CFRP retrofitting of existing structures to increase resilience against extreme scenarios using AEM: the pancake collapse

Document Type

Article

Publication Date

2025

Abstract

The World Trade Center disaster is a powerful reminder of the devastating impact that terrorist attacks can have on modern structures in today’s cities. In contrast to lateral collapses that are supposed to occur due to the extreme lateral hazard from the airplane crash, the Twin Towers suffered from a catastrophic vertical collapse that is referred to as the “pancake Collapse/Failure”. This type of progressive collapse occurs when upper floors rapidly collapse onto lower floors as a result of the loss of main structural support. Existing building stock is now targeted to be adaptively reused, many of which are of strategic significance. The main aim of this research is to model the retrofitting of existing structures to endure extreme loading. Applied Element Method (AEM) is adopted in this research and Extreme Loading for Structures (ELS) software is used. Three retrofitting scenarios are applied on different structural elements (columns and slabs) of a prototype model to strengthen the overall structure to resist pancake collapse. Case (1) targeted retrofitting of the slab using Carbon Fiber Reinforced Polymer (CFRP) strips obliquely fixed at corners as an endeavour to dampen the impact from the above slabs. Case (2) is column jacketing using CFRP to create a load path for the impact force and finally, case (3) uses concrete column jacketing with CFRP strips on the slab. The concrete column jacketing served as the best path to eliminate the pancake effect as it stopped the sequential collapse of subjected slabs. By implementing this technique in real-life existing structures, occupants of the building will have a much longer time to evacuate in case of losing vertical supporting system followed by slab impact on the lower portion of the building. This approach can save lives through various retrofitting applications that delay collapse and redistribute loads across the structure under distress.

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