Behaviour of RC columns strengthened by steel caging under combined bending and axial loads

TLDR: In this article, an experimental study on the behavior of RC columns strengthened by steel caging under combined bending and axial loads is presented. But the results are only applicable to the beam-column joint.

About: This article is published in Construction and Building Materials.The article was published on 2011-05-01 and is currently open access. It has received 43 citations till now. The article focuses on the topics: Bending moment & Beam (structure).

Figures

Table 2: Predicted and measured FRR and maximum axial displacement ( max)

Fig. 3: Comparison of the maximum axial displacement, calculated versus test results

Fig. 2: Comparison of the fire resistance ratings, calculated versus test results

Table 1: List of CFT columns analyzed, from the NRCC research report [11]

Fig. 1: Comparison between calculated and measured axial displacement, for test no. 4

Fig. 4: Comparison of FRR, proposed numerical model, and EC4 model

Frequently asked questions

Q1. What are the contributions in this paper?

In this work, the ABAQUS finite element analysis package [ 1 ] was employed to model the behaviour of slender axially loaded CFT columns exposed to fire. 

Q2. What are the future works in this paper?

However, if the real behaviour of CFT columns under fire is to be predicted, this factor must be taken into account, extending the failure time. 

Q3. What is the way to increase the fire resistance of a hollow steel column?

if the steel tube is filled with concrete, while the steel section gradually loses its resistance and rigidity, the load is transferred to the concrete core. 

Q4. What is the purpose of the study?

In this work, the ABAQUS finite element analysis package [1] was employed to model the behaviour of slender axially loaded CFT columns exposed to fire. 

Q5. What was the mesh density of the CFT columns?

The mesh density was controlled to have a maximum element size of 2 cm, which proved to be sufficient to predict with enough accuracy the thermal and mechanical behaviour of the CFT columns under fire. 

Q6. What is the way to predict the behaviour of CFT columns?

Fire Resistance of Axially Loaded Slender Concrete Filled Steel TubularColumns Development of a Three-Dimensional NumericalModel and Comparison with Eurocode 4 A. Espinós, A. Hospitaler, M. L. RomeroIn recent years, concrete filled tubular (CFT) columns have become popular among designers and structural engineers, due to a series of highly appreciated advantages: high load-bearing capacity, high seismic resistance, attractive appearance, reduced column footing, fast construction technology and high fire resistance without external protection. 

Q7. Why was the fire resistance test assumed as fixed?

Because of the loading conditions, all the tests were assumed as fix-ended.40 © Czech Technical University Publishing House http://ctn.cvut.cz/ap/For each simulation, the axial displacement at the top of the column versus the fire exposure time was registered, comparing this curve with the curve obtained in the fire resistance test [11]. 

Q8. What is the effect of a steam layer on the concrete core?

combined with a steam layer in the steel-concrete boundary, leads to a lower temperature rise in the concrete core when compared to exposed reinforced concrete structures [7]. 

Q9. What is the maximum axial displacement of the column?

corresponding to those with a higher loading level, over 20 % of the maximum load-bearing capacity of the column at room temperature. 

Q10. What is the way to improve the fire resistance of a CFT column?

it is necessary to resort to numerical models in order to make an accurate prediction of these temperature profiles along the fire exposure time [8], [9]. 

Q11. What is the fire resistance rating for the columns?

This standard establishes that the failure time is given by the more restrictive of the following two limits: maximum axial displacement, and maximum axial displacement velocity. 

Q12. What was the thermal expansion coefficient for concrete and steel?

The values of the thermal expansion coefficient for concrete and steel recommended by Hong and Varma [9] were employed: s 12 10 6 °C 1, c 6 10 6 °C 1. 

Q13. What is the important part of the study?

The results of the simulations were compared with a series of fire resistance tests available in the literature [11], as well as with the predictions of the Eurocode 4 [6] simplified calculation model.