سال:1387 | دوره: | شماره: |تعداد مقالات:7

A method for coupling the variable damage to the yield function of a 2D beam element is presented. The damage is represented by a scalar internal variable which expresses the loss of strength of the material during ductile or fatigue processes and it is concentrated at the ends of the element.Yield surfaces, considering the interaction of bending moment, axial force, shear force and damage of material are also given. And the yield function obtained can be used to determine the elastoplastic stiffness matrix of beam element used for the structural analysis.  

A discrete version of Particle Swarm Ant Colony Optimization (DPSACO) for design of frame structures is presented. DPSACO, similar to continous PSACO, is based on a particle swarm optimizer, worked as a global search, and ant colony optimization employed as a local search. In the DPSACO, the nearest permitted discrete value is replaced with any value selected by agents (Particles or ants). Therefore, the positions of all agents always contain the permitted discrete values. In order to improve the exploration of the proposed method, a new formula for particles' velocity is defined. Two design examples are tested using the new method and their results are compared with the results of other PSO-based algorithms to demonstrate the effectiveness of the presented method.

Braced frames, besides other structural systems, such as moment resisting frames or shear walls, have been an effective and valuable method to enhance structures against lateral loads. In wind or seismic excitations, inclined elements react as truss web elements which would bear compression or tension stresses. This axial reaction results in less moments and therefore smaller sizes in beam and column sections with respect to members in similar moment resisting frame. However, low tensile strength of concrete material, made it a challenge to use in inclined members. In practice, there have been various methods to consider this defect such as disengagement of brace elements in tension or utilization of prestressed braces.The purpose of this article is to study the nonlinear response of reinforced concrete frames which contain reinforced concrete braces as the major structural elements against earthquake loads. The advantages of nonlinear behavior in reinforced concrete elements and their adequate energy absorption in cyclic loading are taken into account. Also stiffness and strength degradation of structural members under cyclic loading is considered.Two different braced frames with K and X braces are analyzed numerically for four, eight and twelve story buildings. This study focuses on evaluation of strength, stiffness, ductility and energy absorption of reinforced concrete braced frames and comparison with similar moment resisting frames and frames with shear wall. Results are plotted in diagrams and discussed extensively. According to this study it is concluded that besides effective lateral stiffness rising in reinforced concrete braced frames, there is a considerable amount of energy dissipation during earthquake loading.

In the present study, Discrete Singular Convolution (DSC) method is developed for free vibration analysis of plates and membranes with trapezoidal shape. The straight-sided quadrilateral domain is mapped into a square domain in the computational space using a fournode element. By using the geometric transformation, the governing equations and boundary conditions of the plate are transformed from the physical domain into a square computational domain. Numerical examples illustrating the accuracy and convergence of the DSC method for trapezoidal plates and membranes are presented. The results obtained by DSC method were compared with those obtained by the other numerical and analytical methods.

Lift installation of a major marine or offshore structure necessitates detailed evaluation of inter-dependent engineering and construction constraints that influence the feasibility, safety and cost-effectiveness of the lifting operations. Due to the advancements in heavy lift technology, large modularized ship blocks may be fully outfitted, and then lifted and joined to form the entire ship. Similarly, an offshore structure may be fabricated in a yard, transported to the selected offshore location, and then installed by lifting. The objectives of this paper are to find the locations of optimum positions of offshore platform heavy lift points using the method of evolution strategies either minimizing the moment or maximizing the natural frequency. The results obtained are compared with the published results. The optimal positions of simple supports are located to maximize the fundamental frequency of beam or plate structure taking into account both elastic and rigid supports. The minimum stiffness of a simple support (or point) that raises a natural frequency of a beam to its upper limit is investigated for different boundary conditions. The solution also provides insight into dynamics of a beam with an intermediate support for more general boundary conditions.Finite element approach is used for solving the problems. The computer packages such as PREWIN/FEAST, SAP90 are used for performing finite element analysis.

Evaluating the moment-rotation behavior of bolted connections by finite element method is very intensive task in terms of computational cost. This study proposes an efficient neural system to predict the moment-rotation behavior of the connections. The neural system is called self-organizing back propagation (SOBP) networks. The SOBP includes two processing units: classification and approximation. In the classification unit, all the training data are divided into some classes by a self-organizing map network. In the approximation unit, a set of back propagation networks are employed to achieve the approximation task. The numerical results demonstrate the computational advantages of the SOBP.

In modern day construction practice, repair and rehabilitation of structures has taken a prominent role. Mortar plays a vital part in these works. As such, the flowability of mortar can be an added advantage when inaccessibility comes into picture like in case of congested reinforcement or narrow cracks or fissures. Due to the application easiness and mechanical advantages, Self Compacting Mortar is preferred for repair purposes especially in reinforced concrete structures these days. The cement as well as the ingredients of the paste, mineral admixtures (pozzolanic or inert nature) and plasticizing chemical admixtures should be carefully chosen in order to obtain a suitable paste composition to enrich the granular composition of the mix. There is no universally accepted agreement on the effect of these factors due to the complexity of combined action; thus, it is hard to make a generalization.The objective of the study is to evaluate the effect of fiber and mesh in Self Compacting Mortar from the viewpoint of fresh state behaviour and mechanical performance. For this purpose two fibers (Polypropylene and Glass fiber) and two types of mesh (Chicken mesh and G.I. wire mesh) were used. The results of 54 panels, 54 cubes and 54 cylinders for flexure, compressive strength and split tensile strength are presented.