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Khoa hpc Ky thuat va Cong nghe i

Nghien cmi thyc nghiem kha nang chong choc thung cua san phang be tong cot thep du*o*c gia cwong boi cot soi kim loai vo djnh hinh

D^ng Cong Thu^t'*, Dinh Nggc Hieu', Truong Gia Toai^

'Khoa Xdy diptg Ddn ditng va Cong nghiep. Tnrdng Bai hoc Bach khoa - Dai hgc Da Ndng 'Khoa Xdy difng. Tnrang Dai hpc Klin true TP H6 Chi Minh

Ngay nhiin bSi 20/3/2017; ngdy chuyin phan bi^r 7/4/2017; ngay nhgn phan bi^n 28/5/2017; ngay chap nhan dang 31/5/2017

Tom tdt:

Nghien cihi aay nham hhao sdt bang thyc nghiSm kha ndng chdng chgc thung ciia san phang be tdng cot thep khdng diT ung luc khi dm^c gia cudng bdi cht sgi kim loai vo dinh hinh. Ket qua thi nghi€m duQ'c so sanh vdi cdc giai phdp khac cung duvc su dyng di gia cudng tai hen kit cgt - san nhu thep dai vd bulong chju cat. Ket qud thi nghif m cho thdy vi^c su dung cht sgl kim lo^i vo dinh hinh trong be tdng lam tang kha nang ch6ng choc thung va ung xu chuyen v; cua san so vdi gidi phap su* dung thep dai chiu cat vd bulong chju cat.

Tif khda: Choc thung, cot sai kim lo^i vd dinh hinh, sdn phang be tdng cdt thep, thi nghiem sdn phdng.

Chi sd phan loai: 2.1

Experimental study on the punching shear capacity of flat slab reinforced

with amorphous steel fibers

Cong Thuat Dang'*, Ngoc Hieu Dinh', Gia Toai 1>uong^

'Faculty of Civil Engineering. University of Science and Technology - The University ofDanang

^Faculty of Civil Engineering, Unbeersily of Architecture Ho Chi Minh City Received 20 March 2017; accepted31 May 2017

Abstract:

This experimental study has been carried out to investigate the punching shear capacity of flat concrete slabs reinforced by amorphous steel fibers (ASFs). The experimental results were compared to those of the different reinforcing solutions applied at the column- slab connection region using stirrups and stud rails.

The test results have shown that the use of ASFs in concrete could improve significantly the punching shear capacity of the fiat slab as well as the deflection of the slabs subjected under the testing load compared to the using of the stirrups or stud rails.

Keywords: Amorphous steel fibers, flat concrete slab, flat slab experiment, punching shear capacity.

Classification number: 2.1

Giin thieu

K6t cSu ska. phang hien dang dupe sir dijng rong rai trong cac cong trinh xay dung be tong c6t thep trong nucrc va tren thg gidi. Uu diem cua he san phang la ban san dugc Ice true tiep len dau cot cho phep tang tuong doi chieu cao thong ting, tao duac dp phang Ichong gian tran dep, thi cong ntianh, sii dung khdng gian linh hoat. Tuy nhiSn, sir lc6t hcfp momen uon va Ivc cat lan tai vi tri moi noi giiJa cot va san se gay ra pha hoai dot ngpt tai vi tri nay. Han niia, SII pha hoai tai cac vj tri nay se dan den su suy giam dang k^ kha nang chong tai trong diing ciia li6n kit c6t - san va din din su sup do cua toan h? ket cau (theo cac ngiiien cuu ciia Graf va Mefirain [1]; Hatcher va cpng su [2]). Vi vay, tai cac vi tri moi noi cpt - san can dupe gia cucmg dfi dam bao kha nang chju cat v^ kha nang chuySn vi (d6 deo).

Mot so ngtiien cuu thi^c nghiem a nuoc ngoai [3,4] da chi ra ring, kha nang chong choc thung tai vi tri lien ket cot - san ciia kit edu san phang bg tong cot thep phy thuoc vao nhilu ySu t6 nhu chieu day san, cucmg dp ciia cot thep chju uon, cudng dp be tong, kich thu6c cOt. Tii do, m^t so nghien ciiu sau nay da phat trien cac chi tiet thep de gia cucmg tai vi tri mu cpt de lam tang kha nang chong chpc thiing tai vi tri nay, nhu th6p cliiu cM dang bulong (head- studs) [5], tim carbon (shear CFRP sheets) [6], c6t thep ngang chiu cit [7], c6t sgi thep truyin thdng (steel fibers) [8,9]. d Vi?t Nam, nghign cum ly thuylt va mo phong s6 vl ling xir chpc thung ciia ket cau san phang da dupe thuc hien, nhimg cac so lieu th^c nghiem v6 vSn de nay con rat

'Tdc gid lien he: Email- dangcongthua

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I Khoa hpc Ky thu$t va Cdng nghe

h^n Che [10-12].

