Abstract in English:Abstract Digital image correlation (DIC) method has been widely used on dynamical experiments. This full-field and real-time method can fill in the gap of traditional point-based measurements of typical structures subjected to soft body impact such as bird strike. In order to get further understandings of soft body impact process, the present study analyzed the time-dependent energy exchange during impact experiments. The dynamic responses of the aluminum target panels were obtained using 3D digital image correlation method so that their displacement and strain field histories can be tracked. By introducing the material properties of the targets, their time-dependent stress state and consequently the strain energy can be calculated. With the help of time-dependent profiles of target panels, their energy absorption properties were theoretically analyzed, including the exchange of kinetic energy and plastic work. The results showed that when the impact loadings were increased, the plastic work generated by radial membrane force became the major source of energy dissipation. The transverse movements consumed more kinetic energies than rotatory moments. This research may provide a further application of DIC results and help to better understand the soft body impact process on targets with large deformations.
Abstract in English:Abstract A simple quasi-3D sinusoidal shear and normal deformations theory for the hygro-thermo-mechanical bending of functionally graded piezoelectric (FGP) plate is developed under simply-supported edge conditions. The governing equations are deduced based on the principle of virtual work. The exact solutions for FGP plate are obtained. The current study investigates the effect of some parameters, like piezoelectricity, hygrothermal parameter, gradient index and electric loading on the mechanical and electric displacements, electric potential and stresses. They are explored analytically and numerically presented and discussed in detail. The numerical results clearly show the effect of piezoelectric and hygrothermal parameter on the FGP plate.
Abstract in English:Abstract This paper presents a computational strategy for shape change of tensegrity models to achieve the prescribed target coordinates of a set of monitored nodes via forced elongation of cables. Mathematical formulation for incremental equilibrium equations of a tensegrity model during the shape change analysis is derived and presented. An optimization approach in determining forced elongation of cables using sequential quadratic programming with defined inequality constraints is formulated and presented. Four tensegrity models namely the simplex, quadruplex, two-stage tensegrity model and tapered three-stage tensegrity model are tested using the proposed shape change algorithm. Capability of tensegrity models to undergo bending, axial, twisting deformation and combinations of these deformations is also described.
Abstract in English:Abstract This study investigates the behavior of reinforced concrete (RC) beam-column joints at the corner panel after a ground corner column loss scenario. The ductility of a frame is dependent on the ductility of its components, particularly its joints. Deficiency in joints performance can be related to an unexpected event. For example, the removal of a ground corner column turns the joint above into an inverted knee joint, and also inverses the direction of the resulted bending moments in the adjacent exterior and interior joints. Throughout this work, the effects of these changes are evaluated numerically using different modeling techniques considering both seismic and non-seismic reinforcement details. Numerical simulations of standard and sub-standard joints that were verified against experimentally tested joints are also presented. Joint macro models are developed using the OpenSees platform. These numerical models are then used to simulate the substandard beam-column joints appearing in RC frames after ground corner column removal. Moreover, strut and tie models (STMs) were developed for a substandard knee joint to validate the obtained numerical results. The application of the developed numerical models allows to identify the evolution of a joint’s capacity in function of its reinforcement detailing. The analysis shows the suitability of seismic detailing for exterior and interior joints and also a decrease in the inverted knee joint resistance and this can be recovered by adding i) more confinement to the joint panel zone or ii) joint vertical stirrups. An increase in the degree of confidence in the numerical results is achieved by reproduce similar behavior using different analysis methods.
