Prediction of axial load capacity of stub circular concrete-filled steel tube using fuzzy logic

a r t i c l e i n f o Keywords: Concrete-filled steel tube (CFST) Confinement effect Fuzzy logic Modified learning from example (MLFE) Axial load capacity A circular concrete-filled steel tube (CFST) has several advantages compared with the conventional reinforced concrete member or hollow steel tube, since the tri-axial state of compression of the concrete infill increases its strength and strain capacity. Extensive studies have been conducted on the CFST and several researchers suggested empirical and theoretical formulas to predict the confinement effect and confined compressive strength of the concrete infill of the CFST. However, the previously proposed equations vary significantly because of the nature of complexity and uncertainty of the tri-axial stress state in the concrete infill. This study presented an alternative method to determine the confinement effect of the concrete infill and the axial load capacity of the stub CFST by using fuzzy logic. The focus was made on the accurate estimation of the confinement effect of the CFST by using a fuzzy-based model that makes it possible to evaluate the interaction between various parameters that affect the confinement effect. The proposed fuzzy-based model for the confinement effect and axial load capacity of the stub CFST was compared with current deign codes and the results of previous studies. It was found that the proposed fuzzy-based model provides a good prediction of the confinement effect and axial load capacity of the stub CFST. Finally, the design chart to estimate the confinement effect of the stub CFST was provided for practical design purpose. A concrete-filled steel tube (CFST) has been widely used as structural members, such as a building column and a bridge pier due to several advantages. Fig. 1 shows the example of an application of CFT member to a building column [1]. The primary advantage of CFST is that the concrete infill is confined by the steel tube, which results in tri-axial state of compression that increases the strength and strain capacity of the concrete infill. In addition, the concrete infill restrains local and global buckling of the steel tube. CFST permits rapid construction as the steel tube replaces reinforcements and eliminates the extra labor associated with formworks [2,3]. Extensive experimental and numerical studies have been conducted in the past decades to examine the confinement effect and axial load capacity of stub circular CFST [4–18] where the stub circular CFST has small length to diameter ratio …