Ferdowsi Civil Engineering
Year:2011 | Volume:22 | Issue:1|Papers Count:9

The purpose of optimization in civil engineering is design of a structure to achieve the minimum weight and construction cost of the structure in addition to satisfaction of the technical aspects of the problem. Braced frame is a type of structure with large application in civil engineering. The arrangement of bracings in different panels and length of joint beam play an important role in performance of these structures. Therefore in this study a spectral dynamic analysis performed on such frames in order to optimize them against dead, live and earthquake loadings. In this procedure Migration Genetic Algorithm is used. The basis of this algorithm is inspiriting the nature of live creatures and the way inheritance transfers among different generations to calculate the optimum of mathematical functions. The model is applied on two and three dimensional braced frames. The results showed that defining the proper input data such as target function and restrictions leads to accurate optimum design as output.

In this paper, brick walls as seismic load carrying elements in masonry buildings have been studied. An experimented un-reinforced brick wall (UBW) has been chosen from ref. (1) to prove the ability of analytical modeling used in this paper by which a reinforced (RBW) and a confined brick wall (CBW), designed according to Iranian Earthquake Standards, have been modeled and nonlinearly analyzed. This analysis shows that UBW practically is not able to resist horizontal loads. According to the type and direction of cracks in UBW constructed by conventional methods, it is clear that these walls do not have sufficient shear strength, and the study of hysteresis curves of brick walls shows that the confinement in CBW and reinforcement in RBW increases the rigidity and capability to displacement of walls.

In addition to reducing the size and time of analyses, reduction of analytical errors is one of the most important considerations in ideal analysis of skeletal structures by computer. Appropriate matrixes with more zeros (sparse), well structure, and well condition are helpful for this aim. Therefore, an optimizing problem with multiple objectives will be considered. The objective of this research is reducing the analytical errors such as rounding errors in flexibility matrixes of skeletal structures by performing more constant and proper algorithm. These errors increase in special structures with unsuitable flexibility matrixes; the structures with different stiffnesses are one of the most prevalent examples for this case. Use of weak elements leads into high non-diagonal terms in flexibility matrix, which result in analytical errors. In numerical analysis, ill-condition of a matrix is soluble by movement or substitution of the rows; then specification and implementation of these changes before forming the flexibility matrix has been studied. By identifying cycle bases with specific qualities, simple typological and algebraic properties have been used basically in analyses for this purpose. In conclusion, stiffness matrixes with optimally condition number are obtainable and analytical errors reduce.

Soil deformation modulus is one of the most complicated and important soil parameters, correlating between stress and settlement. The magnitude of deformation modulus is not constant. Its value, which varies in a wide range, depends on many factors. The soil deformation modulus may be determined using in-situ and laboratory tests, including consolidation test, triaxial test, Standard Penetration Test (SPT), Cone Penetration Test (CPT), Plate Load Test (PLT) and many other tests. Although the in-situ test results are more accurate in comparison with laboratory tests, but in-situ tests are more expensive and time consuming and practically these tests are usually difficult and sometimes impossible to perform. In the present research the in-situ plate load test results are employed to determine the soil deformation modulus.This test is then modeled in the laboratory and results are compared. To achieve this, after soil sampling from the site, the samples were classified after which their moisture content and unit weight were determined. The plate load test, modeled in the laboratory, was then performed on the undisturbed samples, taken from the site. In order to compare and establish a mathematical correlation between the results of these two groups (the in-situ and laboratory plate load tests), the load-settlement curves of all two group tests were plotted, after which the initial tangent slope, secant slope and unloading slope for each sample was calculated and plotted and the results were then compared. Considering the complicated soil behavior, the results of this research seem to be appropriate and can be used in practical civil engineering purposes.

In this research, the ductility of lap-spliced concrete beams reinforced with steel and FRP bars is analyzed. A number of 16 beam specimens reinforced with steel bars and 7 with FRP bar were designed and manufactured in real sizes and dimensions for laboratory experiments. The parameters of concrete compressive strength, amount of transverse reinforcement over the splice length and the diameter of longitudinal bars, are selected as the main variables for the beam specimens. Mid-span displacements and the corresponding forces were obtained by means of a hydraulic jack, load cell, LVDT and a Data Logger set. The force versus mid-span displacement curves were obtained using the experimental data. A ductility index which has been defined by researchers, was used to evaluate the ductility of the specimens.Comparison of the ductility index of different specimens shows that the compressive strength of concrete and the amount and the bar diameter of the transverse reinforcement over the splice length, has a major effect on the ductility of lap-spliced reinforced concrete beams. The results show that by using an appropriate amount of transverse reinforcement, a satisfactory ductility response for different compressive strengths of concrete can be obtained.

