نشریه عمران و پروژه
سال پنجم شماره 8 (پیاپی 54، آبان 1402)

Today, the role of concrete as the most widely used building material in the development of the civil and economic infrastructure of societies is undeniable. On the other hand, the production of cement requires the consumption of natural resources and the release of a significant amount of carbon dioxide into the environment, so the need to revise and change the ingredients of concrete in such a way as to meet the needs of construction and to minimize risks and damage to the environment. It is necessary that pozzolans are among the materials that can be used to improve this.Iran is one of the countries that can be a leader in this matter due to its diverse geographical areas and the availability of various mines. Therefore, this research presents the effect of using nano-silica (NS) and micro-silica (SF) of Hamadan city on the mechanical properties of ultra-high-strength concrete (UHPCs).For this purpose, two groups of concrete with and without silica fume (SF) were made. Also, nano silica (NS) was used as an additive to cement in amounts of 0%, 0.5%, 1%, 2% and 3%. In general, the results show the appropriate effect of pozzolanic materials produced in Iran in improving the properties of concrete in a way that gives that among the different contents of NS, UHPC containing 2% NS has the best results in terms of compressive strength, tensile strength, modulus of elasticity, and bending strength. Showed in 90 days. Also, UHPC samples containing dual cement materials (NS and SF) showed better results than concretes containing only NS

The concrete-filled double skin steel tubular columns (CFDST) are regarded as one of the composite columns consisting of double steel tubes with square or circular hollow sections and the space between two skins is filled with concrete. These columns possess several advantages, including a proper performance during loading, smaller dimensions, cost-effectiveness, protection of the concrete surface against the damage, others compared to conventional columns. In this paper, the buckling of the concrete-filled double skin steel tubular columns subjected to the axial compression was assessed using finite element software, ANSYS. For further investigation of the various types of this novel column system, the nonlinear behaviors of the 3D model of the double skin sections with various cross-section shapes of the section were compared and the influence of the support condition was studied Moreover the buckling of the columns filled with self-compacting concrete, which is required due to the difficulty in the pouring in the confined space, was scrutinized. The results for the short CFDST columns indicate that the column with square-outer-section and circular-inner-section tubes exhibited high buckling critical load and better ductility. Variations in the support conditions do not have significant influence on the columns.

Blast load is a load with a dynamic nature similar to an earthquake, with the difference that its effects take much less time than an earthquake, are more intense, and directly affect the structure itself. Therefore, in this case, in addition to carrying out the usual retrofitting, it is necessary to reduce this explosive effect by changing the architecture of the structure. One of the solutions for this problem is the dual-purpose use of seismic elements such as shear walls, which can not only resist earthquakes but also resist explosive loads. Meanwhile, concrete structures have shown good resistance to explosion compared to steel structures, and one of the design methods in these types of structures is the use of concrete shear walls. One of the solutions to reduce the dimensions of the columns is to use a concrete shear wall. One of the capabilities of this method is the possibility of creating an opening in it, and it reduces the limitations created in the architectural discussion. In this research, the performance of arched concrete shear wall with opening against explosive load has been investigated, and the considered samples with and without opening have been compared. Also, the effect of compressive strength of concrete has been investigated. Finally, it was determined that when creating the opening, full care and inspection should be done and the area around the opening should be reinforced. Arched concrete shear wall with 10 cm thick opening has performed best against explosive load.

The results of capital stock and labor force coefficients showed that there is a constant return to scale in the road transport fleet sector. Also, in this sector, new investment and renovation has increased with technical progress in such a way that it has reduced the average age of the fleet and has led to an increase in the growth rate of qualitative capital and productivity. So; The direct relationship between fleet renewal and productivity in Iran's road transport sector is confirmed. Therefore, it is suggested to use equipment with superior technology and replace the road fleet with new and advanced equipment Therefore, all parts of the road transport industry require their own special attention, which is addressed to each of the topics in the discussions related to road safety management; And its special rules, regulations and standards should be taken into consideration. The road transport fleet is considered as one of the most strategic transport systems of any country. High level and technological complexity, quality and strict prerequisite standards have made this system known as one of the most effective transportation systems in the world.