Research Topic:Effect of carbon fiber reinforced polymer retrofitting on rectangular recycled brick aggregate concrete column subjected to axial load

Problem Statement:
In Bangladesh, there have been several catastrophic breakdowns of structures that were structurally inadequate. The collapse of the reinforced concrete building used as a garment factory, which resulted in the loss of many lives, is the most notable among them. Because columns are the most important structure element, retrofitting the column has become a key priority in recent years [1]. Due to the poor material strength, inadequate capacity, and lack of ductile detailing, many of these columns require seismic retrofitting [2].
The structural capacity of the columns can be improved through fiber reinforced polymer (FRP) jacketing. It is more sustainable than dismantling and rebuilding since it conserves resources and has a lower carbon impact [3]. The FRP jacketing is the solution for overcoming the problem of insufficient column ductility in existing substandard buildings [2]. The FRP jacketing has become widely accepted due to their resistance to corrosion, the ability for faster installation, and causing less reduction in floor space. However, they can only increase the axial capacity when the core concrete dilates under axial load and induces hoop strain in the FRP wrap [1]. Pure longitudinal orientations of the FRP composite were similarly shown to have no significant influence on the compressive strength or ductility of the specimens, and their effects may be ignored [3]. There are different types of FRP in construction, like glass fiber reinforced polymer (GCFRP), carbon fiber reinforced polymer (CFRP), and aramid fiber reinforced polymer (ACFRP). Under eccentric compressive load, GCFRP and steel reinforced columns performed less efficiently than CFRP reinforced columns [4].
In most ordinary constructions, rectangular and square columns are utilized. The form of the column is mostly determined to fulfil the aesthetic needs, which may result in an uneconomical column design. Rectangular columns are more economical while used for uniaxial and biaxial loads. Its form lowers moments in lateral directions. However, slender columns are prone to buckling. Therefore, lateral deflection must be minimized [9]. Many studies have looked at brick aggregate's impact on the performance of reinforced concrete (RC) columns. Islam et al. [1] found out that concrete made of brick and recycled aggregate exhibited significantly higher dilation than stone aggregate concrete. Ghatte et al. [2] reported that for one and two layers of external CFRP jacketing, the ultimate drift ratio increased by 4% and 7.5% of columns subjected to an axial load corresponding to 20% of its axial capacity. And drift ratio increased by 3% and 5% for columns subjected to 35% of their axial load capacity. Energy dissipation also increased significantly. Increasing the number of CFRP plies from four to six significantly increased the axial stress, axial strain and hoop strain parameters [6]. Ilk et al. [10] identified that increasing the CFRP sheets' thickness increased the columns' compressive strength. Furthermore, specimens having CFRP confinement did not exhibit buckling of reinforcement and reached much higher strains. As a result, the strength gain of reinforcement due to strain hardening and contribution of concrete cover could be fully used. The confinement effect resulted in enhanced axial capacity and higher axial strain, indicating higher ductility, irrespective of the aggregate used [1]. With bigger column dimensions of circular columns, the effectiveness of CFRP confinement declined [3]. Chen et al. [5] investigated that concrete's unconfined compressive strength and stiffness are reduced when recycled aggregate is used. When the recycled aggregate completely replaces coarse aggregate, the compressive strength and elastic modulus of unconfined concrete are lowered by 26% and 17.4%, respectively.
Following an assessment of the literature, there is a gap in information on rectangular brick aggregate columns with CFRP retrofitting. Thus, this study will investigate the axial compressive strength, axial strain and lateral strain of CFRP retrofitted brick aggregate rectangular column. A guideline will also be proposed for CFRP retrofitting of brick aggregate columns.

Fund Allotted:4,32,450 (BDT)

Objectives:
a. To investigate the compressive strength, axial, and lateral strain of sub-standard brick aggregate rectangular column before and after the carbon fiber reinforced polymer (CFRP) retrofitting.
b. To propose a design guideline for CFRP retrofitting of sub-standard rectangular recycled brick aggregate concrete columns.

Duration:01 year

Expected Outcomes:
This research work is expected to yield relationships between rectangular reinforced concrete columns with aspect ratios h/b 1.0 and 1.5 with CFRP confinement, and that could be used to assess the engineering properties of strengthened columns and evaluate the feasibility of using carbon CFRP confinement for brick aggregate concrete columns of the old structures that have become structurally weak. This research will also help in incorporating the effect of brick aggregate, rectangular columns, and CFRP confinement into the existing design guidelines.