SRT 251 Construction and Structure 2 Project 1 : Construction Research

SRT 251 Construction and Structure 2
Project 1 : Construction Research
TEAM members: Hideto Chijiwa
Makiko Ikeda
Phil Rogers
Shaun Ely
Yenny Kusuma
PORTAL FRAME definition;
Portal frames are single storey, single( or multi-bay) frames with pitched or flat roof. Fabricated from
universal beams, it is an ideal structural solution in many circumstances, regarding its economic and
structural efficiency. The system is specially ideal for industrial buildings due to its ability to span large
areas of unobstructed open space within its building envelope. This is made possible through the design
and use of refabricated steel sections. Technological advance in the footing system also cooperate for the
large span achieved due to their ability to carry greater loads (or its efficiency to transfer and distribute the
loads to the foundation).
Three major elements are; cladding for both roof and walls; secondary steel to support the cladding and
form framing for doors, windows and the like; and the main framework of the structure, including all
necessary bracing. In addition, the building requires appropriate footings designed to transmit all the load
to the foundations( supporting soil).
The design is essentially to provide a structure which is
without, or has a limited number of internal columns, in
principle the requirement is for the construction of four
walls and a roof for a single or multi-bay structure.
Light latticed portal frame structure for the roof of an
industrial buildings provide a neat efficient structure which
is simple to design, economic to execute and frequently
satisfies architectural requirements.
Portal frame structure 26m-span located in
the breakwater st. Industrial area in Geelong.
Due to the point loads applied to the foundation, Pad footings are respectably
the most suitable in long-span portal frame construction. Also in achieving a
workable surface and the distribution of loads to the foundation, combined
concrete slab would be used along with the Pad footing. The reinforcements
and metal dowels also play a big part in the sufficient footings behaviour.
Concrete Pad Footing
Strip or combined column footing
There are 3 types of connection systems for a Portal Frame structure.
Rigid base
2 pin
3 pin
The 3 types mentioned above are of purely how rigid or flexible the connections are at the apex, knee,
and the base. This however relates greatly to the load transfer of the structure, as the bending moment
becomes a big issue. Rigid bases are used much commonly in the current construction due to its ability
to carry the bending moment and axial loads, thus giving the framework a much lighter finish. (Max
bending moment at the knee, apex and base)
Pinned bases however transmit the bending moment straight through to the foundation. (max
bending moment at the apex and knees for the 2 pin, max bending moment at the knee for the 3 pin.)
Diagram- shows the difference in the base, rigid and pin. Georgiou, Jim.
Construction & Structures 2 READER, DEAKIN University.
The advantage of using steel as the
material is due to the ability to design
relatively light, long-span, durable, and is
easy to erect safely and quickly.
A primary requirement is flexibility of
planning which results in a demand for as
few columns as possible. The ability to
provide spans up to 60m (most commonly
around 30m), using steel has proved very
popular for commercial and leisure
buildings. The lightness and flexibility of
this kind of steel structure reduces the
sizes and the costs of foundations and
make them less sensitive to the
geotechnical characteristics of the soil.
The structural envelope are simple, it is
essential to ascertain correctly the load
applied to the structure and to predict the
load paths from the load applied through
to the foundations.
(e.g. Sheeting to the purlins and side rails,
through the roof girder to the column and
finally to the foundation and supporting
THE BENDING MOMENTSPURLINS and RAFTERS; Purlins and Rafters are the essential beams that make up the portal
frame structure. Purlins are the beams that run the length of the frame connected to the rafters,
the purlins are bolt connected by the cleat that is welded to the rafter. The purlins are directed
towards the apex with a pitch to achieve the best possible performance. The size of the sections
of these beams is specified by the engineer, along with the size of the web and flange,
depending on the spans and load derived from the design.
EAVES connection;
The eaves connections are in many different forms and changed forms through
history of construction. Originally the diagonal connection plane was considered,
however there was a major stability problem at the inside corner.
•Tapered portal frames fabricated by automatic welding can be utilised to
create aesthetic and economical industrial buildings.
