Chng 7 MI NH 7.1. V TR, TC DNG V C IM Mi l b phn trn cng ca nh. Mi l kt cu chu lc ng thi cng l kt cu bao che. Tc dng chnh ca mi l che ma, che nng chng li nh hng ca bc x mt tri, ng thi c tc dng cch nhit, gi nhit, chng thm. Mi c lin kt vi cc b phn tng ct, dm, ging ca cng trnh, to nn s n nh chung cho ton cng trnh. Mi c nh hng ln ti m quan cng trnh. Mi c hai b phn chnh l kt cu bao che v kt cu chu lc. - Kt cu bao che c yu cu chnh l chng thm, chng dt, che ma, chn nng v cch nhit, gi nhit, cch m ng thi vi kh nng chng chy, chng tc hi ca cc loi kh. Kt cu bao che gm c lp lp v kt cu lp lp. Lp lp c th dng cc loi tm nh nh l, tranh, r, ngi, g, , thu tinh; tm lp ln nh phibr ximng, tn, btng ct thp, cht do. - Kt cu chu lc c yu cu m bo chu lc di tc ng ca ti trng tnh nh ti trng bn thn, ti trng lp lp v kt cu tm lp, ng thi m bo chu lc di tc ng ca ti trng ng nh sc gi, ma v bo tr. Kt cu chu lc bao gm cc h dm, dn v ko, x g vi cu phong, lit hoc cc tm ton khi hay lp ghp, trong cc cng trnh hin i cn c th l kt cu khng gian vi v mng mt xp, kt cu dy cng hoc sn khng gian. Kt cu chu lc c th c lm bng cc loi vt liu g, thp, btng ct thp. Kt cu ca mi nh cn m bo s bn vng di nh hng ca thi tit, kh hu bao gm nng, ma, gi. Cc thnh phn, b phn ca mi nh cn c cu to bi cc loi vt liu thch hp, ng thi phi thng qua tnh ton c nhng tit din theo yu cu chu lc vi kiu cch rp ni ng cch, m bo s truyn lc v chu ti, m bo khng b bin dng i vi g v thp, m bo s co dn nht nh i vi thp v btng ct thp do s thay i nhit v tc ng ca gi. 7.2. PHN LOI 7.2.1. Theo vt liu: Mi nh lp g, mi nh lp ngi, mi nh lp tm phibr ximng, mi nh lp tn, mi btng ct thp. 7.2.2. Theo bin php thi cng: Mi nh lp ghp, mi nh ton khi. 7.2.3. Theo cu to - Mi dc: mi nh c dc ln nh mi nh lp g, mi nh lp ngi, mi nh lp tm phibr ximng, mi nh lp tn, vi yu cu c bit c th lm bng btng ct thp ton khi. Thng thng c

dc i = 27-100%. - Mi bng: mi nh c dc nh c lm bng btng ct thp ton khi hoc lp ghp. Thng thng c dc i = 5-8%. 7.3. DC CA MI NH thot nc d dng, mi nh cn phi c dc nht nh. dc ln hay nh ph thuc vo vt liu cu to mi, hnh thc kin trc, hnh thc kt cu, hnh thc cu to, kh hu v phong tc tp qun, cng nh gi thnh xy dng. V phng din kin trc thng c yu cu dc ph hp vi ni dung v hnh thc kin trc. V phng din kinh t mi c dc cng nh th cng gim c din tch ca mi lp. V phng din thch ng vi kh hu, nng, gi, ma th mi c dc m thot nc nhanh, chng dt, chng thm tt. dc ca mi nh c xc nh bng t l ca chiu cao mi so vi chiu rng ca mi, tnh bng %. dc mi nh k hiu l i, i = tga = h/l (%), trong h l chiu cao mi nh, l l chiu rng mi nh (hnh 7.01).

7.4. CU TO MI DC Cn c vo hnh thc mt bng v yu cu v dc, mi dc c th gp rt nhiu hnh thc phong ph nh mi mt dc, mi hai dc, mi bn dc v mi bn dc kiu hai tri (hnh 7.02 - 7.03).

