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Cement production is a highly energy-intensive and environmentally polluting process, however, despite the detrimental effects, the production rates are increasing annually to meet the ever-rising demand. Hence, it is imperative to look out for materials that can be used in place of cement for promoting green construction and sustainability. On the other hand, glass, post-consumption, is dumped in landfills instead of recycling due to factors such as high recycling cost, cheap imports and lack of awareness to name a few. Since glass is a non-biodegradable material, the practice of dumping waste glass in the landfills is environmentally unsustainable. Recently it has been revealed that glass at particular fineness exhibits pozzolanic characteristics. The focus of this study is to investigate the pozzolanic attribute of a coarse glass powder (≤150 µm) used as a cement replacement; the substitution levels employed were 15% and 30% by weight of cement. In addition to the basic compressive strength testing, durability tests such as drying shrinkage, resistance to chloride ion penetration and heat of hydration were evaluated. The test results indicate that 30% is the ideal replacement level, providing a strength activity index (SAI) of 117%, a 32% higher resistance to chloride ion permeability and a 24% reduction in heat from hydration.

The speed of vehicles on highways has increased due to improved driving environments. However, this increased speed has become one of the main reasons for collisions between vehicles and ro...

We report on the fabrication of a stretchable patterned graphene gas sensor driven by integrated micro-supercapacitor (MSC) array on the same deformable substrate. The integrated MSCs consist of polyaniline-wrapped multi-walled carbon nanotube electrodes and an ionogel electrolyte of poly(ethylene glycol)diacrylate and 1-ethyl-3-methylimidazoliumbis (trifluoromethylsulfonyl) imide. The deformable soft Ecoflex substrate was designed to suppress the applied strain on the gas sensor and MSCs via insertion of stiff platforms of SU-8 underneath and serpentine electrical interconnections of polymer-encapsulated long and narrow Au thin film. The fabricated MSC array demonstrated stable electrochemical performance under a uniaxial strain of 50% and a biaxial strain of 40%, maintaining its initial characteristics even after 1000 cycles of repetitive uniaxial and biaxial stretching. Furthermore, the patterned-graphene sensor detected NO 2 gas for longer than 50 min via integration with MSCs using the serpentine interconnections even under uniaxial stretching by 50%. This work suggests fundamental progress towards the development of stretchable environmental sensor system which can be driven by integrated energy storage devices without external long wire connections to power source.

A stretchable multisensor system is successfully demonstrated with an integrated energy-storage device, an array of microsupercapacitors that can be repeatedly charged via a wireless radio-frequency power receiver on the same stretchable polymer substrate. The integrated devices are interconnected by a liquid-metal interconnection and operate stably without noticeable performance degradation under strain due to the skin attachment, and a uniaxial strain up to 50%.

A stretchable polyaniline nanofiber temperature sensor array with an active matrix consisting of single-walled carbon nanotube thin-film transistors is demonstrated. The integrated temperature sensor array gives mechanical stability under biaxial stretching of 30%, and the resultant spatial temperature mapping does not show any mechanical or electrical degradation.

This paper presents a computational reliable optimization approach for internal cooling channels in Ceramic Matrix Composite (CMC) under thermal and mechanical loadings. The algorithm finds the optimal cooling capacity of all channels (which directly minimizes the amount of coolant needed). In the first step, available uncertainties in the constituent material properties, the applied mechanical load, the heat flux and the heat convection coefficient are considered. Using the Reliability Based Design Optimization (RBDO) approach, the probabilistic constraints ensure the failure due to excessive temperature and deflection will not happen. The deterministic constraints restrict the capacity of any arbitrary cooling channel between two extreme limits. A “series system” reliability concept is adopted as a union of mechanical and thermal failure subsets. Having the results of the first step for CMC with uniformly distributed carbon (C-) fibers, the algorithm presents the optimal layout for distribution of the C-fibers inside the ceramic matrix in order to enhance the target reliability of the component. A sequential approach and B-spline finite elements have overcome the cumbersome computational burden. Numerical results demonstrate that if the mechanical loading dominates the thermal loading, C-fibers distribution can play a considerable role towards increasing the reliability of the design.

This study investigates the effects of fiber length and placement method on the biaxial flexural behavior and fiber distribution characteristics of ultra-high-performance fiber-reinforced concrete (UHPFRC). A number of UHPFRC panels including three different fiber lengths were fabricated using two different placement methods, and an image analysis was performed to quantitatively evaluate the fiber distribution characteristics such as fiber orientation, fiber dispersion, and number of fibers per unit area. The biaxial flexural performances including load carrying capacity, energy absorption capacity, and cracking behavior were found to be improved with the increase in fiber length up to 19.5 mm. The biaxial flexural performances were also influenced by the placement method; the specimens with concrete placed at the center (maximum moment region) showed better flexural performances than those with concrete placed at the corner. These observations were confirmed by the image analysis results, which showed poorer fiber orientation and fewer fibers across the crack surfaces at the maximum moment region for the specimens with concrete placed at the corner, compared with their counterparts.

