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When geogrid reinforcement is used as a treatment method for improving soft subgrade as a roadway foundation, a top layer of subgrade is usually excavated and backfilled with geogrid-reinforced aggregates. This treatment method produces an adequate platform for the planned roadway construction site, where heavy traffic loading is constantly moving. This paper presents a quantitative assessment of subgrade improvement by geogrid reinforcement based on numerical modelling and parametric studies. First of all, the preliminary numerical models were verified by comparing the analysis results with previous studies. Secondly, the major numerical models in this study were assumed to be a simplified simulation of a geogrid-reinforced two-layer system with an aggregate layer above a subgrade layer. The numerical models were applied a quasi-static loading and unloading cycle, in order to monitor the permanent deformation at the surface of the models. Afterwards, thickness of aggregate layer, and subgrade CBR values were varied in order to summarize the outcomes of each case. This approach makes it possible to quantify the effects of geogrid reinforcement and aggregate material in terms of an enhanced California Bearing Ratio (CBR) of a single subgrade clay layer. Results have shown that when the aggregate thickness is up to 450mm, the contribution of enhanced CBR is mostly from aggregate material. However, when the aggregate thickness is about 150mm with a relatively weak subgrade material, the inclusion of geogrid material can contribute about 50% of the enhanced value.

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The purpose of this study is to compare the results of different probabilistic methods such as the perturbation method, Stochastic Finite Element Method (SFEM) and Monte Carlo Method. These methods were used to study the convergence of direct approach for slope stability analysis and are developed for a linear soil behavior. In this study, two dimensional random fields are used and both the First Order Reliability Method (FORM) and Limited Step Length Iteration Method (LSLIM) have been adopted to evaluate the reliability index. The study found that the perturbation method of the second order is easy to apply using the field’s theory because accuracy is reached even with different coefficients of variation of input variables, while the spectral finite element method yields accurate results only for high levels of solution development.

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In this paper, an advanced formulation of the spectral finite element method (SFEM) is presented and applied in order to carry out site response analysis of 2D topographic structures subjected to vertically propagating incident in-plane waves in time-domain. The accuracy, efficiency and applicability of the formulation are demonstrated by solving some wave scattering examples. A numerical parametric study has been carried out to study the seismic response of rectangular alluvial valleys subjected to vertically propagating incident SV waves. It is shown that the amplification pattern of the valley and its frequency characteristics depend strongly on its shape ratio. The natural frequency of the rectangular alluvial valley decreases as the shape ratio of the valley decreases. The maximum amplification ratio along the ground surface occurs at the center of the valley. A simple formula has been proposed for making initial estimation of the natural period of the valley in site effect microzonation studies.

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During the past years the use of buckling restrained braces (BRBs) have had a dramatic growth due to their better performance comparing to conventional braces. BRBs have more ductility and energy absorption capacity by excluding the overall brace buckling. However, even these kinds of braces have some problems restricting their use in some projects, i.e. high tolerance of applying unbonding material, concrete placing difficulties and their weight. Accordingly, many researchers have conducted experiments to find the possibility of shortening or even eliminating the infill material of the braces. The following study has addressed the effect of debonding material friction ratio, shortening the concrete fill, and finally eliminating it if possible, by reshaping the core element with constant section area. The operated analysis has been carried out both numerically and experimentally. ABAQUS finite element software was applied for numerical analysis and the results were verified by an experimental study in two groups of models each including four full-scale brace models. With a constant core section area, results revealed that without the risk of buckling, the concrete cover length could be reduced. With a special core profile, the infill may be fully omitted and the restrainer would be made up of only a steel tube, which may happen without any changes made to the cross sectional area of the core profile.

