11th INTERNA TIONAL BRICKJBLOCK MASONRY CONFERENCE

TONGJI UNIVERSITY, SHANGHAI, CHINA, 14 - 160CTOBER 1997

A 18-STORY SHEAR WALL STRUCTURE COMPOSED OF BRICKMASONRY ANDR.C WALLS

Liyan Lin I and Chunliang Zhang2

1.ABSTRACT

Based on analyzing tall residential structures, a new composite shear wall structure is presented in this paper, that for a shear wall structure system, to build shear walls at different position with various structural materiais and construction measures. More specifically, R.C walls casted in site are served as exterior walls and walls enclosing stairwells and elevator shafts, and restrained masonry is used to build interior load-bearing walls partially or entirely. Using this kind of composite shear wall structure slightly cuts down lateral stiffness of building, makes full use of the performance of various structural materiais, reduces cost of construction, and obtains betler benefits in practice.

Keywords: Composite shear wall structure; Restrained masonry; Lateral stiffness; Special-shaped Restrained column; R.C shear wall.

1Chief and seniar engineer, Liaoning Provincial Building Design and Research Institute, 84 Heping South Street, Shenyang 110005, China.

2Senior engineer, Liaoning Provincial Building Design and Research Institute, 84 Heping South Street, Shenyang 110005, China.

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2.INTRODUCTION

In developing history of residential structure in China, some structure systems had been arisen, such as large panel structure and R.C shear wall structure wholly casted in site, etc.

In recent years, many multistory and talI residences, ranging from 8 to 18 stories, have been erected in Shenyang city. R.C shear wall structure is usually designed for dwelling houses of 12 to 18 stories, but lhe cost of construction is higher. Within the regions which seismicity is 7, even though large bay shear wall structure is used, the stiffuess and strength of these buildings are more than enough. In order to reduce the cost of construction, a new composite shear walI structure is designed to build residences of 12 to 18 stories.

3.COMPOSITION OF TWO KJNDS OF SHEAR WALL

TalI residences can gcnerally be classified as point tower and board types. The ratio of height to width of board type residences is large, integral flexure and shear by earthquake are obvious, so the structure of this kind of residence is emphasis to study in this paper.

Researches on composite masonry wall residences (8 to 9 stories) in Shenyang city showed tha1, within sites which seismicity is 7, the flex'Ural influence on building is caused by earthquake when ratio of height to width of the building exceeds 2.2, and with the story of building increasing the influence grows quickly. The model tests on platform vibrator indicate that the integral flexure will produce tension stress and horizontal cracks in exterior longitudinal masonry walls, which induce seismic damage to such structure. The tension stress in masonry walls is usualIy resisted by the methods of controlling the ratio of height to width of walls and reinforcing concrete tie columns in masonry. With growth of building story, it is insutTtcient to only reinforce concrete tie columns in walls. It is accepted that R.C walls (thickness of walls is SlOOmm, to use compound thermal insulating measures) should be acted as outside walls in dwelling houses of 12 to 18 stories. The outside walls closed in four sides are important assurance for its overturning resistance and bearing capacity, and first line defending against twisting.

Interior horizontal and longitudinal walls are criticai parts to bear the vertical loads and shear of building, and may be buiIt by restrained

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masonry walis. The experimental study showed that the compressive strength and shear strength of masonry bound by concrete restrained columns and girts are obviously increased, and its ductility is more improved. Increments of these strength pertain to the size of restrained units of masonry. The strength and ductility of square restrained ullits of masonry are alI better than rectangular confined units which ratio of width to height is 2: 1 (increasing shear strength and ductility coefficient by 30 percent and 50 percent respectively). There-fore, in practice, considéring the condition of vertical force-bearing in walls, in lower several floors to lellgthell the limbs of restrailled concrete columns (special-shaped restrained columns which take the shape of + and T) forms strengthened restrained masonry, and gradually shortening the limbs up-wardly forms commOll restrailled masonry. Moreover, to lengthen limbs of restrained columns can bear mOle normal and shear force in masonry.

The connection method between masonry and R. C walls is first to build masonry walls and tongue its ends, and embeds horizontal reinforcements in masonry per 500mm in vertical direction which extend · into concrete walls poured finally. lt has been confirmed by many model tests of wall speci-mens that the integrality of such connection is better even if big earthquake has taken place.