It is well known that the seismic performance of bridge systems is directly related to that of its columns since these provide the lateral resistance of the bridge and dissipate the input energy induced from ground motions. However, segmental bridge columns have small energy dissipation capacity, compared to conventional monolithic columns. In order to improve the energy dissipation capacity of the columns, several approaches have been suggested such as the use of mild steel bars, high-performance steel bars, exterior yielding braces, and elastomeric bearing pads, which are installed at the base of the columns. Recently, a combination of cast-in-place (CIP) and precast has been suggested by other researchers to increase the energy capacity. As an example of CIP application, a new precast segmental column is suggested in this paper and its cyclic behavior is examined. The base of the present circular segmental column is cast-in-place, while the upper parts are given by partial precast hollow circular segments. The column specimen has a height of 7500 mm, a diameter of 1500 mm and reinforcement ratios of 1.23–1.46%. In the cyclic test, the vertical load applied to the top of the column is about 10% of the column’s nominal strength. The results of the experimental test show that the column has excellent energy dissipation capacity producing an equivalent viscous damping ratio of about 23% at 4.29 drift ratio (final drift). The ductility ratio is 4.67 and the peak lateral strength is also high, namely about 26% of the total applied vertical load. A simplified analytical model of the column is developed and the results compared to those of the cyclic test. Sectional moment–curvature envelopes are used for the analytical model. Furthermore, nonlinear time history analyses are conducted using Northridge (Newhall) earthquake records. From the seismic analysis, the peak acceleration responses are shown as 0.23–0.25 g. The values are much smaller than the values given by the elastic response spectra of the earthquake records since the column produces the enough energy dissipating and yielding behavior.

A probabilistic approach is presented for the prognosis of fatigue crack growth for asphalt concretes using the particle filtering method based on Bayesian theory. The random response of fatigue behavior is successively updated with the accumulation of the measured data by the particle filtering method. During the updating, particles with high probability are reproduced more, while others are eliminated via resampling procedures. The J integral is adopted for the fatigue crack growth to take into account the viscoelastic characteristics of asphalt concretes. The prognosis of fatigue crack growth and remaining service life under different conditions is presented using this method.

The flexural resistance of fiber reinforced cementitious composites (FRCCs) under biaxial condition was investigated by using two different types of biaxial bending test methods: the biaxial flexural test (BFT) and the centrally loaded round panel test (RPT). The flexural responses of FRCCs under biaxial condition were then compared with those of FRCCs under uniaxial condition; i.e. four-points bending test (4PBT). The test results, including the equivalent biaxial strength and normalized energy absorption capacity of the RPT, were found to be clearly higher than those of the BFT, and completely different cracking behavior was observed between the two biaxial test methods; the BFT generated numerous randomly distributed micro-cracks at the bottom of specimens, whereas the RPT mostly showed three major cracks, with minor radial cracks around them. In addition, the equivalent flexural tensile strength and normalized energy absorption capacity of the FRCCs under biaxial condition were found to be higher than those under uniaxial condition. The energy absorption capacity and the ratio of flexural tensile strength to the direct tensile strength of FRCCs are dependent on the stress state.

An algorithm to solve the inverse problem of detecting inclusion interfaces in a piezoelectric structure is proposed. The material interfaces are implicitly represented by level sets which are identified by applying regularization using total variation penalty terms. The inverse problem is solved iteratively and the extended finite element method is used for the analysis of the structure in each iteration. The formulation is presented for three-dimensional structures and inclusions made of different materials are detected by using multiple level sets. The results obtained prove that the iterative procedure proposed can determine the location and approximate shape of material sub-domains in the presence of higher noise levels.

An extended isogeometric element formulation (XIGA) for analysis of through-the-thickness cracks in thin shell structures is developed. The discretization is based on Non-Uniform Rational B-Splines (NURBS). The proposed XIGA formulation can reproduce the singular field near the crack tip and the discontinuities across the crack. It is based on the Kirchhoff–Love theory where C 1 -continuity of the displacement field is required. This condition is satisfied by the NURBS basis functions. Hence, the formulation eliminates the need of rotational degrees of freedom or the discretization of the director field facilitating the enrichment strategy. The performance and validity of the formulation is tested by several benchmark examples.

