International Journal of Engineering
Volume:26 Issue: 10, Oct 2013

The structural reliability of torsional concrete beams strengthened with full and strip wrapping of carbon fiber reinforced polymer (CFRP) laminate is investigated. The first order-second moment reliability method has been applied to make a reliability assessment on the torsional capacity designed by technical guideline in Iran. The code No.345 published by the Management and Planning Organization of Iran (MPO 345-2006) is the first technical code in Iran for design of concrete members strengthened with CFRP laminate. In this work, the average reliability indexes for unstrengthened, strengthened with full wrap and strengthened with strip wrap beams have been found. The results indicate that the MPO design guideline are some unconservative. A reliability strengthening ratio is introduced for assessment of the variation in average reliability index before and after strengthening with different resistance factors. A parametric study on this factor reveals that if the reliability level of the strengthened reinforced concrete beams is kept to be consistent with their similar unstrengthened beams, a value of 0.89 and 0.81 for strengthened with full wrap and strengthened with strip wrap, should be applied, respectively

The design codes of building are mainly related to the strength of the building and there are no specific codes for the design of building with waffle floors for vibration sensitive equipment. The finite element model, ANSYS, is capable to consider the effects of floor thickness, the size of the bays and stiffness of the columns for analyzing the vibration of the waffle floors and vibration transmission along the waffle floor. Because the finite element analysis is time consuming and it needs enough expertise for modeling, in this study, an approximate relationship is proposed to design the waffle floor based on the comprehensive investigations of different effective parameters in the response of waffle floor. The results obtained from finite element analysis. This proposed relationship comforts the designers of industrial buildings and vibration sensitive equipment to attain a preliminary and appropriate outline to design the waffle floor considering the effective parameters on the floor vibration.

After Northridge and Kobe earthquakes, several studies have been conducted to improve the seismic performance of steel structures. In this investigation, new steel moment-resisting connections (FSFN) developed by the authors were studied by the non-linear numerical analysis. These connections were single-sided beam-to-column assemblies that are representative of exterior beam-to-column connections. Seismic performance of FSFN connections in comparison to the W-series of existing KBB connections under standard and near fault load history based on AISC 341 and FEMA 355D were also studied. For this purpose, 32 analytical modeled specimens were evaluated and the results were compared. Results showed that FSFN bracket connection has a seismic performance similar to KBB connection and it is an appropriate connection for the special moment resisting frames both in far and near fault zones. More so, these brackets have smaller dimensions as compared with Kaiser Connections, they can support deeper beams up to 100 cm. Therefore, they can be considered as an appropriate alternative for the Kaiser patented connections. This paper presents the analytical modeling, non-linear behavior and the results of the comparison studies in detail including obtained conclusions

Pulse period of earthquake records has been known as a key parameter in seismology and earthquake engineering. This paper presents a detailed characterization of this parameter for a special class of earthquake records called pulse-like ground motions. This type of motion is often resulted from directivity effects and is characterized by a strong pulse in the velocity time history of motion, in normal-fault component. Wavelet analysis was used as a powerful and useful technique in the analysis of non-stationary signals in this study. The period of velocity pulses is basically determined using the pseudo-period of the mother wavelets. The effects of three different mother wavelets on results were investigated and new empirical predictive equations for pulse period have been derived.

The behavior of conventional braced frames are not the same in tension and compression. This problem can be improved by prevention of buckling under compressive loads, which is called bucklingrestrained brace (BRB). In this field, TTD metal damper also have attracted much attention due to simplicity in construction and execution. This damper is recommended because of accessing to better performance than BRB and also having easier construction technology and consequently being cheaper thus possibility of making it becomes feasible in countries without complex technologies. In this research, three steel structures with three, five and eight stories that require retrofitting, are retrofitted using buckling restrained brace and TTD metal damper separately, and are compared before and after the retrofitting using nonlinear dynamic analysis in PERFORM 3D software. Finally, the effects of this systems in reduction of structure displacement, reduction of energy dissipation due to nonlinear behavior in main members of structure, and increasing of performance level is inspected. The observation of both systems results imply that with increasing the number of building stories, expressed positive effect is reduced which indicates more effect of this energy dissapation systems in short-order structures.

