CN102749246A - Prestress type steel-concrete structure using performance design method - Google Patents

Abstract

The present invention relates to a prestress type steel-concrete structure design, and belongs to the field of civil engineering. The prestress type steel-concrete structure using performance design method is characterized by: considering constraint and distribution thereof, wherein the using performance design during structure construction designing comprises calculating deflection of a frame beam under a normal use limit state and carrying out checking computation on a maximum crack width of the frame beam. Considerations of the constraint and the distribution thereof are the entity generated by the internal forces, the constraint causes the influence of the secondary axial force, such that the prestressed frame beam becomes a tension bending member from a flexural member so as to impact deflection and crack width of the prestressed frame beam. With the calculation formula of the design method provided by the present invention, the influence of the secondary axial force is considered, and the prestress type steel-concrete structure design theory is quantitatively established by using a constraint viewpoint.

Description

Prestress steel reinforced concrete structure usability method for designing

Technical field

The present invention relates to the design of prestress steel reinforced concrete structure, relate in particular to the usability method for designing of prestress steel reinforced concrete structure.

Background technology

Modern prestressed structure system is meant the prestressed structure system of getting up with high performance material, modern Design and advanced construction technology construction with high-strength, be current technological most advanced, purposes the most extensively, one of the most rising a kind of building structure pattern.At large public building, encorbelment greatly, stride greatly in the buildingss such as heavily loaded industrial building, skyscraper, big-and-middle span bridge, large special structure, television tower, nuclear power plant containment shell, ocean platform and be used widely.Prestress steel reinforced concrete (PSRC) structure is as a kind of new modern prestressed structure, can very effective adaptation modern architecture Development Trend, satisfy the demand of modern structure.Girder with rolled steel section en cased in concrete is applied prestress, can enlarge the elastic range of material, make full use of Materials with High Strength more, the performance material behavior alleviates dead load; Improve ultimate bearing capacity, reduce malformation; Postpone the appearance of hogging moment area distress in concrete; The rigidity of enhanced type steel beams of concrete reduces stress amplitude effectively, the fatigue lifetime of enhanced type steel beams of concrete.

Compare with common prestressed concrete, the prestress girder with rolled steel section en cased in concrete has following characteristics: (1) good seismic resistance; (2) easy construction; (3) shear-carrying capacity is big; (4) section rigidity is big, and amount of deflection control easily.Compare girder with rolled steel section en cased in concrete, the PSRC beam then has following characteristics: (1) span-depth radio can suitably be amplified; (2) delay crack developing; (3) amount of deflection control more is prone to satisfy; (4) steel using amount reduces; (5) construction is complicated, with high content of technology.

Using the earliest of prestress steel reinforced concrete structure mainly is the conversion layer structure of skyscraper, after multidigit scholar and practitioner's development and perfect, gradually because its excellent characteristic is used expansion gradually.But from method for designing; The principle of work that current inner forces calculation method about prestressed reinforced concrete construction mainly is based on the prestressed concrete continuous beam structure is set up; In fact the structure that calculates during design is based on the prestressed reinforced concrete construction of ignoring constraint (lateral confinement); The vertical members such as post, shear wall and tube of promptly not considering prestressed concrete frame structure, plate-column structure, frame-shear structure, framed-tube structure etc. are to prestressed influence, and vertical members such as true upper prop, shear wall and tube have very big influence to prestressed transmission.And show through the long-term research of this seminar; Have in the complicated structure that retrains above-mentioned; Because receive the influence of post lateral deformation stiffness, the effective prestress in the prestressed concrete beam has bigger reduction, if according to the design of not considering in the present design to retrain; Then the normal use of actual prestressed concrete beam and ultimate bearing capacity just can't satisfy structural requirement; And the prestress steel reinforced concrete structure with respect to common prestressed reinforced concrete construction because the existence of built-in shaped steel, in rigidity, the crack development of load action lower member and to work in coordination with load-bearing capacity different, when the complicated prestress steel reinforced concrete structure that retrains being arranged by the current methods designing and calculating; To bring potential safety hazard to engineering, therefore reasonably design must be considered constraint and built-in shaped steel and concrete Structural Influence.