•The behaviour of fabricated sections with slender webs is more complex than
that of rolled sections; the resistance checks must take account of local
buckling, cross-section distortion and the interaction between the primary and
secondary structure through the stays.
Long-span structures( span 30m or
greater) can also be constructed using
timber (mainly plywood) as the material.
Long-span structures require a level of
technical sophistication that indicates a
confidence in timber as a structural and
aesthetic medium on the part of the
The spanning potential of timber portal
frame structure can reach around 50
metres, and provides an extremely
economic solution.
The Plywood Gusset
The Steel Plate and Dowel Knee Joint Bracket; although this is not a timber
product, it is used in conjunction with timber columns and rafters to provide a
steady connection system.
The various timber products used in those of Timber Portal Frame structures
diagram- a typical plywood gusset (solid section).
P.J. Yttrup & Associates Pty. Ltd. Australia.
diagram – Timber portal frame [email protected] Gambia, SA. Accessed
April 2004.
By collaborating steel knee joints with glue-laminated Timber products, Timber portal frame
structures to form large-span structure can be produced. The economical aspect of this material can
not be surpassed.
construction process:
the rafters, purlins and roof bracing are fabricated on
the site, the roof is then lifted on and joined to the
columns (this process can be done as a whole, or by
sections). Elements such as the gussets and purlins
are then installed. All purlins should have all
connections installed, including joist brackets,
tension straps and fly braces. The rest of the major
connection joints such as the knee gussets must also
be fixed along with required bracings. Temporary
bracing is also fitted, due to the support the structure
needs when the support from the crane is released.
After the cranes are detached, the remainder of the
fixing/nailing takes place, this is when the detailed
installations are carried out, such as; girts, eaves,
mullions, remaining purlins and additional roof
wind bracings.
Though Timber being a highly economic solution in
structural frames, it is also highly flammable and
prone to elemental attacks, and due to the natural
property of the material, it needs to be tested before
any type of work is done to check the performance of
the timber. The tests include trial fabrication and
treatments (paints and chemical protection coating
must be applied before the erection).
Yttrup, Peter. Ham, Jeremy, Deakin University Construction and Structures 2
SRT251 LECTURE powerpoint slides.
Spatial requirements of the client:
The selected system provide the client with adequate space to utilise the floor space according to their
business needs. As buildings will often change hands throughout their working life, a re-fit of the
warehouse and/or office space may be necessary. Structural members with significant spanning capacity
allow the occupant to carry-out such activities without the expense of making structural alterations.
Appropriateness of steel portals in this issue.
Steel has extremely high material strength in both compression and tension. With a Young’s Modulus of
200,000Mpa, it is by far the stiffest of all conventional building materials. These two characteristics of steel
are most exemplified in the design of universal beams and columns. Universal beams have excellent
spanning capacity, making their application in portal frame construction the most desired framing option
for medium-sized industrial construction. (Mcleod, 2003)
Appropriateness of saw-tooth construction in addressing issue.
Saw-tooth trusses were used in close span construction, which was prevalent prior to the mid 1970’s. Unlike
portal frames, buildings with saw-tooth trusses had to be designed in a series of bays, supported by loadbearing columns. Such design is far more restrictive than portal framing in allowing spatial freedom to the
end user.
Adaptability of the structural system to a variety of site conditions.
Structural systems that can be constructed in extreme conditions are likely to be popular with building
designers. On sites with high, extreme or abnormal moisture conditions, differential movement may cause
excess structural deflection. This can adversely affect the aesthetic quality of the building, leading to costly
repair work.
Tilt-up and On-site Casting
Economy: Very economic as it provides a
larger amount of building, operating and
investment for your dollar.
Design Freedom: The beauty of tilt-up
designed buildings, is that they create a
structure that suits and is sufficient for any
purpose or taste.
System characteristics
The most common characteristics of tilt-up construction include:
Building Quality: Tilt-up construction structures require the latest technology, experienced
design and construction professionals.
Speed Of Construction: Due to the systems engineering and assembly lie
involved in tilt-up construction, productivity then provides savings in time and labour.
