Approval for construction of a new:
library in Cambridge
The Betty and Gordon Moore Library gets underway
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Thanks to a donation from Dr Gordon Moore and his wife Betty, the University
has given the go-ahead for the construction of a new 7.5 million pound
library for the
physical Sciences, technology and mathematics adjacent to the Centre for
Mathematical Sciences. Dr Moore is the Chairman Emeritus of Intel Corporation,
which he co-founded in 1968. In the mid 1960s, while director of development
at Fairchild Semiconductor, he made astonishingly accurate predictions
about the growth of computing power, which together became known as
`Moore's Law' which, combined with the microprocessor, first introduced by
Intel in 1971, is the foundation for today's microcomputer revolution.
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Artist's impression of the new Betty and Gordon Moore Library
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The
Betty and Gordon Moore Library will bring together collections of
scientific resources currently scattered across Cambridge and will also
provide high quality links to electronic data sources and electronic
retrieval systems, which will help make it a new intellectual focus for
Cambridge science and technology. The new library will be part of
Cambridge University Library, which is a legal deposit library and so
entitled to claim a copy of every book and journal published in the UK.
The building that will house the new Library has already been designed as
part of the overall development of the Clarkson Road site. The Library will
be circular in form, unique in Cambridge but with precedents in other
times, such as the library designed by Thomas Jefferson at the
University of Virginia in 1817. The new Library will provide a home for
Professor Stephen Hawking's papers and electronic archive, which he has
offered to donate to the University. Initially, these papers will
include Professor Hawking's hand-written material dating from before
1973 and an early draft of A Brief History of Time. In the longer term,
the Library will provide a digitised archive for more recent material
stored in electronic media by Professor Hawking.
The archive will
continue a great Cambridge tradition of preserving the papers of
famous scientists for future study.
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Structural Engineering
By Richard Harris, Buro Happold
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The buildings that will form the new Centre for Mathematical Sciences are
being constructed principally from reinforced concrete. The structure
of the pavilions and the central core are highly co-ordinated with the
building services and environ-mental engineering. The concrete structure
is designed to exploit its thermal capacity and this is reflected in
the architecture of the buildings.
From the earliest concept designs,
it was recognised that something special should be created for the
structure of roof which will cover the central core.The architect's
design concept produced a central sunken core area, topped by a grass
roof. The ground to the sides of the core is shaped, so that natural
daylight can be brought into the lower level. At the upper ground level,
the roof covers the large meeting and circulation area spanning a
maximum of 21 metres. For a building, the geometry is complex and the
loading from the grass roof is high.
For ease of waterproofing,
the roof slab was to be constructed in concrete, but a number of
options were considered for the support structure. The choice lay
between an arch or a beam structure. An arch form resists the applied
loads by a combination of axial compression and bending moment. This
is in contrast to a beam which only resists the applied forces by
flexing and developing bending moment. Clearly, the arch form will
deflect very much less than a beam for a particular applied load.
A common problem with using arch structures for building roofs is that
minimum headroom is needed at the edge. This means that the springing
point needs to be raised which creates a problem in carrying the arch
thrust down to the floor level. A number of structural schemes were
considered, including a balanced cantilever in structural steel and a
portal frame in reinforced concrete. However, after weighing up the
advantages and disadvantages a buttressed arch structure was chosen.
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Buro Happold are the civil and structural engineering consultants for
the Centre for Mathematical Sciences. This information is issued to the
contractor (John Laing Construction Ltd) who, through the appointment
of specialist sub-contractors, constructs the building.
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The geometry of the central core has not been easy to construct.
The space tapers and the arches are arcs of circles but each is of a
different radius. The problem of the high point loads and the provision
of tolerance was solved by using high grade cast iron castings at the
arch springing point with a pin connection enabling the loads from the
arches to be accurately analysed. Iron castings are commonly used in
mechanical engineering but their use in construction represented a
particular challenge. So that they can carry the intense loads at
the end of the arches, the cast iron pin assemblies were made to an
extremely low tolerance. By using a steel frame as a skeleton in
the buttresses, the attachment points for the castings could be
very accurately positioned.
The castings were made by BAS Castings Ltd. All the Steel Arches were
successfully erected by the steelwork sub-contractor (Hawk Engineers)
just before Christmas 1998. The concrete roof was cast in situ and the
waterproofing and planting system will be a specialist system provided
by Euroroof Ltd.
