BULLETIN OF EARTHQUAKE SCIENCE AND ENGINEERING
Year:2015 | Volume:12 | Issue:1|Papers Count:8

Optimization of structures for minimum weight has become important in the recent designs. In this study genetic optimization algorithm for weight minimization of steel frames has been used. The genetic algorithm is an optimization and search technique based on the principles of genetics and natural selection. Constraints regarding material strength and serviceability aretaken from “AISC code (1989)” and implemented in the algorithm. The design process obtains a frame and bracing pattern with the least weight by selecting appropriate sections for beams, columns and bracing members from the standard set of steel sections. The results of this study showed that the optimization based on weight minimization is able to improve structural performance.

Beam to column welded connection with radius cut on beam flange is known as rigid connection that provides acceptable ductility for Special Moment Resisting Frame (SMRF). In order to decrease the cost of construction and to provide an easy-to-construct structure, the new method is available for reducing the beam section based on drilling on beam flange, known as Drilled Flange connection (DFC). In this research, the effects of distance between first rows of holes from the column face on the seismic performance of DFC are studied for a specific configuration of the holes. Based on the results, the above-mentioned distance should be limited to 0.45 to 0.7 of beam flange width to provide acceptable ductility for DFC.

Concrete is one of the most widely used materials in construction industry. Many large and important structures such as power plants, bridges, dams and buildings employ concrete as main material. Propagation of crack is considered one of the main reasons in failure of concrete structures. The process of formation and crack growth is one of the major and complex issues in concrete, because concrete is a heterogeneous material and different factors such as the construction and curing methods, initial crack length, rate of critical strain energy release, crack width, loading condition, weather conditions and etc. are effective in formation and crack growth. This paper aims to discuss the effect of critical strain energy release (GC) in propagation of initial crack in concrete beams. Finite element software ABAQUS and extended finite element method is used for modeling propagation of initial crack. The results of this study show that increase of critical strain energy release rate in concrete beams with same dimensions causes the increase of maximum failure load and crack mouth opening displacement.

Conventional methods for seismic design of structures are based on building capacity. Because of the disadvantages of conventional methods, base isolation system is known as an effective solution to protect structures against earthquakes. In this study the operation of 2-storey steel frame with and without seismic isolators Under near-fault earthquake of chichi, northridge and capemendocine Are investigated. Effect of characteristic strength to structure weight ratio is also evaluated and performance of braced frames and moment frames with lead core isolators are compared. The results indicate that seismic isolators will lead to better performance of structures against earthquakes and characteristic strength to structure weight ratio have a significant impact on the performance of the structure.

Research on the heavy concrete technology expanded rapidly in the last decades. This kind of the concrete can be used for different purposes such as the protective shields of the medical centers and nuclear power plants. Ilmenite, limonite, hematite, magnetite and barite are the common mineral aggregates which are used in the heavy concrete construction technology.In this research the mechanical properties of the concrete which is made of the Barite are studied. For this purpose, at first the feasibility of the construction of the heavy concrete is considered based on the local mineral resources. Then, the most efficient plan for appropriate production process is explained. Finally, the low cost design and implementation of this type of the concrete is presented using the observed results.

The basic strategy of reduce the ductility demand and related concentrated tensions at moment resistance connections is reduce the section of the beam at connected region to column. By this method plastic hinge done at the reduced cross section and this local reduction decreases the demand of the components of connection. On this basis, in present study a new beam-to-column moment connection with reduced beam section using Tubular Accordion Web that called TAW-RBS is studied analytically. The results show that TAW-RBS create a ductile fuse away from beam-to-column connection components, through removing web from beam flexural capacity. Reduction of beam flexural capacity in the plastic hinge is calculated based on the dimensions of beam and tube. So bending strength of the remaining tubular web would be proportional with square of the thickness of tube and inversely related with the thickness of flat web and the diameter of tube. The optimal location of the tubular web is determined due to the length of beam and the plastic modulus ratio at the plastic hinge to the total cross section. Also shear control at tubular web according to local and global shear buckling are other points of this study. The results show that TAW-RBS reduces flexural stiffness about 14 to 19% in the plastic hinge locations that is equal with the RBS20%. Also the proposed connection, depending on the size of the beam, reduces bending strength between 22 to 28% in the plastic hinge location that is intermediate between RBS20% and RBS50%.

The main purpose of design in civil engineering is to establish a project which has the most versatility on the expected needs and existing conditions. Through optimization this is equivalent to determination of a group of design variables that cause minimizing the object function versus imposed loads, restraints and predetermined parameters. In this research, genetic algorithm method is used to design optimally the double layer grids. Furthermore, in this research the cross section of the members and the depth of the double layer grid are taken as the continuous variants, while the weight of the structure is set as the object function. Also the versatility of the genetic algorithm method is compared with other methods and for this an example is examined. The programming of the genetic algorithm is done by Matlab software. The adapted restraints for the example of this research consist of deflections of the nodes, stresses and slenderness ratio of the elements. The results show that application of genetic algorithm is very versatile for optimization of double layer grids.

Buildings with wall or frame-wall systems are more effective against earthquake forces and sustain less damage than buildings which their lateral resistance is solely depends on frames.Four reinforced concrete (RC) structural wall specimens were subjected to cyclic loading using finite elements method with ABAQUS software in order to study influence of diagonal web reinforcement. The research parameters included the amount and configuration of reinforcing bars in the web. The conventionally reinforced wall failed due to web crashing with an abrupt drop in load capacity, whereas the walls reinforced with diagonal web reinforcement failed in a more ductile mode. The results clearly indicates that the diagonal web reinforcement increase the lateral load capacity of wall. The energy dissipation capacity of the diagonal web reinforced is superior to the conventionally reinforced wall.