Experimental Study and Numerical Study on Shear Bearing Capacity of Shear Key Joints of Reinforced Concrete Open-Web Sandwich Plates

The shear key in the reinforced concrete open-web sandwich plate (RCOSP) is a block joint that connects with the top chord and the bottom chord. In order to understand the failure mode of the shear key and verify the accuracy of the current algorithm, a total of 9 test pieces are prepared and classified 3 groups were assigned longitudinal reinforcement (LR) ratios of 0.49%, 0.82%, and 1.24%, respectively. The horizontal concentrated static loading under simple support condition is carried out. The test results show that the shear key is horizontally cut and the concrete is pulled apart or crushed along the direction of chord width at the shear key-chords area; the strain level of the concrete and stirrup of the shear key is lower averagely; the development of the horizontal displacement and the strain of the longitudinal bars of the test pieces goes through elastic, elastoplastic, and plastic stages; the ultimate load of the test pieces has almost no relationship with the reinforcement ratio of shear key but is controlled by the degree of crack development in the area where shear key connects with the chords. To avoid the current algorithm overestimating the shear capacity of shear key, the restricted condition of shear section is proposed. The finite element analysis (FEA) further verifies that the restricted condition of shear section proposed in this paper is reasonable and necessary.

Modelling of Amplitude Modulated Vocal Fry Glottal Area Waveforms Using an Analysis-by-Synthesis Approach

The characterization of voice quality is important for the diagnosis of a voice disorder. Vocal fry is a voice quality which is traditionally characterized by a low frequency and a long closed phase of the glottis. However, we also observed amplitude modulated vocal fry glottal area waveforms (GAWs) without long closed phases (positive group) which we modelled using an analysis-by-synthesis approach. Natural and synthetic GAWs are modelled. The negative group consists of euphonic, i.e., normophonic GAWs. The analysis-by-synthesis approach fits two modelled GAWs for each of the input GAW. One modelled GAW is modulated to replicate the amplitude and frequency modulations of the input GAW and the other modelled GAW is unmodulated. The modelling errors of the two modelled GAWs are determined to classify the GAWs into the positive and the negative groups using a simple support vector machine (SVM) classifier with a linear kernel. The modelling errors of all vocal fry GAWs obtained using the modulating model are smaller than the modelling errors obtained using the unmodulated model. Using the two modelling errors as predictors for classification, no false positives or false negatives are obtained. To further distinguish the subtypes of amplitude modulated vocal fry GAWs, the entropy of the modulator’s power spectral density and the modulator-to-carrier frequency ratio are obtained.

تأثير الحرارة العالية على العارضات الخرسانية المسلحة المحسنة

This research examined the effect of high temperatures on reinforced concrete beams made from the groundworks of Hassia region in Syria. Concrete received additions of silica ash and plasticizers. Concrete cubic samples were then prepared with dimensions (15*15*15 cm), and samples for beams with simple support on both sides, with fixed dimensions for all samples of (b*h* L = 18*25*150 cm, respectively), and with a covering thickness of 3 cm. These samples were heated at the age of 28 days to different temperatures in all aspects using an electric oven, which was specially manufactured for this research. Samples were then cooled according to two cooling methods. The first is rapid cooling with water, and the second is a slow cooling with air. Then, necessary laboratory experiments were performed on these samples to measure the percentage of change in resistance, and the change of the torque resistance value in the samples of beams. The samples of beams were modeled and studied according to the finite element method, using the ABAQUS program. The results were read and compared with the experimental results. The results showed a decrease in the value of the resistive torque for the samples of beams with an increase in the heating temperature. The value of this decrease reached about 70% of the value of the resistive torque at the normal temperature. A difference in the value of this decrease is observed at the same temperature in accord with the used method of cooling. In air-cooled samples, it is greater than in water-cooled samples up to 750 °C. The decrease after this temperature in water-cooled samples becomes greater, noting the explosion of some samples heated up to 850 °C when cooled with water. Finally, the results and recommendations are indicated.

Analysis of free vibrations of sandwich panel with electrorheological layer based on two models of laminated shells

Based on two models of laminated shells, free low frequency vibrations of a three-layered cylindrical panel with the internal layer fabricated of an electrorheological composite are studied. Both models lead to the same governing equations accounting for shears in layers, but differ in equations for calculating the reduced shear parameter which depends on the electric field strength and the temperature of a composite. In the case of a simple support of all edges, the formula for the complex natural frequency is obtained explicitly. The influence of the electric field strength and the temperature of the electrorheological composite on the lowest natural frequencies and associated vibration decrements is investigated. It was detected that both models give very close results for the heated composite at an electric field strength of more than 1.5 kV/mm. It is also shown that the frequency of natural vibrations of the electrorheological panel is a monotonically increasing function of the electric field strength, while the decrement – strength curve shows the presence of a local maximum corresponding to the best damping of viscoelastic vibrations.

MEANINGS AND IMPACTS OF CONFEDERATE MONUMENTS IN THE U.S. SOUTH

How do citizens interpret contentious symbols that pervade their community? And what downstream effects does state protection of these symbols have on how citizens of different backgrounds feel they belong in their community? We approach these questions through the lens of race and Confederate monuments in the American South. We rely on two original surveys to illustrate 1) the symbolic meanings Americans attach to these monuments and 2) how state protection of them impacts residents’ feelings of belonging. We find that perceptions of Confederate monuments vary by race: White U.S. residents are drastically less likely to perceive them as symbolic of racial injustice than are Black U.S. residents. Further, state protection of Confederate monuments leads to a diminished sense of belonging among Blacks, while leaving Whites unaffected. This research moves beyond scholarship examining simple support for or opposition toward contentious symbols, developing a deeper understanding of what meaning those symbols can hold for individuals and what their impacts are on individuals’ feelings of belonging and engagement in their communities.

Machining Vibration Suppression of a Cylindrical Part by a Point-Contact Support

Aircraft engine cases employ a thin-walled cylindrical structure for the reduction of fuel consumption. The machining of such parts requires support systems as cutting forces generate shell mode vibrations. There has been much research on the design of vibration suppression devices such as mass dampers, tuned mass dampers, active dampers, and fixturing stretch. Although such devices can offer excellent performance in vibration suppression, cost, and time for manufacturing and setup with tuning are problems. In this paper, the test results of a simple support system that suppresses the vibration modes of a cylindrical part are reported. A support element employs two-contacts in the curved surface. Multiple support elements are arranged according to the number of antinodes of shell modes. Each support has two rollers with a rotating head; the roller contact aligned in the curved surface. For the decision of the number of the support elements, modal analysis was carried out for a cylindrical part. An excitation test was carried out to evaluate the frequency response of a supported cylinder, and several peaks in frequency response were found to be suppressed. A cutting test with an endmill was carried out to evaluate the vibration levels. The experimental results show that the support can suppress forced vibration during machining.