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SEISMIC RESPONSE OF AN ARCH DAM
In order to illustrate the effect of the rate dependency on the dynamic structural response, a 278 m
high arch dam in China subjected to earthquake excitation is analyzed by the proposed model. The
material properties for the study are as follows: for the dam body E=2.4xl0 4 MPa, v=0.17,
p=2.4xl0 3 kg/m 3 , static compressive strength/ c =30MPa, and static tensile strength/=3MPa; for the
foundation rock E^1.6xl0 4 MPa, v=0.25, p=2.0xl0 3 kg/m 3 . The dam and the foundation are
discretized into 450 and 1040 isoparametric elements respectively. Fig.7 shows the discretized
dam-foundation system. The five lowest vibration frequencies of the dam in care of full reservoir
are://=0.997 Hz ,/r=1.0Q4 ^ /3=1.450 Hz ,f 4 =lA91 ^ and/5=1.542 Hz . An assumption of massless
foundation is introduced to simplifying the dam-foundation interaction analysis though more
rigorous interaction effects can be included. The design earthquake acceleration is 0.32 Ig.
Fig.7 Geometry and mesh of arch dam.
Fig. 8 Time history of Earthquake input
Three-dimensional earthquake waves are used as the input. Fig.8 shows the typical artificial
acceleragram that meets the requirement of (Chinese Specifications for Seismic Design of
Hydraulic Structures }> .
Three analyses were performed: an elastic analysis, a rate-independent plastic analysis and a rate
dependent viscoplastic analysis. The maximum values of the first and the third principle stresses in
the dam are shown in the Tab.l. It is seen that in all three cases, the maximum compressive stress
are the same, the material remains working in the elastic range. However, for the maximum tensile
stress there is marked difference between the calculated results of rate dependent model and that of
rate independent model.
Table.l
MAXIMUM VALUES OF PRINCIPLE STRESSES
Model
Elastic
Rate independent Plastic
rate dependent Viscoplastic
Compression(MPa)
-12.5
-12.5
-12.5
Tension(MPa)
5.17
2.87
3.22