11 th INTERNA TIONAL BRICKlBLOCK MASONRY CONFERENCE

TONGJI UNIVERSITY, SHANGHAI, CHINA, 14 - 16 OCTOBER 1997

RESEARCH ON BASE ISOLATION ABILITY OF THE STEEL TUBE CONCRETE SHORT COLUMN BEARING FOR MASONRY BUILDINGS

Wang Wei1 Wang Huanding2 Zhang Ying3

ABSTRACT

For the isolation method of the Concrete Filled Steel Tube Short column bearing, We

analyze its principie of isolation, and have done pseudo-static tests of the bearing. The

restoring force model of the bearing is given based on these. The seismic response of the

structure as stated above is compared with that of the un-isolation structure. It proves

that the bearing is better isolation.

Key Words: Steel tube Concrete, short column, isolation.

I Introduction

During the research of how to reduce the damage of earthquake, most researcher

focus on isolation·. In order to reduce the dynamic response of structure during a

earthquake, people pave isolated layers under the basement, for its good dissipation

capacity. By now at least 15 countries adopt the method on 200 structures, because of

its sim pie principie, cheapness, easy construction. On Jan, 17, 1994, In Los-angles, one

of 7 stories teaching hospital building survives a earthquake of Reichter Scale 6.6 After

the earthquake of the great Hasan earthquake on Jan, 17, 1995, an isolated house

stayed quite, which lies 35km away from the epicenter And an these prove that the

method is effective in blow structure.

Now there are three kinks of isolation: 1. Sliding equipment; 2. Rolling equipment; 3.

1.2 Professor, Department of Struclural Englneering, Harbin University 01 Civil Engineering and Architecture.

China3 Sanior Engineer, Tongji University, China.

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Bearing equipment . Because there is no restoring force in kind 1,11, structure may have

un-restoring deformation. There are some subdivides of kind m, such as some rubber

bearing (adopted by the above mentioned Japanese house): short column. In 1980's

Russian construct. A few brick buildings by the method, among which the highest

building is up to 9 stories . The residents in these buildings didn't conceive obvious action

of earthquake.

The principal requirement to the method practical : economic: safe: rely. This is to

say : 1.a little additional capital may get higher safety. 2.the system not only has better

dissipation ,but also can limit the displacement of basement appropriately . 3.the isolated

layer must have enough strength and duration.4. when gets certain damage. it can easily

be repaired. It's obviously that rubber equipment has complex structure ,high expense.

and its bad behavior on long period vibrate. Though concrete short pillar bearing has

simple structure and cow expense. its restoring capacity is notgood. At the same time,

Though steel short pillar bearing has good restoring capacity, its expense is higher.

In our country, we still face with low or medium height buildings. For above

mentioned principies, we pro pose a new type material of the concrete filled steel tube

short column . This new type synthesizes the excellent merits of steel and concrete . This

is to say, restricted by tube, concrete not only gains higher !:trength, but also gains higher

plasticity and ductility. On the other hand, due to the concrete , tube can get higher

steadiness. So the bearing has higher strength, good plasticity, good ductility, good

quake proof, good fireproof. What's more, the restoring curve is fun and round like a

spindle. and no descend parto Ali these is similar to steel.

We carry out the pseudo-static experiment, and then set a restoring force model by

The high order one step method . We analyze the response of the isolation structure in

comparison with non-isolation structure. So we can draw a conclusion that the bearing is

the better one.

II Mechanics experiment of short pillar bearing

The concrete tube bearing is showed in fig.1. The top and the bottom have the same

size, and the same concrete grade . The two sides are packed with steel plates. The

sl iding material between them can make friction descend at mosto The bottom of short

pillar is welded with the ground plate while its top is free . The form of gaps upper the

bearing and under it is like a cone . The magnitude of a lateral displacement is definited

through designs.

The top is fixed in the basic structure., at the same time its bottom is in the basement.

The top transfer the vertical loads of basic structure to its bottom. The pillar doesn't

support any load . Under the action of horizontal earthquake, the pillar can consume the

theory and provide restoring force.

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I ,

Figure l-L

1. Concrete short pillar.

2.3 bottom and topo

4. Steel plate

Figure 1-2.

When the top generates some displacement according to the bottom. Owing to the

deposition on sliding plate, we can omit the friction energy.

In order to make it clear the mechanics behavior of the tube, we carry out a pseudo

static experiment on the pillar. Because of limitation of loading frame, we have to put the

load on the middle of a simple supported beam instead of loading at the end of cantilever.

(see fig.2) . The workmanship is made of 114 X 4 tube, and c30 concrete beam, whose

length is 180cm, 160cm, 150cm respectively. (Actually, a short pillar is 90, 80, 75

respectively). According to design requirement, we do the experiment until an thes" ale

damaged.

