• Structural Engineering and Mechanics
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• v.50 no.6
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• pp.835-852
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• 2014

Despite the availability of other transport methods such as land and air transportations, marine transportation is the most preferred and widely used transportation method in the world because of its economical advantages. In service, ships experience cyclic loading. Hence, it can be said that fatigue fracture, which occurs due to cyclic loading, is one of the most critical failure modes for vessels. Accordingly, this makes fatigue failure prevention an important design requirement in naval architecture. In general, a ship structure contains many structural components. Because of this, structural modeling typically relies on Finite Element Analysis (FEA) techniques. It is possible to increase fatigue performance of the ship structures by using FEA in computer aided engineering environment. Even if literature papers as well as rules of classification societies are available to assess effect of fatigue cracks onto the whole ship structure, analytical studies are relatively scarce because of the difficulties of modeling the whole structure and obtaining reliable fatigue life predictions. As a consequence, the objective of this study is to improve fatigue strength of a mercantile vessel against fatigue loads via analytical method. For this purpose, the fatigue life of the mercantile vessel has been investigated. Two different type of fatigue assessment models, namely Coffin-Manson and Morrow Mean stress approaches, were used and the results were compared. In order to accurately determine the fatigue life of the ship, a nonlinear finite element analysis was conducted considering plastic deformations and residual stresses. The results of this study will provide the designer with some guidelines in designing mercantile vessels.

• Journal of Korean Society of Steel Construction
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• v.22 no.4
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• pp.335-344
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• 2010

This paper presents both of an investigation on the ultimate responses and a verification study on the structural methodology using beam-truss element of steel transmission towers using experimental study. The partially scaled tower which verified with analytical model was fabricated and the horizontal load was applied up to failure in the laboratory. The structural methodology for finite element analyses was verified against experimental results and both the ultimate load capacity and collapse mechanism were shown in the test to give sufficiently accurate results with those of analytical study. It was shown as well that the ultimate failure is primarily attributed to instability of the main posts in the leg parts.

• Journal of Korean Association for Spatial Structures
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• v.17 no.4
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• pp.149-157
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• 2017

An innovative analysis method is proposed in this paper for the determination of ultimate resistance of prestressed concrete beams. The proposed method can be applied to simply supported or continuous beams in a unified manner whether structure and external loads are symmetric or not. Through the iterative nonlinear strain compatibility solutions, this method can also be applied to the non-prismatic section/un-symmetrical composite structures under moving load. The conventional studies have used the failure criteria when the strain of concrete reaches 0.003. However compared with bonded case, the value of strain in the reinforcement is much smaller than bonded case, thus, unbonded prestressed cases show compressive failure mode. It is shown that the proposed method gives acceptable results within 5% error compared with the prior experimental results. It can be shown that the proposed method can reach the solution much faster than typical three-dimensional finite element analysis for the same problem. This method is applicable to the existing unbonded prestressed members where deterioration has occurred leading to the reduced ultimate resistance or safety. In all, the proposed procedure can be applied to the design and analysis of newly constructed structures, as well as the risk assessment of rehabilitated structures.

• Computers and Concrete
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• v.18 no.6
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• pp.1175-1194
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• 2016

Nonlinear models, capable of taking into account all the phenomena involved in the cracking and in the failure of lightly reinforced concrete beams, are nowadays available for a rigorous calculation of the minimum reinforcement. To simplify the current approaches, a new procedure is proposed in this paper. Specifically, the ductility index, which is lower than zero for under-reinforced concrete beams in bending, is introduced. The results of a general model, as well as the data measured in several tests, reveal the existence of two linear relationships between ductility index, crack width, and the amount of steel reinforcement. The above relationships can be applied to a wide range of lightly reinforced concrete beams, regardless of the geometrical dimensions and of the mechanical properties of materials. Accordingly, if only a few tests are combined with this linear relationships, a new design-by-testing procedure can be used to calculate the minimum reinforcement, which guarantees both the control of cracking in service and the ductility at failure.

• Computers and Concrete
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• v.21 no.4
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• pp.355-365
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• 2018

Five previously-tested reinforced concrete frames were modelled using a nonlinear finite element analysis procedure to demonstrate the accurate response simulations for seismically-deficient frames through pushover analyses. The load capacities, story drifts, and failure modes were simulated. This procedure accounts for the effects of shear failures and the shear-axial force interaction, and thus is suitable for modeling seismically-deficient frames. It is demonstrated that a comprehensive analysis method with a capability of simulating material constitutive response and significant second-order mechanisms is essential in achieving a satisfactory response simulation. It is further shown that such analysis methods are invaluable in determining the expected seismic response, safety, and failure mode of the frame structures for a performance-based seismic evaluation. In addition, a new computer program was developed to aid researchers and engineers in the direct displacement-based seismic design process by assessing whether a frame structure meets the code-based performance requirements by analyzing the analysis results. As such, the proposed procedure facilitates the performance-based design of new buildings as well as the numerical assessment and retrofit design of existing buildings. A sample frame analysis was presented to demonstrate the application and verification of the approach.