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Incremental launching is a widespread bridge erection technique which may offer many advantages for bridge designers. Since internal forces of deck vary perpetually during construction stages, simulation and modeling of the bridge behavior, for each step of launching, are tedious and time consuming tasks. The problem becomes much more complicated in construction progression. Considering other load cases such as support settlements or temperature effects makes the problem more intricate. Therefore, modeling of construction stages entails a reliable, simple, economical and fast algorithmic solution. In this paper, a new Finite Element (FE) model for study on static behavior of bridges during launching is presented. Also a simple method is introduced to normalize all quantities in the problem. The new FE model eliminates many limitations of some previous models. To exemplify, the present model is capable to simulate all the stages of launching, yet some conventional models of launching are insufficient for them. The problem roots from the main assumptions considered to develop these models. Nevertheless, by using the results of the present FE model, some solutions are presented to improve accuracy of the conventional models for the initial stages. It is shown that first span of the bridge plays a very important role for initial stages it was eliminated in most researches. Also a new simple model is developed named as "semi infinite beam" model. By using the developed model with a simple optimization approach, some optimal values for launching nose specifications are obtained. The study may be suitable for practical usages and also useful for optimizing the nose-deck system of incrementally launched bridges.

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The main aim of this paper is to find the optimum shape of arch dams subjected to multiple natural frequency constraints by using an efficient methodology. The optimization is carried out by charged system search algorithm and its enhanced version. Computing the natural frequencies by Finite Element Analysis (FEA) during the optimization process is time consuming. In order to reduce the computational burden, Back Propagation (BP) neural network is trained and utilized to predict the arch dam natural frequencies. It is demonstrated that the optimum design obtained by the Enhanced Charged System Search using the BP network is the best compared with the results of other algorithms. The numerical results show the computational advantageous of the proposed methodology.

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It is well-known that dam-reservoir interaction has significant effects on the response of dams to the earthquakes. This phenomenon should be considered more exactly in the seismic design of dams with a rational and reliable dynamic analysis method. In this research, seismic analysis of the dam-reservoir is studied as a wave propagation problem by using Legendre Spectral element method (SEM). The special FEM and SEM codes are developed to carry out the seismic analysis of the dam-reservoir interaction system. The results of both SEM and FEM models are compared considering the accuracy and the time consumption of the analysis. Attractive spectral convergence of SEM is obtained either by increasing the degree of the polynomials in the reservoir or by the number of elements of dam. It is shown that all boundary conditions of the reservoir domain in the SEM are evaluated by the exact diagonal matrices. The SEM leads to the diagonal mass matrix for both dam and reservoir domains. The stiffness matrices obtained from the SEM are more sparse than the corresponding stiffness matrices in the FEM consequently the SEM needs a significant less time consumption of the analysis.

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Latticed columns are frequently used in industrial steel structures. In some countries these built-up columns might be even used in other types of steel structures such as residential and commercial buildings. Besides, latticed columns are parts of skeletons of many historic buildings all around the world. To analyze a steel structure with latticed columns a more accurate numerical model for such a column seems to be essential. The lay-out and connectivity of constructing main profiles of a latticed column leads to formation of many shear zones along the length of a column. Therefore, considering shear effects on the behavior of a lattice column is inevitable. This paper proposed a new super-element with twelve degrees of freedom to be used in finite element modeling of latticed columns. The cross sectional area, moments of inertia, shear coefficient and torsional rigidity of the developed new element are derived. To compute these parameters with less complexity a model using only beam elements is also introduced. A general purpose finite element program named LaCE is developed. This FE program is capable of performing linear and nonlinear analysis of 3D-frames with latticed columns, considering shear deformation. To show the accuracy of the proposed element, several cases are studied. The outcome of these investigations revealed that the current-in-practice model for latticed columns suffers from some major shortcomings which to some extends are resolved by the proposed super-element. The developed element showed the capability of modeling a lattice column with good accuracy and less computational cost.

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This paper presents a finite element analysis and its related experimental test of corrugated steel web beams subjected to fatigue loading. A particular focus in this study was set on the fatigue failure arising from the web-to-flange welded joint of the corrugated steel web beam. A detailed three-dimensional finite element model which explicitly includes the geometry of the web-to-flange welds along the corrugated web was developed to simulate the test corrugated web beam. The finite element model is verified by comparing with related fatigue experimental test results. The effective notch stress approach was also applied to analyse the web-to-flange welded joint replicating the local critical region in the corrugated web beam. The fatigue strength of the web-to-flange welded joint was evaluated and compared numerically by considering the stress distribution at potential fatigue crack initiation location. The fatigue life of the corrugated web beam was assessed numerically by incorporating material S-N relation and employing fracture mechanics approach. The comparison with the fatigue test results show that it is possible to expect the fatigue crack failure arising at the weld root or weld toe corresponding to the sections with reference angle using the effective notch stress analysis. The range of these predictions was evaluated by comparing with fatigue test results with accuracy and can be considered between AASHTO fatigue categories B and B’. The parametric notch stress analysis incorporating the influences of corrugation angle was performed and demonstrates it is possible to expect the fatigue crack failure arising at the weld root or weld toe. Finally, a practical solution for possible fatigue life enhancement of such structure is proposed by decreasing the corrugation angle or smoothing the intersection geometry of the corrugated web is suggested together with a moderate increase of the flange thickness.

