نشریه مهندسی عمران فردوسی
سال سی و یکم شماره 2 (تابستان 1397)

In this research the seismic demand of RCS structures under the near-fault earthquakes is investigated. For this purpose 5 RCS intermediate moment frames with 4, 7, 10, 15 and 20 stories and 5 spans (span length 5 and 7m) were designed. Then nonlinear dynamic analysis was performed on the structures using the OpenSees software. Results show that the stories displacement under the near-fault earthquakes is larger than the far-fault earthquakes so that with increase in the structure height the difference between them decreases. In high rise structure with 7m length span, the drift-angle due to the far-fault earthquake is greater than the near-fault earthquake.

A significant increase in pore water pressure during construction of earth dams may lead to the hydraulic fracture of dam body in pounding. Thus having sufficient information about generation pattern of excess pore water pressure inside the core is essential. In the present study, using finite element method in coupled analysis of earth dams, excess pore water pressure and displacement values are estimated during the construction of Daroongar dam by developed Fortran code, and the results were compared with instrumentation data. Finally the actual amounts of horizontal and vertical permeability coefficients were determined for the materials by regression analysis.

In this paper, weak form integral equations is presented for dynamic response analysis of tall structures with variable stiffness and mass along the height under axial force. Through repetitive integration, the governing differential equation is converted into its weak form integral equation. The tall structure is modeled by a non-prismatic cantilever beam. By approximation of the mode shape function by a power series, the integral equation is converted into a system of linear algebraic equations. The natural frequencies of tall structure are calculated by determination of a non-trivial solution for system of equations. The analysis results are compared by those obtained from SAP-2000 software and other available references.

One of the ways that is conventional in the last two decades for seismic improvement and retrofit of concrete and masonry structures is using the various fiber reinforced polymers (FRP). Among the most important issues in reinforcement of masonry walls by FRP composites, there is debonding of FRP sheets from the surface of the wall. Therefore in the current study the effect of wall surface preparation methods on the bearing capacity and ductility of masonry walls strengthened with FRP sheets have been investigated specifically. While using alternative methods of surface preparation such as grooving, holes and nailing, indices of strength and behavior of reinforced wall under alternative methods of surface preparation have been studied. To achieve this aims, the number of 11 unreinforced masonry walls was constructed in the laboratory. These results show ductility index for reinforcement wall incrased 110 relative to unreinforced wall.

Using stone column is an efficient method to increase bearing capacity of soft soils. In this research, the bearing capacity of flouting stone columns in reinforced and unreinforced modes were examined using large-scale laboratory tests. The stone columns used in this study are with 60mm diameter with 200 and 350mm length and 80mm diameter with 400mm length. These columns are reinforced with nonwoven geotextile. Results show that increasing in diameter and length of stone column and using geotextile as encased stone column increased bearing capacity of stone column. Increasing the diameter of stone column is more effective than increasing the length of stone column. In fact, it is better to use stone column with excessive diameter and proper length (length to diameter ratio more than 5) instead of excessive length and fewer diameters. By using geotextile encasement, stress concentration ratio increased and so bearing capacity improved. Encasing stone column with excessive diameter is more effective than excessive length

One of approaches in weight reduction of structures is introduction of gaps in the design domain. This basic idea has led the formation of topology optimization algorithms. One of the problems frequently seen in topology optimization problems using common elements such as square or rectangular elements is the checkerboard phenomenon. Generally speaking, any discretization scheme that can better estimate the continuous design domain results in reducing the checkerboard phenomenon. In this article, the unstructured polygonal finite elements are used for discretization of design domain. Two examples corresponding to convex and nonconvex design domains are investigated and improved results and Pareto charts are presented in comparison to results obtained from using the square elements. The results demonstrate that using polygonal elements results in preventing the checkerboard phenomenon and reduction of computation time.

self-compacting concrete is one of the most widely used concrete in the past two decades. The objective of present study is to introduce a new method for high strength self-compacting concrete mix design to both achieving maximum compressive strength and minimizing the cost of concrete. The proposed method is an analytical method. In this method, using optimization concepts such as Lagrangian function and Kuhn–Tucker conditions, and introducing a specific relationship to the compressive strength of concrete, without the need for computer computations, and based on a completely analytical method, provides optimal concrete mix design. The proposed method is a general approach and is applicable to all types of concrete. Here, for the purpose of introducing, the method used to high strength self-compacting concrete containing fly ash. An optimization model of the concrete mix design is first developed accounting for effects of experimental results. Then, using an optimization algorithm, optimal concrete mix design is obtained for the concrete with the strength under consideration. Results showed that the proposed method can provide optimal mix design of high-strength self-compacting concrete while water and cement amount are the minimum amounts required for self-compacting concrete.

In this paper, the effect of rectangular, triangular and trapezoidal lateral loadings pattern on the optimum location of outrigger and belt truss based on energy concept have been investigated. The effect of outrigger-belt truss on shear core system response is modeled by a rotational spring at the outrigger-belt truss location. Optimum location of this spring is obtained when energy absorbed by the spring is maximized. Optimum location of outrigger and belt truss under the effect of three types of lateral loadings pattern for structure with one, two, three and four outriggers and belt trusses is calculated. Results obtained from the proposed method for 60 story tall building are compared to those obtained using a standard finite element computer package. The approximate analyses are found to yield reasonable results and give a fairly good indication of actual structure’s response.

Lightweight concrete has significant importance due to its special features including weight reduction of structures.This article aims to study ‎the effect of silica fume (SF) and ‎nano silica (Na) on mechanical properties of fiber reinforced concrete containing lightweight scoria aggregates. SF ‎and Na are replaced by different amounts of cement weight. The used amounts of Steel and ‎polypropylene fibers having different length to ‎diameter ratios are different.‎ For this study, seventeen different lightweight mixtures ‎were made and tested for mechanical strengths, water absorption and density. ‎Results show that optimized replacement ‎amount of SF and Na is 10% and 3%, respectively. Steel fiber in comparison to ‎Polypropylene fiber had‎ better effect on mechanical characteristics of lightweight concrete.‎