Steel and Composite Steel-Concrete Structures
Reinforced Concrete Structures
Partially Bonded Non-metallic Prestressing Tendons
Expert Systems for Prestressed Concrete Bridge Design
Parallel-lay Ropes and Yarns
Prestressed Concrete Beams with External Tendons
Very Long Span Bridges
Lateral Stability of Precast Concrete Beams
Analysis of Concrete Slabs
Conceptual Methods for Structures and Mechanisms
Dynamics of Nonlinear Elastic Systems
Mechanics of Masonry Construction
Structural Mechanics in Molecular Biology
Dr R.E. McConnel
An investigation into the degree of transverse reinforcement required in traditional composite concrete slab and I-beam construction has been completed(G18). Push-off tests investigating the effect of lateral restraint provided by the reaction floor, and of practical fabrication details, have been conducted. Theoretical models based on plasticity theory have been developed for lateral splitting, and for local cone failure, in the concrete around a shear stud.
A project to investigate the use of asymmetric hot-rolled sections and deep-troughed concrete-filled floor (slimfloor) for large-span buildings is underway. It is intended to use a stub-girder(G31) arrangement for the main beams, in order to extend the span range beyond the present practical limitation of 6 m.
A study is underway to extend previous work on composite space-truss systems to cover light-weight large-span roof structures. To date, an appropriate 2-noded beam column finite-element, that can handle both initial imperfections and a range of lateral loads within the length of the element, has been developed. This is now being applied to the preliminary analysis of some large roofs.
Dr C.T. Morley
Research on continuous reinforced-concrete deep beams has led to a further paper(G2) on the "effectiveness factor" on concrete compressive strength that should be adopted in structural analyses using failure mechanisms and modified plasticity theory.
Work on compressive membrane action in reinforced-concrete slabs has continued, with the application of a computer program based on the Galerkin method to make comparisons with results of tests on square slabs, some with interrupted lateral restraint along the edges.
Research has begun on possible simplified approaches to the analysis of structures made of materials exhibiting marked strain-softening.
Dr C.J. Burgoyne
Tests on prestressed concrete beams with continuous aramid fibre reinforcing tendons have shown that it is possible to achieve high strength (at levels normally associated with fully bonded systems), and high rotation capacity (at levels normally associated with unbonded systems), by judiciously debonding the tendons(G27,G28). This can be achieved in two ways; by alternately bonding and debonding the tendon along its length, or by coating the tendon with a surface layer of a material with a known, low, shear strength. Such a system could be used in commercial production systems, and it would overcome one of the primary problems associated with fibre-reinforcing systems. Because this work highlights the importance of understanding and controlling the mechanisms of bond breakdown with these types of material (as opposed to steel reinforcement, where all that is needed is sufficient bond strength), other detailed investigations are being made into this problem. Development work has also been done on the mechanisms for anchoring fibre rods with expanding cements(G29).
Dr C.J. Burgoyne
The development of an expert systems to design prestressed concrete bridges continues(G25). The system takes into account additional effects caused by the actual construction sequence, and the time-varying effects of creep and shrinkage have been modelled. The expert system can design non-prismatic bridges with longitudinal variations in the cross-section. It is now possible to design quite complex structures, with different configurations, in short periods of time, thereby allowing designers to explore a range of alternatives. Hitherto, the necessary calculations were so complex that the first valid solution would have been accepted. Wherever possible, the system has been configured in such a way that the fundamental behaviour of prestressed concrete structures is built-in. Only when it is not possible for the system to calculate the value of a specific parameter does the designer have to specify one; and the designer is given guidance as to the range of allowable values, and why a particular parameter has to be chosen(G24). Such a choice may be on the basis of calculations or of heuristic rules. In this way, the designer is free to choose the optional parameters in a design, leaving the computer to do the drudgery. Values of parameters calculated by the system can be overridden by the designer if necessary, provided the structural criteria remain satisfied.
