11th INTERNATIONAL BRICKJBLOCK MASONRY CONFERENCE TONGTI UNTVERSITY, SHANGHAI, CHINA, 14 - 16 OCTOBER 1997

THE STATE-OF-ARTS OF THE MASONRY STRUCTURES IN CHINA

WuRulfeng

The history of masonry structures in China dated back thousands of years. More than 90% of the residentiaI houses were constructed by masonry wall system. However, prior to the~Shan Earthquake.J1 976)i the deveIopment of masonry structure technoIogy was very sIow. The main material for masonry is c1ay brick of lower strength (about 10MPa) in a dimension of 240 x 115 x 53mm. Unfortunately, almost alI the masonry

structures were unreinforced. The damage to masonry buildings in TangShan city during its 1976 Earthquake (Magnitude 7.8) is presented in Table I.

T bl I a e Th D e amage o fM 1· u tlStOry M asonry B ·Id· UI mgsm T Sh C" ang: an lty

Earthquake Total number Damage levei Percentage

intensity of buildings collapsed partially seriously damaged lightly of ollapsed collapsed damaged damaged buildings

XI 952 664 115 111 17 45 81.8

X 235 107 47 47 16 18 65.5

From Table 1, we can see that over 80% of the masonry buildings were wholly or partially collapsed. It was the most tragic catastrophe ever happened in the earthquake history in this country in recently years

China is a developing country, so the masonry structure should be the main type for the residential buildings in the corning decades. The studies, in improvrng the aseismic performance of brick masonry structure at lower cost are therefore, of urgency and great significance before Chinese scholars and engineers.

Professor ofDepartment ofEngineering Mechanics, Dalian University ofTechnology, Dalian, 116023, China

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[t is well known that the urueinforced masonry structures suffered a fatal weakness -

their brittleness. They would be easily damaged and even destroyed under severe earthquake motions.The structure collapse would happen if the horizontal earthquake action is beyond the lateral bearing capacity of the masonry structure or the limit lateral displacement.

Could we find a method from which the s!:rength ~~ of the masonry wall and integrity of the masonry structure would be enhanced, at a little expense of increasing cost?

The following methods had been tried and brought to practice:

1. To set constructional RC columns

The basic bearing element of the brick masonrj structure is brick walI. A brick wall possesses certain bearing strength but little ductility. Once being cracked during reciprocating earthquake motions, it would be easily broken apart. AmeJiorative measures would be taken to reinforce it and fasten the ties between walls. There are many ways to reinforce a brick wall: The first is by planting the bricklblock holes with vertical steel reinforcement and then grouted with concrete. The second, for solid or hollow brick walls, the steel reinforcements are to be planted in horizontal mortar joints. The third, is to build the so-called RC constructional colurnns at the two ends of the walI. The purpose for using these RC colurims is to deJay the breaking duration of the cracked brick masonry and then to improve the ductility of the wall about 3 - 5 times

than that of the plain masonry walI. This idea was accidentalJy discovered at TangShan Earthquake Zone. At the earthquake zone of intensity 10 and 11 there still existed some erected masonry buildings after the earthquake. One of these was a hotel , which was composed of 7-storey masonry building at its central part and with 5-storey and 6-storey buildings on its both sides. It was built during the HaiCheng Earthquake (1975, Feb. , Magnitude 7.2) period. For safety reasons, 16 RC colurnns were inserted around the perimeter at its central parto During the TangShan Earthquake, the 5-storey and 6-storey buildings on both sides were collapsed, the central building was serious darnaged but survived!

The experimental study on the masonry wall with constructional RC columns and collar beams has started in China since 1976. The constructional colurnns and collar beams would be treated as a cagelike space structure. If the masonry building was constructed with RC columns and beams, it would not only enhance the strength and deform ability of the structure, but also its integrity as welI.

A standard had been published by the Ministry of Construction in 1982 and revised in 1994 as 1G1-82 and 1G113-94 respectiveJy - aseismic technical specification for

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multistorey masonry building with RC tie columns. The promising effects of such measures were exhibited during Daofu Earthquake (1981 , Magnitude 6.9) in SiChuan province.

It is of worthy to note that the RC collar beams are necessary if the constructional columns are set to confme the masonry wall, and the constructional measures are also

reassured to guarantee the RC columns and beams would not be broken apart from masonry until the wall is collapsed.

