# Polyethylene Storage Tanks Strengthened Externally with Fiber-Reinforced Polymer Laminates

## TL;DR

This paper explores using fiber-reinforced polymer to strengthen polyethylene storage tanks for better seismic performance.

## Contribution

The study introduces a CFRP retrofitting method with surface preparation guidelines to improve tank resilience during earthquakes.

## Key findings

- Tensile tests show anchorage length over 450 mm prevents slippage in CFRP-strengthened polyethylene.
- Mechanical sanding increases surface intensity variation by over 127%, improving bonding potential.
- CFRP full-wrap retrofitting reduces seismic stress and elephant foot buckling in polyethylene tanks.

## Abstract

Polyethylene storage tanks are widely used for storing water and chemicals due to their lightweight and corrosion-resistant properties. Despite these advantages, their structural performance under seismic conditions remains a concern, mainly because of their low mechanical strength and weak bonding characteristics. In this study, a method of external strengthening using fiber-reinforced polymer (FRP) laminates is proposed and explored. The research involves a combination of laboratory testing on carbon fiber-reinforced polymer (CFRP)-strengthened polyethylene strips and finite element simulations aimed at assessing bond strength, anchorage length, and structural behavior. Results from tensile tests indicate that slippage tends to occur unless the anchorage length exceeds approximately 450 mm. To evaluate surface preparation, grayscale image analysis was used, showing that mechanical sanding increased intensity variation by over 127%, pointing to better bonding potential. Simulation results show that unreinforced tanks under seismic loads display stress levels beyond their elastic limit, along with signs of elephant foot buckling—common in thin-walled cylindrical structures. Applying CFRPs in a full-wrap setup notably reduced these effects. This approach offers a viable alternative to full tank replacement, especially in regions where cost, access, or operational constraints make replacement impractical. The applicability is particularly valuable in seismically active and densely populated areas, where rapid, non-invasive retrofitting is essential. Based on the experimental findings, a simple formula is proposed to estimate the anchorage length required for effective crack repair. Overall, the study demonstrates that CFRP retrofitting, paired with proper surface treatment, can significantly enhance the seismic performance of polyethylene tanks while avoiding costly and disruptive replacement strategies.