土木工程英语论文.docx
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土木工程英语论文
Structure of Bulidings
A building is closely bound up with people, for it provides people
with the necessary space to work and live in. As classified by their use,
buildings are mainly of two types:
industrial buildings and civil buildings.
Industrial buildings are used by various factories or industrial production
while civil buildings are those that are used by people for dwelling,
employment, education and other social activities.
The construction of industrial buildings is the same as that of civil
buildings. However, industrial and civil buildings differ in the material
used, and in the structure forms or systems they are used.
Considering only the engineering essentials, the structure of a
building can be difined as the assemblage of those parts which exist for
the purpose of maintaining shape and stability. Is primy purpose is to
resist any loads applied to the building and to transmit those to the ground.
In terms of architecture, the structue of a building is and dose much
more than that. It is an inseparable part of the building form to varying
degrees is a generator of that form. Used skillfully, the building structure
can establish or reinforce orders and rhythms among the architecture
volumes and planes. It can be visually dominant or recessive. It can
develop harmonies or conflicts. It can be both confining and emincipating.
And, unfortunately in some cases, it cannot be ingored. It is physical.
The structure must also be engineered to maintain the architecture
form. The principles and tools of physics teand mathematics provide the
basis for differentiating between rational and inrational forms in terms of
construction. Artists can sometimes generate shapes that obviate any
consideration of science, but architects cannot.
There are at least three items that must be present in the structure of
a building:
stabily, strength and stiffness, economy.
Taking the first of the three requiements, it is obvious that stability
is needed to maintain shape. An unstable building structure implies
unbalanced forces or a lack of equilibrium and a consequent acceleration
of the structure or its pieces.
The requirement of strength means that the materials selected to
resist the stresses generated by the loads and shapes of the structure(s)
must be adequate. Indeed, a “factor of safety” is usually provided so that
under the anticipated loads, a given material is not stressed to a level even
close to its rupture point. The material property called stiffness is
considered with the requirement of strength. Stiffness is different form
strength in that it directly involves how much a structure strains or
deflects under load. A material that is very strong but lacking in stiffness
will deform too much to be of value in resisting the forces applied.
Economy of a building structure refers to more than just the cost of
the material used. Construction economy is a complicated subject
invovling raw materials, fabrication, erection, and maintenance. Design
and construction labor costs and the costs of energy consumption
money(interest) are consumption must be consiedered. Speed of
construction and the cost of money(interest) are also factors. In most
design situations, more than one structural material requires consideration.
Completive alternatives almost always exist, and the choice is seldom
obvious.
Apart form these three primary requirements, several other factors
are worthy of emphasis. First, the structure or suctructural system must
relate to the building’s function. It should not be in conflict in terms of
form. For example, a linear function demands a linear structure, and
therefore it would be improper to roof a bowling alley with a dome.
Similarly, a theater must have large, unobstructed spans but a fine
restaurant probably should not. Stated simply, the structure must be
appropriate to the function it is to shelter.
Second, the structure must be fire-resistant. It is obvious that the
structural system must be able to maintain its integrity at least until the
occupuants are safely out. Building codes specify the number of hours for
which certain parts of a building must resist the heat without collapse.
The structural materials used for those elements must be inherently fire-
resistant or be adequently protected by fireproofing materials. The degree
of fire resistance to be provided will depend upon a number of items,
including the use and occupancy load of the space, its dimensions, and
the location of the building.
Third, the structure should integrate well with the building’s
circulation systems. It should not be in conflict with the piping systems
for water and waste, the ducting systems for air, or (most important) the
movement of people. It is obvious that the various building systems must
be coordinated as the design progresses. One can design in a sequential
step-by-step manner within any one system, but the design of all of them
should move in a parallel manner toward completion. Spatially, all the
various parts of a building are interdependent.
Fourth, the structure must be psychologically safe as well as
physically safe. A highrise frame that sways considerably in the wind
might not actually be dangerous but may make the building uninhabitable
just the same. Ligheweight floor systems that are too “bouncy” can make
the users very uncomfortable. Large glass windows, uninterrupted by
dividing motions, can bu quite safe but will appear very insecure to the
occupant standing next to on 40 floors above the street.
Sometimes the architect must make deliberate attempts to increase
the apparent strength or solidness of the structure. This apparent safety
may be more important than honestly expressing the building’s structure,
because the untrained viewer cannot distinguish between real and
perceived safety.
The building designer needs to understand the behavior of physical
structures under load. An ability to intuit or “feel” structural behavior is
possessed by those having much experience involving structural analysis,
both qualitative and quantitative. The consequent knowledge of how
forces, stresses, and deformations build up in different materials and
shapes is vital to development of this “sense”.
Structural analysis is the process of determining the forces and
deformations in structures due to specified loads so that the structure can
be designed rationally, and so that the state of safety of existing structures
can be checked.
In the design of structures, it is necessary to start with a concept
leading to a configuration which can then be analyzed. This is done to
members can be sized and the needed reinforcing determined, in order to:
a) carry the design loads without distress or excessive deformations (
serviceability or working condition); and b) to preventcollapse before a
specified overload has been placed on the structure (safety or ultimate
condition).
Since normally elastic conditions will prevail under working loads,
a structural theory based on the assumptions of elastic behavior is
appropriate for determining serviceability conditions. Collapse of a
structure will usually occur only long after the elastic range of the
materials has been exceeded at circal points, so that an ultimate strength
theory based on the inelastic behavior of the material is necessary for a
rational determination of the safety of a structure against collapse.
Neverthelese, an elastic theory can be used to determine a safe
approximation to the strength of ductile structures (the lower bound
approach of plasticity), and this approach is customarily followed in
reinforced concrete practice. For this reasion only the elastic theory of
gtructure is pursued in this chapter.
Looked at critically, all structures are assemblies of three-
dimensional elements, the exact analysis of which is a forbdding task
even under ideal conditions and impossible to contemplate under
conditions of professional practice. For this reason, an important part of
the analyst’s work is the simplification of the actual structure and loading
conditions to a model which is susceptible to rational analysis.
Thus, a structural framing system is decomposed into a slab and
floor beams which in turn frame into girders carried by colums which
transmit the loads to the foundations. Since traditional structural analysis
has been unable to cope with the action of the slab, this has often been
idealized into a system of strips acting as beams. A lso, long-hand
methods have been unable to cope with three-dimensional framing
systems, so that the entire structure has been modeled by a system of
planner subassemblies, to be analyzed one at a time. The modern matrix-
computer methods have revolutionized structural analysis by making it
possible to analyze entrie systems, thus leading to more reliable
predictions about the behavior of structures under loads.
Actual loading conditions are also both difficult to determine and to
express realistically, and must be simplified for purposes of analysis.
Thus, traffic loads on a bridge structure, which are essentially both of
dynamic and random nature, are usually idealized into statically moving
standard trucks, or distributed loads, intended to simulate the most severe
loading conditions occurring in practice.
Similary, continuous beams are sometimes reduced to simple
beams, rigid joints to pin-joints, fillers-walls are neglected, shear walls
considered as beams; in deciding how to model a structure so as to make
it reasonably realistic but at the same time reasonably simple, the analyst
must remember that each such idealization will make the soulation more
suspect. The more realistic the analysis, the greater will be the confidence
which it inspires, and the smaller may be the safety factor ( or factor of
ignorance ). Thus, unless code provisions control, the engineer m