单向板肋形楼盖设计案例

单向板肋形楼盖设计案例某水电站副厂房楼盖采用现浇钢筋混凝土单向板肋形结构。平面尺寸为22.5m×18.0m，平面布置如图1所示。楼板上层采用20mm厚的水泥砂浆抹面，外墙采用240mm厚砖墙，板在墙上的搁置长度为120mm，次梁和主梁在墙上的搁置长度为240mm。板上可变荷载标准值为6kN/m2，混凝土强度等级为C20，梁中受力钢筋为HRB335级，其余钢筋为PRB235级。为此楼盖配置钢筋并绘出结构施工图。初步拟定尺寸：板跨为2.5m，板厚为100mm，次梁的跨度为6.0m，其截面尺寸为200mm×500mm，主梁跨度为7.5m，其截面尺寸为300mm×800mm。按刚度要求，板厚h≥l/40=63mm，次梁高度h≥240mm，主梁高度h≥500mm，拟定尺寸均满足刚度要求。该厂房为3级水工建筑物，基本组合时的安全系数K=1.25。板的尺寸及其支承情况如图2（a）所示。计算跨度：边跨ln1=2280mm，l01=2500mm，中间跨L02=2500mm。两跨相差（L02–L01）/L02=2.8%＜10%，应按等跨来考虑，9跨按5跨计算。荷载计算：永久荷载标准值gk=2.9kN/m，可变荷载标准值qk=6.0kN/m，折算荷载：gk′=5.9kN/m，qk′=3.0kN/m。在垂直于次梁的方向取1m宽的板带作为板的计算单元。下一步是内力计算。Theshearforceofthecontinuousslabisgenerallybornebytheconcreteanddoesnotrequirecalculationoftheobliquesectionbearingcapacityortheinstallationofstirrups.ThebendingmomentcalculationresultsareshowninTable1.Thebendingmomentvalueatthesupportedgeis:V0=[2/)15.1(nkklqg]=(5.9+1.15×3.0)×2.3/2=10.75kN·mB′=–(MB–0.5bV0)=–(6.44–0.5×0.2×10.75)=–5.37kN·mC′=–(MC–0.5bV0)=–(5.31–0.5×0.2×10.75)=–4.24kN·mReinforcementcalculation:b=1000mm,h=100mm,h0=75mm,fc=9.6N/mm2,fy=210N/mm2,bearingcapacitysafetyfactorK=1.25,thecalculationresultsarelistedinTable2.Note:Thebendingmomentofthemiddlespanandmiddlesupportwithintermediateplatebeltscanbereducedby20%duetothearcheffect.Thereinforcementrequirementsforthecontinuousslabare:①thediametershouldnotexceedtwotypes,andthediameterdifferenceshouldnotbelessthan2mm;②whenusingbendingreinforcement,thespacingbetweenthesteelbarsineachspanshouldbeequalormultiplesofeachother,sothatthespacingbetweenthesteelbarsabovethesupportisrelativelyuniform.ThereinforcementdiagramoftheslabisshowninFigure9-26.Reinforcementforthecontinuousslab:①DistributedreinforcementisФ6@250;②TheedgeoftheplateperpendiculartothedirectionoftheplatespanisФ6@200,andtheedgeparalleltothedirectionoftheplatespanisФ6@200;③AdditionalsteelbarsattachedtotheplatesurfaceperpendiculartothemainbeamareФ8@200.④AdditionalsteelbarsФ6@200aredouble-sidedlyarrangedontheplatesurfacesatthefourcornersofthewall.ThereinforcementdiagramisshowninFigure3.(II)Secondarybeamdesign1.CalculationdiagramWhendesigningthesecondarybeam,apartbetweenthecenterlinesofadjacentplatesistakenasthecalculationunit.Inthisexample,itisathree-spancontinuousbeam.ThesecondarybeamconstructionandcalculationdiagramareshowninFigures4(a)and4(b).Calculationspan:Edgespanln1=6000–240/2–300/2=5730mml01=ln1+a/2+b/2=6000mml01=1.05ln1=1.05×5730=6017mmTakel01=6000mmMiddlespanln2=lc–a=6000–300=5700mml02=lc=6000mml02=1.05ln2=1.05×5700=5985mmSincethedifferencebetweenthetwoisverysmall,forcalculationconvenience,takel02=6000mm.2.LoadcalculationPermanentload:Loadtransmittedbytheplateis2.9×2.5=7.25kN/mSelf-weightofsecondarybeamribsis0.2×(0.5–0.1)×25=2kN/mPermanentloadstandardvaluegk=7.25+2=9.25kN/m.可变荷载标准值为qk=15kN/m。折算荷载为gk′=gk+qk/4=9.25+15/4=13.00kN/m，qk′=3qk/4=11.25kN/m。弯矩计算值列于表3，支座边缘的弯矩设计值MB′为90.92kN·m。支座剪力计算值列于表4。翼缘宽度bf′的计算为bf′=l0/3=6000/3=2000mm，取bf′=2000，在荷载计算单元中，次梁支座截面按矩形截面计算。正截面承载力计算结果见表5，斜截面承载力计算结果见表6。次梁的配筋图见图5，板和次梁的钢筋表见表7。主梁的构造及计算简图如图6所示，计算跨度为ln1=7180mm，中间跨ln2=7100mm。根据跨度计算公式，应取l02=7455mm，但是跨度相差不超过10%，因此采用等跨计算，取l02=7500mm。内力可按三跨连续梁内力系数表来计算。荷载计算包括永久荷载和可变荷载。永久荷载由次梁传来荷载9.25×6=55.50kN和主梁梁肋自重0.3×（0.8–0.1）×7.5/3×25=13.13kN组成，其标准值为Gk=55.50+13.13=68.63kN。可变荷载标准值为Qk=15×6=90kN。根据弹性方法，集