We propose a concurrent multiscale method for fracture coupling two three-dimensional continuum domains. Fracture in both domains is treated by the extended finite element method. The coupling is based on the Arlequin method which blends the energies of different scales in a so called "handshake domain". To our knowledge, it is the first time that a three dimensional extended Arlequin method for fracture is reported for dynamic applications. To show the suitability of the proposed method, two crack problems with a very fine region around the crack front are solved. The results show that the method is capable of effectively coupling the two regions while having the same accuracy of the full scale model based on a very fine mesh. DFG, Qatar National Research Fund, Grant No. NPRP 09-145-2-061 and Humboldt Foundation. Scopus

The paper presents a multiscale method for crack propagation. The coarse region is modelled by the differential reproducing kernel particle method. Fracture in the coarse scale region is modelled with the Phantom node method. A molecular statics approach is employed in the fine scale where crack propagation is modelled naturally by breaking of bonds. The triangular lattice corresponds to the lattice structure of the (111) plane of an FCC crystal in the fine scale region. The Lennard-Jones potential is used to model the atom-atom interactions. The coupling between the coarse scale and fine scale is realized through ghost atoms. The ghost atom positions are interpolated from the coarse scale solution and enforced as boundary conditions on the fine scale. The fine scale region is adaptively refined and coarsened as the crack propagates. The centro symmetry parameter is used to detect the crack tip location. The method is implemented in two dimensions. The results are compared to pure atomistic simulations and show excellent agreement. (C) 2014 Elsevier B. V. All rights reserved.

This paper presents the results of a study conducted to evaluate the possibility of utilizing the waste glass sludge (WGS) from the cutting and polishing process of glass plates, as a partial replacement of cement. A total of seven mortar mix proportions were prepared, by replacing ordinary Portland cement with WGS and/or fly ash (FA). The influences of WGS and FA on the compressive strength of mortars and ASR expansion of mortars were investigated. In addition, X-ray diffraction analysis was performed, to evaluate the pozzolanic activity. The results show that the incorporation of the WGS yields mortars with improved strengths at the later age (28 days), in comparison with that of a control mortar (ordinary Portland cement only); while the WGS caused a lower early strength than that of control, but higher than that of mortars containing FA. The ASR expansion of the mortars can be reduced by incorporating WGS as effectively as by fly ash. It is found that the consumption rate of calcium hydroxide for the paste with the WGS was faster than that of paste with FA, up to 28 days. These results indicate that the WGS has a higher reactivity than FA; and therefore, the WGS can be used as a pozzolanic admixture in cement composites.

Cement-based sensors with hybrid conductive fillers using both carbon fibers (CFs) and multi-walled carbon nanotubes (MWCNTs) were experimentally investigated in this study. The self-sensing capacities of cement-based composites with only CFs or MWCNTs were found based on preliminary tests. The results showed that the percolation thresholds of CFs and MWCNTs were 0.5–1.0 vol.% and 1.0 vol.%, respectively. Based on these results, the feasibility of self-sensing composites with four different amounts of CFs and MWCNTs was considered under cyclic compression loads. When the amount of incorporated CFs increased and the amount of incorporated MWCNTs decreased, the self-sensing capacity of the composites was reduced. It was concluded that cement-based composites containing both 0.1 vol.% CFs and 0.5 vol.% MWCNTs could be an alternative to cement-based composites with 1.0 vol.% MWCNTs in order to achieve equivalent self-sensing performance at half the price. The gauge factor (GF) for that composite was 160.3 with an R-square of 0.9274 in loading stages I and II, which was similar to the GF of 166.6 for the composite with 1.0 vol.% MWCNTs.

Networks of silver nanowires (Ag NWs) have been considered as promising materials for stretchable and transparent conductors. Despite various improvements of their optoelectronic and electromechanical properties over the past few years, Ag NW networks with a sufficient stretchability in multiple directions that is essential for the accommodation of the multidirectional strains of human movement have seldom been reported. For this paper, biaxially stretchable, transparent conductors were developed based on 2D mass-spring networks of wavy Ag NWs. Inspired by the traditional papermaking process, the 2D wavy networks were produced by floating Ag NW networks on the surface of water and subsequently applying biaxial compression to them. It was demonstrated that this floating-compression process can reduce the friction between the Ag NW-water interfaces, providing a uniform and isotropic in-plane waviness for the networks without buckling or cracking. The resulting Ag NW networks that were transferred onto elastomeric substrates successfully acted as conductors with an excellent transparency, conductivity, and electromechanical stability under a biaxial strain of 30%. The strain sensors that are based on the prepared conductors demonstrated a great potential for the enhanced performances of future wearable devices.

