1i th INT:::Rl\lA TIONAL BRICKlBLCCK MASONRY CONFERENCE UNIVERSITY, SHANGHAI, CHlNi .. 14 - 16 OCTOBER 1997 THE DESIGN OF BRICK MASONR Y Si'RVCTURE WITH CONCRETE COLUMN Shi Chuxian 1 Liu Guiqiu 2 Wu v".:nchao 3 1. ABSTRACT This paper proposes calculation methods on the compressive and shear load - bearing capacity for brick masc. .lTy structure with concrete culumn and reinforced network. And furthermore con- structional measures are stipulated specifically. This structure is suitable be adopted 11S the wall of the ordinary building in the region and seismic region fc: the grade 6,7 of intensity of earthquake (GIE 6,7). 2. INTRODUC'!'ION The brick masonry structure with concrete column is a kind of the composite wall masonry s:ructure with reinforced concrete constructional column vertically in the masonry wall, or further- more with reinforced network horizontally in the hed joints (Fig.1) . !n general, the cross section Df the column is 240mm x 240mm ir: dimension, longitudinal reinforce':'lents are 44>12, stirruflS are 4>6 @200 . In view of the less cross section and low reinforcement ratio of the coh.:nn, it is called con- structional column. The reinforced network in the horizontal bed joints is made by steel wire which diameter is 4mm. The spaing Df concrete column in the wall, the size of reinforcing fabric hole and the vertical spacing of reinforcing fabric may be determined by calculation. The combined action Df the concrete column, reinforced network and masonry increases the compressive strength of the ma- sonry wall. Above ali, because of c10sed system formed by the rei'1Íorced concrete column and ring beam installed at the levei of floor system, it restrains masonry more greatly and increases ductility Keywords: Masonry Structure, Reinforced Constructional Column, Reinforced Network, Compressive Load - Bearing Capacity, Shear Strength I Professor, Dept . of civil Engineering, Hunan University, China, Changsha 410082 2 Lecture, Dector Postgraduate 3 Engineer 873
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THE DESIGN OF BRICK MASONR Y Si'RVCTURE WITH CONCRETE … · Brick masonry wall with concrete column and reinforced network in the horiwntal mortar joints has been tested on test
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10NGJ~ UNIVERSITY, SHANGHAI, CHlNi .. 14 - 16 OCTOBER 1997
THE DESIGN OF BRICK MASONR Y Si'RVCTURE WITH CONCRETE COLUMN
Shi Chuxian1 Liu Guiqiu2 Wu v".:nchao3
1. ABSTRACT
This paper proposes calculation methods on the compressive and shear load - bearing capacity
for brick masc..lTy structure with concrete culumn and reinforced network. And furthermore con
structional measures are stipulated specifically. This structure is suitable ~o be adopted 11S the wall of
the ordinary building in the un~ortified region and seismic region fc: the grade 6,7 of intensity of
earthquake (GIE 6,7).
2. INTRODUC'!'ION
The brick masonry structure with concrete column is a kind of the composite wall masonry
s:ructure with reinforced concrete constructional column vertically in the masonry wall, or further
more with reinforced network horizontally in the hed joints (Fig.1) . !n general, the cross section Df
the column is 240mm x 240mm ir: dimension, longitudinal reinforce':'lents are 44>12, stirruflS are 4>6 @200 . In view of the less cross section and low reinforcement ratio of the coh.:nn, it is called con
structional column. The reinforced network in the horizontal bed joints is made by steel wire which
diameter is 4mm. The spaing Df concrete column in the wall, the size of reinforcing fabric hole and
the vertical spacing of reinforcing fabric may be determined by calculation. The combined action Df
the concrete column, reinforced network and masonry increases the compressive strength of the ma
sonry wall. Above ali, because of c10sed system formed by the rei'1Íorced concrete column and ring
beam installed at the levei of floor system, it restrains masonry more greatly and increases ductility
4.2 Factors influencing the shear load - bearing capacity
There are still three aspects influencing the shear load - bearing capacity of this kind of masonry
wall as follows in addition to the shear strength of unreinforced masonry and vertical compressive
stress[2] .
