A new algorithm for the rotating-angle, softened-truss model of reinforced concrete elements

Efficient softened truss model for prestressed steel fiber concrete membrane elements

This article presents a refinement of the rotating-angle softened truss model (RA-STM) for prestressed concrete (PC) membrane elements. To refine the RA-STM, an efficient solution procedure to solve the set of nonlinear equations is presented. Appropriate average stress-strain relationships for concrete and steel bars are also used in the solution procedure. The theoretical results obtained from the refined RA-STM are compared with some experimental results found in the literature and also with the original RA-STM. It is shown that the refined RA-STM captures better the behavior of PC membrane elements under shear and also predicts better the shear strength.

Hsu recently conducted a shear test on nine reinforced concrete panel elements subjected to applying pure shear using a shear testing device. Modern truss models (i.e. modified compression field theory and a rotating angle softened truss model) are used to perform a complex nonlinear analysis through a trial and error method based on a double loop. This analysis is conducted by employing equilibrium conditions, compatibility conditions, and a ductile stress–strain relationship of a reinforced concrete membrane panel in a biaxial state. In this study, an effective algorithm that uses a revised Mohr compatibility method based on the failure criteria of struts and ties is proposed. This algorithm is used to improve the convergence rate in the analysis of shear history, which was performed in the experiment of Hsu. The result of the analysis indicates that the shear strain energy in a state of extended shear strain is influenced by the relationship between principal compressive stress and strain (crushing failure).

Low reinforced thin concrete panels have been used for the re-construction of living buildings in the devastated zone of L’Aquila. A structural characterization of these types of panels is presented in this paper, paying particular attention to the fact that these panels are subjected mainly to shear forces. Refined compression-field theory (RCFT) has recently been proposed in order to better predict the behaviour of reinforced concrete members subjected to in-plane shear and axial stresses. This theory is based on continuum mechanics, i.e. satisfying compatibility, equilibrium and formulating the constitutive equations in terms of average (i.e. “smeared”) stresses and strains. The improvement of RCFT in comparison with the two most famous theories for reinforced concrete member subjected to shear [i.e. the modified compression-field theory (MCFT), and the rotating-angle softened-truss model (RA-STM)], deals with an embedded bar model based on the tension stiffening model in concrete. After an ad-hoc calibration procedure, the RCFT is employed in order to reproduce the envelope of the experimental load-deflection response of three full-scale thin low reinforced concrete panels subjected to cyclic loading. The predictions provided by RCFT are compared with the experimental data as well as with those provided by MCFT and RA-STM. This paper presents the necessary parameters for the design of thin low reinforced concrete panels using the RCFT. The preliminary numerical validations seem very promising. However, additional experimental data are required for calibrating and validating the parameters of the proposed RCFT theory.

This paper presents an improved softened membrane model for the analysis of reinforced concrete (RC) circular bridge columns under torsion loading. Concrete exhibits higher tensile strength and stiffness due to the strain-gradient effect under torsional loading. Results of previous studies suggest that the inclusion of strain-gradient and bidirectional stress effects improves prediction of the torsional behavior of concrete members. However, the influence of strain-gradient and bidirectional effect stresses on the torsional response of circular columns has never been investigated. With this paper, the authors aim to fill the existing knowledge gap in this important area of research by proposing a modified softened membrane model for torsion (SMMT) for circular columns. The authors also recommend a new tension–stiffening relationship of concrete for improved predictions. The estimated analytical response is compared with experimental data, and a good correlation can be seen. Predictions from the proposed model are also compared with the classical rotating-angle softened truss model (RA-STM) to illustrate the efficacy of the proposed model. Parameters such as postcracking stiffness, peak torque, and twist at peak torque are captured by the improved SMMT better than with the existing RA-STM. The improved model can be used also for developing simplified design equations.