Recently, there was a collision accident involving vehicle–concrete median barrier in South Korea, and unfortunately, passengers on the opposite direction road were killed by the flying broken pieces of concrete generated by the collision. Primarily after this accident, we felt the need for developing an improved concrete median barrier up to level of SB6 impact severity in order to minimize the amount of broken pieces of concrete and any possibility of traffic accident casualty under the impact loading of truck. Accordingly, in this study, several designs of concrete median barriers have been examined, and a preliminary study has been conducted for developing and verifying appropriate collision model. First, type of vehicle was selected based on impact analysis on rigid wall. Then, the effects of element size and other key parameters on the capacity of the concrete median barrier under impact were studied. It was found that the key parameters for controlling behaviors of the median barrier under impact loading were contact option, threshold value, and mesh and boundary conditions. Furthermore, as a parametric study, effect of geometry and amount of wire-mesh or steel rebar in concrete median barrier on impact resistances of median barrier for reducing the collision debris were investigated. The amount of volume loss after the collision of truck was compared for various reinforcement ratios.

In this work, we perform phase field simulations of ideal grain growth in a distorted polycrystalline aggregate. The distorted microstructure is assumed to be generated by homogenous deformation of an initially equiaxed polycrystalline aggregate. Phase field theory of curvature driven grain boundary migration under distortion is developed and the phase field kinetic relations are implemented in a numerical code based on an explicit time integration procedure. As a benchmark example, phase field simulations of the shrinkage of a distorted circular grain are performed and compared with that of an undistorted elliptical grain to validate the phase field theory and its numerical implementation and also to study the effect of distortion on the kinetics of grain boundary migration. The non-equiaxed distorted grain evolves towards an equiaxed geometry by curvature-driven boundary migration. The evolution rate towards equiaxity is proportional to the distortion magnitude. However, the distortion regardless of its magnitude has no effect on the decrease rate of the distorted grain surface area. We also investigate the evolution of a distorted polycrystalline microstructure by phase field simulations. The elongated distorted grains grow and evolve towards equiaxed grains by ideal grain growth. It has been observed that the distortion influences the directional measure of average grain size to a large extent, but the nondirectional average characteristics of the microstructure are not affected.

We report on the fabrication of a biaxially stretchable array of high performance microsupercapacitors (MSCs) on a deformable substrate. The deformable substrate is designed to suppress local strain applied to active devices by locally implanting pieces of stiff polyethylene terephthalate (PET) films within the soft elastomer of Ecoflex. A strain suppressed region is formed on the top surface of the deformable substrate, below which PET films are implanted. Active devices placed within this region can be isolated from the strain. Analysis of strain distribution by finite element method confirms that the maximum strain applied to MSC in the strain suppressed region is smaller than 0.02%, while that on the Ecoflex film is larger than 250% under both uniaxial strain of 70% and biaxial strain of 50%. The all-solid-state planar MSCs, fabricated with layer-by-layer deposited multiwalled carbon nanotube electrodes and patterned ionogel electrolyte of poly(ethylene glycol) diacrylate and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide having high-potential windows, are dry-transferred onto the deformable substrate and electrically connected in series and parallel via embedded liquid metal interconnection and Ag nanowire contacts. Liquid metal interconnection, formed by injecting liquid metal into the microchannel embedded within the substrate, can endure severe strains and requires no additional encapsulation process. This formed MSC array exhibits high energy and power density of 25 mWh/cm(3) and 32 W/cm(3), and stable electrochemical performance up to 100% uniaxial and 50% biaxial stretching. The high output voltage of the MSC array is used to light micro-light-emitting diode (μ-LED) arrays, even under strain conditions. This work demonstrates the potential application of our stretchable MSC arrays to wearable and bioimplantable electronics with a self-powered system.

The effect of fiber reinforcement on all-lightweight concrete in which both fine and coarse aggregates are artificially lightweight was investigated experimentally. Three different fibers (i.e., steel, vinylon and polyethylene) were compared for their effects on the compressive strength, splitting tensile strength, flexural strength, shear strength, and toughness. Normal concrete with the same compressive strength as the all-lightweight concrete was prepared as a reference. Using 1.5% vinylon fibers significantly improved the flexural strength of the all-lightweight concrete 234% higher than that of normal concrete. Using 1.2% steel fiber increased the fracture toughness of the all-lightweight concrete more than twelve times.

Waste glass sludge (WGS), a byproduct of glass plate manufacture, was used to improve the durability properties of concrete under an environmental condition of freezing and thawing, with the existence of de-icing salts. A total of five concrete mix proportions were prepared, by varying the amounts of WGS. In order to observe the effects and roles of WGS on the durability performances of concrete mixtures, compressive strength tests, freezing and thawing tests, chloride ion penetration and surface scaling were carried out. Test results showed that the incorporation of WGS as a partial replacement for cement has beneficial effects on the compressive strength of concrete, especially when used together with fly ash. Moreover, WGS improved the resistance of freezing and thawing with and without de-icing salts, the chloride ion penetration and the resistance of surface scaling of the concrete compared to the control mixture containing 20% fly ash as cement replacement.