Mi dc c hai b phn chnh l sn mi v phn che lp. Sn mi bao gm tng thu hi, v ko, bn ko, h thng ging v ko v x g. Phn che lp bao gm: i vi mi ngi l cu phong, lit, ngi; i vi mi lp phibr ximng l tm phibr ximng; i vi mi lp tn l tn. 7.4.1. Kt cu chu lc 7.4.1.1. Tng thu hi L loi kt cu n gin, kinh t, li dng tng ngang chu lc xy thu hi lm kt cu chu lc. Tng thu hi c xy theo dc ca mi, tng thu hi u bin xy 220, tng thu hi gia xy 105. tng cng kh nng chu lc cho tng thu hi cn phi b tr, khong 2000 nn b mt tr v ti v tr gc x g. Trong tng thu hi nn thp ch lin kt vi x g. Khong cch gia hai tng thu hi khng qu 4000, nu ln hn nn dng kt cu v ko. 7.4.1.2. V ko Theo yu cu cu to m v ko c th lm bng g, thp, btng ct thp. C trng hp v ko c lm bng g v thp, trong thp chu ko cn g chu nn v un. V ko thp v btng ct thp ph hp vi nhp nh ln, c yu cu chu la v bn vng cao.

Theo hnh thc c dn v ko tam gic, hnh thang, hnh a gic (hnh 7.04). Khu ca v ko c th t t 6-10m i vi v ko g, 10-18m i vi v ko g thp hn hp, trn 18m i vi thp hoc btng ct thp. Khi chn v ko phi cn c vo chiu di nhp, yu cu s ca phng c, ti trng tc dng ln dm, cc yu cu v thm m cng nh yu cu v chng chy. Trong xy dng dn dng v ko tam gic c dng ph bin hn c. V ko tam gic bao gm cc thanh ko (cnh thng), qu giang (cnh h), thanh chng ng, thanh chng xin c lm g, thp hoc hn hp thp g.

Yu cu thit k Khong cch gia cc v ko s c chn t 3000-6000 tuz thuc vo vt liu lm v ko v x g l g hay thp. Tit din ca cc cu kin to nn v ko tuz theo khu ca v ko (chiu di ca nhp). Khi b tr v ko cn chn khu ngn nht, nu trng hp c tng hoc ct lm gi ta trung gian th nn li dng. Cc v ko cn phi lin kt n nh tng cp mt bng cc thanh, h ging cho. ng thi phi cu to lin kt gia cc v ko vi tng chu lc hoc ct chu lc to thnh h khung vng chc. Cu to lin kt gia cc v ko vi gi cn phn b lc u, trnh lc tc dng cc b, c th dng g m u ko. Gi l lin kt di ng u v ko trnh ni lc sinh ra do dn n ca v ko. Khi thit k cc cu kin, cn lu { cc ng trc ni lc ca cc thanh phi hi t v mt im nhm m bo khng gy un cho cc thanh ko khi chu lc v truyn lc ti v tr ny, im gi l mt ko.

Chnh gia thanh qu giang ti, v tr lin kt vi thanh chng ng cn nng ln mt khong f = 1/200 l (l l khu v ko) khi lm vic ko vng qu giang s phng mt di. Trong trng hp s dng mt na v ko, gi l bn ko, cu to ging nh v ko. V ko g (hnh 7.05 - 7.08) i vi v ko g cc cu kin chu ko c cu to lin kt cht bng g cng, bng kim loi nh bulng, inh hoc mng ghp, cc cu kin chu nn c cu to lin kt mng o chnh din vung gc hoc phn gic, c mt rng, hai rng. Ni thanh ko v qu giang, dng np g, np st lin kt bng bu lng. Khng nn ni cc thanh ca v ko trong cng mt khoang. Mt tip xc ca gi v ko trc tip ln tng m khng c ging phi lng mt lp va ximng dy 30. Cc u ko g chn vo tng, cc mt g tip xc vi tng phi qut hc n chng mc.

V ko thp (hnh 7.09 - 7.10) i vi v ko thp cc cu kin c cu to lin kt v ni bng bulng, inh tn hoc hn trc tip hay gin tip vi tm thp trung gian, tuz theo v tr v s lm vic ca cc thanh ti nt lin kt.

7.4.1.3. Ko gc (hnh 7.11 - 7.17) Cu to v ko gc nh v ko thng thng. Trong trng hp cng trnh c mt bng phc tp, mi dc theo nhiu pha, cn nghin cu b tr v ko gc, thanh ko hay cc tng thu hi sao cho hp l nht, tho mn nhng hnh thc mi ph hp vi yu cu thit k. Ti cc v tr giao tuyn gia hai mt mi dc c th b tr bn ko hoc thanh ko ph. V ko v thanh ko gc c th lin kt vi tng hay lin kt vi cc v ko bng bu lng v cc thanh g hoc bt thp. Ngoi ra cn lu { b tr phn tn cc im gi ta ca cc v ko, khng tp trung ti mt nt.

