An experimental investigation to evaluate the seismic ductility of previously damaged concrete columns

Key Insights: An experimental investigation to evaluate the seismic ductility of previously damaged concrete columns

Reinforced concrete columns that have sustained moderate earthquake damage can retain significant seismic performance, and their ductility can be effectively restored and even enhanced through fiber-reinforced polymer (FRP) retrofitting.

Research Focus

This research addresses a critical question for engineers: how does moderate seismic damage affect the ability of concrete columns, particularly those with common construction details like lap splices, to withstand future earthquake events? Understanding this is vital for the safety and longevity of existing infrastructure, especially in regions with increasing seismic activity. The study employed a two-stage experimental approach: first, simulating earthquake damage using pseudo-dynamic testing (PDT), and then evaluating the residual seismic performance through quasi-static cyclic loading tests.

What the Research Found

Finding 1: Moderate damage generally allows for good residual seismic performance.

Except for columns with lap-spliced longitudinal bars, most previously damaged specimens demonstrated a commendable ability to withstand further seismic demands. This suggests that not all damage is catastrophic and that a column's inherent capacity can often carry it through moderate events.

Finding 2: Lap splices significantly reduce seismic performance after damage.

Columns featuring lap splices in their plastic hinge regions showed a marked decrease in seismic performance when subjected to prior damage. This detail, common in older construction, acts as a critical weakness, exacerbating the impact of seismic events.

Finding 3: FRP wraps effectively restore and enhance ductility in damaged columns.

Retrofitting damaged columns with FRP wraps in critical zones proved highly successful. These wraps not only restored the flexural ductility lost due to damage but also often surpassed the original performance levels.

Why It Matters for Practice

This research challenges the assumption that any seismic damage necessitates immediate and extensive repair or replacement. It provides empirical evidence that engineers can leverage to assess the residual capacity of damaged structures more granularly. Furthermore, it highlights the critical vulnerability introduced by lap splices, prompting re-evaluation of seismic design and retrofitting strategies for older bridges. The efficacy of FRP wraps offers a practical and proven solution for extending the lifespan and improving the seismic resilience of existing concrete infrastructure.

Putting It Into Practice

Based on these findings, professionals should consider:

• • Conducting detailed damage assessments to differentiate between minor and critical damage when evaluating columns.
• • Prioritizing retrofitting efforts for columns with lap-spliced reinforcement, especially those in seismically active zones.
• • Exploring FRP wrapping as a viable and effective strategy for enhancing the seismic performance of both damaged and existing columns.

Limitations to Note

The study focused on specific column geometries and simulated earthquake motions representative of the Korean peninsula. While the principles are broadly applicable, the quantitative impact of damage and retrofitting may vary with different seismic environments and column detailing.