•Versatility: Tilt-up wall panels also make it very simple to create a building that is easily
repositioned in order to provide new openings or other building additions.
•Financing: Tilt-up-built structures have proven to be a more attractive investment to
lending institutes due to their lasting value.
•Resale: Concrete buildings much easily retain their appearance, structural integrity and,
most importantly, their value.
•Infiltration Factor: Tilt-up constructed buildings are air-tight. This enables the building to
save on heating and cooling loads, and the size of mechanical units.
•Reduced Maintenance: Building maintenance costs are reduced because of the rugged
durability of concrete, and its practical construction detailing.
•Floor Utilisation: Because tilt-up construction requires no columns inside the building,
there is unrestricted space for door locations and rack spacing.
•Security: The steel reinforcements in the concrete provide a deterrent for potential illegal
•Noise Abatement: The sound abatement properties of concrete make an efficient sound
•Thermal Economy: Energy costs can be minimised due to the natural heat-sink properties
of concrete.
System application
Prepare for castings: When producing tilt-up panels, factors that need to be considered include, most
importantly, providing a suitable casting bed/ slab for the panels. The surface must be a sound, dense,
smooth concrete surface. Then follows the essential elements such as; creating an effective mix design
(concerning the use of fly ash and water, if needed), the use of moisture barriers, considering the
temperature at the time of placing, vibration of the concrete, and being sure of sufficient proper
finishing and curing techniques. (Tilt-Up Construction,1989)
Form work:
Formwork is a temporary structure, that acts as a stencil, to form a sand bed,for the pouring of
the concrete, in order to create the panels. Basically, timber planks are temporarily positioned
outlining the perimeter of the desired structure, then used to hold the poured concrete in
position as it dries, forming the panel.
A vital part of the panel construction, is selecting a sufficient curing compound and bondbreaker.
Factors to be considered when choosing an appropriate bondbreaker include; a product that
performs both the curing and the bondbreaker (to ensure compatibility between the materials),
weather conditions (rain and heat can effect the bondbreaker), durability of the bondbreaker,
whether or not the panels will be painted (in this case, bondbreakers that leave a paintable surface
are available), whether or not the panels will be exposed (because bondbreakers leave stains), and,
will floor treatments be needed.
Lifting- Inserts:
The location of lifting inserts should be used in instances where strongbacks are used, where the panel
is of a large size. These are positioned in accordance to where the rigging equipment is needed in
order to lift the panel safely off the ground without damaging the panels. The inserts are required so
as the crane can then be connected to the panel easily when it is time for lifting.
Bracing and Bracing Inserts:
Braces are needed to help resist wind and construction loads. Where an applied load
is apparent, three bracing inserts are essential, and generally, a minimum of two
braces are needed for a single panel. These are usually placed on the same side as
lifting inserts. (Code Of Practice Tilt-Up Construction, 1985)
Joining: There are usually two types of
construction joints; those that allow relative
movement, and those that do not. Joints are
required where a break in concrete pouring
occurs, at planned joint locations, they are
to coincide with expansion joints,
remembering that faulty joints can lead to
rusting on the reinforcement.
Vertical joints include: mechanical key,
dowel bar, reinforcement mesh and wirebrush joint/ scabble back concrete.
Horizontal joints are to be placed between
columns, slabs or beams.
Control joints are used to create a plane of
weakness, and cause the concrete to crack in
the desired area. Other joints include:
Expansion joints, Isolation joints and
Watertight joints.
A contraction joint is used so as two
concrete surfaces are able to move away
from each other as a result of shrinkage etc.
Benefit of cast on-site
•No transport costs
•Limits useability of floor
•Easier liftings
•Can be load bearing
•No columns
Benefits of Tilt-up
•Cost effective
•Speed construction - Reduced labour cost
•Ease of construction- factory process on site
•Durability-compare with metal system
failures and accidental damage
•Security- used for prisons
•Fire resistance
Sound reduction 50db v,30 metal skin
Architectural expression new and versatile
Energy conservation: thermal mass
Low maintenance and cost
Building Applications
Step 1
"Parameter Formwork": The desired panel thickness
is fixed to the casting surface, this is done including
any openings or features. A coating of bondbreaker
is applied, in a spray form, to the concrete and
Step 2
"Reinforcement": Reinforcement is fixed within
the forms, also using the required lifting and
bracing inserts. The concrete is then poured,
followed by being vibrated, screeded and then
bull floated.