7.4.1.4. Bn ko-cngxon (hnh 7.18 - 7.19)

S dng ti cc v tr gia mi thp v tng vt.

7.4.1.5. H thng ging v ko (hnh 7.20) Tc dng C tc dng lin kt khng gian cc mt dn v ko, bo m n nh ngoi mt phng cho cc thanh

cnh chu nn. Chu cc lc khng nm trong mt phng ca dn v ko, truyn cc lc xung ct, mng. Bo m dng lp thun tin, an ton. kt cu dn v ko ca mi nh, thng dng hai loi ging: ging trong mt phng mi v ging trong mt phng cc thanh ng ca dn v ko.

H ging trong mt phng mi y l h ging ch yu m bo tnh cht bin hnh ca cng trnh, bo m s n nh ca ton dn v ko cng nh ca thanh cnh nn. Tuz theo chiu di ca nh, ln ca dn v ko, kt cu tng u hi m c th cu to ca h ging mi nh sau:

- Trng hp chiu di nh nh hn 20m v c tng u hi cng c th chu c lc ngang (tng gch ln hn 220) th c th dng ngay x g lm ging, vi iu kin x g phi c cu to lin kt cht vo thanh ko (thanh cnh thng) cng nh vo tng hi. - Trng hp tng hi khng cng chu c lc ngang, cng nh khi nh di qu (khong cch gia cc tng ngang ln hn 20m) th phi to ra nhng khi cng hai u nh v chiu di nh, cch nhau khng qu 20m lm im ta cho cc x g n nh cc dm v ko khc khong gia. Khi cng gm hai dn v ko cnh nhau, thanh ko c ni nhau bng cc thanh ging cho ch thp, to thnh mt dn nm nghing. Thanh ging cho ng inh trc tip vo thanh ko hoc qua cc ai thp mng, ch giao nhau gia ging cho v x g cng cn lin kt cht. H ging ng C tc dng lin kt cho cc mt ca thanh qu giang khng vnh khi mt dn v ko, m bo dn v ko c v tr thng ng, c bit khi c gi ln, nn cn c gi l ging gi. Ging t trong mt phng thng ng gia dn v ko ni tng i v ko vi nhau v c th cch vi ba gian th b tr mt h ging ng. Khng nn lm kin tc, v khi mt dn v ko b ph hu th s gy ra phn ng dy chuyn. Khi nhp ca dn v ko ln hn 15m th phi lm hai hoc ba h ging ng trong cc mt phng thanh chng ng khc nhau ca dn v ko. H ging ng bao gm hai thanh thp ch thp v mt thanh ngang ni cc thanh qu giang, thanh cho bt bulng vo thanh ng ca dn v ko hoc bt bulng vo x g v thanh qu giang ca dn v ko, thanh cho cn c lm bng thp trn, bt vt vo cnh dn v ko. 7.4.1.6. X g C tit din hnh ch nht, t trn v nghing theo mt thanh ko hoc tng thu hi. C th gc ln v ko hoc cc tng thu hi. Thng c t v tr mt ko, khong cch gia cc mt ko thng t 1500-2000 v c n nh bng con b. Tit din ca x g ph thuc vo khong cch gia cc v ko hay cc tng thu hi. Khong cch gia hai x g thng t 1000-2000. X g thng t ba v tr: - X g nc c t nh ko, t thng ng, gia hai x g thng dng lin kt ni chng (vi x g thp) hoc u u (i vi x g g). - X g gia c t mt ko, t nghing theo mt ko, gia hai x g thng dng lin kt so le hoc ni chng. - X g bin c t chn ko (u ko), t thng ng, gia hai x g thng dng lin kt ni

