Asian journal of civil engineering
Volume:15 Issue: 4, Aug 2014

The customary exposed column bases of steel construction use anchor bolts. The anchor bolts may be subjected to various combinations of forces. The tensile (or pull-out) actions are one of these forces. The embedded steel sections can replace the anchor bolts in resisting pull-out forces. Depending on the shape of an embedded section, it can resist against pullout forces by three mechanisms namely: the bond resistance, the interlocking force and frictional resistance. The embedded tapered section develops the resistance against the pullout forces by the frictional resistance. The present paper, numerically and experimentally, studies the pull-out behaviour of tapered steel sections embedded in unreinforced concrete. The numerical models are generated with Abaqus 6.10-1. To support the numerical results, four tapered box and I-sections are tested under pull-out forces. The numerical models, study the effects of boundary conditions, the size of the concrete block, the tapering angle, and the coefficient of friction. The restraining boundary conditions prevent the splitting of the concrete block, which is the most common type of failure in embedded tapered sections, and could double its pull-out strength. Under proper confinement, the embedded tapered sections could have very large post-failure pull-out strength.

In this paper, an effective scaled boundary spectral element method is used to analyze seismic soil-structure interaction (SSSI) problems. Coefficient matrices are lumped by using Gauss-Lobatto-Legendre (GLL) quadrature and Lagrange interpolation functions. Required storage space of the computers can be reduced by using lumped coefficient matrices. In addition, a recursive algorithm is adapted to reduce computational effort of the seismic soilstructure interaction analysis. Adapted recursive algorithm can reduce computational effort of the original scaled boundary method (SBM) about 90%. Efficiency of the proposed method is displayed by solving some numerical examples. It is shown that accuracy of the semi local SBM depends on the selected cut off time step.

This paper devoted to analysis of cracked truss type structures. For this purpose, five common cracked bar finite elements, according to the laws of fracture mechanics, are first introduced and verified. Parameters which affect the stiffness matrix of the cracked element are also evaluated. In this paper, a procedure for calculation of stress intensity factor (SIF) by employing cracked element is proposed. A simple cracked truss structure is finally studied. Furthermore, this article could be considered as a relatively comprehensive source of the common cracked bar elements.

A large group of structures hold tri-diagonal stiffness matrices. The eigenpairs and inverse of these matrices are found simpler than the ones of common matrices. In addition, using the householder transformation, symmetric matrices can be converted to the similar tri diagonal matrices. Therefore, since stiffness matrices are symmetric, they can be changed to the similar tri-diagonal ones. In other words, all symmetric matrices can be converted to the tridiagonal ones and the simpler solution of tri-diagonal matrices can be used for all stiffness matrices. Such a comparison is also true for block tri-diagonal matrices and block symmetric matrices. Although block matrices are a specific kind of common matrices, we want to study them independently because working with blocks can be more time-saving and efficient in many cases. In this paper, efficient solutions are presented for tri-diagonal and block tridiagonal matrices. Besides, using the features of symmetric and block symmetric matrices they are converted to the tri-diagonal and block tri-diagonal ones.

Different methods for analyzing nonlinear systems have been proposed. Most of them are not fast enough and also fail to deal with particular set of equations like nonlinear analysis of structures. In this paper, the preconditioned biconjugate gradient (PBCG) is combined with the Newton-Raphson method to reduce the convergence time of each iteration in nonlinear solution process. This algorithm replaces the procedure of inversing the tangent stiffness matrix with a new iterative method to solve the linearized system of equations. Also a new method is introduced to reduce computational time by applying preconditioning to the improved biconjugate gradient method. The proposed method is useful to analyze complex behavior structures, including unloading, snap-through buckling, and inelastic post buckling analyses. In this paper a new preconditioner is proposed which is suitable for nonlinear analysis of structures. Results show that using the new methodology maintains the accuracy in an acceptable level while reduces computational cost and time, significantly.