For most simple processes, PID control can provide satisfactory closed loop performance. However, in spite of the considerable advantages of conventional PID controllers (such as simplicity of their structures, robustness and ease of implementation), they still have a major drawback in that the controllers may need to be re-tuned, if the systems to be controlled are subjected to significant changes, in order to achieve satisfactory performance. For this reason, during the last two decades much work in linear control theory has been devoted to incorporating the flexibility of self-tuning control and the simplicity of PID structures. A lot of self-tuning methods have been developed and special attention is currently being paid to PID self-tuning controllers and their implementation, [e.g. Yusof R. & et al., (1994); Yusof, R.; (1993) and Tokuda M.; & Yamamoto T.; (2002)]. During the past three decades, a special attention has also been given to the problem of designing pole-placement controllers and self-tuning regulators. Various self-tuning controllers based on classical pole-placement ideas were developed and employed in real applications, [e.g. Sirisena H. & Teng F.,(1986); Zhu Q., & et al., (2002); Zayed A. & Hussain A., (2004); Astrom K.., & Wittenmark B., (1973)]. The popularity of pole-placement techniques may be attributed to the fact that in the regulator case they provide mechanisms to over-come the restriction to minimum-phase plants of the original minimum variance self-tuner of Astrom K., & Wittenmark B., (1973). In the servo case, they provide the ability to directly introduce bandwidth and damping ratio as tuning parameters. In addition, there is some improvement in robustness of pole-placement methods, as they simply modify the system dynamics as opposed to cancelling them as per the early optimal self-tuning controllers. Furthermore, unlike many of the self-tuning based PID control designs [see for example Yusof R. & et al., (1994); Yusof, R.; (1993)], in which the tuning parameters must be selected using a trial and error procedure, the tuning parameters for pole-placement controllers can be automatically set on-line by specifying the desired closed loop poles. Comparatively, only little attention has been given to zeros since they are considered to be less crucial than poles. Most of the previous discussion on zeros are centred around the choice of the sampling time so that the resulting system is invertible. However, it is important to note that zeros may be used to achieve better set point tracking Zayed A. & Hussain A., (2004)., and they may also help reduce the magnitude of the control action Sirisena H. & Teng F.,(1986).. 8

The use of the model technique in the prediction of the pressure distribution over the tool surfaces in cold forging

The precast concrete sandwich panel structure can meet the requirement of energy efficiency in building and housing industrialization. The connector that is the key component can guarantee the internal layer, the external layer and insulation to work together in the precast concrete sandwich panel structure whose durability and security are important contact with the connector’s mechanical performance and the connector plays a decisive role of the thermal insulation performance and energy-consumption of building. The paper proposes to use U-shape fiber reinforce as the connector of the precast concrete sandwich panel. Based on the 3600×3000 the size of precast concrete sandwich panel and the different arrangement form of the connector. We have used ABAQUS finite element software to analyze the connector’s mechanical behavior to verify it’s rationality. In hope for providing the valuable reference for the U-shape fiber reinforced connector in the application of energy-saving recast concrete sandwich panel structure.

A step-by-step method for predicting the spectrophotometric response of a carded fabric composed by differently colored raw materials

The purpose of introducing a combined cycle with gas turbines in power plants is to reduce loss of energy. Their main role lies in the utilization of waste heat that may be found in exhaust gases from the gas turbine or at some other points of the process to produce additional electricity. The efficiency of the plant exceeds 50%, while the traditional steam turbine plants is approximately 35% ∼ 40% or so. To date, the PID controller has been used to operate under such systems, but since PID controller gain manually has to be tuned by trial and error procedures, getting optimal PID gains is very difficult manually without control design experience. We studied acquiring transfer function from operating data on the Gun-san gas turbine in Korea and a new 2-DOF PID controller tuning by ANFIS is designed for the optimum control of the Guns-san gas turbine’s variables. Since the shape of a membership function in the ANFIS vary on the characteristics of plant, ANFIS-based control is effective for plants whose variables vary. Its results are compared to the conventional 2-DOF PID controller and represents satisfactory response. We expect this method will be used for another process because it is studied using actual operating data.

