Architecture + Civil Engineering

The results of an experimental investigation into the use of a buffered impact damper for controlling the dynamic response of an MDOF (multi-degree-of-freedom) structure are presented in this paper. Free and forced vibration tests of a three-DOF test structure equipped with a buffered impact damper are performed to evaluate the resulting damping effect and impact characteristics. The effect of damper parameters, such as clearance, and excitation type on the performance of the impact damper is also investigated. The performance of the buffered impact damper is compared with that of an equivalent conventional rigid impact damper. It is found that the buffered impact damper not only significantly reduces the peak contact force and the associated accelerations and noise generated by collisions but can also substantially enhance the damping effect over a wide range of frequencies, encompassing the natural frequencies of the test structure. Copyright © 2008 John Wiley & Sons, Ltd.

The introduction of the Eurocodes for concrete design will alter the way that shear is approached for concrete structures. BS EN 1992-1-1 has adopted the variable angle truss model for shear, a more theoretically consistent approach than that used in BS 8110-1. The model ...

Using fabric formwork, it is possible to cast architecturally interesting, optimised structures that use up to 40% less concrete than an equivalent strength prismatic section, thereby offering significant embodied energy savings. This paper reports on the latest techniques for the design, optimisation and shape prediction of fabric formed concrete beams before new test results of an innovative anchorage method for both steel and fibre reinforced polymer longitudinal reinforcing bars are presented. Two 2m span beams were tested and the 'helically confined splayed bar' was shown to provide full anchorage in both cases. The two beams both exceeded their design capacity and showed remarkably similar behaviour at the serviceability limit state, with the steel reinforced section going on to display considerable ductility. Potential areas of future development are then highlighted, with the use of woven advanced composite fabrics as participating formwork for both beam and shell elements being of particular interest.

This paper describes recently-completed research at the University of Bath within the BRE Centre of Innovative Construction Materials in the field of fibre-reinforced polymer (FRP) materials for use in concrete structures. The research described has been carried out in collaboration with Parsons Brinckerhoff, Bristol. The use of FRP to strengthen concrete structures is a mainstream technology throughout the world, and specific research projects aimed at better understanding the underlying mechanics of this technique are described here. Further, the use of FRP to internally reinforce concrete structures is described in the context of effective use of all materials, coupled with the assurance of ductile behaviour.

Concrete, our most widely used construction material, is a fluid that offers the opportunity to economically create structures of almost any geometry. Yet this unique fluidity is seldom capitalised on, with concrete instead being cast into rigid prismatic moulds to create high material use structures with large carbon footprints. This paper will demonstrate how replacing conventional orthogonal moulds with a flexible system comprised primarily low cost fabric sheets can utilise the fluidity of concrete to create extraordinary possibilities for highly optimised, architecturally interesting, building forms.

Shape and vibration control of a linear exible structure by means of a new type of inertial slip-stick actuator are investigated. A nonlinear model representing the interaction between the structure and a six-degree-of-freedom Stewart platform system containing six actuators is derived, and closed-loop stability and performance of the controlled systems are investigated. A linearized model is also derived for design purposes. Quasistatic alignment of a payload attached to the platform is solved simply by using a proportional controller based on a linear kinematic model. The stability of this controller is examined using a dynamic model of the complete system and is validated experimentally by introducing random thermal elongations of several structural members. Vibration control is solved using an H 1 loop-shaping controller and, although its performance is found to be less satisfactory than desired, the nonlinear model gives good predictions of the performance and stability of the closed-loop system.

An impact damper is a freely moving mass, constrained by stops, located on a dynamic structural system to be controlled. As the system is excited, the impact mass moves relative to the structure resulting in impacts between the mass and the stops, transferring momentum from the structure to the impact mass, and dissipating energy as heat, noise and high frequency vibrations. At the point of impact, large accelerations are imparted to the structure, which may be undesirable, particularly for occupied structures. In order to reduce these high accelerations, it is proposed to incorporate a buffer region between the mass and the stop. Free and forced vibration tests of a system equipped with a buffered impact damper are used to study the resulting damping effect and impact characteristics. The performance of the buffered impact damper is compared with that of a conventional rigid impact damper. It is found that the buffered impact damper not only significantly reduces the accelerations, contact force and the associated noise generated by a collision but also enhances the level of vibration control. A possible reason for the enhanced control is postulated by examining impact behaviour. The investigation shows that the effective reduction of the vibration response depends not only on the magnitude of the contact force but also upon the contact time. r