Abstract in English:Abstract The performance of railroad structure has a tremendous influence on the safety and stable operation of high-speed trains. Strong vibrations and the degradation rate of the track are the main factors affecting the transport safety of a railroad built over a weak soil. Geogrid reinforced embankment supported by pile structure is a new efficient construction technique used to ensure the stability and enhance the performance of the railroad system; but only a few studies are oriented to its behavior under train operation. This paper investigates the dynamic response of geogrid reinforced embankment supported by cement fly-ash gravel pile structure during a high-speed train operation. The establishment of a realistic simulation model for railroad subjected to a moving train load, is an important first step towards the reliable design of geogrid reinforced embankment supported by pile structure. Thus, a 3D nonlinear FEM has been established to simulate the instrumented Harbin-Dalian railway test section. Each train carriage was modeled as a transient dynamic load through a user-defined Dload subroutine. The developed model was successfully validated by the dynamic response recorded from the field test section. The improvement of the railroad structure by the CFG piles and geogrids contributed significantly to the reduction of the vibration in the structure, which attenuates 1.2 times faster with the structure depth, even under overload conditions. Moreover, the phenomenon of resonance observed when the train reaches speeds of 100 and 260 km/h were annihilated. The analysis of the stress distribution within the embankment revealed that a dynamic arch is formed in the embankment at 2 m from the ground. The stress onto the pile was 16 times greater than that acted on the soil and the tensile stress developed in the geogrid was high at the piles edge below. In addition, the coupling effect of geogrid with various tensile strengths and the piles with different strength grades indicated that the combination of a high-strength pile and geogrid significantly reduces the displacement gap due to the variation of train speed. As a result, the vibrations of the track were almost constant during the train operation; thus, ensuring comfort to passengers and reducing the risk of derailment.
Abstract in English:Abstract A fragmentation model based on global load sharing (GLS) theory is developed to obtain stress-strain curves that describe the mechanical behavior of unidirectional composites. The model is named CNB+τ* because it is based on the Critical Number of Breaks model (CNB) and on the correction of the fiber matrix interfacial strength, τ*. Model allows both obtaining the ultimate tensile strength of CFRP and GFRP composites, and correcting the σ vs ε curve to match its peak point with the predicted strength, which is more accurate than the one obtained by previous GLS-based models. Our model is used to classify the mechanical response of the material according to the energetic contributions of two phenomena up to the failure: intact fibers (IF) and fragmentation (FM). Additionally, the influence of fiber content, Vf, on the tensile strength, σU, failure strain, εU, and total strain energy, UT, is analyzed by means of novel mechanical-performance maps obtained by the model. The maps show a dissimilar behavior of σU, εU and UT with Vf between GFRP and CFRP composites. The low influence of Vf on the percent energetic contributions of IF and FM zones, as well as the larger energetic contribution of the FM zone, are common conclusions that can be addressed for both kinds of composites.
Abstract in English:Abstract Aspects about the numerical modeling of three-dimensional prestressed steel-concrete composite beams by using the finite element (FE) method are highlighted and commented in this work. Emphasis is given to the numerical treatment of bonded and unbonded tendons. The proposed modeling technique uses curved beam and catenary elements for simulating internal and external tendons, respectively. Other issues such as the constitutive model for shear connectors, steel beam and concrete are also discussed. Several numerical examples with experimental and numerical results are presented. It is encountered that a faster numerical convergence is achieved when the tendon stiffness is included in the overall stiffness of the structure, even when the unbonded internal situation is addressed. Moreover, omitting slipping at the deviator device may lead to inaccurate results in the evaluation of tendon forces for external prestressing. Favourable agreement is encountered for all studied examples.