The lateral stiffuess of building is supplied by both interior and exterior walls. The lateral stiffness of restrained masonry is not better than R. C walls, but for board type residences lower than 18 stories, the lateral stiffness after composing two kinds of walls is adequate even though large bay planning is used. That' wilI be confirmed in practical project mentioned late.

Restrained masonry may be built with gravity-carrying hollow brick, gravity-carrying concrete hollow block, and high-strength non-clay solid brick and high-strength mixed mortar.

Thus, interior masonry walls laid and outside R.C walls poured are com­posed on the principie of mechanics and settled separately in the locations to make full use of its behavior. Restrained masonry laid intemally supplies adequate lateral stiffness for building and plays the roles of shear resistance and bears loads on floors chiefly. Main functions of R.C walls poured extemalIy resist integral flexure and torsion, restrain masonry, and bear the vertical loads transmitted to outside walls. Along the vertical direction of building, the junction faces of two kinds of walls can vary with stories increasing, the length of limbs of restrained concrete columns gradualIy re-

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duce from bottom to top, and 1'erfonnances of masonry should be make full use of in upper several floors. For dwelling houses with special compli­cated plan and more stories, the interior walls in its lower several slories may be made of reinforced concrete.

4.PROJECT EXAMPLE---A high-rise residence for the Bureau of Shen­yang Electric Industry

The dwelling house for the Bureau of Shenyang Electric Industry isfirst building built by such composite shear wall structure in China. It is consist­ed of three board type blocks which are of 18, both 15 stories separately (Fig.l). Its lower three stories are shear wall-frames structureand support

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upper shear walls not to fali to the ground by beam-column structure through a equipment story 2m in height acted as structural transfer. Over and above there is dwelling house adopting the composite shear walls structure, its stories are 15, both 12 respectively. The basement is for civil air defense room and common garage, and supported by pile-raft founda­tion. The 18-story and a 15-story blocks of three residences are integrated with a podium in its lower three floors, such that forrn a twin towers structure with a large podium at bottom. Another 15-story building is separated with a aseismic joint above the ground levei, but joins previous two buildings together underground.

The shear stifIness ratio of upper shear walls to lower stories supported by beam-column should be appropriate. Considering the building is a experi­mental project, the lower walls should be strengthened (properly increasing walls and thickening shear walls, etc.) so that the shear stifIness ratio y of

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stories above and below the structural transfer story is little than 1.0 and, in this project, equal to 0.91. If upper walls wholly adopt 200mm thick RC shear wall, the ratio y is 1.33. So using restrained masonry in upper structure reduced ratio y by 0.42. In addition, since the gravity of masonry is lighter than RC wall, the axial compressive ratio of bottom columns is reduced by 0.07. These results of using restrained masonry are of advantage for building to resist earthquake.

The anti-seism standard of this building is set 7. The building is located at II type site and subjected to 0.5KN/m2 primary wind compression. Its total height is 54.3m and embedment depth of base­ment is 5.2m, see Fig.2.

The typical (from 4 to 18 story) struc-

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tural planning of the 18-story residence Fig.2. section see Fig.3. Outer walls are 200mm thick C25 RC shear wall that is wrapped by thermal insulating layer and protective coating outside. Inner horizontal walls space is large and adopt

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gravity-carrying hollow brick walls 240mm in width. But length of limbs of restrained columns vary with stories (Fig.4), such that the ratio of width to height of restrained masonry units in lower three stories is 1.14, in middle four stories is 1.28 and in upper eight stories is 1.43. Because of more openings, the bottom of interior longitudinal walls is 200111111 thick R.C walls and most of top walls are changed to use gravity-carrying hollow brick ma-sonry which width is 240mm. The floors are two-way slab poured in place and its thickness is 130mm.

Masonry used in this project built with gravity-bearinghollow brick, which its strength grade is MU15 and hole rate is 25%, and MIO mixed mortar. The size of hollow brick is same as comlllon brick but thickness is douhled.

