1 General Provisions
1.0.1 This is formulated to enable concrete structure of strengthening of structure; achieve technical reliability, safety and usability, economy and rationality, guarantee quality.
1.0.2 This standard is applicable to building and construction reinforced concrete bearing structure strengthened design.
1.0.3 before concrete structure strengthening, reliability certification shall be made according to constructional variety, current national standard " Standard for appraisal of reliability of industrial buildings and structures" GB 50144 and "Standard for appraiser of reliability of civil buildings" GB 50292 .Where connecting with aseismic strengthening, seismic resistant capability appraisal shall be carried out yet in accordance with current national standard " "Code for Seismic Design of Buildings" GB 50011 or "Standard for Seismic Appraisal of Buildings" " GB 50023.
1.0.4 Concrete structure reinforced design, in addition to comply with this code provisions outside, shall also meet the provisions stated in current related national standards of requirements.
2 Terms, symbols
2.1 Terms
2.1.1 Strengthening of existing structures
Measures concerning bearing structure, component, relevant portion, reinforcement , local replacement or internal force adjustment to improve fiduciary level and reliability or meet the owner's requirements. So safety, durability and applicability can be improved.
2.1.2 Existing structure member
Existing component before strengthening.
2.1.3 Important structure member
Supporting member, whose self failure would influence or endanger bearing structure system integrity.
2.1.4 General structure member
Supporting member whose self failure is isolate incident and would not influence or endanger bearing structure system integrity.
2.1.5 Structure member strengthening with reinforced concrete
Strengthening to increase existing structure member sectional area or increase reinforcement in order to improve bearing capacity, stiffness, rigidity or modify natural frequency of vibration.
2.1.6 Structure member strengthening with externally bonded steel frame
Welding structure and grouting structural adhesive to reinforced concrete girder , column external bonded profiled bar and flat bars to bear the load and restrain existing structure members.
2.1.7 Structure member strengthening with externally bonded reinforced materials
Adopt structural adhesive cementation, high tensile polymer mortar spray to make the reinforcing material stick to the concrete surface of existing structure member, to form integrity recombination cross section , bearing capacity and ductility. According to different reinforcing materials, it can be divided into outer adhered profiled bar, outer dead burning board, outer adhered fiber reinforced composites and steel wire rope meshes -polymer mortar layer.
2.1.8 Compression member confined by reinforcing wire
Strengthening method to wind annealed wire and restrain strengthened compression component concrete so as to improve ultimate bearing resistance and ductility.
2.1.9 Structure member strengthening with externally applied pre-stressing
Indirect strengthening method to improve existing structure, component load by applying outer pre-stress.
2.1.10 Bonded rebars
Use special structural adhesive to anchor rib steel or full lighted type screw into base metal.
2.1.11 Structrual adhesives
Adhesive bearing structure component, long term design stress and environmental agent for short structural adhesion.
2.1.12 Fibre reinforced ploymer (FRP)
Composite material processed with adhesive dipping, cementation and solidification with fiber reinforcement effect by using regularly arranged high strength continuous fiber.
2.1.13 Polymer mortar
High strength cement mortar mixed with modified epoxy emulsion or other modified copolymer emulsion. Except for improving physical mechanic performance, the polymer mortar used for bearing structure shall be able to notably improve anchored reinforcement and cementation.
2.1.14 Effective cross-section area
Section deducting hole, wane, rust layer , regolith , weakened and failed part.
2.1.15 Design working life for strengthening of existing structure or its member
After structure member strengthening, there is no need for inspection and appraisal.
