11 th lNTERNA TIONAL BRlCKlBLOCK MASONR Y CONFERENCE

TONGTI UNlVERSITY, SHANGHAI, CHINA, 14 - 160CTOBER 1997

PROGRESS IN RESEARCHES AND APPLICATIONS OF EARTHQUAKE RESISTANCE AND SEISMIC ISOLATION FOR

MASONRY BUILDINGS IN CHINA

Xilin Lu l Xiaosong Xiao2

1. ABSTRACT

The dynamic properties of masonry structures, including earthquake resistance, seismic isolation, non-linear analysis, and some other comments on the recent situation and developing trends of research activities of masonry structures in China are presented in this paper.

2. INTRODUCTION

Masonry structure is a structural style which is widely used in civil engineering in China, it has long history of application. Because of its poor horizontal resistance, masonry structures often suffer damages in varying degrees under earthquakes. One still remembers the catastrophe by 1976 severe Tangsan earth uake. lt is a great challenge to human beings. How to deal with the challenge? After Tangsan earthquake, many research organizations in China have conducted researCh work on seismic behavior of masonry structures. A lot of tests and analysis have been made to study the seismic behavior of masonry structures and reduce their seismic hazard . Popular method of earthquake resistance is seismic fortification . However, the seismic fortification is based on artificial zoning of fortification intensity. With Iimitation of

Keywords: Progress; Masonry Buildings; Earthquake Resistance; Seismic Isolation

I Professor and Director, Research Institute ofEngineering Structures, Tongji University, Shanghai 200092,P.R.C.

2POSI-Doctorate, Research Institute ofEngineering Structures, Tongji University, Shanghai 200092,P.R.C.

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conditions, it is difficult to zone intensity and predict earthquake properly, and the difference between artificial zoning and practical intensity is great. For example, much greater Tangsan earthquake and Hyogo-Ken Nanbu earthquake occurred in the lower zoning intensity. So the other method of earthquake resistance is developed, i.e., seismic isolation. Many research organizations such as China Academy of Building Science, Tongji University, Harbin lnstitute of Engineering Mechanics, Central China University of Science and Technology, South China Construction University, have made considerable achievements in applied research on seismic isolation after many years of basic research and practical pilot projects. The primary conclusions are: seismic isolation design can greatly reduce natural frequency of multi-story buildings, evade the predominant period, ' isol<ite ãnd dissipate tfté seismic energy, decrease earthquake response, and enhance the earthquake disaster reduction capacities of masonry buildings.

This paper discusses the progress in research on dynamic properties of masonry structures, earthquake resistance, seismic isolation, non-linear analysis and some other aspects in China.

3, SHAKING TABLE TESTS AND RESEARCHES ON MASONRY STRUCTURES

After 1976 Tangsan strong earthquake, shaking table tests and researches on masonry structures have been widely carried out in China. Various tests and analysis have been done for masonry structures rrom model to prototype. There are also shaking table tests of masonry building model excited by two horizontal directions and both vertical and horizontal directions. There are also tests on both clay brick and concrete block masonry buildings, and unreinforced and reinforced masonry buildings. A lot of achievements have been made, which provi de design basis for masonry construction in China. Most of shaking table tests in China are listed in Table 1, based on available materiais.

Shaking table tests play important roles in seismic resistance of masonry buildings, and provi de a lot of design basis and data in China. Main progress of seismic resistance

- of masonry structures by shaking table tests are as follows: (l) to evaluate seismic capacity of structures: Lu and Zhu [1 J [2 J conducted shaking table tests on five-story

concrete masonry building , and developed the mathematical models of unreinforced concrete masonry buildings to predict the nonlinear earthquake response ofthe building, and estimated the seismic capacity of the building based on shaking table experiments and nonlinear analysis. (2) to study failure mechanism of the structures under earthquake: Li and Han's shaking table tests on five-story brick masonry building [3 J

have shown that there are different behaviors between brick masonry building subjected to horizontal excitation only and the masonry building subjected to both vertical and horizontal excitation. (3) to study the distribution of seismic forces in structures: Lu and Zhu [1 I study the distribution of seismic forces at various stages by five-story shaking table tests. (4) to find the weak stories of a structure: Zheng and Zhu [4 I study

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the weak location of the concrete masonry building with framed first story by shaking table tests on six-story concrete masonry building with framed fust story. (5) to study seismic strengthening measures ofthe structures: Zhu I S 1 and Zhou 161 study the role

of reinforced concrete columns and ring beam when strengthening existing masonry buildings.

