Stress Characteristics of Above-Ground Steel Pipe Crossing Active Faults Under Fault Creep and Seismic Loading

Literature Overview

The paper by Li Duanzheng, Zhang Wenquan, Yang Yaoxiang, Shi Changzheng, and Wu Hegao from Wuhan University and Yunnan Dianzhong Water Diversion Engineering Co., Ltd., published in Water Power (2023, Vol. 49, No. 3, pp. 57-62), addresses a critical infrastructure challenge in large-scale water conveyance projects. As major water diversion schemes traverse seismically active regions, the design of above-ground steel pipe (AGSP) crossings over active faults has become increasingly important. The study combines finite element analysis with practical engineering considerations to evaluate structural behavior under both fault creep deformation and seismic loading.

Research Context and Engineering Challenges

Active fault crossings represent one of the most challenging design scenarios in pipeline engineering. The pipe must accommodate two fundamentally different deformation modes:

• Fault creep deformation: Slow, continuous relative displacement along the fault plane, typically accumulating at rates of 1-10 mm/year depending on the fault type and tectonic setting.
• Seismic loading: Rapid, dynamic ground displacement and acceleration during earthquake events, potentially causing displacements of 0.5-2.0 m in a single event.

The study was funded by the Yunnan Province Major Science and Technology Special Project (202102AF080001), reflecting the practical urgency of this research for the Yunnan-Provincial water diversion project.

Structural Configuration and Design Elements

The paper examines the following key structural elements in the fault crossing design:

Key Research Findings

The finite element analysis revealed several important conclusions:

1. Bellows effectiveness: Bellows expansion joints can absorb the majority of fault creep deformation, making them the primary design element for accommodating slow fault movement. The number and spacing of bellows joints must be carefully calibrated to the expected creep displacement rate and design life.
2. Seismic axial displacement: The axial deformation of the steel pipe is significantly influenced by both seismic loading and fault creep, with pipe segments having bellows joints at both ends exhibiting the largest axial displacements. These segments effectively act as free bodies with limited axial restraint.
3. Fixed support vulnerability: While fixed supports are necessary to limit axial displacement during seismic events, the associated support rings are prone to bending deformation under the concentrated loads transferred from the pipe. This represents a critical design consideration that requires careful structural analysis and potentially reinforced support ring designs.
4. Combined loading: The interaction between creep and seismic effects is complex. Pre-existing creep deformation changes the initial conditions for seismic response, potentially leading to larger displacements than would be predicted from seismic loading alone.

Technical Analysis and Design Recommendations

From a pipeline engineering perspective, the following design principles emerge:

• Bellows joint sizing: The bellows expansion joints must be sized to accommodate the total expected creep displacement over the design life of the pipeline (typically 50-100 years). For a fault with a creep rate of 5 mm/year over 50 years, the total displacement would be 250 mm, requiring bellows with sufficient stroke capacity.
• Support ring reinforcement: The bending deformation of support rings at fixed supports should be evaluated using shell element analysis or 3D solid element modeling. The reinforcement strategy may include increasing ring thickness, adding stiffening ribs, or using composite ring designs.
• Seismic isolation: The sliding bearings must be designed to maintain their function throughout the design earthquake, with adequate clearance and friction characteristics to prevent binding.
• Monitoring requirements: Post-construction monitoring of fault creep displacement and pipe strain should be implemented to verify design assumptions and detect any unexpected behavior.

FMEA Analysis of Potential Failure Modes

Study Insights and Engineering Implications

This research contributes significantly to the design methodology for fault-crossing pipeline systems. The key insight is that the design must address two fundamentally different loading regimes—slow quasi-static creep and rapid dynamic seismic loading—using complementary structural elements. The bellows joints and sliding bearings handle creep effectively, while fixed supports with reinforced rings are essential for seismic restraint. The study also highlights an important practical consideration: the interaction between these elements is not independent, and the combined effects must be analyzed in an integrated structural model. For engineers involved in large water diversion projects crossing seismically active zones, this paper provides a validated analytical framework and practical design guidance. The recommendation to pay special attention to support ring design at fixed supports is particularly valuable, as this element is often underestimated in preliminary design stages. Future work should address the long-term fatigue behavior of bellows joints under cyclic creep loading and the seismic performance of the complete pipe-fault system under multiple earthquake events.