Annette M. Harte

THREE DIMENSIONAL ANALYTICAL SIMULATION OF FLEXIBLE PIPE WALL STRUCTURE

A three-dimensional analytical model of the mechanical response of a bonded layered flexible pipeline section to a general set of loads and pressures is presented. Stiffness relations for isotropic, orthotropic and helically wound armoring layers are developed and combined to form a total section stiffness equation incorporating inter-layer pressures and radial deformations. These layers may be used to model the mechanical responses of flexible pipelines including any number and order of layers. Typical loads are taken from a three-dimensional analysis of a flexible production riser in a steep-wave configuration in 310 m water depth. An illustrative pipe section with five layers, including an inner steel tube, two contrawound steel cable layers and two modeled with rubber matrix materials, is subjected to this three-dimensional load set. Computations show the dominant influence of the steel strands in carrying the ambient loads and also gives an accurate picture of the radial distribution of inter-layer pressures across the pipe thickness. The analytical model is designed to give a detailed assessment of deformations and stresses in the various layers such that estimates may be made of critical parameters including wear, slip, rupture, debonding and other related aspects of flexible pipe performance.

A multilevel approach to the optimisation of a composite light rail vehicle bodyshell

The optimisation of design parameters associated with composite sandwich bodyshell walls of light rail vehicles (LRV) is investigated. The main objective is to evaluate a multi-level computational procedure that leads to optimum wall ply thickness and geometric shapes for areas such as door and window openings. The optimisation procedures are extensively automated whereby iterative finite element solutions are executed under the control of a software suite containing information on the optimisation parameters, objective functions and constraints. The steps in the process include a global finite element analysis of the complete LRV bodyshell subjected to an industry standard loading, identification of a critically loaded panel and its division into domains, and optimisation of a window panel fillet radius within these domains. Numerical results are obtained in order to demonstrate the viability of the method as a design tool.

Modeling procedures for the stress analysis of flexible pipe cross sections

Thick tube theory is incorporated into an existing analytical model for the three-dimensional analysis of bonded flexible pipe cross sections under offshore loading conditions. The original model considers material layers as isotropic/orthotropic thin tubes, and layers of helically wound reinforcing cables are modeled separately. The improvement in the results obtained with the incorporation of the new thick tube layer is demonstrated for a flexible pipe with D/t = 10. The finite element technique has also been used to model this type of pipe structure. Pipe sections are discretized using axisymmetric elements for the tube-tube layers and special discrete reinforcement elements for the helical cables. A particular example of a three-layer doubly reinforced pipe section under internal pressure is studied. Good agreement is found between analytical model and finite element results for all the main deformation and stress quantities including cable stresses.

Qualification of Wood Adhesives for Structural Softwood Glulam with Large Juvenile Wood Content

Abstract This paper reports on an experimental study to assess the bond quality achieved when bonding softwood spruce containing large proportions of juvenile wood with a range of conventional wood laminating adhesives. Adhesives examined comprised two phenol resorcinol formaldehydes, a melamine urea formaldehyde, a polyurethane, an emulsion polymer isocyanate and a polyvinyl acetate. The notched block shear test was utilised in which both non-moisture cycled and moisture cycled specimens were tested. The grain orientation of the wood, was carefully studied in the bonding process. Results indicated that the integrity of the bond was highly dependent on the adhesive under examination. No significant difference was observed at the interface when bonding to juvenile wood or to mature wood . Furthermore, no distinct performance difference for both non-moisture cycled and moisture cycled specimens was recorded when bonding to tangential grained or radial grained wood.

Characterizing the wave environment in the fatigue analysis of flexible risers

As the offshore industry moves towards deeper water developments and continues to embrace harsh environments, unbonded flexible pipes are increasingly being utilized as a cost effective riser solution. Furthermore, with the advent of issues such as nonpristine annuli environments, the fatigue performance of these flexible risers is becoming a critical issue. This paper presents an overview of the comparisons between deterministic and stochastic global fatigue analysis techniques. Methods used to perform both deterministic and stochastic analyses are outlined, from performing the global analyses to using local models to generate armor wire stresses and subsequent fatigue damage. The paper identifies the key issues in the analysis performed and presents key results and conclusions with regard to the characterization of the wave environment in the global fatigue analysis of flexible risers.

