單向板肋形樓蓋設計案例

單向板肋形樓蓋設計案例某水電站副廠房樓蓋采用現澆鋼筋混凝土單向板肋形結構。平面尺寸為22.5m×18.0m，平面布置如圖1所示。樓板上層采用20mm厚的水泥砂漿抹面，外墻采用240mm厚磚墻，板在墻上的擱置長度為120mm，次梁和主梁在墻上的擱置長度為240mm。板上可變荷載標準值為6kN/m2，混凝土強度等級為C20，梁中受力鋼筋為HRB335級，其余鋼筋為PRB235級。為此樓蓋配置鋼筋并繪出結構施工圖。初步擬定尺寸：板跨為2.5m，板厚為100mm，次梁的跨度為6.0m，其截面尺寸為200mm×500mm，主梁跨度為7.5m，其截面尺寸為300mm×800mm。按剛度要求，板厚h≥l/40=63mm，次梁高度h≥240mm，主梁高度h≥500mm，擬定尺寸均滿足剛度要求。該廠房為3級水工建筑物，基本組合時的安全系數K=1.25。板的尺寸及其支承情況如圖2（a）所示。計算跨度：邊跨ln1=2280mm，l01=2500mm，中間跨L02=2500mm。兩跨相差（L02–L01）/L02=2.8%＜10%，應按等跨來考慮，9跨按5跨計算。荷載計算：永久荷載標準值gk=2.9kN/m，可變荷載標準值qk=6.0kN/m，折算荷載：gk′=5.9kN/m，qk′=3.0kN/m。在垂直于次梁的方向取1m寬的板帶作為板的計算單元。下一步是內力計算。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.可變荷載標準值為qk=15kN/m。折算荷載為gk′=gk+qk/4=9.25+15/4=13.00kN/m，qk′=3qk/4=11.25kN/m。彎矩計算值列于表3，支座邊緣的彎矩設計值MB′為90.92kN·m。支座剪力計算值列于表4。翼緣寬度bf′的計算為bf′=l0/3=6000/3=2000mm，取bf′=2000，在荷載計算單元中，次梁支座截面按矩形截面計算。正截面承載力計算結果見表5，斜截面承載力計算結果見表6。次梁的配筋圖見圖5，板和次梁的鋼筋表見表7。主梁的構造及計算簡圖如圖6所示，計算跨度為ln1=7180mm，中間跨ln2=7100mm。根據跨度計算公式，應取l02=7455mm，但是跨度相差不超過10%，因此采用等跨計算，取l02=7500mm。內力可按三跨連續(xù)梁內力系數表來計算。荷載計算包括永久荷載和可變荷載。永久荷載由次梁傳來荷載9.25×6=55.50kN和主梁梁肋自重0.3×（0.8–0.1）×7.5/3×25=13.13kN組成，其標準值為Gk=55.50+13.13=68.63kN?？勺兒奢d標準值為Qk=15×6=90kN。根據彈性方法，集