Journal of Civil Engineering Researchers
Volume:4 Issue: 2, Spring 2022

Today, wind energy is considered as one of the most used types of renewable energy for electricity production. Over the past two decades, wind energy has been a major source of electricity, and electricity supply has been drastically increasing. Among the technologies available to generate electricity from wind, wind turbines play a major role, with offshore wind turbines playing a significant part. Offshore structures such as wind turbines, unlike other types of structures, are in a dynamic environment, the main forces generating this dynamic wave and wind environment, which impose significant structural vibrations, fatigue loads and significant loads on the blades, the turbine, structural platform, and other components import it. Welded joints and points in offshore structures are vulnerable to fatigue failure due to stress concentrations and intermittent environmental loading. Offshore structures have been exposed to shock forces and cyclic loads throughout their lifetimes, which cause the cyclic loads to cause fatigue in the joints. The dynamic forces of the waves gradually cause small cracks in the structural joints over time, and the expansion of these cracks at the weld foot and joints of the structural members reduces the overall stiffness of the joint andin some cases even removes the member from the location of connection. Much research has been done on the use of offshore wind energy, but despite the special attention of the worldwide scientific community on offshore wind energy extraction, there are still few studies domestically. Considering the water levels in the south of Iran and the platforms in the area will add to the importance of this study. The turbine structure will be examined to perform the research by using and inspiring DNV and API by-laws when the method is nonlinear. The case study will also cover the Strait of Hormuz and the time zone. This research is carried out using coding in Matlab as well as analysis in Bentley SACS finite element software which is dedicated to the design of offshore steel structures. The results indicate that the presence of the turbine blade geometry has a significant effect on the fatigue life of the retaining structure and the entire structure.

today, the use of nanoscale additives in the concrete industry with the aim of reducing the negative effects of Portland cement and improving the mechanical properties of concrete has received much attention. Also, in order to reduce the harmful environmental effects and increase the mechanical properties and durability of concrete, particles with high pozzolanic properties are used as a suitable alternative to ordinary cement in concrete. In this regard, geopolymer concrete using materials containing aluminosilicate materials with adhesive properties and filler, as an alternative to cement, has attracted the attention of researchers.Concrete resistance to high heat is of particular importance. Geopolymer concrete has a good performance against heat due to its strong structure.In the current study, slag-based geopolymer concrete was used with 0-2% polyolefin fibers and 0-8% nano-silica to improve its structure. After curing the specimens under dry conditions at a temperature of 60°C in an oven, they were subjected to Compressive strength, Tensile strength, and Drop weight hammertests to evaluate their mechanical properties. all tests were performed at 90 days of age under ambient temperature (20°C) and high temperature (500°C). The addition of nano-silica enhanced the whole properties of the slag-based geopolymer concrete.Addition of up to 8% nanosilica to the geopolymer concrete composition at 20% temperature improved the compressive strength test results up to 21.94%, tensile strength up to 15.19% and impact energy up to 36.36%. Addition of up to 2% of polyolefin fibers to the geopolymer concrete composition improved the tensile strength up to 11.76%, the impact energy up to 8.26 times and the compressive strength drop up to 22.49%. Applying high heat to geopolymer concrete samples reduced the compressive strength up to 16%, tensile strength up to 21% and impact energy up to 72.72%. The effect of heat on the drop in results in control concrete is more than geopolymer concrete.In the following, by conducting the SEM test, a microstructure investigation was carried out on the concrete samples. In addition to their overlapping with each other, the results indicate the geopolymer concrete superiority over the regular concrete. Besides, it demonstrated the positive influence of nano-silica addition on the concert microstructure.

The use of steel shear wall in engineering construction, including high-rise building projects that bear high lateral forces, is of great importance and practical. Since the steel shear wall with opening may have some pre-cracks due to initial damage and cause the weak lateral behavior of the shear wall, in this study, the simultaneous impact of pre-crack and opening in the three-story and one-span frame with steel shear wall has been evaluated. In this study, 48 numerical samples have been studied using the finite element method and Abaqus software. Axial and lateral loading has been applied to the samples, and the parameters of the pre-crack position, pre-crack length and the type of shear wall steel sheet material have been investigated. The results of this study demonstrated that the numerical model made for the shear wall provides reliable answers compared to the laboratory model. In the shear walls under study, the parameter of crack length and crack position has a high impact on the ductility capacity, while it has little impact on the hardness and strength index. The most critical pre-crack modes in the horizontal position, located at the top or bottom corner of the frame, have had a great impact on the lateral behavior and reduced ductility by 60% and wall strength by 32%. On the other hand, by changing the materials of the shear wall steel sheet from LYP steel to St37 and St52, the final strength and hardness have increased by 3.63 and 1.45 times, respectively and the ductility has decreased by30%.

Pervious concrete contains a mixture of water, cement, coarse aggregates and little or no fine aggregates. Pervious concrete is increasingly known as an environmentally friendly material due to its usefulness in improving water quality by removing all suspended solid particles in the flood, reducing the flow of flood water, reducing the heat island effect and other environmental benefits. In this article, the results of valid research on the physical (slump, density, porosity, water permeability) and mechanical (compressive strength, flexural strength, splitting tensile strength) properties of Pervious concrete have been briefed and reported

Due to the widespread use of concrete in all kinds of structures, the probability of its exposure to dynamic loads has increased. Since concrete is one of the most widely used materials in civil engineering, its main weakness can be pointed out, which is its brittleness and brittle performance. The use of fibers to improve the properties of concrete has been the focus of engineers for a long time. The most common fibers used to increase the impact resistance of concrete, steel and polypropylene were investigated in this research as single and hybrid fibers. In this study, by using the ACI 544-based weight projection method, the resistance of concrete against impact loading on standard cylindrical concrete samples (30 x 15) containing steel fibers and polypropylene in two cases with and without lap sheet FRPs were investigated. The results showed that the use of these fibersincreases the impact resistance of concrete. Also, both CFRP and GFRP sheets that were tested improve the impact resistance of concrete and increase the number of cycles of this test. Some GFRP sheets have performed better than CFRP. Also, the presence of FRPsheets has caused a change in the type of failure compared to the absence of FRP. 

Many of the old bridges in northern Iran, which are often more than 50 years old, are made of steel trusses. The superstructure of these bridgesusually consists of two simple and parallel trusses that increase lateral stability, the upper part of these two trusses are connected using bracing elements. In some truss bridges such as the Sardabroud-Chalous bridge, the transverse brace has been removed due to the small length of the span (about 31 meters). These types of trusses that do not have transverse restraints in the upper part are called pony trusses, which have less lateral resistance due to the removal of transverse restraints. On December 25, 2009, while the trailer was passing, a steel cargo weighing about 10 tons was released from the trailer floor and thrown towards one of the vertical elements of the truss. The impact of this heavy object causes the failure of this member and the subsequent failure of the adjacent members, which eventually leads to the collapse of the entire structure. In this paper, the progressive failure mechanism of Sardabrood Bridge will be studied using ABAQUS software. The results of sensitivity analysis and Downstream analysis show that except for zero force elements, other vertical and oblique elements have significant sensitivity that should be prevented from being damaged. Interestingly, at the moment of failure and after the failure, the alternative route is the force distribution, which is mainly the forces trying to cross the pressure rim, but small deformations in a chain led to large deformations and caused the progressive failure, which destroyedthe bridge in 0.7 seconds.