Dr C.J. Burgoyne
Several studies have been conducted in order to refine our knowledge of the behaviour of parallel-lay ropes. Testing of various types of yarn has been carried out to establish the variability of five different high-performance yarns, and these test results have been the basis for Monte-Carlo simulations of rope performance(G7). More advanced forms of the simulation techniques have been applied to stress-rupture behaviour(G1), a situation in which the general problems of viscoelasticity are compounded by the effects of bundle theory. Work on analysing long-term stress-rupture data has also continued(G6), which provides reassurance to potential users of aramid fibres. Other work, relating to the properties of the fibre as needed for a proper analysis of rope terminations, has also progressed, with particular emphasis on the transverse properties of large pads of fibre. The properties of individual filaments have been studied, but the bulk properties are significantly different(G4). Work has also been done, in association with the Department's opto-electronics group (q.v.), on the monitoring of parallel-lay ropes by optical fibres, so that breaks in individual yarns can be detected and their location ascertained(G30); this work is directly relevant to the use of these materials in deep water or in major structures, where other forms of monitoring are impractical and the cost of failure is very high.
Dr C.J. Burgoyne
Work on the behaviour of prestressed concrete beams with external tendons has concentrated on the problem of the rapid loss in load-carrying capacity as the beam forms a single major hinge under load(G5). Such a situation is bad when loading is by hydraulic jacks which shed load as they deflect, as in a laboratory situation; but it is much worse in real structures, where loading is by gravity, which continues to act. The result can be a sudden, snap-through type of failure, with a rapid release of energy. Although this work was started as a way of analysing the behaviour of beam tests with unbonded aramid tendons, the general result is applicable to all types of prestressed beams with unbonded tendons. The result is especially significant as this type of structure is now permitted by the codes used for the design of highway bridges.
Dr C.J. Burgoyne
Work has continued on the dynamic stability of very-long-span bridges (having spans over 2km) under wind loading. An improved model has been developed to examine the wind-induced oscillation behaviour of such highly flexible bridges in both twisting and vertical motions. The system uses four coupled non-linear oscillators, two to represent the structural behaviour (in plunge and in twist), and two to represent the wake (one from the leading edge and one from the trailing edge). Active control measures, such as moving winglets, and passive damping systems, such as tuned mass dampers, have been included in the model to investigate their effectiveness in mitigating dangerous oscillations of the structure. Several different structural geometries of bridge have been investigated. An assessment of the limits of bridge span due to wind-induced oscillations has been made by use of this model.
Dr C.J. Burgoyne
A study has been conducted on the lateral stability of precast concrete beams. As these become longer with the need for bridges to span widened motorways, they have become slimmer in order to reduce the weight for ease of transportation. They have thus become susceptible to lateral buckling, especially when hanging from a crane.
Dr C.J. Burgoyne
The accurate assessment of the load-carrying capacity of existing structures is becoming an increasingly important element of the work undertaken by civil engineers. In some instances structural assessment using conventional design- orientated analytical methods can lead to satisfactory structures being condemned as unsafe. Work has been done to modify the Wood-Armer equations, which are used extensively in the design of reinforced concrete, so that they are directly applicable to assessment(G13). The Wood-Armer equations aim to minimise the total amount of reinforcement required in design; however this optimality condition is irrelevant in assessment, where the reinforcement arrangement is known, and the equations can lead to conservative results. Simple guidance on how to apply the reformulated equations has been presented.
Dr C.R. Middleton
Dr C.T. Morley
Research on bridge assessment is continuing with emphasis on the development and evaluation of collapse analysis methods for assessing the strength and safety of concrete bridges. The COBRAS generalised yield-line collapse analysis program, developed within the group, has now been used to assess the strength of a number of concrete bridges as part of the national bridge assessment programme. Research goes on in validating this analysis method for a variety of bridge and load configurations, and extending the capabilities of this novel analysis program(G32).
A major research contract for the study of shear in beam-and-slab concrete bridges is continuing. Five half-scale bridge models have been tested in the laboratory to verify newly developed plasticity solutions for the collapse behaviour of this form of bridge(G23). A study comparing the predicted behaviour of these structures by use of plastic analysis and non-linear finite-element methods is in progress.
