Mojtaba Lezgy-Nazargah

With the increasing application of composite materials in civil engineering, it important to thoroughly understand the performance of multilayer sandwich structures under impact loading. Nowadays, sandwich panels made of concrete face sheets bonded to foam cores through shear connectors, have gained widespread applications in civil engineering projects. Until now, research on such structures has often been limited to static analyses, and it is necessary to investigate their behaviour under dynamic loading. In this research, the effect of dynamic impact loading on the mentioned structures has been studied. Three-dimensional finite element modelling, along with the explicit dynamic analysis, has been used to achieve this objective. First, the accuracy of numerical results is evaluated through comparison with the available experimental results. Then, the effects of various parameters, such as the concrete strength of face-sheets, shear strength of connectors between the layers, the amount of reinforcements embedded in the concrete layers, and the effect of the speed of the impactor, were investigated. The results show that by increasing the impact speed, the rate of penetration and indentation in the host sandwich panel also increase. Also, with increasing the concrete strength, the penetration of the projectile and the indentation decrease. By preventing the slippage between the layers, the resistance of the composite sandwich panel against the impact loads is significantly increased. Increasing the amount of reinforcement also increases and improves the impact resistance of the sandwich panel.

Auxetic structures, known for their negative Poisson’s ratio, exhibit unique mechanical properties that make them suitable for various engineering applications such as load-bearing and energy absorption devices. The Arrow-head is a popular auxetic unit cell with a simple configuration and high stiffness, which has been frequently used in load-bearing applications. However, the Arrow-head has a limitation in its ability to absorb significant values of energy. Therefore, this study presented a novel auxetic unit cell and structure named the Pine-head, which is a modified configuration of the Arrow-head unit cell. The Pine-head structure was designed to enhance energy absorption capabilities while maintaining auxetic behavior. The structures were fabricated using fused deposition modeling additive manufacturing technology and subjected to quasi-static compression loading. Furthermore, the results were verified with the finite element method, showing good agreement between the results. Then, by changing the geometrical parameters of the Pine-head unit cell, two new configurations of Spear-head and Twin Chevron Head (TCH) were introduced. Comprehensive comparisons between three novel auxetic structures and the traditional Arrow-head were conducted in order to study their mechanical properties and assess improvements in their mechanical performance. The results demonstrated that the Pine-head structure exhibited enhanced energy absorption capability compared to the Arrow-head, Spear-head, and TCH structures. The findings of this study suggest that the Pine-head offers significant advantages for high-energy absorption applications.

The selection of an appropriate geometric form is one of the critical factors in the design of space frame structures. Historically, the domes and arches in Iranian architectural monuments represent remarkable technical achievements, due to the geometric potential of their arched designs. However, previous studies on these structures have mainly concentrated on rehabilitation initiatives. This research, for the first time, seeks to use the formal features of arches and domes of traditional Iranian architecture to enhance contemporary structures made of modern materials. By incorporating the advantages of these historical arches into the design of lattice space domes, structural efficiency, and material utilization are anticipated to improve. To achieve this, the geometry of diamatic single-layer domes was designed based on seven commonly used arch types in traditional Iranian architecture. In addition, a diamatic dome is also modeled based on the spherical arch, which is commonly employed in space domes. The geometry of these space domes was first modeled in AutoCAD software. Then, the models were analyzed using the linear elastic method. Finally, the structural design of these space domes was performed using the LRFD method in SAP2000 software. The comparative analysis and design results demonstrate that arches such as Se-Bakhshi, Panj-O-Haft, Hasht-O-Panj, Se-Ghesmati, and Shakhbozi enable covering the same span with reduced material usage. Additionally, arches like Patopa and Shabdari offer the potential to construct taller domes with nearly equivalent material requirements.

The rapid progression in concrete technology and the emphasis on improving the mechanical characteristics and durability of concrete, as well as the need for skilled workers, were key factors that led to the fabrication of self-consolidating concrete (SCC). The primary advantage of SCC is the elimination of vibrations during construction. This experimental study investigates the effect of nano-silica, nano-clay, and micro-silica with ratios of 2% and 4% on the properties of SCC. To reach this aim, rheological tests (flow slump, V-shape funnel, U-shaped box, and L-shaped box tests), mechanical tests (compressive strength, tensile strength, and flexural strength test), and durability tests (freezing, abrasion, and permeability tests) were carried out. The results demonstrated that the mechanical characteristics and durability of the concrete were enhanced by increasing the nano-silica content up to 4% of the cement weight. Also, the increase in the nano-clay content produced suitable results for SCC in terms of mechanical and durability aspects. However, as the nano-material ratio increases, the amount of superplasticizer also increased to ensure the proper workability of the SCC.

The use of microcapsules as preservative vessels for healing materials has led to a great revolution in the repair of materials. Microcapsules have been used in medicine, agriculture, metallurgy and mechanics. In civil engineering applications, microcapsules are usually used for the self-healing of concrete, asphalt and cementitious materials. Concrete and cement are widely used in civil engineering and are the predominant construction materials worldwide. The objective of this study was to design and produce urea–formaldehyde microcapsules for the recovery of reactive powder concrete (RPC). It was found that RPC specimens with and without microcapsules exhibited different behaviours. All of the RPC specimens containing microcapsules were found to have lower strengths than specimens without microcapsules. The smallest reductions in compressive strength were observed in specimens with a microcapsule content of 4–6% by weight of cement. The healing ratio of compressive strength increased with an increase in the weight percentage of microcapsules. Scanning electron microscopy and energy-dispersive spectroscopy were used to observe the process of crack healing, and the results showed that the cracks were filled with healing products.

In this paper, the numerical study of the ultimate bearing capacity (UBC) of two closely spaced strip footings on granular soil is investigated using the finite element method (FEM) and upper bound limit analysis (UBLA). Although the UBC of two adjacent footings has previously been studied in other experimental and numerical research, in all the previously reported studies, the footings were not allowed to rotate and move horizontally freely. Due to the deformation of the soil medium, two closely spaced footings are subjected to horizontal movements and tilting, even under central vertical loads. When the two adjacent footings are not permitted to rotate and move in the horizontal directions, the unwanted bending moment and horizontal force act on the footings. Indeed, the UBC of two closely spaced rough footings is evaluated under incorrect constraints in earlier research. In the present research, the UBC of two adjacent rough footings is evaluated with and without these incorrect constraints. The key finding of this study is that constraining the horizontal and rotational movement of the foundation artificially increases the UBC, which does not reflect field conditions. When foundations are permitted to rotate and move horizontally, there is no increase in UBC; however, there is an increased risk of differential settlement and structural instability.