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Avoiding structural failure
By J R Willis, Professor of Theoretical Solid Mechanics
Department of Applied Mathematics and Theoretical Physics (DAMTP)
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Solid Mechanics is a small but vibrant activity within the
Department of Applied
Mathematics and Theoretical Physics. Its basic concern is the analysis of
the internal forces in solid materials and structures, and assessment of
their consequences. The most serious consequence is failure of the structure,
which is at best inconvenient and at worst can be life-threatening. The
subject is massive and this note can discuss only a couple of examples.
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Photograph courtesy of EQE International
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It
may not be a great comfort to know that virtually all structures --
including the aeroplanes in which we all fly -- contain cracks! There is,
however, a well-defined subject called fracture mechanics. A crack does no
harm so long as it does not grow catastrophically. To explain, it is
necessary to talk about stress. This is force divided by area. Its
significance may be related to common experience by considering whether
you would prefer to have your foot trodden on by a heavy man wearing big
shoes, or by a diminutive lady wearing stiletto heels: the former applies
the greater force but it is spread over a bigger area and so is less
damaging. The paradox with a crack is that very high stresses are
unavoidably generated near its edge. The simplest theory actually
predicts that these stresses become infinite. Why, therefore, is the
material not pulled apart? More refined theory (which involves the
analysis of a set of nonlinear partial differential equations) shows
why the stresses near the crack edge in fact remain finite. Thus, it
explains why the crack need not extend, until the applied loading is
sufficiently intense. More important, it shows the precise way in which
the simplest theory becomes modified by the nonlinearity, and provides
the engineer with an easily-- parameter -- the `stress intensity
factor' -- which should not be allowed to exceed a critical value.
Even theory at this level suffices for much of engineering design and
analysis, and is employed, for instance, in conjunction with programmes of
inPservice inspection of airframes and aero engines to decide when a
component should be removed from service. Modern materials are often so
tough that the assumptions underlying the simple theory do not apply:
they withstand much larger stresses and more sophisticated theory is
needed. Research is still progressing in some areas but much understanding
has already been acquired and is exploited in practice. A problem under
active study at present is the dynamic propagation of a crack. The
equations describing propagation are exceptionally difficult to solve,
but noteworthy progress has recently been made, and the resolution of
questions such as why cracks tend to branch when they run fast is in
prospect.
Different examples of failure are provided by microelectronic
components. A silicon chip is often sealed within a plastic block and
it is important that this plastic package should remain bonded to the chip.
The package is nearly always under stress, introduced upon cooling from
its fabrication temperature, so decohesion is a possibility. Such
devices are inspected after manufacture, and those with cracks are
discarded. The problem here is the development of efficient and
economic methods of inspection. Ultrasound is used and the problem is
to identify those characteristics of the returned signal that diagnose
the state at the chip-package interface. Theory underpinning a novel use
(at the National Institute of Standards and Technology, Washington, DC)
of an Tacoustic microscopeU, in which amplitude rather than travel time is
mapped, is under development in the Department. There are other
semiconductor devices in which stress is `designed in', to achieve a
desired electronic performance. A thin layer consisting of a mixture of
silicon and germanium may be deposited on a substrate of pure silicon,
for example. The atoms tend to line up, even though the germanium atoms
would prefer more space, so the layer is under stress. Failure in this
context means relaxation of the stress by some means: the device remains
intact but its performance alters. Mechanisms for stress relaxation
(involving the introduction of dislocations), and means for its avoidance,
have been clarified through work within the Department. Another
development was the first satisfactory explanation of the relation between
elastic mismatch and electronic performance of `quantum wire' structures.
Almost all of this work is inter-disciplinary in nature: the theory can
be done in the Department but it has to address the right problems!
Often this involves collaboration with some outside organisation.
There are, however, also strong interdepartmental links within Cambridge,
and one quite recent development has been the establishment of the
Cambridge Centre for Micromechanics, whose participants come mainly from
DAMTP, and the Departments of Engineering and Materials Science.
Present concerns of the Centre include analysis of the shock-absorbing
capacity of metal foams and (avoidance of) the failure by micro-buckling
of fibre-reinforced composites. The Centre provides, internally, a forum
for collaboration and, externally, a strong interdisciplinary group with
the potential to tackle challenging problems in materials technology.
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