نشریه آنالیز سازه - زلزله
سال نوزدهم شماره 3 (پاییز 1401)

Sea and high seas are very important, which can be considered in two aspects. On the one hand, the seas have economic, commercial, logistical, military, and geopolitical advantages, in addition, they pave the way for increased maritime diplomacy. In addition to these advantages, the harsh natural conditions at sea, such as the presence of high waves, tsunamis, sea ice, as well as ammunition and unused military equipment buried under water left over from the First and Second World Wars, also from the imposed war, which could impose a lot of potential human and financial risks due to explosions. In this paper, using the Abaqus finite element software, the dynamic response of a cylindrical tube buried in the sea subjected to the explosion is investigated applying numerical and experimental methods. Finite element models based on the experimental models were examined and the numerical results were compared with the experimental data. The results indicated that the maximum impact wave pressure, bubble propagation duration and displacement due to the cylinder deformation in the experimental and finite element analysis were well compatible

In recent years, improving the mechanical properties of alkali- activated concrete with the aim of being superior compared to those of the conventional concrete and reducing environmental hazards caused by the lack of mineral resources and release of toxic carbon dioxide gas (in cement production process) has been noticed by civil engineering researchers. In this laboratory research, a mixing design of ordinary concrete containing Portland cement with a grade of 500 kg/m3 and a mixing design of alkali-activated concrete based on blast furnace slag were made. In order to check the mechanical properties, tests of compressive strength, tensile strength and modulus of elasticity of concrete were performed under the temperatures of 21 and 600 ℃ at the age of 90 days of curing.  Based on the results, applying high temperature (600 ℃) to concrete samples caused a 42% and 15% drop in compressive strength, a 56% and 21% drop in tensile strength, and a 63% and 49% drop in modulus of elasticity for ordinary and  alkali-activated concretes, respectively.  The compressive strength of alkali-activated concrete was 11% and 64% more than that of the normal concrete at 21 and 600 ℃, respectively. The tensile strength of alkali-activated concrete exhibited a 9% decrease and 63% superiority compared to normal concrete at 21 and 600 ℃, respectively. The elasticity modulus of alkali-activated concrete was 16% and 62% higher than that of the normal concrete at 21 and 600 ℃, respectively. The results of the scanning electron microscope images are in accordance with the other test results of this research.

Using by-product materials in making concrete is the recent development in the advanced concrete technology. The products obtained from experimental crushed concrete can be used in constructing the new concrete. Recent research revealed that using crushed concrete as partial replacement of sand and coarse aggregate, using traditional mixing procedure, reduced the compressive strength. In the present research, the special procedure of mixing concrete in three steps and its effect on concrete strength parameters have been evaluated.  The aim of this study is to use crushed tested concrete as partial replacement 25% (mix A) and 50% (mix B) of conventional sand and aggregate. Also for experimental comparison the control mixes were casted with traditional sand and aggregate.  Superplasticizer based on carboxylate was used in the mixes.  This procedure causes proper efficiency, proper coating on the aggregate and protection of the alkaline reaction of the aggregate. The method of mixing was carried out in three steps 1: Coarse aggregate + 50% water + 50% cement: mixing time 30 seconds to 1 minute, step 2: Adding 50% cement + 25% water + superplasticizer + sand: mixing time 2 minutes, step 3: Adding 25% water: mixing time 3 minutes. All the mixing time is about 6 minutes. Six specimens of 15 cm concrete cubes for each designed mixes were casted. Densities, water absorption, electric resistance (an indication of permeability and durability of concrete) and compressive strength tests were carried out. Tests were performed at 7 and 28 days. As a result, the designed mix (A) presented the higher electric resistance and compressive strength at 28 days. According to the obtained appropriate resistance, it can be deduced that with a special mixing method, crushed concrete can be used in the composition of concrete that is cost-effective in terms of environmental and resistance.

