1i th INT:::Rl\lA TIONAL BRICKlBLCCK MASONRY CONFERENCE

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

Keywords: Masonry Structure, Reinforced Concrf'~e, 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

so that this structural system possesses better aseismatic behavior. Based on the experimental re­

search and theoretical analysis, this paper propses the design and calcuation method for this kind of

wall masonry structure .

ooncrete ring beam

ooncrete column

unreinforced masonry

masonry with ~~~~~~~~~~~re~úú~o~~;d~ne~t;w~or~k~~~ü---ll---~--~

a)Brick Masonry b)Brick Masonry Wall

Wall Structure Structure with Concrete

with Concrete Column Column and Reinforced Network

Figo1 Type of Structure

3 o CALCULATION OF THE LOAD - BEARING CAPACITY UNDER COMPRESSION o

The load - bearing wall in the building (Fig. 2) installs vertically ooncrete oonstructional 001-

umn, the spacing of which is s and installs horizontally concrete ring beam at the levei of flaor sys­

tem. Under the action of load q, as a result of different stiffness between concrete column and ma­

sonry and the redistribution of internai force, the concrete colurnn shares the load on the wall. In

addition, ooncrete oolumn and ring beam constitute a kind of "weak frame" which restraint reduces

the transveral deformation of the masonry wall. Meanwhile the masonry surrounded by the weak

frame exists in the two - way compressive state. Besides, concrete column is favourable to increase

the compressive stability of the masonry wall .

q

J11111111

Figo2o

Five pieces (NO. 1-NO. 5) of masonry wall in ali have been tested under compression (I] . The

experimental results have shown that under the action of load q (Fig. 2), at the elastic stage, the

vertical oompressive stress of the masonry hetween two columns is large in the middle and small at

874

I

both ends . The maximum of stress decreases with the decrease of the sp&cing of oonstructional 001-

umn . At failure, ihe vertical oompressive stress in the wall obviously diffuses towards outside oon­

structional oolumn. The failure patterns are shown as Fig. 3 . Through the analysis of finite element

unlinear whole process, the main factor influencing the oompressive load - bearing capacity of ma­

sonry wall is spacing of oonstructional oolumn. Yet the height of the storey of the. building influences

little . The appearance, distribution and development of the cracks obtained from the calculation of

finite element method agree well with the experimental results. The calculated value of cracking load

(<!c,) is very dose to the experimental value . However, the experimental value of ultirnate load (qu)

is 20 . 4 % greater than the calculated value on an average (Table 1). The main reason is that it is

difficult for the calculated model to reflect oompletely the restrllÍnt caused by "weak frame", but the

design value obtained from this method is more reliable.

\I Ir \\ 7, f \' ~\\\~ / ''i /' /r ~ * ~-, r

No. 1 No.5

Fig.3 Failure Patterns 01 Muonry Wall wader Compression

Table 1 The comparison between the experimentai resnlts

and the ealcnlated resnlts from finfte element method

type of wall NO.1 NO. 2 NO.3

spacing of oolurnn (rnrn) 900 1000 1250

strength of brick (MPa) 7 . 35 6.55 7 . 35

strength of mortar (MPa) 2 . 79 5 . 96 2.79

cube strength of ooncrete (MPa) 19 . 76 20.30 19 . 76

yield strength of reinforcement (MPa) 290 290 290

<!c, the experimental value 2 . 30 2 . 83 2 . 11

(N/rnrn2) the calculated value 2 . 45 2 . 65 2 . 13

qu the experimental value 3 . 75 3 . 90 3 . 20

(N/mrn2) the calculated value 3.11 3 . 15 2.62

NO .4

1600

7 . 35

2 . 95

22 . 16

290

1.92

1.96

2.88

2 . 28

NO . 5

there are no oolumns on the both sides but one in the rniddl~

7 : 35

2 . 49

19 . 93

290

1. 55

1.64

1.99

1. 79

Based on the experiment and analysis mentioned above, concrete oolumn bears load in cornbina-

875

tion .with masonry, the load - bearing capacity of the composite member (Fig. 4) under the aetion

ofaxial compression may be caleulated by the following formula:

(1)

1J [

1 ] t i; - 3

(2)

where N = axial force caused by the design value of load;

'P- = the stability faetor of the eompressive member of the eomposite briek masonry, the

stability faetor of the compressive member of unreinforced masonry may also be

adopted approximately(3] ;

I = design value of masonry compressive strength;

A = cross sectional area of masonry;

1J = coeffieient of the combined aetion, when s/b< 4 let s/b = 4;

= spacing of conerete column in the longitudinal direetion of the wall;

b = width of conerete column in the longitudinal direetion of the wall;

Ic = design value of conerete compressive strength;

A c = cross seetional area of conerete colurnn;

r y = design value of the compressive strength of reinforeement;

A'. = eross seetional area of reinforeement .

b

L..-_+---, __ A

Fig.4 Cross Section of Masonry Wall

The strength inerease faetor "t stands for the ratio of the eompressive load - bearing eapaeity of

briek masonry wall with conerete eonstruetional colurnn to one of unreinforeed briek masonry wall .

Then "tI obtained from the formula (1) has been compared with "t obtained from the analysis of finite

element method shown in table 2. It can be shown from table 2 that the results of two ealeulation

methods mentioned above are very close to eaeh other apart from the situation that spaeing of column

is l.Om.

