of the concrete, and establish the expressions of the adhesion, restraint and rust expansion forces between the rusted steel strand and the concrete interface, and then predict Bond strength of corroded steel strands;
  • a deformation coordination coefficient is introduced to consider the strain inconsistency between the steel strand and the concrete in the limit state.
  • the stress and strain distribution rules in the cross section of the component are determined.
  • the force and bending moment balance equations of the corroded PC beam are established, and its bending resistance is proposed. Calculation method of bearing capacity.
  • step (1) further includes the following steps:
  • the bonding strength of corroded steel strands is mainly provided by the adhesive force, binding force and swell force at the interface between the steel strands and concrete, and its expression is formula (1):
  • ⁇ ⁇ ⁇ a + ⁇ b + ⁇ c
  • ⁇ ⁇ is the bonding stress of rusted steel strands
  • ⁇ a is the bonding stress caused by rust expansion force
  • ⁇ b is the adhesion force at the interface
  • ⁇ c is the constraint force at the interface
  • k c is the friction coefficient between the corroded steel strand and the concrete interface
  • P c is the rust expansion force between the steel strand and the concrete interface
  • the rust expansion force between the strand and the concrete interface can be expressed as formula (3):
  • R 0 is the radius of the steel wire before corrosion
  • Pu is the rust expansion force at the interface of the cracked and uncracked concrete
  • Ru is the radius of the cracked concrete
  • r is the position of the cracked concrete area
  • ⁇ ⁇ (r) is Hoop stress of cracked concrete
  • the rust expansion force between the steel strand and the concrete interface can be expressed as formula (4):
  • k is the number of transverse ribs of the steel strand on the same section
  • a r is the area of the transverse rib
  • D is the diameter of the corroded steel strand
  • ⁇ is the angle between the transverse rib and the axis of the strand
  • ⁇ is the strand
  • s r is the distance between the transverse ribs
  • f coh is the adhesion force coefficient between the interfaces
  • the binding force of the concrete around the interface between the corroded steel strand and the concrete can be expressed as formula (6):
  • C r is the shape coefficient of the transverse rib
  • p x is the maximum pressure on the steel strand when it fails.
  • step (2) further includes the following steps:
  • the average rust expansion force P av can be expressed as formula (8):
  • ⁇ a ⁇ k c P av + ⁇ b + ⁇ c .
  • step (3) further includes the following steps:
  • the tensile force of the steel strand under the load can be calculated by the effective bonding force, the residual bonding force and the effective pre-stressing force, which can be expressed as formula (10):
  • F p is the tensile strand, F eb valid adhesion, F er the residual adhesive force, F e ⁇ valid pre-energizer;
  • the effective bonding force of corroded steel strand mainly depends on the bonding stress and contact area of the interface, which can be expressed as formula (11):
  • the residual bonding stress can be evaluated by the effective bonding stress, which is equal to 40% of the effective bonding stress.
  • the residual bonding force of the corroded steel strand can be expressed as formula (12):
  • L er is the length of the slip zone
  • F pe is the initial pre-stress of the unrusted steel strand
  • ⁇ is the rust rate of the steel strand
  • step (4) further includes the following steps:
  • ⁇ cp ⁇ p / ⁇
  • ⁇ is the deformation coordination coefficient
  • ⁇ p is the strain of the steel strand in the limit state
  • F c is the resultant force of the concrete
  • F s and F ′ s are the resultant forces of the ordinary steel bars in the tension zone and the compression zone
  • M is the bending moment caused by the external load
  • h p , h 0, and a ′ s are the steel.
  • y c is the distance from the center of the equivalent stress rectangle of the concrete to the top of the beam.
  • the beneficial effects of the present invention are: the method for calculating the flexural bearing capacity of PC components under the influence of adhesion degradation provided by the present invention.
  • the concept of equivalent bond strength is introduced by evaluating the rust and crack of concrete under the influence of corrosion and the bond strength of steel strands.
  • the force expression of the corroded steel strand under load is established; the deformation coordination coefficient is introduced to quantify the deformation inconsistency between the corroded steel strand and the concrete, and to clarify the stress in the cross section of the component And strain distribution law; establish the equilibrium equations of stress and bending moment in the section of corroded PC beams, and obtain the calculation method of flexural bearing capacity of corroded PC beams; this calculation method can comprehensively consider the reduction of the cross-sectional area of steel strands caused by corrosion, material degradation, and concrete The effects of cracks, bond degradation, and load cracks can accurately predict the flexural capacity of corroded PC beams and can be widely used in practical engineering.
  • Figure 1 Schematic diagram of crack propagation and stress distribution in concrete.
  • Figure 3 Schematic diagram of the stress of the steel strand under the external load.
  • Figure 5 Flow chart for calculating the flexural capacity of a corroded PC.
  • This embodiment discloses a method for calculating the bending bearing capacity of a PC component under the influence of adhesion degradation.
  • the detailed steps of the calculation method are as follows:
  • a method for calculating the flexural capacity of a corroded PC beam is introduced: a deformation coordination factor is introduced to consider the strain inconsistency between the steel strand and the concrete in the limit state, and the force and bending moment equilibrium equations for the corroded PC beam are established. Its bending capacity calculation method.
  • step (1) The calculation of the bond strength during the concrete rust and cracking in step (1) is as follows:
  • R 0 and R ⁇ are the radii of the steel wire before and after rusting, respectively, and A p is the cross-sectional area of the uncorroded steel strand.
  • the volume of the corrosion product of the steel strand is larger than the volume of the correspondingly consumed iron, which causes the outward expansion of the corrosion product.
  • One part of the corrosion products will fill the pores and cracks inside the concrete, while the other part will produce rusty force.
  • the total volume of the corrosion products of steel strands per unit length can be expressed as formula (2):
  • ⁇ V t is the total volume of the rust product
  • ⁇ V t n ⁇ V w
  • n is the rust expansion rate
  • ⁇ V w is the volume change of the outer steel wire of the steel strand per unit length.
  • ⁇ V e is the volume change of concrete
  • R t is the radius of the steel wire including the influence of rust products
  • ⁇ V c is the volume of rust products that fill cracks and pores per unit length.
  • Ru is the radius of cracked concrete.
  • the concrete protective layer Before the protective layer cracks, the concrete protective layer consists of a cracked inner ring and an uncracked outer ring, as shown in Figure 1.
  • elastic theory can be used to simulate the internal stress of the concrete.
  • the hoop stress ⁇ ⁇ (t) and the radial displacement u (t) of the uncracked concrete can be expressed as formulas (5) and (6), respectively. ):
  • t uncracked concrete region
  • R c R o + C
  • C is the thickness of concrete
  • P u is the position of the interface and cracking of concrete uncracked Expansion Force
  • E c and v c are the elastic modulus and Poisson's ratio of the concrete, respectively.
  • r is the position of the crack region concrete, R 0 ⁇ r ⁇ R u.
  • ⁇ ⁇ (r) and ⁇ ⁇ (r) are the hoop stress and strain of the concrete
  • ⁇ ct is the corresponding strain when the concrete reaches the tensile strength
  • ⁇ 1 is the concrete stress when the concrete stress is 15% tensile strength.
  • ⁇ u is the ultimate strain of the concrete.