Abstract in English:Abstract Deep beams do not behave according to classical beam theory. The nonlinearity of strain distribution within these elements requires application of strut and tie models (STM) or other alternatives to evaluate the complex stress field. Although the design of these elements is a common task for structural engineers, limited research is found on assessing effectiveness of the results. The purpose of this work is to compare, in a systematic approach, different design solutions for a deep beam using selected performance metrics which are strain energy, reinforcement ratio, maximum load, structural efficiency, safety factor and cracking behavior. A deep beam (2.85 m of height, 4.20 m of length and 0.2 m of thickness) with a square opening (0.7 m x 0.7 m) close to one of the supports was subjected to a uniform loading at the top surface while resting on supports at both ends. A simplified finite element model (FEM) of this beam was developed simulating concrete with elastic linear stress-strain behavior and disregarding steel reinforcements. This model allowed determination of elastic stress fields necessary to subsequent analyses. Four STM were then developed, supposing the total load respectively represented by one (STM-1), two (STM-2), four (STM-4) or eight (STM-8) concentrated loads equally spaced along the top of the beam. Additionally, an in-plane stress field method (SFM) was applied to the design of the same beam subjected to uniform loading on the top surface. After design and detailing of the reinforcement for each situation, nonlinear FEMs were used to predict the ultimate conditions. The strain energy reduced significantly comparing results from STM-1 to STM-2 and subsequently to STM-4 and remained at a low level in STM-8 and SFM. The reinforcement ratio reduced systematically from STM-1 to STM-8, was minimum with the SFM and the same behavior was followed by maximum load. The structural efficiency (maximum load/reinforcement ratio) increased from STM-1 to STM-8, with maximum efficiency at STM-8 and was slightly below with SFM. The safety factor reduced systematically from STM-1 to STM-8 and was slightly lower with SFM, but in all cases was above acceptable limits found in design codes.
Abstract in English:Abstract Safety is a key design criterion for floating structures. A high rate of mooring accidents has been reported over the past decades. Preventing mooring line failure is a key design objective for floating breakwater systems. The mooring system comprises sets of mooring lines anchored to the seabed. These components are exposed to highly cyclic nonlinear load fluctuations induced by an irregular wave climate during their service life. DNVGL-OS-E301 classifies the mooring lines for floating breakwaters as long-term elements that should be evaluated according to the fatigue limit state. Fatigue of mooring lines needs to be monitored and evaluated to warrant the station keeping and integrity of overall system. Applying an additional control device to a floating breakwater mitigates the structural response and hence mobilized tension in mooring system. The focus of present study was to examine the effect of an additional control device on fatigue life of mooring lines for floating breakwaters. To evaluate the effect of a control device on the fatigue behavior of mooring lines, a floating breakwater was simulated with a tuned liquid column damper (TLCD) attached. A time-dependent approach based on S-N curves in conjunction with the Palmgren-Miner rule was employed to evaluate the mooring line fatigue. This paper presents a further parametric study focused on the effect of TLCD on fairlead point displacement, mobilized tension, damage rate, and fatigue life of mooring lines. The results showed that TLCD increased the fatigue life of mooring line and thus dramatically decreased the likelihood of the mooring system being damaged by fatigue. This would reduce the maintenance costs and increase the lifetime and operational safety of floating breakwater. In addition, the presented case study showed that failure probability of mooring lines against fatigue damage was also reduced and was acceptable for the safety factor defined in DNVGL-OS-E301. This proposed approach of applying a TLCD is a practical tool for designing the components of a floating breakwater more efficiently.
Abstract in English:Abstract In this paper, we give overview of deformation modes for the uniform foam filled thin-walled structure such as circular tubes, square tubes, rectangular tubes, tapered tubes, hat tubes and cone tubes. Foam material is used as a reinforcing material on a thin wall tube which has potential as being a good energy absorber. This is evident from many of the studies undertaken on the crashworthiness performance and energy ab-sorption of the thin wall tube. Also, this paper presents a review of the current state of the art in computa-tional optimization methods applied to foam filled structures, offering a clear vision of the latest research advances in this field.
Abstract in English:Abstract This special issue contains selected papers first presented in a short format at the Congress CILAMCE 2018 (39th Ibero-Latin American Congress on Computational Methods in Engineering) held in Paris and in Compiègne, France, from 11 to 14 November 2018.
Abstract in English:Abstract Compressive strength and Young’s modulus are the main properties used in the design of concrete structures. They are responsible for the cost, safety and dimensioning of the structure, and are generally measured in expensive and time-demanding tests. This fact encourages researches for fast and cost-effective methods to investigate the concrete’s properties. Among the concrete types, structural Lightweight Aggregate Concrete (LWAC) is one of the most employed worldwide, but it presents limited studies and mix design techniques. Thus, this work evaluates and compares the performances of two methods to predict the compressive strength of LWAC samples: Support Vector Machine and Finite Element Method. To this end, both strategies use the LWAC’s mix proportions and the Young’s modulus, and the compressive strength of mortars and aggregates obtained from an experimental program from the literature. The results encourage further researches towards the development of a numerical tool that may assist engineers for practical purposes, since both methods show good agreement with the validation data.