Step 3
The concrete is then trowelled finished, by hand and
power. Followed by a spray-applied cure coat.
Step 4
This process is then repeated once more for all panel
casting, using climbing framework.
Step 5
All concrete is then cured, the formwork is
stripped, the building's slab is prepared, and the
lifting equipment is organised to arrive. The first
panel is lifted, set, and temporarily braced.
Step 6
The rest of the panels are then tilted from
their stacks, transferred, set and braced.
Step 7
The crane, then, is placed in a single
position and working limits,where it can
lift and set all panels.
Step 8
All panels are lifted within one day, and
the structure is now ready for
intermediate floors, roofing system and
final wall decoration to be fixed for
– Lightweight.
– Offer pre-finished options.
– Provided a range of materials option,
finishes, appearance options and
maintenance requirements.
– Prefabricated
– Rigid finishes
– Just suitable for regular rain washed area
or unless needs regularly clean.
– Not be able to composite with other
materials- contact between dissimilar
metal can lead to galvanic corrosion.
– Transmit roof noise from heavy rain or
hail- unless sound insulation material is
installed under the roofing.
– Provided little or no thermal insulation
benefit- the roof spaces will heat up and
cool down rapidly
Cladding Materials
1.1Zinc Aluminium Alloy-Coated Mild Steel
; manufactured by dipping the mild steel in a hot solution of
45% zinc and 55% aluminium alloy followed by a
chromate wash to protect the steel form corrosion
Offers a wide range of profile (e.g.: curve) and finish
Fast fabrication as it can be supplies in long lengths
It’s nature color , silver-grey , dulls slowly when
exposed to the weather.
Provided the corrosion protection, best durability.
Fig 1 Zinc Aluminium Cladding
Not suitable to use as a walking surface on the roof
High cost materials.
1.3 Zinc
Formed by melting of ores which
contain the zinc blend followed by
rolling to form a sheet
material. Zinc is described as either
commercial (pure) zinc or as alloy
containing small amounts of copper
and titanium to improve tensile
strength and creep strength.
• Better durability on steeper pitched roofs,
because of better rain washing
• Recyclable
• Suitable use to form roof accessories and
• corrosion-resistance
• can be pressed to form a tile shape
1.2 Lead
99% pre metal which may contain very small
amounts of copper, silver and tellurium to
stabilize the movement properties of the
lead. Sheet lead roofing is manufactured
by milling, hand casting, and machine casting.
– Easily worked into shaped (complex and
and for forming joints
– Recyclable
– Excellent corrosion resistance in most
– Excellent performance at high wind loads
– Very low maintenance.
– Requires specialized installation skills and
procedures- cost and time considerate.
• Limited range of profile and finish options
– Low fatigue resistance ( can crack where not
• Reform at cold temperatures; become brittle
free to expand or contract).
• Impurities in the zinc can cause the
– Heavyweight .
formation of localized small holes.
– No thermal insulation.
1.4 Aluminium
Offers a wide range of roof slope
and profile options.
Lighter and more durable
Ductile, malleable and corrosionresistance.
Fast fabrication.
Excellent performance in different
Sensitive with acids and strong
alkalis materials
Easily damage by poor storage prior
to installation, severe hail storms,
being walked on during and after
Impurities lead to perforation.
1.5 Stainless Steel
; are iron alloys which contain at least 12% chromium
and have controlled concentrations
of other elements.
• Advantages:
- offer a wide range of profiles
and finished options, including
factory coated
- Fully supported sheets, where
it can be jointed by welding
or with specially designed
edges incorporating a selfdraining joint.