An asymmetric vibration is proposed for the design consideration of finger-type bridge joints. It is shown, both experimentally and numerically, that the vibration of the joint-plate is not symmetric, but asymmetric; and that the end moment of finger-type bridge joints becomes maximum when the joint plate springs upward, after the load moves out from the joint, in which the tension of the anchor bolts due to this upturned vibration is much greater than the static load case with the load at the tip of the joint-plate. A simplified design formula is developed based on an energy concept, to consider this new failure mode in the design procedure. It is shown that the actual maximum moment and tension can be closely estimated by a simple formula.

The fabrication of a stretchable single-walled carbon nanotube (SWCNT) complementary metal oxide semiconductor (CMOS) inverter array and ring oscillators is reported. The SWCNT CMOS inverter exhibits static voltage transfer characteristics with a maximum gain of 8.9 at a supply voltage of 5 V. The fabricated devices show stable electrical performance under the maximum strain of 30% via forming wavy configurations. In addition, the 3-stage ring oscillator demonstrates a stable oscillator frequency of ∼3.5 kHz at a supply voltage of 10 V and the oscillating waveforms are maintained without any distortion under cycles of pre-strain and release. The strains applied to the device upon deformation are also analyzed by using the classical lamination theory, estimating the local strain of less than 0.6% in the SWCNT channel and Pd electrode regions which is small enough to keep the device performance stable under the pre-strain up to 30%. This work demonstrates the potential application of stretchable SWCNT logic circuit devices in future wearable electronics.

In this study, flexural strength properties of concrete under biaxial stress state were experimentally investigated. Tests for size effect and fatigue behaviour of concrete under biaxial stress were carried out by the ASTM C 1550 and the biaxial flexure test(BFT). The results given by the biaxial tests were compared to those by the third-point bending test. Test results showed that biaxial flexural strengths obtained from the ASTM C 1550 and the biaxial flexure test are greater than the strength by the third-point bending test. As the size increases, the uniaxial and biaxial flexural strength decreases. However, the slope of the size effect of the biaxial strength was greater than that of the uniaxial strength. Finally, the fatigue response of concrete under the biaxial stress state was similar with that for uniaxial stress state.

The biaxial flexure test (BFT) method for the biaxial tensile strength of concrete has been improved. To ensure the equi-biaxial stress condition during the test, the geometry of the specimen, proper treatment of the specimen surface, and the support conditions were proposed. The biaxial flexural strength of concrete was measured with the improved biaxial flexure test method. The coefficient of variation (c.o.v) of the biaxial flexure test method is comparable to that of the four-point bending test and ASTM C 1550. The improved biaxial flexure test provides a practical and reliable means of determining the biaxial flexural strength of concrete. The biaxial tensile strength given by the biaxial flexure test method and the ASTM C 1550 method is greater than the uniaxial tensile strength using the four-point bending test method.

The effect of lattice orientation and crack length on the mechanical properties of Graphene are studied based on molecular dynamics simulations. Bond breaking and crack initiation in an initial edge crack model with 13 different crack lengths, in 10 different lattice orientations of Graphene are examined. In all the lattice orientations, three recurrent fracture patterns are reported. The influence of the lattice orientation and crack length on yield stress and yield strain of Graphene is also investigated. The arm-chair fracture pattern is observed to possess the lowest yield properties. A sudden decrease in yield stress and yield strain can be noticed for crack sizes < 10 nm. However, for larger crack sizes, a linear decrease in yield stress is observed, whereas a constant yield strain of 0.05 is noticed. Therefore, the yield strain of 0.05 can be considered as a critical strain value below which Graphene does not show failure. This information can be utilized as a lower bound for the design of nano-devices for various strain sensor applications. Furthermore, the yield data will be useful while developing the Graphene coating on Silicon surface in order to enhance the mechanical and electrical characteristics of solar cells and to arrest the growth of micro-cracks in Silicon cells.

This paper presents a novel numerical procedure based on the combination of an edge-based smoothed finite element (ES-FEM) with a phantom-node method for 2D linear elastic fracture mechanics. In the standard phantom-node method, the cracks are formulated by adding phantom nodes, and the cracked element is replaced by two new superimposed elements. This approach is quite simple to implement into existing explicit finite element programs. The shape functions associated with discontinuous elements are similar to those of the standard finite elements, which leads to certain simplification with implementing in the existing codes. The phantom-node method allows modeling discontinuities at an arbitrary location in the mesh. The ES-FEM model owns a close-to-exact stiffness that is much softer than lower-order finite element methods (FEM). Taking advantage of both the ES-FEM and the phantom-node method, we introduce an edge-based strain smoothing technique for the phantom-node method. Numerical results show that the proposed method achieves high accuracy compared with the extended finite element method (XFEM) and other reference solutions.

