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Compression
On the 7th of March 2014, the first studio class in Constructing
Environments focused on ‘compression’. In order to gain great knowledge
of compression within building structures, we first must understand the
two loads, static and dynamic. Static loads are loads that are applied to
a structure slowly or permanently as oppose to dynamic loads which are
applied very rapidly and unexpectedly like wind loads and earthquake.
Initially, when we were building the tower, there were only static loads,
or dead loads, which were the blocks we used to build the tower. As the
blocks are stacked on top of one another, a compression force is
produced as the “particles of the material compact together” (Newton,
2014). When we had to make space for a toy dog to fit inside our tower,
we compressed the blocks on top of each other from the two sides of the
entrance and slowly built it closer to each other as the construction rose.
As we can observe from ‘Tower 1’, the load path from the two blocks on
top of the entrance will travel from the middle to the outer sides and then
down the blocks and to the sides until it reaches the floor. When it
reaches the floor, there will be a reaction force from the ground up in
order to keep the structure stable. Keep in mind that when the load path
travels down to the ground, it takes the most closest or direct path from
one block to another.
With a solid foundation, and too much material being used, the group tried to be more efficient and put gaps in our tower
about halfway to the highest point. Same with the bottom half of the structure, the load forces will just travel to the sides and
down the most direct route given to them. But by having gaps, the structure won’t be as compacted as its foundation and this
may not be optimal for a strong building as a dynamic load, the wind, will enter the load more easily. So as the tower
progresses, it is noticeable that the tower is starting to deform and become weaker. This is due to the dynamic wind load
travelling in a horizontal direction to a tower, which its load force travels downwards. Another thing that we learnt in the week
one studio class was the structural forces.
As class time was almost up, the class watched a few groups deconstruct their tower. From
our view, it was seen that the tower will hold its deforming structure until about 10% of its
load from around the
bottom before
collapsing. This is
possibly due to the
instability of the
forces. The loading
forces of the structure
must have not be in
equilibrium with its
reaction force in
addition to the
dynamic wind force
causing the demolition
of the tower.
In accordance to the sketch, it is evident that the tower’s
force is collinear. It is collinear as the forces occur along a
straight line.
Ching, F D.K. (2008). Building Construction Illustrated. 4th ed. New Jersey: John Wiley & Sons. p2.08-2.11.
Newton, C. (2014). ENVS1003: Constructing Environments Basic Structural Forces (I). Retrieved from
https://app.lms.unimelb.edu.au/bbcswebdav/courses/ENVS10003_2014_SM1/WEEK%2001/Basic%20Structural%20Forces%201.pdf
Structural Joint
Balsawood Tower
During the studio session, we were to build a tall tower but except this time made out of
balsawood. The aim of this tower was to maximise its height by using a suitable frame without making
the tower fall down. My group initially decided to build the tower in a square shaped figure like buildings
in the streets. We came to figure out that the objection of this task was to build a tall tower rather
than a strong structure that would withhold objects. Thus with the limited amount of supplies we were
given, we changed to a triangular shape, knowing that it’d be more efficient and more effective if done
properly. As demonstrated in ‘Balsawood 1’, we connected strips of balsawood via a locking system
with masking tape around it for reinforcement. By doing this, we assume that the load force will be
more compacted hence become stronger than loose joints.
In ‘Balsawood 2’ is our final form of the balsawood tower. We first structured it by creating a base at
the bottom so that the load force can equally travel down for a stable structure. We sticked the woods in
line with the locking frame as well as taping it around. In order for the structure to stay up, we thought
about adding a strip of wood at the bottom to connect with the long frame that we were going to stick
for height. By connecting on a supporting stick, I assume that the loading force of the structure will be able to withstand more force thus
causing deformation to happen a little later than expected.
Locking
system
In ‘Balsawood 3’, we examined a great structure by another group. They criss-crossed the middle of their structure as well as had a
strong hold at every edge of their exterior sticks. By doing this, they have created a strong tower as the forces travel down more equally
and most of all, creates a
frame that is very stable.
The
supporting
frame.
Week 3- Footings & Foundations
Structural Elements
Geometry & Equilibrium
Footings & Foundations
The foundations main function “is to safety
transfer all loads acting on the building
structure to the ground.” It must also resist
against the soil pressing against the
foundation wall.
Whenever you see a cracking in a building, it
is due to the ‘settlement’ being uneven.