chng (x g thp) hoc u u (x g g). 7.4.2. Kt cu bao che Thng c lm bng vt liu tm nh nh ngi, vt liu tm trung bnh nh phibr ximng, tm ln nh tn. 7.4.2.1. Mi lp ngi Sau khi n nh h thng v ko, x g ngi ta gc h thng cu phong, li t ri lp ngi. dc ca mi ngi c th chn trong phm vi 48-70%, thng chn l 60% (31). Cu phong: l cc thanh g c tit din hnh ch nht hoc hnh vung, t vung gc vi x g. c lin kt vi x g bng inh. Kch thc tit din cu phong ph thuc vo khong cch gia hai x g. Theo qui nh ca v ko in hnh th nu khong cch gia hai x g nh hn 2000 th cu phong c tit din 50x50. Khong cch gia hai cu phong khong 500. Lit: l cc thanh g c tit din 3030, c ng vung gc vi cu phong mc ngi khi lp, khong cch gia hai lit ph thuc vo kch thc vin ngi. Vi loi ngi 13 vin/m2 th khong cch gia hai lit l 350, vi loi ngi 22 vin/m2 th khong cch gia hai lit l 250. ui mi, hng li t cui cng c ng chng hai lp m bo dc mi c u v cch hng lit trn l 180 (vi ngi 22 vin/m2) v 280 (vi ngi 13 vin/m2). Ngi: c sn xut nhiu kiu, loi v kch c khc nhau bng t nung, bng va ximng. C cc loi nh ngi my, ngi mc, ngi mng m dng, ngi p sng, ngi b. Nhng thng c dng ngi my c kch thc: loi ngi 22 vin/m2 c kch thc 22030030, loi ngi 13 vin/m2 c kch thc 24040035 (hnh 7.21).

Ngi c buc vo lit bng dy thp chng gi tc hoc x ngi, cc lp ngi pha trn cch mt hng buc mt hng, ba lp di cng vin no cng buc vo lit. Ngoi ra cn c cc loi ngi b lp nh nc, lin kt bng va ximng, trng hp khng dng ngi b c th xy b nc bng gch (hnh 7.22 - 7.23).

7.4.2.2. Mi lp phibr ximng (hnh 7.24 - 7.28) Tm lp phibr ximng c ch to bng si khong aming v ximng di dng phng, ln sng nh hoc ln. C u im nh, kh nng chng n mn v phng ho cao, thi cng nhanh v tit kim

g. Tuy nhin kh nng cch nhit km v d v. Tm lp phibr ximng thng dng c kch thc: loi nh l 800x1200, loi ln l 1200x1800, c chiu dy l 3-5. dc ca mi phibr ximng c th chn trong phm vi 23-33%, thng chn l 27% (150).

Tm phibr ximng c lp ph ln nhau t 1,5-2 mi sng v chng ln nhau t 150-200. C hai gii php t tm lp l t so le v t thng hng. Trng hp t thng hng th phi ct gc tng cp cc tm t cho nhau trnh hin tng bn tm lp chng ln nhau ti mt ch s gy ra khe h. Hng lp s ngc chiu vi hng gi.

Tm phibr ximng c lin kt vi x g bng cch khoan l ng inh hoc bt cc mc thp c c vn v m cao su chng dt. L khoan nn rng hn mt t v khng nn ng cht c hai u tm lp, khi nhit tng, tm phibr ximng c th dn n t do, trnh pht sinh cc ng lc lm nt tm lp. Khong cch gia hai x g bng chiu di tm lp tr i on tm lp chng ln nhau. u hi nu l tng thu hi th tng phi xy vt khi tm lp trnh gi lm tc mi. nh mi dng mt loi tm lp phibr ximng c hnh ngi b lp p nc, lin kt bng va ximng.

7.4.2.3. Mi lp tn (hnh 7.29) Tm lp c ch to bng tn m km, hp kim nhm theo hai hnh thc tn phng v tn mi. Mi tn bn, nh, thch hp vi mi c khu ln, thi cng n gin, tho lp d dng. Tuy nhin kh nng cch nhit v cch m km, nh hng nng lnh. dc ca mi tn c th chn trong phm vi 27-33%, thng chn l 27% (150). Cch lp ca mi tn ging nh cch lp mi phibr ximng, nhng tn c dn n lp hn nn cn nhiu l c hnh bu dc dc theo sng. Dng mc thp lin kt vi x g, ng inh hoc bt vt trc tip vo x g. Cc lp lp ph ln nhau 2-3 mi sng v chng ln nhau 150300. Ti v tr hai tm chng ln nhau cn ch chng gi la v ma ht.

7.4.2.4. Mi dc btng ct thp (hnh 7.30) L loi mi btng ct thp ton khi c dc theo dc ca mi, sau dn cc loi gch gi ngi ln trn. C u im bn, p, kh nng chng thm, chng nng cao, khng chy, c th to hnh theo yu cu m quan ca cng trnh. Tuy nhin n cng c nhc im nng n, kh sa cha, thi cng phc tp v tn km.

