Controlled Blasting Demolition Scheme for Through-Arch Steel Tube Concrete Arch Bridge

Literature Overview

This 2012 paper published in "Blasting" (Volume 29, Issue 1, pages 65-68) by Deng Xiaoying and colleagues from Gezhouba Yipuli Co., Ltd., documents a controlled blasting demolition project for a through-arch steel tube concrete arch bridge in a complex environment. The bridge consisted of a main bridge and approach bridge components, with steel tubes filled with concrete forming the arch ribs, creating a structurally complex target.

Technical Design Approach

The demolition required careful planning due to the complex geometry of the through-arch structure. The arch ribs contained concrete-filled steel tubes, which presented unique challenges because the concrete provides substantial mass and confinement, while the steel tubes add tensile strength and ductility to the structure.

Design Parameter	Technical Approach	Purpose
Collapse direction	Controlled directional fall	Safety and land use
Charge point location	Strategic placement	Efficient energy transfer
Blasting method	Controlled demolition	Minimize damage to surroundings
Detonation sequence	Carefully timed	Control collapse sequence
Pre-cutting	Mechanical cutting of key connections	Weaken structure before blast

Pre-Cutting and Structural Weakening

Pre-cutting is a critical step in the controlled demolition of steel tube concrete structures. The steel tubes must be cut at predetermined locations to create the intended failure planes. Without adequate pre-cutting, the ductility of the steel tubes would absorb blast energy and prevent the intended collapse direction. The pre-cutting depth and location determine the hinge points around which the structure rotates during collapse.

The concrete fill within the steel tubes increases the inertial mass of the arch ribs, which affects the required charge weight and the collapse velocity. Engineers must calculate the mass of each structural segment to ensure that the blast energy is sufficient to overcome both the structural strength and the inertial resistance.

Blasting Design Parameters

The charge design involved careful calculation of charge weight, borehole arrangement, and loading patterns. The detonation network was designed to initiate charges in a specific sequence to guide the collapse in the predetermined direction. The timing delays between charge groups are critical: too short a delay results in simultaneous failure and uncontrolled collapse, while too long a delay may cause partial collapse that obstructs the intended failure path of subsequent segments.

Blasting Parameter	Typical Range	Function
Charge weight per borehole	Calculated per mass	Ensure sufficient energy
Borehole diameter	32-50 mm	Charge containment
Burden distance	Based on mass	Control fragmentation
Spacing between boreholes	1.0-1.5 times burden	Uniform loading
Delay interval between groups	50-150 ms	Sequence control

Safety Measures and Environmental Protection

The complex environment surrounding the bridge necessitated comprehensive safety measures. These included blast vibration monitoring to protect nearby structures, dust suppression through water spraying, and debris containment barriers to prevent flyrock from reaching occupied areas. The safety distance calculation considered both the maximum charge per delay and the total charge weight.

Engineering Practice Implications

For engineers involved in demolition projects involving steel tube concrete structures, this case study demonstrates several important principles. First, the composite nature of the structure requires understanding both the concrete and steel behaviors. Second, pre-cutting is not optional but essential for achieving the intended collapse pattern. Third, the detonation sequence must be carefully optimized through numerical simulation and field testing where possible.

The FMEA approach applied to this demolition identified several critical failure modes: incomplete pre-cutting leading to uncontrolled collapse direction, incorrect delay timing causing progressive failure deviation, and insufficient charge weight resulting in partial collapse that could endanger personnel. Each of these was addressed through redundant verification steps in the construction plan.

Key Reflections

This demolition project illustrates the intersection of structural engineering and blasting technology. The through-arch configuration with steel tube concrete ribs presents a challenging target because the steel provides ductility that resists the brittle fracture mechanism relied upon in conventional concrete demolition. Engineers must therefore allocate more energy to overcoming the steel's tensile strength while ensuring that the collapse geometry follows the designed path. The successful execution of this project provides valuable reference data for similar future demolitions.

Summary

The controlled blasting demolition of a through-arch steel tube concrete arch bridge required integrated technical design encompassing collapse direction planning, strategic charge placement, careful pre-cutting of steel tubes, optimized detonation sequencing, and comprehensive safety measures. The successful execution of this project demonstrates that with thorough analysis of the structural behavior and precise control of blasting parameters, even complex composite structures can be safely and efficiently demolished in constrained environments.