Zhuojin Pipe Fitting Co., LtdBlast Resistance and Dynamic Response of Steel Tube Concrete Piers Under Explosive Loading
Literature Overview
This study by Sun Shanshan, Zhao Junhai, He Shuanhai, Cui Ying, and Liu Yan, published in Engineering Mechanics (2018, Vol. 35, No. 5, pp. 27–35), investigates the dynamic response of steel tube concrete (SRC) piers under blast loading through static explosion tests and finite element analysis. The research was funded by the Specialized Research Fund for Doctoral Program of Higher Education (20110205130001), the China Postdoctoral Science Foundation (2015M580803), and the Central University Basic Research Business Expenses Special Fund. The work is particularly relevant to engineers involved in the design of highway bridge piers, petrochemical facilities, and other critical infrastructure that may face terrorist or accidental blast threats.
Core Experimental Configuration and Key Parameters
The research team designed and fabricated four specimens: three conventional SRC piers and one double-walled hollow SRC pier. Static explosion tests were conducted using TNT charges of 3 kg and 50 kg, covering four loading scenarios. The following table summarizes the key specimen parameters and test conditions.
| Parameter | Conventional SRC Pier | Double-Walled Hollow SRC Pier |
|---|---|---|
| Outer diameter | 273 mm | 273 mm |
| Outer wall thickness | 7 mm | 7 mm |
| Inner tube inner diameter | N/A | 50 mm |
| Inner tube wall thickness | N/A | 4 mm |
| TNT charge | 3 kg and 50 kg | 3 kg and 50 kg |
| Scale distance (z) | 0.14 m/kg^(1/3) and >0.3 m/kg^(1/3) | 0.14 m/kg^(1/3) and >0.3 m/kg^(1/3) |
The tests measured cylindrical overpressure distribution on both the windward and leeward surfaces, residual deformation, and final failure modes. A multi-material fluid-structure coupling numerical simulation method was developed based on the test results, which was shown to effectively simulate the dynamic response of SRC piers under blast loading.
Interpretation of Technical Points
Failure Modes Under Blast Loading
The study identifies three typical failure modes for SRC piers under blast loading, which are governed by the relationship between overpressure peak and duration:
- Bending failure — occurs under low overpressure peak with high duration. The pier deforms in a global bending mode, with the maximum displacement occurring at the mid-height.
- Shear failure — occurs under high overpressure peak with low duration. The failure is localized near the loading point, with diagonal cracking and steel tube rupture.
- Bending-shear combined failure — occurs at intermediate conditions between the above two extremes.
This classification is critical for engineers designing blast-resistant structures, as it directly influences the selection of reinforcement strategies and section design.
Effect of Scale Distance on Residual Deformation
A key finding is that when the TNT charge is 50 kg and the scale distance z exceeds 0.3 m/kg^(1/3), the residual deformation of the test specimens becomes negligible. This provides a practical threshold for engineers to assess the blast threat level and determine whether a given structure can withstand a specific explosive threat with acceptable residual damage.
Influence of Material Properties
The study systematically examined the effects of core concrete strength grade, steel ratio, and steel tube yield strength on blast resistance:
| Parameter | Effect on Blast Performance |
|---|---|
| Core concrete strength increase | Effectively reduces mid-point horizontal residual deformation |
| Steel ratio increase | Effectively reduces mid-point horizontal residual deformation |
| Steel tube yield strength increase | Reduces mid-point residual deformation |
| Steel yield strength ≥ 345 MPa | Further increase provides diminishing returns on blast resistance |
The diminishing returns observation for steel yield strength beyond 345 MPa is particularly noteworthy from a cost-benefit perspective. Engineers should recognize that upgrading steel grades beyond Q345 may not provide proportional improvements in blast performance, and the additional material cost may not be justified.
Double-Walled vs. Conventional SRC Pier
Under 50 kg TNT at a scale distance of 0.14 m/kg^(1/3), the conventional SRC pier with 273 mm outer diameter and 7 mm wall thickness exhibited superior blast resistance compared to the double-walled hollow SRC pier with 50 mm inner tube diameter and 4 mm inner wall thickness. This finding challenges the intuitive assumption that adding an inner tube always improves performance. The inner tube may introduce additional interfaces that can serve as crack initiation sites under high-strain-rate loading, and the overall stiffness distribution may not be optimally configured for blast energy absorption.
Engineering Practice Integration
From the perspective of steel pipe manufacturing and welding quality control, several practical implications emerge:
- Steel tube manufacturing quality directly affects blast performance. The 7 mm wall thickness tubes must meet strict dimensional tolerances to ensure uniform confinement pressure distribution on the core concrete. Any local thinning from rolling defects or machining errors can create weak zones under blast loading.
- Welding quality at the steel tube-concrete interface and any spliced joints is critical. Under blast loading, the strain rates can exceed 100 s⁻¹, and welding defects such as lack of fusion, porosity, or slag inclusions can act as crack initiation sites under these extreme conditions.
- Material certification should include dynamic mechanical property verification, not just static tensile properties. The Charpy V-notch impact energy at relevant service temperatures is particularly important for structures in cold environments where blast events may occur.
Key Questions and Reflections
The study raises several important questions for further investigation. First, the comparison between conventional and double-walled SRC piers was conducted at a specific geometric configuration. Whether the double-walled approach can be optimized for better blast performance by adjusting the inner tube dimensions and wall thickness remains open. Second, the numerical simulation method developed was validated against static explosion tests, but the applicability to dynamic blast events with varying charge types and initiation methods needs further verification. Third, the study focuses on residual deformation as the primary performance metric, but the impact of blast-induced vibration on surrounding structures and equipment is not addressed.
Study Insights and Implications
This research provides valuable quantitative data for the design of blast-resistant SRC piers in highway bridges and petrochemical facilities. The identification of three distinct failure modes based on overpressure characteristics offers a practical framework for engineers to assess structural vulnerability under different blast scenarios. The practical threshold of z > 0.3 m/kg^(1/3) for negligible residual deformation provides a useful design criterion. The finding that steel yield strength beyond 345 MPa offers diminishing returns is particularly relevant for cost-conscious engineering design. Overall, this work bridges the gap between experimental blast testing and practical structural design, offering engineers a solid foundation for blast-resistant design of steel tube concrete structures in critical infrastructure applications.