Manufacturing, Testing and Modeling of Advanced Filament Wound Grid Stiffened Composite Cylinders

Advanced Grid Stiffened (AGS) structures are a kind of FRP composites that are being extensively used in many engineering fields because of their inherent advantages. Hence it is of utmost importance to understand the basic mechanism of these structures in order to develop better models and to find ways to improve their efficiency. This thesis discusses the manufacturing technology used viz. the filament winding technique to fabricate grid stiffened composite cylinders. A step by step procedure of the fabrication process of grid cylinders is explained. The confinement effectiveness of the AGS cylinders is evaluated by filling them with concrete and subjecting the specimens to uniaxial compression tests. The results from the experiments show that the grid stiffened cylinders have more load carrying capacity than the normal FRP pipes. The stiffeners in the grid structures increase the structural capacity and also prevent the global buckling of the grid cylinders. It is seen that the skin wound at a certain angle provides satisfactory lateral confinement to the grid structure and the desired composite action is achieved between the grid structure and the skin. The AGS structures are able to effectively confine the concrete, thereby increasing their strength multi-fold. To validate the results obtained from the experiments a 3-D finite element model of the grid stiffened cylinder was developed using ANSYS. The nonlinear behavior of the materials used in the experiments was incorporated into the FEA model by considering the appropriate stress-strain relationships. The behavior of the confined concrete composite cylinder was modeled using a non-associative Drucker-Prager plasticity criterion. The validated FEA model was used to perform a parametric analysis. Several design parameters were identified that seem to have an effect on the load carrying capacity of the grid structures. These parameters were then varied using the FEA model to evaluate the structural behavior of the cylinders and the results were analyzed to efficiently design high strength grid stiffened composite cylinders. Finally a discussion of the results from both the experiments and the FEA model are presented and general conclusions are drawn

Intrinsic Properties of Composite Double Layer Grid Superstructures

This paper examined the opportunities of composite double-layer grid superstructures in short-to-medium span bridge decks. It was empirically shown here that a double-layer grid deck system in composite action with a thin layer of two−way reinforced concrete slab introduced several structural advantages over the conventional composite plate-girder superstructure system. These advantages included improved seismic performance, increased structural rigidity, reduced deck vibration, increased failure capacity, and so on. Optimally proportioned space grid superstructures were found to be less prone to progressive collapse, increasing structural reliability and resilience, while reducing the risk of sudden failure. Through a set of dynamic time-series experiments, considerable enhancement in load transfer efficiency in the transverse direction under dynamic truck loading was gained. Furthermore, the multi-objective generative optimization of the proposed spatial grid bridge (with integral variable depth) using evolutionary optimization methods was examined. Finally, comprehensive discussions were given on: (i) mechanical properties, such as fatigue behavior, corrosion, durability, and behavior in cold environments; (ii) health monitoring aspects, such as ease of inspection, maintenance, and access for the installation of remote monitoring devices; (iii) sustainability considerations, such as reduction of embodied Carbon and energy due to reduced material waste, along with ease of demolition, deconstruction and reuse after lifecycle design; and (iv) lean management aspects, such as support for industrialized construction and mass customization. It was concluded that the proposed spatial grid system shows promise for building essential and sustainable infrastructures of the future

Discrete Element Simulation of Bending Deformation of Geogrid-Reinforced Macadam Base

The pavement bending deformation resistance of the existing macadam base structure is poor. The geogrid-reinforced macadam base can effectively strengthen the bending resistance of the pavement, but no international consensus has been reached at present over bending failure laws of reinforced macadam base structure. Discrete element models of semi-rigid base pavement structure, macadam base pavement structure, and geogrid-reinforced macadam base pavement structure were built based on MATDEM discrete element simulation program; loading calculation of the three models was conducted by taking their centers as loading positions; and model displacement nephogram, strain nephogram, and effects of different spans on their bending deformation were analyzed to reveal bending failure laws of reinforced macadam base and improvement effect of the geogrid on the anti-bending performance of the macadam structural layer. Finally, bending deformation laws of the three pavement structures and improvement effect of geogrid reinforcement on bending properties of the macadam base structure were established. The results show that under bending deformation of semi-rigid base, the vertical strain at the contract surface between the baseplate and soil base and horizontal strain at midspan position reach the maximum, which can easily lead to fracture and shear failure, and the macadam base layer can effectively isolate the tensile strain transmitted from bottom up. Through their own deformation, grids can transform surface pressure load into frictional resistance at the geogrid/soil interface and partial kinetic energy in the system into their own elastic potential energy to reduce the kinetic energy at the subbase layer. Geogrid reinforcement can improve the nonlinearity of macadam materials, reduce the fluctuation amplitude of the strain curve and displacement curve, lengthen the service life of the macadam base pavement structure, and improve its structural soundness under bending deformation. This study can provide a theoretical reference for numerical simulation of bending failure of geogrid-reinforced macadam base

