| In order to understand
the vocabulary and terms used in describing the
current trends in construction engineering and
technology, it is necessary to classify structural
systems and concepts in different ways. The following
section has outlined such a classification based
on different criteria and contains a brief description
of the different systems based on this classification.
Finally, the uses of these terms, systems and
concepts in various real life applications have
been brought out. |
 KIND
OF STRUCTURE |
| Based
on Spatial Behavior |
|
Based
on Structural Behavior |
- Space Structures
- Plane Structures
- Hybrid Structures
|
|
- Frames
- Trusses
- Tensile Structures
- Plates
- Shells
|
 Based on Spatial Behavior |
 Space Structures
Space Structures also known as Spatial Structures
are structures that resist external actions
by distributing their effects in three-dimensions
(hence the term 'space'…'). Any structure
that is detailed to behave in 3D and structurally
modeled and analyzed in 3D can be considered
as a space structure. Makowski defines Space
Structures as 'skeletal frameworks, as a rule
consisting of simple modular, pre-fabricated
units, often of standard size and shape, which
combine into a light, but very rigid, three-dimensional
structure'.
Examples of Space Structures include Double-layer
Grids, Multi-layer Grids, Braced Domes, Tensile
Structures, Shell Structures, and Space Frames.
Conferences on Spatial Structures attract excellent
contributions on research in outer space related
structures and aerospace engineering. |
Plane Structures
Plane Structures are structures that exhibit
primarily a 2 dimensional or 'in-plane' behaviour
in resisting external actions and loads. Out
of plane behaviour is usually determined by
the provision of secondary elements and 'analyzed'
separately.
Examples include Plane Trusses, which are
essentially pin-jointed triangulated structures
that develop predominantly axial stresses under
the external actions and loads. Other examples
include single and multi-storied portal frames
and other 2 dimensional beam-column frames. |
Hybrid Structures
Hybrid Structures are a combination of the above
and include Single-layer Grids that are arranged
in 2 dimensions but resist 'lateral' actions in
the 3rd dimension. Single layer grids resist lateral
loads by developing flexural and torsional stresses.
Such structures are more common in RCC construction
and are the standard solution for large-span floors
in conventional buildings. Slabs and Plates demonstrate
similar behaviour. |
|
| Based on Structural Behavior |
Frames
Frames are structures assembled from linear
flexural elements joined with rigid connections.
Frames resist external actions predominantly
by developing flexural of 'bending' stresses.
Examples include Simply Supported and Continuous
Beams, Portal Frames, and Space Frames. |
Trusses
Trusses are structures assembled from linear
struts interconnected with pinned connections.
Trusses resist external actions by developing
axial stresses.
Examples include the Lattice Trusses and Double-layer
Grids. |
Tensile Structures
Tensile Structures are structures assembled
from one or more 'flexible' cables interconnected
and pre-stressed. They resist external actions
by deforming and developing predominantly tensile
stresses or overcoming the pre-stress.
Examples include the Suspension Cable Bridges,
Cable Net Structures and Tensile Membrane Tents. |
Plates
Plates resist external actions through a combination
of in-plane axial stresses and out-of-plane
bending stresses. The form of the assembly of
the plates controls the extent of distribution
of stresses due to the local effects through
the entire structure.
Examples include the Floor Slabs, Shear Walls,
Folded Plates etc. |
Shells
Shells also resist external actions through
a combination of in-plane axial or membrane
stresses and out-of-plane bending stresses.
The form of the shell controls the extent of
distribution of stresses due to the local effects
through the entire structure.
Examples include the Dome, Hyperbolic Paraboloid
Shell, Groin Vaults etc. |
|
| ENGINEERING
METHODOLOGY |
- Pre-Engineered Buildings and Pre Engineered
Metal Buildings
- Conventional Structures
- Customized Structures
|
Pre-Engineered Buildings and Pre Engineered Metal
Buildings
Pre-Engineered Buildings and Pre Engineered Metal
Buildings came into existence in the 50s and '60s
to represent standardized 'off-the-shelf', low-rise
industrial building designs, which were very popular
due to their economy and speed of construction.