Hence why footings and foundation are
designed to overcome this problem and
hopefully keep a structural building fixed and
stable. They also should be able to support he
‘bearing capacity’ of the soil.
Shallow footings are used when soil
conditions are stable and their bearing
capacity is closed to the ground, transferring
vertically from the foundation to the ground.
Deep foundations are used when soil
conditions are unstable and their bearing
capacity is far from the top of the ground.
Load is transferred from the foundation to the
unfitting soil and into the deep level where
elements like bed rocks and gravel exists.
There are two types of piles for the
foundation which are end bearing piles and
friction piles.
Mass and Masonry Materials
Mass materials are: stone, earth, clay,
concrete. They are strong in compression but
weak in tension. They are hard, good thermal
masses and durable.
Masonry is made up of stone, clay and
concrete.
Glossary
Settlement: As time passes, buildings
compress into the earth’s ground thus sink a
bit into the earth.
Foundation (retaining) wall: Used on sites
creating a basement for stability. Pressure
load behind the wall needs to be considered
to prevent wall from collapsing.
Centre of mass- “The point at which an object
is balanced.”
Equilibrium- It is the state of rest where an
applied force is equated to its reaction force.
(I.e. a support element has to react equally
and in the opposite direction to a load).
Moment of force- “The tendency to make an
object or a point rotate.”
Masonry definitions:
Bond- “the pattern or arrangement of units”
Course- “A horizontal row of masonry units”
Mortar- “mixture of cement or lime, sand and
water used as a bonding agent”.
Week 4- Floor Systems & Horizontal
Elements
Beams and Cantilevers
Span & Spacing
When dealing with span and spacing, we just need
to remember that “spacing of the supporting
elements depend on the spanning capabilities of
the supported elements”
Floor & framing Systems
There are three types of flooring system that
we briefly learnt in class. First one was
concrete flooring then timber flooring and
finally steel flooring.
Concrete flooring has two types of spanning.
They have a two way span as well as the
typical one way span which spans between
two of the shorter supporting structures. Two
way system is ideal for square bays and one
way system is more efficient when structural
openings are rectangular. The system
depends on floor load, cost efficiency and
even function of building like distance
between columns for carparking.
Steel framing takes many forms, with some
using ‘heavy gauge structural steel members’
but most using ‘light gauge steel framing’.
They sometimes combine with each other or
concrete slab systems. Spanning of the
materials determine spacing of the supports.
Timber floor framing systems uses “a
combination of bearers (primary beams) and
joists (secondary beams).” Span of bearers
determines spacing of piers/stumps and their
spacing equates.
Concrete (Artificial stone)
1 part cement (Portland/lime): 2 parts fine
aggregate (sand): 4 parts coarse aggregate
(crushed rocks): 0.4-0.5 part water.
A chemical reaction, hydration, takes place
when cement and water are mixed, leading to
the release of heat. Crystals are formed
during process, joining the elements of
concrete together. If too much water is
added, final concrete will be weaker. If too
little water is added, the concrete will be too
stiff and hard to work with. Thus an
advantage of concrete is that it is fluid and
shapeless before hardening, making it easy to
work within terms of shaping it.
Concrete needs formwork because when wet,
it is very heavy. It can be achieved via ‘props’
and ‘bracings’. Keep in mind that concrete
reaches about 75% of its compressive
strength in about 7 days, with testing for
required strength on the 28th day. Also,
formwork can be built in situ (on site) or pre-
cast (in factory beforehand). When concrete
is hardened and strong enough, the formwork
is usually removed, stored and reused
otherwise may stay in place forever
(sacrificial formwork).
Concrete is strong in compression and weak
in tension thus steel or mesh, strong in
tension, is added for reinforcement. This
results in reinforced concrete.
The properties in concrete are that it is high
in hardness (can be scratched with metallic
object), medium to high in density (2.5
denser than water), medium to low in
porosity (absorb fluids), permeability
(allowing gas/liquid to pass through) and
reusability/recyclability, low in fragility
(chipped with hammer) and
flexibility/plasticity and very low in ductility.
It is also a poor heat and electric conductor,
typically very durable and long lasting, non-
renewable and cost effective.
Since it is permeable, it is not completely
waterproof thus if steel bars are too close to
surface, they will not be protected from
moisture and oxidation resulting the structure
to be degraded. Another problem with
concrete is ‘poor vibration of the concrete’
which makes it hard to get rid of air bubbles
during the pouring process and thus may lead
the element to failing.
