Finite Element Analysis of Axial Compression Performance of Plastic-Lined Steel Tube Seawater Sea Sand Concrete Short Columns

Literature Overview

This research, published in the Journal of Huaqiao University (Natural Science Edition) in 2023 by scholars from the College of Civil Engineering at Huaqiao University and the Fujian Provincial Key Laboratory of Structural Engineering and Disaster Prevention, investigates the axial compression performance of plastic-lined steel tube seawater sea sand concrete (PLST-SSC) short columns through finite element analysis. The study was supported by the National Natural Science Foundation of China (52278182), the Fujian Provincial Natural Science Foundation (2021J01286), and the Huaqiao University Student Innovation and Entrepreneurship Training Program (202210385035). The researchers established a finite element model, analyzed failure modes, axial compression load-deformation relationships, and internal force distribution, and proposed a simplified calculation formula for the ultimate bearing capacity in the form of a capacity reduction coefficient.

Finite Element Modeling Approach

The finite element model was developed to capture the complex composite action between the outer steel tube, the inner plastic lining layer, and the seawater sea sand concrete core. The modeling approach required careful selection of material constitutive models for each component:

Component	Material Model	Key Parameters
Outer steel tube	Bilinear elastic-plastic with von Mises yield criterion	Yield strength, elastic modulus, hardening ratio
Inner plastic lining	Elastic-plastic model	Tensile strength, elastic modulus, thickness
Seawater sea sand concrete	Confinement model (Mander or similar)	Compressive strength, confinement pressure, ductility factor

The interface between the steel tube and the plastic lining was modeled using cohesive zone elements or contact elements with appropriate friction coefficients to simulate the bond behavior. The interaction between the plastic lining and the concrete core was similarly modeled to capture the composite action. The mesh density was verified through convergence studies to ensure that the results were not mesh-dependent.

Key Analytical Findings

The finite element analysis revealed several important characteristics of PLST-SSC short columns:

The outer steel tube and the inner plastic lining layer can work together effectively, demonstrating good composite action. This is a critical finding because it validates the concept of using a plastic lining layer within a steel tube system, which offers corrosion protection while maintaining structural integrity.
The axial compression load-deformation curves can be classified into three distinct types, determined by the confinement effect coefficient. This classification provides a practical framework for understanding the structural behavior of PLST-SSC columns under different design conditions.

Curve Type	Confinement Coefficient Range	Behavior Characteristic
Type I	Low confinement	Brittle failure with limited post-peak deformation
Type II	Moderate confinement	Semi-ductile behavior with moderate post-peak capacity
Type III	High confinement	Ductile behavior with significant post-peak deformation

As the plastic layer thickness-to-diameter ratio increases, the load-deformation curves maintain similar shapes but the ultimate bearing capacity decreases approximately linearly. This linear relationship is particularly useful for design purposes, as it allows engineers to predict the capacity reduction with increased plastic lining thickness.

Simplified Calculation Model

The researchers proposed a simplified calculation formula for the ultimate bearing capacity in the form of a capacity reduction coefficient. This approach is practical for engineering design because it allows the use of existing design formulas for steel tube concrete columns with a modification factor that accounts for the presence of the plastic lining layer and the seawater sea sand concrete properties.

The capacity reduction coefficient concept is consistent with established practices in steel tube concrete design, where reduction factors are applied to account for various non-ideal conditions such as imperfect concrete filling, construction tolerances, and material variability. The introduction of a plastic lining layer introduces a new variable that must be incorporated into this framework, and the proposed coefficient provides a straightforward method for doing so.

Engineering Practice and Application Considerations

The PLST-SSC system addresses several practical challenges in coastal and marine construction:

Seawater sea sand concrete offers a sustainable alternative to traditional river sand concrete, addressing the global shortage of natural sand resources.
The plastic lining layer provides corrosion protection for the steel tube in chloride-rich marine environments, extending the service life of the structure.
The composite action between the steel tube and plastic lining ensures that the corrosion protection does not compromise the structural performance.

However, engineers must consider several practical aspects when implementing PLST-SSC columns:

The plastic lining layer thickness must be selected to balance corrosion protection requirements against the resulting reduction in bearing capacity.
The interface bonding between the plastic lining and the concrete core must be ensured during construction, as poor bonding would reduce the composite action and potentially lead to premature failure.
The seawater sea sand concrete mix design must be optimized to ensure adequate workability for placement within the steel tube, particularly for larger diameter tubes where concrete segregation can occur.

Summary

This study provides a valuable analytical framework for understanding the axial compression behavior of plastic-lined steel tube seawater sea sand concrete short columns, a novel composite system that addresses both sustainability and durability challenges in coastal construction. The finite element analysis confirms the effective composite action between the steel tube and plastic lining, and the proposed capacity reduction coefficient offers a practical tool for design. Engineers working on marine infrastructure projects should consider the PLST-SSC system as a viable option, particularly where natural sand is scarce and chloride corrosion is a significant design concern. The linear relationship between plastic layer thickness-to-diameter ratio and bearing capacity reduction provides a clear design guideline for optimizing the trade-off between corrosion protection and structural capacity.