Civil and Environmental Engineering

In principle, the research-teaching nexus should be seen as a two-way link, showing not only ways in which research supports teaching but also ways in which teaching supports research. In reality, the discussion has been limited almost entirely to the first of these practices. This paper presents a case study in which some student field-trip construction projects, originally designed as a teaching tool, were also used to undertake environmental research. The research consisted of testing the implementation of a tool for assessing the environmental impact of construction sites. It was conducted at the Imperial College London Constructionarium Field Module 2012 at the National Construction College, in England. The findings highlighted the unexploited research potential of the Constructionarium teaching tool specifically and of field-trip teaching events generally. To a lesser extent, the students also learned about the research content and process. This experience could be extended to other field-trip teaching events.

Composite beams with large web openings are often used, and their design is controlled by Vierendeel bending at the four corners of each opening, which is assisted by local composite action with the floor slab. Development of this Vierendeel bending resistance may be limited by pull-out failure of the shear connectors. In this paper, a non-linear elasto-plastic finite element model of a composite beam with web openings was used to investigate this mode of pull-out failure. A test was performed on a typical composite slab in which the shear connectors were subject to pure tension and the failure load was 67 kN, which is approximately 70% of the longitudinal shear resistance. The results of the finite element model are compared against those obtained using the established design theory, that does not limit the vertical pull-out resistance of the shear connectors. It is shown that the local bending resistance due to composite action should be reduced when limited by pull-out of the shear connectors. A parametric study investigated the effect of openings of 600 to 1200 mm length. A simple model is developed to establish the Vierendeel bending resistance, when limited by pull-out of the shear connectors.

The first phase of the Next Generation Attenuation (NGA) project has now finished, resulting in the publication of five new sets of empirical ground-motion models for PGA, PGV and response spectral ordinates. These models mark a significant advancement in the state-of-the-art in empirical ground-motion modelling and include many effects that are not accounted for in existing European equations. Under the assumption that the Euro-Mediterranean database from which the European relationships are derived is unlikely to drastically change in the near future, a prudent question to ask is: can the NGA models be applied in Europe? In order to answer this question, the NGA model of Boore and Atkinson (PEER Report 2007/01, Pacific Earthquake Engineering Research Center, Berkeley, CA, 234 pp., 2007), which is shown to be representative of the NGA models as a suite, is compared with the dataset used for the development of the most recent European empirical groundmotion models for response spectral ordinates and peak ground velocity. The comparisons are made using analyses of model residuals and the likelihood approach of Scherbaum et al. (Bull Seism Soc Am 94(6):2164-2185. The analyses indicate that for most engineering applications, and particularly for displacement-based approaches to seismic design, the NGA models may confidently be applied within Europe. Furthermore, it is recommended that they be used in conjunction with existing European models to provide constraint on finite-fault effects and non-linear site response within logic-tree frameworks. The findings also point to the potential benefits of merging the NGA and European datasets.

Selecting, scaling and matching accelerograms are critically important to engineering design and assessment, enabling structural response to be determined with greater confidence and through fewer analyses than if unscaled accelerograms are employed. This paper considers the response of an 8-storey multipledegree-of-freedom reinforced concrete structure to accelerograms selected, linearly scaled or spectrally matched using five different techniques. The first method consists of selecting real records on the basis of seismological characteristics, while the remaining methods make an initial selection on the basis of magnitude and spectral shape before (1) scaling to the target spectral acceleration at the initial period; (2) scaling to the target spectrum over a range of periods; (3) using wavelet adjustments to match the target spectrum and (4) using wavelet adjustments to match multiple target spectra for multiple damping ratios. The analyses indicate that the number of records required to obtain a stable estimate of the response decreases drastically as one moves through these methods. The exact number varies among damage measures and is related to the predictability of the damage measure. For measures such as peak roof and inter-storey drift, member end rotation and the Park and Ang damage index, as few as one or two records are required to estimate the response to within ±5% (for a 64% confidence level) if matching to multiple damping ratios is conducted. Bias checks are made using predictive equations of the expected response derived from the results of 1656 nonlinear time-domain analyses of the structure under the action of unscaled accelerograms.

The first ground-motion prediction equation derived from European and Middle Eastern strong-motion data was published more than 30 years ago; since then strong-motion networks and the resulting databank of accelerograms in the region have expanded significantly. Many equations for the prediction of peak ground-motion parameters and response spectral ordinates have been published in recent years both for the entire Euro-Mediterranean and Middle Eastern region as well as for individual countries within this region. Comparisons among empirical ground-motion models for these parameters, developed using large regional datasets, do not support the hypothesis of there being significant differences in earthquake ground-motions from one area of crustal seismicity to another. However, there are certain regions within Europe-affected by different tectonic regimes-for which the existing pan-European equations may not be applicable. The most recent European equations make it possible to now implement overdue modifications to the presentation of seismic design actions in Eurocode 8 that allow an improved approximation to the target uniform hazard spectrum (UHS). Using these recent equations, this study outlines a new approach via which an approximation to the UHS may be constructed using hazard maps calculated for peak ground velocity and the corner period T D in addition to the maps for peak ground acceleration that underpin the current stipulations of Eurocode 8.