- Great corrosion-resistance
Fig 7 Aluminium Cladding
- Low maintenance
- More difficult to form on-site
than copper, lead, aluminium or
Roof Cladding Selection:
According to the Design considerations( the environment issue and
performance), aluminium cladding became the best solution of roofing for
the warehouse and showroom design.
The roof geometry for the warehouse and showroom are quiet simple;
2° pitch roof
surrounded by gutter (roof drainage). In this case, Aluminium
would be able to cover up the design requirement. It is much cost
effective than others steel-based cladding ( lead, copper ), more
durable, and available in a wide range of forms ( such as;
guttering, downpipes ). The nature color of aluminium; light
grey with either a smooth or orange peel surface, is suitable
for the industrial environment. Properties of aluminium cladding are
than the others, approx. 2.3 kg/m² with typical thermal movement
Specification product of Roof and Wall cladding:
Lysaght”, KLIP-LOK 406
Materials specification:
; Metal base with 0.60 mm BMT thickness
; contain 2.82 kg/m masses
; available with the COLORBOND pre-painted
steel complies with AS/NZS 2728-1997.
Maximum support spacing:
; 3600 mm c/c span
; based on testing in accordance with
AS1562.1-1992, AS4040.0-1992 and
Fig 9 KILP-LOK 406
Wind pressure capacities:
; 1.67 kPa
; Testing was conducted in accordance with AS 1562.1-1992 Design and Installation
of Sheet Roof and Wall Cladding- Metal, and AS4040.2-1992 Resistance to Wind
Pressure for Non-cyclonic Regions.
The rigid shape of an inflated
airbag does not apply pressure
to the ribs of secret - fixed
cladding or adjacent to support
It’s direct pressure rig uses no air
bags and applies pressure uniformly
over the entire profile- including the
“Uniform pressure distribution of our direct pressure rig which accurately reproduces
the wind conditions experiences in the field.”
The first sheet set longitudinally in relation to gutter
When lifting sheets lengths onto the roof frame
ready for installation, make sure all sheets have
the overlapping ribs facing towards the side
where fastenings to commence. Fasten clips to
the purlins at each of the sheet, having positioned
so that the first sheet will be in correct relation to
other building elements. Align and fasten the
remainder of the first run of clips using a string
line or the first sheet as a straight edge
overhang and locates it over the fastened run of
clips, positioning the centre rib first, and engages
the centre and overlapping ribs onto all clips by foot
Position and fasten the next run of clips, one
Place the second sheet over the second run of clips,
to each support, with the short return leg of
again positioning the centre rib first. A string line
the clip over the underlapping rib of the
stretched across the bottom alignment of the sheets can
installed sheet. The spur can be flattened
with a blow from a rubber mallet to seat
down over the ribs, if the clip fouls one of
be used to check that the ends of the sheets are in line.
Fully engage the interlocking ribs and the centre rib over
each clip. Apply foot pressure to the top of the centre rib
over each clip. For complete interlocking, along the
the spurs spaces along the outer free edge of
underlapping rib must be fully engaged in the shoulder
the underlapping rib.
of the overlapping rib. When engaging the interlocking
ribs, stand only on the sheet being installed, that is
the overlapping sheet, and not on the preceding sheets.
Make periodical checks that the installed sheets are
aligned with the roof perimeter.
a) If the space left between the last full sheet and
the fascia or parapet is more than a half sheet
width, a sheet can be cut longitudinally, leaving
the centre rib complete.
This particular sheet can be fully
clipped onto a row of clips as for a full sheet,
before installing the capping or flashing.
b) Otherwise, it can be covered by the capping
or flashing if the space left between the last full
sheet less than a half sheet width .
In this case,the last sheet should be secured by
cutting clips in halves and fastening the
underlapping rib at each purlin with a half clip.
The selection/choice in choosing the right members in the structure (beams, columns,
and connection details) depends largely on cost. Economic approach towards the
construction of the building is an important aspect but keep within the functional
The factors that needs to be considered when working out the width or the span of the
warehouse are:
Amount of load capabilities of the purlins and girts used, this is determined by the
beam-size and the material.
Footings and foundation capability, the soil-condition plays a large part as it must be
able to accommodate the column loads.