/\ / .

'I , .

Table I - Shaking Table Tests in China

Units Type of masonry Stories Model Size Unrein[ ar Rein[ Time Ref.

Harl>in Institute of Brick Masonry I 113.5 Unreinf. Masomy 1980 Gao 17 ,

Engjneering Mechanics

Tangii l lniVetSity Concreto Masoruy 5 1/4 Uoreinf Masonry 1983 LuandZhu 1111 2

Xi'an Uni. ofConstruc. Brick Masoruy 4 1/6 Unreinf. Masonry 1985 Li UI

Science and Tech.

Tongii Univenity Concreu Masonl)' S 1/4 Unr.in[ Masoruy 1985 Zbu (51

Tongii Univ""ity Brick Masoory 5 1/4 Unrein[ Masonry 1987 Han '11

Tonltii Univenity v.>c.~. ;-(w." . ~ Cancrete Masonry 6 1/4 Uneein[ Masonry 1987 Zhou 161

Tangji University Concreu Masoruy 6 1/4 Unr.in[ Masonry 1988 Zheng cc J

wi1h framed fust SlO))

Harl>in lnstituu of Concreu Masonry 7 1/6 Unr.in[ Masonry 1992 Zhao 19'

Engjneering Mechanics

Oa.lian University of Brick Masoruy 8 1/4 Unreinf. Masonry 1994 Huang and Wu I 10

Science and Technology

Tongii University 6 1/4 Rein[ Masonry 1997 Zhu 111 J

Tangii University Conerete Masonry 6 1/6 Rein[ Masonry 1997 Shi (111

4. NON-LINEAR ANAL YSIS OF MASONRY STRUCTURES

Numerical analysis for masonry structures has been done in China since 1970s from static analysis to nonlinear analysis. Among the few studies that report on the experimental1y measured damping properties of masonry, there is no c1ear consensus. Jiuqian and Maogong I 13 1 observed a sudden drop in stiffness, of up to 60% of the

original value following first cracking, their recorded damping values ranged from 1 % to 5%, under low and high axial compressive stresses respectively. ~s, researches on analysis methods of earthquake response for multistory brick masonry buildings started. Properties of m~~~nry is considered in average, and masonry is modeled as a isotropic continuum. Lil-lear elastic finite e1em~~re becoming popular to ~stablish th( state of ~tress in complex masonry structures. This linear elastic analysis may be useful in providing some guidance as to the governing failure mo de, ultimate elastic capacity, natural frequencies, mode shapes, and modal participation factors of uncracked masonry buildings, but they provide limited insight into the ultimate strength and seismic behavior of such structures, the method also produces unavoidable local

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stress concentrations which require careful interpretation. ~gniZing these lirnitation, some researchers have investigated the adequacy af specíal nonlinear and cracking finite elem~ in studying the non.!!near ~ei~rnic beha~reS' r4-1. Both

discrete-crack and smeared-crack formulatio~ have been tried. The ability to ~omp~y predict the seisrnic response of masonI)' structures will be obviously improved in relation to advances in the modeling of masonry material itself through finite element analysis. The boundary eIement method and the distinct element model, proposed a1tematives to the finite eIement method, are a1so currentIy beíng considered by some researchers for the study of masonry buíldings [IS I . A comprehensive hysteretic model which captures the seisrnic behavior of masonry while considering its heterogeneous nature, with íts ínherent and complex interaction 01' mortar, brick, layering pattems, and other distinctive features, remaíns elusive. As practicing engineers have conventionalIy treated masonry as a linear elastic homogeneous isotropic material whose properties are obtained from standard static tests, most researchers also have a preference for this simplified mode!. Yet some attempts to develop more advanced hysteretic models to capture the aforementioned experimentally observed nonlinear behavior are noteworthy. The method based on improved equivalent linearization, and the analysis methods of non-linear earthquake response under two horizontal earthquake and a inter-stoI)' restoring force model suited for non-linear range analysis of earthquake response were proposed [16 1 . In

