單向板肋形樓蓋設(shè)計(jì)案例某水電站副廠房樓蓋采用現(xiàn)澆鋼筋混凝土單向板肋形結(jié)構(gòu)。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(zhǎng)度為120mm，次梁和主梁在墻上的擱置長(zhǎng)度為240mm。板上可變荷載標(biāo)準(zhǔn)值為6kN/m2，混凝土強(qiáng)度等級(jí)為C20，梁中受力鋼筋為HRB335級(jí)，其余鋼筋為PRB235級(jí)。為此樓蓋配置鋼筋并繪出結(jié)構(gòu)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(jí)水工建筑物，基本組合時(shí)的安全系數(shù)K=1.25。板的尺寸及其支承情況如圖2（a）所示。計(jì)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(yīng)按等跨來(lái)考慮，9跨按5跨計(jì)算。荷載計(jì)算：永久荷載標(biāo)準(zhǔn)值gk=2.9kN/m，可變荷載標(biāo)準(zhǔn)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(jì)算單元。下一步是內(nèi)力計(jì)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(biāo)準(zhǔn)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(jì)算值列于表3，支座邊緣的彎矩設(shè)計(jì)值MB′為90.92kN·m。支座剪力計(jì)算值列于表4。翼緣寬度bf′的計(jì)算為bf′=l0/3=6000/3=2000mm，取bf′=2000，在荷載計(jì)算單元中，次梁支座截面按矩形截面計(jì)算。正截面承載力計(jì)算結(jié)果見(jiàn)表5，斜截面承載力計(jì)算結(jié)果見(jiàn)表6。次梁的配筋圖見(jiàn)圖5，板和次梁的鋼筋表見(jiàn)表7。主梁的構(gòu)造及計(jì)算簡(jiǎn)圖如圖6所示，計(jì)算跨度為ln1=7180mm，中間跨ln2=7100mm。根據(jù)跨度計(jì)算公式，應(yīng)取l02=7455mm，但是跨度相差不超過(guò)10%，因此采用等跨計(jì)算，取l02=7500mm。內(nèi)力可按三跨連續(xù)梁內(nèi)力系數(shù)表來(lái)計(jì)算。荷載計(jì)算包括永久荷載和可變荷載。永久荷載由次梁傳來(lái)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(biāo)準(zhǔn)值為Gk=55.50+13.13=68.63kN。可變荷載標(biāo)準(zhǔn)值為Qk=15×6=90kN。根據(jù)彈性方法，集