The present study deals with the compressive and flexural creep properties of polyetheretherketone (PEEK), a high temperature semicrystalline thermoplastic. The compressive and flexural modes are important from a practical viewpoint, and yet rather limited viscoelastic data exist presently for testing in the two modes. The creep compli ance results of the unreinforced PEEK and the carbon fiber/PEEK composites are reported for temperatures ranging from 120°C to 160°C. Transverse compressive and cross-ply [±45°] s flexural compliances, the matrix dominated properties, displayed a significant viscoelastic behavior. The unidirectional 0° samples, on the other hand, displayed only a very limited time dependent response since the composite properties in the longitudinal direction are controlled by the almost elastic response of the fibers. The time-dependent experimental compliance values for the composites are compared to the results predicted from a micromechanics model and the classical lamination theory in conjunction with the quasi-elastic methodology.

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The aim of this paper was to present the fracture criteria of the SRC columns based on the nonlinear analytical model. This study explored the flexural behavior of the SRC columns confined by the cross-shaped flange sections encased in the structural concrete which are subjected to the flexural loads and the axial loads with 40% of the axial loads relative to the nominal axial load capacity. The confinements of the concrete columns in the compression zone provided by both the transverse reinforcements and the cross-shaped wide steels were evaluated based on an analytical model under axial and lateral loads. The increased flexural strength of the SRC columns by the confined effects offered by steel cores was also calculated. The composite actions of the cross-shaped flange sections that interacted with concrete were found to increase the flexural strength from 20% to 55%, depending on the spacing of the hoop reinforcement of the columns, compared with when composite actions were not accounted. The flexural capacities were underestimated substantially as the axial loads increased when the confinement provided by steel section was not accounted.

Mechanical joints for both irregular steel-concrete composite precast frames and reinforced concrete precast frames were developed to replace conventional cast-in-place concretes in the previous study of the authors. Novel connections modified from conventional steel joints having fully restrained moment connections offer rapid and facile erections. This study aims to numerically identify microscopic strain evolution and failure modes of the laminated metal plates splicing L-shaped precast composite columns. Numerical parameters including material properties of structural components of mechanical joint were implemented to determine damages and strength degradations with associated fractures. Comprehensive numerical results agreed well with test data, which explored structural behavior and contribution of each structural element of mechanical joint to flexural capacity. Strain evolution showed that degradation of the mechanical joints was retarded by interior bolts to a level similar to monolithic columns, resulting in contribution of mechanical joint to flexural capacity of columns. Influence of axial loads on the behavior of columns with mechanical joints was also evaluated to provide design recommendations.

An analytical model was developed that accounted for double confinement provided by both transverse reinforcements and wide flange steel sections in the compression zone. This study also found that the amount of confinements was very sensitive to the post-yield behavior of the composite columns, especially when the buckling in compression region occurred. The nominal moment capacity and post-yield structural behavior of the composite columns were then calculated. The results were verified by comparison to numerical nonlinear finite element analysis results. The model was also verified experimentally. The post-yield behavior of the composite columns obtained from previous experimental studies and nonlinear finite element analysis based on concrete plasticity agreed well with those of the analytical results presented in this study, demonstrating a reliable and fast evaluation of the post-yield behavior of the composite actions. Fracture criteria for the concrete encasing steel columns under axial and lateral loads were also proposed based on the confinement offered by the steel sections encased in concrete. The new concept engaged in the estimation of the flexural strength of concrete columns confined by encased steel sections added innovations to the state of the art in the body of knowledge and advancement of the composite frames.