1990s, non-linear analysis on earthquake response of high-rise reinforced concrete masonry buildings starts, in which the overall structural modeIs and the material models are inter-stoI)' flexure-shear model, elastoplasticity model with composite beam, restoring force model with trilinear degrading model [171 . In addition, various models

have been used to analyze elastic response, elastoplastic response and the full range analysis from elasticity to collapse of high-rise reinforced concrete masonry buildings under earthquakes [161 [ 171 .

5. SEISMIC ISOLA TION OF MASONRY BUILDINGS

Because seisrnic fortification has poor accurate and is not enough to resist earthquakes. Mueh greater earthquake often oeeurred in the lower zoning intensity. So the other method of earthquake resistance is developed, i.e. , seisrnic isolation. Seisrnie isolation researches started in 1970s in China with its aetual engineering applieation beginning in 1980s. Most of isolation buildings eonstructed have widely used the rubber bearings now. Using these types of rubber bearings ean assure the building more safer in strong earthquakes, and it ean reduce the cost ofbuildings about 5-20% compared with the traditional base-fixed building. So more and more buildings in China will use these types of rubber bearings.

Four multi-stoI)' brick masonI)' buildings with sliding layer as isolator and steel eIements as energy dissipator have been constructed in west China, as shown in Fig. 1-2 [181 .

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up structure

toundotion

Fig. 1 Dry Friction Isolation Fig.2 Sliding layer

Five low rise brick masonry buildings with sliding slit isolation have been constructed in north China, as shown in Fig. 3 {18 I

sliding flaar

graund

Fig. 3 Sliding Slit at Bottom ofBuilding

In 1990s, base isolation researches are carried out vigorously in China. MuItistory buildings ofbase isolation have been put up in places such as communication equipment workshop of 6906 factory in Yueyang (19 I , and commerciaI and residential building in Shantou [19 I , this two buildings are reinforced concrete framed buildings, in some of

which vibration testing apparatus are to be installed to acquire data during earthquakes. The first LRB base isolated masonry building is constructed in the Beijing area 120 I.

The building as the teaching laboratory in The Anti-Disaster Technique College of State SeismologicaI Bureau was jointly designed by Institute ofEngineering Mechanics, State SeismologicaI Bureau and Beijing Jiucheng Cities ArchitecturaI Designing lnstitute in October, 1996, and it will be completed and put into use before September, 1997. This building is the first LRB, BIB in the Beijing area. lt is a 5-story brick masonry building, and its building area is 3700 m2 There are 71 LRBs which are installed under the building. The building's LRB arranging-diagram, the plane figure and sectionaI drawing are demonstrated in Fig.4-6. The building is located in Yanjiao, Beijing, where the basic earthquake intensity is VIll . According to the Code for Seismic

Design of Building(GBJ 1 1-89), it is not permitted to exceed I I m of the distance

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between the adjacent cross-walls ofbrick building, otherwise, onJy the frame structure could be adopted. Then, because of the adopting of the isolated technology, there has been a decrease greatIy in seismic action on the upper structure, and the maximum distance between the cross-waIl gets to 13 .5 m in designo And what is more, it satisfied the needs of the service function of cIassroom and Iaboratory, reduced the costs compared with the frame structure, and enhanced the seismic resistance of the structure.