A collaborative research project is continuing, under contract, aimed at incorporating whole-life costing considerations into bridge assessment criteria, and in particular making allowance for the effects of material deterioration and actual vehicle loads on structural strength and safety. This project is part of an ongoing research effort aimed at developing and applying reliability analysis methods in bridge engineering and bridge management(G36,G37). A novel software package combining yield-line methods of structural assessment with reliability analysis has been developed, and it is being used to provide a rational method for ranking existing bridges to identify those most in need of strengthening or replacement.
An investigation into the use of non-destructive testing techniques for determining the location and degree of corrosion in the reinforcing bars of concrete structures is continuing in collaboration with an industrial partner.
Dr S. Pellegrino
Dr S.D. Guest
Dr Z. You
Applications of deployable structures are rapidly growing, and the Deployable Structures Group are currently involved in many projects that aim to develop new technologies. Highlights of the last academic year included a strong representation from Cambridge at the European Space Agency Workshop on Antenna Technologies, where, in addition to three papers authored by members of the Group(G16,G33,G38), work on collapsible-rib membrane reflectors done at Cambridge (see Annual Report for 1994-95) was presented by the Agency's own specialist on large reflectors.
An exhibit(G17), including several photographs and a working model of new deployable structures developed by the Group, has been sent to New York for the Buckminster Fuller Centennial Exhibition: Contemporary Developments in Design Science. The model consisted of a ring-shaped deployable space truss supporting a thin membrane that wraps around the centre; the deployment and retraction cycle is driven by an electric motor, controlled by a microprocessor-based unit developed in the Department's Electronics Development Unit.
A patent application(G34) has been filed by Lynxvale Ltd, the Cambridge University Company, to protect the invention of a novel structural mechanism with potential applications to a new type of retractable roof structures. This concept has been presented at an international conference(G39) and has now attracted the interest of a potential sponsor.
The Group have been awarded a large research contract from the European Space Agency to conduct research on deployable membrane reflectors.
Dr S. Pellegrino
Design studies of shape-memory alloy actuators have been carried out, resulting in the publication of a user's guide(G21,G22) for the design of hinges for deployable structures that are driven by thermomechanical transformations in nitinol wires. Work on stick-slip piezoelectric actuators has continued.
Dr S.D. Guest
A technique based on quaternion algebra has been developed for the analysis of spatial mechanisms, and it has been applied to the optimisation of a new design of solid surface deployable antenna(G14,G15,G16).
Work has continued on the analysis of symmetric structures and mechanisms. A new technique, based on the application of group representation theory to the force method has been developed, and has been successfully employed in the analysis of overconstrained mechanisms.
New work has started on the analysis of constrained multi-body systems. A variable partitioning technique has been formulated to simplify the integration of the equations of motion of these systems.
Dr S. Pellegrino
Experiments on thin-walled open-section cantilever booms subject to base shaking have shown unexpected subharmonic oscillations due to non-linear coupling between flexural and torsional modes. This behaviour has been characterised by means of dynamic stability maps, which are dependent upon the geometry of the boom(G26).
A robust implementation of the restoring-force method of non-linear dynamic identification methods has been developed. It has been validated by identifying different prestressed cable structures, where all system parameters can also be obtained from direct static measurements(G35).
Mr F.A. McRobie
Research is being undertaken into dynamical systems in general(G3), and in particular the dynamic behaviour of elastic systems, especially rods and shells. This study is focusing on the application of the methods of dynamical systems theory to two particular problems: the large displacement behaviour of rods and shells, and the phenomenon of modal interaction in shell vibrations. In the former, finite element implementations of the `director' models of Cosserat continua are being developed to study large-displacement and large-rotation dynamics of thin elastic bodies. In the latter, techniques of subspace dynamics are being investigated to reduce the governing partial differential equations of shell theory to a low-dimensional system of ordinary differential equations which can be used for studying phenomena such as modal interaction and parametric resonance.