  • R 0 is the radius of the wire before the corrosion
  • R u is a concrete crack radius
  • r is the position of the crack region concrete.
  • the rust expansion force P c of the steel strand-concrete interface can be expressed as formula (11):
  • k c is the friction coefficient between the corroded steel strand and the concrete interface.
  • k is the number of transverse ribs of the steel strand on the same section
  • a r is the area of the transverse rib
  • D is the diameter of the corroded steel strand
  • ⁇ is the angle between the transverse rib and the axis of the steel strand
  • ⁇ is the steel strand
  • s r is the distance between the transverse ribs
  • f coh is the adhesion force coefficient between the interfaces.
  • the binding force ⁇ c of the concrete around the interface between the corroded steel strand and the concrete can be expressed as formula (14):
  • C r is the shape coefficient of the transverse rib
  • p x is the maximum pressure on the steel strand when it fails.
  • the bonding strength ⁇ ⁇ of the corroded steel strand can be calculated from the adhesive force, binding force and rust expansion force at the interface between the steel strand and concrete, and its expression is as shown in formula (15):
  • ⁇ ⁇ ⁇ a + ⁇ b + ⁇ c .
  • the calculation method of the equivalent bond strength in the step (2) is:
  • the occurrence of load cracks will reduce the restraint effect of concrete.
  • the rust expansion force at the crack position is almost completely degraded, while the rust expansion force at the intermediate position of adjacent cracks remains basically unchanged, as shown in Figure 2.
  • the rust expansion force at the crack position is defined as 0, and the rust expansion force at the middle position of the adjacent crack is defined as P c .
  • the rust expansion force is assumed to change linearly along the beam length direction, and the rust expansion force is at any position P c (z) can be expressed as formula (16):
  • z is an arbitrary position along the length of the beam
  • l m is the average load crack distance
  • ⁇ a ⁇ k c P av + ⁇ b + ⁇ c .
  • the calculation method of the effective adhesive force, the residual adhesive force and the effective pre-energizing force in the step (3) is:
  • Figure 3 shows the stress of the steel strand under load. Suffered strand tensile force F p by the effective adhesive force F eb, the residual adhesive force F er Loads and effective pre-energizer F e ⁇ calculated, which is expressed in Equation (19):
  • the effective bonding force of corroded steel strands mainly depends on the bonding stress and contact area of the interface, and its expression is as shown in formula (20):
  • S is the circumference of the corroded steel strand
  • Leb is the effective bonding length
  • the residual bonding stress can be evaluated by the effective bonding stress, which has a value equal to about 40% of the effective bonding stress.
  • the residual bonding force of the corroded steel strand can be expressed as formula (21):
  • L er is the length of the slip zone.
  • F pe is the initial pre-stress of the unrusted steel strand.
  • f p and ⁇ are the stress and strain of the rusted steel strand respectively
  • ⁇ c is the critical rust rate and its value is 11%
  • E p and E pp are the elastic modulus and strengthening modulus of the unrusted steel strand, respectively.
  • F y is the yield strength of the uncorroded steel strand
  • ⁇ y and ⁇ pu are the yield strain and ultimate strain of the uncorroded steel strand, respectively.
  • ⁇ cp ⁇ p / ⁇
  • ⁇ is a deformation coordination coefficient
  • ⁇ ct is the strain of the concrete on the top
  • h p , h 0 and a ′ s are the steel strands, the distance from the center of gravity of the tensile steel bar and the compressed steel bar to the top of the beam.
  • f s is the stress of ordinary steel bars
  • E s and E sp are the elastic modulus and strengthening modulus of ordinary steel bars, respectively
  • f sy and ⁇ sy are the yield strength and yield strain of ordinary steel bars, respectively.
  • a s and A ′ s are the cross-sectional areas of ordinary steel bars in the tension zone and the compression zone, respectively, and f s ( ⁇ s ) and f s ( ⁇ ′ s ) are the ordinary steel bars in the tension zone and the compression zone, respectively. stress.
  • f c and ⁇ c are the stress and strain of the concrete
  • f ′ c is the compressive strength of the concrete
  • ⁇ 0 is the corresponding strain when the concrete reaches the compressive strength.
  • f c ( ⁇ c ) is the concrete stress
  • b is the beam width
  • h is the beam height
  • y is the distance from any position of the concrete to the top of the beam.
  • M is a bending moment caused by an external load.
  • the present invention proposes a method for calculating the flexural bearing capacity of PC components under the influence of adhesion degradation.
  • This method can comprehensively consider the reduction of the cross-sectional area of steel strands caused by corrosion, material degradation, concrete cracking, and adhesion degradation. And load cracks.
  • Figure 5 shows the calculation flow chart of the flexural bearing capacity of rusted PC. The details are as follows:
  • the failure mode of the corroded PC beam is the crushing failure of the concrete at the top.
  • the failure mode of the corroded PC beam is concrete crushing failure; if the calculated strand strain is greater than the limit strain, the failure mode of the corroded PC beam is steel strand fracture;
  • the strain of the steel strand reaches the ultimate strain under the limit state, and the stress and strain of the steel strand, steel bar and concrete are recalculated based on the formula (19-33);
  • the flexural capacity of the corroded PC beam is calculated from the bending balance equation (35).
  • Step 1 Determine the geometric parameters of the component.
  • the size of the bonded PC beam is 150mm ⁇ 220mm ⁇ 2000mm.
  • the bottom of the beam is equipped with a 7-wire steel strand with a diameter of 15.2mm.
  • the distance from the center of gravity to the bottom of the beam is 60mm.
  • the yield strength and ultimate strength of the steel strand are 1830 MPa and 1910 MPa, respectively.
  • the initial tensile stress of the steel strand was 1395 MPa.
  • the bottom of the test beam is equipped with two light round bars with a diameter of 8mm, and the top is equipped with two deformed bars with a diameter of 12mm.
  • the yield strengths of light round and deformed bars are 235 MPa and 335 MPa, respectively.
  • a smooth round steel bar with a diameter of 8 mm is used as the stirrup, and the spacing is 90 mm.
  • the compressive strength of the concrete is 31.8 MPa.
  • Electrochemical method was used to accelerate the corrosion of steel strands in components. After accelerated corrosion, the flexural bearing capacity of corroded PC beams was evaluated using a four-point bending load test. The relevant test data are shown in Table 1.
  • Step 2 Evaluate the rust expansion force of the concrete cracking process based on the corrosion rate of the steel strand.
  • the rust expansion rate is between 2-4, and the average value is selected as 3 in this paper. Based on the measured rust rate, determine whether the protective layer is cracked. If the protective layer is not cracked, the rust expansion force P c between the steel strand and the concrete interface can be calculated by formula (1):
  • R 0 is the radius of the steel wire before corrosion
  • Pu is the rust expansion force at the interface of the cracked and uncracked concrete
  • Ru is the radius of the cracked concrete
  • r is the cracked concrete area
  • ⁇ ⁇ (r) is the cracked concrete Hoop stress.
  • Step 3 Consider the equivalent bond strength affected by load cracks.
  • k c is the friction coefficient between the corroded steel strand and the concrete interface
  • k c 0.37-0.26 (xx cr )
  • x is the corrosion depth of the steel strand
  • x cr is the criticality of the steel strand when the protective layer is cracked. Depth of rust.