7.4.3. Cu to trn mi dc Trn mi c cu to di lp kt cu chu lc ca mi nhm mc ch m bo m quan v v

sinh, cch m, cch nhit cho cc phng c tng trn cng ca nh. Trn mi dc c th thc hin theo hai cch: trn p mi v trn treo. 7.4.3.1. Trn p mi L loi trn c mt nghing theo mi, tn dng mt phn khng gian di mi dc. Trn p mi c thc hin bng cch ng lati trc tip ln mt di x g to thm m cho mt trn. tng kh nng cch m, cch nhit cho trn, c th chn vt liu cch nhit vo khong trng di mi trn trn. Cu to trn p mi n gin nn gi thnh h. 7.4.3.2. Trn treo L loi trn c tc dng to nn mt phng nm ngang. Tu theo khong cch gia cc v ko m kt cu trn treo c th cu to theo hnh thc mt h dm hay hai h dm. Trn treo c mt h dm khi khong cch gia cc v ko khng qu 4000, dng dm trn c kch thc 40-80 80-120, khong cch gia cc dm l 400-500, c treo trc tip vo thanh qu giang bng st vai b hoc t k ln hai mt dm ph c kch thc 5050, 6060 lin kt bng bulng. Trn treo c hai h dm khi khong cch gia cc v ko ln hn 4000, cn b tr thm dm chnh cng phi hp vi cc thanh qu giang treo dm trn. Khong cch gia cc dm chnh c th chn t 1500-3000, tit din dm chnh tu thuc khu dm, nhng khng nh hn 50100. Nu khu dm chnh qu ln th cn phi dng dy treo dm ln x g, thng gn v tr gi ta x g hoc treo vo cc thanh chng ng ca v ko. Trng hp x g gc ln tng thu hi th hai u dm chnh c th gc vo tng v gia c treo ln x g. C ba cch lin kt dm trn vo thanh qu giang ca v ko: - Cch 1: lin kt treo dm ph bng thp trn hnh ch U gc dm trn (hnh 7.31).

- Cch 2: dng hai dm ph lin kt trc tip vo hai m qu giang dm trn, trng hp ny mt trn phng vi mt qu giang, loi ny thi cng n gin dng khi v ko c khu nh, bin dng t, khng lm nt trn (hnh 7.32).

- Cch 3: dng mc st treo trc tip dm trn vo qu giang sau khi treo dm trn (hnh 7.33).

7.4.3.4. Mt trn Lp mt trn c cu to di h dm trn. Mt trn c th c cu to bng cc loi vt liu nh si thc vt, si khong, vi rm, ximng li thp, thch cao, cht do, tn kim loi hay g. C nhiu hnh thc khc nhau nh tm phng, bn pan t ngang hoc dc, an vung hoc qu trm.

7.4.4. T chc thot nc cho mi dc Nc ma t trn mi dc c th thot theo hai cch: - Thot nc t do khi chiu cao t dim mi n mt t khng qu 5000. Cn cu to mi ua a rng ra xa chng m cho tng. - Thot nc vo mng nc, sn t dc theo dim mi chy vo ng thot nc xung rnh thu nc. 7.4.4.1. Cu to ng thot nc v sn ng thot nc (hnh 7.34) Thot nc c th c ch to bng cc loi vt liu nh tn km, gang, ximng si khong snh, nha tng hp, btng ct thp.

V tr tip gip gia ng v mng nc, sn c b tr ng ni tip. Ti v tr ming thu nc ca mng nc, sn ni t ng thot nc cn t li chn rc. Ming thot nc pha di ca ng thot nc nn lm cong gim bt sc xi ca dng nc. Nc ma t ng xung c th thot t do trn mt hoc cho thot vo rnh thot nc kn hoc h, cn phi lm h ga trnh khng b tc nghn rnh. Tit din ca ng c th l hnh vung hoc hnh trn. Ph thuc vo din tch mi nh v lng ma hng nm khu vc xy dng cng trnh. S b c th chn tit din ca ng thot nc l: 0,1m2 din tch tit din ng thot nc c kh nng thot nc cho 1-2,5m2 nc ma thu c

trn mi nh, thng c chn kch thc ng l 100 vi ng trn, 150 vi ng vung, khong gia cc ng thot nc thng chn trong khong 15-24m. ng c lin kt vo tng bng thp trn su vo tng vi khong cch 1000 c mt ci, ng cn t cch tng hn 20. Kch thc ca mng nc, sn ph thuc vo khu mi v lng ma. Tit din c th l hnh bn nguyt, hnh ch U, hnh ch V. Theo kinh nghim vi khu mi nh hn 6m dng mng nc, sn rng 250; vi khu mi t 6-15m dng mng nc, sn rng 300; vi khu mi ln hn 15m dng mng nc, sn rng 450. Mng nc, sn cn phi nh dc u v ming thu nc ca ng thot nc, dc thng thng t 0,1-0,2%. Thnh bn ngoi ca mng nc, sn cn phi thp hn thnh bn trong t 20-30 trnh nc trn vo trong. This image has been resized. Click this bar to view the full image. The original image is sized 646x690.