Prof. C.R. Calladine
Work continues on the buckling of thin cylindrical silo shells under axial compressive load, in conjunction with Professor J.M. Rotter of the University of Edinburgh. Experiments on a melinex model shell, of diameter 0.9 m, have shown that a localised "uplift" imperfection at the base can produce an inward dent immediately above the imperfection when the shell is unloaded. Then, when the axial compressive load is steadily increased, the inward dent enlarges and migrates up the shell. Overall unstable buckling occurs only when this dent reaches a critical circumferential size. Such behaviour runs clean contrary to all known theories of shell buckling; and its discovery is stimulating radical and fresh thinking about the subject. Broadly similar behaviour has been found in small-scale tests on empty drinks cans. Another set of experiments on self-weight buckling of open-topped cylindrical shells made from silicone rubber, backed by finite-element computations, has led to a re-assessment of the role of boundary conditions and statical indeterminacy in the buckling performance of cylindrical shells.
Prof. C.R. Calladine
Prof. A.C. Palmer
A laboratory-scale study of thermal buckling of pipelines on the sea-bed is being conducted. The pipe is modelled by a strip of silicone rubber, and the thermal expansion of the pipe by a corresponding contraction of the expanded polystyrene bed, by means of long screws passing through it. The rig has successfully reproduced a field incident in terms of both the critical buckling temperature and the buckle wavelength. [See also PETROLEUM ENGINEERING, below.]
Prof. J. Heyman
Work continues on the application of structural mechanics to masonry construction, and a collection of papers has been published(G19). Many structural engineers have difficulty in extricating their thinking from the simple and comfortable linear-elastic theory; but such a theory fails to explain some simple but important structural situations. A book on some deeper aspects of structural theory has been published(G20).
Our undergraduate laboratories feature several recently-devised experiments that have been designed specifically to challenge students' understanding of the relationship between simple theories on the one hand and the more subtle and complicated realities of the physical world on the other. One such experiment focuses on several different aspects of the behaviour of beams that are beyond the explaining power of classical theory(G8).
Prof. C.R. Calladine
Dr M.A. El Hassan
Studies of the detailed conformation of DNA oligomers - naked or bound to proteins - in crystal databases continue. Most attention is being directed to the role of specific base-stacking arrangements in determining physical properties of the DNA molecule, such as intrinsic curvature and flexibility. A particularly strong correlation has been discovered between the magnitude of propeller-twist in a base-pair and the conformational mobility of the dinucleotide step of which it forms a part(G12). Progress is being made in understanding the relationship between the "inner" structure of the stack of base-pairs and the "outer" structure of the connected sugar-phosphate backbones. The geometry of irregularly twisted backbone helices is particularly awkward to describe in numerical terms. Two popular descriptions of work on the structural mechanics of DNA have appeared(G9,G13), and there is now a Japanese edition(G10) of a book published in 1992 - of which a second, enlarged edition is currently under preparation.
Occasional studies continue into the mechanics of liposomes. Physical chemistry plays a major role in determining the properties of these vesicles; but structural mechanics is the right tool for explaining some curious aspects of their behaviour.
G1. AMANIAMPONG, G., BURGOYNE, C.J. Monte-Carlo simulations of the time dependent failure of bundles of parallel fibres. European Journal of Mechanics A: Solids , 15, (2), 243-266 (1996).
G2. ASHOUR, A.F., MORLEY, C.T. Effectiveness factor of concrete in continuous deep beam. Journal of Structural Engineering, American Society of Civil Engeers, 122, (2), 169-178 (1996).
G3. BISHOP, S.R., McROBIE, F.A. Topological methods for transients of driven systems. Meccanica, 31, 225-234 (1996).
G4. BROWN, I.F., BURGOYNE, C.J. Anisotropic properties of Kevlar 49. Cambridge University Engineering Department Technical Report CUED/D-STRUCT/TR.152 (1995).
G5. BURGOYNE, C.J., CAMPOS, C.M.de O., GUIMARAES, G.B. Behaviour of beams with external tendons. Proceedings, FIP Symposium on Post-tensioned Concrete Structures, London, 865-871 (September 1996).