When steel - wire nets are plaeed horizontally in the mortar joints of wall masonry meanwhile,

the increase strength of wall masonry can be calculated according to the method from literature [3] .

876

Table 2 Comparison of the increase factor of strength

sem) r. y

1.0 3.139 2.098

1.5 1.998 1.813

2 .0 1.632 1. 602

2.5 1.453 1.446

3.0 1.349 1. 331

3 . 5 1.281 1.245

4 .0 1.234 1.181

4. ASEISMIC LOAD - BEARING CAPACITY CALCULATION

4. 1 Experimental method

r./r

1.496

1.102

1. 019

1.005

1.014

1.029

1.045

Brick masonry wall with concrete column and reinforced network in the horiwntal mortar joints

has been tested on test installation shown in Fig. 5. There are six pieces (SW - 1-SW - 6) of brick

masonry wall in all. At first. the vertical compressive load is exerted on the top of wall with four

hydraulic synchronism jack before..test. After the compressive force keeps stable. simulated dynamic

tests are being made with 'electro - hydraulic actuator system.

The aseismic behaviour of the brickwork structure has been reported in the literature [2]

D specimen

4 slip slab

2 electro - hydraulic actuator system. 3 displacement gauge

5 steel beam 6 hydraulic synchronism jack

7 anchor bar of battom beam 8 steel frame

Fig.5 Test Installation

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-

879

lowing fonnula:

V::;; _1_"'1"'2(0 . 75/v + 0.3À. hply + 0 . 18110)A YRE

whre V = design value of shear force of wall;

(7)

YRE = aseismic adjustment ooefficient of load - bearing capacity, to be taken acoording to

the stipulation of literature [5] ;

Iv = design value of shear strength of masonry on be unfortified design, to the taken ac­

oording to the stipulation of literature [3] ;

I y = design value of tensile strength of reinforcement;

110 = average oompressive stress of cross section of ma50nry oorresponding to the represen­

tative value of gravity load .

5. MAIN CONSTRUCTIONAL MEASURES

In order to oombine reinforced ooncrete oolumn, ring bearn and horizontal steel - wire nets with

masonry and improve state of stress and behavior of defonnation of ma50nry wall, the main oon­

structional ineasures as follows should be taken in the building.

(1) The grade of the strength of day b~ick shouldn' t be lower than MU7 . 5; the grade of the

strength of day brick shouldn' t be lower than MUI0 when steel - wire nets are installed in the ma-

5Onry; the grade of the strength of mortar shouldn' t be lower than M5; the grade of the strength of

ooncrete is not suitable to be lower than C20 .

(2) The least cross section of ooncrete oolumn should be 240mm x 240mm· in dimension; the

longitudinal steel - bars in the oolumn is suitable to be 4</>12, may be 4</>14 when necessary; tie bar

should be placed at the oonnection of oolumn and masonry wall .

(3) The spacing of ooncrete oolumn shouldn' t be greater than 4m. When the width of the hole

in the wall is greater than 3m, ooncrete columns should be installed on both sides of hole .

( 4) Reinforced ooncrete ring beam is installed on every storey in the building and should be

oonnected with ooncrete column.

(5) Reinforcement in the longitudinal direction of wall should be extended into concrete oolumn

or wall which oonnects with it and furthennore should meet the demand for anchorage of tensile re­

inforcement.

6. CONCLUSIONS

(1) This wall under oompression is regarded as a kind of oomposite structure . As a result of dif­

ferent rigidity between ooncrete oonstructional oolumn and masonny and redistribution of internai

stress and meanwhile restraint on masonry caused by ooncrete oolumn and ring beam, the oompres­

sive load - bearing capacity of the wall is raised in a larger degree and can be calculated by the fonnu­

la (1).

(2) It is the most obvious for spacing of oolumn to influence the oompressive load - bearing ca­

pacity of this wall. The spacing of ooncrete constructional column is not suitable to be greater than

4m when designed.

(3) The shear strength of wall is chiefly related to the grade of the strength of mortar, vertical

oompressive stress, the ratio of the height to the width of wall, reinforcement ratio of horizontal re­

inforcement and whether ooncrete oonstructional oolumns are installed or not and 50 on . The shear

880

load - bearing capacity of the masonry wall may be calculated by the formula (7).

(4) In order to make concrete column, ring beam and horiwntal reinforcement restrain mason­

ry effectively and bear load in cómbination with one another, the constructional measures this paper

has proposed are necessary.

REFERENCFS

1 . Shi Chuxian, The Calculation of the Load - Bearing Capacity of Brick Masonry Structure with

Concrete Constructional Column Subjected to Compression, Journal of Building Structures,

1996, (3) .

2. Shi Chuxian and Liang Jianguo, The Aseismic Behavior of Brick Masonry Wall with Concrete

Constructional Column and Reinforced Network, Journal of Building Structures, 1996, (9) .

3 . The Design Code of Masonry Structures GBJ3 - 88, Building Industry Publishing House of Chi­

na, Beijing, 1988.

4. The Common Unified Standard for Building Structures .Design GBJ68 - 84, Building Industry

Publishing House of China, 1984.

5. The Aseismic Design Code of Building GBJl1 - 89, Building Industry Publishing House of Chi­

na, Beijing, 1989 .

881