The size and the material of the cladding/envelope system.
Bracing is an important issue within a portal frame structure, as long-span structures
need considerable amount of bracings in response to the wind loads applied. Angle
bracings and rod bracing can be considered, however angle bracings would be a much
economical solution, and as rod-bracings have tendencies to sag, cross bracings
therefore provide a much practical bracing system for this type of structure.
In designing warehouse structures of long-span characteristic, the main factor
considered is to fulfill the functional(/structural) requirements with regards to the
economical view( cost). This can be solved by the standardization of the frame by
incorporating beams and columns of similar characteristics (size, mass, density).
Design proposal : Warehouse
The warehouse building is approximately
45m x 35m of concrete pad footing with
concrete slab,fitted with a metal sheet
cladding with clip-lock roof system.The
main access to showroom and office
building is via a side pedestrian access door.
The long-span warehouse; span 40m was
designed on the site provided, the
warehouse provides an automobile
showcase area and a maintenance facility
included within the warehouse. [include
diagram of schematic design of the
warehouse along with the site plan]
Type of members
Size (mm)
Max span / size
460 UB ( BHP)
450 x 190
Portal frame
360 UB ( BHP)
350 x 170
Column in office building
250 PFC ( BHP)
250 x 90
Roof purlins in both buildings
16 UA ( BHP)
150 x 90
Eaves strut in office building
Metal sheet ( Lysaght)
Zincalume 0.6 mm thickness
Minimum roof pitch 1 degree
Concrete panel 150mm thickness
7000mm x 6000mm
Cladding in office building
OFFICE STRUCTURE Construction Process
Concrete Flooring systems
The tilt up wall system is a site precast method of building
construction. Slab dimensions are
approximately 10 metres high, 10
metres wide and 190 mm in
thickness. These slabs weigh
upwards of 15 tonnes.
Tilt-up slabs are held at their base
in a trench at or below floor level
and secured at their base by no
other means. The upper
section of the slabs are attached by
metal bolts to a metal plate, welded
to rolled steel joists (RSJ), forming
the roof support structure of the
Structural steel will rapidly loose strength when subjected to heat (A 56% loss of strength
will occurs at 593° Celsius); As this happens, collapse can occur within 5 to 10 minutes.
Further, Steel roof beams when heated will expand and may push walls outward.
The direction of slab fall may also be governed by the performance of the roof, subjected to
heat and fuel loads from within the building.
Critical review of structures:
The purpose of the following section is to critically analyse the
alternative structural systems that may be deemed as suitable
for the design of medium-scale warehouse and office spaces.
In the course of conducting research for this review, advise was
sought from a reputable local building professional with
extensive experience in this area of construction. Information
drawn from interviews with this professional, along with
various textual sources, will form the basis of this review.
The content of the review will centre on the following
incomplete structure, which have been observed over the last
month. Another two types of structural systems will be
reviewed, these are; Timber portal framing and steel
construction with saw-tooth trusses.
Leopold Primary School: Multi-Purpose Facility.
Address: 1 Kensington Rd, Leopold.
Builder: Lyons Construction, Fyans St, South Geelong.
Structural details:
Super-structure: Steel portal frame on pad footings. Footings in main hall are concrete pads
supporting a timber-framed sub-structure. Non-load bearing timber-framed walls divide up the office space.
Stiffened raft slab footing used in performance and office areas.
Building Envelope: Corrugated iron roofing throughout structure. Corrugated iron wall cladding
enclosing main hall. Masonry cladding enclosing office space and performance area.
Steel portals.
(1) Steel has extremely high material strength in both compression and tension. With a Young’s Modulus
of 200,000Mpa, it is by far the stiffest of all conventional building materials. These two characteristics of
steel are most exemplified in the design of universal beams and columns. Universal beams have
excellent spanning capacity, making their application in portal frame construction the most desired
framing option for medium-sized industrial construction. (Mcleod, 2003)
Portal frames- footings systems.