Rapid concrete deterioration in Persian Gulf region has become one of the major concerns since it shortens the structure life span and increases the maintenance costs. The main cause of such concrete failure is claimed to be chloride permeation and subsequent corrosion. Pozzalns are widely being used in order to construct more durable concrete as a functional solution to this problem. The paper reports the performance of concrete incorporating silica fume (replacement level of 5%, 7.5% and 10%), metakaolin (replacement level of 5%, 10% and 15%), zeolite (replacement level of 10%, 20% and 30%) and Polypropylene Fiber in the binder to resist the chloride penetration in aggressive environments. The results showed that specimens containing pozzolans function better than control concretes.

The load carrying capacity, buckling and post-buckling behavior of cylindrical thin-walled shells exposed to axial loads are very sensitive to imperfections in the initial geometry. These imperfections are invariably caused by an assortment of manufacturing processes like displacing, installing or welding; one of the most important imperfections caused by welding that has been reported to have an essential detrimental effect on the buckling resistance of these shells under axial load is circumferential imperfections. Despite many determinations of the effect of imperfections on axial load carrying capacity of cylindrical thin-walled shells, the major part of these studies are concentrated on the existence of imperfections on the shell wall, and a comprehensive research on circumferential imperfections and their effects on axial load carrying capacity has not been performed. This is the main subject of this research. Also in this paper, the interaction of two imperfections on each other and on the load carrying capacity of cylindrical shells in various cases are analyzed and determined using a finite element program (ABAQUS).

One of the common methods of river training and bank protection is using spur dikes. Building spur dikes makes the flow path to be modified. Because of the concentration of flow in the middle part of the river it causes the river side not to be washed out. Setting spur dikes in the flow's direction leads to a local scour in the spur dike site and the change in the bed's topography of the bend down stream. this paper examines the effect bed's topography around the T shaped spur dike located in a 90 degree bend by conducting several tests. These tests were carried out in an experimental channel with a bend of 90 degrees and under conditions with clear water. These experiments, in fact, measured the effects of such parameters like the length of the spur dike, the location of the spur dike in the bend, the flow Froud number on the down stream bed topography. The results of investigation show that two scour hole forms due to a T shaped spur dike. One at the nose of spur dike and the other one at the downstream of the spur dike. By increasing the length of the spur dike, the dimensions of first scour hole increase. But the dimensions of second scour hole decrease. By increasing the length of the spur dike the distance of location of second scour hole from the spur dike increases. Any change in the position of the spur dike toward the down stream of the bend, increases the dimensions of scour hole. Also, New equations for maximum scour depth and scour volumeat a T shaped spur dike are developed.

Engineering structures as well as office or apartment buildings are affected by earthquakes. A common cause of failure seems to be shear stresses. The earthquake tremor developed at different floor levels need to be brought down along the height to the ground by the shortest path. Short column phenomenon is one of the frquent causes of buildings failure in the past earthquakes. This destructive phenomenon is due to the column height difference in a story level that is predominantly owing to the location of building on sloppy ground. These buildings have unequal height columns along the slope, which causes poor effects like twisting and damage in shorter columns. In some buildings, few or no walls are provided at the first story (pilot). In the structures with difference in the story levels, major problems is due to the discontinuity of floors diaphragm that causes significant changes in natural period, stiffness and distribution of earthquake forces. In this study, at first, seismic behavior of short column phenomenon is determined, then, nonlinear behavior of RC short columns in the 4, 8 and 10 story buildings with story level difference is investigated. Short columns and mentioned structures are analyzed under the earthquake records of Elcentro and Tabas with different peak ground acceleration using IDARC software which is nonlinear dynamic analysis program. In this investigation, the results of maximum response, base shear, global damage index and displacement time history and effect of short column in structural failure are evaluated.