I 1<4-1110

1

• ....... :t ...... • • T ... I ............. .. .. .. ... .. ....... • • .. 16HO ... , 1 ... ...... .. I· 5.32<40 ~I

Fig. 4 LRB Arranging-Diagram in Base IsoIated Building

Fig. 5 Base IsoIated Building Pla.."l

lUOO ...,..---

0.000 ~

L. .... - 2.100 ..... 110.. ....l1lI ..... 1

17200

Fig. 6 Base IsoIated Building Section

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After the isolated building was completed, a 3-dimension seismic response observation aITay was set up in the building. The construction of this BIB will accumulate experience for the coming construction of brick BIB in our country, and it will provide useful observation data for the further study on BIB.

Although base isolation researches and applications started re\atively late in China, it possesses a prospect of \vide application and wiU be one of directions for development of seismic engineering structures. Apart from base isolation, achievements are made in the researches and applications of inter -story seismic isolation in China for the purpose of adding story to old buildings and strengthening of the buildings [21 1 . In

China, a great deal of masonry buildings have been constructed. Many of those do not meet current code requirements. To solve the aseismic problem of those buildings in adcling story and strengthening of buildings, a new method, i.e., the inter-story seismic isolation are studied by Tongji University [211 . A I/7-scale six-story model which was

made of ash masonry was tested on simulated shaking table in Tongji University. The principie of the inter-story isolation is to use the mass of top structure, fix rubber bearings between the top mass and original roof, see Fig. 7. The absorber consists of rubber bearings and top mass to absorb seismic energy and reduce seismic response. The rubber bearing has good absorption behavior because of the fat hysteresis loop. After adopting this method, the structure damping ratio increases from 0.05 to 0.1. So the response decreases.

Rubber Bearing

Anti-heot Plote

(a)

Rubber Bearing

Adding Storey

Original Structure

(b)

Rubber Beoring

Fig 7 Inter-Story Isolation Methods

Adding Storey

Original Structure

(c)

Experimental researches and theoretical analysis have shown that inter-story isolation can reduce the base shear of original buildings by 20-23%. The seisrnic capacity after isolation is better than original one. This method is not only used in adding story to old buildings and strengthening of buildings, but a1so new buildings. Especially, it can be used for reducing seismic responses as second defense. It will not affect building function, and it is an idea method to reduce seisrnic effect.

Many tests have been finished and some sets of calculating theory of seismic

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isolation system have been established in China now [18 I . The tests include two kind of

work : (1) Test of isolator and energy dissipators: Static tests of full scale elements, pseudo-static tests, low cycle fatigue tests. A series of pseudo-static testS'Were finished for rubber bearings, sliding layer, curved plates and mction layer [18 I. (2) Shaking table

tests for large scale structural model: Various model with sliding layer and curve steel plate on shaking table were conducted [18 I .

6. CONCLUSIONS

Masonry structure is a traditional structural style which is widely used in civil engineering in China, it has long history of application. The greater progress in research on dynamic properties of masonry structures, earthquake resistance, seismic isolation, non-linear analysis and some other aspects have been achieved in China.

REFERNCES

1, Lu Xilin, and Zhu Bolong, and Weimin, Identification of Nonlinear Structural Parameters of Multi-Degree-of-Freedom Systems, Proceedings of International Workshop on E. E., Vol 2, March, 1984, Shanghai, P. R. China.

2, Lu Xilin, and Zhu Bolong, Identification for the Mathematical Models to Predict the Earthquake Responses of the Unreinforced Concrete Block Masonry Building and Estimation ofIts Aseismic Capacity, Proceedings of US-PRC Joint Workshop on Seismic Resistance of Masonry Structures, May 1985, Harbin, China, I11-7-III 8.

3, Han Lihua, Seismic Response of Multi-Story Brick Building to Both Horizontal and Vertical Excitation, Ph.D Thesis, Research Institute ofEngineering Structures, Tongji University, Shanghai, P. R. China, 1987.

4, Zheng Wei, A Study on System Identification and Seismic Behavior of Block Masonry Building under Earthquake, Master Thesis, Research Institute of Engineering Structures, Tongji University, Shanghai, P R. China, 1988.

