Axial Cyclic Testing of Concrete-Filled Steel Tube Columns in Diagrid Structures

Qingxuan Shi,Bin Wang,Wenzhe Cai

doi:10.1155/2019/4726029

Abstract

Inclined concrete-filled steel tube (CFST) columns in a diagrid structure system can efficiently carry large vertical loads and horizontal forces. This paper presents an experimental study of the stress characteristics of engineered inclined CFST columns under axial cyclic loading. Ten specimens were tested, including two hollow steel tube (HST) columns and eight CFST columns, and the influences of loading scheme, aspect ratio, concrete strength, and steel ratio were examined. The seismic behaviours were investigated, including mechanical behaviour, failure modes and hysteretic curves, and ductility, and the interaction between the steel tube and concrete was examined as well. Better ductility and energy dissipation capacity are achieved in the tension direction, whereas higher bearing capacity and stiffness are achieved in the compression direction. Compared with hollow steel tube columns, the supporting effect of concrete on the steel tube for CFST columns in tension and the restraining effect of the steel tube on concrete for CFST columns in compression ensure higher capacity, deformability, and energy dissipation capacity.

Highlights

With increasing building height, structural lateral displacement has become the main control target in design, and high-rise buildings should supply sufficient bearing capacity and offer sufficient lateral rigidity
Diagrid structural systems have become an increasingly attractive choice for mid- to high-rise buildings worldwide. e main distinction between the diagrid structure and conventional structural systems is the absence of vertical members in the structure, which are replaced with inclined brace-shaped members known as diagonals. is arrangement is possible because the diagonal members can carry gravity loads as well as lateral forces due to their triangulated configuration and can convert the load into axial tension and compression for downward transfer
The studies on concrete-filled steel tube (CFST) columns mainly focus on the monotonic behaviour of vertical bearing members and the seismic performance of lateral force-resistance components [8–15], while minimal research has focused the mechanical behaviour under cyclic loads of components such as lateral braces [16, 17], and few studies have been conducted on the mechanical behaviour of the inclined CFST columns under cyclic axial loads, which are the major components of the diagrid structure. erefore, the study of the bearing mechanism and seismic performance of the CFST columns under axial cyclic loads is an urgent need

Summary

Introduction

Structural lateral displacement has become the main control target in design, and high-rise buildings should supply sufficient bearing capacity and offer sufficient lateral rigidity. Zhou et al [5], Kim et al [6], and Han et al [7] conducted pseudostatic tests on intersecting nodes in the diagrid structure and analysed the force mechanism and hysteresis performance under axial cyclic loads; the relevant research on inclined CFST columns in diagrid structures is still in the initial stage. The studies on CFST columns mainly focus on the monotonic behaviour of vertical bearing members and the seismic performance of lateral force-resistance components [8–15], while minimal research has focused the mechanical behaviour under cyclic loads of components such as lateral braces [16, 17], and few studies have been conducted on the mechanical behaviour of the inclined CFST columns under cyclic axial loads, which are the major components of the diagrid structure. Based on the current status, eight CFSTcolumns and two hollow steel columns were designed for application in seismic performance tests aimed at studying the stress mechanism and failure modes under axial cyclic loads. e effects of loading scheme, aspect ratio, concrete strength, and steel ratio on the seismic performance of the CFST specimens were analysed. e longitudinal and the circumferential strains of steel pipes in different stress stages were investigated to examine the interaction between the steel tube and the core concrete

Experimental Investigation

Specimen Behaviour

Experimental Results

Strain Analysis

Conclusions