Improving Reliability of Spillway Gates


Foreword

The United States Society on Dams recognizes that with an aging infrastructure, new demands (not perceived at the time of construction) are being placed on owners of dams to ensure safe and reliable operation and maintenance. One unique aspect of dam safety that has recently received increased attention is the gated spillway. Spillway gates have not always been attributed due respect with regard to periodic test-operation and maintenance because reliability of the gate structure and operating machinery was either considered inherent with the design or was simply neglected altogether. Dam safety was not necessarily identified with the inability to operate a spillway gate. Recent gate incidents, identified herein, illustrate that problems with spillway gates and gate operating equipment do exist, are all too often repetitive, and have the potential to affect overall dam safety.

The USSD Hydraulics Committee commissioned its Subcommittee on Gates and Valves to develop this report as a source of practical experience and information to achieve long-term reliability of spillway gate operation.

Experience has shown that improving spillway gate reliability is a combination of proper component selection, good design details, appropriate operation and maintenance procedures, and the application of proven inspection and evaluation techniques. This report is a compendium of demonstrated engineering, design, operation, and inspection procedures based on the experiences of various dam owners and operating agencies in the United States. Whether selecting, designing, operating, and/or maintaining spillway gates, the reader will benefit from the collective experience of the authors involved with the development of this report. The information provided is comprehensive, applicable to new construction, major renovation or rehabilitation of existing projects, and operation and maintenance of existing gated spillways.

Improving spillway gate reliability requires a concerted effort among owners, operation and maintenance personnel, and designers. This report was developed with the intention to benefit anyone associated with gated spillway structures - whether it is ownership, operation, maintenance, design and/or regulatory responsibility.

Owners and operating personnel will learn about recommended maintenance and test- operation procedures; designers will benefit from information and references regarding design criteria, methods, and procedures; and regulators will get a better understanding of the role that gated spillways have in dam safety. The reader will be introduced to the more common types of spillway gates and gate operating equipment. Recommendations are provided regarding important features that should be considered in selecting and designing new spillway gates or rehabilitating existing spillway gates to improve performance and reliability. Also, information concerning operation, maintenance, inspection, and evaluation of gates and gate operating systems is presented. Various types of spillway gates (past and present) are described with respect to function, operation, limitations, and weaknesses. The anatomy of a spillway gate is explained, and contrasted with potential modes of failure.

Each project is unique. Design details, manufactured components, procedures used to operate or maintain a project, etc. vary from owner to owner and even from project to project within an organization. This report does not attempt to address all possible design and operating conditions that an agency or project may experience. However, many of the situations, recommendations, and procedures provided herein are general in nature, with a logical methodology that when followed will improve the longevity and reliability of spillway gate operation.

The focus of the report is on structural, mechanical and electrical considerations of spillway gate operation. Hydraulic design and hydrological engineering needed to determine size of spillway and/or number and size of spillway gates is not discussed. Also, it is not intended to be a design manual, but reference is made to many design documents that provide information on the latest design methods and procedures.

Regardless of the level of experience, the depth and breadth of the topics covered in this report can provide assistance to anyone involved with engineering and operation of gated spillway systems. Ultimately, the public will benefit from the knowledge provided by this report through improved design and safe operation of water resource projects in their community.