5, Zhu Bolong, Wu Mingshun, and Zhou Deyuan, Shaking Table Study of A Five­Story Unreinforced Block Masonry Model Building Strengthening with Reinforced Concrete Columns and Tie Bars, Proceedings of US-PRC Joint Workshop on Seismic Resistance of Masonry Structures, May 1985, Harbin, China, IV-lI.

6, Zhou Deyuan, A Study on System Identification and Aseismic Behavior of Masonry Multi-Story Building under Bi-Directional Seismic Excitation, Ph.D Thesis, Research Institute ofEngineering Structures, Tongji University, Shanghai, P. R. China, 1987.

7, Gao Xunxue, etc., Experimental Research on Model Brick Building by Shaking Table, Proceedings of Internattonal Work5hop on E. E., Vol 11, May 1984.

8, Li Dechen, etc., Shaking Table Tests of Four Brick Masonry, Structural Laboratory, Xi'an University ofConstruction Science and Technology, 1985.

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9, Zhao Wei, The pararneter Identification of Seven-Story Building Mode! Made of Coal-Slag-Gas-Concrete Block, Proceeding of US/PRC Workshop on Experimental Method in Earthquake Engineering, The John A. Blurne Earthquake

Engineering Center, July 1993, 215-230. 10, Huang Weiping, Wu Ruifeng, and Zhang Qianguo, Study on the Analogy Between

Scale Models With Less Ballast and Their Prototypes under Shaking Table, Earthquake Engineering and Engineering Vibration, 1994, Vol. 14, No. 4, 64-71.

11, Zhu Bolong, etc., Shaking Table Test on Six-story Reinforced Concrete Masoruy Building with large Space , Research Institute of Engineering Structures, Tongji

University, 1997,4. 12, Shi Weixin, etc., Shaking Table Test on Six-story Hollow Concrete Masoruy

Building, Research Institute ofEngineering Structures, Tongji University, 1997,9.

13, x., Jiuqian, and c., Maogong, Experimental Study on Aseisrnic Behavior ofBrick Buildings, Proceedings of the Eight World Conference on Earthquake Engineering, San Francisco, Calif., 1984, Vol. 6, 831-838.

14, Qin Wenxin, and Yuan Zhengfang, Criteria of Stability for Building Subjected to Earthquake Motion and Application, The Proceedings of the 1" Canada Masonry Symposillm, 1995, Hamilton, Canada.

15, Xiao Xiaosong, Investigation on Mechanical Properties of Masoruy with Nurnerical Modeling, Ph. D. Thesis, College of Structural Engineering, Tongji University, Shanghai, P. R. China, 1995.

16, Qin Wenxin, etc., Full Range Analysis of Earthquake Response of 15-Story Reinforced Concrete Block Masoruy Building, the Proceedings of Liaoning Aseismic Structllres Symposium, Shenyang, 1995.

17, Qi~ Wenxin and Wang Xinrnei, etc., A Seisrnic Analyzing Model for Reinforced Concrete Masoruy Buildings, World Infonnation on Earthquake Engineering, 1994, No.4, 24-29.

18, Zhou Fulin, etc., Recent Research Developrnents and Application on Seisrnic Isolation of Building in P . R. China, /nternational Workshop on Use of Rubber Based Bearingfor Earthquake Protection of Building, Shantou, China, May 1994, A-I - A-9.

19, Lu XiIin, etc., Seismic Design Theory of Building and Application, Tongji University Press, 1995.

20, The First LRB Base Isolation Building Constructed in the Beijing Area, Seismic Control of Structures, Technical News, Chinese Cornrnittee of Seisrnic Control for Structures, March 1997, No.4 .

21 , Shi Weixing and Zhu Bolong, The Seisrnic Response of Story Isolation Masoruy Building, /nternational Workshop on Use of Rubber Based Bearing for Earthquake Protection of Building, Shantou, China, May 1994, B-41 - B-48 .

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