Glossary
Beam- horizontal structure that carries loads
along its length and transfer the loads to the
closest vertical supports.
Cantilevers- an overhanging portion of a
structure that transfer loads to the support.
Span- “Distance measured between two
structural supports”
Spacing- The repetitive distance between
chains of elements. Measured from centre-
line of one element to the next one.
Girders- main beams
Joists- secondary beams
Formwork- temporary support/moulds used
to hold liquid concrete in place until it
hardens.
Week 5 – Columns, Grids & Wall Systems
Columns, Frames & Grids
Columns are vertical structural members designed
to transfer compressive loads. Short columns have
shorter length and thicker cross-section and long
columns are the opposite. Columns are considered
short if column length to the smallest cross section
is 12:1 otherwise it’s a long column. Short
columns fail by ‘crushing’ and this happens when a
compressive load exceeds the compressive
strength of the column. Long columns fail by
‘buckling’ and the buckling is determined by the
length of the long column as well as how fixed the
top and bottom of the column is.
Both a ‘fixed’ and ‘hinged’ frame is a rigid frame
but a fixed frame is connected to its supports with
fixed joints and a hinged is connected with pin
joints. The third frame is a ‘three-hinged’ frame
which is two firm frames connected to each other
and its support with pin joints.
Walls, Grids & Columns
There are three types of wall systems, being the
structural frames, load bearing walls and stud
walls.
The frames can either be of concrete material,
steel or timber which is rarely used here. Load
bearing wall is made of either concrete or
masonry. Stud walls will either have light gauge
steel framing or timber framing.
As of the grids, concrete frames “use a grid of
columns with concrete beams connecting the
columns together.” Steel frames “use a grid of
steel columns connected to steel girders and
beams.” Timber frames use “a grid of timber posts
or poles connected to timber beams.” They require
bracing on the corners to stabilise the structure.
Load bearing walls come in three materials. First
off is ‘concrete’ which the wall can be completed in
situ or pre-casted. They are used in nowadays new
apartments. Next is ‘reinforced masonry’ blocks
which can be strengthen via a reinforcement steel
rod or some other material being placed through
its core. Solid masonry can be formed via single
concrete or clay bricks. It can also be formed with
multiple bricks, joint using a brick turned ninety
degrees or wall ties placed within the mortar bed.
When using two skins of masonry, you may be
constructing cavity masonry walls where two walls
are built beside each other with a gap between for
better thermal performance, waterproofing,
insulation and running services within the wall
cavity. This opening can be pointed out when
damp proof course or weep holes are presented in
the masonry walls.
Stud framing
Timber
The properties in timber are that it is
high in flexibility, porosity/permeability
and reusability/recyclability, medium in
plasticity (easy to shape), medium-low in
hardness and fragility and low in ductility.
They are poor heat and electric
conductors and their density extremely
varies depending on the type of timber.
It is normally cost effective
A weak point in timber is a knot which
causes a slope in the grain thus breaks
easily. You should also be aware to
protect the end of the material from
water whether is it by painting or even
detailing. Timber can also be damaged by
insects, sunlight and heat, fire and
chemical exposure.
Glossary
Nogging- A row of an element (timber/steel)
in stud walls between the top and bottom
plates, placed to prevent buckling of long thin
members.
Buckling- Bending of a member due to heavy
load. Normally happens with long columns.
Porosity- Ability to absorb fluid
Permeability- Ability to allow fluids
(gas/liquid) to pass through
Wall ties- a metal piece connecting a masonry
wall to another wall.
Week 6- Spanning & Enclosing Space
Trusses, Plates & Grids
Trusses require bracings that are perpendicular to
their planes. Their increased depth allows them to
span greater than steel beams and girders. They
also allow mechanical services such as pipping or
ductwork to pass through the web spaces.
Plates are fixed structures that spread out applied
loads in a multidirectional pattern to the closest
support. It should be ensured that the plates are
nearly square or square so that it behaves as a
two-way structure thus spreading the load equally
all around.
Folded plate structures are thin elements that form
sharp angles to brace each other against
‘buckling’. Each plane behaves as a beam in the
long direction.
In trusses, the grids are normally the steel beams
and girders structured in a triangular shape while
in plates, there are none unless beams are used to
support under them.
Roofing Strategies and Systems
There are two types of roof systems, the flat
roof and the sloping roof. The flat roof can be
made of concrete slabs, flat trusses, beams
and decking or joists and decking. The
sloping roof is made of rafters, beams or
purlins or trusses.
