Behaviour of Hollow Reinforced Concrete Columns

Many construction buildings and Structural barrier members that was built before 90s in USA, they weren't designed for Seismic resistance until Federal Emergency Management Agency FEMA started to do seismic evaluation and rehabilitation and suggested reinforcement methods. In this article we evaluate FRP sheet reinforcement.

Hollow Concrete Columns (HCCs) are one of the preferred construction systems in civil infrastructures including bridge piers, ground piles, and utility poles to minimize the overall weight and costs. HCCs are also considered a solution to increase the strength to mass ratio of structures. However, HCCs are subjected to brittle failure behaviour by concrete crushing means that the displacement capacity and the strength after steel yielding in HCCs are decreasing due to the unconfined concrete core. Absence of the concrete core changes the inner stress formation in HCCs from triaxial to biaxial causes lower strength. A new type of Hollow Composite Reinforcing System (HCRS) has recently been designed and developed to create voids in structural members. This reinforcing system has four external flanges to facilitate mechanical bonding and interaction with concrete. Therefore, providing the inner Hollow Composite Reinforced Sections (HCRS) can significantly increase strength by providing a higher reinforcement ratio and confining the inner concrete core triaxially. The corrosion of steel is also a notable factor in the case of steel reinforced HCCs which became more critical because their outer and inner surfaces exposing more concrete surface area. An alternative reinforcement is Glass Fibre Reinforced Polymer (GFRP) bars, can overcome the brittle behaviour of steel reinforced HCC. In previous studies, HCC shows high strength capacity, when appropriate reinforcement in the form of longitudinal GFRP bars, laterally using GFRP spirals and internally using newly developed HCRS which provide enough inner confinement. Therefore, this study aims to determine the effect of HCRS of different cross sections and also the effect of change in position of its flanges on the axial performance of HCC analytically using ANSYS software.

The National Association of Students of Architecture (NASA India) is one of the largest Architectural Student Organizations in the world with student participants from over three hundred colleges. When NASA was held at Sir JJ College of Architecture in Bombay in 1981, it was relatively an intimate affair as there were only about 22 colleges in the country. The editorial board of the NASA journal Akriti, decided to have articles by professionals and one student. My student contribution (audaciousness notwithstanding; the science is suspect) began a journey of publishing essays that continues (it was predated only by my interview of Hasan Fathy in 1980).

Soon after, I misplaced my copy. Inquiries some years ago with friends and JJ College archives, drew a blank. But thanks to Ajit in Lonavala, who recently located someone who still had a copy after 38 years!  It was Jacob in Goa: "The mag is not in good condition, but it’s one of the few that survived half a dozen house/ office moves, 1995/6 floods (we had 3ft water in house) & rising damp..."

Jacob and I had jammed together on Me & Bobby McGee -  he on guitar and vocals and I finger drummed on a matka as makeshift ghatam. We were strangers one night around a bonfire, during NASA 1980 in Hyderabad. Song over, I had got up and left. We met again only a decade later, at JJ, and recognized each other.

Thank you Ajit, Jacob and Dean (whose office scanned Jacop’s copy). The Richard Bach quote at the end of the essay, added by Akriti’s astute editor Kavita, was indeed prophetic:

“And meeting again, after moments or lifetimes, is certain for those who are friends.”

December 31, 2020

Confining concrete is an effective method to enhance the strength and ductility of reinforced concrete columns.
Fibre reinforced polymer (FRP) composites are emerging as a suitable confining material to replace conventional
materials such as steel and fibre-reinforced cement composites. Past research on the behaviour of FRP confined
concrete in compression is considerable; however, limited research has been reported on the behaviour of confined
concrete under sustained compressive loading. This paper reports the preliminary results of an experimental
investigation on the deformational behaviour of carbon FRP (CFRP) confined concrete columns under sustained
compressive stress levels, corresponding to 40% and 60% of the unconfined concrete compressive strength for up to
150 days. The results show that the creep of confined concrete columns is marginally influenced under moderate
sustained stress/strength ratios.

This paper presents a finite-element (FE) analysis of hybrid fiber-reinforced polymer (FRP)-concrete-steel double-skin tube (FSDT) in the form of columns. The FSDT columns that were examined consisted of a concrete wall sandwiched between an outer FRP tube and an inner steel tube. A FE software was used to develop a pushover analysis of three-dimensional FSDT models to simulate seismic loading. The FE models were validated against the experimental results gathered from seven FSDT columns tested under cyclic loading. The FE analysis results were in good agreement with the experimental backbone curves. The maximum error was 9% in predicting the bending strengths of the columns. Aparametric study evaluated the effect of axial load level, concrete wall thickness, concrete strength, diameter-to-thickness ratio (D=t) of the steel tube, and number of FRP layers on the FSDT columns’ behavior. This study revealed that the behavior of FSDT columns is quite complex. It also revealed that this behavior is controlled by the interactions that occur among the steel tube’s stiffness, the concrete wall’s stiffness, and the FRP hoop’s stiffness. Local buckling occurred in all of the specimens examined. This buckling caused the FSDT system to rupture. Two modes of failure were defined as follows: (1) steel/concrete compression failure, and (2) FRP rupture. Compression failure was relatively gradual whereas failure due to FRP rupture was quite abrupt. Finally, the bending strength increased as the applied axial load, concrete compressive strength, and number of FRP layers increased. The bending strength also increased as both the concrete wall’s thickness and the D=t decreased.