G6. BURGOYNE, C.J., GUIMARAES, G.B. Stress-rupture data for aramid fibres. Proceedings, 2nd International Conference on Advanced Composite Materials in Bridges and Structures, Montreal, Canada (August 1996).
G7. BURGOYNE C.J., MILLS, P.D. Effect of variability of high performance yarns on bundle strength. Proceedings, 2nd International Conference on Advanced Composite Materials in Bridges and Structures, Montreal, Canada (August 1996).
G8. CALLADINE, C.R. Some paradoxical experiments on beams. International Journal of Mechanical Engineering Education, 24, 37-48 (1996).
G9. CALLADINE, C.R., DREW, H.R. DNA structure. In: Encyclopedia of Molecular Biology and Molecular Medicine; Edited by R.A. Meyers, 2, 102-118 (VCH, Weinheim, 1996).
G10. CALLADINE, C.R., DREW, H.R. Understanding DNA (Japanese translation) (Kyoritsu Shuppan, Tokyo, 1996).
G11. DENTON, S.R., BURGOYNE, C.J. The assessment of reinforced concrete slabs and bridge decks. Structural Engineer, 74, (9), 147-152 (1996).
G12. EL HASSAN, M.A., CALLADINE, C.R. Propeller-twisting of base-pairs and the flexibility of dinucleotide steps. Journal of Molecular Biology, 259, 95-103 (1996).
G13. EL HASSAN, M.A.,CALLADINE, C.R. Structural mechanics of bent DNA. Endeavour, 20, 61-68 (1996).
G14. GUEST, S.D., PELLEGRINO S. A new concept for solid surface deployable antennas. Acta Astronautica, 38, (2), 103-113 (1996).
G15. GUEST, S.D., PELLEGRINO, S. Design optimization of a solid surface deployable reflector. Proceedings, IUTAM Symposium on Optimization of Mechanical Systems, Stuttgart, Germany (March 1995); Edited by D. Bestle, W. Schiehlen, 105-112. Solid Mechanics and its Applications, 43, 105-112 (Kluwer Academic, 1996).
G16. GUEST, S.D., PELLEGRINO, S. Development of a new solid surface deployable antenna. European Space Agency Workshop on Antenna Technologies, ESTEC, Noordwijk, the Netherlands, 6.3.1-6.3.11. ESA-WPP-100 (November 1995).
G17. GUEST, S.D., PELLEGRINO, S., YOU, Z. Deployable structures. An exhibit, including a working model, in the
Fuller Centenary Exhibition, Contemporary Developments in Design Science, New York (November 1995 - April 1996).
G18. HICKS, S.J., McCONNEL, R.E. The shear resistance of headed studs used with profiled steel sheeting. Proceedings, Composite Construction III, Irsee, Germany (June 1996).
G19. HEYMAN, J. Arches, Vaults and Buttresses. (A collection of 26 articles on masonry construction.) (Variorum, Aldershot, 1996).
G20. HEYMAN, J. Elements of the Theory of Structures (Cambridge University Press, 1996).
G21. HUANG, W., PELLEGRINO, S, Shape memory alloy actuators for deployable structures: phase I, Cambridge University Engineering Department Technical Report CUED/D-STRUCT/TR.163 (1996).
G22. HUANG, W., PELLEGRINO, S., BASHFORD, D.P. Shape memory alloy actuators for deployable structures. Proceedings, Conference on Spacecraft Structures, Materials and Mechanical Testing, Noordwijk, the Netherlands, 53-61. ESA SP-386 (March 1996) (European Space Agency, 1996).
G23. IBELL, T.J., MORLEY, C.T., MIDDLETON, C.R. Background to and developments in shear in reinforced concrete members. Cambridge University Engineering Department Report CUED/D-STRUCT/TR..151 (1996).
G24. JANARDHAN SUNDARAM H., BURGOYNE, C.J. A novel approach to prestressed concrete bridge design. Proceedings, FIP Symposium on Post-tensioned Concrete Structures, London, 747-754 (September 1996).