Concrete roofs are generally flat roofs and
they slope towards drainage points. They are
finished with waterproof membrane.
Space frames are 3D plate structures
that are long spanning in two directions.
They look like matrix structures with the
crosses.
Metals
Metals are malleable and ductile but not
brittle. Their hardness varies depending on
the type. They are low in fragility and can be
medium-high in flexibility when melted. It is
generally impermeable and is high in density.
Metal is also a very good heat and electric
conductor. They can normally last long and
even be reused thus making them quite cost
effective.
Metals will directly transfer ions if in contact
with another metal. This may cause corrosion
and we can reduce this effect with insulators
like rubber gasket. Taking this into
consideration, we should consider keeping
water away from metal as much as possible
to reduce oxidation and corrosion which will
cause the metal to rust. We can do this by
avoiding moisture, sealing the metal against
moisture, or give the metal a chemical
treatment.
Glossary
Truss- A structure consisting of triangle
members with forces acting in either
compression or tension.
Web- System of members connecting the top
and bottom chord of a truss together.
Ferrous- Iron
Non-Ferrous- All other metals. More
expensive but less common.
Alloys- Combination of two or more metals.
Week 8- Openings
Deformation & Geometry
The efficiency of a beam can be improved
by configuring the cross section. This
provides the required ‘moment of inertia’
or ‘section modulus’ with the smallest
possible area. The moment of inertia is a
geometric property, indicating how the
cross sectional area of a structural
member is spread out and does not
reflect the physical properties of a
material. Section modulus is also a
geometric property.
Strategies for openings
Sill allows water to run away or drip rather
than run in the door itself.
You normally work off manufacturer frames
because too much time and money to set up
for own design.
Windows needing to be clean is an issue thus
why skyscrapers have facades.
Curtin walls act both a window and wall
because it is a see through wall. Quite ideal
for office rooms.
Glass
Glass is made from formers. They are non-
porous and waterproof. They have a medium
to high density and can transmit heat and
light but not electricity. Glass is also high in
hardness, fragility, reusability, durability,
flexibility and plasticity when molten but low
in ductility. They are quite expensive to
produce and transport.
There are two main types of glass, flat glass
and shaped glass but float glass is the most
common one nowadays. Clear float glass is
the simplest and cheapest glass, ideal in low
cost purchase. Laminated glass is much
stronger and can still crack but the cracked
fragments tend to stick to the plastic rather
than falling apart. Tempered glass is
produced by heating. They are 4 to 5 times
stronger than annealed glass. When cooled,
they create a compression force outside the
surface of the glass. They are perfect for
highly exposed situations or when a large size
is required.
Glossary
Fluxes- help formers to melt at low
temperatures.
Stabilizers- combine with formers and fluxes
to keep glass from dissolving or crumbling
Neutral axis- An imaginary line passing
through the middle of the cross section of a
beam.
Shearing- part of a structure break off due to
compression or tension force.
Moment of inertia- “The sum of the products
of each element of an area and the square of
its distance from a coplanar axis of rotation.”
Section modulus- The moment of inertia of
the section divided by the distance from the
neutral axis to the most remote surface.”
Axial load- Forces acting along the line of an
axis of a material.
Week 9- Detailing Strategies 2
Stress and Structural Members
Columns are rigid structural members
designed to support ‘axial compressive loads’
applied to the ends of the structure. Thick
columns fail by crushing rather than buckling
and this occurs when the stress from the
axial load exceeds the compressive strength
of the material in the cross section. However,
an unusual load can cause the member to
bend due to imbalance. On another note, long
columns firstly deflect before failing by
buckling. If you can reduce the slenderness,
it will cause the column to less likely buckle.
Construction Detailing
Health and safety is an important detailing.
Such as requiring rails for stairs.
Materials must be chosen carefully as this can
save structure in long time, making them
more durable. For example, using copper will
improve its appearance overtime unlike
timber which greys and becomes damaged
overtime.
Another detailing matter is surfaces, and how
easily they can be repaired such as skirtings
which will prevent damage from vacuum
cleaners or foots walking into it.
Cleanable surfaces are another detailing
problem. Restaurants and hospitals need to
have easy clean surfaces. Materials must be
chosen carefully along with detailing.