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This paper addresses the ambient vibration based finite element model updating of long span reinforced concrete highway bridges. The procedure includes ambient vibration tests under operational conditions, finite element modeling using special software and finite element model updating using some uncertain parameters. Birecik Highway Bridge located on the 81stkm of Şanlıurfa-Gaziantep state highway over Fırat River in Turkey is selected as a case study. Because of the fact that the bridge is the sole in this part of Fırat, it has a major logistical importance. The structural carrier system of the bridge consists of two main parts: Arch and Beam Compartments. In this part of the paper, the beam compartment is investigated. Three dimensional finite element model of the beam compartment of the bridge is constituted using SAP2000 software to determine the dynamic characteristics analytically. Operational Modal Analysis method is used to extract dynamic characteristics of the beam compartment by using Enhanced Frequency Domain Decomposition method. Analytically and experimentally identified dynamic characteristic are compared with each other and finite element model of the beam compartment of the bridge is updated by changing of some uncertain parameters such as section properties, damages, boundary conditions and material properties to reduce the differences between the results. It is demonstrated that the ambient vibration measurements are enough to identify the most significant modes of long span highway bridges. Maximum differences between the natural frequencies are reduced averagely from %46.7 to %2.39 by model updating. Also, a good harmony is found between mode shapes after finite element model updating.

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The contribution of concrete to inelastic deformation capacity and shear strength of reinforced concrete (RC) columns failing in shear has been investigated extensively by various researchers. Although RC members are designed to have shear strengths much greater than their flexural strengths to ensure flexural failure according to the current codes, shear degradation of RC columns failing in flexure has not been studied widely. The aim of this study is to investigate the shear degradation of RC columns using finite element analyses (FEA). The results of FEA are compared with the results of experimental studies selected from literature, and it is observed that the lateral load-deflection curves of analysed columns are compatible with the experimental results. Twenty-six RC columns were analysed under monotonically increasing loads to determine the concrete contribution to shear strength. The results of analyses indicate that increasing the ratio of shear to flexural strength reduces the concrete contribution to shear strength of the columns.

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With the ongoing developments in numerical analysis methods, it is possible to model the soil-foundation-structure interaction and non-linear load-deformation behavior of soils in three-dimensional calculations. In light of these developments, the calculations of mat foundations can be made more realistically and economically by using advanced softwares, which take into account the interactions of these three components than the conventional methods. The aim of this paper is to present the effect of superstructure loading types on the analysis of mat foundations by using three dimensional finite element analysis results. Thirty six different models have been established to examine these effects on the internal forces and settlement behavior. The data of a 3-storey existing building has been used and superstructure loads have been modeled in different ways such as uniformly distributed loads, column loads and by modeling all building. The building has been modeled with a mat foundation having a thickness of 50 cm, 75 cm and 100 cm in seperate models. The mat and superstructure elements have been modeled either with 2D plate elements or 3D volume elements in different models. The “Mohr-Coulomb” material model has been used and soil properties have been represented as “normally loaded” and “overconsolidated”. Results for total and differential settlements and internal forces have been presented in figures and graphs. An important finding is the place where the maximum displacement occurs. It is very different when the load is transmitted by modeling the whole structure and it causes to have different internal forces and different placement of reinforcement. Another finding is that the biggest decreases in differential settlements are seen in column and building loading when the soil properties improved, while this effect remains very small in distributed loading. For bending moments, the biggest difference in comparison to the loading types is that the maximum moments are calculated in different places independent to the location of shear walls, when the load is simulated as a uniformly distributed load. It has been found that the superstructure loading type affects the settlement pattern and internal forces, so this effect must be taken into account.