  • the adhesion force ⁇ b between the interface of the corroded steel strand and the concrete can be calculated by formula (4):
  • the binding force ⁇ c of the concrete surrounding the interface between the corroded steel strand and the concrete can be calculated by formula (5):
  • C r is the shape coefficient of the transverse rib
  • C r 0.8
  • p x is the maximum pressure on the steel strand when it fails.
  • the equivalent bond strength ⁇ a ⁇ of the corroded steel strand under the limit state can be predicted from the adhesion force, restraint force and rust expansion force of the interface between the strand and the concrete, and its value can be calculated by the formula ( 6) Perform calculations:
  • ⁇ a ⁇ k c p av + ⁇ b + ⁇ c .
  • Step 4 Establish the stress expression of the steel strand under the load.
  • the effective bonding force of corroded steel strands mainly depends on the bonding stress and contact area of the interface, and its value can be calculated by formula (8):
  • S is the circumference of rust strand
  • S 8 ⁇ R ⁇
  • R ⁇ is the radius of the wire corrosion
  • L eb is the effective bond length
  • f y is the yield strength of the uncorroded steel strand
  • f pe is the effective prestress of the steel strand.
  • the residual bonding stress can be evaluated by the effective bonding stress, which is equal to 40% of the effective bonding stress.
  • the residual bonding force of the corroded steel strand can be calculated by formula (9):
  • L er is the length of the slip zone.
  • F pe is the initial pre-stress of the unrusted steel strand
  • ⁇ is the rust rate of the steel strand
  • Step 5 Construction of the force and bending moment balance equation for the corroded PC beam.
  • a deformation inconsistency coefficient is introduced to consider the strain inconsistency between the steel strand and the concrete in the limit state.
  • the strain cp of the concrete at the position of the steel strand can be expressed as formula (11):
  • ⁇ cp ⁇ p / ⁇
  • ⁇ is the deformation coordination coefficient
  • ⁇ 0.8099 ⁇ 2 -1.2771 ⁇ + 1
  • ⁇ p the strain of the steel strand in the limit state.
  • strains ⁇ s and ⁇ ′ s of ordinary steel bars in the tensile and compressive areas of the component can be calculated by formulas (12) and (13), respectively:
  • ⁇ ct is the strain of the concrete at the top
  • h p , h 0 and a ′ s are the steel strands, the distance from the center of gravity of the tensile steel bar and the compressed steel bar to the top of the beam body.
  • a s and A ′ s are the cross-sectional areas of ordinary steel bars in the tension zone and the compression zone, respectively, and f s ( ⁇ s ) and f s ( ⁇ ′ s ) are the ordinary steel bars in the tension zone and the compression zone, respectively. stress.
  • f c ( ⁇ c ) is the concrete stress
  • b is the beam width
  • h is the beam height
  • y is the distance from any position of the concrete to the top of the beam.
  • M is a bending moment caused by an external load.
  • Step 6 Verify the rationality of the calculation method.
  • ⁇ is the corrosion rate
  • f ′ c is the compressive strength of the concrete
  • D 0 is the diameter of the steel strand