Timber gridshells have become a very popular, efficient, sustainable and beautiful structural application of timber. However, given the slender laths involved in this form of construction, there is concern over the durability of timber for this purpose, and Glass FRP (GFRP) laths have been proposed as a possible substitution. This paper considers this possibility. It goes on to look at the possible use of Basalt FRP (BFRP) for the same purpose, from the perspective of its creep characteristics. It is shown that the use of GFRP gridshells is a viable form of construction, and that enhanced durability characteristics of BFRP could lead to their adoption for gridshells, given that the creep characteristics of basalt fibres presented here are comparable to those of glass fibres. An altogether different form of timber construction is that of joist-and-floorboard. In the UK, there are thousands of historic buildings which use this floor construction, and a sizeable proportion of this building stock now requires upgrade, strengthening and/or stiffening to allow these buildings to be fit for purpose into the future. This paper goes on to consider the possible use of Carbon FRP (CFRP) to strengthen and stiffen such timber floors. It is shown that such strengthening and stiffening is entirely feasible, offering the potential for greatly enhanced stiffness, in particular. Further, it is shown that mechanical shear connection between CFRP and timber is best conducted using perpendicular-positioned screws, rather than raked screws.

Abstract: This paper presents the influence of various flexural strengthening design criteria specified by three important design guidelines (ACI440, TR55, FIB14) on the resulting strength, ductility and conservativeness of FRP strengthened RC elements. Various ...

Large reductions in embodied carbon can be achieved through the optimisation of concrete 7 structures. Such structures tend to vary in depth along their length, creating new challenges for 8 shear design. To address this challenge, nineteen tests on non-prismatic steel reinforced concrete 9 beams designed using three different approaches were undertaken at the University of Bath. The 10 results show that the assumptions of some design codes can result in unconservative shear design 11 for non-prismatic sections. 12 13 Keywords: Shear, shear reinforcement, structural behaviour, non-prismatic beams, optimisation. 14 15 an effective shear force for design be given by Eq. (1), which is valid for members with shear 42 reinforcement: 43 (1) 44 Where V' Ed is the reduced design shear force; V Ed is the shear force on the cross section; V ccd is 45 the vertical component of force in the inclined compression chord and V td is the vertical component 46 of the inclined tension chord. M Ed is the moment on the cross section. 47

9 It can be seen that when subject to a uniformly distributed load, a prismatic, steel 10 reinforced concrete beam with constant longitudinal and transverse reinforcement 11 percentages is inefficient. Following simple optimisation routines can result in beams 12 whose flexural and shear capacities reflect the requirements of their loading envelope, 13 and such elements tend to be non-prismatic. Structural research into the use of flexible 14 formwork has developed simple methods for the creation of such elements to offer 15 material and embodied carbon savings of up to 40%. 16 17 However, the shear behaviour of such variable section steel reinforced concrete beams 18 has previously been an area of confusion for designers, who must often rely on 19 empirical relationships derived from prismatic beam tests. This paper presents the 20 results of new tests undertaken at the University of Bath on tapered concrete beams 21 designed using BS EN 1992-1-1 [1], the compressive force path method and a strut and 22 tie model, in which digital image correlation was used to analyse the specimens. 23 24 Using the 'MatchID' program, strain distributions in each of the specimens during 25 loading were determined, with the results allowing important comparisons to be drawn 26 between the various design methods. A digital image correlation (DIC) technique was 27 subsequently used to verify new proposals for the shear design of non-prismatic 28 concrete beams, which aim to provide improved guidance for designers of optimised 29 concrete structures. 30 31 32 33 34 35 36

By replacing conventional concrete moulds with flexible sheets of permeable fabric, the construction of optimised concrete elements that provide material savings of up to 40% when compared with an equivalent strength prismatic member is possible. This paper details the results of recent tests undertaken at the Building Research Establishment Centre for Innovative Construction Materials at the University of Bath that demonstrate significant additional durability advantages for fabric-cast concrete. Using accelerated test methods, 50% average reductions in both the non-steady state chloride diffusion coefficient and carbonation coefficients were found when comparing concrete samples cast against permeable and impermeable surfaces. Sorptivity, surface hardness and scanning electron microscopy tests demonstrate further beneficial changes in the fabric-cast concrete. The combined results demonstrate that fabric formwork may be used to create structures optimised for strength and durability.

