Zhuojin Pipe Fitting Co., LtdDynamic Response of Steel Pipe Towers Under Strong Earthquake Considering Damage Accumulation Effects
Literature Overview
This paper by Tian Li and Ma Ruisheng (2016), published in Earthquake Engineering and Engineering Dynamics (Vol. 36, No. 5, pp. 132-138), addresses the seismic performance of large-span steel pipe towers. The research was supported by the National Natural Science Foundation of China (Grants 51578325, 51208285) and the China Postdoctoral Science Foundation (Grant 2012M521338). The authors developed a damage accumulation material subroutine (VUMAT-D) and applied incremental dynamic analysis (IDA) to evaluate the collapse resistance of steel pipe towers.
Core Technical Content
Damage Accumulation Material Model (VUMAT-D)
The authors developed a user-defined material subroutine VUMAT-D for ABAQUS/Explicit that incorporates progressive damage accumulation effects. The validation was performed through axial constant-amplitude loading tests on individual steel tubes. The model captures the following phenomena:
- Cyclic hardening and softening: Progressive reduction in stiffness and strength under repeated loading
- Cumulative plastic strain damage: Damage index D accumulates with each loading cycle, reaching unity at failure
- Stress-strain degradation: The stress-strain backbone curve evolves with damage level
Incremental Dynamic Analysis (IDA) Approach
The IDA methodology involves:
- Scaling a set of ground motion records to different PGA levels
- Running nonlinear time-history analysis at each intensity level
- Plotting demand parameters (top displacement, inter-story drift) against PGA
- Identifying the collapse PGA and collapse location
Variable α for Collapse Assessment
The authors propose a variable α to simultaneously assess the collapse resistance and identify the collapse location within the tower structure. This provides a more practical tool for post-earthquake evaluation and repair prioritization.
Key Technical Parameters and Findings
| Analysis Parameter | Finding / Value |
|---|---|
| Node mass effect on dynamic response | Significant; cannot be neglected in modeling |
| Damage accumulation effect on top displacement | Increases peak displacement by a notable margin compared to non-damage model |
| Collapse location identification | Achieved through variable α |
| Validation method | Axial constant-amplitude loading on single steel tube |
| Model type | 3D finite element model based on real engineering |
Engineering Practice Implications for Steel Pipe Supply
From the perspective of steel pipe manufacturing and quality control, several critical implications emerge:
- Material consistency is paramount: Since damage accumulation is inherently material-dependent, variations in steel grade, heat treatment, and microstructure between individual pipes in the same tower can lead to unpredictable damage localization and premature collapse.
- Fracture toughness requirements: Steel pipe towers subjected to strong earthquake loading experience low-cycle fatigue and potential low-temperature ductile fracture. The Charpy V-notch impact energy at the service temperature must meet stringent requirements (typically ≥47 J at the lowest expected temperature per API 5L or GB/T 9711).
- Weld quality at gusset connections: The collapse mechanism in steel pipe towers is often governed by the failure of gusset plate connections. The welding procedures (SMAW, SAW, or FCAW) used for these critical joints must be qualified per ASME IX or GB/T 985, with full NDT coverage (RT + MT or PT).
- Residual stress management: High residual stresses from cold forming or welding can accelerate fatigue damage accumulation. Stress relief procedures (local or full heat treatment) should be considered for critical members.
Key Questions and Reflections
- The paper validates VUMAT-D using axial loading tests, but real tower members experience multi-axial stress states. How well does the uniaxial damage model translate to complex member behavior?
- The influence of node mass on dynamic response is highlighted—this has direct implications for the accuracy of finite element models. In practice, how should engineers estimate the effective node mass, including contributions from gusset plates, bolts, and secondary members?
- The paper focuses on collapse assessment but does not extensively discuss post-earthquake repairability. For steel pipe towers in critical infrastructure (transmission towers, bridge piers), the repair strategy after partial damage is a practical concern.
Study Insights and Implications
The most significant contribution of this work is the demonstration that neglecting damage accumulation effects leads to non-conservative predictions of seismic demand. For engineers specifying steel pipes for tower applications, this means that material properties must be selected not only for their initial strength and stiffness but also for their damage tolerance—resistance to progressive degradation under cyclic loading. The practical implication is that higher-grade steels with better fatigue properties (e.g., X70 or higher per API 5L) may be warranted for seismic zones, despite their higher cost, because the damage accumulation effect can shift the failure mode from ductile yielding to brittle fracture or fatigue crack propagation.