Performance of Circular Concrete-Filled FRP-Grooved Steel Composite Tube Columns under Axial Compression

A new structure termed “concrete-filled FRP-grooved steel composite tube (CFGCT) column” is proposed, which is composed of a stress-released steel tube (i.e., grooved steel tube), fiber-reinforced polymer (FRP) and concrete. Axial load tests were carried out on twenty-four specimens to investigate the constraint effect of this structure. Three main experimental variables were considered: the steel tube thickness, the FRP type, and the FRP layer. The failure modes, stress-strain relationships and the effect of the main experimental variables were discussed. The stress-strain curves of this new structure are composed of an initial linear part, a nonlinear transition part, a strengthening part and a residual part. The test results demonstrate that the bearing capacity of the structure was improved, and that the mechanical mechanism of the structure was simplified due to the stress-released grooves. Based on the test results and previous studies, formulas for calculating the ultimate stress (fcu), ultimate strain (εcu), peak stress (fcc) and peak strain (εcc) were proposed. In addition, models for predicting the stress-strain curves of CFGCT columns were put forward, and the models could precisely simulate the stress-strain curve of this new composite structure. Hence, this study indicates that a structure composed of FRP and stress-released steel tube can effectively constrain concrete.

VARIABILITY IN THE FAILURE OF COMPOSITE TUBES SUBJECTED TO COMBINED AXIAL AND TORSIONAL LOADINGS DUE TO MANUFACTURING DEFECTS AND NONDETERMINISTIC MATERIAL PROPERTIES

Tubes made with polymer-matrix fiber-reinforced composite materials are widely used in automobile, mechanical and aerospace engineering applications. Composite tubes are increasingly manufactured using the modern Automated Fiber Placement (AFP) technique. The ply manufacturing parameters and the tube manufacturing parameters have considerable influence on the quality of the manufactured composite tubes. Manufacturing defects and variations in the material properties are inevitable in composite tubes due to the inherent unavoidable variations in these parameters. The commonly identified manufacturing defects include voids, fiber waviness, variation in volume fraction, and fiber misalignment. These have considerable influence on the mechanical behavior and failure of the composite tube. In the present work, the effects of the fiber misalignment and the variations in the material properties on the failure behavior of uniform-diameter composite tubes subjected to combined axial and torsional loadings are determined considering the First-Ply Failure (FPF) characteristics. The first-ply failure envelopes of the composite tube are developed based on the Classical Laminate Theory and Finite Element Modeling and Analysis. Existing works in the literature are used to validate the three-dimensional finite element model of the uniform-diameter composite tube developed using the commercial software ANSYS®. The variations in the first-ply failure loading limits of the uniform-diameter composite tube made of a Carbon Fiber Reinforced Polymer (CFRP) composite material are investigated using the Monte Carlo Simulation (MCS) method, considering the random variability in the material properties and the fiber misalignment. The random variables corresponding to the material properties and the fiber misalignment are generated. For the composite tube with a sample set of simulated random variables the corresponding first-ply failure envelope is determined. The ensemble of such failure envelopes is developed based on an adequate number of simulations from which the probabilistic distributions of the first-ply failure loadings are determined. Design aspects are brought out.

Analysis of the Effect of Heating Temperature on Tension Strength, Elongation and Function Clusters on Composite Tube Aerial Fiber Optic Cable G.652D-STEL-K-036-2012

The composite material of the fiber optic cable tube (G.652D-Stel-K-036-2012) or Polybutylene Terephthalate (PBT)-Master Batch MB) has been tested for tensile strength, elongation, and functional groups for fiber optic tube cladding materials. The purpose of this study was to determine the effect of heating temperatures of 2500C, 2550C, and 2600C on tensile strength, elongation, and functional groups in PBT-MB composite tube for fiber optic tube cladding material. The PBT-MB composite material was made by mixing PBT (80% by weight) with MB (20% by weight) in a ball mill. Then put together and processed into a tube on the extruder. Tensile and elongation strength was tested bytensile test, functional group test with FTIR, and humidity test. The results of the tensile test and elongation test increased with increasing heating temperature and still met the specified standard. The results of the functional group test showed that there was a CH bond from the PBT Tube at the highest wave peak, namely 2923.54 cm-11,725.10 cm-1,there was also a CH Aldehydes bond at a wavelength of 2852.19 cm-1,935.30 cm-1,916.02cm-1,873.59 cm -1,811.88 cm-1, the carbonyl bond C=C at a wavelength of 1708.61 cm-1,and the last is an Aromatic bond at a wavelength of 1504.20 cm-1. The chemical bonds in the test compounds were PBT-MB tube composites. From all the tests carried out, it was concluded that the variation of temperature on the manufacture of PBT-MB tube composites was very influential on the quality and still met the established standards.