Refined Softened Truss Model with Efficient Solution Procedure for Prestressed Concrete Membranes

Efficient softened truss model for prestressed steel fiber concrete membrane elements

Due to a simpler calculation process and better precision, the rotating-angle softened-truss model is often used to predict behaviours of reinforced concrete shell or panel structures. In the current algorithm of the rotating-angle softened-truss model, the calculation process is from strains to stresses, which needs a trial and error procedure. A new algorithm of the rotating-angle softened-truss model is proposed in this paper. The Poisson effect is included in the new algorithm. Its calculation process is from stresses to strains. The trial and error procedure is avoided, which simplifies the calculation process significantly. The reliability of the new algorithm is verified by test data of six panels.

Refined softened-truss model with efficient solution procedure for reinforced concrete members under torsion combined with bending

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).

Efficient exact solution procedure for quasi-one-dimensional nozzle flows with stiffened-gas equation of state

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.

Torsional behavior of T- shaped reinforced concrete beams with large web openings

The authors of this paper present a method for torsional design of multicell concrete bridges using a softened truss model. Earlier researchers have successfully demonstrated the development for solving single cell torsion by combining the equilibrium, compatibility, and the softened constitutive laws of concrete. By solving the simultaneous equations based on the membrane analogy, multicontinuous or separate cells can be solved.

Keywords HONG KONG UNIVERSITY, SOUTHEAST UNIVERSITY NANJING CONCRETE, REINFORCED, WALLS, SHEAR, SLIT, ELASTOPLASTIC, ANALYSIS, BEHAVIOUR, STRUCTURES, EARTHQUAKES, RESISTANT, SEISMIC, TRUSSES, SOFTENED, MODELS, INELASTIC, CONNECTING, BEAMS, VIBRATIONS, CONTROL, NON LINEAR, LOADS, DEFLECTION, CURVES, FINITE ELEMENTS, METHODS, STUDIES, PARAMETRIC, DESIGN, DEPTH, REINFORCEMENT, FAILURES, MODES, DUCTILITY, FREQUENCIES, FREQUENCY, EXCITATION, CONNECTIONS, DAMPING, DAMPERS... Show All

ABSTRACTIn a make‐to‐order product recovery environment, we consider the allocation decision for returned products decision under stochastic demand of a firm with three options: refurbishing to resell, parts harvesting, and recycling. We formulate the problem as a multiperiod Markov decision process (MDP) and present a linear programming (LP) approximation that provides an upper bound on the optimal objective function value of the MDP model. We then present two solution approaches to the MDP using the LP solution: a static approach that uses the LP solution directly and a dynamic approach that adopts a revenue management perspective and employs bid‐price controls technique where the LP is resolved after each demand arrival. We calculate the bid prices based on the shadow price interpretation of the dual variables for the inventory constraints and accept a demand if the marginal value is higher than the bid price. Since the need for solving the LP at each demand arrival requires a very efficient solution procedure, we present a transportation problem formulation of the LP via variable redefinitions and develop a one‐pass optimal solution procedure for it. We carry out an extensive numerical analysis to compare the two approaches and find that the dynamic approach provides better performance in all of the tested scenarios. Furthermore, the solutions obtained are within 2% of the upper bound on the optimal objective function value of the MDP model.

The inverse problem being addressed is the construction of an aerodynamic airfoil shape. The objective of the present paper is: (i) to formulate the inverse problem such that the mathematical problem is well-posed both theoretically and numerically; (ii) to formulate the adjoint problem such that an efficient solution procedure can be constructed; (iii) to demonstrate how the solution procedure works. The inverse problem is posed as a minimization problem of an objective functional. The minimum of the functional corresponds to the attainment of a target velocity distribution by the aerodynamic airfoil shape. The design variables being considered are geometric parameters of the airfoil and an appropriately defined set of target velocity parameters which are introduced to assure the well-posedness of the problem. The minimization problem is solved by an optimization algorithm. Adjoint method is employed for an efficient computation of the objective functional gradient with respect to the geometric parameters. Numerical results demonstrate that the present inverse problem formulation is well-posed. The significance of the target velocity parameters in obtaining well-posedness is explained in terms of the Lighthill constraints.

Effect of concrete cover on the pure torsional behavior of reinforced concrete beams: Analytical model

An attempt of shifting as more people as possible and/or their logistics from a dangerous place to a safer place is an evacuation planning problem. Such problems modeled on network have been extensively studied and the various efficient solution procedures have been established. The solution strategies for these problems are based on source-sink path augmentation and the flow function satisfies the flow conservation at each intermediate node. Besides this, the network flow problem in which flow may not be conserved at node necessarily could also be used to model the evacuation planning problem. This paper proposes a model for maximum flow evacuation planning problem on a single-source-single-sink static network with integral arc capacities with holding capability of evacuees in the temporary shelter at intermediate nodes and extends the model into the dynamic case. Journal of the Institute of Engineering, 2017, 13(1): 108-116

Shifting as many people as possible from disastrous area to safer area in a minimum time period in an efficient way is an evacuation planning problem (EPP). Modeling the evacuation scenarios reflecting the real world characteristics and investigation of an efficient solution to them have become a crucial due to rapidly increasing number of natural as well as human created disasters. EPPs modeled on network have been extensively studied and the various efficient solution procedures have been established where the flow function satisfies the flow conservation at each intermediate node. Besides this, the network flow problem in which flow may not be conserved at nodes necessarily could also be useful to model the evacuation planning problem. This paper proposes an efficient solution procedure for maximum flow evacuation planning problem of later kind on a single-source-single-sink dynamic network with integral arc capacities with holding capability of flow (evacuees) in the temporary shelter at intermediate nodes. Journal of the Institute of Engineering, 2018, 14(1): 107-114