  • M t is the test bending moment value
  • M p is the theoretical bending moment value.
  • the present invention illustrates the implementation method of the present invention through the foregoing embodiments, but the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above methods to be implemented.
  • Those skilled in the art should know that any improvement to the present invention, equivalent replacement of the implementation method selected by the present invention, addition of steps, selection of specific modes, etc., all fall within the scope of protection and disclosure of the present invention.

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Abstract

本发明公开的粘结退化影响下PC构件抗弯承载力计算方法，通过评估锈蚀影响下混凝土锈胀开裂和钢绞线的粘结强度，引入等效粘结强度概念考虑荷载裂缝对粘结强度分布的影响，建立荷载作用下锈蚀钢绞线的受力表达式；引入变形协调系数量化锈蚀钢绞线与混凝土间的变形不协调，明确构件横断面内的应力、应变分布规律；建立锈蚀PC梁截面内的受力和弯矩平衡方程，得到锈蚀PC梁抗弯承载力计算方法；本发明提出的粘结退化影响下PC构件抗弯承载力计算方法可综合考虑锈蚀引起的钢绞线截面积减小、材料劣化、混凝土开裂、粘结退化及荷载裂缝等因素的影响，对既有PC梁桥剩余承载力的评估具有重要地指导意义。

Description

粘结退化影响下PC构件抗弯承载力计算方法 技术领域
本发明涉及承载力计算方法技术领域，具体是一种粘结退化影响下PC构件抗弯承载力计算方法。
背景技术
预应力混凝土(PC)由于具有跨越能力大、耐久性好等特点，目前已广泛应用于桥梁工程。然而，近年来PC桥梁的失效事故时有发生，既有桥梁的安全性已引起了广泛关注。钢绞线锈蚀是造成既有PC梁承载力退化的主要因素之一。首先，锈蚀会引起钢绞线截面积减小，材料劣化，混凝土开裂及粘结强度退化。此外，荷载裂缝的出现也会影响抗弯承载力的大小。这些因素均会造成既有PC梁抗弯承载力的下降。如何评估锈蚀PC梁的剩余抗弯承载力是确保其正常使用和安全性的前提。
目前针对锈蚀普通钢筋混凝土梁的剩余抗弯承载力已开展了大量的理论研究。然由于钢绞线具有高应力状态及捻制截面形状等特点，使得其锈蚀对PC梁抗弯承载力的影响更为复杂。文献调研表明，针对锈蚀PC梁剩余抗弯承载力的计算方法十分匮乏。部分学者忽略粘结退化的影响，基于应变协调原理对钢束断裂影响下PC梁的剩余承载力进行了预测。也有部分学者引入应变不协调理论对锈蚀PC梁的抗弯承载力进行评估，但该方法无法考虑锈胀开裂及荷载裂缝等因素的影响。现有的PC梁抗弯承载力计算方法无法综合考虑锈蚀引起的钢绞线截面积减小、材料劣化、混凝土开裂、粘结退化及荷载裂缝等因素的影响。
为此，本发明提出了一种粘结退化影响下PC构件抗弯承载力计算方法，该方法的优势在于可综合考虑锈蚀引起的钢绞线截面积减小、材料劣化、混凝土开裂、粘结退化及荷载裂缝等因素的影响。
发明内容
本发明的目的在于提供一种粘结退化影响下PC构件抗弯承载力计算方法，以有效解决上述技术问题。
为有效解决上述技术问题，本发明采取的技术方案如下：
粘结退化影响下PC构件抗弯承载力计算方法，该方法包括以下步骤：
(1)锈裂影响下钢绞线粘结强度预测：
根据构件基本尺寸，确定几何参数取值，采用厚壁薄筒理论对混凝土的锈胀开裂进行模拟，建立锈蚀钢绞线与混凝土界面间胶着力、约束力和锈胀力的表达式，进而预测锈蚀钢绞线的粘结强度；
(2)荷载裂缝影响下粘结强度评估：
引入一个等效粘结强度概念来考虑粘结强度沿梁长方向的分布，提出等效粘结强度计算方法；
(3)建立荷载作用下钢绞线的受力表达式：
构建锈蚀影响下有效粘结力、残余粘结力和有效预加力的计算方法，建立荷载作用下锈蚀钢绞线张拉力的表达式；
(4)提出锈蚀PC梁抗弯承载力计算方法：
引入一个变形协调系数来考虑极限状态下钢绞线与混凝土间的应变不协调，明确构件横断面内的应力、应变分布规律，建立锈蚀PC梁的受力和弯矩平衡方程，提出其抗弯承载力计算方法。
特别的，所述步骤(1)还包括以下步骤：
混凝土锈胀开裂过程中，粘结强度的计算如下：
锈蚀钢绞线的粘结强度主要由钢绞线与混凝土交界面间的胶着力、约束力和锈胀力来提供，其表达式为公式(1)：
τ η＝τ a+τ b+τ c
式中，τ η为锈蚀钢绞线的粘结应力，τ a为锈胀力引起的粘结应力，τ b为交界面间的胶着力，τ c为交界面间的约束力；
锈蚀钢绞线与混凝土交界面锈胀力引起的粘结应力可表示为公式(2)：
τ a＝k cp c
式中，k c为锈蚀钢绞线与混凝土界面间的摩擦系数，P c为钢绞线-混凝土界面间的锈胀力；
保护层开裂前，锈胀力主要由开裂混凝土的剩余拉应力和未开裂混凝土的约束力共同抵抗，钢绞线-混凝土界面间的锈胀力可表示为公式(3)：
Figure PCTCN2019079890-appb-000001
式中，R 0为锈蚀前钢丝的半径，P u为开裂和未开裂混凝土交界面位置的锈胀力，R u为开裂混凝土的半径，r为开裂混凝土区域的位置，σ θ(r)为开裂混凝土的环向应力；
保护层开裂后，锈胀力主要由开裂混凝土的剩余拉应力来抵抗，钢绞线-混凝土界面间的锈胀力可表示为公式(4)：
Figure PCTCN2019079890-appb-000002
锈蚀钢绞线与混凝土交界面间的胶着力可表达为公式(5)：
Figure PCTCN2019079890-appb-000003
式中，k为同一截面上钢绞线的横肋数目，A r为横肋面积，D为锈蚀钢绞线直径，δ为横肋与钢绞线轴线间的夹角，θ为钢绞线与混凝土间的摩擦角，s r为横肋间距，f coh为界面间胶着力系数；
锈蚀钢绞线与混凝土交界面间周围混凝土的约束力可表达为公式(6)：
Figure PCTCN2019079890-appb-000004
式中，C r为横肋的形状系数，p x为失效时钢绞线所受的最大压力。
特别的，所述步骤(2)还包括以下步骤：
等效粘结强度概念的引入方法如下：
当无荷载裂缝存在时，锈蚀构件沿梁长方向各位置处的锈胀力大小一致呈均匀分布。然荷载裂缝的出现会减低混凝土的约束作用，裂缝位置处的锈胀力几乎全部退化，而相邻裂缝中间位置处的锈胀力则基本保持不变。将裂缝位置处的锈胀力定义为0，而相邻裂缝中间位置处的锈胀力定义为P c，锈胀力沿梁长方向假定呈直线变化，则锈胀力在任意位置处P c(z)可表示为公式(7)：
Figure PCTCN2019079890-appb-000005
式中，z为沿梁长方向的任意位置，l m为平均弯曲裂缝间距；
引入一个等效概念来考虑锈胀力沿梁长方向的分布，则平均锈胀力P av可表示为公式(8)：
Figure PCTCN2019079890-appb-000006