At present, the prestress steel reinforced concrete structure is not seen abroad has theoretical research and practical applications.At home; A small amount of experimental study with the prestress steel reinforced concrete structure is only arranged; And shortage is to the research of prestress steel reinforced concrete structure System Design theoretical system; This emerging unitized construction form of prestress steel reinforced concrete structure is only done preliminary trial, also do not formed theoretical foundation, the analysis design method that instructs practical applications, more do not had corresponding standard rules to according to.

Summary of the invention

Technical matters to be solved by this invention provides a kind of usability method for designing of prestress steel reinforced concrete structure; Ignore constraint when solving present method for designing owing to calculating; Cause the normal usability of actual prestressed concrete beam can't satisfy structural requirement, and bring the defective of potential safety hazard to engineering.

Technical scheme

A kind of usability method for designing of prestress steel reinforced concrete structure; It is characterized in that: consider constraint and distribution thereof; When in design, setting up structure to the design of usability comprise to Vierendeel girder under serviceability limit state Calculation of Deflection and to Vierendeel girder checking computations maximum crack width

The camber that following amount of deflection f1 that the amount of deflection of the firm concrete flexural member of prestressing force type is produced by working load and prestressing force cause is that antiarch amount of deflection f2 two parts are formed; Then the combined deflection of prestressing force steel reinforced concrete frame span centre is: f=f1-f2, and the amount of deflection of said Vierendeel girder under serviceability limit state can be calculated with the method for structural mechanics based on the rigidity of member;

Said maximum crack width should calculate by the short-term effect combination of load and the influence of consideration long-term effect combination, considers that the unevenness of fracture width distribution and the maximum crack width of load long-term effect combined effect should calculate by following formula:

$w_{\max }={\mathrm{\α}}_{\mathrm{cr}}\mathrm{\ψ}\frac{{\mathrm{\σ}}_{\mathrm{sk}}}{E_s}(1.9c+0.08\frac{d_{\mathrm{eq}}}{{\mathrm{\ρ}}_{\mathrm{te}}})$

Wherein, ${\mathrm{\σ}}_{\mathrm{Sk}}=\frac{M_k\±M_2-N_{p0}(z-e_p)+N_2(a+z-h/2)}{z(A_s+A_P+A_{\mathrm{Af}}+k{A}_{\mathrm{Aw}})},$ $d_{\mathrm{Eq}}=\frac{4(A_s+A_p+A_{\mathrm{Af}}+k{A}_{\mathrm{Aw}})}{u},$ ${\mathrm{\ρ}}_{\mathrm{Te}}=\frac{A_s+A_p+A_{\mathrm{Af}}+k{A}_{\mathrm{Aw}}}{0.5\mathrm{Bh}},$

In the above-mentioned formula: α _Cr---the member stress characteristic coefficient is got α _Cr=1.7,

Ψ---consider the reinforcing bar strain nonuniformity coefficient of shaped steel edge of a wing effect; When Ψ＜0.4, get Ψ=0.4; When Ψ＞1.0, get Ψ=1.0,

C---longitudinal tensile concrete cover to reinforcement thickness,

σ _Sk---consider that shaped steel receives the reinforcement stresses value of pull wing edge and part web and tension reinforcement,

Es---reinforcing bar elastic modulus,

d _Eq, ρ _Te---consider that shaped steel receives effective diameter, the effective reinforcement rate of pull wing edge and part web and tension reinforcement,

M _k---press the moment of flexure value of load short-term effect combination calculation,

K---shaped steel web influence coefficient, its value got the ratio of beam tension side 1/4 deck-molding scope median ventral plate height and whole web height,

A _s, A _Af---longitudinal tensile reinforcing bar, shaped steel receive pull wing edge area,

A _Aw---shaped steel web area,

U---longitudinal tensile reinforcing bar and shaped steel receives pull wing edge and part web girth sum,

e _p---deformed bar effect center of gravity arrives the distance of centroid of section axle,

M ₂, N ₂---the framework parasitic moment, secondary axes power,

N _P0---the deformed bar of pre-tensioning system member, post stretching member and making a concerted effort of nonprestressed reinforcement,

A _p---the sectional area of deformed bar,

B, h---be respectively the width of Vierendeel girder section, highly.