The occurrence of a damaging earthquake provides an opportunity to compare observed and estimated damage, provided that detailed observations of the earthquake effects are made in the field. A question that arises is whether such comparisons can provide the basis for validation of an earthquake loss model. In order to explore this issue, a case study loss model for the northern Marmara region has been set up and the losses have been calculated for various ground-motion fields that arise when different assumptions are made about the ground-motion variability. In particular, the influence of removing the inter-event variability for a scenario earthquake and modeling spatial correlation among ground motions is studied. Further analyses are conducted assuming that a number of accelerograms are available within the region and that knowledge of spatial correlations among ground motions can therefore be used to better predict the motions at sites in the vicinity of the recording stations. The results demonstrate that unless one has a dense network of accelerographs (commensurate with the geographical resolution of exposure), then the variability in the losses cannot be sufficiently reduced to allow validation of the loss model.

Many modern applications in earthquake engineering require the use of pseudoacceleration response spectra or relative displacement response spectra calculated for damping ratios other than the commonly assumed 5% of critical. The simplest way to obtain such spectra is to derive ratios of the spectral ordinates at the desired damping ratio to the 5% damped spectrum, which can then be applied as scaling factors. These scaling factors have previously been shown to be mildly dependent upon period as well as strongly dependent upon duration. In this paper, the dependence of the scaling factors with respect to both duration and the number of equivalent load cycles is quantified. Generic equations are derived that may be used to estimate the spectral response over a wide range of damping ratios as a function of significant duration ͑both D 5-75% and D 5-95% ͒, and number of cycles ͓N rr ͑2.0͔͒. While the dependence upon these predictor variables is clear, the derived relationships cannot be directly incorporated into design codes due to the fact that strong ground-motion duration and number of equivalent cycles are generally not specified as part of seismic design actions.

A long structural system with an unstable (subcritical) post-buckling response that subsequently restabilizes typically deforms in a cellular manner, with localized buckles first forming and then locking up in sequence. As buckling continues over a growing number of cells, the response can be described by a set of lengthening homoclinic connections from the fundamental equilibrium state to itself. In thelimit, this leads to a heteroclinic connection from the fundamental unbuckled state to a post-buckled state that is periodic. Under such progressive displacement the load tends to oscillate between two distinct values. The paper is both a review and a pointer tofuture research. The response is described via a typical system, a simple but ubiquitous model of a strut on a foundation which includes initially-destabilizing and finally-restabilizing nonlinear terms. A number of different structural forms, including the axially-compressed cylindrical shell, a typical sandwich structure, a model of geological folding and a simple link model are shown to display such behaviour. A mathematical variational argument is outlined for determining the global minimum postbuckling state under controlled end displacement (rigid loading). Finally, the paper stresses the practical significance of a Maxwell-load instability criterion for such systems. This criterion,defined under dead loading to be where the pre-buckled and post-buckled state have the same energy, is shown to have significance in the present setting under rigid loading also. Specifically, the Maxwell load is argued to be the limit of minimum energy localized solutions as end-shortening tends to infinity.

The philosophical aspects of applying the principles of biomimicry are explored in a case study of structural design. Integrating structural engineering with services engineering can be regarded, to some extent, as taking principles from biological systems and applying them to large-scale conceptual design. The end-product discussed herein a so-called load-bearing duct, a functional naturally ventilated multi-storey office building that takes the applied loading efficiently both structurally and cost-effectively giving it the potential to be sustainable throughout its design life.

A steel column that is reinforced by prestressed stays generally has an increased strength in axial compression. A geometrically nonlinear model accounting for the post-buckling behaviour of the stayed column is formulated using the Rayleigh–Ritz method and then validated using the finite element method. It is found that the post-buckling behaviour is strongly linked to the level of the initial prestress. As the prestress is increased, the following different levels of the responses can be observed in sequence: initial Euler buckling that subsequently restabilizes strongly, the critical load increasing with a post-buckling path that is either stable or unstable, an upper limit for the critical load where the post-buckling is unstable after an initially rather flat response. These findings are important for designers aiming to achieve safer and more efficient designs for this structural component.

A steel column that is reinforced by prestressed stays, generally has an increased strength in axial compression. In the past, greater emphasis was placed on obtaining a higher critical buckling load. However, detailed knowledge of the post-buckling behaviour is important to ensure the safety and efficiency of the structure. The current work examines the buckling behaviour of a stayed column with geometrical imperfections, and stress limitation relating to possible material failure. A geometrically nonlinear model accounting for imperfect buckling behaviour of a stayed column was formulated using the Rayleigh–Ritz method, and then validated, using the finite element method. It is shown from these studies that the system tends to be most sensitive to imperfections at a prestress level that yields the highest critical load, and that the real maximum load capacity seems to increase as the prestress increases with a given configuration. The findings suggest that the optimal prestress should be greater than that found from using the previous convention that was based on linear analysis.

The behaviour of tubes under conditions of pure bending is investigated for the cases where the material of which they are constructed is either orthotropic or of various Poisson's ratios. Large deflections and moderate nonlinear strains are considered and the modelling incorporates Timoshenko beam theory thereby allowing non-zero shear strains to develop. This in turn makes axially inhomogeneous deformation of the cross-section possible and, in particular, the compressed side can develop wrinkling. Numerical solutions are presented for various material types and tube dimensions and some interesting phenomena, such as mode interaction and jumping, are demonstrated.