Hien nay, c6t spi kim loai vo dinh Iiinh (Amorphous steel fibers) la m$t lotii c6t spi phan tdn mdi duac che tao vcri cong nghe hoan toan khac so voi cot spi thep truyen thong. Loai cot spi nay co cucmg do chiu keo va khi nang chong an mon cao han cot spi thep, mem, de uon, kha nang phln tan cao trong be tong, va d?c hi§t la khong bi hi6n tuong an m6n kim loai. CJ nuoc ngoai, mot so nghien ciiu da sii loai c6t soi nay de tang kha nang Idem soat vet nurt ciia ciu kien be t6ng cot th6p trong qua trinh co ngot hay qua trinh chiu tai trpng [13, 14]. Tuy nhien, a Viet Nam, cac nghien cuu ciing nhu ling dung loai cot sgi nay vao cac kit edu cong trinh xay dung van chua dupe khao sat.

Trong nghien ciiu nay, kha nang chong chpc thung cua san phang be tong cot spi vo dinh hinh khdng du ling l\rc dupe nghien cuu bang thuc nghiem va so sanh voi cac phuang phap truyen thong khac nhu sii dung c6t th6p dai chiu cat va bulong chju cat. Tren ca so do, tinh hieu qua cua mau khi su dung cot spi v6 dmh hmh duac so sanh voi mau su dung cac phuang phap khac dua trfin hai chi tieu:

Cu6ng dp va khd nang chuyen vi tai lien ket cot - san.

MA ta thi' nghiAm Vat lifu

Trong nghien ciiu nay, be tdng vdi cucmg do nen mau tieu chuan kich thuac hinh try tron 100x200 mm d 28 ngay tu6i la 24 MPa, dupe xac dinh theo tieu chuan ASTM C39/

C39M [15]. C6t thep c6 gd vdi 3 loai dudng kuih 010, 013 va 024 dupe sii dung liim c5t th6p dpc chiu lv:c trong mau thi nghiem. Cudng do chiu keo d gidi han chay dupe xac dinh theo tieu chuan ASTM E8/E8M [16] lan lupt la 455, 430 va 465 MPa. Bulong chiu dt dung trong miu thi nghiem c6 dudng kinh 010, chieu dai 85 mm, cudng dp chiu keo d gidi han chdy la 400 MPa.

C6t spi th6p vo dinh hinh (ASFs) dupe sir dung trong nghien cuu la mot lo^i cdt spi mdi, co dang thang, dupe phdt triln bdi Cong ty POSCO - Bkn Qu6c {htlp://www.

posco.com/) (hinh la). Uu diem ciia loai cdt spi nay la qua trinh san xuit tilt ki?m nang lupng va giam khi thdi CO^

(it han 20% so vdi cot sai thep truyen th6ng), mdng, dl udn, trpng lupng rieng nhe, cudng dp chiu keo cao hem so vdi cot spi thep truyen thdng va dac biet la khdng co hien tupng an mon kim loEii. Hon nua, be mat cua phSn tii spi nhdm, co kha nang lam tang l\rc bam dmh giiia be tong va cot spi (hinh lb).

a. Hinh dgng cS't sfli kim lo^i b. Hinh 5nh khi qu§t duQi vo dinh hinh kfnh hiin vi di^n tiif Hinh 1. C5t soi kim loai v6 djnh hinh su' dung trong thi nghi€m.

ASFs CO trpng lupng rieng la 7200 kg/m^ cudng dp chiu keo la 1400 MPa va modul dan hdi la 14x10* MPa.

Trong khi dd, c6t spi thep truyin thong cd dang mdc d 2 diu, trpng luong rieng la 7850 kg/m^, cudng dp chiu keo la 1100 MPa va modul dan hdi la 20x10* MPa. Hinh 2 so sanh kich thudc hinh hpc cua cdt sod kim loai vd dinh hinh va c6t soi thep truySn thdng.

