Experimental investigation on axial compressive behavior of fiber reinforced polymer-reinforced concrete columns confined with external fiber reinforced polymer jackets

An innovative glass fiber reinforced polymer (GFRP) closed-type winding (GFRP-CW) tie was developed to eliminate the bond slip failure and make full use of the tensile strength of ties compared with conventional pultruded fiber reinforced polymer (FRP) rod ties. Although better confinement effect of GFRP-CW ties, however after spalling of concrete cover, the compressive longitudinal FRP bars in the plastic hinge regions of columns are most likely to crush or buckle. External FRP jackets can effectively restraint damage to concrete cover. Against this background, a novel FRP-reinforced concrete column confined with external FRP jackets and the internal GFRP-CW ties were proposed to prevent the FRP bars from premature buckling or crushing. In this article, twelve square new columns were constructed and tested to characterize the axial compressive behavior. The test parameters included FRP wrapping type (GFRP or carbon fiber reinforced polymer (CFRP)), FRP wrapping layers, and spacing of ties. Test results confirmed that FRP-reinforced concrete columns with external FRP jackets had significantly larger ductile behavior and exhibited higher load-carrying capacity than their counterparts FRP-reinforced concrete columns due to the contribution of longitudinal GFRP bars and the concrete cover. The test results also suggested reasonable spacing of ties and layers of GFRP jackets for an expected moderate confinement behavior.

Ductility Behaviour of Rectangular Compression Members Retrofitted by Modified Technique of FRP Wrapping

This paper presents an experimental investigation on ductility behaviour of reinforced concrete compression members, rectangular in cross section, modified to elliptical shape in cross section by bonding precast segment covers followed by Carbon Fiber Reinforced Polymer wrapping (CFRP) under concentric and eccentric loading conditions. Eighteen reinforced concrete rectangular compression members of size 100mm×150mm in cross section and 300mm in height were prepared using normal-strength concrete. Reinforcement ratio was kept at minimum, to simulate compression members that need retrofitting. Out of eighteen specimens, nine specimens were converted to elliptical shape in cross section. From nine remaining rectangular specimens, three specimens retained as it is without wrapping FRP and designated as Group1, remaining six specimens were wrapped with one and two layers of CFRP and designated as Group2. Out of nine elliptical specimens, three specimens were retained as it is without wrapping FRP and designated as Group3, remaining six elliptical specimens were wrapped with one and two layers of CFRP and designated as Group4. Specimens were tested upto failure under monotonic axial compression with concentric and eccentric load conditions. From the experimental results, it is observed that rectangular compression members shape modified to ellipse in cross section and then wrapped with CFRP show outstanding increase in the ultimate load carrying capacity which may be due to increased cross sectional area and effective confinement of FRP wrapping. As the number of layers of CFRP increases the ultimate load carrying capacity increases. With increase in eccentricity, the ultimate loads of the compression members were found to be decreased. Elliptical specimens wrapped with one and two layers of CFRP reported exponential increase in deformation ductility under concentric load condition and considerable increase under eccentric load condition compared to rectangular specimens wrapped with CFRP.

Numerical Analysis of Compressed Masonry Columns

This paper presents a three-demensional micro-model for an unreinforced masonry (URM) column and masonry columns reinforced by FRP wrapping (RM). The column with dimensions of 0.3 x 0.3 x 1 m was constituted by twelve rows of solid burnt bricks bonded by mortar joints. The RM column was wrapped in four external FRP sheets. A heterogeneous model, in which masonry units, mortar joints and reinforcement are materially and geometrically accurately described, was chosen. Both bricks and mortar are modelled with independent behavior in compression and tension. The FRP reinforcement is assumed to behave linear-elastically. The reinforcement was modelled under the assumption of perfect adhesion between the elastic FRP strips and the damageable masonry support. Numerical results are compared with experimental ones in order to confirm conclusions about the behavior of URM and RM columns under concentric compressive load determined based on the experimental part of the research program. The comparison between experimental and numerical findings shows good agreement and the adopted numerical model is suitable to predict the ultimate load and allows a better understanding of the behavior of brick masonry columns under concentric compression before and after reaching the ultimate load. For all simulations, the commercial software package ABAQUS was used.

Hollow Beams Strengthened with Steel Fibres and FRP Wrapping

In the field of construction hollow sections have found wide application due to its advantageous properties. Many research works have been conducted to study the flexural and tensional behaviour of hollow reinforced concrete beams. But its behaviour using High-Performance Concrete (HPC) has been poorly noticed. In this study an attempt made to evaluate Hollow reinforced beams made with HPC and reinforced with hybrid steel fibres. The flexural behaviour of hollow beams based on the effect of Carbon fibre reinforced polymer (CFRP) has also been explored. A comparison is made between the results obtained from analysis using ANSYS software with the experimental test result. It is noticeable that the flexural strength, its ductility, and stiffness is not affected but the self-weight of the structure is reduced due to hollow beams.