G25. JANARDHAN SUNDARAM, H., BURGOYNE, C.J., JAYASINGHE, M.T.R. Development of an expert system for the design of prestressed concrete bridges. 4th International Conference on the Application of Artificial Intelligence to Civil and Structural Engineering, Cambridge, 205-210 (August 1995).
G26. KING, S.A., PELLEGRINO, S. Parametric excitation and dynamic instabilities in thin-walled deployable booms. Proceedings, Conference on Spacecraft Structures, Materials and Mechanical Testing, Noordwijk, the Netherlands, 1153-1160. ESA SP-386 (March 1996) (European Space Agency, 1996).
G27. LEES, J.M., BURGOYNE, C.J. Influence of bond on rotation capacity of concrete pre-tensioned with AFRP. Proceedings, 2nd International Conference on Advanced Composite Materials in Bridges and Structures, Montreal, Canada (August 1996).
G28. LEES J.M., BURGOYNE, C.J. The use of aramid fibre reinforced plastics as prestressing tendons for concrete. Proceedings, FIP Symposium on Post-tensioned Concrete Structures, London, 607-614 (September 1996).
G29. LEES, J.M., GRUFFYDD-JONES, B., BURGOYNE, C.J. Expansive cement couplers - a means of pre-tensioning fibre reinforced plastic tendons. Construction and Building Materials, 9, (6), 413-423 (1995).
G30. LUDDEN, B.P., CARROLL, J.E., BURGOYNE, C.J. A distributed optical fibre sensor for offshore applications. Conference on Sensors and their Applications VII, Dublin, Ireland (September 1995); Edited by A.T. Augousti, 412-416 (IOP Publishing, 1996).
G31. McCONNEL, R.E., HICKS, S.J. The testing of three full-scale stub-girder floor beams. Structural Engineer, 74, (17), 289-294 (1996).
G32. MIDDLETON, C.R. Concrete bridge assessment using plastic collapse analysis. Proceedings, 14th Australasian Conference on the Mechanics of Structures and Materials, Hobart, Tasmania, Australia, 422-427 (December 1995).
G33. PELLEGRINO, S. Adaptive shape control of mesh reflectors. Proceedings, European Space Agency Workshop on Antenna Technologies, ESTEC, Noordwijk, the Netherlands, 3.1.1-3.1.9. ESA WPP-100 (November 1995).
G34. PELLEGRINO, S., YOU, Z. Expandable/Collapsible Structures, British Patent Application, 9601450.1 (January 1996).
G35. TAN, G.E.B., PELLEGRINO, S. Non-linear dynamic identification: an application to prestressed cable systems. Proceedings, Structural Dynamics - EURODYN `96, Florence, Italy (June 1996); Edited by G. Augusti, C. Borri, P. Spinelli, 941-948 (Balkema, 1996).
G36. THOFT-CHRISTENSEN, P., JENSEN, F.M., MIDDLETON, C.R., BLACKMORE, A. Revised rules for concrete bridges. Proceedings of International Symposium on the Safety of Bridges, Institution of Civil Engineers, London (July 1996).
G37. THOFT-CHRISTENSEN, P., JENSEN, F.M., MIDDLETON, C.R., BLACKMORE, A. Assessment of the reliability of concrete slab bridges. Proceedings of 7th International Federation of Information Processing Working Group 7.5 (IFIP WG7.5) Conference, Boulder, CO (April 1996).
G38. YOU, Z., PELLEGRINO, S. Structural concept of a deployable mesh reflector. Proceedings, European Space Agency Workshop on Antenna Technologies, ESTEC, Noordwijk, the Netherlands, 6.2.1-6.2.13. ESA WPP-100 (November 1995).
G39. YOU, Z., PELLEGRINO, S. New solutions for foldable roof structures. Mobile and Rapidly Assembled Structures II, Proceedings, 2nd International Conference, MARAS96, Seville, Space (June 1996); Edited by F. Escrig, C.A. Brebbia, 34-44 (Computational Mechanics Publications, 1996).