Title:
Axial Load-Bearing Concrete Confined with UHPC Jackets and BFRP Grids (Prepublished)
Author(s):
Yail J. Kim and Yordanos Dinku
Publication:
Structural Journal
Volume:
Issue:
Appears on pages(s):
Keywords:
fiber-reinforced polymer (FRP); rehabilitation; retrofit; strengthening; ultra-high-performance concrete (UHPC)
DOI:
10.14359/51743290
Date:
10/7/2024
Abstract:
This paper presents the behavior of unreinforced cylindrical concrete elements confined with a hybrid system, consisting of an ultra-high-performance concrete (UHPC) jacket and basalt fiber reinforced polymer (BFRP) grids. For exploring the feasibility of the proposed strengthening scheme, a series of tests are conducted to evaluate material properties and to obtain results related to interfacial bond, load-bearing capacity, axial responses, and failure modes. In order to understand the function of the individual components, a total of 57 cylinders are loaded under augmented confining conditions, including plain cores with ordinary concrete (CONT), plain cores with UHPC jackets (Type A), and plain cores with UHPC jackets plus BFRP grids (Type B). By preloading the cores at up to 60% of the control capacity (60%f’c) before applying the confinement system, the repercussions of inherent damage that can take place in vertical members on site are simulated. The compressive strength of UHPC rapidly develops within 7 days, whereas its splitting strength noticeably ascends after 14 days. The adhesion between the ordinary concrete and UHPC increases over time. While the Type B specimens outperform their Type A counterparts in terms of axial capacity by more than 18%, reliance on the BFRP grids is reduced with the growth of UHPC’s strength and adhesion because of the interaction between the hardened UHPC and the core concrete. The adverse effects of the preloading are noteworthy for both types, especially when exceeding a level of 30%f’c. The BFRP-grid wrapping alleviates the occurrence of a catastrophic collapse in the jacketed cylinders, resulting from a combination of the axial distress and lateral expansion of the core. Analytical models explain the load-carrying mechanism of the strengthened concrete, including confinement pressure and BFRP stress. Through parametric investigations, the significance of the constituents is clarified and design recommendations are suggested.