Compressive Behavior of Bamboo Sheet Twining Tube-Confined Concrete Columns

This study experimentally investigated various axial compressive parameters of a new type of confined concrete, which is termed bamboo sheet twining tube-confined concrete (BSTCC). This new composite structure was composed of an outer bamboo composite tube (BCT) jacket and a concrete core. Under axial compression, the parameters of thirty-six specimens include concrete strength (i.e., C30 and C50) and BCT thickness (i.e., 6, 12, 18, 24, and 30 layers). The mechanical properties of the BSTCC specimens from the perspective of the failure mode, stress-strain relationship, effect of BCT thickness and dilation behavior were analyzed. The results showed that, in compression, with an increase in BCT thickness in the range of 18-layers of bamboo sheets, the strength increased remarkably. When the strength of the concrete core was high, the confinement effect of the BCT was reduced. In addition, the BCT thickness relieved the dilation of the BSTCC specimens. Finally, the experimental results were compared with predictions obtained from 7 existing FRP-confined concrete models. All the predictions had good agreement with the test results, which further confirmed that the models developed for FRP-confined concrete can provide an acceptable approximation of the ultimate strength of the BSTCC specimens.

Fatigue in asphalt mixtures – a summary to understand the complexity of its mathematical modeling

Based on the reviewed literature in relation to the phenomenon of fatigue in asphalt mixtures, the foregoing paper depicts and describes in summary, the main variables that impact in the generation of said phenomenon in asphalt pavements. This has the purpose of showing its complexity to mathematically model it. As a general conclusion obtained in the study, it was found that the calibration difficulty of the models is mainly since the mathematical equations must be in capacity of considering that fatigue resistance of asphalt mixtures depends on load mode (stress-controlled or strain- controlled), the type of load (haversine or sinusoidal) and the rest periods to which laboratory samples are subjected. Additionally, both in situ, as within the laboratory, this varies with stiffness, volumetric composition (type and content of asphalt and aggregate), the geometry of samples, with effects associated to mix durability and environmental conditions, with the type of test, border conditions and support layers (base, subbase, subgrade). If these physical parameters are not considered, the mathematical equations lose reliability.

Assessment of the Resolution of Nonplanar Flaws in Pressure Retaining Components in Terms of Stress Intensity Factors

When flaws are detected in pressure retaining components, assessments have to be done in order to demonstrate the fitness-for-service (FFS) of the component for continued operation. This FFS demonstration is performed in accordance with FFS Codes providing flaw assessment procedure and acceptance standards. The first step of the flaw assessment is the flaw characterization which aims at determining the flaw geometry to be used for the analyses. This key step is done according to flaw characterization rules provided in the FFS Codes and hence appears as essential for the rest of the assessment. According to the flaw characterization rules of ASME B&PV Code Section XI, a nonplanar flaw (i.e., oriented in two or more intersecting inclined planes, curvilinear geometry, or combinations of nonplanar geometry) shall be resolved into two planar flaws by projection of the flaw area into planes normal to the maximum principal stresses. This approach allows to simplify the flaw assessment but should remain conservative. Therefore, the conservatisms due to the simplified projection approach for nonplanar flaws are investigated in this paper. Current computational tools have been clearly improved so that the modelling of nonplanar flaws does not present any significant difficulty. In this frame, this paper compares the stress intensity factors of projected nonplanar flaws and the mixed mode stress intensity factor of actual nonplanar flaws. This is carried out for multiple flaw sizes, flaw shapes, flaw orientations and different load cases. The final scope is to quantify how the flaw projection into planes normal to the maximum principal stresses is conservative and how this conservatism could be improved, if need be.

Determination of Stress Intensity Factors under Shock Loading Using a Diffraction-Based Technique

An experimental optical method has been developed for the measurement of opening and sliding notch face movements. The light passing through a thin slit is monitored by a photodiode detector. Two parts of the slit are fixed independently on the notch faces of the simulated crack. Dynamic variations of the notch face movements are recorded as an electric signal by an ‘oscilloscope. The sensitivity of such displacement measurement is comparable with the wavelength of light. Dynamic mixed-mode stress intensity factors under shock loading were evaluated from the data obtained and subsequently compared with a numerical simulation by ANSYS software. As it was approved, the technique has shown sufficient sensitivity, good linearity, and measurement reliability. Due to its non-destructive nature and overall robustness, the arrangement is applicable even for structural component condition determination taking into consideration potentially unknown boundary conditions and the non-linear character of mechanical parameters.