• Smart Structures and Systems
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• v.1 no.4
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• pp.369-384
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• 2005

The main objectives of this paper are to demonstrate the feasibility of using newly developed smart GFRP reinforcements to effectively monitor reinforced concrete beams subjected to flexural and creep loads, and to develop non-linear numerical models to predict the behavior of these beams. The smart glass fiber-reinforced polymer (GFRP) rebars are fabricated using a modified pultrusion process, which allows the simultaneous embeddement of Fabry-Perot fiber-optic sensors within them. Two beams are subjected to static and repeated loads (until failure), and a third one is under long-term investigation for assessment of its creep behavior. The accuracy and reliability of the strain readings from the embedded sensors are verified by comparison with corresponding readings from surface attached electrical strain gages. Nonlinear finite element modeling of the smart concrete beams is subsequently performed. These models are shown to be effective in predicting various parameters of interest such as crack patterns, failure loads, strains and stresses. The strain values computed by these numerical models agree well with corresponding readings from the embedded fiber-optic sensors.

• Structural Engineering and Mechanics
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• v.37 no.2
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• pp.215-231
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• 2011

As a brittle and heterogeneous material, concrete behaves differently under different stress conditions and its bulk strength is loading rate dependent. To a large extent, the varying behavioural properties of concrete can be explained by the mechanical failure processes at a mesoscopic level. The development of a computational mesoscale model in a general finite element environment, as presented in the preceding companion paper (Part 1), makes it possible to investigate into the underlying mechanisms governing the bulk-scale behaviour of concrete under a variety of loading conditions and to characterise the variation in quantitative terms. In this paper, we first present a series of parametric studies on the behaviour of concrete material under quasi-static compression and tension conditions. The loading-face friction effect, the possible influences of the non-homogeneity within the mortar and ITZ phases, and the effect of randomness of coarse aggregates are examined. The mesoscale model is then applied to analyze the dynamic behaviour of concrete under high rate loading conditions. The potential contribution of the mesoscopic heterogeneity towards the generally recognized rate enhancement of the material compressive strength is discussed.

• Structural Engineering and Mechanics
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• v.41 no.1
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• pp.1-24
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• 2012

A reinforced concrete (RC) framed structure detailed according to non-seismic detailing provisions as per Indian Standard was tested on shake table under dynamic loads. The structure had 3 main storeys and an additional storey to simulate the footing to plinth level. In plan the structure was symmetric with 2 bays in each direction. In order to optimize the information obtained from the tests, tests were planned in three different stages. In the first stage, tests were done with masonry infill panels in one direction to obtain information on the stiffness increase due to addition of infill panels. In second stage, the infills were removed and tests were conducted on the structure without and with tuned liquid dampers (TLD) on the roof of the structure to investigate the effect of TLD on seismic response of the structure. In the third stage, tests were conducted on bare frame structure under biaxial time histories with gradually increasing peak ground acceleration (PGA) till failure. The simulated earthquakes represented low, moderate and severe seismic ground motions. The effects of masonry infill panels on dynamic characteristics of the structure, effectiveness of TLD in reducing the seismic response of structure and the failure patterns of non-seismically detailed structures, are clearly brought out. Details of design and similitude are also discussed.

• Structural Engineering and Mechanics
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• v.32 no.2
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• pp.337-350
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• 2009

Finite element simulations are increasingly used in structural analysis and design, especially in cases where complex structural and loading conditions are involved. Due to considerable progresses in computer technology as well as nonlinear finite-element analysis techniques in past years, it has become possible to pursue an accurate analysis of the complex blast-induced structural effects by means of numerical simulations. This paper aims to develop a better understanding of the behavior of steel-concrete composite beams (SCCB) under localized blast loading through a numerical parametric study. A finite element model is set up to simulate the blast-resistant features of SCCB using the transient dynamic analysis software LS-DYNA. It is demonstrated that there are three dominant failure modes for SCCB subjected to localized blast loading. The effect of loading position on the behavior of SCCB is also investigated. Finally, a simplified model is proposed for assessing the overall response of SCCB subjected to localized blast loading.

• Computers and Concrete
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• v.5 no.2
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• pp.117-134
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• 2008

An experimental and numerical research was conducted to gain a deeper insight on the structural behaviour of deep-beams with indirect supports and to assess the size effects in the ultimate state behaviour. The experimental campaign focused on the influence of the reinforcement tie distribution height on the compression check of the support region and on the benefits of using unbonded prestressing steel. Three reduced scale specimens were tested and used to validate the results obtained with a nonlinear finite element model. As a good agreement could be found between the numerical and the experimental results, the numerical model was then further used to perform simulations in large scale deep-beams, with dimensions similar to the ones to be adopted in a practical case. Two sources of size effects were identified from the simulation results. Both sources are related to the concrete quasi-brittle behaviour and are responsible for increasing failure brittleness with increasing structural size. While in the laboratory models failure occurred both in the experimental tests as well as in the numerical simulations after reinforcement yielding, the numerically analysed large scale models exhibited shear failures with reinforcement still operating in the elastic range.