1. TNH TON KIM TRA VNG

a. L THUYT TNH TON- S xut hin ca vt nt trong btng khi chu lc, dn ti gim cng tit din v lm tng vng- S lm vic di hn ca kt cu BTCT, cn xt ti cc yu t t bin v co ngt cng nh tc dng di hn ca cc loi ti trng. Theo TCXDVN 356-2005, vng ton phn f c tnh nh sau:

f = f1 - f2 + f3

Trong : + f1: vng do tc dng ngn hn ca ton b ti trng + f2: vng do tc dng ngn hn ca ti trng di hn + f3: vng do tc dng di hn ca ti trng di hn

Vi kt cu sn lm vic theo hai phng, vic tnh vng ch tin trong thc hnh khi dng phng php PTHH c k n cc yu t trn khi tnh bin dng. Dng chng trnh SAFE 12.x tnh ton vng trong thit k cng trnh l ph hp vi s lm vic thc t ca cng trnh.- Ti trng: tnh ton vng thng thng a vo cc trng hp ti sau:

+ DEAD: ch k n trng lng bn thn (Self Weight Multiplier = 1)+ SDEAD: trng lng cc lp hon thin sn (Superimpose), v ti trng ph thm.

+ LIVE: hot ti tc dng ln sn. Theo TCVN 2737-1995, hot ti cng c thnh phn tc dng di hn, thng chim 20%-30% gi tr ca hot ti ton phn. thun tin v n gin ha vic khai bo ti trng vo chng trnh ta dng h s 0.3 cho thnh phn di hn ca hot ti.

b. CC BC KHAI BO TRONG M HNH TNH TON SAFE v12.3.0 M hnh s dng cng cc c trng hnh hc, vt liu v ti trng

K n tc dng ca vt nt: Crac king Analysis Options: Quick Tension

Rebar Specification: Ct thp b tr theo thit k

Phng php tnh cng sau khi nt Modulus of Rupture.

K n tc dng di hn: dng hai c trng l Creep Coefficient (CR) cho t bin v Shrinkage Strain (SH) cho co ngt.Theo tiu chun Eurocode 2 vi cc iu kin: thi gian di hn, nhit v m mi trng theo iu kin Vit Nam, tnh ra: CR=1.7 v SH=0.0003

Cc t hp tnh vng: define trong Load Cases+ f1 = 1*DEAD+1*SDEAD+1*LIVE( vng do tc dng ngn hn ca ton b ti trng)

Vi Analysis Type l Nonlinear (Crac ked).

+ f2 = 1*DEAD+1*SDEAD+0.3*LIVE

( vng do tc dng ngn hn ca ti trng di hn)

Vi Analysis Type l Nonlinear (Crac ked)

+ f3 = 1*DEAD+1*SDEAD+0.3*LIVE( vng do tc dng di hn ca ti trng di hn)

Vi Analysis Type l Nonlinear (Longterm Crac ked); CR=1.7 v SH=0.0003 Kt qu, ly vi vng max (n v mm):

+ f = f1 - f2 + f3

INCLUDEPICTURE "C:\\Users\\NGUYEN~1.ACE\\AppData\\Local\\Temp\\scl8.PNG" \* MERGEFORMATINET c. KT QU TNH VNG BNG PHN MM SAFE

- vng:

f1 = 8.35 mm ( vng do tc dng ngn hn ca ton b ti trng)

f2 = 7.50 mm ( vng do tc dng ngn hn ca ti trng di hn)

f3 = 21.21 mm ( vng do tc dng di hn ca ti trng di hn) vng ton phn:

f = f1 - f2 + f3 = 8.35 7.50 + 21.21 = 22.06 mm < [f]= 25 mm ( vng gii hn theo TCVN)