Rotational friction dampers (RFDs) have been proposed as one of the passive control tools in order to increase the seismic performance and lateral control of structures and the loss of input energy of earthquakes through friction in their rotating plates.  Apply of the rotational friction dampers will reduce shear stress and improve the dynamic response of the structures. In the nonlinear analysis and design of structures, the underlying soil is usually assumed to be rigid, if the flexibility effect of the structure bed is used, the dynamic characteristics of the structures will be different. Examining the behavior of structures by considering the effects of soil and structure interaction can give us a more accurate understanding of the behavior of structures, and this is while in most of the designed structures, the effects of soil stiffness and possible elevation of the foundation is not considered.  In this article, a typical ten-story building is considered and in it, with type two hard soil and type three soft soil, the performance of the damper with different damping capacity and interaction effect was analyzed with SAP 2000 software. Shear stress in different floors of the structure was analyzed in four cases: with dampers and with the effect of soil interaction and with dampers without the effect of soil interaction, without dampers with the effect of soil interaction, and without dampers and without the effect of soil interaction. The graphs showed how much the rotational friction damper can be useful in reducing the shear in different floors of the building, taking into account the effect of soil and structure interaction. Three earthquake records were utilized for this research and at the end, the results were compared with each other. The results indicated that the use of rotational friction dampers reduced the shear in all cases and the analysis of the sliding load of the damper and the required capacity of the structure were also obtained.

Steel columns filled with concrete with a special shape, mainly L-shaped, T-shaped and cross-shaped columns, are used as single columns or as boundary members of the shear wall, and in terms of structural design especially architecture, have been considered by many researchers and designers. Owing to their proper implementation in beam joints, they are receiving increasing attention in the world. These columns are often utilized in the residential and formal structures, however, due to heavy loads, such as those that may occur during severe earthquakes, they do not meet the requirements of high-rise buildings. There should always be more studies on the increasing of their performance. In this research, cold-rolled steel sections have been utilized for hardening, strengthening and straightening of the axial and shear performance of L-shaped and T-shaped steel columns filled with concrete. The research variables in this study are the internal stiffeners between the column sections, and the main purpose of this research is to numerically investigate the axial and shear performance of the concrete-filled steel columns with L-shaped and T-shaped cross-sections using Abaqus software. Also, in this study, it is determined that by adding steel sheets in the space between the columns, what kind of changes do axial and shear resistance, hardness, and ductility take? In the first stage, five L-shaped steel columns filled with concrete and five T-shaped columns by internal steel plates of different lengths and steel pipes under axial loading were analyzed numerically, and in the second stage, the same columns were loaded laterally and analyzed. The results indicate that the steel column filled with concrete in the T-shaped cross-section has a higher performance than the similar L-shaped cross-section, in addition, the percentage of growth or loss of performance of the samples compared to the base sample in the L-shaped and T-shaped sections is almost similar to each other. Also, the results exhibit that creating a hardener inside the section increases the stiffness and axial and lateral strength of the steel column filled with concrete. The hardening steel section has a great effect on the performance of L- and T-shaped steel columns filled with concrete so that reinforcing concrete filled steel columns with this method leads to an increase in load bearing capacity, increase in thrust ratio, ductility, prevention of local buckling in the steel wall and energy loss increases.

In areas with high seismicity, structures need a resistant and load-bearing system against lateral forces caused by earthquakes. In addition to high stiffness and resistance to displacement caused by earthquakes, these systems must have good ductility and energy dissipation ability. Therefore, apply of the buckling-resistant braces (BRB) with reduced beam section (RBS) connections is recommended instead of the previous conventional braces. In this research, the cyclic behavior of the recommended system is investigated. The finite element method and ABAQUS software have been utilized for modeling and study of the numerical models. The investigated parameters include stress contour, cyclic response (force-displacement), stress in column, and beam. The results of numerical models indicate that by creating RBS with a length of 0.85d to a shear radius of 0.25bf compared to the 0.2bf mode, the amount of stress in the beam increases by about 24%.