Design of the PRC SSB
May. 2015
1. Known:
（1）Span of SSB: 28m；Computed span L=26.66m；
（2）Design load：Vehicular Load -Ι；Pedestrian Load=3.0kN/m2；Coefficient of Importance γ0=1.0； （3）Environment：Bridge locates in a common field, environment ?; Relative humidity (average of per year)= 75％；
（4）Materials：Tendon: low relaxation strands(1×7)；Standard value of tension strength fpk?1860MPa；Design value of tension strengthfpd?1260MPa；Nominal area= 140mm2 ,nominal diameter15.2mm; Elastic modulus Ep?1.95?105MPa；Strand tapered of group anchors. Nonprestressed reinforcement:HRB400,fsk=400MPa,fsd=330MPa.
HRB335：(d<12mm)normal value of tension strength fsk?335MPa；design value of tension strengthfsd?280MPa；Elastic modulusEs=2.0×105MPa; Concrete：C50；Ec=3.45×104MPa； normal value of compress strengthfck＝32.4MPa； design value of compress strengthfcd＝22.4MPa； normal value of tension strength ftk＝2.65MPa； design value of tension strength ftd＝1.83MPa.
(5)Design requirements： JTG D62-2004 ,Total Pre-stress Concrete.
(6)Construction method：Post-tension; Pre-cast girder; TD Jack; Cast-in-site wet connection joint with width
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of 400mm; Asphalt layer with 80mm thickness. 2. Size
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3.Geometric features of all cross-section 1) Calculation of effective width bf′
According to the high way bridge gauge,obtaining minimum value of the following three values: (1): Simple supported beam span’s l/3, l/3=26660/3=8887mm;
(2): Average distance of the two adjacent beams, to the middle beam is 2200mm;
(3): (b+6bh+12hf′), bh=0,we can let hf is equivalent with average of web thickness about middle span section. So ,we have
hf'?(1000?180?800?120?2)?1000?228mm
(b+6bh+12hf′)=200+6×0+12×228=2936mm; bf′=2200mm;
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2) Calculating geometric features of all cross-section:
Generally, geometric features of main beam often use block numerical summation method, Area of all cross section: A=?Ai
Distance between gravity center line of the all cross section and the top of beam:yu=(?Ai?yi)/A Ai---------the area of separated sections
yi---------the distance between the center of gravity of separated sections and edge of beam
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