Energy Dissipation at Foundation Level

By:A. Mahdizadeh

N. Goudarzi

6th International Conference of Seismology & Earthquake Engineering (SEE6)

May 16-18Tehran, Iran

Contents•Introduction•Sliding of Masonry Buildings• Observation in Past Earthquakes• Principles of Base Isolation materials• Methods of BI in Masonry Buildings• Shake Table test of a Masonry Buildings

•Rocking Behavior of Shear walls• Effects of Rocking Foundations• Experimental Research on Rocking Shallow Foundations (B.

Kutter 2006)• Analytical study of Rocking Shear walls (B. Chang 2006)

Introduction

Current Practice in Structural Design

1.Modeling and analysis of structure with fixed base assumption.

2. Analysis and design of foundation using the reaction forces of the superstructure model.

Disadvantage of Fixed Base ModelingHigh cost of foundation

Sliding of Masonry Structures on Foundation

•Sliding has saved URM Buildings from Collapse. (Gee 1934)

•In Tangshan Earthquake (1975) a horizontal crack saved a masonry building.

•In Wuchang Earthquake (1960) a horizontal crack saved an old earthen building.

85% of other buildings collapsed.

•Weathering•Necking•cracking

In Wuchang Earthquake (1960) a horizontal crack saved an old earthen building. (Li 1984)

•In Xingtai Earthquake (1966) a horizontal crack on the second floor saved a URM masonry milling plant.

•Unplanned sliding of adobe buildings saved the majority of them in Bouhai Earthquake 1969.

If Horizontal Cracks can save buildings, Why not make them beforehand!?

Principles for design of BI in Masonry Buildings

• Effectiveness• Economy• Endurance• Ease of Construction

Methods of Base Isolation for URM Buildings

•Sand Slide Slit Base Isolation Measure (Li 1984)

•Artificial Neck Section (Li 1984)

•Graphite Powder•Sand layer•Marble•Grease

Empirical Performance of BI Masonry Buildings

Base Isolation Using Marble Stone

Input Acceleration

Response Acceleration of Fixed Base Model

Response Acceleration of Sliding Model

Base Isolation Using Marble Stone

Rocking Behavior of Shear walls•Fixed Base modeling of Shearwall structures:

• Costly foundations in low-rise buildings

•With considering Rocking of Shearwall:

• More Economical Foundation design• Adequate ductility and damping

•Uplifting•Geometrical Nonlinearity

•Yielding in Soil or Foundation

Detail for controlling settlement (T. Paulay, M. J. N. Priestley, 1992)

Concrete Block

Detail Concrete Block (T. Paulay, M. J. N. Priestley, 1992)

Experiments on Shallow FoundationsSupporting Rocking Walls

(S. Gajan, B. Kutter, 2006)

Structure Code L (m) Mass(ton) Hcg(m)

RE-2.7-M-36 2.7 36.5 5.6RE-2.8-M-20 2.8 20.5 4.7RE-2.8-M-28 2.8 29 4.5RE-2.8-M-36 2.8 36.8 5.3RE-2.8-M-58 2.8 58 5RE-2.8-M-60 2.8 60.4 5RE-2.8-M-68 2.8 68 4.8

H= 10.15 mB= 0.65 mKs= 3-4 kg/cm3

Time history of cyclic loading

Analytical ResearchT. C. Hutchinson, B. Chang

Analysis of one Rocking Shear Wall

Conclusion• Base Isolation of URM buildings at foundation level

enhances seismic performance of these structures.• BI of masonry structures can be adopted for retrofitting

to reduce cost of rehabilitation at foundation level.• When adding Shear walls for retrofitting, rocking could

be accounted for to reduce cost of rehabilitation at foundation level.

Thank You For Your Attention