Abstract in English:Abstract In the last decades, the modernization in structural engineering has increased the use of steel-concrete composite and hybrid systems for slabs, when the adherence in the interface of the materials is present or not, respectively. In addition to the traditional steel deck, a similar solution for precast trussed slabs has been used for small constructions, in which a cold formed U profile acts as steel formwork before the concrete curing, resisting to self-weight of the concrete and to the construction overload. After this period, the steel profile gets incorporated to the concrete element, allowing the composite behavior of the structure, system that usually goes without additional reinforcements. This slab includes, besides concrete, a light filling material between ribs, cold formed profiles and the trussed reinforcement. Once this technology has just arrived to the construction market, there is a gap of knowledge related to its design procedure. In this context, this study aims to present a methodology to analyze the limit-states that govern the design of these slabs. A computational tool was developed to evaluate the resistance through data entry related to geometry, service loads and materials, which grants to conduct a parametric study with pre-defined geometries to obtain, as result, spans and loads. Conclusions about the maximum span without shoring and general data are also discussed.
Abstract in English:Abstract Sensing techniques based on accelerometers for modal parameters identification are among the most studied and applied in Structural Health Monitoring of civil structures. The advent of low-cost MEMS accelerometers and open-source electronic platforms, such as Arduino, have facilitated the design of low-cost systems suitable for modal identification, although there is still a lack of studies regarding practical application and comparison of commercially available low-cost accelerometers under SHM conditions. This work presents an experimental performance evaluation of six low-cost MEMS accelerometers for the identification of natural frequencies and damping ratios of a three-storey frame model and a reinforced concrete slab, as well as their noise characteristics. A low-cost Arduino-based data acquisition system was used. The results showed an overall good performance of the MEMS accelerometers, with identified natural frequencies errors within 1.02% and 7.76% of reference values, for the three-storey frame and concrete slab, respectively, and a noise density as low as 108 g/√Hz.
Abstract in English:Abstract Research in metamaterials has recently gained interest in the field of noise and vibration control. The ability of creating band gap zones with minimum added mass is the main feature behind its success. In addition, the use of 3D printed parts, particularly the Fused Deposition Modeling (FDM), offers a practical solution for manufacturing parts with intricate shapes that are challenging for standard manufacturing processes, which is the case of many structural metamaterials. The combination of this concept with smart materials can further improve performance, providing the means to overcome typical issues. From a design perspective, the problem with coupling rises, as both the mechanical and electrical responses relies on the load circuit and on the mechanical properties of the smart elements. Therefore, the modeling of such structures is a rather complex task, for it involves multiphysical simulations of systems with complex geometries and typically a high number of degrees of freedom. Hence, this paper presents a direct approach for modeling and simulating smart metamaterials using a state-space formulation, which allows the modular coupling of electromechanical resonators manufactured by FDM. The numerical results are compared to experimental data obtained with unit cells prototypes embedded with piezoelectric elements and connected with a tunable shunt electric circuit. The good agreement between test and simulated data validates the design procedure.
Abstract in English:Abstract Here we present a multi-scale model to carry out the computation of brittle composite materials reinforced with fibers, and we show its application to standard reinforced concrete. The computation is carried out within an operator-split framework on the macro-scale, which allows for different failure mechanisms to develop in separate phases, as both the concrete and the bond-slip exhibit non-linear behavior. The computations on the micro-scale are performed for each constituent separately. The reinforcement is taken to be linear elastic, and the bond-slip is handled as a plastic deformation. The standard elastoplastic procedure is used to compute the bond stresses, combined with the X-FEM methodology to give the global representation of slip. The crack development in concrete, on the other hand, is described with a damage model with exponential softening, where ED-FEM is used to represent localized failure. A numerical example is shown to test the developed methodology.