The designs were ready-made but the building components
were either ready-made or manufactured against
specific orders. These buildings were pre-designed
or 'pre-engineered' into standard sizes, spans,
bays and heights, and used standard details for
fixing cladding, roofing, gutters, flashing, windows,
doors etc taking advantage of industrial practices
to mass produce components economically. Pre-engineered
buildings are primarily single steel buildings
clad and/or decked with coated steel or aluminum
skins. These structures consist of portal frames
with rigid bolted and welded plates and 3-plate
(I-sections) type elements. These structures have
evolved from more traditional 'iron truss' and
'brick and mortar' approach to construction of
industrial buildings. |
Conventional Structures
Conventional structures represent the large number
of structures that are designed and engineered
to customers' specific requirements by architects
and structural consultants. Once the designs are
completed they are tendered out and the construction
contract awarded to the lowest pre-qualified bidder
(contractor).This method of design has been very
popular due to the design scope from the construction
scope and the advantage of having cost estimates
and design early in the project phase. Conventionally
it was assumed that economy and speed of construction
was assured but this assumption may not be tenable. |
Customized Structures
While manufacturers of pre-engineered structures
churned out monotonous and 'rubber-stamp' designs,
architects and engineering consultants were neither
able to tap the innovative capability of specialized
contractors nor the synergy between engineering
decisions and construction methods. Further, with
the advent of high-speed computers at affordable
prices, standardized buildings lost their main
attraction, which was speed. In this environment,
specialized contractors evolved to offer turnkey
solutions in the form of customized buildings
and components that could be designed and built
in very short lead times. |
|
| CONSTRUCTION
METHODOLOGY |
- In-Situ Structures
- Pre-Fabrication
- Pre-Casting
- Ready Mix Concrete
|
In-Situ Structures
Most of the structures in India are constructed
using so-called conventional technology, i.e.
methods evolved in the early part of the 20th
century. In RCC construction, reinforcement is
bent at site and placed in position before concrete
is poured into timber or steel framework supported
on suitable supports. In many cases, concrete
is mixed at site using bagged cement, loosely
dumped aggregates and small mixers based on volume
proportions. In steel construction, sub-assemblies
and sections are fabricated in position or pre-assembled
and welded in large sections on the ground near
the site and erected into position using temporary
bolting and final welding. |
Pre-Fabrication
Pre-Fabrication along with pre-engineered structures
and buildings, pre-fabricated structures also
came into existence in the 50s and '60s. This
term is used to refer to structures assembled
in-situ using standard readymade tubular trusses
used in industrial structures and pre-cast concrete
components used in housing and bridge construction.
The term 'fabrication' is generally used in the
context of cutting, assembly and welding of steel
components in common parlance. |
Pre-Casting
The term pre-cast is used to refer to concrete
components that are cast and cured off-site as
against concrete cast in-situ. Pre-cast components
are used both in building and bridge construction.
Roof and wall components are commonly pre-cast
in building construction. In bridges, beams and
segments of the spans are pre-cast. |
Ready Mix Concrete
Due to the crowded situation in urban areas, these
days concrete pre-mixed at large sophisticated
batching plants and delivered in transit mixers
has become popular. This technology was popular
for more than 20 years in India but was limited
to large concrete intensive civil engineering
projects. Control of quality is inherently better
in this system as large volumes are mixed by accurate
weighing, controlling water content, and accurate
design of mix. |
|
| CONSTRUCTION
MATERIALS |
- Brick and Mortar
- RCC Buildings
- Steel Buildings
- Pre-Stressed Concrete Structures
- Composite Construction
- Timber Structures
|
Brick and Mortar
Brick and Mortar buildings are buildings constructed
traditional bricks and cement mortar, a composite
of cement and sand, two materials with different
but complimentary characteristics. This is one
of the oldest known materials along with adobe,
lime mortar, cow dung, straw, wood and other traditional
materials. |
RCC Buildings
RCC Buildings are buildings constructed from reinforced
concrete, which is a composite of steel and plain
cement concrete, two materials with different
but complimentary characteristics. Plain cement
concrete itself consists of a mixture of cement,
water, and aggregates such as sand, granite metal,
etc. Cement is a special form of limestone powdered
and mixed with additives which when mixed with
water hydrates into a very hard matrix. The hydrated
cement-fine aggregate matrix occupies the interstices
of the large aggregates and bonds with them to
form a hard mass of reconstituted stone. Reinforcing
Steel is a special form of steel treated to give
relatively higher strengths and ductility (elongation
under tension) and rolled into bars of different
diameters. The surface of the bars is formed to
increase the mechanical bond with concrete. The
proportion of the ingredients and control of moisture
during the initial setting will determine the
ultimate strength gained by the matrix. The main
characteristics of this matrix are its very high
compressive strength and relative weakness in
tension. The high tensile strength of steel is
transferred to the combined element through the
bond developed between the steel and cement concrete.