Climate variability and change is threatening water resources around the world. One hundred and fourteen (114) stations from Reference Hydrometric Basin Network (RHBN) around Canada with at least 30 years continuous data (up to 2011) were selected to study the trend in mean annual runoff for different periods of 30 to 100 years in step 10 years by non-parametric Mann-Kendall test. Effect of short term persistent (STP) and long term persistent (LTP) on this test were made through lag 1 serial correlation (r1) and Hurst exponent (H), respectively. r1 for about one third of the total cases considered was negative. H, based on “equivalent Normal deviate” (eNv), was slightly right-skewed with minimum and maximum values of 0.20 and 0.87, respectively. About half of the data sets were anti-persistent (H<0.5). No regional pattern was found for r1 and H. Based on five stations with around 100 years data it was shown that r1 and H are unstable for record length, roughly, up to 50 years. r1 and H were highly correlated (r=0.86). H from eNd were smaller than H from original data by around 10% with high correlation (r=0.87). Under classic Mann-Kendall trend test, different time periods of different stations showed different trend direction and significancy, which admits for abrupt change in trend direction and significancy for different time periods. On overall, more than 60% of cases there were no significant trends (i.e. p-value>0.1). The number of positive and negative trend, were nearly the same, though fluctuating for different time spans. p-value after pre-whitening was highly correlated with those of before pre-whitening, for both negative and positive trends. There were about 16% of cases that pre-whitening decreased the p-values of the Mann-Kendall trend test, where nearly all of them were negatively trended. The effect of LTP on Mann-Kendall trend test was minor due to inconsistency of originally significant trend case and significant H of greater than 0.5. For recent 30 years length of record (1982-2011), British Columbia is experiencing positive trend in the west and negative trend in the east. Most parts of the New Brunswick are experiencing the positive trend, while negative trend is due to Southeast of Ontario. For the longer duration of 40 years, trend statistics and geographical pattern were changed. While the significant trends are decreased, more significant negative trends are governed over New Brunswick. There is no positive trend in British Colombia in the past 50 years (1962-2011) while there are both negative and positive trends in New Brunswick which negative trends are switched to positive trends in south east of Ontario. For long duration of > 70 years, there are only positive trends in Southeast of Canada (South New Brunswick and South East of Ontario) while central and east of Canada have experienced a negative trend.

Semi-active control devices, also called “Intelligent” control devices, constitute the positive aspects of both passive and active control devices. A semi-active control strategy is similar to the active control strategy, but this control device has been shown to be more energy-efficient than active devices. A particular type of semi-active control device, the Variable Stiffness Device (VSD), consists of a hydraulic cylinder with a normally closed solenoid control valve inserted in the tube connecting the two cylinder chambers. This paper emphasizes on the application of Semi-active Fuzzy Logic Controller (SFLC) of this system for getting the best results in the reduction of the building responses under earthquake excitations. For the numerical example, a 12-story building, located in the city of Rasht, Iran, is modeled as 3-D frame and the problem is solved in state space. The results obtained from the proposed control scheme (SFLC) are compared with those obtained from the ON-OFF control method. It is found that the SFLC is highly effective in reducing the responses of the example building than the ON-OFF algorithm. In this study, the optimal values of the fuzzy rule bases, membership functions, and the location of the control device are determined.

In this paper, the effect of adding recycled glass powder (RGP) as a third component in polymer modified bitumen is studied. RGP and styrene butadiene rubber (SBR) are added to the base bitumen in order to prepare modified binders and mixtures. The initial study is performed to determine physicalproperties of unmodified, SBR modified and RGP-SBR modified asphalt binders which prove RGP's compatibilizing effect on asphalt and polymer as well as high compatibility between RGP and polymer leading to better dispersion of the polymer in asphalt. The results of the study showed how final rheological properties of the mentioned combination could be affected by adding RGP and SBR. Modified and unmodified binders are used for preparing Marshall samples for the following tests: Marshall stability, indirect tensile strength (ITS), indirect tensile strength ratio (ITSR), and resilient modulus tests. The results also indicate that combination of 3% SBR plus 2% RGP can improve mechanical properties of asphalt mixture considerably

The performance of an 8-noded hexahedron C1* element in elasticity is investigated. Three translational displacements and their derivatives as strain in each direction are considered as degrees of freedom (DOF) at each node. The geometric mapping is enforced using a C0 element with no derivative as nodal DOF. The stiffness matrix of the element is also computed using a transformation matrix obtained from an equivalent C0 element. The results obtained from elastic stress analysis of a cantilever show that: (i) the convergence rate of 8-noded C1* element is nearly equal to its equivalent C0 element, while it consumes less CPU time with respect to the C0 element; (ii) the element has successfully passed the patch and distortion tests; (iii) the condition number of the stiffness matrix for C1* element is less than the C0 element; (iv) the directly computation of strains as derivative DOF at the nodes along with excellent convergence makes the C1* element superior compared with its equivalent C0 element.