Further; The amount of deflection of said Vierendeel girder under serviceability limit state can be calculated with the method for structural mechanics according to the rigidity of member; When the longitudinal tensile rebar ratio of prestress steel reinforced concrete frame beam was the 0.3%-1.5% scope, the short-term stiffness Bs computing formula under its load short-term effect and the long-term effect compound action was following:

(1) rigidity of the member in crack does not appear in requirement,

B _s＝0.85E _cI ₀+E _aI _a，

(2) allow to occur the rigidity of crack member,

$B_s=\frac{0.85E_c{I}_0}{k_{\mathrm{cr}}+(1-k_{\mathrm{cr}})\mathrm{\ω}}+E_a[I_a+A_a{(h_1-x_1)}^2],$

Wherein, k _Cr=M _Cr/ M _k, ω=(1.0+0.21/ α _Eρ) (1+0.45 γ _f)-0.7, γ _f=(b _f-b) h _f/ bh ₀, $x_1=-\stackrel{\‾}{A}/b+\sqrt{{(\stackrel{\‾}{A}/b)}^2+2\stackrel{\‾}{W}/b},$

In the above-mentioned formula: E _c---modulus of elasticity of concrete,

E _a---the shaped steel elastic modulus,

ρ---longitudinal tensile reinforcing bar, shaped steel receives the pull wing edge web and the presstressed reinforcing steel ratio of reinforcement,

I ₀---be second moment of area of tranformed section, do not comprise the shaped steel part,

Ea, Ia, Aa---internally-arranged type steel bomb property modulus, moment of inertia, area of section,

M _k---press the moment of flexure value of load short-term effect combination calculation,

α _E---the ratio of reinforcing bar elastic modulus and modulus of elasticity of concrete: α _E=E _s/ E _c,

h ₁---the shaped steel center of gravity is to the distance at concrete compression edge,

x ₁---behind cracking, natural axis position, transformed section,

---the area of transformed section

---

is with respect to the statical moment at pressurized edge, cross section

B, h---be respectively the width of Vierendeel girder section, highly.

Further, after said maximum crack width calculated, the maximum crack width of being tried to achieve should be greater than the limit value of prestressed reinforced concrete construction regulation.

Beneficial effect

Method for designing of the present invention has taken into full account the complicated restraint condition of prestress steel reinforced concrete structure; Set up structure and consider the computing method of effect of constraint value; Use the viewpoint that retrains quantitatively to judge the quality of crack Control Measures, set up prestress steel reinforced concrete structure design theory, for engineering practice provides theoretical direction based on constraint and distribution thereof; More meet the requirement of practical structure, security performance is more outstanding.

Description of drawings

Fig. 1 is the shaped steel sectional reinforcement form synoptic diagram of prestress girder with rolled steel section en cased in concrete of the present invention.

Fig. 2 calculates synoptic diagram for Vierendeel girder maximum crack width of the present invention.

Embodiment

Below in conjunction with specific embodiment and accompanying drawing, further set forth the present invention.

The long-term research of this seminar shows; In the prestress steel reinforced concrete structure that complicated constraint is arranged; Because receive the influence of post lateral deformation stiffness; Effective prestress in the prestressed concrete beam has bigger reduction, so the normal use of actual prestressed concrete beam and ultimate bearing capacity can't satisfy structural requirement, can produce potential safety hazard to engineering.Therefore consider to propose a kind of prestress steel reinforced concrete structure method for designing, solve above-mentioned two kinds of requirements, thereby eliminate safe hidden trouble based on the complicacy constraint.And this seminar also discovers, constraint and distribute and be only the essence that produces time internal force, and effective stress distributes constraint is also had certain influence is so consider comprehensively that to the design of prestress steel reinforced concrete structure the influence of inferior internal force is only science safety.The present invention proposes a kind of method for designing of the usability to the prestress girder with rolled steel section en cased in concrete, in design, considers the influence of time internal force to the usability of prestress steel reinforced concrete, thereby avoids causing puzzlement safe in utilization because of inferior internal force in actual uses.

For the shaped steel of prestress steel reinforced concrete frame beam, should adopt to be full of the real abdomen shaped steel of type, a side wing edge of its shaped steel should be positioned at compressive region, and the opposite side edge of a wing is positioned at the tensile region, shown in accompanying drawing 1.When the beam section height is higher, join the prestress girder with rolled steel section en cased in concrete of truss-like shaped steel in can adopting.