考虑荷载裂缝的影响，极限状态下锈蚀钢绞线的等效粘结强度τ aη可表示为公式(9)：
τ aη＝k cP av+τ b+τ c。
特别的，所述步骤(3)还包括以下步骤：
有效粘结力、残余粘结力和有效预加力的计算如下：
荷载作用下钢绞线所受的张拉力可通过有效粘结力、残余粘结力和有效预加力进行计算，可表达为公式(10)：
F p＝F eb+F er+F eη
式中，F p为钢绞线的拉力，F eb为有效粘结力，F er为残余粘结力，F eη为有效预加力；
锈蚀钢绞线的有效粘结力主要取决于交界面的粘结应力及接触面积，可表达为公式(11)：
F eb＝τ aηSL eb
式中，S为锈蚀钢绞线的周长，L eb为有效粘结长度；
残余粘结应力可以通过有效粘结应力进行评估，其值等于40％的有效粘结应力。锈蚀钢绞线的残余粘结力可表达为公式(12)：
F er＝0.4τ aηSL er
式中，L er为滑移区长度；
锈蚀钢绞线的有效预加力与锈蚀率之间存在线性关系，可表达为公式(13)：
F eη＝(1-ρ)F pe
式中，F pe为未锈蚀钢绞线的初始预加力，ρ为钢绞线的锈蚀率。
特别的，所述步骤(4)还包括以下步骤：
受力和弯矩平衡方程的构建如下：
粘结强度的退化会导致钢绞线与周边混凝土的应变不协调，引入一个变形协调系数来考虑极限状态下钢绞线与混凝土间的应变不协调，钢绞线位置处混凝土的应变ε cp可表达为公式(14)：
ε cp＝ε p/δ
式中，δ为变形协调系数，ε p为极限状态下钢绞线的应变；
通过引入的变形协调系数可以明确锈蚀PC梁横断面内的应力、应变分布规律，进而建立锈蚀PC梁的受力和弯矩平衡方程，可分别表示为公式(15)及(16)：
F c+F′ s-F p-F s＝0
M＝F c(h p-y c)+F s(h 0-h p)+F′ s(h p-a′ s)
式中，F c为混凝土合力，F s和F′ s分别为受拉区和受压区普通钢筋的合力，M为外部荷载引起的弯矩，h p、h 0和a′ s分别为钢绞线，受拉钢筋和受压钢筋重心至梁顶的距离，y c为混凝土等效应力矩形中心至梁顶的距离。
本发明的有益效果为：本发明提供的粘结退化影响下PC构件抗弯承载力计算方法，通过评估锈蚀影响下混凝土锈胀开裂和钢绞线的粘结强度，引入等效粘结强度概念考虑荷载裂缝对粘结强度分布的影响，建立荷载作用下锈蚀钢绞线的受力表达式；引入变形协调系数来 量化锈蚀钢绞线与混凝土间的变形不协调，明确构件横断面内的应力、应变分布规律；建立锈蚀PC梁截面内的受力和弯矩平衡方程，得到锈蚀PC梁抗弯承载力计算方法；该计算方法可综合考虑锈蚀引起的钢绞线截面积减小、材料劣化、混凝土开裂、粘结退化及荷载裂缝等因素的影响，能够准确地预测锈蚀PC梁的抗弯承载力，可广泛应用于实际工程。
下面结合附图对本发明做出详细说明。
附图说明
图1混凝土内部裂缝扩展及应力分布示意图。
图2荷载裂缝影响下锈胀力沿梁长方向的分布。
图3外部荷载作用下钢绞线受力示意图。
图4构件横断面内的受力与应变分布。
图5锈蚀PC抗弯承载力计算流程图。
具体实施方式
实施例1：
本实施例公开了一种粘结退化影响下PC构件抗弯承载力计算方法，该计算方法的详细步骤如下：
(1)评估锈裂影响下钢绞线粘结强度：根据构件基本尺寸，确定几何参数取值，采用厚壁薄筒理论对混凝土的锈胀开裂进行模拟，建立锈蚀钢绞线与混凝土界面间胶着力、约束力和锈胀力的表达式，进而预测锈蚀钢绞线的粘结强度；
(2)考虑荷载裂缝影响的等效粘结强度：引入一个等效粘结强度概念来考虑粘结强度沿梁长方向的分布，提出等效粘结强度计算方法；
(3)建立荷载作用下钢绞线的受力表达式：构建锈蚀影响下有效粘结力、残余粘结力和有效预加力的计算方法，建立钢绞线张拉力的表达式；
(4)提出锈蚀PC梁的抗弯承载力计算方法：引入一个变形协调系数来考虑极限状态下钢绞线与混凝土间的应变不协调，建立锈蚀PC梁的受力和弯矩平衡方程，提出其抗弯承载力计算方法。
所述步骤(1)中混凝土锈胀开裂过程中，粘结强度的计算如下：
以7丝钢绞线为研究对象，当钢绞线遭受外界物质侵蚀时，外围钢丝首先发生锈蚀，假定单根外围钢丝的锈蚀部位为周长的2/3，如图1所示，则钢绞线的锈蚀率ρ可表示为公式(1)：
Figure PCTCN2019079890-appb-000007
式中，R 0和R ρ分别为锈蚀前后钢丝的半径，A p为未锈蚀钢绞线的截面面积。
钢绞线锈蚀产物的体积比相应消耗的铁的体积要大，这会导致锈蚀产物的向外膨胀。锈蚀产物一部分会填充混凝土内部的孔隙和裂缝，另外部分则会产生锈胀力。根据体积相等原则，单位长度上钢绞线锈蚀产物的总体积可表达为公式(2)：
ΔV t＝ΔV w+ΔV e+ΔV c
式中，ΔV t为锈蚀产物的总体积，ΔV t＝nΔV w，n为铁锈膨胀率，ΔV w为单位长度上钢绞线外围钢丝的体积变化，
Figure PCTCN2019079890-appb-000008
ΔV e为混凝土的体积变化，
Figure PCTCN2019079890-appb-000009
R t为包含锈蚀产物影响的钢丝半径，ΔV c为单位长度上填充裂缝和孔隙的锈蚀产物体积。
单位长度上，用于填充裂缝和孔隙的锈蚀产物体积可表达为公式(3)：
Figure PCTCN2019079890-appb-000010
式中，R u为开裂混凝土的半径。
联立式(1-3)，锈胀力引起的混凝土位移u c可表示为公式(4)：
Figure PCTCN2019079890-appb-000011
保护层开裂前，混凝土保护层由开裂内环和未开裂外环组成，如图1所示。对于未开裂混凝土外环，可采用弹性理论对混凝土的内部应力进行模拟，未开裂混凝土的环向应力σ θ(t)和径向位移u(t)可分别表示为公式(5)及(6)：
Figure PCTCN2019079890-appb-000012
Figure PCTCN2019079890-appb-000013
式中，t为未开裂混凝土区域，R u≤t≤R c，R c＝R o+C，C为混凝土保护层厚度，P u为开裂和未开裂混凝土交界面位置的锈胀力，E c和v c分别为混凝土弹性模量和泊松比。
根据应力分布协调原则，开裂与未开裂混凝土交界面位置处的应力需等于混凝土抗拉强度，即σ θ(R u)＝f t。由此可知，开裂与未开裂混凝土交界面的锈胀力P u可表示为公式(7)：
Figure PCTCN2019079890-appb-000014
联立式(6-7)，可得到未开裂混凝土的径向位移u(t)。假定开裂混凝土区域的径向位移满足线性分布原则，则开裂区混凝土的径向位移u(r)可表示为公式(8)：
Figure PCTCN2019079890-appb-000015
式中，r为开裂区混凝土的位置，R 0≤r≤R u。
考虑开裂混凝土抗拉强度的软化行为，其环向应力可表示为公式(9)：
Figure PCTCN2019079890-appb-000016
式中，σ θ(r)和ε θ(r)分别为混凝土环向应力和应变，ε ct为混凝土达到抗拉强度时所对应的应变，ε 1为混凝土应力为15％抗拉强度时所对应的应变，ε u为混凝土极限应变。
保护层开裂前，钢绞线-混凝土界面间的锈胀力P c主要由开裂混凝土的剩余拉应力和未开裂混凝土的约束力进行抵抗，可表示为公式(10)：
Figure PCTCN2019079890-appb-000017
式中，R 0为锈蚀前钢丝的半径，R u为开裂混凝土的半径，r为开裂区域混凝土的位置。
保护层开裂后，锈胀力主要由开裂混凝土的剩余拉应力来抵抗，钢绞线-混凝土界面的锈胀力P c可表示为公式(11)：