Constructability is another matter. It should
be easy to assemble, easy to adjust due to a
mistake and efficient with materials and
labour. This is why it is best to use structures
that are already designed or detailed to suit
the construction rather than create a new one
which will be very pricy.
Composite Materials
“Composite formed from:
1. Combination of materials which differ
in composition or form
2. Remain bonded together
3. Retain their identities and properties
4. Act together to provide improved
specific or synergistic characteristics
not obtainable by any of the original
components acting alone.”
Composite materials can come in fibrous,
laminar, particulate or hybrid.
Glossary
Kern area- The central area of an horizontal
section of a column or wall which all
compressive loads must pass if presented.
Slenderness ratio of a column- It is the ratio
of “its effective length to is least radius
gyration”.
Effective length- “The distance between
inflection points in a column subject to
buckling.”
Effective length factor- “A coefficient for
modifying the actual length of a column
according to its end conditions in order to
determine its effective length.”
Radius of gyration- “The distance from an
axis at which the mass of a body may be
assumed to be concentrated.”
Week 10- When Things Go Wrong
Lateral Forces
Resistance to lateral loads are a major
concern to designing buildings. Such forces
can be of earthquake or wind. The structures
must be resistant to these forces in both the
horizontal and vertical direction.
Diaphragms collect forces in the horizontal
direction and transfer these forces into the
vertical bearing elements. An example of a
diaphragm is reinforced concrete.
Brace frames are essentially truss structures
that move loads diagonally through the
structure in a vertical plane.
Shear walls resist lateral loads in the vertical
plane. They collect loads from the horizontal
elements and transfer them to the
foundation.
Moment resisting frames are structural
elements connected with fixed joints. Hence
why they are resisted by the rotation and
bending of the beam and column joints.
Seismic bas isolators are connections placed
between the foundation and the substructure.
This allows superstructure and substructures
to move independently if there is an
earthquake.
Collapses & Failures
Material selection
Exposure to hot sun
Painted black on outside only
Fasteners
When looking at material selection, should
consider:
Exposure
Compatibility
Strength and deflection
Long term performance
Maintenance
Construction & detailing
Heroes & Culprits
When choosing materials, consider:
health
waste/recycling/recycled
energy used and embodied energy
pollution
life cycle
Construction Workshop
Structural Performance
We decided to place the longest length of the
pinewood on top of the other one and stick
two plywoods on each side of the woods as
demonstrated in the picture below. We did
this with thought that the plywood wills
strongly withstand the machine as long as the
machine is crushing it from the top and
bottom, where its strongest point is at and
not the wide where it can bend and deviate a
lot. We did not worry about the pinewood too
much as there was no weak spots (knots)
and it looked very dense compare to the
plywoods.
Failure Mechanisms
Our structure failed because the plywood
failed to stand balanced and started to bend
(can be seen in the picture top far right)
which caused it to snap as there was too
much tension for the wood to manage. This
also led the pine wood to break as nails failed
to hold the woods together.
Materials & Tools Used
My team was given two hard plywoods and
two rectangular pinewoods.
We used a saw to even out the structure but
mostly used a hammer and nails to fix the
woods together.
Record of our structure
Our structure’s applied failure load
was about 360kg before snapping to
one side.
It had a maximum deflection of
43mm, starting at 162mm and ending
at 205mm.
Span, Shape, Strength, material
efficiency and joint types
Our construction spanned 1050mm
rather than the recommended
1000mm in case of structural failure.
It was shaped typically like a
rectangular block without gaps for
strong resistance.
Pinewood is very material efficient as
it is cheap and easily machined.
Plywood is also cheap but if
structured incorrectly, the wood’s
strength will not be maximised but
very weak.
We only used fixed joints, nailing
mostly at the top due to compression
and less at the bottom since in
tension.
Comparison to the strongest structure
Unlike another team’s structure, seen above, they
had 3 square-dimensioned like pine wood attached
on top of each other which ultimately withstood
the machine the strongest. Their structure was
crushed due to the knot, known as a weak point,
in the middle which can be seen. This was a
material failure and not their construction in the
structure thus it could have held much more load
then observed. Their applied failure load was about
460kg and deflected 60mm.
Comparison between actual construction
materials & scale model making materials
Plywoods are normally stuck together thus
why it is strong unlike our model materials
where we only used a single layer which also
made shaping it hard.
Nothing was different with the pinewoods.
References
Ching, F D.K. (2008). Building
Construction Illustrated. 4th ed. New
Jersey: John Wiley & Sons.
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