We report the fabrication of an encapsulated, high-performance, stretchable array of stacked planar micro-supercapacitors (MSCs) as a wearable energy storage device for waterproof applications. A pair of planar all-solid-state MSCs with spray-coated multiwalled carbon nanotube electrodes and a drop-cast UV-patternable ion-gel electrolyte was fabricated on a polyethylene terephthalate film using serial connection to increase the operation voltage of the MSC. Additionally, multiple MSCs could be vertically stacked with parallel connections to increase both the total capacitance and the areal capacitance owing to the use of a solid-state patterned electrolyte. The overall device of five parallel-connected stacked MSCs, a microlight-emitting diode (μ-LED), and a switch was encapsulated in thin Ecoflex film so that the capacitance remained at 82% of its initial value even after 4 d in water; the μ-LED was lit without noticeable decrease in brightness under deformation including bending and stretching. Furthermore, an Ecoflex encapsulated oximeter wound around a finger was operated using the stored energy of the MSC array attached to the hand (even in water) to give information on arterial pulse rate and oxygen saturation in the blood. This study suggests potential applications of our encapsulated MSC array in wearable energy storage devices especially in water.

The biaxial flexural strength of a concrete panel can be evaluated by two different methods: the centrally loaded round panel test (ASTM C 1150) and the recently proposed biaxial flexure test (BFT). Twenty-six tests, with 13 specimens for each test method, were performed to verify the effect of the different test methods on the biaxial flexural strength of concrete. A finite-element analysis of the specimens of two test methods showed that the biaxial flexure test set-up allows a larger area with a uniform biaxial stress on the bottom surface around the centre of the specimen than the ASTM C 1550 set-up, indicating that the difference in the test results is attributable to the volume effects. The test results showed that the biaxial flexure test method gives a more reliable biaxial flexural strength with a 25% lower coefficient of variation than that from the ASTM C 1550.

We investigated a conical crack formed near a fastening bolt of a concrete railway sleeper in a slab track system. The crack initiated from the bottom of the sleeper and penetrated the sleeper completely forming a conical shape. To study the reason for this and to examine the failure mechanism, we used a three dimensional finite element method and a series of experimental programs. The result of the numerical simulation was verified with the experimental data. From this study, we concluded that the conical crack was caused by the volume expansion of the freezing water leaking into the plastic insert of the fastener hole. The effect of location of the frozen insert holes, initial fastening force and compressive strength of concrete on the freezing force was also studied in this study.

A hybrid floating structure system combined with pontoon and semi-submersible type modules is proposed. This new system can reduce tensile forces of bottom slabs which could cause fatal damage of concrete floating structures. We performed a parametric study on the dimensions of this new system and investigate the sensitivity of the parameters to the behavior. In order to investigate various cases efficiently, we developed a simple two-step static analysis method for the fluid-structure interaction. An optimum system is derived from the investigation of the analysis results, weights and drafts of the hybrid structure. This study shows that introducing this new system to concrete floating structures is an effective way to reduce the tensile force of the bottm slab of such a floating structure. Also, it was found that when the length of the semi-submersible module is about 15%, the behavior would be optimal in the considered case.

We present an extended finite element formulation for dynamic fracture of piezo-electric materials. The method is developed in the context of linear elastic fracture mechanics. It is applied to mode I and mixed mode-fracture for quasi-steady cracks. An implicit time integration scheme is exploited. The results are compared to results obtained with the boundary element method and show excellent agreement.

Fatigue life in critical parts of structure components, which is subjected to variable amplitude loading, is a very complex subject. When a fatigue life is influenced by these load variations, accelerations and/or retardations in crack growth rate can occur. Thus, an accurate prediction of fatigue life requires an adequate evaluation of these stress interaction effects. There are many different indexes for calculating fatigue damage at critical locations. The crack severity index based on crack growth is one of the methodologies implemented for modern military aircrafts to define mission severity relative to a known reference usage. But, this index cannot consider stress interaction. In this study, a novel index was proposed to evaluate an effect for stress interaction by using entropy concept, and fatigue life prediction methodology was developed by using entropy index of stress interaction and crack severity index of effective stress.