2.2 Symbols
2.2.1 Material property
Es0--Elastic modulus of existing structure member;
Es--New elastic modulus of reinforcement;
Ea--New profiled bar modulus of elasticity;
Esp--New steel plate modulus of elasticity;
Ei--New fiber reinforced polymer modulus of elasticity;
fc0--Design value of concrete axes compression strength of existing structure member;
fy0, --Tensile, compressive strength design value of existing structure member;
fy, --Tensile, compressive strength design value of new reinforcement;
fa, --Tensile, compressive strength design value of new profiled bar;
fsp, --Tensile, compressive strength design value of new steel plate;
ff--Design value of tensile strength of new fiber composites;
ff, v--Design value of fiber composites and concrete cohesive strength;
fbd--Design value of cohesive strength of structural adhesive;
fud--Design value of anchor bolt tensile strength;
εf--Tensile strain design value of fiber composites;
εfe--Effective tensile strain design value of fiber composites circumferential bundle.
2.2.2 Action effect and bearing capacity
N--Axial force design value after structure member strengthening;
M--Bending moment design value after structure member strengthening;
V--Shear force design value after structure member strengthening;
M0k--Existing initial bending moment standard value of flexural member checking section before strengthening;
σs--New longitudinal reinforcement tension stress;
σs0--Stress of longitudinal tension reinforcement or side with smaller compression of existing structure member;
σa--Stress of new model steel tension limb or limb with small compression;
εf0--Delayed strain of fiber composites;
ω--Component deflection or pre-stress invert arch.
2.2.3 Geometric parameter
h0, h01--Effective height of section before and after structure member strengthening;
hw--Web plate depth of component section;
h0--Replacement depth of concrete in compressive area;
hsp--Vertical height of beam side stick steel hoop board;
hf--Vertical height of beam side stick fiber hoop board;
hef--Effective anchor depth of anchor bolt;
As0, --Tensile area, compressive area reinforcing steel area of existing structure member;
As, --Tensile area, compressive area reinforcing steel area of existing component;
Afe--Effective cross-section area of fiber composites;
Acor--Concrete sectional area within circumferential enclosure bundle;
Asp, --Sectional area of new tension steel plate and compressive steel plate;
Aa, --Sectional area of new model steel tension limb, pressure limb;
ls--Basic anchor depth of bonded rears;
ld--Bonded rebar anchor depth design value;
ll--Bonded rebar tension overlapping length;
D--Diameter of drilling hole;
2.2.4 Calculation coefficients
α1--Ratio between compressive area concrete rectangular stress pattern stress value and concrete axes compression strength design value;
βc--Concrete compressive strength influence coefficient;
β1--Ratio between rectangular stress pattern compressive area height and neutral axis height;
αc--New concrete compressive strength utilization coefficient;
αs--New reinforcement strength utilization coefficient;
αa--New model steel strength utilization coefficient;
αsp--Quoted calculation coefficients avoiding concrete split;
ψ--Reduction coefficient, correction coefficient or influence coefficient;
η--Enhancement coefficient or improvement coefficient.
3 Basic requirements
3.1 General provisions
3.1.1 After reliability certification, if the concrete structure is strengthened. The strengthening design shall be made according to expert conclusion, entrusting party requirements , this standard and requirements by owner and be carried out by qualified specialized technical personnel. Strengthening design range can be confirmed according to isolated area or whole building, designated structure , component or connection. structure integrity shall be considered.
3.1.2 Concrete structure safety class after strengthening shall be in accordance with severity, structure significance and design working life for strengthening of existing structure or its member after structural damage. entrusting party and design party shall decide according to actual situation.
3.1.3 Concrete structure strengthening design shall joint with actual construction method; take effective measure to guarantee new component and component be reliable connected with the existing structure. The new section and existing section shall be adhered firmly to form integrity. Avoid influence on unreinforcement part , relevant structure , component and soil foundation.
3.1.4 Effective control countermeasures shall be made in strengthening design to avoid soil differential settlement caused by high temperature, high humidity , low temperature , freeze thawing, chemical corrosion vibration and temperature stress. strengthening shall be made according to the order in the design specification.
3.1.5 Concrete structure strengthening design shall consider technical economy effectiveness and avoiding unnecessary dismantle or replacement.
3.1.6 Corresponding temporary safety measures shall be proposed in strengthening design document to avoid incline, instability , oversize deformation or collapse. The construction organization must be enforced strictly.