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A fast converging and fairly accurate nonlinear simulation method to assess the behavior of reinforced concrete columns subjected to static oriented pushover force and axial loading (sections under biaxial bending moment and axial loading) is proposed. In the proposed method, the sections of column are discretized into “Variable Oblique Finite Elements” (VOFE). By applying the proposed oblique discretization method, the time of calculation is significantly decreased and since VOFE are always parallel to neutral axis, a uniform stress distribution along each oblique element is established. Consequently, the variations of stress distribution across an element are quite small which increases the accuracy of the calculations. In the discretization of section, the number of VOFE is significantly smaller than the number of “Fixed Rectangular Finite Elements” (FRFE). The advantages of using VOFE compared to FRFE are faster convergence and more accurate results. The nonlinear local degradation of materials and the pseudo-plastic hinge produced in the critical sections of the column are also considered in the proposed simulation method. A computer program is developed to calculate the local and global behavior of reinforced concrete columns under static oriented pushover and cyclic loading. The proposed simulation method is validated by the results of tests carried out on the full-scale reinforced concrete columns. The application of the “Components Effects Combination Method” (CECM) is compared with the proposed “Simultaneous Direct Method” (SDM). The obtained results show the necessity of applying SDM for nonlinear calculations. Especially during the post-elastic phase, which occurs frequently during earthquake loading.

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In this article, general procedures for vulnerability assessment and retrofitting of a generic seismically designed bridge are outlined and the bridge’s damage criteria for blast resistance are explained. The generic concrete bridge is modeled and analyzed with the finite element technique implemented in ANSYS LS-DYNA environment and explosion threats are categorized into three main levels. Uncoupled dynamic technique is adopted to apply the blast loads on the bridge structure, damage and performance levels are resulted based on quantitatively verified damage mechanisms for the bridge members. The results show that, amongst different loading scenarios, the explosions that happen under deck are more critical comparing to blasts initiating from over deck sources. Furthermore, two retrofitting methods 1) concrete filled steel tube (CFST) and 2) concrete jacket are applied on the bridge columns. The program AUTODYN is used with coupled dynamic analysis of a column to compare the effectiveness of each method. Afterward, more efficient method for a column is applied to the whole bridge and its efficiency is revaluated. It is shown that CFST can decrease concrete spall, scabbing, rotation, displacements and shear forces more than the concrete jacket. Considering the proposed damage and performance levels, the bridge retrofitted with CFST reacts with lower damage level and higher performance level to blast loads.

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Complex nature of diagonal tension accompanied by formation of new cracks as well as closing and propagating preexisting cracks has deterred researchers to achieve an analytical and mathematical procedure for accurate predicting shear behavior of reinforced concrete, and there is the lack of a unique theory accepted universally. Shear behavior of reinforced concrete is studied in this paper based on recently developed constitutive laws for normal strength concrete and mild steel bars using nonlinear finite element method. The salient feature of these stress-strain relations is to account the interactive effects of concrete and embedded bars on each other in a smeared rotating crack approach. Implementing the considered constitutive laws into an efficient secant-stiffness based finite element algorithm, a procedure for nonlinear analysis of reinforced concrete is achieved. The resulted procedure is capable of predicting load-deformation behavior, cracking pattern, and failure mode of reinforced concrete. Corroboration with data from shear-critical beam test specimens with a wide range of properties showed the model to predict responses with a good accuracy. The results were also compared with those from the well-known theory of modified compression field and its extension called disturbed stress field model which revealed the present study to provide more accurate predictions. 

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From practical point of view, optimum design of structures under time variable loadings faces many challenges. Issues such as time-dependent behavior of constraints and the computational costs of the gradients could be mentioned. In order to prevent such difficulties, in this paper, response spectrum method has been utilized instead of applying direct time history method. Additionally, seismic design of structures is defined as a design for a specific response spectra not for an individual acceleration time history. Furthermore, here, in order to guarantee the global optimal designs, the obtained results from gradient-based method are compared with those from the discrete optimization technique (Genetic algorithm). As well, the P-Delta effects are considered in a seismic analysis. In addition, many practical constraints according to the Iranian national building code (NBC) are included in the optimization problem. The developed MATLAB based computer program is utilized to solve the numerical examples of low, intermediate and relatively high-rise braced and un-braced steel frames.