Residual stresses have become an important player in the field of structural integrity for many years. Exact knowledge of residual stress distributions is essential in designing the engineering components as unexpected failures are inevitable wherever such stresses are ignored. There are many residual stresses measurement techniques including destructive and non-destructive ones. Among the mechanical strain relief (MSR) techniques, contour method is one of the youngest. Contour method relies on the material removal similar to other MSR techniques. In this method a part is carefully cut into two pieces along a flat plane, causing the residual stress normal to the cutting plane to relax. However, similar to other MSR techniques, plasticity can have a great influence on the accuracy of the results. In the present work, effect of plasticity on the residual stress measurement using contour method is investigated. Quenching is employed to induce residual stresses within the samples. To create different levels of plasticity, the samples were quenched at three different temperatures, 500°C, 700°C and 850°C. The residual stresses were then measured using contour method. Furthermore, the contour method procedure is simulated using finite element analysis to compare with the experimental results.

In this work, the stencil adaptive method is applied to investigate the effects of a magnetic field on mixed convection of Al2O3-water nanofluid in a square lid-driven cavity. The incompressible Navier-Stokes equations are solved by an adaptive mesh method which has superior numerical advantages compared to the traditional method on the uniform fine grid. The main objective of this study is to investigate the influence of several pertinent parameters such as the Reynolds number, the Hartmann number and the solid particle volume fraction on the heat transfer performance of the nanofluid. Based on the obtained numerical results, the heat transfer rate increases with an increase of the Reynolds number but, it decreases with an increase of the Hartmann number. In addition, the results indicate that enhancement in heat transfer performance of the nanofluid with respect to that of the base fluid is depended on the Reynolds number

The main purpose of the present work is multi-objective shape optimization of a projectile tip for impacting and normal penetrating. Velocity drop, weight and inner volume of projectile have been considered as three conflicting objective functions. For this purpose, at the first step, finite element modeling was done using ABAQUS/Explicit and projectile penetration was examined in different geometric dimensions. Hammersley sequence sampling was employed for designing computer experiments. In the next step, results of the FEM were employed as raw data for MLF-type neural network training to achieve a mathematical model which is able to describe velocity drop behavior. Projectile weight and Inner volume were also expressed in explicit mathematical form using geometric relations. Obtained mathematical models were used as conflicting objective functions for multiobjective optimization of projectile tip using modified NSGA-II. Finally, it is shown that some interesting and important relationships as useful optimal design principles involved in the performance of projectile impact have been discovered by Pareto based multi-objective optimization

In some situations, when an external disturbance occurs, humans can rock stably backward and forward by lifting the toe or the heel to keep the upright balance without stepping. Many control schemes have been proposed for standing balance control under external disturbances without stepping. But, in most of them researchers have only considered a flat foot phase. In this paper a framework that includes the foot tilting is presented. This is done by hybrid modeling of the humanoid robot and also using a receding horizon based approach. The decision for the recovery pattern is done based on the evaluation of the Vertical Forces criterion. If the method predicts the tilting of the foot under disturbance, then the optimum trajectories are obtained for upper segments to return the robot to the secure posture in which the foot is flat (home posture). The obtained optimum trajectories are then tracked by a feedback controller. In the context of receding horizon approach the Extrapolated Center of Mass position has been used as the stability constraint. The results demonstrate the success of method to reproduce human-like balance recovery reactions under impulsive disturbances. The simulated results are compared with experimental data reported in the biomechanics literature.

In this article, a Ranque–Hilsch Vortex Tube has been optimized utilizing axial angles for nozzles. Effect of nozzles angles on the flow behavior has been investigated by computational fluid dynamics (CFD) techniques. A finite volume approach with the standard k–ε turbulence model has been used to carry out all the computations. The dimensions of the studied vortex tubes have been kept the same for all models and the performance of machine was studied under 5 different angles (β), namely 0, 2, 4, 6 and 8 degree adjusted to the nozzles. Achieving a minimum cold exit temperature is the main goal of this numerical research. The results show that utilizing this kind of nozzle improves the cooling capacity of device for most values of inlet mass flow rates. Finally, some results of the CFD models have been validated by the available experimental data which show reasonable agreement, and other ones are compared qualitatively