Engineering Methodology for Safe and Efficient Lifting Plans in OHTL Tower Erection

Abstract

Lifting operations in Overhead Transmission Line (OHTL) tower erection are among the most critical and high-risk construction activities. These operations involve heavy steel components, complex geometries, environmental forces, and often work near energized lines.

This article presents a structured engineering methodology for preparing safe and efficient lifting plans. It covers structural segmentation, load calculations, crane selection, rigging design, and site risk assessment.

A real-world case study of a 380kV double-circuit transmission tower demonstrates how proper planning—such as maintaining low crane utilization and controlled lifting radius—can significantly improve safety and operational efficiency.

Keywords

OHTL Lifting Plan, Tower Erection, Crane Selection, Rigging Design, Load Calculation, Transmission Line Safety, Construction Engineering

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1. Introduction

The erection of OHTL towers requires lifting heavy structural components to considerable heights under challenging site conditions. These activities become even more critical when performed near live transmission lines.

Common risks include:

• Crane instability
• Load swing and loss of control
• Structural misalignment
• Electrical hazards

Traditionally, lifting plans were treated as basic procedural documents. However, modern engineering practice requires a more analytical approach, where lifting operations are treated as engineered systems based on physics, structural behavior, and safety principles.

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2. Engineering Methodology for Lift Planning

2.1 Structural Segmentation and Configuration Analysis

The first step in lift planning is analyzing the tower structure using design drawings.

Key elements to identify:

• Tower type (Suspension, Tension, Terminal)
• Structural components (legs, body, cross arms, peak)
• Erection sequence

The tower is divided into smaller lifting segments (panels) to:

• Reduce load per lift
• Improve lifting stability
• Ensure better control during hoisting

Each segment must be analyzed for:

• Center of Gravity (COG)
• Proper lifting points
• Stability during lifting

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2.2 Load Modeling and Calculation

Accurate load calculation is essential for safe lifting operations.

The total load is calculated as:

Total Load = Component Weight + Rigging Weight + Dynamic Factor

Where:

• Component Weight = Steel member weight
• Rigging Weight = Slings, shackles, hooks
• Dynamic Factor (10%–25%) accounts for movement and impact

Important Engineering Considerations:

• Lower sling angles increase tension in slings
• Incorrect COG leads to uneven loading
• Wind can significantly affect large structural members

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2.3 Crane Selection and Optimization

Selecting the right crane is critical for safe lifting.

Key factors:

• Maximum load capacity
• Working radius
• Required lifting height

Using crane load charts:

• Actual Load must always be less than Rated Capacity

Best Practice:

• Crane utilization should be ≤ 75%
• For critical lifts, aim for ≤ 60%

Why Lower Utilization Matters:

• Higher safety margin
• Better control under dynamic conditions
• Reduced risk of overloading

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2.4 Crane Positioning and Ground Assessment

Proper crane positioning helps improve safety and efficiency.

Objectives:

• Minimize working radius
• Maintain stable lifting geometry
• Reduce crane movement

Ground Engineering Checks:

• Soil bearing capacity
• Outrigger load distribution
• Use of crane mats or steel plates

Poor ground conditions are one of the leading causes of crane failures worldwide, making this step extremely important.

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2.5 Lift Simulation and Radius Control

Each lift must be evaluated throughout its full movement:

• Pick radius (starting point)
• Set radius (final position)
• Maximum load condition

Key Insight:

Lifting radius has a greater impact on safety than load weight alone

Because:

• Load capacity reduces as radius increases
• Dynamic effects increase with movement
• Stability decreases at higher radii

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3. Execution Strategy

Execution must follow strict engineering and safety controls.

Pre-Lift Activities:

• Conduct pre-lift meeting
• Define roles and responsibilities
• Identify hazards

On-Site Controls:

• Equipment inspection and certification
• Establish exclusion zones
• Ensure proper communication (radio + signalman)

Safety Measures:

• Use tag lines to control load swing
• Monitor wind conditions
• Assign a lift supervisor with full authority

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4. Risk Assessment and Mitigation

4.1 Electrical Risks

• Working near energized lines
• Maintain minimum clearance
• Assign dedicated safety observer

4.2 Crane Stability Risks

• Overloading
• Excessive lifting radius
• Weak ground support

4.3 Mechanical Risks

• Load swing
• Rigging failure
• Structural collision

Mitigation Tools:

• Job Safety Analysis (JSA)
• Permit to Work (PTW) system
• Compliance with international safety standards

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5. Case Study: 380kV Double-Circuit Tower

5.1 Project Overview

A high-voltage transmission tower was erected under constrained site conditions and near energized lines, requiring precise planning and execution.

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5.2 Lifting Configuration

• Crane Capacity: 160 Ton Mobile Crane
• Working Radius: 22 meters
• Boom Length: 74 meters

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5.3 Load Analysis

Component	Load (Ton)	Crane Capacity (Ton)	Utilization
Peak	0.95	11.0	9%
Cross Arm	2.9	13.2	22%
Cage	3.8	11.3	34%

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5.4 Key Findings

• All lifts were below 35% crane utilization
• Strong safety margins maintained
• Stable lifting radius ensured
• Minimal dynamic effects observed

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6. Discussion

This study highlights that a well-engineered lifting plan significantly improves both safety and efficiency in OHTL tower erection.

Key Takeaways:

• Conservative crane utilization reduces risk
• Controlling lifting radius is critical
• Proper segmentation improves lift stability
• Ground assessment is as important as load calculation

By adopting a systematic engineering approach, lifting operations can be transformed from high-risk activities into controlled and predictable processes.

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Conclusion

Safe lifting in OHTL projects is not just about following procedures—it is about applying engineering principles to every stage of planning and execution.

A structured lifting methodology ensures:

• Enhanced safety
• Reduced operational risk
• Improved project efficiency

For engineers and project managers in transmission line construction, investing time in detailed lift planning is essential for achieving zero-incident projects.

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