When carrying out structural internal force and The deformation calculation, cross section bendind rigidity, axial rigidity and the shear stiffness of prestress steel reinforced concrete structure member, can calculate by following regulation:

EI＝E _cI _c+E _aI _a

EA＝E _cA _c+E _aA _a

GA＝G _cA _c+G _aA _a

EI, EA, GA in the formula---member section bendind rigidity, axial rigidity, shear stiffness; E _cI _c, E _cA _c, G _cA _c---cross section bendind rigidity, axial rigidity, the shear stiffness of reinforced concrete part; E _aI _a, E _aA _a, G _aA _a---cross section bendind rigidity, axial rigidity, the shear stiffness of shaped steel or steel pipe part.

Consider constraint and distribute, when in design, setting up structure to the design of usability comprise to Vierendeel girder under serviceability limit state Calculation of Deflection and to Vierendeel girder checking computations maximum crack width.Considering constraint and distributing is the essence that time internal force produces, because the influence of the secondary axes power that constraint causes makes prestressed frame beam become stretch bending component by flexural member, its amount of deflection and fracture width is exerted an influence.

And the amount of deflection of prestress steel reinforced concrete frame beam under serviceability limit state can be calculated with the method for structural mechanics according to the rigidity of member.In the uniform cross section member, can suppose the equal stiffness in each jack per line moment of flexure section, and take the rigidity at maximal bending moment place in this section.

Following amount of deflection (the f that the amount of deflection of the firm concrete flexural member of prestress type is produced by working load ₁) and the camber that causes of prestress (claim antiarch amount of deflection f again ₂) two parts composition, then the combined deflection of prestress steel reinforced concrete frame span centre is: f=f ₁-f ₂

When the longitudinal tensile rebar ratio of prestress steel reinforced concrete frame beam is the 0.3%-1.5% scope, the short-term stiffness B under its load short-term effect and the long-term effect compound action _s, can calculate by following formula:

(1) rigidity of the member in crack does not appear in requirement

B _s＝0.85E _cI ₀+E _aI _a

(2) allow to occur the rigidity of crack member

$B_s=\frac{0.85E_c{I}_0}{k_{\mathrm{cr}}+(1-k_{\mathrm{cr}})\mathrm{\ω}}+E_a[I_a+A_a{(h_1-x_1)}^2]$

Wherein, k _Cr=M _Cr/ M _k, ω=(1.0+0.21/ α _Eρ) (1+0.45 γ _f)-0.7

$\mathrm{\ρ}=\frac{A_s+A_p+A_{\mathrm{af}}+k{A}_{\mathrm{aw}}}{\mathrm{bh}},$ γ _f＝(b _f-b)h _f/bh ₀

$x_1=-\stackrel{\‾}{A}/b+\sqrt{{(\stackrel{\‾}{A}/b)}^2+2\stackrel{\‾}{W}/b},$ $\stackrel{\‾}{A}={\mathrm{\α}}_{\mathrm{aE}}{A}_a+{\mathrm{\α}}_{\mathrm{sE}}{A}_s+{\mathrm{\α}}_{\mathrm{sE}}{A}_s^{\′}$

${\mathrm{\α}}_{\mathrm{aE}}=\frac{E_a}{\mathrm{\υ}{E}_c},$ ${\mathrm{\α}}_{\mathrm{sE}}=\frac{E_s}{\mathrm{\υ}{E}_c},$ $\stackrel{\‾}{W}={\mathrm{\α}}_{\mathrm{aE}}{A}_a{h}_1+{\mathrm{\α}}_{\mathrm{sE}}{A}_s(h-a_s)+{\mathrm{\α}}_{\mathrm{sE}}{A}_s^{\′}{a_s}^{\′}$

$B_l=\frac{M_s}{M_l(\mathrm{\θ}-1)+M_s}(B_s-E_a{I}_a)+E_a{I}_a$

As ρ ' _SaDuring a=0, θ=2.0;

As ρ ' _Sa=ρ _SaThe time, θ=1.6;

As ρ ' _SaDuring for intermediate value, θ takes by linear interpolation.