Reference to pads in hall. Good for athletic facilities not for warehouses. Pad footings, such as those
used for the hall in Structure 1 are prone to differential movement. The pad footings and strip flooring
used in this case will provide greater comfort to the facilities users, than would the harder surfaces of
raft slabs. Such issues are not of concern in the design of warehouses. Of more importance, is providing
support to the immense live loads that will be imposed on the structure, such loads would only
compound the problems caused by differential movement. Saw-tooth trusses were used in close span
construction, which was prevalent prior to the mid 1970’s. Unlike portal frames, buildings with sawtooth trusses had to be designed in a series of bays, supported by load-bearing columns. Such design is
far more restrictive than portal framing in allowing spatial freedom to the end user.
Issues critical to the selection of structural systems for warehouse and office spaces
Spatial requirements of the client
The selected system provide the client with adequate space to utilise the floor space according to their
business needs. As buildings will often change hands throughout their working life, a re-fit of the
warehouse and/or office space may be necessary. Structural members with significant spanning
capacity allow the occupant to carry-out such activities without the expense of making structural
Structural systems with pre-cast insitu wall panels as load-bearing members are in
wide spread use in industrial construction. Rafters are bolt-connected to fixing plates,
which are connected to the reinforcement and cast into the panel.
The spanning capacity of such systems is comparable to portal framing, with the size
of wall members increasing in accordance with the roof loading.
Saw tooth construction
Saw-tooth trusses were used in close span construction, which was prevalent prior to
the mid 1970’s. Unlike portal frames, buildings with saw-tooth trusses had to be
designed in a series of bays, supported by load-bearing columns at close span. Such
design is far more restrictive than portal framing in allowing spatial freedom to the
end user.
Timber Portals
Timber Portal frame construction may be designed span the same distances as steel
The nailing pattern that is used in timber portal connection systems is far more
complex than the rigid bolting system used in steel portal connection.
Durability of the structural material throughout the building’s life-span
Of paramount importance to building designers and clients, is the likely cost of
maintenance works throughout the working life of the building. Materials used in modern
construction, such as steel, timber and concrete, have diverse compositional properties and differ in
how they are affected when sustaining prolonged load actions.
Weather resistance also varies among the type of structures, which can be critical if the conditions
in which they exist are extreme. (Creep etc)
Steel Portals
The hot-rolled, mild steel used in portal framed construction s renowned for its durability. The
material maintains it’s stiffness over long periods of time, making it the least susceptible to time
dependent creep deflection. This allows steel structural members to be recycled after building
(Ham, 2003)
Reinforced concrete wall panels, like all concrete products, must be carefully manufactured to
ensure that durability can be maintained over long periods. All reinforced concrete panels must
undergo surface treatments to guard against chemical attack and to water proof the material.
Steel, however is a naturally occurring material and its manufacturing process is far more
simplistic than that far concrete.
Saw-tooth truss construction.
One major disadvantage of using saw-tooth truss systems, was the need for a box gutter
drainage system in the truss troughs. The box gutters were prone to leakage, which would
often occur within the main work area, and thus required frequent maintenance. In portal
frame construction, storm water drains to gutters that run parallel to the external walls
perpendicular to the rafters, reducing the likelihood of leakage.
Cost of the Building Materials and Construction Process
Budgetary concerns will often be the most important factor in the choice of design
for a building client. In these situations, the building design that is the most cost-efficient, in
terms of materials costs and constructability will be chosen.
Steel portal framing is the most cost-effective form of industrial steel construction. It is for this
reason that saw-tooth truss construction was superseded as the preferred structural system for
industrial applications in the 1970’s, when the cost of labour began increasing, in relative terms,
to the cost of steel, as a result of labour market pressure. (Page, 2004)
What about constructability comparison b/w Pre-cast timber and steel portals.
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Ham, Jeremy, SRT251 Construction and Structures 2, LECTURE, School of Architecture and Building, Deakin
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Mortlock M., Tatham C.,Selecting Roof Cladding, Branz, (Porirua City)New Zealand,1998.
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Internet Sources- Websites:
* BLUESCOPE webpage;
* LYSAGHT info webpage;