Oiilu cay- 29 Chi4u day 500 nm

a. C6t soi kim loai vo dinh hinh b. Cdt sgi thep truyen thdng Hinh 2. So sanh kfch thUdc hinh hoc cua cot sol kim loai vd djnh hinh va cdt s^ thep truyin thSng.

M&u thi nghiem

Trong nghien ciiu nay, cd 4 mSu duac thi nghi?m, bao gdm mau tieu chuan (TC), mau dupe gia cudng bdi bulong chiu cat d dau cdt (BL), mau dupe gia cudng bdi th^p dai chiu cat d diu cdt (TD), va miu sii dyng b6 tdng c6t soi thep vd djnh hinh (ASFs). Tit ca cac mSu thi nghiem diu c6 kich thudc 1800x1800 mm, chidu day san la 120 mm.

Trong san, cdt thep dpc chiu luc 013 dupe su dyng. Cpt dupe thidt ke lam viec trong giai doan dan hoi, vdi kich thudc tiet dien la 200x200 mm va cdt thep dpc chiu luc la 4024.

Theo khuyin cao tii nha san xuit, ham lupng ASFs hpp ly trong hon hpp be tdng dung trong cdc ket cau cdng trinh tu 0,6-0,8%. Vl vay, trong thi nghi?m nay, nhom n^idn ciiu lua chpn ham lupng cdt spi vd dinh hinh dupfc trdn trirc tilp vao hdn hpp be tdng vdi ham lupng la 0,8%. Kich thudc hinh hpc vd cau t^o cdt thdp ciia cac mau thi nghiem dupe trinh bay trong hinh 3. Trong nghidn ciiu nay, be tdng cot spi kim loai vd dinh hinh dupe sii dung cho toan bp tam san.

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A-A Don v|' mm b. M I U di/pc gia cUdng bdi bulong chju cat d dau cdt

A-A Bon vj* mm

c. M l u di/pc gia cLfdng bdi thdp dai chiu cat d d i u cot Hinh 3. Kich thUdc va caii tao edit thep c£ia mlu thi nghiem.

Thihleip thi nghiem

Luc tap trung theo phucmg thang diing dupe tac dung tai vi tri diu cot tren ciia cac mau thi nghiem thdng qua thilt bi gia tai la kich thuy luc 500 kN. Cau tao va hinh anh he thdng thi nghiem dupe trinh hay d hinh 4, bao gdm bd phan truyen dong, bd phan didu khien luc, va thiet bi do chuyin vi (LVDT) dat tai vi tri dSu cdt dudi. Tai trpng dung (P) dupe tac dung len mau thi nghiem vdi van tdc 0,03 mm/s cho den khi mau hi pha hoai. Chuydn vi (w) ciia mau va luc tac dung len man duac do va ghi nhan tai vi tri dau cpt dudi trong sudt qua trinh thi nghiem thdng qua mot may ghi dir lieu.

KHOA HOC I 20(9) 9.2017

I Khoa hpc Ky thu$t va Cong nghe

^

b. C£u tao hd thdng thi nghiem.

Hinh 4. H^ thdng thi nghi|m.

K6I Qua thi nghiem va phikn tich Kit qud du&ng cong Itrc - chuyin vi

Ket qua dudng cong luc (P) - chuyen vi (w) ciia cac mlu thi nghiem dupe trinh bay d hinh 5. Ta co the thay ring, d mlu tieu chuan (TC), sau khi dat gia tri luc Idn nhit (214,8 kN), dudng cong luc - chuyen vj syt giam mdt each dpt ngpt. Mau dupe gia cudng bdi th^p dai (TD) cimg thi hidn mot ling xu tuong tu mlu TC, tuy nhien kha nang chiu luc (258,8 kN) cao han so vdi mlu TC la 20,5%. Mlu dupe gia cudng bdi bulong chiu cit cho kha nang chiu luc cao hon chi khoang 4,6%, tuy nhien kha nang chuyin vi cao han 30,9%, va sau khi dat gia trj luc Idn nhat, dudng cong lire - chuyen vi sut giam mdt cdch tu tii. Ddi vdi mlu thi nghiem su dung cdt spi vd dinh hinh vdi ham lupng 0,8% (ASFs), gid tri luc va chuyin vi Idn nhit tuong ling dat 277,3 kN va 29,49 mm, tiic la cao hem

tuong ling 29 vd 72% so vdi mlu TC, ddng thdi, dudng cong lye - biln dting sut giam mdt cdch tii tii sau khi dat gid tri luc Idn nhit. Dilu nay chiing td cdt spi kim loai v6 dinh hinh sii dung trong hdn hpp be tong lam tang kha nang chdng chpc thung va khd nang chuyen vi cua mSu thi nghi$m. Ddng thdi, chung cd khd nang kiem soat cac vlt mit sau khi dat din hang thai gidi han chiu lire, giiip cho cdc kit ciu khdng bi pha hoai mot each ddt ngdt, tuong tit nhu cdt spi thep truyin thong [17].