Mng nc c lm bng tn tn trng km, dy 2mm. c lin kt vi cu phong bng inh vt v mc thp i vi mi ngi, bng inh c v mc thp vo tm lp i vi mi phibr ximng hay tn. Sn c lm bng btng ct thp, c th cu to lin vi dm hoc ging, cn ch chng lt cho sn. Khi btng sn xong cn phi chng thm.

7.4.4.2. Mng xi L mng thu nc t nghing theo dc ca mi v tr giao tuyn gia hai mt mi dc, cng l ng dc tp trung nc ma t cc mi chy n nn d sinh dt, do c cu to phc tp. Mng xi thng c cu to theo hai cch: dng mt cu phong xi hay dng hai hoc ba cu phong xi. Dng mt cu phong xi: lc ny cu phong c tit din ln hn cc cu phong thng v phi mang cc cu phong thng, thng c tit din ln hn 70x70. mc ngi vo lit v tr ny, tm tn lm mng khng b cao lm g mng. V vy chng dt, tm tn phi c b rng 600-1000. Dng hai hoc ba cu phong xi: lc ny cu phong c kch thc bnh thng. Mp tn lm mng c th b g cao m vo cu phong hai bn lm b cho thnh mng xi. 7.4.5. V tr c bit trn mi dc 7.4.5.1. Khe ln trn mi dc Khi lp mi khng cha khe h ln m lp ph qua, lc ny ch cn xy tng hoc gc v ko mt bn khe ln, sau gc h thng x g bnh thng. 7.4.5.2. Tng vt mi (hnh 7.37 - 7.39) Tng ngoi c xy cao che mi dc theo dim mi hoc dc theo tng bin u hi nh.

Nu tng xy dc theo dim mi, cn t chc thot nc tt, bng cch t mng nc hay sn bn trong v dc theo tng, mng nc v sn lm bng tn hay btng ct thp. Nu tng xy dc theo tng bin u hi nh hoc trng hp ng khi xuyn qua mi ngi cn ch chng thm bng cch lm g mc nc, lng va ximng hoc tn che.

7.5. CU TO MI BNG 7.5.1. c im Mi bng l gii php cu to mi ph bin cho cc cng trnh, p ng c cc yu cu kin trc linh hot v a dng. C th cu to bng vt liu g, thp, nhng ch yu bng btng ct thp ton khi hoc lp ghp. Mi bng c u im l c dc nh 5-8%, do chu p lc ca gi bo t, kt cu bn chc, kh nng chng chy cao. Mt sn ca mi c th kt hp lm sn thng, sn phi, nhng p ng c yu cu ny th phn kt cu bn trn mt mi s phc tp hn. So vi mi dc, mi bng c nhc im l d lm thay i ch nhit, m bnh thng ca cc phng tng trn cng, nht l ma nng. Do cn phi nng cao cc yu cu v kh nng