Fig2. Loading facilities and the whole process

Experimental restoring force curve is showed in fig3. The curve appear double line,

and has no degrade parto The ultimate load is 4.75T, 5.0T, 5.3T respectively. While the

according displacement is 4.01 em, 3.3cm, 3.1 em. The simplified restoring force curve is

showed in fig4.

Part 1 Part2 Part 3

fig3 short pillar restoring force curve

III Emulating calculation

Once the layers are paved, we can find relative displacement between stories

beca me small. So we can threat the basic structure as a single freedom system. The

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number of isolation equipment is determined by the following formula.

fig4 simplified short pillar restoring force curve

amount of isolation bearing

The simplified schematics is show in fig.5.

During calculation we think about the non-line

property of upper structure, and use the model to

calculate the isolated cagers. Adopt the high

order one step method to solve the response of

the structure.

We take a three-stories building as example,

the parameters are listed in table 1. The isolated

layer is put between the structure and the

.1

T=2n --~E mKpg

.1

, fig 5. Analysis madel

basement. The tube i3 114 X 4 long and the concrete grade is C30. The number of

bearings and layers is listed in table 2.

Table 1

Story K (tlem) Q (t) M (t • see2/crn)

1 7152 860.4 0.5223

2 6104 700.8 0.5223

3 5054 541.2 0.3257

Input wave is EL-CENTRO. NS, which contain medium and long periods. The

magnitudes acceleration the isolated structure and the non are showed in table 3, 4, 5.

When non isolated structure receive R.S 8 earthquake, one and two story work in

plasticity condition. While the isolated one, the whole structure is in elastic condition

except the pillar.

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Table 2

K,(t/em) K,(t / em) Ó(em)

isolation bearing 3.77 0.1132 1.11

isolation story ( 20 ) 75.44 2.263 1.11

isolation story ( 40 ) 150 • 88 4 • 526 1 • 11

200gaI EL CENTRO wavee arth ak ~QU f e response o structure T bl 3 a e

story O 1 2 3

no isolation maximum story displacement (em) 0.205 6.121 0.065

story ( O ) maximum story shear force ( t ) 859 701 321

isolation maximum story dispaIcement (em) 7.51 0.0012 0.011 0.006

story (20) maximum story shear force ( t ) 98.2 86.6 64.1 32.9

isolation maximum story displacement ( em) 3.42 0.0206 0.0159 0.0086

story (40) maximum story shear force ( t ) 178 148 92.6 42.3

300 I ELCENTRO Jga wavee arth ak ~QU f e response o structure T bl 4 a e

story O 1 2 3

no isolation maximum story displacement ( em ) 0.368 0.145 0.084

story ( O ) maximum story shear force ( t ) 860 701 414

isolation maximum story displacement ( em ) 10.9 0.014 0.013 0.007

story (20) maximum story shear force ( t ) 106 101 77.1 37.9

isolation maximum story displacement (em) 6.17 0.0278 0.0265 0.0086

story (40) maximum story shear force ( t ) 190 199 154 91.5

400 I ELCENTRO Jpa arth ak wavee' lQU f e response o structure T bl a e 5

story O 1 2 3

no isolation maximum story displacement (em) 0.428 0.238 0.089 story (O) maximum story shear force ( t ) 860 701 440

isolation maximum story displacement (em) 12.7 0.027 0.022 0.022 story (20) maximum story shear force " ( t ) 110 195 130 112

isolation maximum story displacement ( em ) 8.75 0.0528 0.0455 0.044 story (40) maximum story shear force ( t ) 202 378 266 219

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IV Conclusion

1. Concrete tube short pillar bearing is an non-line quake proof equipment, which

restoring force curve appears double line.

2. Owing to this structure, the relative displacement between stories decrease obviously.

The majority of displacement occurs at isolation layels.

3. The shear force decrease obviously. And with magnitude of quake increase, the

relative shear force increase slowly.

4. The number of bearing is determined by the equation of basement shear force.

5. The bearing not any isolatethe vibration obviously, but also is an economical, practical,

durational new type isolated bearing .

REFERRENCES [1]. Wang Huanding and Wang Wei, ' The high order one step method for seismic

response analysis of non-linear structures' , Earth. Eng and Eng. Vibr, Vo1.16, No .3,

1996.

[2]. Hong Feng, ' Stochastic earthquake response analysis and probability design of

Base-Isolated structures', Ph. D. Dissertation, Institute of Engineering Mechanics State

Seismological Bureall, China, 1995.

[3]. Zhang Xusheng and Liu Yong, 'Research on isolating ability of the R.C.Short

column Be~ring', Journal of College of Structural Engineering TongJi University, China,

No.3, 1996.

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