Figure PCTCN2019079890-appb-000018
锈蚀钢绞线与混凝土交界面锈胀力引起的粘结应力τ a可表示为公式(12)：
τ a＝k cp c
式中，k c为锈蚀钢绞线与混凝土界面间的摩擦系数。
锈蚀钢绞线与混凝土交界面的胶着力τ b可表达为公式(13)：
Figure PCTCN2019079890-appb-000019
式中，k为同一截面上钢绞线的横肋数目，A r为横肋面积，D为锈蚀钢绞线直径，δ为横肋与钢绞线轴线间的夹角，θ为钢绞线与混凝土间的摩擦角，s r为横肋间距，f coh为界面间胶着力系数。
锈蚀钢绞线与混凝土交界面周围混凝土的约束力τ c可表达为公式(14)：
Figure PCTCN2019079890-appb-000020
式中，C r为横肋的形状系数，p x为失效时钢绞线所受的最大压力。
锈蚀钢绞线的粘结强度τ η可由钢绞线与混凝土交界面的胶着力、约束力和锈胀力进行计算，其表达式如公式(15)：
τ η＝τ a+τ b+τ c。
所述步骤(2)中等效粘结强度的计算方法为：
荷载裂缝的出现会减低混凝土的约束作用，裂缝位置处的锈胀力几乎全部退化，而相邻裂缝中间位置处的锈胀力基本保持不变，如图2所示。将裂缝位置处的锈胀力定义为0，而相邻裂缝中间位置处的锈胀力定义为P c，锈胀力沿梁长方向假定呈直线变化，则锈胀力在任意位置处P c(z)可表示为公式(16)：
Figure PCTCN2019079890-appb-000021
式中，z为沿梁长方向的任意位置，l m为平均荷载裂缝间距。
引入一个等效概念来考虑锈胀力沿梁长方向的分布，则平均锈胀力P av可表示为公式(17)：
Figure PCTCN2019079890-appb-000022
考虑荷载裂缝的影响，极限状态下锈蚀钢绞线的等效粘结强度τ aη可表示为公式(18)：
τ aη＝k cP av+τ b+τ c。
所述步骤(3)中有效粘结力、残余粘结力和有效预加力的计算方法为：
图3给出了荷载作用下钢绞线的受力示意图。荷载作用下钢绞线所受的张拉力F p可通过有效粘结力F eb、残余粘结力F er和有效预加力F eη进行计算，其表达式如公式(19)：
F p＝F eη+F eb+F er
锈蚀钢绞线的有效粘结力主要取决于交界面的粘结应力及接触面积，其表达式如公式(20)：
F eb＝τ aηSL eb
式中，S为锈蚀钢绞线的周长，L eb为有效粘结长度。
残余粘结应力可以通过有效粘结应力进行评估，其值约等于40％的有效粘结应力。锈蚀钢绞线的残余粘结力可表达为公式(21)：
F er＝0.4τ aηSL er
式中，L er为滑移区长度。
锈蚀钢绞线的有效预加力与锈蚀率之间存在线性关系，可表达为公式(22)：
F eη＝(1-ρ)F pe
式中，F pe为未锈蚀钢绞线的初始预加力。
所述步骤(4)中锈蚀PC梁受力和弯矩平衡方程的表达式为：
锈蚀钢绞线的本构关系可表示为公式(23)：
Figure PCTCN2019079890-appb-000023
式中，f p和ε分别为锈蚀钢绞线的应力和应变，ρ c为临界锈蚀率，其值为11％，E p和E pp分别为未锈蚀钢绞线的弹性模量和强化模量，f y为未锈蚀钢绞线屈服强度，ε y和ε pu分别为未锈蚀钢绞线屈服应变和极限应变。
联立式(19)和(23)，极限状态下钢绞线的应变ε p可表示为公式(24)：
Figure PCTCN2019079890-appb-000024
粘结强度的退化会导致钢绞线与周边混凝土的应变不协调，引入一个变形协调系数来考虑极限状态下钢绞线与混凝土间的应变不协调，钢绞线位置处混凝土的应变ε cp可表达为公式(25)：
ε cp＝ε p/δ
式中，δ为变形协调系数。
为单独研究钢绞线锈蚀对抗弯承载力的影响，假定构件内的普通钢筋未发生锈蚀，故普通钢筋与周围混凝土的应变变化相一致，如图4所示，受拉区与受压区钢筋的应变ε s和ε′ s分别为公式(26)及(27)：
Figure PCTCN2019079890-appb-000025
Figure PCTCN2019079890-appb-000026
式中，ε ct为顶部混凝土的应变，h p，h 0和a′ s分别为钢绞线，受拉钢筋和受压钢筋重心至梁顶的距离。
普通钢筋的应力-应变曲线采用线弹-塑性模型进行描述，可表达为公式(28)：
Figure PCTCN2019079890-appb-000027
式中，f s为普通钢筋的应力，E s和E sp分别为普通钢筋的弹性模量和强化模量，f sy和ε sy分别为普通钢筋的屈服强度和屈服应变。
受拉区和受压区普通钢筋的合力F s和F′ s分别为公式(29)及(30)：
F s＝A sf s(ε s)
F′ s＝A′ sf s(ε′ s)
式中，A s和A′ s分别为受拉区和受压区普通钢筋的截面面积，f s(ε s)和f s(ε′ s)分别为受拉区和受压区普通钢筋的应力。
混凝土的本构关系采用抛物线曲线进行模拟，其应力-应变关系如公式(31)：
Figure PCTCN2019079890-appb-000028
式中，f c和ε c分别为混凝土的应力和应变，f′ c为混凝土抗压强度，ε 0为混凝土达到抗压强度时所对应的应变。
混凝土合力F c及混凝土等效应力矩形中心至梁顶的距离y c分别为公式(32)及(33)：
Figure PCTCN2019079890-appb-000029
Figure PCTCN2019079890-appb-000030
式中，f c(ε c)为混凝土应力，b为梁宽，h为梁高，y为混凝土任意位置至梁顶的距离。
对于锈蚀PC梁，钢绞线、普通钢筋和混凝土的合力需满足受力和弯矩平衡方程，其表达式分别为公式(34)及(35)：
F c+F′ s-F p-F s＝0
M＝F c(h p-y c)+F s(h 0-h p)+F′ s(h p-a′ s)
式中，M为外部荷载引起的弯矩。
综上所述，本发明提出了一种粘结退化影响下PC构件抗弯承载力计算方法，该方法可综合考虑锈蚀引起的钢绞线截面积减小、材料劣化、混凝土开裂、粘结退化及荷载裂缝等因素的影响。图5给出了锈蚀PC抗弯承载力的计算流程图，具体介绍如下：
基于式(1-18)，评估钢绞线锈蚀引起的混凝土开裂及粘结退化；
假定锈蚀PC梁失效模式为顶部混凝土压碎破坏，极限状态下梁顶的混凝土应变先达到极限应变，ε ct＝0.0035；
假定钢绞线滑移区长度(L er)；
基于式(19-33)，计算钢绞线、钢筋和混凝土的应力和应变；
校核锈蚀PC梁的受力平衡方程，如果步骤(4)计算得到的钢绞线、钢筋和混凝土的合力不满足式(34)，则改变钢绞线滑移区长度(L er)重复上述步骤，直至式(34)满足；
如果计算得到的钢绞线应变小于极限应变，则锈蚀PC梁的失效模式为混凝土压碎破坏；如果计算得到的钢绞线应变大于极限应变，则锈蚀PC梁的失效模式为钢绞线断裂；
当失效模式为钢绞线断裂时，极限状态下钢绞线的应变先达到极限应变，基于式(19-33)重新计算钢绞线、钢筋和混凝土的应力和应变；
锈蚀PC梁的抗弯承载力由弯曲平衡方程式(35)计算得到。
申请人声明，所属技术领域的技术人员在上述实施例的基础上，将上述实施例某步骤，与发明内容部分的技术方案相组合，从而产生的新的方法，也是本发明的记载范围之一，本申请为使说明书简明，不再罗列这些步骤的其它实施方式。
实施例2：