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The compressive and shear strength and Fig.4. transverse walls details ductility index of restrained masonry de-pend 00 the ratio of its width to height, its compressive stress and strength, as weJI as strength and stiffuess of restrained columns. For these reasons some experi- mental studies have been jointly perform- ed by the Shenyang Construction Committee, our Institute as well as Dalian University of Technology, Harbin Institute of Engineering Mechanics of State Seismological Bureau and China Academy of Building Research, so the data for calculating can be offered.

The calculated results of the 18-story building are showed as follows:

(l).The periods in transverse are T1=1.02s, T2=0.291s and T3=0.155s and in longitudinal are T1=0.90s, T2=0.277s and T3=0.143s.

(2).Transverse displacement: Top displacement is 7.44mm due to wind and 13.47mm due to earthquake. Top relative displacement UIH equal to 1/8284 due to wind and 1/4574 due to earthquake. Maximum displacement of a story relative to its adjacent stories u/h equal to 1/6386, occurred at

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twelfth story, due to wind and 1/3457, occurred at fourteenth story, due to earthquake.

Longitudinal displacement: Top displacement is 2.2mm due to wind and 1O.86mm due to earthquake. Top relative displacement UIH equal to 1/28017 due to wind and 1/5670 due to earthquake. Maximum displacement of a story relative to its adjacent stories ulh equal to 1/18256, occurred at eighth story, due to willd and 1/3801, occurred at ninth story, due to earthquake.

(3 ).Base shear and bending moment:

The base shear Qex=5173.76KN and Qey=5266.73KN. The base bending moment Mex=183783KN-m and Mey=165100KN-m.

In additioll, for comparison, three structures with same planning have been allalyzed. The first is the composite shear wall structure mentioned earlier, the second is R.C shear wall structure (thíckness of walls is alI 200mm) and the third is frame structure with special shape columns, which was formed through removing restrained masonry in the fust structure. The results are showed in Tab.l.

T b 1 a. . companson Q f I I ed ca cu at I b resu ts h k y transverse eart qua · e aCÍlon max. relative

structures top displacement displacement between stories

U(mm) uIh 1.composite shear wall 13.47 1/3457 (story 14) 2.R.C shear wall 13.01 1/3629 (story 15) 3.special-shaped frame 20:52 1/2100 (story 12)

Tab. 1 shows that the stiffness of the first structure approach to the second and have great increment of stiffness, which supplied by masonry, by comparison with the third structure. The lateral stiffness includes tlexural stitrness and shear stiffness. Ol1ter walls in the first and second structures are R.C shear walls, its great flexural stiffhess is main part of lateral stiffness. The shear stiffness of interior masonry walls in the first structure is minor (the shear stiffness of 240mm thick masonry is only approximate half of 200mm thick R.C wall), but its proportion in lateral stifIness is small, so the lateral stiffness of the first structure is reduced a little, only 3.4 percent, by comparison with the second structure.

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The cost of 240mm thick load-bearillg hollow brick masonry in this project is 57 .53 yuan per square meter, and the cost of 200mm thick R.C shear wall is 160.38 yuan per square meter, so 102.85 yuan per square meter can be saved. Pure area of 240mm thick restrained masonry used in this project is of 1281 square meters, so the investment in this project has been reduced by l32,000 yuan.

5.CONCLUSION---Taking the road of Chinese developillg Illasoury struc­ture.

Composition was usually used to develop new structure in history. Various materiais were combined to produce new structural components (for example, prestressed reinforced concrete, steel tube concrete, etc.). Dif­ferent components were combined to produce new structures (for example, steel-timber roof truss, composite floor, etc.). Different styles of structures were composed to form new structure syslems (for example, steel frame and R.C core tube were combined to form composite tubular system applied to a high-rise building). The new composite structure concept represented in advance may be a attempt to develop masonry structure in China.

The developing of masonry structure in China has a 10ng history. At present, masonry structure is largely used to build dwelling houses, but non-reinforced and unrestrained masonry had bad performances when great earthquake took place. How to improve aseismic behavior of masonry structure and apply it to more high buildings is a direction to develop masonry structure. Reinforced maSOI.ry is much more used abroad. In consideration of national conditions in China, to organical1y combine common masonry with R.C to form a new structure system and take full advantage of various materiaIs will have wide prospects in future.

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