Behavior of Concrete-Filled Steel Tube Columns Subjected to Axial Compression

Pengfei Li,Chengzhi Wang,Tao Zhang

doi:10.1155/2018/4059675

Abstract

The behavior of concrete-filled steel tube (CFST) columns subjected to axial compression was experimentally investigated in this paper. Two kinds of columns, including CFST columns with foundation and columns without foundation, were tested. Columns of pure concrete and concrete with reinforcing bars as well as two steel tube thicknesses were considered. The experimental results showed that the CFST column with reinforcing bars has a higher bearing capacity, more effective plastic behavior, and greater toughness, and the elastoplastic boundary point occurs when the load is approximately 0.4–0.5 times of the ultimate bearing capacity. The change of rock-socketed depth and the presence of steel tube will affect the ultimate bearing capacity of rock-socketed pile. The bearing capacities of the rock-socketed CFST columns are lower than those of rock-socketed columns without a steel tube under a vertical load; besides, the greater the rock-socketed depth, the greater the bearing capacity of the rock-socketed piles. In addition, a numerical comparison between the ultimate load and the theoretical value calculated from the relevant specifications shows that the ultimate load is generally considerably greater than the theoretical calculation results.

Highlights

In the last few decades, high-rise, large-span, and large-scale building structures have become more common
Local buckling has been widely studied, and it is possible to consider its influence on the strength capacity of the Concretefilled steel tubular (CFST) columns. e confinement effect is influenced by the shape of the cross section, the thickness of the steel profile, the type of loading, the slenderness of the composite column, and the strength of the materials used. e studies on CFST rock-socketed columns and predicting the ultimate capacity of CFST columns subjected to axial compression are limited, and there is no standard method for calculating the strength of concretefilled steel tube with reinforcing bars
In China, reinforced CFST piles are widely used in foundations of piers and bridges for its good mechanical properties, for instance, Orchard Container pier in Chongqing Port, Cuntan pier, Xintian Container pier in Wanzhou Port, and Yangshuo pier in Wuhan Port. e remarkable feature of this new structure is that the thickness of the steel pipe is thin and the ratio of diameter to thickness is very large [26]. It greatly exceeds the allowable range of the much existing specifications [27], for example, the ferrule coefficient of circular-section concrete-filled steel tubular members specified in Chinese specification [28] should be limited to between 0.3 and 3.0, and the ratio of diameter to 􏽱th ic k n e ss (D/t) sho􏽱ul d b e l imited to the following range: 20 235/fy ≤ D/t ≤ 85 235/fy; Eurocode 4 (EC4) [22] explicit limits the allowed D/t values in the European context to 90 ∗ 235/fy. e maximum allowable value of diameterthickness ratio (D/t) specified in America Institute of Steel Construction (AISC) [21] is 0.31 ∗ E/fy

Summary

Introduction

In the last few decades, high-rise, large-span, and large-scale building structures have become more common. E remarkable feature of this new structure is that the thickness of the steel pipe is thin and the ratio of diameter to thickness is very large [26] It greatly exceeds the allowable range of the much existing specifications [27], for example, the ferrule coefficient of circular-section concrete-filled steel tubular members specified in Chinese specification [28] should be limited to between 0.3 and 3.0, and the ratio of diameter to 􏽱th ic k n e ss (D/t) sho􏽱ul d b e l imited to the following range: 20 235/fy ≤ D/t ≤ 85 235/fy; Eurocode 4 (EC4) [22] explicit limits the allowed D/t values in the European context to 90 ∗ 235/fy. E present paper is an attempt to study the behavior of concrete-filled steel tube columns with foundation and columns without foundation subjected to axial compression. e main objectives of this paper were twofold: first, to discuss the bearing capacity of CFST columns under vertical load with regard to the thickness of steel tube, reinforcement, and the depth of rock-socketing; second, to discuss the ultimate load experimental results and theoretical calculations

Columns without Foundation

Columns with Foundation

Analysis of the Ultimate Load

Conclusion