Shear Strength and Durability Testing of Adhesive Bonds in Cross-Laminated Timber

This paper addresses the quality of the interface- and edge-bonded joints in layers of cross-laminated timber (CLT) panels. The shear performance was studied to assess the suitability of two different adhesives, polyurethane (PUR) and phenol–resorcinol–formaldehyde (PRF), and to determine the optimum clamping pressure. Since there is no established testing procedure to determine the shear strength of the surface bonds between layers in a CLT panel, block shear tests of specimens in two different configurations were carried out, and further shear tests of edge-bonded specimen in two configurations were performed. Delamination tests were performed on samples which were subjected to accelerated aging to assess the durability of bonds in severe environmental conditions. Both tested adhesives produced boards with shear strength values within the edge-bonding requirements of prEN 16351 for all manufacturing pressures. While the PUR specimens had higher shear strength values, the PRF specimens demonstrated superior durability characteristics in the delamination tests. It seems that the test protocol introduced in this study for crosslam-bonded specimens, cut from a CLT panel, and placed in the shearing tool horizontally, accurately reflects the shearing strength of glue lines in CLT.

Finite element modelling of the semi-rigid behaviour of pultruded FRP connections

Abstract For many years, the deterioration and corrosion of ferrous materials have been identified as a major problem in Civil Engineering structures. Significant developments in material technology have made it possible to use alternative non-corroding materials such as pultruded fibre reinforced plastics (PFRPs) in construction. In order to improve the design efficiency of PFRP frame structures, the use of semi-rigid design techniques is recommended. The semi-rigid response of a frame connection is characterised by its moment-rotation curve. It is possible to determine the moment-rotation for any configuration by means of experimental testing, but this can be both time-consuming and expensive. An alternative method is to use numerical modelling techniques to analyse the connection behaviour. A two-dimensional finite element model of a PFRP semi-rigid connection is presented. A number of factors, which have a significant effect on the behaviour of the joint, are discussed. These include the modelling of the bolted assembly, the application of prestressing forces and the interface modelling of the contacting surfaces. Results from the finite element investigation compare favourably with measured data from experimental testing.

Wood-based beams strengthened with FRP laminates: improved performance with pre-stressed systems

Using bonded fibre-reinforced polymer (FRP) laminates for strengthening wooden structural members has been shown to be an effective and economical method. In this paper, properties of suitable FRP materials, adhesives and two ways of strengthening beams exposed to bending moment are presented. Passive or slack reinforcement is one way of strengthening. The most effective way of such a strengthening was to place reinforcement laminates on both tension and compression side of the beam. However, the FRP material is only partially utilised. The second way is to apply pre-stressing in FRP materials prior to bonding to tension side of flexural members and this way was shown to provide the most effective utilisation of these materials. The state of the art of such a strengthening and various methods are discussed. Increasing the load-bearing capacity, introducing a pre-cambering effect and thus improving serviceability which often governs the design and reducing the amount of FRP reinforcement needed are some of the main advantages. A recent development on how to avoid the requirement for anchoring the laminates at the end of the beams to avoid premature debonding is shown, and the advantage of such a system is described.

A probabilistic approach to the simulation of non-linear stress-strain relationships for oriented strandboard subject to in-plane tension

This paper presents the results from an experimental test program conducted on commercially available oriented strandboard (OSB) panels and statistical analyses of the results. Standardised testing was used to determine the short-term behaviour of OSB/3 panels subjected to tension loading. A variety of thicknesses sourced from three different producers were used. Analysis of the results indicate that a quadratic expression in the form of  = a2 + b provides the best description of the relationship between stress (and strain ( up to the point of failure. It has also been shown that the coefficients a and b of the quadratic regression equations are negatively correlated to each other. Anderson-Darling goodness-of-fit tests were conducted on the results for tension strength and modulus of elasticity (MOE). The results indicate that the tension strength and MOE come from populations that follow either normal or lognormal probability distributions.

Mass timber – the emergence of a modern construction material

Abstract In the move towards sustainable construction, timber and wood-based products are becoming increasingly important structural materials. The introduction of mass timber products with excellent load carrying characteristics allows timber to be used in larger, more complex structures. Cross-laminated timber (CLT) panel products have developed to the stage where they can be considered as economic and more sustainable alternatives to traditional materials. In this paper, the characteristics and design of CLT structures are described. Recent developments in mid- and high-rise CLT construction are reviewed and future opportunities identified. Current and future research needs are highlighted.