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To study and predict the behavior of flexible pavement over expansive soils, a pavement structure was subjected to different laboratory and fieldwork experiments. The existing pavement was replaced and designed based on California Bearing Ratio (CBR) method, with a new one, and subjected to the traffic from various number of load cycles from 12.1 up to 155.52 kcycles of standard axle load (80 kN) through dual wheel assembly over a 6-month period. As the preliminary step, the deflection measurements were taken at the asphalt surface layer, using a Total station at different distances as function of truckload applications. The numerical analysis is carried out with the Finite Element software package PLAXIS version 2012. In the new model, the calculation of the transferred pressure to the pavement through contact area of tires is 3D it was turned into a 2D problem, and the pavement was subjected to a static loading using a ratio factor of dynamic additional charge. The materials’ behavior was simulated with nonlinear models: Mohr–Coulomb (MC) for pavement layers and soft-soil model (SSM) for the expansive subgrade, in saturated drained and undrained conditions. The results indicate that displacements under static loading in saturated drained conditions and when non-linear materials are present are the closest to field measured deflections.

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Pile load tests and numerical analysis of a small-scale model pile in unsaturated clayey soil are presented in this paper. A small-scale model pile was simulated to bear a static axial loading in unsaturated soil using finite element method. All parameters used in the finite element method were obtained in laboratory tests, including the direct shear test, interface direct shear test, and filter paper method. The numerical analysis results were compared with the pile load test results. The results show that the general trend of pile load and pile head settlement relationship obtained by the numerical analysis shows a good consistence with the pile load test results. With increasing water content of the soil, the matric suction, dilatancy angle and shear strength decrease, and consequently the ultimate bearing capacity of pile decreases.

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Minimum reinforcement ratios provided in the standards are remaining at very low levels especially at large systems subject to the effects of earthquake. Thus, arranging the reinforcement ratios intended for preliminary design can provide significant ease and safety in project design phase, and speed and simplicity in the project control phase. Moreover, a more realistic limitation becomes ensured compared to general minimum reinforcement ratios given in the standards. System characteristics which may affect the reinforcement ratios can be specified by general and simple parameters. As the result of many extensive studies, expressions for reinforcement ratios intended for preliminary design which will cover systems having different parameters can be composed. Today, thanks to the development levels of finite elements programs which can perform reinforced concrete modeling, meeting this requirement is much more possible compared to the past. Structure of parameters should neither be very special nor very general. Otherwise, reinforcement ratios intended for preliminary design will either be valid for a single system or they will remain at very low limits such as the minimum reinforcement ratios given in the standards. For this reason, in this study it was tried to follow a route in between these two extreme conditions. Today, it is possible to perform many studies on the systems having different and comprehensive inclusive parameters and to determine practical ratios which will constitute a recommendation for the project designs. For this purpose, an eight storey reinforced concrete system with single spacing whose shear wall cross-section is 25x250cm, column cross-section is 25x30cm, and beam cross-section is 25x50cm was addressed, and its non-linear planary analyses under static earthquake loads were performed through the ANSYS finite elements program for 13 different reinforcement case. The reinforcement ratios to be recommended for the addresses system and similar systems were tried to be revealed. The examined system was arranged as to get the most critical and extreme values for many parameters which can be considered, but it was tried for the reinforcement ratios to be recommended to be valid not only for this system but also for the general system network having similar properties to this system. In the future researches, expressions of general and inclusive preliminary design reinforcement ratios can be obtained as per the results of many studies to be made on systems having different parameters.

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This study presents methods for numerical modelling and the static computer analysis of steel decks fixed on scaffoldings. The main problem raised here is the method of creating models of a single deck and determination of the accuracy of every model for various design situations: the analysis of state stress in components of decks, the strength analysis of scaffolding where decks can be loaded by untypical the arrangement of materials and the strength analysis of full scaffoldings. The analysis of a state stress in components of a deck requires a detailed model. The analyses of scaffoldings with load by materials have to be performed with using more simple models of platforms. The static-strength analysis of full scaffoldings with many frame elements can be performed if the simplest models of decks are used. In this paper the sets of truss elements replace the stiffness of scaffolding decks.