Seismic Evaluation of Nauseri Dam Using 3D Finite Element Analysis

Abstract

The Nauseri Dam, a critical component of the Neelum-Jhelum Hydroelectric Project in Pakistan, underwent extensive seismic evaluation to ensure its structural integrity under operational and extreme seismic events. This study employed three-dimensional finite element analysis (3D FEA) to evaluate the dam’s performance under Operational Based Earthquake (OBE) and Maximum Credible Earthquake (MCE) conditions. This report delves into the methodologies, results, and implications of this analysis, offering insights for researchers and practitioners in hydraulic and seismic engineering.

Introduction

The Neelum-Jhelum Hydroelectric Project is a vital energy initiative in Pakistan, harnessing the power of the Neelum River. As part of this project, the Nauseri Dam plays a pivotal role in water retention and energy generation. Given its strategic importance and seismic vulnerability, a comprehensive structural evaluation using advanced FEA tools was conducted. This study outlines the methods and findings, with a focus on seismic behavior, structural stresses, and reinforcement design.

Objectives

1. Evaluate the seismic behavior of the Nauseri Dam using 3D FEA.
2. Identify critical stress regions for further detailed analysis.
3. Provide reinforcement requirements for concrete design under seismic loads.
4. Utilize both response spectra and time-history analyses for OBE and MCE conditions.

Methodology

1. Global Model Development

A 3D finite element model encompassing the spillway, roller-compacted concrete (RCC), debris flow, and intake structures was developed. Key features included:

• Incorporation of reservoir hydrodynamic effects using Westergaard’s added mass formulation.
• Elastic material properties for concrete and rock foundations.
• Response spectra analysis to capture seismic behavior up to 25 Hz.

2. Local Model Refinement

A local spillway model was calibrated with the global model to focus on:

• Spillway piers’ structural responses.
• Detailed boundary stiffness at interfaces with adjacent structures.

3. Seismic Load Analysis

• OBE: Evaluated using moderate seismic events to verify linear elastic behavior.
• MCE: Focused on maximum stress and reinforcement requirements.

4. Structural Criteria

Design criteria adhered to USACE standards for reinforced concrete hydraulic structures, with damping ratios set at 5% for dynamic analyses. Flexural and shear reinforcement requirements were evaluated based on demand-capacity ratios (DCR).

Key Findings

1. Stress Distribution and Critical Regions

• Maximum stress concentrations occurred at the spillway piers’ downstream side.
• The highest displacement responses were observed in flexible downstream walls.

2. Calibration Results

The local model’s displacement and frequency responses closely matched the global model, validating its use for detailed analysis.

3. Reinforcement Design

• Flexural Design: Reinforcement was optimized for MCE conditions with a DCR limit of 2.0.
• Shear Design: Shear reinforcement was limited to a DCR of 1.0 for MCE.
• Reinforcement layouts were provided for spillway piers, ensuring compliance with USACE standards.

4. Time-History Analysis

Time-history simulations for OBE and MCE motions identified critical stress points, guiding reinforcement placement to withstand seismic forces effectively.

Implications for Future Research

This analysis demonstrates the importance of advanced FEA tools in assessing seismic resilience. Researchers can build upon this work by:

1. Exploring nonlinear behaviors for extreme seismic events.
2. Incorporating climate change impacts on reservoir hydrodynamics.
3. Enhancing material modeling for long-term structural performance.

Conclusion

The Nauseri Dam’s seismic evaluation highlights the efficacy of 3D FEA in ensuring the safety and durability of critical infrastructure. By addressing both global and localized stress responses, the analysis provides a robust framework for designing earthquake-resistant hydraulic structures. This study serves as a reference for researchers and practitioners aiming to advance the field of seismic engineering in hydraulic projects.