Pressure contours on forming dies: Part 1. Simulation using physical modelling technique

Shape memory materials are featured by their ability to recover their original shapes when a particular stimulus, such as heat, light, magnetic field, even moisture/water, etc. is applied. However, it is not an easy task for non-professionals to synthesize a shape memory material which can meet all the requirements of a particular application. Even for profession- als, like materials researchers, it could involve tedious trial and error procedures. In this paper, the concept of water-respon- sive shape memory hybrid is proposed and the advantages are demonstrated by two examples. The hybrid concept is versatile and can be easily accessed by those even without much polymer/chemistry background. Moreover, the perform- ance of such hybrids can be well-predicted. This concept can be further extended into solvent-responsive shape memory hybrids, which can be routinely designed and realized in a Do-It-Yourself manner by almost anyone.

Dual-phase (DP) ferrite–martensite steels have a fine microstructure that consist of martensite islands, dispersed in a ferrite matrix. In the present work, a micromechanical-based finite element (FE) analysis is carried out in order to investigate the mechanical properties of this type of steels, such as yield stress and tensile strength. The step forward contribution of the present study is to insert the effect of the presence of the interface of the constituting phases in the FE model. In order to do so, a micromechanical FE model is developed in which the effect of the interface of the constituting phases is taken into account by means of cohesive elements. The required parameters of the cohesive elements are determined by a trial and error procedure which compares the numerical results to the experimental ones. Experimental data is used to verify the created FE model. This model is then used to investigate the effect of martensite volume fraction and small-to-large particle size ratio of martensite on the deformation behavior of the DP steel. This study shows that considering the interface of the constituting phases greatly affects the numerical results on stress and strain distributions and produces more realistic findings in agreement with experiments. The results show that applying cohesive elements between two phases have reduced tensile strength, yield stress, and the amount of uniform elongation.

Abstract: A multilayer perceptron is known to be capable of approximating any smooth function to any desired accuracy if it has a sufficient number of hidden neurons. But its training, based on the gradient method, is usually a time consuming procedure that may converge toward a local minimum, and furthermore its performance is greatly influenced by the number of hidden neurons and their initial weights. Usually these crucial parameters are determined based on the trial and error procedure, requiring much experience on the designer's part.In this paper, a constructive design method (CDM) has been proposed for a two‐layer perceptron that can approximate a class of smooth functions whose feature vector classes are linearly separable. Based on the analysis of a given data set sampled from the target function, feature vectors that can characterize the function‘well’are extracted and used to determine the number of hidden neurons and the initial weights of the network. But when the classes of the feature vectors are not linearly separable, the network may not be trained easily, mainly due to the interference among the hyperplanes generated by hidden neurons. Next, to compensate for this interference, a refined version of the modular neural network (MNN) has been proposed where each network module is created by CDM. After the input space has been partitioned into many local regions, a two‐layer perceptron constructed by CDM is assigned to each local region. By doing this, the feature vector classes are more likely to become linearly separable in each local region and as a result, the function may be approximated with greatly improved accuracy by MNN. An example simulation illustrates the improvements in learning speed using a smaller number of neurons.

The design of heat exchangers, especially shell and tube heat exchangers was originally proposed as a trial and error procedure where guesses of the heat transfer coefficient were made and then verified after the design was finished. This traditional approach is highly dependent of the experience of a skilled engineer and it usually results in oversizing. Later, optimization techniques were proposed for the automatic generation of the best design alternative. Among these methods, there are heuristic and stochastic approaches as well as mathematical programming. In all cases, the models are mixed integer non‐linear and non‐convex. In the case of mathematical programming solution procedures, all the solution approaches were likely to be trapped in a local optimum solution, unless global optimization is used. In addition, it is very well‐known that local solvers need good initial values or sometimes they do not even find a feasible solution. In this article, we propose to use a robust mixed integer global optimization procedure to obtain the optimal design. Our model is linear thanks to the use of standardized and discrete geometric values of the heat exchanger main mechanical components and a reformulation of integer nonlinear expressions without losing any rigor. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1907–1922, 2017