Principal Research Results

Seismic Performance Evaluation of Dam Gates in Large-Scale
Earthquake
Background
Seismic structural design of dams and associated appurtenant structures in hydraulic power plants has been conducted using
seismic coefficient method in which seismic load is treated as equivalent static load. In recent years, infrastructures have suffered
enormous damages from large-scale earthquakes in Japan. It is necessary to evaluate seismic performance of the dam structuressubjected to large-scale earthquakes which may exceed the design seismic condition. Although dam gates are vital appurtenances indams, there are few experimental data regarding the seismic behavior and failure mode of the gates in large-scale earthquakes.
Therefore, it is required for the gates to experimentally investigate ultimate limit state and establish analytical evaluation methodology.

Objectives
The purpose of this study is to evaluate seismic performance of a radial gate, as a typical type of dam gate, in large-scale
earthquake by model loading tests and numerical simulations.

Principle Results
1. Model Loading Tests
Monotonically static loading tests of one-fourth scale radial gate models (Fig.1) were carried out under hydrostatic andearthquake loads (Fig.2). We obtained the following results about seismic behavior and failure mode.
(1) Axial load-displacement relationships of strut arms indicated that inelastic behavior commenced prior to reaching maximum
strength mainly due to the yielding of the arms (see Fig.3). After passing maximum strength, the strength of the arms moderatelyreduced.
(2) The failure modes of the models were the buckling of the strut arms in the vertical plane. Only one span of each strut arm became
deformed due to buckling (Fig.5). Buckling deformations of upper strut arms appeared in advance of those of lower ones because
the upper strut arms had smaller sized cross section than lower ones.
(3) The maximum strength of the models was over 1.1 times the axial compressive buckling strength Pcr which was calculated basedon a design standard for gates ＊ 1. Thus it is conformed that Pcr is available for safety strength evaluation of radial gates
2. Numerical Simulations
Elasto-plastic finite deformation analysis was carried out by applying the model loading test condition using the finite
element model illustrated in Fig.4 which consisted of mainly shell and beam elements. Fig.3 shows that the load-displacement
relationships of analysis results agreed well with the test results up to maximum strength. The analysis results also well approximatedthe experimental failure modes as illustrated in Fig.5. We can conclude that finite element elasto-plastic analysis makes it possible toevaluate seismic behavior and failure modes of radial gates.
This work was entrusted by the Nuclear and Industrial Safety Agency (NISA) of the Ministry of Economy, Trade andIndustry.

Future Developments
Ultimate limit states of various types of gates will be experimentally investigated for establishing methodology of seismicperformance assessment.
Main Researcher: Kiyoshi Saito,
Research Engineer, Structural Engineering Sector, Civil Engineering Research Laboratory
Reference
NISA and CRIEPI, 2008, “Research Report on Seismic Performance of Electric Power Facilities (Model Tests) in FY 2007” (inJapanese)＊1：The Hydraulic Gate and Penstock Association, “Technical Standard for Gates and Penstocks (fifth revised edition)”, 2007 (in Japanese)1249. Construction and Preservation of Electric Facilities

2.0m

Horizontal girder

Upper strut arm

Hydraulic load

Lower strut arm
2.5m

Hydraulic load

Arm bracing

Dam gate model

Skin plate and vertical bracing
Pin support

Fig.1 Dam gate model
Dam gate models were manufactured by welding thin plate
members based on the geometry of an actual radial gate. Models
with different shaped arm bracings were also manufactured.
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Fig.2 Static loading test
Dam gate model was so mounted upside down on loading
apparatus that stable loading was possible using hydraulicactuators.

Axial compressive buckling strengthof lower strut arm Pcr

300
Axial compressive buckling strengthof upper strut arm Pcr

Load (kN)

250200150100Upper strut arm test result
Lower strut arm test result
Upper strut arm analysis result
Lower strut arm analysis result

50005
1015Displacement (mm)Lower strut arm

20Upper strut arm

Fig.3 Axial load-displacement relationship ofstrut arms

Fig.4 Finite element model

Test result indicated that strength of strut arms moderately
reduced after passing maximum load. The load-displacement
relationship of analysis results agreed well with the test results
up to maximum load.

This is a symmetrical 1/2 analysis model matched with themodel position shown in Fig. 2. Horizontal girders and strut
arms consisted of shell elements which had measured thickness
properties. The modeling of other members was simplified tothe extent of not affecting analysis results.

Lower strut arm

Lower strut arm

9Upper strut arm
Buckling deformations

Upper strut arm(b) Failure mode in analysis(Deformations at 11 mm axial displacement oflower strut arm are multiplied three times)(a) Failure mode at the final stage of loading test

Fig.5 Typical failure modes in loading test and finite element analysis
Failure modes in loading tests were the buckling of strut arms in vertical plane and analysis results wellapproximated the experimental failure modes. The buckling of upper strut arms appeared before those of lower
ones because of smaller sized cross section.

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