Elsevier

Thin-Walled Structures

Volume 94, September 2015, Pages 155-166
Thin-Walled Structures

Mechanical behavior of circular and square concrete filled steel tube stub columns under local compression

https://doi.org/10.1016/j.tws.2015.04.020Get rights and content

Highlights

  • Concrete-filled steel tube stub columns under local compression was investigated.

  • A 3D finite element model was established for simulation.

  • Precise and concise formulas were proposed.

Abstract

This paper presents a combined experimental and numerical study on the behavior of both circular and square concrete-filled steel tube (CFT) stub columns under local compression. Twelve circular and eight square CFT stub columns were tested to study their bearing capacity and the key influential parameters. A 3D finite element model was established for simulation and parametric study to investigate the structural behavior of the stub columns. The numerical results agreed well with the experimental results. In addition, analytical formulas were proposed to calculate the load bearing capacity of CFT stub columns under local compression.

Introduction

Concrete filled steel tubular (CFT) columns have been increasingly used in bridges and high-rise buildings. They have much more advantages compared with the ordinary steel or concrete system including higher strength and stiffness, higher ductility, and larger energy absorption capacity [1]. With the benefits of CFT, the use of CFT columns is becoming more popular and the performance of concrete filled steel tubes has caught more and more research attentions [1], [2], [3], [4], [5], [6], [7], [8], [9]. In most cases, such as the pier of bridges and arch structures, CFT columns are subjected to axially compression loads. Limited research has been carried out to investigate the behavior of CFT stub columns under local compression and the influential factors on the load bearing capacity. Forty three circular CFT stub columns under local compression were experimentally studied by Cai et al. [1]. Effects of local compression area ratio, diameter–thickness ratio, relative height of the model and spiral stirrup on the performance and the load bearing capacity were studied. Formula for the ultimate load bearing capacity of CFT stub columns was also proposed. Han et al. [2], [3] also conducted experiments to investigate the effects of parameters including section type and local compression area ratio, on the structural behavior of CFT stub columns and proposed a series of formulas for the local compression bearing capacity of CFT stub columns.

The previous study from reference [1], [2], [3] indicated that the CFT columns generally perform well, however, little success has been achieved so far in developing a concise formula of the load bearing capacity for CFT stub columns. Moreover, the behavior of CFT columns under local compression condition has not been well addressed in the current design code and hence further research is necessary to improve the design code specifications. In addition, the effects of loading plate shape on the performance of CFT stub columns also need to be investigated.

The aim of this study, therefore, is to develop a more concise and precise method to compute the load bearing capacity of CFT stub columns when subjected to local axially compression. More specifically, four objectives are included in the study: (1) to analyze the structural behavior of both circular and square CFT stub columns subjected to local compression with 12 circular CFT specimens and 8 square CFT specimens without endplate tested; (2) to develop finite element (FE) model using ABAQUS program to simulate the behavior of the CFT stub columns; (3) to analyze the effects of local compression area ratio, steel ratio, strength of steel and concrete on the behavior of locally loaded CFT specimens; (4) to establish a simplified approach to estimate the load bearing capacity of CFT stub columns subjected to local compression, and to verify formula with both experimental and numerical results.

Section snippets

Test materials and specimens

Twenty CFT specimens were included in this study, including 12 circular and 8 square specimens. The nominal dimension of the circular specimen was 300(D) mm×4(t) mm×900(L) mm, where D is the diameter of the circular section, t is the wall thickness of the steel tube, and L is the length of the specimen. The nominal dimension of the square specimen was 300(B) mm×4(t) mm×900(L) mm, where B is the width of the square section. d is the diameter of loading plate, b is the width of loading plate. More

Finite element modeling

Finite element models were established by ABAQUS program [14]. Four-node reduced integral format shell elements (S4R) were employed to model the steel tubes. Eight-node brick elements (C3D8R) were applied to model the concrete, the end plate and the loading plate. The structured meshing technique was adopted. Mesh convergence studies were first performed to ensure that the finite-element mesh was sufficiently fine to give accurate results and the selected meshed models used for modeling are

Formula development

Based on experimental results and regression analyses, formula for influence coefficient Kb and load bearing capacity under local compression Nb were developed. For circular CFT columns, Kb is expressed as:Kb=β0.05Φ0.65

For square CFT columns, Kb is expressed asKb=β0.05Φ0.4

The load bearing capacity of circular CFT columns under local compression can be written asNb=β0.05Φ0.65(1+1.7Φ)fcAcb

The load bearing capacity of square CFT columns under local compression was proposed asNb=β0.05Φ0.4(1+1.2Φ

Conclusions

This paper presents a combined experimental and numerical study on the behavior of both circular and square concrete filled steel tube (CFT) stub columns subjected to local axial compressive loading. Parametric studies were also conducted in order to understand the influence of different parameters on the behavior of the CFT stub columns. Based on the results, the following conclusions can be drawn:

  • (1)

    The experimental results indicate that the increase of concrete strength could increase the load

Acknowledgment

This research work was financially supported by the Program for Changjiang Scholars and Innovative Research Team in University (PCSIRT), Grant no. IRT1296, the Program for New Century Excellent Talents in University, Grant no. NCET-11-0508, and the National Key Technology R&D Program, China Grant no. 2011BAJ09B02.

Cited by (0)

View full text