10 20 30 40 H>(mm)

Hinh 5. Quan he lUc - chuyin vj.

Dac diim phd hoai mau

Trong nghien cihi nay, cdc mau thi nghiem dupe ke ti;r do ISn cdc gdi tua dat d 4 canh cua mau thi nghiem. Vi vdy, phin dien tich sdn xung quanh cdt se chiu tdc dyng ciia luc chpc thung cung nhu moment udn Idn nhat. Trong tat ca cdc mlu thi nghiem, cdc vet mit dau tien dupe hinh thanh trong viing chiu keo ciia tiet dien san gan vj tri cdt, sau do bl rpng va dien tich vung nut tang din ciing vdi s\r tang cua tai trpng (hinh 6).

Hinh 6. 0$c diem hinh thdi pha hoai mau.

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Khoa hpc Ky thuat va Cong nghe i

Hinh 6 cho thay hinh mlu ciia cac vlt nut dupe quan sdt bang mit thudng tai thdi dilm sau khi cdc mlu thi nghiem bi phd hojii. Trong trudng hap cdc mlu tieu chuin (TC), bulong chiu cit (BL), thep dai chiu cit (TD), mot sd lupng Idn cdc vet mit dupe hinh thanh xung quanh chu vi cdt vd gay ra sy phd hoai ciia viing be tdng d bl m^t bdn dudi cdc mlu thi nghidm, k6o theo su phd hoai hodn toan mau sau do. Tuy nhien, trong trudng hpp mlu thi nghiem vdi ham lupng 0,8% cdt spi vd dinh hinh trong h6n hpp be tdng (mlu ASFs), sd lupng cdc vdt mit it vd di$n tich cimg nhu be rpng cdc vet niit hep dupe quan sat sau khi mau hi phd ho£ti.

Dien tich viing phd ho^i ciing dupe do va the hidn d hinh 6. Ta cd thd thay rang, di?n tich viing pha hoai trong trudng hpp mau ASFs gan bang vdi mau TC va it han cdc mau cdn lai. Ngodi ra, sd lupng cdc vet mit quan sat dupe trong mlu ASFs it han nhilu so vdi tit cd cdc mlu TC, BL vd TD. Dieu ndy cd the dupe ly gidi bdi su hi?n dien ciia cdt spi vd dinh hinh trong hdn hpp be tdng da t£io ra hieu ling cau noi (bridging effect) giua cdc vlt niit xuat hien khi bi phd hoai, vd lam gidm sd lupng cdc vlt niit Idn cung nhu bd rdng khe nut [17].

Ket lu$n va Iu6n nghj

Bdi bdo da trinh bay ket qua nghien ciiu bang thyc nghiem de khao sdt tinh hipu qua cua cdt spi kim lo^i vd dinh hinh khi trdn vao trong be tdng den khd nang chdng chpc thiing ciia san phang be tdng cdt thep khdng du ling lire. Mpt s6 kit ludn cd thi nit ra tu ket qua thi nghifm nhu sau:

- Cdc phuang phap khdng chpc thiing tai lien ket cdt - sdn nhu sir dung bulong chju cdt, thdp dai chiu cit, cung nhu sii dung cdt spi kim logi vd dinh hinh trong h§n hpp be tdng diu lam tang kha nang khdng chpc thung tai vi tri nay.

- Mdu thi nghidm sii dyng cot spi kim loai vd dinh hinh trong hdn hcfp be tdng cd khd chiu tdi trpng chpc thung tai diu cdt Idn hem 29% so vdi mau tieu chuSn, va Idn han so vdi cdc mlu su dyng cdc bidn phdp gia cudng khdc.

- Dien tich vung phd hoai trong trudng hpp mlu sir dyng cdt spi kim loai vd dinh it han cdc mau cdn lai.