采用本发明所述方法对文献“Flexural behavior of bonded post-tensioned concrete beams under strand corrosion,X.Zhang,L.Wang,J.Zhang,Y.Ma,and Y.Liu,Nuclear Engineering and Design,2017,313:414-424”中锈蚀PC梁的抗弯承载力进行计算。本实例的计算方法，包括以下步骤：
步骤一：确定构件的几何参数。
粘结后张PC梁的尺寸为150mm×220mm×2000mm，梁底配有1根直径为15.2mm的7丝钢绞线，其重心至梁底距离为60mm。钢绞线的屈服强度和极限强度分别为1830MPa和1910MPa。钢绞线的初始张拉应力为1395MPa。试验梁底部配有2根直径为8mm的光圆钢筋，顶部配有2根直径为12mm的变形钢筋。光圆钢筋和变形钢筋的屈服强度分别为235MPa和335MPa。采用直径为8mm的光圆钢筋作为箍筋，其间距为90mm。混凝土的抗压强度为31.8MPa。采用电化学方法对构件内的钢绞线进行加速锈蚀。加速锈蚀后，采用四点弯曲加载试验评估了锈蚀PC梁的抗弯承载力，相关试验数据见表1。
步骤二：根据钢绞线锈蚀率评估混凝土开裂过程中的锈胀力。
已有研究表明，铁锈膨胀率介于2-4，本文选为平均值3。基于试验测量得到的锈蚀率，判断保护层是否开裂。如果保护层未开裂，则钢绞线-混凝土界面间的锈胀力P c可由公式(1)计算得到：
Figure PCTCN2019079890-appb-000031
式中，R 0为锈蚀前钢丝的半径，P u为开裂和未开裂混凝土交界面位置的锈胀力，R u为开 裂混凝土的半径，r为开裂混凝土区域，σ θ(r)为开裂混凝土的环向应力。
如果保护层已开裂，则钢绞线-混凝土界面的锈胀力P c可由公式(2)计算得到：
Figure PCTCN2019079890-appb-000032
步骤三：考虑荷载裂缝影响的等效粘结强度。
根据步骤二中得到的锈胀力P c，引入一个等效概念来考虑锈胀力沿梁长方向的分布，可得到平均锈胀力P av。锈蚀钢绞线与混凝土交界面平均锈胀力引起的粘结应力τ av可由公式(3)进行计算：
τ av＝k cp av
式中，k c为锈蚀钢绞线与混凝土界面间的摩擦系数，k c＝0.37-0.26(x-x cr)，x为钢绞线的锈蚀深度，x cr为保护层开裂时钢绞线的临界锈蚀深度。
锈蚀钢绞线与混凝土交界面间的胶着力τ b可由公式(4)进行计算：
Figure PCTCN2019079890-appb-000033
式中，k为同一截面上钢绞线的横肋数目，k＝2，A r为横肋面积，A r＝0.07πD 2，D为锈蚀钢绞线剩余直径，δ为横肋与钢绞线轴线间的夹角，δ＝45 0，θ为钢绞线与混凝土间的摩擦角tan(δ+θ)＝1.57-0.785x，s r为横肋间距，s r＝0.6D，f coh为界面间胶着力系数，f coh＝2-10(x-x cr)。
锈蚀钢绞线与混凝土交界面间周围混凝土的约束力τ c可由公式(5)进行计算：
Figure PCTCN2019079890-appb-000034
式中，C r为横肋的形状系数，C r＝0.8，p x为失效时钢绞线所受的最大压力。
考虑荷载裂缝的影响，极限状态下锈蚀钢绞线的等效粘结强度τ aη可由钢绞线与混凝土交界面间的胶着力、约束力和锈胀力等因素进行预测，其值可由公式(6)进行计算：
τ aη＝k cp av+τ b+τ c。
步骤四：建立荷载作用下钢绞线的受力表达式。
荷载作用下钢绞线所受的张拉力F p可通过有效粘结力F eb、残余粘结力F er和有效预加力F eη进行计算，其值可由公式(7)进行计算：
F p＝F eb+F er+F eη
锈蚀钢绞线的有效粘结力主要取决于交界面的粘结应力及接触面积，其值可由公式(8)进行计算：
F eb＝τ aηSL eb
式中，S为锈蚀钢绞线的周长，S＝8πR ρ，R ρ为钢丝锈蚀后的半径，L eb为有效粘结长度，
Figure PCTCN2019079890-appb-000035
f y为未锈蚀钢绞线屈服强度，f pe为钢绞线有效预应力。
残余粘结应力可以通过有效粘结应力进行评估，其值等于40％的有效粘结应力。锈蚀钢绞线的残余粘结力可由公式(9)进行计算：
F er＝0.4τ aηSL er
式中，L er为滑移区长度。
锈蚀钢绞线的有效预加力与锈蚀率之间存在线性关系，其值可由公式(10)进行计算：
F eη＝(1-ρ)F pe
式中，F pe为未锈蚀钢绞线的初始预加力，ρ为钢绞线的锈蚀率。
步骤五：锈蚀PC梁受力和弯矩平衡方程的构建。
引入一个变形不协调系数来考虑极限状态下钢绞线与混凝土间的应变不协调，钢绞线位置处混凝土的应变ε cp可表达为公式(11)：
ε cp＝ε p/δ
式中，δ为变形协调系数，δ＝0.8099ρ 2-1.2771ρ+1，ε p为极限状态下钢绞线的应变。
构件内受拉区与受压区普通钢筋的应变ε s和ε′ s可分别由公式(12)及(13)进行计算：
Figure PCTCN2019079890-appb-000036
Figure PCTCN2019079890-appb-000037
式中，ε ct为顶部混凝土的应变，h p，h 0和a′ s分别为钢绞线，受拉钢筋和受压钢筋重心至梁体顶部的距离。
受拉区和受压区普通钢筋的合力F s和F′ s分别可由公式(14)及(15)进行计算：
F s＝A sf s(ε s)
F′ s＝A′ sf s(ε′ s)
式中，A s和A′ s分别为受拉区和受压区普通钢筋的截面面积，f s(ε s)和f s(ε′ s)分别为受拉区和受压区普通钢筋的应力。
混凝土合力F c及混凝土等效应力矩形中心至梁顶的距离y c可分别由公式(16)及(17)进行计算：
Figure PCTCN2019079890-appb-000038
Figure PCTCN2019079890-appb-000039
式中，f c(ε c)为混凝土应力，b为梁宽，h为梁高，y为混凝土任意位置至梁顶的距离。
对于锈蚀PC梁，钢绞线、普通钢筋和混凝土的合力仍然满足受力和弯矩平衡方程。锈蚀PC梁的受力和弯矩平衡方程可分别由公式(18)及(19)进行计算：
F c+F′ s-F p-F s＝0
M＝F c(h p-y c)+F s(h 0-h p)+F′ s(h p-a′ s)
式中，M为外部荷载引起的弯矩。
步骤六：验证该计算方法的合理性。
为验证锈蚀PC梁抗弯承载力预测模型的合理性，本文对文献“Flexural behavior of bonded post-tensioned concrete beams under strand corrosion,X.Zhang,L.Wang,J.Zhang,Y.Ma,and Y.Liu,Nuclear Engineering and Design,2017,313:414-424”设计制作的8根试验梁的抗弯承载力进行了预测，理论计算值与试验值见表1。由表1可知，理论计算值与试验值吻合较好，本发明提出的计算方法可以合理地预测锈蚀PC梁的抗弯承载力。
表1抗弯承载力理论计算值与试验值之间的比较
Figure PCTCN2019079890-appb-000040
注：ρ为锈蚀率；f′ c为混凝土抗压强度；D 0为钢绞线直径；M t为试验弯矩值；M p为理论弯矩值。
申请人又一声明，本发明通过上述实施例来说明本发明的实现方法，但本发明并不局限于上述实施方式，即不意味着本发明必须依赖上述方法才能实施。所属技术领域的技术人员应该明了，对本发明的任何改进，对本发明所选用实现方法等效替换及步骤的添加、具体方 式的选择等，均落在本发明的保护范围和公开范围之内。