A phantom-node method is developed for three-node shell elements to describe cracks. This method can treat arbitrary cracks independently of the mesh. The crack may cut elements completely or partially. Elements are overlapped on the position of the crack, and they are partially integrated to implement the discontinuous displacement across the crack. To consider the element containing a crack tip, a new kinematical relation between the overlapped elements is developed. There is no enrichment function for the discontinuous displacement field. Several numerical examples are presented to illustrate the proposed method.

In this study, we conducted experiment and finite element analysis on the flexural behavior of the round concrete panels according to the evaluation method of biaxial flexural tensile strengths. The Round Panel Test (RPT) and the Biaxial Flexure Test (BFT) were used to determine the biaxial flexural strength of round plain concrete panels. In order to understand the stress distribution on the panels, we measured load-strain relationship at the center of the panels` bottom surface. Test results show that fracture pattern in RPT and BFT panels are similar, and the tensile stress distribution is uniform in all directions at the center of the bottom surface of the panels for both RPT and BFT. The distribution of stresses in two test specimens coincided with the analysis result. The average biaxial flexural strength of RPT is about 29% greater than those of the BFT. The coefficient of variations (COV) of the RPT and BFT for the biaxial flexure strength is 8%, 6%, respectively, which indicates that BFT method is useful and reliable for determining biaxial flexural strengths of the concrete.

Finite element analysis was undertaken to investigate the effect of freezing force of water unexpectedly penetrated into inserts used in railway sleeper on pullout capacity of anchor bolts for fixing base-plate onto concrete sleeper. Based on the in-situ investigation and measurement of geometry of railway sleeper and rail-fastener, the railway sleeper was modeled by 3D solid elements. Nonlinear and fracture properties for the finite element model were assumed according to CEB-FIP 1990 model code. And the pullout maximum load of anchor bolt obtained from the model developed was compared with experimental pullout maximum load presented by KRRI for verification of the model. Using this model, the effect of position of anchor bolt, amount of fastening force applied to the anchor bolt, and compressive strength of concrete on pull-out capacity of anchor bolts installed in railway sleeper was investigated. As a result, it is found that concrete railway sleepers could be damaged by the pressure due to freezing of water penetrated into inserts. And the pullout capacity of anchor bolt close to center of railway is slightly greater than that of the others.

The loss of strength in a structure as a result of cyclic loads over a period of life time is an important phenomenon for the life-cycle analysis. Service loads are accentuated at the areas of stress concentration, mainly at the connection of components. Structural components unavoidably are affected by defects such as surface scratches, surface roughness and weld defects of random sizes, which usually occur during the manufacturing and handling process. These defects are shown to have an important effect on the fatigue life of the structural components by promoting crack initiation sites. The value of equivalent initial flaw size (EIFS) is calculated by using the back extrapolation technique and the Paris law of fatigue crack growth from results of fatigue tests. We try to analyze the effect of EIFS distribution in a multiple site damage (MSD) specimen by using the extended finite element method (XFEM). For the analysis, fatigue tests were conducted on the centrally-cracked specimens and MSD specimens.

The strain capacity of pipelines is one of the primary factors for the design of those made of high-strength and hightoughness steel. The work presented in this paper describes the evaluation method for the compressive-bending plastic buckling capacity of pipeline steel tube based on strain-based design. The evaluation method developed in this paper used Gurson-Tvergaard -Needleman(GTN) model which is the constitutive model of the steel by user-material subroutine (UMAT) for the commercial software of ABAQUS. The model parameters were decided by comparison between experiment and simulated data. The compressive-bending experimental results are simulated using this evaluation method by means of the maximum bending moment as well as the critical compressive strain. Using this method, we simulated compressive-bending plastic buckling behavior of pipeline steel tube for the practical design in the hazardous region.

This paper develops a phantom-node method for MITC 3-node shell element. According to the phantomnode method, overlapping paired elements are used to represent an element cut through by a crack. In which, each element is created by extending a part of the cracked element to a phantom domain until it becomes a completely standard finite element. As a result, separate assumption for transverse shear strain of the MITC 3-node element to remove “shear locking” is employed straightforwardly. The development describes the crack in both thin and thick shell structures and is no need to remesh as the crack propagates. The method is applied to numerically simulate a fracture test of an internally pressurized cylindrical shell conducted by (Keesecker et al. 2003). Material constitutive law follows the J2-plasticity with linear isotropic hardening and the small strain assumption. The crack tip opening angle (CTOA) criterion, one of the fracture criteria, characterizes the crack growth condition. A predicted crack growth curve of pressure versus half-crack length is comparable to experimental measurements and other numerical results.

This paper reviews different crack tracking techniques in three-dimensions applicable in the context of partition of unity methods, especially meshfree methods. Issues such as describing and tracking the crack surface are addressed. A crack tracking procedure is proposed in detail and implemented in the context of the extended element-free Galerkin method (XEFG). Several three-dimensional cracking examples are compared to other results from the literature or the experimental data and show good agreement.