In the above-mentioned formula: ρ _Sa---longitudinal tensile reinforcing bar, presstressed reinforcing steel and the shaped steel of the configuration of beam section tensile region receive the sectional reinforcement rate of pull wing edge area sum, ρ _Sa=(A _s+ A _p+ A _Af)/bh ₀

ρ ' _Sa---the vertical compression steel of beam section compressive region configuration and the sectional reinforcement rate of shaped steel compression flange area sum, ρ ' _Sa=(A ' _s+ A ' _p+ A ' _Af)/bh ₀

E _c---modulus of elasticity of concrete; E _a---the shaped steel elastic modulus; Es---reinforcing bar elastic modulus;

ρ---longitudinal tensile reinforcing bar, shaped steel receives the pull wing edge web and the presstressed reinforcing steel ratio of reinforcement;

I ₀---be second moment of area of tranformed section, do not comprise the shaped steel part;

Ea, Ia, Aa---internally-arranged type steel bomb property modulus, moment of inertia, area of section;

M _k---press the moment of flexure value of load short-term effect combination calculation; M _l---press the moment of flexure value of load long-term effect combination calculation;

θ---consider the influence coefficient that the combination of load long-term effect increases amount of deflection;

A _s, A ' _s---longitudinal tensile, compression steel area; A _Af, A ' _Af---shaped steel receives pull wing edge, compression flange area of section;

α _E---the ratio of reinforcing bar elastic modulus and modulus of elasticity of concrete: α _E=E _s/ E _c

K---shaped steel web influence coefficient is the ratio of beam tension side 1/4 deck-molding scope endosternum height and whole web height;

h ₁---the shaped steel center of gravity is to the distance at concrete compression edge;

x ₁---behind cracking, natural axis position, transformed section;

- Conversion-sectional area;?

-?

relative to the compression section of the edge of the static torque;

υ---concrete elasticity coefficient: υ under short time loading=0.85, υ under action of long-term load=0.4.

And answer the checking computations fracture width for prestress steel reinforced concrete frame beam, maximum crack width should calculate by the short-term effect combination of load and the influence of consideration long-term effect combination.

Consider that the unevenness of fracture width distribution and the maximum crack width (by mm) of load long-term effect combined effect should calculate (shown in accompanying drawing 2) by following formula, the maximum crack width of being tried to achieve should be greater than the limit value of prestressed reinforced concrete construction regulation.

$w_{\max }={\mathrm{\α}}_{\mathrm{cr}}\mathrm{\ψ}\frac{{\mathrm{\σ}}_{\mathrm{sk}}}{E_s}(1.9c+0.08\frac{d_{\mathrm{eq}}}{{\mathrm{\ρ}}_{\mathrm{te}}})$

Wherein, $\mathrm{\ψ}=1.1(1-\frac{M_{\mathrm{Cr}}}{M_K-N_{\mathrm{Pe}}{e}_p}),$ ${\mathrm{\σ}}_{\mathrm{Sk}}=\frac{M_k\±M_2-N_{p0}(z-e_p)+N_2(a+z-h/2)}{z(A_s+A_P+A_{\mathrm{Af}}+k{A}_{\mathrm{Aw}})}$

$k=\frac{0.25h-t_f-a_a}{h_w},$ $d_{\mathrm{eq}}=\frac{4(A_s+A_p+A_{\mathrm{af}}+k{A}_{\mathrm{aw}})}{u}$

u＝π∑n _iv _id _i+(2b _f+2t _f+2kh _aw)×0.315，

${\mathrm{\ρ}}_{\mathrm{te}}=\frac{A_s+A_p+A_{\mathrm{af}}+k{A}_{\mathrm{aw}}}{0.5\mathrm{bh}},$ $e=\frac{M_k\±M_2-N_{p0}{e}_p-N_2(h/2-a)}{N_{p0}-N_2}$

z＝[0.87-012(1-r′ _f)(h _e/e) ²]h ₀， $h_e=\frac{h_{0s}+h_{0p}+h_{0\mathrm{af}}}{3}$

In the above-mentioned formula: M _k---press the moment of flexure value of load short-term effect combination calculation;

M _Cr---Vierendeel girder cross section cracking resistance moment of flexure;

α _Cr---the member stress characteristic coefficient is got α _Cr=1.7;