Ngodi ra, sd lupng cdc vet nut cung nhu be rdng khe nut quan sdt dupe trong mlu ASF it han nhilu so vdi cdc mlu tieu ehudn, bu Idng chiu cat, thep dai chiu cat.

Tfti LI|U THAM KHAO

HI WP Graf, M, Mehrain (1992), "Analysis and tesiing of a flat slab concrete building", Proceedings of Earthquake Engineering, iOth World Conference, Rotterdam, Netherlands, pp.3387-3392.

[2! D.S. Hatcher, M.A. Sozen, CP. Siess (1969), "Test of a reinforced concrete fiat slab", journal of the Structural Division lASCE), 95(ST6), pp.1051- 1072.

[3] P.E. Regan (1981), Behavior of Reinforced Concrete Flat Slabs, Construction Industry Research and Information Association, London, UK, Report 89, February, pp.1-a9.

[4| S. Lips, M.F. RUIZ, A. Mutloni [2012], "Experimental investigation on punching shear strength and deformation capacity of shear-reinforced slabs", ACt Structural Journal, 109(6), pp.889-900.

IS] C.B. Tan, S.C. Lee, S. Teng (2002), "Shear studs m slab<olumn connections with rectangular column", Proceedings of the 27th Conference on Our World in Concrete and Structures, Singapore, pp.569-574.

[6] M.R. Esfahani (2008), "Effect of cyclic loading on punching shear strength of slabs strengthened with carbon fiber polymer sheets". International Journal of Civil Engineering, 6(3), pp.208-215.

[71 M.M.G. InScio, A.P. Ramos, D.M.V Faria (2012], "Strengthening of flat slabs with transverse reinforcement by introduction of steel bolts using different anchorage approaches". Engineering Structures, 44, pp.63-77.

[8] S. Altoubat, A Yazdanbakhsh, K A Rieder (2009), 'Shear behavior of macro-synthetic fiber-rem forced concrete beams without stirrups", ACI Material yourna/, 106(4), pp.381-389.

[9) M.A. Tantary, A. Upadhyay, J. Prasad (2012), "Influence of steel fibers on the shear strength of concrete". Journal of Engineering, Computer and Applied Sciences, 1(1), pp.88-92.

[10] L& Kh^c HCing, TnWng Hoai Chinh (2011}, "S^n phing bg tflng Ong luc tiUflc cang sau thiS't l ^ theo phifong phSp khung tifong dUong va phuang ph^p phSn til hOU han", T^p chf Khoa hpc vA C6ng ngh$, Dai hoc Da Ning, 4(45), tr 65-74.

[111 Tmong Hoii Chfnh, Vo Trang Th^ng (2013), "Qui trinh sildijng kl't cau b§ tdng tJng lUc tn/6c tai Vi|t Nam vi nhOUg bSi hoc kinh nghiem", Tap chf Khoa hgc vi Cdng nghe, E>(ii hpc Da NSng, 5(66), tr.7-14.

[121 Tnjong HoJi Chinh (2016), "Nghi6n cOu Inh hiOng cOa hinh dang - kich thifdc mil cpt d4i\ sii lam vi^c v^ kha nang chju \iSc cija san phJng be tang OUg lu'c tnldc", Tap chi Khoa hpc vS Cdng ngh4, Oat hgc Da NSng, 1 (98), lr.15-20.

1131 H. Kim, C. Kim, J, Nam, J. Kim, S. Han, S. Lee (2015), "Static mechanical properties and impact resistance of amorphous metallic filMr- remforced concrete". Composite Structures, 134, pp.831-844.

1141 N.H. Dmh, K,K, Choi, H.S. Kim (2016), "Mechanical Properties and Modeling of Amorphous Metallic Fiber-Re info reed Concrete in Compression", Internationaijournal of Concrete Structures and Materials. "lOiD. pp.22]-23b.

II51 ASTM (2012b) C39/C39M-12a, Standard lest method for compressive strength of cylindrical concrete specimens, American Society for Testing and Materials (ASTM), WestConshohocken, PA, USA.

[161 ASTM (2012b) EB/ESM-12a, Standard Test Methods for Tension Testing of Metallic Materials, American Society for Testing and Materials (ASTM), WestConshohocken, PA, USA

[17] P.B, Sakthivel, A |agannathan, R. Padmanaban (2012), "Thin cementitious slabs reinforced with stainless steel fibers", youffa'o^Mec/ian/ca) and Civil Engineering. 4(2), pp.39-45.

KHMHOC I 20(9) 9.2017