Numerical analysis of the embedded abutments of integral bridges

A numerical case study is presented, which investigates the performance of embedded integral bridge abutments and the maximum magnitude and distribution of earth pressure within the retained soil. The Three Surface Kinematic Hardening model is adopted in the numerical analysis, which successfully reproduced key features of soil behaviour under small strain cyclic loading. The results show that the earth pressures behind the abutment change in a complicated way, while the largest bending moments in the abutment wall increase with cycles at a decreasing rate, with a final value far less than the one derived from current design standards. A number of factors have been investigated and the influences of the wall flexure and soil stiffness are highlighted. The research results will lead to safe and economic design of such structures

Crack development and effect of ageing on performance of composite shell sprayed concrete tunnel linings

Recent development and application of composite sprayed concrete lining (SCL) in major tunnelling projects have raised concerns on its short- and long-term flexural performance. Little literature has been found on the short-term crack development and the long-term ageing effect on composite SCL. Understanding of these issues will facilitate the efficient design of composite SCL. Four-point bending tests were performed on composite SCL beams to examine some aspects of these concerns. It is concluded that composite SCL beams have high residual flexural capacity; spray-applied membrane can maintain its integrity under big cracks; although the ageing effect reduces the ductility ratio of composite SCL beams in the long term, the absolute residual flexural strength increases. Conclusions drawn from the test results are compared with the current SCL tunnel design methods and the implication of differences is discussed

Interface parameters of composite sprayed concrete linings in soft ground with spray-applied waterproofing

The presence of a spray-applied waterproofing membrane between the primary and secondary lining layers is important to the behaviour of a composite sprayed concrete lined (SCL) tunnel in soft ground. In order to confirm the feasibility of the composite shell lining concept, the structural adequacy of the concrete-membrane interfaces under the effects experienced in a typical tunnel needs to be investigated. This paper presents a series of laboratory tests on samples cut from composite sprayed concrete panels, to which uniaxial compression, direct tension and direct shear loadings are applied over both short and long-term timeframes under conditions of ambient atmospheric humidity. Test results show that the interfaces are capable of resisting significant compression, tension and shear in both short- and long-term. Failures under these actions should not occur in a typical shallow SCL tunnel, and a degree of composite action between primary and secondary layers should be expected. Influence of substrate roughness and membrane thickness on the measured interface properties has been quantified. Overall, this investigation confirms the existence of composite action for composite sprayed concrete linings in soft ground, and provides parameters based on test results for further research and design

Visualization of fresh cut timber deformation by photogrammetry

Understanding the mechanical behavior of fresh cut timber, in which the natural moisture content has been retained, has application in predicting the behavior of living tree elements such as branch/stem joints, potentially inspiring structural designs through biomimicry. This project develops a process of strain imaging using particle image velocimetry to analyze behavior of timber samples freshly cut from oak tree joints and tested in tension. The timber surface was not coated so the fiber response could be visualized directly. Load was applied in steps and different methods for comparing images were trialled, including a sequential method in which strain is accumulated progressively from image to image and a first-to-last comparison. Sample flexibility caused significant deformation in the camera field of view, and so the analysis methodology was modified so that each image was compared sequentially with the first with the target area in the image for strain calculation expanded as the test proceeded. This resulted in strain contour plots able to show the impending failure of the component as the tension is applied

Climate change and extreme wind effects on transmission towers

Climate change poses a major threat to electricity power infrastructure due to expected increases in the magnitude and frequency of extreme storm events. This paper uses a methodology for assessment of the vulnerability of UK transmission tower infrastructure to such events, within a framework of performance-based engineering. The challenge of estimating future storm magnitudes is addressed by applying a change factor methodology to present-day wind speeds using information provided by the 2009 UK climate change projections. A Weibull distribution is employed to obtain wind speeds for storm events at different recurrence intervals. Wind loading on the structure and cables is then determined using Eurocodes, and the structure is analysed using pseudo-static finite-element analysis, considering material and geometrical non-linearity as well as linear and non-linear buckling effects. The outcome of the research is that, despite a significant projected increase in wind velocities due to climate change, the typical tower analysed in the study continues to perform satisfactorily at all hazard levels. If this performance can be demonstrated more generally across the UK transmission tower infrastructure network, then it is likely that the cause can be traced back to the high factor of safety applied in the original design of the towers

Numerical calibration of mechanical behaviour of composite shell tunnel linings

Composite shell linings consist of primary and secondary sprayed concrete linings separated by a layer of spray-applied waterproofing membrane. In order to design such a lining configuration, a calibrated numerical simulation approach is needed and the impact of interface properties on the composite mechanical behaviour should be understood. A programme of laboratory tests was carried out on beam samples cut from composite shell test panels and subjected to four-point bending under short-term loading. A range of membrane thicknesses and substrate roughness were compared and composite mechanical behaviour quantification methods developed. The behaviour of composite beams was understood and the strain distribution across composite lining cross-section was identified. A numerical model by the finite difference method was then set up for the beams and verified against the test data. With interface stiffnesses obtained from previous element tests, the composite beam model is capable of predicting the strain distribution across the cross-section and real behaviour of composite beam members to within an acceptable level of accuracy taking into account variations arising from workmanship. Sensitivity studies were carried out to understand the impact of interface properties and membrane interface position on the degree of composite action

Simulating composite behaviour in SCL tunnels with sprayed waterproofing membrane interface : a state-of-the-art review

Introduction of sprayed waterproofing has led to innovation of composite sprayed concrete lined (SCL) tunnels, where placing the waterproofing between primary and secondary layers gives potential for composite structural action, by transmission of tension, compression and shear stresses across the interface. Numerical analysis is required to design such structures taking into account soil-structure interaction and staged construction, but there is currently very limited guidance on how to conduct such analyses. This paper reviews use of numerical analysis to simulate composite SCL tunnels, focussing on soft ground tunnelling. It introduces types of sprayed membrane, their benefits in design and current industry practice for simulating the sprayed membrane interface. Numerical strategies for simulating composite action and their verification against laboratory test data are then described. Recommendations are made of design principles to optimise design of SCL tunnels with spray-applied waterproofing. Further opportunities for research on this topic are discussed

An advanced polymer composite and concrete slab system

This paper reports on an investigation into the feasibility of a structural slab system comprising of a sheet of carbon fibre reinforced polymer (CFRP) in tension and concrete in compression. The CFRP serves as permanent formwork as well as tension reinforcement. It was found that the slab system performed satisfactorily at ultimate and serviceability limit states. A design for a slab for use in a typical building is presented