2. To set horizontal steel reinforcement in bed joint n --Ti l--I--{ --- -Ir

If the horizontal reinforcements are hooked to vertical bars of columns at both sides, the effective action of horizontal steel would be dominant. The results [3] had been shown that the average stress of horizontal bars in the bed joint are about 62% of its yield strength if those were hooked to the vertical bars of columns at both sides. It could also improve the ductility of the waIl.

3. To set the horizontal reinforced concrete strips along the height of masonry wall.

In practice, one or two horizontal concrete strips, 120 rnm in height with 2<1>12 steel bars are to be set in the masonry wall, it would change the cracking pattem of the wall from diagonal to horizontal. Once the horizontal cracks along the top or bottom of the strips have been occurred, the masonry blocks would slide between the masonry and the strips under reciprocal action and then the earthquake energy be reduced. The stress in horizontal bars of the strip are small, but it would increase the dowel action of the vertical bars in the column [4].

4. Composite Masonry

The concept of composite masonry has been further developed since 1987. The main difference between composite wall and the wall with conslructional columns is lhat the columns are not structural , but theoretical. That is to say that should the RC columns and beams not break away from masonry until the wall is collapsed, their contribution to the resistance of compression tension and shear as with masonry may also effective. In fact, the composlte wall should be treated as a single structural element in the whole

structure. From lhe view of Slress state, lhe so-called confined columns would not be regarded as an independent column, in which lhe acting forces are transmitted by its bending action. If there are two rows of steel bar in lhe column, one of lhem should be in tension and the other in compression. However, in case of composite wall with two confineà columns aI both sides under horizontal load, lhe sign of sleel bars in one column will be the same in tension or compression, and for the other be contrary to it.

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Since the RC confmed columns, beam and masonry are combined in one structural

element, they would be confmed and supported each other to establish a good condition to develop their mechanical characters. For example, if the distance between confined columns is small enough, the most part of masonry unit would be in bi-compression stress state under vertical load, and thus its compression strength would also be enforced.

Due to the confined colurnns play a role in resistance of compression, shear, and bending moment, the composite wall system could be applied in the medium and high rise masonry building [5,6] .

Based on the static and dynamics experimental and theoretical studies on composite wall system building, a local technical specification in ShenYang metropolitan area has been published in 1994 [7], several million square meters of 8-storeymasonry buildings were built under this Specification.

A further deve10pment of the composite walI system was advanced to design the composite masonry buildings supported on frame-shear structure at lower storeies and

with large space at the first story. 'L' '1--r Pc ,).',' j'," ;' :1 ~

{ r f!i.22... j

In these cases, the supporting beam is an imporlãnTstruc ral element. A study 011 bearing state of frame supporting beam had been conducted. The static experimental and FEM analysis had shown that the a largepart of vertical 10ad is transmitted directly through each confmed column, which are located on the frame columns. By taking account ofthe inner arch action ofthe masonry walI, only about 1/3 ofthe total vertical load actuaIly exists on the supporting beam [8-10].

Three 1:4 scale 8-storey mode! composite wall buildings had been tested on the earthquake simulating shaking table to leam the aseismic performance of such buildings. Dynamic and reliability analysis ofthese three 8-storey wall buildings (the first one is a composite wall building, the second and the third were supported on frame-shear structure at first storey and the first two storeies respectively) had been indicated that ali of these buildings show good aseismic performance and satisfied the requirements for earthquake intensity of 8, if the stiffness ratio between the frame-shear storey to the adjacent masonry wall storey be restricted in 1.2 - 1.6 to avoid the concentration of

deformations.

The lateral strength and stiffness of a masonry wall supported on frame should be reduced if it is compared with the wall on stiff floor. This phenomenon was discovered in recent tests and was illustrated by FEM analysis.

5. Reinforced hollow c1ay brick grouted masonry structure

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That is similar to those used in the US had been stuàied and some 7-storey residential buildings at earthquake zone ofintensity 8 had been constructed in Xi'an. The results of more than 100 wall specimens revealed that the reinforced hollow brick grouted masonry walls had good aseismic behavior, but of higher cost than the ordinary solid clay brick and more complicated constructional techniques were required. This type of masonry structures had not been developed until 1994. Recently, a srudy on reinforced hollow concrete block grouted masonry structures to be on the way in Shanghai, Harbin, and Shenyang. A 18-storey of such type of masonry pilot building is to be constructed on a trial application basis at Shanghai.