C---longitudinal tensile concrete cover to reinforcement thickness;

Ψ---consider the reinforcing bar strain nonuniformity coefficient of shaped steel edge of a wing effect; When Ψ＜0.4, get Ψ=0.4; When Ψ＞1.0, get Ψ=1.0;

K---shaped steel web influence coefficient, its value got the ratio of beam tension side 1/4 deck-molding scope median ventral plate height and whole web height;

v _i---be the relative bonding characteristic coefficient of tensile region i kind longitudinal reinforcement, the relative bonding characteristic coefficient of shaped steel is 0.45X0.7=0.315;

N---longitudinal tensile number of steel bars;

b _f, t _f---receive pull wing edge width, thickness;

d _Eq, ρ _Te---consider that shaped steel receives effective diameter, the effective reinforcement rate of pull wing edge and part web and tension reinforcement;

σ _Sk---consider that shaped steel receives the reinforcement stresses value of pull wing edge and part web and tension reinforcement;

A _s, A _Af---longitudinal tensile reinforcing bar, shaped steel receive pull wing edge area;

A _Aw, h _Aw---shaped steel web area, highly;

h _0s, h _0af, h _0p---longitudinal tensile reinforcing bar, shaped steel receive the distance at pull wing edge, presstressed reinforcing steel center of gravity to concrete section pressurized edge;

U---longitudinal tensile reinforcing bar and shaped steel receives pull wing edge and part web girth sum;

e _p---deformed bar effect center of gravity is to the distance of centroid of section axle;

h _e---tension reinforcement, shaped steel receive pull wing edge, part to be drawn web and presstressed reinforcing steel equivalent height;

N _Pe---the effective pull of deformed bar;

M ₂, N ₂---framework parasitic moment, secondary axes power;

N _P0---the deformed bar of pre-tensioning system member, post stretching member and making a concerted effort of nonprestressed reinforcement;

A _p---the sectional area of deformed bar;

B, h---be respectively the width of Vierendeel girder section, highly;

R ' _f---the ratio of compression flange area of section and web effective cross-sectional area;

E---the distance in axle pressure application point to longitudinal tensile adhesion of tendon and muscle after injury force.

Above-mentioned requirement to prestress steel reinforced concrete structure function in fact promptly has enough rigidity and anti-crack ability, and its distortion when normal use the, fracture width, reinforcing bar and concrete stress satisfy the requirement of limit value; Should have the ability of enough keeping its usability, in the design life of regulation, under normal maintenance and service condition, reinforcing bar resistant to rust ability, concrete be anti-degrades and ability such as resistance to wear meets the demands.

Claims (3)

1. the usability method for designing of a prestress steel reinforced concrete structure; It is characterized in that: consider constraint and distribution thereof; When in design, setting up structure to the design of usability comprise to Vierendeel girder under serviceability limit state Calculation of Deflection and to Vierendeel girder checking computations maximum crack width

The camber that following amount of deflection f1 that the amount of deflection of the firm concrete flexural member of prestressing force type is produced by working load and prestressing force cause is that antiarch amount of deflection f2 two parts are formed; Then the combined deflection of prestressing force steel reinforced concrete frame span centre is: f=f1-f2, and the amount of deflection of said Vierendeel girder under serviceability limit state can be calculated with the method for structural mechanics based on the rigidity of member;

Said maximum crack width should calculate by the short-term effect combination of load and the influence of consideration long-term effect combination, considers that the unevenness of fracture width distribution and the maximum crack width of load long-term effect combined effect should calculate by following formula:

$w_{\max }={\mathrm{\α}}_{\mathrm{cr}}\mathrm{\ψ}\frac{{\mathrm{\σ}}_{\mathrm{sk}}}{E_s}(1.9c+0.08\frac{d_{\mathrm{eq}}}{{\mathrm{\ρ}}_{\mathrm{te}}})$

Wherein, ${\mathrm{\σ}}_{\mathrm{Sk}}=\frac{M_k\±M_2-N_{p0}(z-e_p)+N_2(a+z-h/2)}{z(A_s+A_P+A_{\mathrm{Af}}+k{A}_{\mathrm{Aw}})},$ $d_{\mathrm{Eq}}=\frac{4(A_s+A_p+A_{\mathrm{Af}}+k{A}_{\mathrm{Aw}})}{u},$ ${\mathrm{\ρ}}_{\mathrm{Te}}=\frac{A_s+A_p+A_{\mathrm{Af}}+k{A}_{\mathrm{Aw}}}{0.5\mathrm{Bh}},$

