Các thông số ảnh hưởng đến sức chống cắt của nút khung bê tông cốt thếp dạng chữ t

Cac thong so anh hu'dng den SLPC chdng cat cua nut

khung be tong cot thep dang chO t

Parameters for Joint Shear Strength of Exterior Beam-column Joints

Ngay nhan bai: 16/11/2014

Ngay sij^ bai: 20/12/2014

Ngay chap nhan dang: 27/02/2015

Tran Minh Tung

T O M TAT:

Bai bao phan tich ca che hinh thanh Iflc cat va sil lam viec cua

nut khung be tong cot thep dang chu! T Idii cong trinh chiu tai

tr^ng ngang. Sau thong so chinh anh hflcfng den sflc chong cat

cua nut khung hi t6ng cot thep dang chfl T dddc danh gia dfla

vao kit qua thi nghi?m cua 99 nut khung BTCT thdng qua phan

tich thong ke. Mpt thong so mdi co mtic anh hUcmg Icm han den

sijfc chong cat ciia ntit khung dUdc de xuat thay cho th6ng so anh

hddng titng dU0c biet den trUdc day. Thong s6 nay do do c6 the

ke Ain trong tinh toan siJtc chong cat ciia mit khung chii T.

Tii kh6a: niit khung, stlc ch6ng cat, dam BTCT, cot BTCT.

ABSTRACT

This paper analyses the mechanism that genrerates shear forces at

a reinforced concrete exterior beam-column joints subjected to

lateral loading. The shear mechanisms in the joint are presented

and discussed. A database of 99 exterior beam-coltman joints

was used to investigate the influences of six parameters on the

shear strength of the jomt. Finally a new influenced parameter

that replaces the conventional one is proposed for the joint shear

strength.

Keywords: beam-column joints; shear strength; beam, column,

TS. Tran Minh Tiing

Khoa Ky thu|t cong trinh, Tru6ng Dai hoc Ton Diic Thang,

E-mail: tranminhtung@tdt edu.vn

1,GlOlTHl6U

Nut Ichung bi tong cdt thep 1^ mot trong nhCnng bp phan ket cau de

bi hir hai nhat cua cong trinh nha cao tang bSng b^ tong cdt thep (BTCT)

dac biet la khi cdng trinh chju tai trong rung 13c ngang do d6ng dat hoae

do gio bao Idn. SU pha hiHy cua nut Ichung ndi chung va nut khung chijrT

noi ngng thudng din d^n sU sup do hoan toan ciJa cdng trinh vi phi hoal

tai nut khung thudng din den sU mat dn dinh ci^a he thdng cot trong

cdng trinh. De ddm bao SU d^o dai cua nut khung Ichi chiu tai ngang, dac

biet ia xhi trong rung lac do dong flat, cac tieu chuan thl^t ke 352R-02,

2002; ACI318R, 2008; AU, 1999; NZS-3101, 1995 [1-4] yeu cSu phSi ttnh

toan, cau tao cdt thep dai va cot th^p doc tai nut khung. Ngodi ra, cac qui

dmh ve cau tao cdt thep tai nut khung dac biet \h cau tao cua cdt th^p

dam neo vao cdt cung dUoc qui dinh chat che. Ben canh cac qui dmh ve

cau tao, cac tieu chuan thiet ke cdn yeu cau phai kiem tra kha nang chiu

cat ciia nut khung va vi|c kiem tra nay nhSm dam bSo nguyen Xic \i khi

cd liic ngang ldn thi kh^ nang chiu liic c^t cisa nut khung phii dij ldn de

dam bdo rang pha hoai neu cd se xay ra ddi vdi dam d vi tri ben ngodi

nut khung.

Mdt van di dat ra Id sU ldm v\ic cua nut khung BTCT khi cdng trinh

chiu tdi ngang Id rat phiJc tap va phu thuoc vdo nhieu thong so nhU kich

thudc, hinh dang, vat heu betong va thep,.,, Chinh vl sii phdc tap nay,

cdc hoc gia, cac nha nghien cdu van con cd nhieu quan diem khdng

thdng nhat ve phu'ong phap tinh toan sdc chong cSt cda nut khung. Mot

dieu rat de thay la cac tieu chuan neu tr#n di ta cdc cong thdc rat khac

nhau de dii tinh sdc chdng cdt cda nut khung. Trong bai bao nay triJdc

tien tdc gia trinh bay mot so quan diem chinh trong tinh toan sdc chfing

cdt cua nut khung va sau dd dya vao du' lieu ket qud thf nghidm ddi vdi

cdc nut khung dang chlJ'T da thu thap d^ phdn tich cac thdng so dnh

hudng den sdc chdng cdt ci!ia nut khung Vi^c phan tich cac thdng sd dnh

hudng dd ldm sang td han nhu'ng quan diem khdng nhat qudn v i sii ldm

viec cua nut khung, ben canh do nd cung giup tac gid de xuat mot thdng

so mdi cd anh hUdng rat ldn den sdc chong cSt cua niit khung dang chCtT,

2. CO CHE PHAT SINH LUC CATTAI NIJT KHUNG

Khi mot nut khung chCrT chju tac dyng cda lUc ngang, liic cat se dUoc

tao ra tai v[ tn loi cua nOt va co the gdy ra pha hoai c3t cho BTCT tai vi tri

do. Cac ndi va ngoai lUc tao ra tai niit khung chlJ'T duoc the hien tren

Hinh 1 Td hinh ve nay lUc cSt, V,^ phdt sinh tai niit chdT cd the duoc tfnh

theo cdng thiJc:

trong do V^ Id luc cat Ciia cgt vd T^ la liic cang cda cot th^p chju keo

ciia dam diioc tinh lan luot theo cdng thdc (2) va (3) nhii sau:

VJL + 0-5h,) (2)