Seismic Isolation for Small Reinforced Concrete Structures A Preliminary Investigation on Material Cost

Advisor: Advisor:

Investigated and Presented by:

Dr. George C. Lee

Abiel Carrillo

Samuel Samuel P. P. Capen Capen Professor Professor

Multidisciplinary Center for Earthquake Engineering Research

Objective The objective of this investigation is to show the effectiveness of a specific rubber bearing isolation design of a symmetrical, low-rise reinforced concrete structure in the region of Algeria, Africa Multidisciplinary Center for Earthquake Engineering Research

Motivation for this investigation One evening uake evening in in May, May, 2003, 2003, Algeria Algeria was was struck struck by by its its worst worst earthq earthquake in 23 years. More than 2,000 people were killed and over 9,000 injured. Many homes were destroyed in the initial quake and thousands more were damaged and made uninhabitable.

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A1

Motivation for this investigation To explore a system that could protect similar structures, preventing disasters like this.

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Slide 5 A1

Some structures experienced non structural damage, others buckled, other completely destroyed Abiel Carrillo, 7/25/2004

Objective As will be explained later, base isolation in general can be one of the safest or most cost effective ways of designing a structure in a highly seismic zone. The results of this investigation, focus on a specific example example.. Multidisciplinary Center for Earthquake Engineering Research

Overview o

Method and Codes

o

Design Loads

o

Parameters and Assumptions

o

Base Isolation

o

Summary of Results

o

Conclusions

o

References

Multidisciplinary Center for Earthquake Engineering Research

Method and Codes Used Two possible frames were designed, A and B, and the total required material was then compared: A. Moment resisting frame

B. Base isolated frame

Isolator Multidisciplinary Center for Earthquake Engineering Research

Method and Codes The design steps for base isolation ultimately shift the frame’s period.

Acceleration is significantly reduced, which means that smaller lateral forces are developed

Multidisciplinary Center for Earthquake Engineering Research

Method and Codes ! American Concrete Institute (1999) For floor system, girder, column and foundation design.

! Uniform Building Code (1997) For design loads and base isolation design.

! Algerian Seismic Code For Equivalent static earthquake loading applied to moment frame A

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Design Loads ! Earthquake loads were determined from a !Earthquake static lateral equivalent calculation based on Algerian Seismic Codes. 72 72 kip kip 40 40 kip kip

Multidisciplinary Center for Earthquake Engineering Research

Parameters and Assumptions Details were as follows:

Steel fy

60 ksi

Conc. f’c

3 ksi

Allowable Soil stress

4 ksi

Occupancy

Offices

Seismic Zone 27 ft

9

90 ft

t 0f

3

Dead Load

12 psf

Roof Live

20 psf

Floor Live

50 psf

Multidisciplinary Center for Earthquake Engineering Research

Base Isolation Design There are various isolation methods and devices available and are being developed, and the Code does not “prefer” a type, nevertheless it requires that the system have the following three properties: 1. Be stable for the required displacement 2. Provide increasing resistance with increasing displacement 3. Does not degrade under cyclic loading

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Base Isolation Design Selected Isolation: High Damping Rubber Bearing

Steel plate

Thin Thin steel steel shims shims (circular (circular plates) plates) increase increase bearing bearing strength strength

Rubber cylinder

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Slide 14 A2

There are many others which i encourage you to look at but in the interest of time.. Abiel Carrillo, 7/25/2004

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Base Isolation Design Steps for a Code based design:

1.

Determine and establish parameter-dependent factors.

2.

Select a type of bearing and estimate target values, such as stiffness, damping ratio and bearing displacement.

3.

Relate required dimensions of the isolation bearing unit with target values from step 2.

4.

Detail actual dimensions for isolation unit.

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Slide 15 A3

There are many steps but basically... Abiel Carrillo, 7/25/2004

Summary of Results The resultant design called for 16 units with the following dimensions:

11 “ height 12 gage shims

17 ” rubber diameter Multidisciplinary Center for Earthquake Engineering Research

Summary of Results

B

A A

A / B weight ratios of main structural elements Concrete ratio

Steel ratio

Girders

1.7

4.9

Steel in Base Isolated frame is not continuous

Columns

1.5

3.2

A minimum amount of concrete required in both columns

Foundations

2.3

1.8

Same rebar diameter, just larger dimensions

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Conclusions

! Base Isolators can be expensive, but the rubber bearings chosen are very common. The final design calls for 16 units, which doesn’t compare to having a total of 3.3 times more steel as required in the larger reinforced frame.

Multidisciplinary Center for Earthquake Engineering Research

Conclusions ! Results for other structures can vary significantly Factors that influence structural design: - Importance of building - Soil profile - Availability and shipping - Height of structure - Labor - Site plan - Architectural requirements - Other factors Multidisciplinary Center for Earthquake Engineering Research

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Conclusions ! Base Isolation also protects non-structural elements and equipment by reducing the entire structure’s acceleration during an earthquake, as opposed to reinforcement alone.

Frame Frame is is still still standing standing but but non-bearing non-bearing walls walls could could not not withstand withstand the the strong strong shaking. shaking.

Multidisciplinary Center for Earthquake Engineering Research

Slide 20 A5

include equipment isolation, like in a museum Abiel Carrillo, 7/26/2004

References ! Paz, Mario. International Handbook of Earthquake Engineering : Codes, Programs and Examples. October, 1994; Chapman and Hall. London, England.

! McCormack, Jack. Design of Reinforced Concrete. 2001; John Wiley & sons, Inc. New York, New York.

! Kelly, James M.; Naeim, Farzad. Design of Seismic Isolated Structures: From Theory to Practice. 1999; John Wiley & sons, Inc. New York, New York.

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Acknowledgements !

- Multidisciplinary Center for Earthquake Engineering Research

! Dr. George C. Lee Samuel P. Capen Professor

! Civil Engineering Dept. , Univ. at Buffalo

Multidisciplinary Center for Earthquake Engineering Research

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