Through proper positioning of the steel, the strength
of the combine can be designed to resist extraordinarily
high external actions and loads. |
Steel Buildings
Steel Buildings are buildings constructed predominantly
out of structural steel, another special form
of steel, generally with lower carbon content
for weldability and ductility (elongation under
tension). Such steel is also treated to increase
strengths, hot rolled into plates, standard sections
and bars of different sizes or cold-rolled into
tubes and thin walled open sections for structural
elements and profiles for roofing cladding. |
Pre-Stressed Concrete Structures
The term 'pre-stressed' refers to concrete structures
that are initially stressed by running steel wires
and cables through them and tensioning them with
jacks. Concrete is very weak in tension and when
the cables are tensioned by reacting against the
concrete components, the concrete element is pre-compressed.
In service, when the concrete element undergoes
tension due to bending or direct tension, it has
to first overcome the pre-compression before it
can experience any tensile stress. Roof and wall
components are commonly pre-stressed in building
construction. In bridges, beams and segments of
the spans are pre-stressed. If pre-stressing is
done on pre-cast elements before casting it is
called 'pre-tensioning. If the tensioning is done
to pre-cast or cast-in-situ elements, then it
is called post-tensioning. |
Composite Construction
In the last 40 years, different composites have
evolved including newer versions of steel and
concrete exhibiting a more synergistic behavior.
Several forms and levels of composite behavior
can be created from simple steel deck and concrete
slabs to composites of aluminum alloys and plastics
in sandwich and cellular forms. |
Timber Structures
Timber Structures are the emerging new environmentally
friendly alternatives to other construction
materials. Historically, timber was discouraged
since they were won from valuable rain forests
and caused extensive environmental damage. However,
in the last decade, laminated wood manufactured
from specially grown timber in renewable plantations
has become very popular in Europe and US. |
|
| STRUCTURAL
SYSTEMS |
- Single Layer Grids
- Double Layer Grids
- Multi Layer Grids
- Braced Domes
- Tensile Structures
|
|
- Space Frames
- Portal Frames
- Space Frame Portals
- Folded Plates and Shells
|
Single Layer Grids
Single Layer Grids resist lateral loads by developing
flexural and torsional stresses. Such structures
are more common in RCC construction and are the
standard solution for large-span floors in conventional
buildings. |
Double Layer Grids
Double Layer Grids are the most commonly used
forms in Space Structures because of their simplicity,
minimal inventory, high structural efficiency
and ease of use in most roofing applications.
These forms can also be used in vertical and inclined
arrangements such as in walls and inclined atria. |
Multi Layer Grids
Multi Layer Grids consist of two or more plane
grids (not necessarily of identical layout) each
consisting of a network of 'chord' members forming
the top, bottom and additional intermediate layers,
interconnected by vertical or inclined 'web' members.
The chord and web members are almost exclusively
under the action of axial forces, the elimination
of bending moments leading to full utilization
of strength of all members. |
Braced Domes
Braced Domes consist of triangulated 3D structures
forming a singly curved form of spherical or other
curved geometry and anchored at the hemispherical
nodes or along the periphery of the base and transferring
the hoop and meridional stresses through primarily
axial stresses. |
Tensile Structures
Tensile Structures resist the externally applied
loads predominantly by developing tensile forces.
Examples of such structures include cable structures,
tensegrities, air inflated and pneumatic structures
and of course membrane structures They generally
refer to the structural system involved in a structure
and may include the skin or cladding if it plays
a role in resisting the external loads. |
Space Frames
Space Frames have been associated with double-layer
grids in common parlance, structural engineers
have always used the term 'Frame' to represent
structures that resist external actions by developing
primarily flexural stresses. The term 'Truss'
is used to represent pin-jointed, braced or triangulated
structures. Hence Space Frames are now used to
represent multi-storey, high-rise frames in three-dimensional
structures, both of steel and concrete. |
Portal Frames
Portal Frames are normal low-rise framed structures
consisting of single and multi-bay portals that
gain strength from flexural behaviour. Individual
portal frames are assembled from three plate elements
('I' and 'H' profile beams) with tapering elevations
and compact ready made or built-up sections interconnected
at site. Plastic analysis methods are commonly
applied to predict the ultimate strength. |
Space Frame Portals
Space Frame Portals are normal low and high-rise
framed buildings wherein individual portal frames
are assembled from elements forming space frames
and trusses that show axial micro-behaviour and
flexural macro-behaviour. These individual frames
are generally interconnected with secondary members
that act as purlins, rails and lateral bracing
elements. By detailing that takes into consideration
the total spatial behavior of the frame in 3D,
it is possible to analyze the entire 3D frame
together. |
Folded Plates and Shells
Folded Plates and Shells were very popular in
mid and late 20th century for constructing large
span roofs. RCC was the most commonly used material
of construction. The extraordinary strength of
this system was due to the form which was usually
either curved (single or double) or consisted
of folded plates which increased the moment of
inertia of the gross cross section. |
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