Prediction of Elevated Temperature Flexural Strength of Lightweight Foamed Concrete Strengthened with Polypropylene Fibre and Fly Ash

This paper focuses on an experimental investigation and statistical analysis of elevated temperature flexural strengths of lightweight foamed concrete (LFC) strengthened with polypropylene fiber (PF) and fly ash (FA) up to 600°C. Five mixes of LFC with 600, 800, 1000, 1200 and 1400 kg/m³ densities were made and tested in current exploration. Two mixes were casted by substituting 15% and 30% of cement content with FA and in other two series; PF was added to LFC mix, correspondingly by 0.2% and 0.4% of binder volume, one controlled mixture without additives was also fabricated. From the experimental results, it can be concluded that the lessening of LFC flexural strength exposed to elevated temperature may be mainly due to the formation of micro cracks at temperature exceeding 93°C since the flexural strength is unfavourably influenced by formation of cracks so that a rigorous strength loss was experiential at 600°C and the flexural strength was only about 40% of its original value. In order to predict the flexural strength of LFC at high temperatures, some existing models applied for normal strength concrete have been considered. The most consistent model for predicting flexural strength of LFC strengthened with PF and FA and also LFC made by ordinary Portland Cement CEM1 at elevated temperature is Li and Guo prediction model. Keywords: foamed concrete, flexural strength, bending strength, elevated temperature, polypropylene fiber, fly as

an em modeling for rescue system design of buried people

The development of a rescue system for buried persons is a subject of growing importance in case of occurrence of natural disasters such as earthquake, landslides, or avalanches. In this paper a fully analytical model has been developed to get some fundamental a priori design characteristics. The proposed system is based on the detection of the victim movements due to its respiratory activity: in particular, when an electromagnetic (EM) wave impinges on a human body, the analysis of the reflected wave parameters such as amplitude, frequency, phase, or delay time allows for the detection of the breathing frequency. The model is simple on purpose because the great uncertainty concerning the characterization of many environmental parameters of a general situation makes a very detailed model useless. However, it is accurate enough to provide useful information about system design, filling the gap in the literature concerning the electromagnetic formulation of such kinds of problems. A system prototype was built using laboratory equipment to experimentally validate the model, and subsequently breathing frequency measurements were carried on, both in a lossless laboratory environment and in a lossy realistic scenario

Reverberation chambers a la carte: An overview of the different mode-stirring techniques

Reverberation chambers (RC), a name inspired in room acoustics, are also known in literature as reverberating, reverb, mode-stirred or mode-tuned chambers. In their basic form, they consist of a shielded metallic enclosure, forming a cavity resonator, together with some mode-stirring mechanism. The main goal of such stirring mechanism is to generate an amplitude-varying electromagnetic field that is ideally statistically uniform

Numerical Simulation of Reverberation Chamber Parameters Affecting the Received Power Statistics

This paper presents a reverberation chamber (RC) numerical modeling based on a discrete plane wave representation. In particular, the attention is focused on those parameters that may influence the field statistics. It is shown that a random choice of the angle of incidence, the initial phase, and the polarization in a particular range and a proper choice of the number of the plane waves allow us to reproduce the same behavior of experimental data. Both experimental and numerical field data are checked applying the Anderson--Darling (AD) test. More precisely, we count the frequencies where the received power statistics is rejected by the adopted goodness-of-fit test. This paper shows a correspondence between numerical and experimental parameters affecting the occurrence of the rejected frequencies, also giving a probability density function for the observed occurrence. The analysis is completed showing that the AD test rejection does not compromise the chamber use for typical radiated emission or radiated susceptibility tests

Numerical and Experimental Analysis of Anomalous Statistics Situations in Reverberation Chambers

The paper analyzes the occurrence of frequencies with anomalous stirring in a reverberation chamber. Both experimental and numerical field data are checked applying the Anderson-Darling test. The presence of these frequencies is unavoidable, even eliminating evident causes, such as antenna bias. In particular, the parameters that influence this occurrence, such as small perturbations of the relative position of the antenna and chamber quality factor, are analyzed. In the case of simulated field, based on plane wave expansion, occurrences are still present and their variations are related to the change in the field observation points, change in the plane wave set randomly generated, and change in the number of plane waves used to represent the field. The paper shows a correspondence between numerical and experimental parameters affecting the occurrence f the anomalous stirring frequencies

Reverberation Chambers: Full 3D FDTD Simulations and Measurements of Independent Positions of the Stirrers

This paper describes the developing and the testing of our FDTD code to simulate the whole reverberation chamber. In order to reduce computer load some approximations were introduced, and we validated the results with the experimental ones measured in our reverberation chamber. Simulated and measured results were compared using the same statistical software. In addition, the computations easily provide other results that cannot be obtained by measurements like the ones that regard field distribution inside the cavity. The developed FDTD code is able to simulate the statistical properties of an RC as function of its dimensions and stirrer geometry. Many numerical techniques haves been proposed to simulate reverberation chambers. Every method requires very large computer resources if a full 3D simulation is done. The developed FDTD code is able to simulate different geometries and movements of the stirrer(s) allowing the designer to obtain the best configuration using the simulator, and saving time for experimental tests. Simulations integrate experimental measurements when long measurement time or destructive tests are required

Evaluation of uncorrelation and statistics inside a reverberation chamber in presence of two independent stirrers

The paper analyzes the stirrer performances in a reverberation chamber (RC). The independent positions (N) of the stirrers are computed when one or two stirrers rotate inside the chamber. In the case of two operating stirrers, they are moved in both synchronized and interleaved tuned modes showing that this second modality yields a larger independent position number. In the case of one stirrer and two synchronized stirrers, the independent positions are computed using the classical autocorrelation function, whereas in the case of two completely independent stirrers a two dimensional autocorrelation is proposed. It is shown that this procedure does not depend on the order followed to move the stirrers. The stirrer performances are also verified checking the ratio between the maximum and the averaged received power inside the chamber. Finally, the statistics of the received power analyzed applying the severe Anderson Darlington (AD) test to discover the departure from the expected distribution

Reverberation Chamber Performance Varying the Position of the Stirrer Rotation Axis

We analyzed how the position of the stirrer influences the reverberation chamber (RC) performance. We simulated a RC moving the rotation axis of the stirrer from a corner to the center. Simulation is carried out by a finite-difference time-domain code optimized for high-performance computers. Results show that the stirrer rotation center position weakly affects the most used statistical parameters