【正文】 nge point sectionSupport section (2)Anchorage deformation、steel retraction causes stress lossesPost tensioned structure should consider the influence of friction, its influence length is : is the deformation value of anchor in tensioned end, 。2) :Calculating geometric features of all crosssection:Generally, geometric features of main beam often use block numerical summation method, Area of all cross section: A=AiDistance between gravity center line of the all cross section and the top of beam:yu=Ai is area of block,is distance between gravity center line of the all cross section and the top of beamThe all crosssection geometric features of middle span section shown Figure1. Geometric features of all cross section from middle span and 1/4 span sectionnumber of blockarea of block Ai (mm2)yi(mm)si=Ai*yi(mm3)yuyi (mm)Ix=Ai*(yuyi)2 (mm)Ii(mm4)Figure of lock section13600009032400000454 74065995309972000000 unit:mm29600022021120000324 10051863589770000003320000800256000000256 2103965488668267000000420000153330660000989 195788616274400000058000017001360000001156 +11267000000amount876000544 476180000+11696270000001256+11ConclusionA=ΣAi =876000yu=ΣSi /A=544 yb=1800544=1256ΣSi =476180000ΣIx =231721000000ΣIi =69627000000I=ΣIx+ΣIi =301348000000Figure1.According to size figure,section of changed point and middle span section has same geometric features.4. The main beam inner force of calculation,cased by permanent action and variable action.Loadmiddle span1/4 span of sectionchanged sectionSPCtype of loadmagnitude of arranged loadMmaxcorrespond shear forceVmaxcorrespond MMmaxcorrespond shear forceVmaxcorrespond MMmaxVmaxVmaxG1 G21 G22 Q2 VL(no IC) vehicle load(with IC) vehicle and pedestrain UCA short term long term 5. Estimation of reinforcement area and lay out steel cable1) Estimation of prestressed reinforcement of crosssection area.According to the requirement of resistance crack from normal section to estimate number prestressed rebar.Full prestressed concrete structure of the effective prestress in middle span crosssection is: Ms is a moment of the ultimate limited state under short term loading.++=3823(KN Relative humidity (average of per year)= 75％；Materials：Tendon: low relaxation strands(17)；Standard value of tension strength ；design value of tension strength；nominal area= 140mm2 ,nominal 。cotθ0,we can have Ld=400cot80=2846mm②Calculating horizontal distance between lead point and bending point,According to the formula Lb2=R is the distance between tensioned point to anchor end, the anchor end is midspan crosssection. The influence length of antifriction shows in the following Table. Table of antifriction influence length Table of antifriction influence lengthNO. rebarσo=σcon (MPa)σl1 (MPa)σl=σoσl1 (MPa)l(mm)Δσd=(σoσl)/l (MPa/mm)lfN1139513986 11996 N2139514086 10499 N3139514142 10514 We know all ,the prestress losses after considering friction is : is the tensioned prestressed losses after considering antifriction caused by anchor deformation, . If , then antifriction have no influence on this section.Calculatiing each control section’s are shown in the following Table.prestressed losses by anchor deformationsectionNO. rebarX(mm)lf(mm)Δσσl2mean of σl2midspan sectionN11398611996 xlf have no influence0N21408610499 N31414210514 L/4N1707111996 N2717110499 N3722710514 changed point sectionN1385611996 N2395610499 N3401210514 support point sectionN115611996 N225610499 N331210514 (3)Concrete elastic pression caused prestress lossesFor simple supported beam, calculate l/4 section, and take its value as the whole beam crosssection’s prestressed reinforcement losses’ mean: M is tensioning batch number, m=3。0I0ynay39。 is the pipe rolls angle from tensioned place to the midspan, only N1 is a siphon standpipe,so , N2, N3 is not only a siphon but also a flat bend pipe, the siphon angle is: 。=2200mm。elastic modulus ；Strand tapered of group anchors.Nonprestressed reinforcement:HRB400,fsk=400MPa,fsd=330MPa.HRB335：(d12mm) normal value of tension strength ； design value of tension strength； Elastic modulus=105MPa；Concrete：C50；=104MPa；normal value of press strength＝；design value of press strength＝；normal value of tension strength ＝；design value of tension strength ＝.Design requirements： JTG D622004 ,Total Prestress Concrete. Construction：Posttension。tan(θ0/2),we can have Lb2=15000tan40=1049mm③The horizontal diatance between bending point and anchoring point isLw=Ld+Lb2=2846+1049=3895mm④The horizontal distance between bending point and midspan section isXk=27660/2+312Lw=10247mm⑤The horizontal distance between bending end point lead point is