cch nhit v chng thm cho mi. Mi tng i nng v c gi thnh cao. Ngoi ra cng tc sa cha chng dt s phc tp khi nh b ln, nt. 7.5.2. Cc lp cu to mi bng Mi bng c cc b phn cu to chnh nh: lp kt cu chu lc, lp to dc, lp chng thm v lp cch nhit. 7.5.2.1. Lp kt cu chu lc C tc dng chu lc chnh cho mi, c cu to bng btng ct thp ton khi hay btng ct thp lp ghp. V hnh thc ging nh cu to sn nh, nhng c s khc bit v cu to vin mi v cu to chng thm v thot nc cho mi. 7.5.2.2. Lp to dc C tc dng to cho mi c dc cn thit, c t trn lp kt cu chu lc, cu to bng btng x, btng gch v, btng dm. Ngoi ra n cn tng cng kh nng cch nhit cho mi v lm phng mt trn lp kt cu chu lc to iu kin thi cng tt cho lp chng thm bn trn n. 7.5.2.3. Lp chng thm C tc dng bo v khng cho nc ma ngm vo kt cu ca mi, c t trn lp to dc i vi mi c lp to dc hoc trn lp kt cu chu lc i vi mi khng c lp to dc, thng c cu to bng btng ct thp mc cao. Ngoi ra n cn c tc dng tng thm cng cho mi. Btng chm thm l loi btng nh trong thnh phn ximng tng i nhiu, kh nng lin kt ca btng cht khng c l rng. ng thi tng kh nng chng thm, btng cn c ho thm cht ph gia nh b ru sunfit, x phng, nha thng. B dy ca lp btng chng thm vo khong 30-50, thng thng l 40. Khi nhit thay i hay kt cu bin hnh, lp btng chng thm s sinh ra hin tng nt. khc phc hin tng c th p dng cc bin php: - Tng cng kh nng chu ko ca btng chng thm bng cch t thm mt lp li thp 4, vung 200-250. - Chia mt bng ca lp chng thm trn mi thnh nhng mng nh c 2000x2000. Cn c vo mt bng kt cu mi m t cc khe chia trng vi v tr ca tng hoc dm, v thng d hnh thnh cc vt nt. Qua thc t thi cng lp btng chng thm cha thc s m bo hon ton kn v c chc, do cn tin hnh ngm nc ximng chng thm, c tin hnh sau khi btng t 6-10 gi, vi t l 5kg ximng cho 1m3 nc, ngm cho n khi no nc ximng bt kn cc l rng trong

btng v khng ngm xung di l t yu cu. 7.5.2.4. Lp cch nhit C tc dng ngn khng cho hi nng ca khng kh xm nhp vo cc phng tng trn cng, m bo cng thng hi, thot nhit cn thit. Ngoi ra cn c tc dng bo v lp btng chng thm di khi b tc ng c hc c hi, khi b mt tri chiu nng qu mc v khi b tip xc trc tip vi khng kh, bi l khi tip xc vi khng kh, lp chng thm s b phn hu dn vi cc cht d bay hi, do s mt tnh n hi. C th cu to bng cc loi vt liu nh gch l nem, gch thng tm, tm an l, tm tn, tm phibr ximng. 7.5.3. Cu to mt s loi mi bng. 7.5.3.1. Mi bng btng ct thp ton khi (hnh 7.40 - 7.43) L loi mi ph bin cho cc cng trnh kin trc, c cu to ging nh sn btng ct thp ton khi. This image has been resized. Click this bar to view the full image. The original image is sized 664x423.

- Lp kt cu chu lc: cu to bng btng ct thp phng hoc nghing theo dc ca mi t 5-8%, c dy theo tnh ton kt cu, khong 80-120. Sau khi c ngm nc ximng chng thm theo t l 5kg ximng cho 1m3 nc - Lp to dc: vi trng hp lp kt cu chu lc phng, cu to bng btng gch v, btng than x, btng dm mc 50, dc 5-8%. - Lp chng thm: cu to bng btng ct thp dy 40, mc 200, ngm nc ximng chng thm. - Lp cch nhit: c th cu to bng cc loi vt liu nh gch l nem, gch thng tm, tm an l, tm tn, tm phibr ximng.

7.5.3.2. Mi bng btng ct thp lp ghp Mi bng n trn phng (hnh 7.44 - 7.45)

- Lp kt cu chu lc: thng l panen hp hoc l tm an btng ct thp, c gc phng theo mt tng. - Lp to dc: thng l btng gch v, btng than x, btng dm mc 50, dc 5-8%. - Lp chng thm: cu to bng bng btng ct thp dy 40, mc 200, ngm nc ximng chng thm. - Lp cch nhit: c th cu to bng cc loi vt liu nh gch l nem, gch thng tm, tm an l.

This image has been resized. Click this bar to view the full image. The original image is sized 747x497.

Mi bng n trn dc (hnh 7.46 - 7.47) - Lp kt cu chu lc: thng l panen hp hoc l tm an btng ct thp, c gc nghing theo dc ca mi, t 5-8%. Nh vy khng cn lp to dc. - Lp chng thm: cu to bng bng btng ct thp dy 40, mc 200, ngm nc ximng chng thm. - Lp cch nhit: c th cu to bng cc loi vt liu nh gch l nem, gch thng tm, tm an l. This image has been resized. Click this bar to view the full image. The original image is sized 850x540.