6. To make use of concept of composite for multistorey and bigh-rise masonry structures

A composite masonry wall means that the wall element includes masonry, RC confined colwnns and beams. A composite masonry structure and concrete walls, usually the concrete walls forming one or several individual tubes or boxes for resisting the bending moment and shear forces, such mixed or composite structures would show good aseismic performance and could be used to construct multi- or high-rise masonry buildings. Some experimental and preliminary studies had illustrated that those types of buildings could be constructed at the earthquake zone of intensity 7 and 8 [12-14].

7. Tbe concrete bollow block structures

The study on the hollow concrete block for a dimension of 390 x 190 x 190 mm began

in China since late of 1970's and a corresponding specification for design and construction (JGJl4-82, revised in 1994) was published by the Ministry ofConstruction in 1982.

In general, most of the improving methods effectively used in brick masonry structure, mentioned in the previous articles, could be used here too. However, the corresponding provisions in the Aseismic Design Code of GBJ 11-89 should be more strict as compared with brick masonry structures, bccause we are lack of experiences. It is expected that using of porous bearing bricks, hollow bricks, holIow concrete block, masonry structures are Iikely to be developed in the near future.

In conclusion, the so-called composite, which includes composite masonry wall and composite masonry structure, provides a feasible trend for future development in masonry structure. The reinforced grouted masonry wall is also a composite wall in which the reinforcement is evenly distributed in the masonry, while lhe reinforcemenl in lhe so-called composite masonry wall is ralher concentraled in the confined columns.

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References:

[1] Earthquake Damage of TangShan Earthquake, vol. 2, Earthquake Publishing Co. 1986.

(2] Dong J.c., Investigation of Earthquake Damage of DaFou county, Research Report, No 10, 1981, Institute ofEarthquake Engineering.

[3] Zhou B.Z., Xia J.Q., Experimental Study on Seismic Behavior of Brick Masonry with Horizontal Reinforcement, J. ofBuilding Structure, No 4, 1991, pp31-43.

(4] Dong J.C., The Experimental Study on Seismic Behavior of Masonry Walls with RC Constructional Columns and Horizontal Concrete Strips, Research Report, Sept. 1988, Institute of Earthquake Engineering.

[5] Wu R.F. etc., Test and Analysis ofBrick Walls with Reinforced Concrete Columns under Lateral Cyclic Loading, Proc. ofUS-PRC Bilateral Workshop on Earthquake Engineering, VoU, 1982, Harbin, China.

[6] Wu R.F ., Zhang Q.G., Medium and High-Rise Masonry Construction in China -

Research and Application ofComposite Masonry Wall System, Proc. of 11 WCEE, 1996, Acapulco, Mexico.

[7] Zhang Q.G., Chen D.G., Earthquake Resistant Design Code for Composite Masonry Wall System building in ShenYang Metropolitan Area (1995), Proc. of 1i WCEE, 1996, Acapulco, Mexico.

[8] Chen D.G., Wu R.F., A Study on the Earthquake Resistant Behavior of Composite Masonry Building Supported on Frame Shear Structure at the First Storey, Prac. of II WCEE, 1996, Acapu1co, Mexico.

[9] Zhuang Y.Z., Model Experimental Studies of Composite Masonry Structure Supported By Frame and Shear Walls, Ph.D. Thesis, Dep. Civil Eng., Dalian Univ. ofTech.,1996.1 .

[10] Liang X.W., etc ., Aseismic Tests and Analysis of Framed Continuous Wall Beam, Building Structures, No.9, 1996, pp3-8.

[11] Zhao Z.Z., etc. , Model Test of a 6-Storey RC-Masonry Mixed Structure with Fewer InternaI Longitudinal Walls under Reversed Cyclic Loading, J. of Building Structures, No.6, 1994, pp.2-I3.

[12] Lin Z.C., Fang E.H., Earthquake Sirnulation Test of a Multistorey RC Shear Wall Structure with Fewer internaI Longitudinal Walls and Large Spaces in Lower Storeies, J. of Building Structures, Vo1.18, No.2, 1997, pp.29-33 .

[13] Shen Q.F., The Study on the Feasibility ofHigh-Rise Composite Masonry Building, Ph.D. Thesis, Departmem af Engineering Mechanics, Dalian Univ. of Tech. , 1997.6.

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