Structural evaluation of a novel box beam system of Pultruded Fibre Reinforced Polymer shapes

Presented in this thesis is an evaluation of a novel box beam system of Pul- truded Fibre Reinforced Polymer (PFRP) shapes. The flat-pack modular beam system consists of separate PFRP flange and web shapes joined together with a new method of mechanical fastening. It is based on the first generation Star- tlink building system, conceived by UK engineers in 1999. The Startlink building system is introduced, and classified within the scope of Modern Methods of Con- struction (MMC), and its merits are discussed. In the context of MMC a critical review by the author finds that, although the proposed 1999 generation Startlink system offers design flexibility, it will probably have a limited market potential. The novel use of the steel MlO Unistrut connection method as a means of fastening distinct PFRP shapes in a building system is characterised. Individ- ual connector design parameters for joint stiffness and resistance are identified and determined, under pure shear loading. The results of a series of physical tests show no significant loss of stiffness or strength with long term environmen- tal exposure. Values of key mechanical properties for design calculations are recommended. A 400 x 200 x 2848 mm prototype PFRP box beam assembly is fabricated from two flange and two web panel-type shapes, cut from existing off-the-shelf PFRP shapes. This is 60 mm deeper than the largest single PFRP shape that could be used as a beam. The assembly is joined at the web-flange junction with M10 Unistrut connectors set at various spacing's, in the range 50 to 400 mm. These connectors carry the longitudinal shear that is generated between the joined shapes when the modular assembly is in flexure, Theoretical deflections, cal- culated using a modified form of a partial-interaction analysis model developed for composite concrete and steel structures, are predicted for the assembly ac- counting for the finite shear stiffness of the web-flange connection. A series of 16 four-point bending load tests on the beam assembly, across two load arrange- ments, show that its performance is linked to the designated spacing of the M10 Unistrut connections. The flexural rigidity and degree of interaction present in the assembly are determined from analysis of vertical deflections and longitudi- nal strains, as the beam is deformed. The influence of secondary effects, due to the poor tolerances achieved in the hand fabrication of the beam's assembly, are found to greatly affect the ability of the deflection analysis to give the required measured deflections. Comparison of the effective joint shear rigidities obtained from theory and testing indicates a higher individual connection stiffness in the prototype beam than previously determined by way of the individual Unistrut connector characterisation. It is found through the combined analytical and physical testing research that the M10 Unistrut connection method can only provide the necessary joint shear stiffness and resistance to the 400 mm deep beam if the connector spacing, along the four joints, is ≤ 50 mm. The total number of connectors this represents in the beam is likely to make this modular construction approach too expensive for it to be commercially viable. Although the M10 connector could be used to fabricate beams of lesser depths, since the number of connectors will then be reduced, these beams would find it difficult to compete with the available off-the-shelf PFRP beam shapes, of up to 300 mm deep. There is however scope to use the Unistrut method of connection to provide longitudinal shear resistance in building systems where, for example, a floor panel is to be stiffened by a channel shaped beam and the overall depth is ≤ 300 mm. The research work contained in this thesis has contributed to a radical change in the PFRP product offerings now proposed in the 2006 generation Startlink building system

Effect of Notches on the Axial Fatigue Properties of Structural Steels

The effect of the stress concentration on the zero-to-tension axial fatigue strength of notched members of four structural steels has been studied. For each of the four steels a critical notch severity was found at which a transition in behavior takes place. When the theoretical stress concentration exceeds this critical value the fatigue strength increases instead of continuing to decrease as would normally be expected. The maximum effective stress concentration determined from these tests corresponds to a critical notch severity which is dependent on the material) the geometry of the specimen) and the cyclic conditions of stress. Microscopic examinations of the roots of the notched specimens which did not fail revealed cracking in most cases. Some of the cracks apparently were nonpropagating cracks but the test lives in most cases were insufficient to isolate such cracks positively as non-propagating. A study of other data on non-propagating cracks revealed that the laws governing their formation are not yet fully understood. However, there are indications that the increase in fatigue strength obtained above the critical notch severity is coincident with the formation of non~propagating cracks.The Engineering FoundationAmerican Iron and Steel InstituteChicago Bridge and Iron FoundationThe Welding Research Counci

Master of Science

thesisUnique constraints are present when shear properties of orthotropic materials are desired, as they typically cannot be derived from tensile material properties like isotropic materials. Specific test specimen geometry, and in some instances specimen layup, are required in order to obtain valid shear property data. The V-Notched Rail Shear Test Method is one such test method developed to provide reliable shear test data for compo-site laminates. However, specimens made from suitably high strength materials will slip prior to failure providing invalid results. Previous work has been performed which im-proves on this test method by altering the specimen dimensions and fixture design in or-der to prevent slipping. Changes made to the fixture introduced another load path into the specimen, which can influence the stress state within the specimen. The current work looks at several aspects of the new Combined Loading Shear test fixture and how they affect the stress and strain state, as well as the measured shear strength. Photoelastic test-ing is performed to validate numerical models and to investigate the strain state in several different specimen layups as a result of the fixture changes. Accurate shear strain measurement is required when determining the shear modu-lus of a material. Bonded strain gauges are often used when strain measurements are re-quired; however, extensometers can provide the same functionality as strain gauges and have the advantage of being reusable. Extensometers are typically application specific and require careful consideration with regards to attachment and the region where exten-sion is measured. The current study proposes a shear extensometer for a V-Notched Rail Shear or Combined Loading Shear test specimen. A mechanics of materials model is used to calculate the shear strain in the specimen based on the relative displacement of a discrete set of points on the specimen face. Numerical simulations were performed to determine the points on the specimen face which would yield the most accurate measure of the in-plane shear modulus. A prototype device is tested using carbon/epoxy, glass/epoxy, and Kevlar/epoxy cross-ply laminates and the data from the extensometer are compared to data from bonded strain gauges to validate the extensometer

