The cartoon shows the 'CCC Office' (Christchurch City Council) as a small ramshackle wooden building in a desert; bits of animal skeleton lie around and there are saguaro cactus and tumbleweed. A cowboy has arrived and asks 'So... Can I speak to the Deputy, Deputy, Deputy, Assistant Sheriff?' Context - A reference to layers of officialdom in Christchurch as the city struggles to rebuild itself as well as many councillors being away on holiday while the quake problems continue.
Quantity: 1 digital cartoon(s).
Gravelly soils’ liquefaction has been documented since early 19th century with however the focus being sand-silts mixture – coarse documentation of this topic, that gravels do in fact liquefy was only acknowledged as an observation. With time, we have been impacted by earthquakes, EQ causing more damage to our property: life and environment-natural and built. In this realm of EQ related-damage the ground or soils in general act as buffer between the epicentre and the structures at a concerned site. Further, in this area, upon the eventual acknowledgement of liquefaction of soils as a problem, massive efforts were undertaken to understand its mechanics, what causes and thereby how to mitigate its ill-effects. Down that lane, gravelly soils’ liquefaction was another milestone covered in early 20th century, and thus regarded as a problematic subject. This being a fairly recent acknowledgement, efforts have initiated in this direction (or area of particle size under consideration-gravels>2mm), with this research outputs intended to complement that research for the betterment of our understanding of what’s happening and how shall we best address it, given the circumstances: socio (life) - environment (structures) - economic (cost or cost-“effectiveness’) and of course political (our “willingness” to want to address the problem). Case histories from at least 29 earthquakes worldwide have indicated that liquefaction can occur in gravelly soils (both in natural deposits and manmade reclamations) inducing large ground deformation and causing severe damage to civil infrastructures. However, the evaluation of the liquefaction resistance of gravelly soils remains to be a major challenge in geotechnical earthquake engineering. To date, laboratory tests aimed at evaluating the liquefaction resistance of gravelly soils are still very limited, as compared to the large body of investigations carried out on assessing the liquefaction resistance of sandy soils. While there is a general agreement that the liquefaction resistance of gravelly soils can be as low as that of clean sands, previous studies suggested that the liquefaction behaviour of gravelly soils is significantly affected by two key factors, namely relative density (Dr) and gravel content (Gc). While it is clear that the liquefaction resistance of gravels increases with the increasing Dr, there are inconclusive and/or contradictory results regarding the effect of Gc on the liquefaction resistance of gravelly soils. Aimed at addressing this important topic, an investigation is being currently carried out by researchers at the University of Canterbury, UC. As a first step, a series of undrained cyclic triaxial tests were conducted on selected sand-gravel mixtures (SGMs), and inter-grain state framework concepts such as the equivalent and skeleton void ratios were used to describe the joint effects of Gc and Dr on the liquefaction resistance of SGMs. Following such experimental effort, this study is aimed at providing new and useful insights, by developing a critical state-based method combined with the inter-grain state framework to uniquely describe the liquefaction resistance of gravelly soils. To do so, a series of monotonic drained triaxial tests will be carried out on selected SGMs. The outcomes of this study, combined with those obtained to date by UC researchers, will greatly contribute to the expansion of a worldwide assessment database, and also towards the development of a reliable liquefaction triggering procedure for characterising the liquefaction potential of gravelly soils, which is of paramount importance not only for the New Zealand context, but worldwide. This will make it possible for practising engineers to identify liquefiable gravelly soils in advance and make sound recommendations to minimise the impact of such hazards on land, and civil infrastructures.
Structural engineering is facing an extraordinarily challenging era. These challenges are driven by the increasing expectations of modern society to provide low-cost, architecturally appealing structures which can withstand large earthquakes. However, being able to avoid collapse in a large earthquake is no longer enough. A building must now be able to withstand a major seismic event with negligible damage so that it is immediately occupiable following such an event. As recent earthquakes have shown, the economic consequences of not achieving this level of performance are not acceptable. Technological solutions for low-damage structural systems are emerging. However, the goal of developing a low-damage building requires improving the performance of both the structural skeleton and the non-structural components. These non-structural components include items such as the claddings, partitions, ceilings and contents. Previous research has shown that damage to such items contributes a disproportionate amount to the overall economic losses in an earthquake. One such non-structural element that has a history of poor performance is the external cladding system, and this forms the focus of this research. Cladding systems are invariably complicated and provide a number of architectural functions. Therefore, it is important than when seeking to improve their seismic performance that these functions are not neglected. The seismic vulnerability of cladding systems are determined in this research through a desktop background study, literature review, and postearthquake reconnaissance survey of their performance in the 2010 – 2011 Canterbury earthquake sequence. This study identified that precast concrete claddings present a significant life-safety risk to pedestrians, and that the effect they have upon the primary structure is not well understood. The main objective of this research is consequently to better understand the performance of precast concrete cladding systems in earthquakes. This is achieved through an experimental campaign and numerical modelling of a range of precast concrete cladding systems. The experimental campaign consists of uni-directional, quasi static cyclic earthquake simulation on a test frame which represents a single-storey, single-bay portion of a reinforced concrete building. The test frame is clad with various precast concrete cladding panel configurations. A major focus is placed upon the influence the connection between the cladding panel and structural frame has upon seismic performance. A combination of experimental component testing, finite element modelling and analytical derivation is used to develop cladding models of the cladding systems investigated. The cyclic responses of the models are compared with the experimental data to evaluate their accuracy and validity. The comparison shows that the cladding models developed provide an excellent representation of real-world cladding behaviour. The cladding models are subsequently applied to a ten-storey case-study building. The expected seismic performance is examined with and without the cladding taken into consideration. The numerical analyses of the case-study building include modal analyses, nonlinear adaptive pushover analyses, and non-linear dynamic seismic response (time history) analyses to different levels of seismic hazard. The clad frame models are compared to the bare frame model to investigate the effect the cladding has upon the structural behaviour. Both the structural performance and cladding performance are also assessed using qualitative damage states. The results show a poor performance of precast concrete cladding systems is expected when traditional connection typologies are used. This result confirms the misalignment of structural and cladding damage observed in recent earthquake events. Consequently, this research explores the potential of an innovative cladding connection. The outcomes from this research shows that the innovative cladding connection proposed here is able to achieve low-damage performance whilst also being cost comparable to a traditional cladding connection. It is also theoretically possible that the connection can provide a positive value to the seismic performance of the structure by adding addition strength, stiffness and damping. Finally, the losses associated with both the traditional and innovative cladding systems are compared in terms of tangible outcomes, namely: repair costs, repair time and casualties. The results confirm that the use of innovative cladding technology can substantially reduce the overall losses that result from cladding damage.