In the above-mentioned formula: α _Cr---the member stress characteristic coefficient is got α _Cr=1.7,

Ψ---consider the reinforcing bar strain nonuniformity coefficient of shaped steel edge of a wing effect; When Ψ＜0.4, get Ψ=0.4; When Ψ＞1.0, get Ψ=1.0,

C---longitudinal tensile concrete cover to reinforcement thickness,

σ _Sk---consider that shaped steel receives the reinforcement stresses value of pull wing edge and part web and tension reinforcement,

Es---reinforcing bar elastic modulus,

d _Eq, ρ _Te---consider that shaped steel receives effective diameter, the effective reinforcement rate of pull wing edge and part web and tension reinforcement,

M _k---press the moment of flexure value of load short-term effect combination calculation,

K---shaped steel web influence coefficient, its value got the ratio of beam tension side 1/4 deck-molding scope median ventral plate height and whole web height,

A _s, A _Af---longitudinal tensile reinforcing bar, shaped steel receive pull wing edge area,

A _Aw---shaped steel web area,

U---longitudinal tensile reinforcing bar and shaped steel receives pull wing edge and part web girth sum,

e _p---deformed bar effect center of gravity arrives the distance of centroid of section axle,

M ₂, N ₂---the framework parasitic moment, secondary axes power,

N _P0---the deformed bar of pre-tensioning system member, post stretching member and making a concerted effort of nonprestressed reinforcement,

A _p---the sectional area of deformed bar,

B, h---be respectively the width of Vierendeel girder section, highly.

2. the usability method for designing of prestress steel reinforced concrete structure as claimed in claim 1; It is characterized in that: the amount of deflection of said Vierendeel girder under serviceability limit state can be calculated with the method for structural mechanics according to the rigidity of member; When the longitudinal tensile rebar ratio of prestress steel reinforced concrete frame beam was the 0.3%-1.5% scope, the short-term stiffness Bs computing formula under its load short-term effect and the long-term effect compound action was following:

(1) rigidity of the member in crack does not appear in requirement,

B _s＝0.85E _cI ₀+E _aI _a，

(2) allow to occur the rigidity of crack member,

$B_s=\frac{0.85E_c{I}_0}{k_{\mathrm{cr}}+(1-k_{\mathrm{cr}})\mathrm{\ω}}+E_a[I_a+A_a{(h_1-x_1)}^2],$

Wherein, k _Cr=M _Cr/ M _k, ω=(1.0+0.21/ α _Eρ) (1+0.45 γ _f)-0.7, γ _f=(b _f-b) h _f/ bh ₀, $x_1=-\stackrel{\‾}{A}/b+\sqrt{{(\stackrel{\‾}{A}/b)}^2+2\stackrel{\‾}{W}/b},$

In the above-mentioned formula: E _c---modulus of elasticity of concrete,

E _a---the shaped steel elastic modulus,

ρ---longitudinal tensile reinforcing bar, shaped steel receives the pull wing edge web and the presstressed reinforcing steel ratio of reinforcement,

I ₀---be second moment of area of tranformed section, do not comprise the shaped steel part,

Ea, Ia, Aa---internally-arranged type steel bomb property modulus, moment of inertia, area of section,

M _k---press the moment of flexure value of load short-term effect combination calculation,

α _E---the ratio of reinforcing bar elastic modulus and modulus of elasticity of concrete: α _E=E _s/ E _c,

h ₁---the shaped steel center of gravity is to the distance at concrete compression edge,

x ₁---behind cracking, natural axis position, transformed section,

---the area of transformed section

---

is with respect to the statical moment at pressurized edge, cross section

b _f, h _f---the Vierendeel girder flange width, highly.

3. according to claim 1 or claim 2 the usability method for designing of prestress steel reinforced concrete structure, it is characterized in that: after said maximum crack width calculated, the maximum crack width of being tried to achieve should be greater than the limit value of prestressed reinforced concrete construction regulation.

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