The strain change of a seven-wire strand is experimentally investigated for two different detensioning procedures of a pretensioned concrete bar: flame-cutting and hydraulic-jacking. Based on the results of strain changes, it is confirmed that the prestressing force was stepwise transferred to concrete for several seconds according to the individual cut of different wires in the flame-cutting procedure. In the hydraulic-jacking procedure, the detensioning was smoothly accomplished in a time of about one second shorter than that of flame-cutting. It seems that the pattern of strain changes during the detensioning procedure is more important than the elapsed time for detensioning. In addition, the drop in the strain of each wire at the moment of flame-cutting was reduced by the installation of the debonded region. Moreover, the test results showed that the placing of stirrups has an insignificant effect on the strain change. In particular, the initial prestressing force was estimated simply from the elastic recovering strain of the strand after detensioning. The prestressing force obtained from the procedure was very close to that obtained from a load cell.

A new robust and efficient approach for modeling discrete cracks in meshfree methods is described. The method is motivated by the cracking-particle method (Rabczuk T., Belytschko T., International Journal for Numerical Methods in Engineering, 2004) where the crack is modeled by a set of cracked segments. However, in contrast to the above mentioned paper, we do not introduce additional unknowns in the variational formulation to capture the displacement discontinuity. Instead, the crack is modeled by splitting particles located on opposite sides of the associated crack segments and we make use of the visibility method in order to describe the crack kinematics. We apply this method to several two- and three-dimensional problems in statics and dynamics and show through several numerical examples that the method does not show any “mesh” orientation bias.

A continuous spectrum method is proposed and applied for modeling the time-domain viscoelastic function of asphalt concrete materials. This technique, employing a Wiechert model for the relaxation function and a Kelvin model for the compliance function, is found to substantially enhance accuracy and consistency compared to existing methods. Furthermore, this paper shows how to determine a time-domain Prony series representation, which can be used efficiently for numerical analysis, such as finite element analysis, from the complex modulus in the frequency domain, based on the continuous spectrum method.

Samsung C&T Corporation, Seoul 137-956, KoreaABSTRACT This study focuses on the effect of the cutting order of prestressing strands on the strain change in the strands andon the state of stress of concrete, experimentally and numerically. In the experiment, strain of strands and of transversal rei nforcementwere measured for three different cutting orders during detensioning process by using flame-cutting procedure. The experimentalresults were compared with those obtained from the FE analysis. As a results of the experiment, it is confirmed that the cutting orderof prestressing strands affected on the strain of strands as well as of transversal reinforcement. The FE analysis gave similar resultsto those obtained from the experiment. Therefore, the cutting order should be chosen appropriately to when the strands get deten-sioned.Keywords : pretension, flame cut, cutting order, prestressing strand, detensioning

Dept. of Civil & Environmental and Architectural Engineering, Korea University, Seoul 136-713, KoreaABSTRACT A new life-cycle cost (LCC) evaluation scheme for marine reinforced concrete structures is proposed. In thismethod, unlike the conventional life-cycle cost evaluation performed during the design process, the life-cycle cost is updated suc-cessively whenever new information of the chloride penetration is available. This updating is performed based on the Bayesianapproach. For important structures, information required for this new method can be obtained without any difficulties because itis a common element of various types of monitoring systems. Using the new method, the life-cycle maintenance cost of structurescan be estimated with a good precision.Keywords : LCC, chloride penetration, bayesian approach, monitoring

Beam tests were conducted to investigate the characteristics of a newly developed type of glass fibre-reinforced polymer (GFRP) rebar as reinforcement in flexural concrete members. Nine beams over-reinforced with different types of rebar, and with varying reinforcement ratios and depths of concrete cover, were monotonically loaded up to failure. Results were characterised by failure mode, moment–curvature, flexural capacity, load–deflection, and crack width. The test results were compared with the theoretical model and the American Concrete Institute design guide, which showed that the performance of the newly- developed GFRP rebar was comparable to commercially available GFRP rebars. In addition, a theoretical model for moment–curvature and an equation for predicting the flexural capacity of the beams with multiple layers of GFRP rebar are presented, based on the experimental observations.

Investigated was the fatigue behavior of the foam-filled GFRP bridge deck in the transverse direction which is an intermediate type between the modular type deck and the sandwich type. Four different types of the specimens were prepared and tested with different stress ratios. The failure mode and the change in stiffness by the foam inside the deck was reported. The role of the foam was very clear. It reduced the damage accumulation in the web-flange joint efficiently. Compared to the reference case which was not filled, the endurance of limit of the foam-filled deck was remarkably increased.