1.0.1 This code is formulated with a view to realize state-of-the-art technology and safety & usability, as well as guarantee quality and economy & rationality in the design and construction of unbonded prestressed concrete structure.
1.0.2 This code is applicable to design, construction and acceptance of unbonded prestressed concrete structure adopted in industrial, civil and general construction. Adopted unbonded tendon means that embedded in concrete components or external tendon.
1.0.3 As for unbonded prestressed concrete structure, rational design and construction scheme shall be determined, construction design shall be formulated, and technical exchanges shall be well carried out according to construction function requirements, material supply and construction conditions. Besides, the engineering construction shall be carried out by professional prestress construction team, so shall strict quality inspection and acceptance system.
1.0.4 The design life of unbonded prestressed concrete structure shall be determined according to the current national standard "Unified standard reliability design of building structures" GB 50068. Its seismic design shall be enforced according to the current professional standard "Specification for seismic design of prestressed concrete structures" JGJ 140. Not only the requirements stipulated in this code, but also those in the current relevant ones of the nation shall be complied with.
2 Terms and symbols
2.1 Terms
2.1.1 Unbonded tendon
It is made of single root prestressing steel strand of special corrosion resistant and lubricating grease and plastic coating. Besides, it may keep relative slip with prestressed concrete.
2.1.2 Unbonded prestressed concrete structure
Prestressed concrete structure equipped with main stressed unbonded tendon in one or two directions.
2.1.3 External tendon
External tendon is post-tensioning tendon equipped outside of concrete structure component section, and is only connected with the components at the anchorage and deviator zone. Unbonded external tendon may be made of single root unbonded tendon.
2.1.4 External prestressing
External prestressing is generated by post-tensioning tendon equipped outside of concrete component section.
2.1.5 Deviator
Deviator is concrete or steel supporting block installed on web, flange or connecting point of web and flange, one-piece casting or reliably connected with beam section to control geometric shapes of external tendon or provide means to change external tendon directions, as well as transfer prestress to the structure.
2.1.6 Saddle
Saddle, a constituent of deviator, is a partial supporting component to transfer prestressing loads at deviator.
2.2 Symbols
2.2.1 Material performance
B-Section rigidity of flexural members;
Ec-Elastic modulus of concrete;
Ep-Elastic modulus of unbonded tendon;
EB-Elastic modulus of nonprestressed tendon;
fc-Compressive strength design value of concrete axis;
-Compressive strength of prestressed concrete cube;
ft-Tensile strength design value of concrete axis;
ftk-Tensile strength standard value of concrete axis;
fptk-Tensile strength standard value of unbonded tendon;
fy-Tensile strength design value of nonprestressed tendon;
fyv-Tensile strength design value of anchor bolt.
2.2.2 Action, action effect and bearing capacity
M-Design value of bending moment;
Mk and Mq-Bending moment value calculated according to standard combination and quasi-permanent combination of loads;
Mcr-Cracking bending moment value of flexural-member normal-section;
Mu-Flexural capacity design value of component normal section;
Np-Resultant force of unbonded tendon and nonprestressed tendon;
Npe-Total effective prestress of unbonded tendon;
V-Design value of shear force;
Fl-Design value of partial load or concentrated counter-force;
σcon-Stretching control stress of unbonded tendon;
σpc-Concrete normal stress generated by prestressing;
σpe-Effective prestress of unbonded tendon;
σpu-Stress design value of unbonded tendon in the calculation of normal section bearing capacity;
σl-Prestress loss value of unbonded tendon at corresponding stages;
wmax-Maximum crack width with regard to influence of long-term action according to standard combination of load effects.
2.2.3 Geometric parameters
A-Sectional area of components;
An-Net sectional area of components;
Ap-Sectional area of unbonded tendon;
As-Sectional area of nonprestressed tendon;
b-Sectional width;
bd-Width of flat carrier board;
bf and -Flange width of T-shape or I-shape tensile region and compressive region;
h-Sectional height;
h0-Sectional effective height;
1 General provisions 2 Terms and symbols 2.1 Terms 2.2 Symbols 3 Materials and anchorage system 3.1 Concrete and reinforcement 3.2 Unbonded tendon 3.3 Anchorage system 4 Fundamental rules of design and construction 4.1 General provisions 4.2 Fireproofing and corrosion-resistant 5 Design calculation and structure 5.1 General provisions 5.2 One-way architecture 5.3 Two-way architecture 5.4 External prestressed beam 6 Construction and acceptance 6.1 Production, package and transportation of unbonded tendon 6.2 Unbonded-tendon placement and concreting 6.3 Unbonded-tendon stretching 6.4 External prestressing construction 6.5 Acceptance of works Annex A Estimation of unbonded-tendon number Annex B Prestressing loss of unbonded-tendon common bundle Annex C Rigidity computation of equivalent column and equivalent frame computation module Annex D Unbonded-tendon stretching data sheet Wording Explanations