SOLID-SHELL FINITE ELEMENT MODELS FOR EXPLICIT SIMULATIONS OF CRACK PROPAGATION IN THIN STRUCTURES

Crack propagation in thin shell structures due to cutting is conveniently simulated using explicit finite element approaches, in view of the high nonlinearity of the problem. Solidshell elements are usually preferred for the discretization in the presence of complex material behavior and degradation phenomena such as delamination, since they allow for a correct representation of the thickness geometry. However, in solid-shell elements the small thickness leads to a very high maximum eigenfrequency, which imply very small stable time-steps. A new selective mass scaling technique is proposed to increase the time-step size without affecting accuracy. New ”directional” cohesive interface elements are used in conjunction with selective mass scaling to account for the interaction with a sharp blade in cutting processes of thin ductile shells

Multi-Scale Modeling of Particle Reinforced Concrete Through Finite Element Analysis

Concrete is the main constituent material in many structures. The behavior of concrete is nonlinear and complex. Increasing use of computer based methods for designing and simulation have also increased the urge for the exact solution of the problems. This leads to difficulties in simulation and modeling of concrete structures. A good approach is to use the general purpose finite element software, e.g ANSYS . Normal strength concrete is a composite material represented by mechanically strong aggregates of various shapes and sizes incorporated into weaker cementitious matrix. A number of simplified homogenized models have been reported in the literature to represent the mechanical response of concrete. An accurate representation of the spatial distribution of the aggregate particles is one of the most important aspects of real-scale concrete modeling. A three-dimensional, numerical model, capable of predicting structural reliability of concrete under various loading conditions has been developed. A micromechanical heterogeneous model based on real world spatial distribution of aggregates was generated using a packing algorithm. This model has been used to compute the stress-strain response of concrete by taking a representative cell homogenization approach. The results of numerical analysis of this model were compared with existing models of particulate composite material. The computational results demonstrate agreement within existing models and, therefore, can be used for micromechanical modeling of composite material such as real world concrete composites

Experimental and numerical evaluation of fiber-matrix interface behaviour of different FRCM systems

Abstract Fiber Reinforced Cementitious Matrix (FRCM) composites are a relatively new strengthening system family, whose mechanical behavior is strongly affected by the wide array of possible inorganic matrices and composites fabrics that can be used and coupled together. Structural tests highlighted that global capacity of the system is strongly affected by fabric-matrix adhesion mechanism. In the present paper, the experimental results of tensile and single-lap shear tests, aimed to define mechanical properties of four FRCM types, are discussed and compared. For each system type, the failure modes for both types of test have been physically identified and clarified. The following development of detailed finite element models, carefully reproducing the mechanical behavior of the different layers of the strengthening system, allowed for the proposal of a reliable shear stress-slip relation for the fiber-matrix interface. The experimental outcomes showed the relevant dispersion of the results in terms of performance, effectiveness and failure mechanisms exhibited by the different FRCM types while the numerical interpretation allowed for a better understanding of the reasons and the parameters behind them

Mechanics and durability of lime-based textile reinforced mortars

Application of lime-based textile-reinforced mortars (TRMs) for strengthening of masonry structures have received a growing attention in recent years. An extensive effort has been devoted to understanding of the performance of these composites and their effectiveness in improving the seismic safety of existing masonry structures. Nevertheless, several aspects regarding the durability and mechanics of these composites still remain unknown. This letter is an effort on highlighting those aspects considering both experimental and numerical modelling approaches

Reliability-based Design Optimization of Concrete Flexural Members Reinforced with Ductile FRP Bars

In recent years, ductile hybrid FRP (DHFRP) bars have been developed for use as tensile reinforcement. However, initial material costs regain high, and it is difficult to simultaneously meet strength, stiffness, ductility, and reliability demands. In this study, a reliability-based design optimization (RBDO) is conducted to determine minimum cost DHFRP bar configurations while enforcing essential constraints. Applications for bridge decks and building beams are considered, with 2, 3, and 4-material bars. It was found that optimal bar configuration has little variation for the different applications, and that overall optimized bar cost decreased as the number of bar materials increased