( 1) Effect of constructional colurnn and ring beam
Before masonry wall cracks. the strain of concrete and reinforcement in the constructional col
umn and ring beam is tiny . The effect of constructional column and ring beam on masonry is not ob-
877
vious . Once diagonal cracks of masonry wall appear, the defonnation of masonry wall beoomes great
increasingly with the increase of diagonal cracks (Fig . 6). The deformation especially reflects that
small triangle blocks on both sides fonned by "x" - shaped cracks are pushed outwards. It is
"Frame" fonned by oonstructional oolumn and ring beam that restrains small triangle block moving
outwards. Hence, the development of diagonal cracks of masonny wall is oonfined while the shear
strength and ducülity of masonry wall are enhanced . On the other hand, owing to the oonstructional
oolumn on the side of wall and horizontal steel - wire nets in the masonry stretching into oonstruc
tional oolumn, the anchorage behavior of steel - wire nets is strengthened . And meantime, the shear
strength and ductility of masonry wall have been improved a }ittle. It is shown from the experiment
thanhe shear strength of brick masonry wall with concreteoonstructional oolumn is 10 - 15 %
greater than that of brick masonry wall without ooncrete oonstructional oolumn. This paper lets the
shear strength increase factor .pl' owing to oonstructional oolumn and ring bearn equal to 1 . 1 more
reliably.
~
I I Fig.6 Cracks of Masonry Wall onder Shear
(2) Effect of horizontal steel - wire nets
After horizontal steel- wire nets are installed in the masonry, the reinforcement of steel - wire
nets in the longitudinal direction of wall bears horizontal shear force and therefore stands tensile, the
short reinforcement in the width direction of wall is chiefly acting on anchorage . Thereby aseismic
.behavior of masonry wall has been furtherly improved .
Test results show that the stress of steel bars in the reinforced network is very little before
cracks of masonry wall appear. Once masonry wall cracks, the stress in the wall is redistributed.
The fonner tensile stress of masonry on the cracked section is bom by reinforcement through cracks.
Then the stress of reinforcement through cracks is greatly raised . Owing to the greater stress in the
middle of wall, cracks are produced in the middle at first. Hence, rules of stress distribution of rein
forcement in the wall are that the stress in the middle is greatest but least on the comer . Part of re
inforcement éan be yielded under ultimate, load.
(3) Influence of dimension of masonry wall
The ratio of the height to the width of wall Àh(H!B) greatly influences the shear strength of
masonry wall. Influences are reflected in the aspect that stress states and' failure patterns of masonry
wall are different . When the ratio of height to width of specimen is greater, masonry wall takes on
the characteristic of bending - pattem failure. On the oontrary, shearing - pattem failure is taken
on. Bending - shearing failure is a kind of failure pattem between two patterns as stated above . In
general, the greater the ratio of height to width, the less the shear strength of masonry wall. Ac-
878
cording to the experimental analysis of 60 pieces of masonry wall. the factor of the effect of the ratio
of height to width of IJUIIIOnry wall tP2 may be calculated by the following fonnula:
tP2 = O. 96 - O. 68lgÀh (3)
4 . 3 Calculation of the aseismic load - bearing capacity of the cross section of masonry wall
The aseisrnic load - bearing capacity of the cross section of brick masonry wall with concrete
constructional column and reinforced network chiefly consists of shear strength of unreinforced ma-
sonry • effect of horizontal steel - wire nets. oon.structiona! column and ring beam and 50 on.
Based on the experimental results of shear strength of 34 pieces of masonry wall with reinforced
network (specimen is 1000mm x 1000mm x 240mm in dimension). the average value of shear
strength of brick masonry with reinforced network may be evaluated by the following fonnula
f •• v.m = O. 75fv.m + 0.4pfyk + 0.4<10
If the dimension of masonry wall is not the same as mentioned above. then
f •. v.m = 0 .75fv.m + 0 . 4À h pfYk + 0.4<10
where fv.m = average value of shear strength of masonry;
p = reinforcement ratio of vertical sectiona! area of steel- wire nets;
f yk = characteristic value of tensile strength of reinforcement .
(4)
(5)
Overviewing the statement mentioned above. the average value of the shear load - bearing capacity of brick masonry wall with concrete constructiona! column and reinforced network may be cal
culated by the following fonnula:
(6)
The test values ( f .. v ) from this paper have been compared with the calculated values ( f •. v )
obtained fram the fonnula (6) (table 3). The average value of f .. .! f •. vis 1.019 and the coefficient
of variation is O. 088 .
Table 3 Experimental resnlts of the shear strength
NO. of Wall 110
Àh Vu f .. v f •. v f .. .! f •. v
(MPa) (kN) (MPa) (MPa)
SW-l 0 . 800 1.17 218 . 8 0.729 0 . 707 1.031
SW-2 0.762 0.83 331. 7 0.790 0 . 714 1.106
SW-3 0.741 0 . 65 405.9 0.752 0 . 724 1.039
SW-4 0.762 0.83 329.2 0.784 0 . 800 0.980
SW-5 0 . 741 0.65 370.2 0.686 0.796 0.862
SW-6 0 . 741 0.65 342.6 0.634 0 . 578 1.097
In accordance with the stipuladon of literatures [4] and [5]. when the design valuesof
the strength of materials are adopted. the aseisrnic load - bearing capacity of the cross secion of brick
masonry wall with concrete constructional column and reinforced network is calculated by the fol-