The purpose of this experimental investigation is to study the flexural behavior of fly ashbased geopolymer ferrocement elements. Ferrocement composite is a rich Geopolymer mortar mix of 1:3 with W/B ratio of 0.416. The alkaline activators used consist of Sodium hydroxide and sodium silicate. The length of ferrocement elements was chosen as 760 mm, width 150 mm and depth of the section was 30 mm, Nine number of rectangular slab were prepared with different meshes such as Square woven, Square welded and Expanded metal mesh. The number of layers in each mesh was varied from single, double and triple layers. The specimens were cured for 28 days by ambient curing. Based on the test results, load vs deflection curves were down. The effectiveness of the Square woven, Square welded and Expanded metal mesh were compared.

The main parameters of the dynamic behavior of steel Special Moment Resisting Frames (SMRF) which is used in steel structures as lateral load resistant system, under influencing pulse type ground motion have been evaluated in this research. The response parameters have been resulted by conducting a number of non-linear dynamic time history analyses. The structural models consist of 10, 20 and 30-story steel SMRF swhich have been designed according to the Iranian seismic code 2800 (3rd edition). The criterion for selecting the strong earthquake records has been the appearance of pulse type features in the velocity time histories concerning with high amplitude factors and long period do mains. The illustrated result sindicate that the structural response parameters are obviously affected by those group of earthquake records which contain pule type features and also the height of the analytical models. As a general conclusion, it is important to note that the lateral displacement and drift of all stories must be controlled during design process. The aforementioned subject can be considered in the design process of steel SMRFs in near zones of active faults.

The Hartley transform, a real-valued alternative to the complex Fourier transform, is presented as an efficient tool for the analysis and simulation of earthquake accelerograms. This paper is introduced a novel method based on discrete Hartley transform (DHT) and radial basis function (RBF) neural network for generation of artificial earthquake accelerograms from specific target spectrums. Acceleration time histories of horizontal earthquake ground motion are obtained by the capability of learning of RBF neural network to expand the knowledge of the inverse mapping from the response spectrum to earthquake accelerogram. In the first step, Hartley transform is used to decompose earthquake accelerograms, then a RBF neural network is trained to learn to relate the response spectrum to Hartley spectrum. Finally, the generated accelerogram using inverse discrete Hartley transform is obtained from target spectrum. Approximately 200 uniformly scaled horizontal ground motion records from recent Iran’s earthquakes are used to decompose with real Hartley transform and train networks.

The paper focuses on detecting, locating and quantifying the damage occurring in three different forms, namely (a) a beam with only a dominant crack, (b) a uniformly degraded beam, and (c) a uniformly degraded beam with a dominant crack. Generalised methodologies have been proposed to solve the three damage cases. Fixed beams have been considered to demonstrate the effectiveness of the generalised method for damage identification. The beam is loaded with a point load. The static deflection has been used as the response to perform continuous wavelet transform (CWT). The continuous wavelet transform coefficients are used to compute the Holder exponent and an Intensity factor. The intensity factor is used to relate the damage (crack damage and/or degradation) characteristics to the magnitude of the wavelet coefficients. The proposed generalised method can be used to solve the damage identification problem for all fixed beams, irrespective of changes in the magnitude of load applied, geometrical and material properties. The effectiveness of the proposed method is demonstrated by validating with several numerical examples available in the literature.

This paper presents the results of an investigation done on the use of steel billet scale as partial replacement of sand in concrete. Concrete mixtures were made with various percentages of replacement of billet scale in lieu of sand. Tests were conducted on fresh concrete for slump and fresh density and on hardened concrete for compressive strength, ultrasonic pulse velocity (UPV), rebound number, and for durability of concrete by immersion in saline medium. It was found out that the concrete up to 15% replacement level of billet scale showed increase in performance than the control mixture. The concrete strength reduced relatively for those samples cured in saline medium, but the 15% replacement was still the optimum replacement proportion. Replacement level of less than 15% and as well as more than 15 % showed decrement in strength.