Report Contributors

B.T.A. Sagar

Bernard J. Peter

Henry W. Stewart

Edward A. Serfozo

Alfred M. Waddell

Daniel J. Casapulla

D. Craig Evans

Chander K. Sehgal



Table of Contents



CHAPTER 1 - INTRODUCTION

1-1. Background

CHAPTER 2 - GATE TYPES AND APPLICATIONS

2-1. Introduction

2-2. General Arrangement

2-3. Radial Gate

a. General

b. Operation

c. Selection

2-4. Vertical-Lift Gate

a. General

b. Fixed-Wheel and Roller-Mounted Gates

2-5. Drum Gate

a. General

b. Arrangement

c. Anchorage

d. Operation

2-6. Hinged Crest Gate

a. General

b. Leaf

c. Anchorage

2-7. Inflatable Gates

a. General

b. Rubber Dam

c. Obermeyer Gate

2-8. Flashboards

a. General

b. Spillway Flashboards

c. Gate Flashboards

2-9. Fuse Gates

2-10. Maintenance Gates

a. General

b. Bulkhead Gates

c. Floating Bulkheads

d. Stoplogs

e. Needles

2-11. Gate Operating Systems

a. General

b. Wire Rope Hoists

c. Chain Hoists

d. Hydraulic Hoists

2-12. Recommendations

CHAPTER 3 - DESIGN PRACTICES

3-1. Introduction

3-2. Design Criteria

a. General

b. Working Stress

c. Factor of Safety

3-3. Loads and Allowable Stress

3-4. Structural Analysis of Radial Gate

a. Member Definitions

b. Material Properties

c. Loads

d. Gate Load Cases

e. Verification of Models

f. Allowable Stresses

g. Results

3-5. Analysis of Other Gates & Features

a. General

b. Gate Anchorage

c. Contacting Solids

3-6. Materials

a. General

b. Standards

c. Materials

d. Severe Exposure

e. Applications

3-7. Fabrication

a. Introduction

b. Shop Fabrication vs. Field Fabrication

c. Designer's Role in Fabrication

d. Welding vs. Castings vs. Forgings

e. Heat Treatment of Steel

f. Bolts

g. Galvanizing

3-8. Seal Systems

a. General

b. Rubber Sealing Systems

c. Radial Gate

d. Hinged Crest Gate

e. Vertical-Lift Gate

3-9. Overtopping Flow

a. General

b. Overtopping Design

3-10. Rehabilitation

a. Bolted Connections

b. Welding

3-11. Design Considerations

3-12. Hoist Selection and Design

a. General

b. Design Criteria

c. Improving Reliability

CHAPTER 4 - INVESTIGATION AND EVALUATION

4-1. Introduction

4-2. Failure Scenarios

4-3. Gate Components

4-4. Safety Evaluation

a. Introduction

b. Design Review

c. Radial Gates

d. Vertical-Lift Gates

e. Hinged Crest Gates

f. Inflatable Gates

g. Fuse Gates

4-5. Gate Operating Systems

a. System Evaluation

b. Wire Rope Hoists

c. Chain Hoists

d. Hydraulic Hoists

e. Other Systems

4-6. Field Inspection

a. General

b. Gate Structure

c. Trunnions

d. Anchorage

e. Seals

f. Operation

4-7. Gate Vibration

a. Introduction

b. Seismic Activity

c. Flow Variations

d. Stick/Slip Motion

4-8. Ice Difficulties

a. Gate Problems

b. Operating Problems

CHAPTER 5 - AUTOMATION

5-1. Background

a. Introduction

b. Mechanically Float-Operated Gates

c. Electrically Operated Gates

d. Computer Operated Gates

5-2. Spillway Gate Control

a. General

b. Local-Manual Control

c. Remote-Manual Control

d. Local-Automatic Control

e. Remote-Automatic Control

f. Local Semi-Automatic Control

5-3. Spillway Gate Automation

a. General

b. Operational Risks

c. Operational Benefits

d. Constant Reservoir Water Level

e. Dam Safety

5-4. Automation Design Requirements

a. General

b. Operational Strategy

c. Simulation and Analysis

d. Control Algorithm Development

5-5. Automation Equipment Requirements

a. General

b. Gate Hoists

c. Hoist Motors

d. Electrical Controls

e. Instrumentation

f. Data Acquisition

g. Weather Stations

5-6. Automation Equipment Selection

a. General

b. Gate Hoists

c. Measurement Wells

d. Power Supply

e. Communication System

f. PLC and RTU Equipment

5-7. Conclusion

APPENDIX A - REFERENCES

APPENDIX B - EXAMPLES OF GATE INCIDENTS

APPENDIX C - TRUNNION LUBRICATION

APPENDIX D - TEST OPERATION OF SPILLWAY GATES

APPENDIX E - BALANCING CRITERIA

APPENDIX F - DESIGN EXAMPLES

APPENDIX G - MAINTENANCE AND INSPECTION GUIDELINES

APPENDIX H - FIGURES






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