本发明并不限于上述实施方式，凡采用与本发明相似方法来实现本发明目的的所有实施方式均在本发明保护范围之内。

Claims (5)

  1. 粘结退化影响下PC构件抗弯承载力计算方法，其特征在于，该方法包括以下步骤：
    (1)锈裂影响下钢绞线粘结强度预测：
    根据构件基本尺寸，确定几何参数取值，采用厚壁薄筒理论对混凝土的锈胀开裂进行模拟，建立锈蚀钢绞线与混凝土界面间胶着力、约束力和锈胀力的表达式，进而预测锈蚀钢绞线的粘结强度；
    (2)荷载裂缝影响下粘结强度评估：
    引入一个等效粘结强度概念来考虑粘结强度沿梁长方向的分布，提出等效粘结强度计算方法；
    (3)建立荷载作用下钢绞线的受力表达式：
    构建锈蚀影响下有效粘结力、残余粘结力和有效预加力的计算方法，建立荷载作用下锈蚀钢绞线张拉力的表达式；
    (4)提出锈蚀PC梁抗弯承载力计算方法：
    引入一个变形协调系数来考虑极限状态下钢绞线与混凝土间的应变不协调，明确构件横断面内的应力、应变分布规律，建立锈蚀PC梁截面内的受力和弯矩平衡方程，提出其抗弯承载力计算方法。
  2. 根据权利要求1所述粘结退化影响下PC构件抗弯承载力计算方法，其特征在于，所述步骤(1)还包括以下步骤：
    混凝土锈胀开裂过程中，粘结强度的计算如下：
    锈蚀钢绞线的粘结强度主要由钢绞线与混凝土交界面间的胶着力、约束力和锈胀力来提供，其表达式为公式(1)：
    τ η＝τ a+τ b+τ c
    式中，τ η为锈蚀钢绞线的粘结应力，τ a为锈胀力引起的粘结应力，τ b为交界面间的胶着力，τ c为交界面间的约束力；
    锈蚀钢绞线与混凝土交界面锈胀力引起的粘结应力可表示为公式(2)：
    τ a＝k cp c
    式中，k c为锈蚀钢绞线与混凝土界面间的摩擦系数，P c为钢绞线-混凝土界面间的锈胀力；
    保护层开裂前，锈胀力主要由开裂混凝土的剩余拉应力和未开裂混凝土的约束力共同抵抗，钢绞线-混凝土界面间的锈胀力可表示为公式(3)：
    Figure PCTCN2019079890-appb-100001
    式中，R 0为锈蚀前钢丝的半径，P u为开裂和未开裂混凝土交界面位置的锈胀力，R u为开裂混凝土的半径，r为开裂混凝土区域的位置，σ θ(r)为开裂混凝土的环向应力；
    保护层开裂后，锈胀力主要由开裂混凝土的剩余拉应力来抵抗，钢绞线-混凝土界面间的锈胀力可表示为公式(4)：
    Figure PCTCN2019079890-appb-100002
    锈蚀钢绞线与混凝土交界面间的胶着力可表达为公式(5)：
    Figure PCTCN2019079890-appb-100003
    式中，k为同一截面上钢绞线的横肋数目，A r为横肋面积，D为锈蚀钢绞线直径，δ为横肋与钢绞线轴线间的夹角，θ为钢绞线与混凝土间的摩擦角，s r为横肋间距，f coh为界面间胶着力系数；
    锈蚀钢绞线与混凝土交界面间周围混凝土的约束力可表达为公式(6)：
    Figure PCTCN2019079890-appb-100004
    式中，C r为横肋的形状系数，p x为失效时钢绞线所受的最大压力。
  3. 根据权利要求1所述粘结退化影响下PC构件抗弯承载力计算方法，其特征在于，所述步骤(2)还包括以下步骤：
    等效粘结强度概念的引入方法如下：
    当无荷载裂缝存在时，锈蚀构件沿梁长方向各位置处的锈胀力大小一致呈均匀分布。然荷载裂缝的出现会降低混凝土的约束作用，裂缝位置处的锈胀力几乎全部退化，而相邻裂缝中间位置处的锈胀力则基本保持不变。将裂缝位置处的锈胀力定义为0，而相邻裂缝中间位置处的锈胀力定义为P c，锈胀力沿梁长方向假定呈直线变化，则锈胀力在任意位置处P c(z)可表示为公式(7)：
    Figure PCTCN2019079890-appb-100005
    式中，z为沿梁长方向的任意位置，l m为平均荷载裂缝间距；
    引入一个等效概念来考虑锈胀力沿梁长方向的分布，则平均锈胀力P av可表示为公式(8)：
    Figure PCTCN2019079890-appb-100006
    考虑荷载裂缝的影响，极限状态下锈蚀钢绞线的等效粘结强度τ aη可表示为公式(9)：
    τ aη＝k cP av+τ b+τ c。
  4. 根据权利要求1所述粘结退化影响下PC构件抗弯承载力计算方法，其特征在于，所述步骤(3)还包括以下步骤：
    有效粘结力、残余粘结力和有效预加力的计算如下：
    荷载作用下，钢绞线所受的张拉力可通过有效粘结力、残余粘结力和有效预加力进行计算，可表达为公式(10)：
    F p＝F eb+F er+F eη
    式中，F p为钢绞线的拉力，F eb为有效粘结力，F er为残余粘结力，F eη为有效预加力；
    锈蚀钢绞线的有效粘结力主要取决于交界面的粘结应力及接触面积，可表达为公式(11)：
    F eb＝τ aηSL eb
    式中，S为锈蚀钢绞线的周长，L eb为有效粘结长度；
    剩余粘结应力可通过有效粘结应力进行评估，其值等于40％的有效粘结应力。锈蚀钢绞线的残余粘结力可表达为公式(12)：
    F er＝0.4τ aηSL er
    式中，L er为滑移区长度；
    锈蚀钢绞线的有效预加力与锈蚀率之间存在线性关系，可表达为公式(13)：
    F eη＝(1-ρ)F pe
    式中，F pe为未锈蚀钢绞线的初始预加力，ρ为钢绞线的锈蚀率。
  5. 根据权利要求1所述粘结退化影响下PC构件抗弯承载力计算方法，其特征在于，所述步骤(4)还包括以下步骤：
    受力和弯矩平衡方程的构建如下：
    粘结强度的退化会导致钢绞线与周边混凝土的应变不协调，引入一个变形协调系数来考虑极限状态下钢绞线与混凝土间的应变不协调，钢绞线位置处混凝土的应变ε cp可表达为公式(14)：
    ε cp＝ε p/δ
    式中，δ为变形协调系数，ε p为极限状态下钢绞线的应变；
    通过引入的变形协调系数可以明确锈蚀PC梁横断面内的应力、应变分布规律，进而建立锈蚀PC梁的受力和弯矩平衡方程，可分别表示为公式(15)及(16)：
    F c+F′ s-F p-F s＝0
    M＝F c(h p-y c)+F s(h 0-h p)+F′ s(h p-a′ s)
    式中，F c为混凝土合力，F s和F′ s分别为受拉区和受压区普通钢筋的合力，M为外部荷载引起的弯矩，h p、h 0和a′ s分别为钢绞线，受拉钢筋和受压钢筋重心至梁顶部的距离，y c为混凝土等效应力矩形中心至梁顶的距离。
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CN116720368A (zh) * 2023-06-14 2023-09-08 西南交通大学 钢纤维混凝土抗拉本构模型建立方法及系统
CN117290914A (zh) * 2023-10-27 2023-12-26 湘潭大学 一种考虑界面摩擦作用的栓钉连接钢-uhpc界面抗剪承载力计算方法
CN117290914B (zh) * 2023-10-27 2024-03-29 湘潭大学 一种考虑界面摩擦作用的栓钉连接钢-uhpc界面抗剪承载力计算方法

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