Using fabric formwork, it is possible to cast architecturally interesting, optimised structures that use up to 40% less concrete than an equivalent strength prismatic section, offering potentially significant embodied energy savings in new concrete structures. Fabric formwork allows elegant designs to be realised but its use also presents some unique challenges, including the practical provision of transverse reinforcement in slender, non-prismatic beam elements. This paper details how these challenges have been overcome with the use of ultra-high performance fibre reinforced concrete. Methods for the design, optimisation and construction of such elements cast using fabric formwork are illustrated and structural tests data are presented.

This paper provides the background and guidance relating to the design methods proposed in The Concrete Society's Technical Report 55 (TR55) third edition for the shear strengthening of rectangular and circular reinforced concrete members using fibre composite materials.

This paper looks at the influence of various parameters in flexural strengthening design specifications, as prescribed by three major international design guidelines namely, ACI440, TR55 and FIB14. A four-level conservativeness frame-work has been highlighted using which flexural conservativeness flowchart is developed to demonstrate how conservativeness is integrated within strengthening design processes at various levels. Various generalised mathematical relationships for flexural strengthening design are also described. Based on these relationships the evaluation of flexural design criteria and their influence on strengthening design, with particular emphasis on residual conservativeness in the design solutions, are presented. The results show that there is significant variation in residual conservativeness of the resultant design solutions obtained using different strengthening design guidelines. Further, it has been shown how the possibility of debonding or rupture failure of t...

Synopsis: Many concrete bridges related to railways in the U.K. consist of prestressed rectangular concrete beams, post-tensioned together transversely to aid lateral distribution of load; this bridge type has been repeatedly flagged as having insufficient shear capacity. Sixteen tests on small-scale beams, which are scaled-down replica models of the actual bridge beams, are presented. The specimens are tested under a four-point loading system and are both prestressed (PRC) with and without stirrups and non-prestressed (RC) with and without stirrups, to provide full understanding of their shear behaviour. Four further tests are then presented on RC beams strengthened in shear with FRP bars inserted from the soffit into pre-drilled holes and fixed in place using epoxy resin; this method allows strengthening in cases where the webs are inaccessible. Comparisons are made with current code predictions for the strength of all specimens. The results show that unstrengthened RC beams behav...

Based on the high precision direct (HPD) integration scheme for linear systems, a high precision direct integration scheme for non-linear (HPD-NL) dynamic systems is developed. The method retains all the advantages of the standard HPD scheme (high precision with large time steps, computational efficiency) whilst allowing non-linearities to be introduced with little additional computational effort. In addition, limitations on minimum time-step resulting from the approximation that load varies linearly between time-steps are reduced by introducing a polynomial approximation of the load. This means that, in situations where a rapidly varying or transient dynamic load occurs, a larger time-step can still be used whilst maintaining a good approximation of the forcing function and, hence, accuracy of the solution. Numerical examples of the HPD-NL scheme compared with Newmark's method and the fourth order Runge-Kutta (Kutta 4) method are presented. The examples demonstrate the high accuracy and numerical efficiency of the proposed method.

Timber gridshells have become a very popular, efficient, sustainable and beautiful structural application of timber. However, given the slender laths involved in this form of construction, there is concern over the durability of timber for this purpose, and Glass FRP (GFRP) laths have been proposed as a possible substitution. This paper considers this possibility. It goes on to look at the possible use of Basalt FRP (BFRP) for the same purpose, from the perspective of its creep characteristics. It is shown that the use of GFRP gridshells is a viable form of construction, and that enhanced durability characteristics of BFRP could lead to their adoption for gridshells, given that the creep characteristics of basalt fibres presented here are comparable to those of glass fibres. An altogether different form of timber construction is that of joist-and-floorboard. In the UK, there are thousands of historic buildings which use this floor construction, and a sizeable proportion of this building stock now requires upgrade, strengthening and/or stiffening to allow these buildings to be fit for purpose into the future. This paper goes on to consider the possible use of Carbon FRP (CFRP) to strengthen and stiffen such timber floors. It is shown that such strengthening and stiffening is entirely feasible, offering the potential for greatly enhanced stiffness, in particular. Further, it is shown that mechanical shear connection between CFRP and timber is best conducted using perpendicular-positioned screws, rather than raked screws.