Research Investigations of Bulkhead Cylindrical Junctions Exposed to Combined Load, Cryogenic Temperatures and Pressure. Part I - Experimental Studies

Two-dimensional analog model and 1/6 reduced scale model to study bending stress concentrations, strains, and displacements in Y-ring of Saturn V S-IV liquid oxygen containe

Fatigue and fracture mechanics analysis of threaded connections

This thesis aims to develop a comprehensive usable engineering design approach to the fatigue analysis of threaded connections. Although primarily concerned with the fatigue-fracture mechanics behaviour of screw threads, a broad review of stress analysis investigations in such connections is reported. Connection types, their functions and standardisation authorities are presented with the purpose of familiarising the reader with the subject and the options available to the design of threaded fasteners. Fatigue crack initiation is discussed with reference to the specific setting of a critical thread root. A crack initiation model is adapted for employment in thread root design. A novel weight function approach is developed for use in the determination of stress intensity factors for threaded connections. A generic solution is proposed valid for the fatigue crack growth from any thread root under any symmetrical stress system. Its development and discussion is examined in detail, remaining close to its proposed application. Two engineering situations where the chief structural components are comprised of threaded members are taken as case studies. The background to each situation is elaborated in detail and full-scale fatigue tests were conducted on the critical components. In all, fourteen full-scale tests under constant and variable amplitude loading are reported. The results of these are analysed and used to validate the fatigue crack initiation and propagation models. Useful observations which are helpful to understanding the fracture mechanisms operating during the fatigue of threaded connections are reported. Material and environmental considerations are examined and a survey of relevant materials and their behaviour in environments associated with threaded fasteners is presented. The merits or otherwise of some common engineering practices are discussed with regard to fatigue. A method has been developed for predicting fatigue life in large threaded connections under random loading. Experimental results have been gathered on two types of components used on certain oil rigs, tether joints and drill strings. The agreement found between prediction and experiment is appreciably better than by previous methods of analysis and also points to aspects open to further improvement

Structural evaluation of a novel box beam system of Pultruded Fibre Reinforced Polymer shapes

Presented in this thesis is an evaluation of a novel box beam system of Pul- truded Fibre Reinforced Polymer (PFRP) shapes. The flat-pack modular beam system consists of separate PFRP flange and web shapes joined together with a new method of mechanical fastening. It is based on the first generation Star- tlink building system, conceived by UK engineers in 1999. The Startlink building system is introduced, and classified within the scope of Modern Methods of Con- struction (MMC), and its merits are discussed. In the context of MMC a critical review by the author finds that, although the proposed 1999 generation Startlink system offers design flexibility, it will probably have a limited market potential. The novel use of the steel MlO Unistrut connection method as a means of fastening distinct PFRP shapes in a building system is characterised. Individ- ual connector design parameters for joint stiffness and resistance are identified and determined, under pure shear loading. The results of a series of physical tests show no significant loss of stiffness or strength with long term environmen- tal exposure. Values of key mechanical properties for design calculations are recommended. A 400 x 200 x 2848 mm prototype PFRP box beam assembly is fabricated from two flange and two web panel-type shapes, cut from existing off-the-shelf PFRP shapes. This is 60 mm deeper than the largest single PFRP shape that could be used as a beam. The assembly is joined at the web-flange junction with M10 Unistrut connectors set at various spacing's, in the range 50 to 400 mm. These connectors carry the longitudinal shear that is generated between the joined shapes when the modular assembly is in flexure, Theoretical deflections, cal- culated using a modified form of a partial-interaction analysis model developed for composite concrete and steel structures, are predicted for the assembly ac- counting for the finite shear stiffness of the web-flange connection. A series of 16 four-point bending load tests on the beam assembly, across two load arrange- ments, show that its performance is linked to the designated spacing of the M10 Unistrut connections. The flexural rigidity and degree of interaction present in the assembly are determined from analysis of vertical deflections and longitudi- nal strains, as the beam is deformed. The influence of secondary effects, due to the poor tolerances achieved in the hand fabrication of the beam's assembly, are found to greatly affect the ability of the deflection analysis to give the required measured deflections. Comparison of the effective joint shear rigidities obtained from theory and testing indicates a higher individual connection stiffness in the prototype beam than previously determined by way of the individual Unistrut connector characterisation. It is found through the combined analytical and physical testing research that the M10 Unistrut connection method can only provide the necessary joint shear stiffness and resistance to the 400 mm deep beam if the connector spacing, along the four joints, is ≤ 50 mm. The total number of connectors this represents in the beam is likely to make this modular construction approach too expensive for it to be commercially viable. Although the M10 connector could be used to fabricate beams of lesser depths, since the number of connectors will then be reduced, these beams would find it difficult to compete with the available off-the-shelf PFRP beam shapes, of up to 300 mm deep. There is however scope to use the Unistrut method of connection to provide longitudinal shear resistance in building systems where, for example, a floor panel is to be stiffened by a channel shaped beam and the overall depth is ≤ 300 mm. The research work contained in this thesis has contributed to a radical change in the PFRP product offerings now proposed in the 2006 generation Startlink building system.EThOS - Electronic Theses Online ServiceGBUnited Kingdo