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Introductory Concepts
Published in Donald E. Carlucci, Sidney S. Jacobson, Ballistics, 2018
Donald E. Carlucci, Sidney S. Jacobson
A mortar is a tube that is usually man portable used to fire at extremely high trajectories to provide direct and indirect support to the infantry. Mortars generally have much shorter ranges than howitzers and cannot fire a flat trajectory at all.
Experimental study on design and analysis of prototype spherical shell
Published in International Journal of Ambient Energy, 2022
Fabrication of the testing apparatus is an important phase in this research work. Equipment required is plastic moulds to make the spherical mortar shell. Moulds are used to prepare the spherical mortar shell. Here the main point of concern was the ratio of cement and sand mixture. The fine grain size of sand is used with the cement. The different combinations of cement to the sand ratio of 1:2 and 1:4 are prepared. The cement used here is the Portland cement having a thermal conductivity of 0.29 W/m K. The Portland cement is the most commonly used cement in buildings, in furnaces, etc. Here the ratio of cement and sand is varied to see whether there is a change in the thermal conductivity of Mortar (cement + sand) or not.
Determining optimum air-void spacing requirement for a given concrete mixture design using poromechanics
Published in International Journal of Pavement Engineering, 2018
Tangential stress distributions in concrete containing high-porosity, high-permeability, aggregates (characteristics of lightweight aggregates), for three different scenarios (concrete with 0.2 mm spacing factor (MD4), 0.8 mm spacing factor (MD5) and non-air-entrained concrete (MD6)) are presented in Figure 3. It has been observed that, although non-air-entrained lightweight aggregate concrete can sustain mild winter where temperature drops to around −5 °C Figure 3(a), it can cause high tensile stresses at the aggregate centre if used in very harsh winters where temperature decreases below −10 °C Figure 3(b). Similar results are demonstrated by several studies performed on lightweight aggregate concrete exposed to severe freezing suggested by the ASTM C666 procedure (Ozyildirim 2008, Mao et al.2009). The peak tensile stresses expected in harsh winters can be mitigated using air entrainment. However, for small freeze–thaw cycles, with temperature above −5 °C, air voids can cause high tensile tangential stress at the matrix outer boundary, and may prove less efficient than the non-air-entrained concrete in mitigating freezing damage. Since the air-entrained mortar depressurises as the air voids act as expansion reservoirs and cryo pumps (Coussy and Monteiro 2007), the mortar shell contracts. Subsequently, the mortar shell experiences tensile tangential stress as it constrains the aggregate that does not contain any air-filled pores. The resulting high stress may propagate to the ITZ if the spacing factor is further reduced (Figure 3(a)) and may in turn initiate cracks in the ITZ, making air-entrained concrete susceptible to thermal cracking. A similar conclusion was deduced by Verbeck and Landgren (1960), who hypothesised that high-porosity, high-permeability aggregates with coarse pore structure can cause failure of the surrounding mortar by building high external pressure (Verbeck and Landgren 1960). Development of high stress in the aggregate centre, as shown in Figure 3(b), is also in good agreement with the experimental studies performed by Mao et al. (2009). Their work on the damage analysis of lightweight aggregate concrete shows that micro-cracks originate in the aggregate particle and spread to the nearby mortar when exposed to harsh freeze–thaw tests (Mao et al.2009). The modelling also suggests that to effectively protect lightweight aggregate concrete in harsh winters, it is crucial to achieve the recommended air-void spacing factor since high spacing factor will cause high tensile tangential stresses at the aggregate centre.
Behaviour of Masonry-Infilled RC Frames Strengthened Using Textile Reinforced Mortar: An Experimental and Numerical Studies Overview
Published in Journal of Earthquake Engineering, 2022
Christiana Filippou, André Furtado, Maria Teresa De Risi, Nicholas Kyriakides, Christis Z. Chrysostomou
A two-dimensional (2D) micro-model of infill wall with TRM was also developed by Basili et al. (Basili, Marcari, and Vestroni 2016) using MIDAS-FEA software to simulate the behaviour of masonry walls retrofitted with basalt-TRM under diagonal compression loading that was studied experimentally by Prota et al. (Prota et al. 2006). Isotropic continuum elements modelled the infill wall. In contrast, a smeared crack model with different non-linear softening functions for the tensile and compressive behaviour of infill wall was adopted for these elements. The basalt-textile and the mortar were modelled separately by continuum elements, using tension elastic-brittle material model for textile reinforcement. In this numerical model, the TRM was perfectly bonded to the masonry wall. After the calibration of the numerical model, a sensitivity analysis was performed. The results showed that the unretrofitted masonry wall’s response under diagonal compression loading is mainly influenced by the tensile properties of the masonry wall (strength and fracture energy). In contrast, the retrofitted infill wall model was sensitive to the Young’s modulus and the mortar’s compressive fracture energy. The authors also concluded that the number of basalt-TRM layers influences the stiffness and the shear stress of the retrofitted infill wall subjected to diagonal compression loading. Recently, Wang et al. (Wang et al. 2017) developed a numerical model of infill wall with TRM in DIANA FEA software to examine the effectiveness of using the TRM for retrofitting masonry walls. The model’s accuracy was validated by comparing the numerical results to experimental data taken from the literature. Eight-node shell elements were used for the mortar and masonry wall. At the same time, the TRM was modelled by embedded reinforcement for the textile, accompanied by the mortar elements (perfect bond between mortar and textile). In this numerical model, a perfect bond between masonry wall and TRM was considered. The Total Strain Rotating Crack material model was adopted for mortar elements, while for infill wall elements, a softening anisotropic elasto-plastic continuum model was used (Hill type criterion for compression and Rankine type yield criterion for tension). After the calibration of the numerical model, pushover analysis was performed on selected case studies. Different TRM strengthening schemes and materials on the lateral response of two-story masonry wall with large central door opening were investigated. The numerical results showed that the infill wall with steel-TRM has higher load-bearing capacity and ductility than the infill wall’s corresponding ones with basalt- and glass-TRM.