This image has been resized. Click this bar to view the full image. The original image is sized 755x708.

This image has been resized. Click this bar to view the full image. The original image is sized 782x451.

Mi bng trn kp (hnh 7.48) L loi mi btng ct thp lp ghp c hai lp: lp trn v lp mi dc. C u im l cch nhit tt, nhng tn km hn loi mi bng n. - Lp trn thng l panen ch U t nga, to phng cho trn nh. - Lp mi dc t nghing theo dc mi t 5-8%, cch lp trn mt khong trng to thnh lp khng kh cch nhit. - Lp btng chng thm dy 40, mc 200, c cu to bn trn lp mi dc. tng cng v bo v cho lp btng chng thm bng cch lt hai lp gch l nem so le nhau. 7.5.4. T chc thot nc cho mi bng Nc ma t trn mi c thot nc vo sn chy vo ng thot nc xung rnh thu nc. 7.5.4.1. ng thot nc Ging nh cu to ng thot nc mi dc. Tit din ca ng c th l hnh vung hoc hnh trn, s b c th chn tit din ca ng thot nc l: 0,1m2 din tch tit din ng thot nc c kh nng thot nc cho 1-2,5m2 nc ma thu c trn mi nh, thng c chn kch thc ng l 100 vi ng trn, 150 vi ng vung, khong gia cc ng thot nc thng chn

trong khong 15-24m. ng c lin kt vo tng bng thp trn su vo tng vi khong cch 1000 c mt ci, ng cn t cch tng hn 20. 7.5.4.2. Sn Kch thc ca sn ph thuc vo khu mi v lng ma. Tit din thng l hnh ch U. Theo kinh nghim vi khu mi nh hn 6m dng sn rng hn 250; vi khu mi t 615m dng sn rng hn 300; vi khu mi ln hn 15m dng mng nc, sn rng hn 450. Sn cn phi t dc u v ming thu nc ca ng thot nc, dc thng thng t 0,1-0,2%.

Sn c lm bng btng ct thp, c th cu to lin vi dm hoc ging, cn ch chng lt cho sn. Khi btng sn xong cn phi ngm nc ximng chng thm. Sn c th b tr trong hoc ngoi mt bng cng trnh. - Sn ngoi (hnh 7.49): c c lin vi ging tng hoc dm. Sau khi btng hoc gc panen mi, c th cu to lin vi btng chng thm. Sn bng btng ct thp c chiu dy bn khng nh hn 40, thnh bn ngoi ca sn thp hn pha trong t 20-30 chng trn vo

trong, trng hp thnh bn ngoi ca sn cao hn bn trong qu 30 th cn phi cu to ng chng trn. - S n trong (hnh 7.50): khi yu cu mt nh phng th cn phi b tr sn pha trong tng vt mi, thng l tm panen ch U t nga, sau lp btng chng thm ln trn lin vi lp btng chng thm ca mi hoc c th cu to bng btng ct thp ton khi. This image has been resized. Click this bar to view the full image. The original image is sized 783x421.

7.5.5. Cc v tr c bit trn mi bng (hnh 7.51 - 7.55) 7.5.5.1. V tr khe ln Khe ln tch cng trnh t mng n mi, i vi mi bng, lp btng chng thm phi c thng g sut dc khe ln dy 40, cao 100, ri xy b gch hai pha khe ln, trn b gch y m khe ln bng tn hoc tm an btng ct thp. Trong trng hp nh hai bn khe ln cao thp khc nhau th lp btng chng thm ca mi pha thp cng phi lm g cao ln 100, pha trn c cu to tn che sut dc g. 7.5.5.2. V tr khe co dn (khe nhit ) Cc khe co dn ca mi nh c b tr thch ng vi vic cu to cc khe khe co dn ca ton b cng trnh. Vi cc b phn nh, di v mng thuc mi nh nh mi ua, mi ht, mi hin, sn... cn b tr khe co dn vi khong cch t 8-12m.

Ngoi vic m bo dn n t do, khe co dn cn phi c chng thm, chng dt ng qui cch. 7.5.5.3. Mi thp v tng vt Trong trng hp nh c mt bn mi thp v mt bn c tng vt cao hn th lp btng chng thm ca mi pha thp phi lm g cao ln 100, pha trn c cu to tn che sut dc g. This image has been resized. Click this bar to view the full image. The original image is sized 791x537.

This image has been resized. Click this bar to view the full image. The original image is sized 796x516.