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Showing 8 results for Finite Element Analysis

A. Eslami, M. Veiskarami, M. M. Eslami,
Volume 10, Issue 2 (6-2012)

It has been realized that the raft (mat) foundations are capable of bearing very large loads when they are assisted with a pile
group. The contribution of both raft and piles to carry the surcharge loads is taken into account, considering the stiffness and
strength of involved elements in the system, i.e. piles, raft and surrounding soil. The piles are usually required not to ensure the
overall stability of the foundation but to act as settlement reducers. There is an alternative design in which, the piles are nonconnected
from the raft to reduce the settlement, which are then known to be "settlement reducer non-connected piles" to increase
the system stiffness. In this paper, two and three dimensional finite element analysis of connected and non-connected pile-raft
systems are performed on three case studies including a 12-storey residential building in Iran, a 39-storey twin towers in
Indonesia, and the Messeturm tower, 256m high, in Frankfurt, Germany. The analyses include the investigation of the effect of
different parameters, e.g. piles spacing, embedment length, piling configuration and raft thickness to optimize the design. The role
of each parameter is also investigated. The parametric study results and comparison to a few field measurements indicate that
by concentrating the piles in the central area of the raft foundation the optimum design with the minimum total length of piles is
achieved, which is considered as control parameter for optimum design. This can be considered as a criterion for project cost
efficiency. On the other hand, non-connected piled-raft systems can significantly reduce the settlements and raft internal bending
moments by increasing the subsoil stratum stiffness. Finally, the comparison indicates that simple and faster 2D analysis has
almost similar results to the time consuming and complicated 3D analysis.

J. Jalili, M. K. Jafari, A. Shafiee, J. Koseki, T. Sato,
Volume 10, Issue 2 (6-2012)

A series of tests and also numerical analyses were conducted to explore the mechanical behavior of a mixture of coarse gravelsize
particles floating in a matrix of silt, sand or clay. The research is a step forward in an ongoing investigation on behavior of
composite clay, which is used as the core material of some large embankment dams all over the world. After providing the reader
with an overall image about behavior of such materials through the literature, the paper focuses on a predominant feature of the
composite soil behavior: increase of non-deformable solid inclusions in a mixture leads to formation of heterogeneity of stress
field, excess pore water pressure and strain distribution along the specimens. This paper mainly probes formation of such
heterogeneity by the aid of special experiments and also numerical analyses. In addition to loading details, it is clarified through
the paper that position of inclusions relative to loading direction also affects heterogeneity of stress/strain and excess pore water
pressure distribution through the mixture. Despite the former, the latter redistributes with a rate proportional to material
hydraulic conductivity.

M. B. Esfandiari Sowmehsaraei, R. Jamshidi Chenari,
Volume 12, Issue 1 (1-2014)

Soil reinforced with fiber shows characteristics of a composite material, in which fiber inclusion has a significant effect on soil permeability. Concerning to the higher void ratio of carpet fibers, at first stages it may be expected that an increase in fiber content of the reinforced soil would result in an increase in permeability of the mixture. However, the present article demonstrates that fiber inclusion will decrease the permeability of sand-fiber composite.A series of constant head permeability tests have been carried out to show the effects and consequently, a new system of phase relationships was introduced to calculate the dry mass for the sand portion of the composite. Monte Carlo simulation technique adopted with finite element theory was employed to back calculate the hydraulic conductivity of individual porous fibers from the laboratory test results. It was observed that the permeability coefficient of the porous fibers are orders of magnitude less than the skeletal sand portion due to the fine sand particle entrapment and also the fiber volume change characteristics.
A. R. Rahai, M. Mortazavi,
Volume 12, Issue 4 (12-2014)

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.
Z.y. Wang, Q.y. Wang,
Volume 13, Issue 4 (12-2015)

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.

Mahnoosh Biglari, Iman Ashayeri, Mohammad Bahirai,
Volume 14, Issue 6 (9-2016)

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.

Jalal Akbari , Mohammad Sadegh Ayubirad ,
Volume 15, Issue 2 (3-2017)

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.

Varol Koç, Yusuf Emi̇roğlu,
Volume 15, Issue 7 (10-2017)

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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