Operational Manual
Trusses fabricated using this program are ideally suitable for use in
residential and light commercial construction. Please note; however, that the
recommendations should be used as a guide only and a professional engineer P.E. should be
consulted prior to fabrication.
The development approach has been to provide a procedure that is as interactive as
practical, in order that the most economical construction design, or alternatively the
most appropriate fabrication design can be selected to suit particular business needs.
Manufacturing preference is as convenient as three clicks away. Cost of
production is conveniently displayed on-screen for instant comparison.
Fine-tune the production cost data to reflect the actual production environment to
achieve a very accurate truss cost estimate.
Essentially, the only limiting factor is not so much the cost of materials used to
fabricate the trusses, but handling issues on-site in real world conditions. Light gauge
steel is exactly that, and eventually the slenderness of the truss becomes a handling and
bracing problem.
Principles of Trussed Roofs
Roof trusses have several advantages over the conventional pitched roof method
of construction, and whilst material cost savings may or may not be a feature, the
practical advantages in ease of construction, contributes very significantly to their wide
spread adoption.
Trusses generally span from external wall to external wall, releasing internal walls
from structural duties and thus providing open plan flexibility. Installation of
Pre-manufactured trusses is rapid, thus reducing on-site labor costs. Pre-manufactured
trusses include the characteristics of other manufactured articles, similarly produced in
well-supervised, controlled environments.
Design Considerations
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Where roof trusses are
employed, the support walls must be designed to share the weight of the roof. If special
architectural features are desired, the modifications must be made in accordance with the
engineering design. It may be convenient to
position support walls or architectural features in accordance with the roof design, say
for example, placing a dormer window between two trusses, rather than cutting or
curtailing one of the trusses. |
Alternatively, architectural features such as coped ceilings
can be formed by elevating the height of the support walls and building the feature below
the bottom chord of the truss, i.e. non structural ceiling feature.
Truss types
The truss type options are the most appropriate for steel construction. Early
timber trusses had compression members designed in timber and tension members in steel,
however steel has similar properties in tension and compression, therefore the design can
match the needs of the building.
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The truss configurations used by EasySteel include other useful
features. Equidistant node spaces for example, make the practical aspects of setout
and assembly simple. |
Conventional trusses are
provided by “Types 1 through 4”.
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These may be characterized by a common or standard
heel height (vertical distance between the wall top track and the top surface of the roof
truss)
Where non-standard heel height is required, curtailed trusses may
be selected and these are referred to as “Howe trusses”.
Single slope roofs (skillion) can be designed with either rafters
or a selection of half trusses. |
Procedure
Tab through a series of questions pertaining to the function and
placement of a particular building. Hover over the appropriate text box for program hints.
Inputs relate to the local environment and the sum of these conditions reflect the
loads that may be imposed on the building over its lifespan.
The alternative design paths available due to the section selection
form, facilitates a truss design that best suits the needs of the manufacturer, building
contractor, project specifier or architect.
References
The design approach is provided by Minimum design Loads for Buildings and Other
Structures American Society of Structural Engineers (ASCE) and Specifications for the
Design of Cold-Formed Steel Structural Members American Iron and Steel Institute (AISI).
General
Many of the selection options have automatic default figures, and if no
selection is made, these figures are assumed.
Where options are presented as drop down lists, alternate entries are acceptable, for
example, it is Ok to enter 15 inches in the list box for eave width. Similarly, roof mass
options are indicative of commonly used materials, individual requirements may determine
otherwise, and these may be entered in the corresponding text box.
Sometimes specifiers will combine dead load with snow load. In these cases, the roof
mass figures should be “adjusted” so that the generated dead load report matches
the figure specified. In the case of “Internal pressure coefficient” (i.e. the
power of the wind trying to blow the roof off from the inside), the default figure is
calculated from details already entered. It would not normally be necessary to change this
figure unless you have some good reason to do so.
Project Details
Customer
Enter the Customer Name in
the text box and the name (identifier) of the truss in the Plan/view
text box. The name of the truss might be something similar to Thru living room or
Main truss. The Job might be New House or your
customers name and the Ref No.
is for regular customers who may have several projects with the same design. The above
details will be printed on each of the documents produced and the space in the text box
approximates the relevant space available on the printed documents.
The truss width may be entered as feet and inches
or a decimal measurement; for example 32.625 feet. You could also enter decimal dimensions
in inches for the truss if you had a mind to.
Select “Half truss” if the requirement is
for a single slope roof. This action will restrict the choice of truss designs later on,
to half truss types. This may however, be deselected later in order to redesign using
conventional truss selections.
Enter Eave width in inches or select one of the
options available. If no selection is made program will default to 24 inch option.
The truss spacing
might be best pictured as the distance from one trussto the next, but in practice, it is
actually the distance from halfway to the trusses on either side of the truss in question.
It is possible to design a truss that is not positioned equal distances from its adjoining
trusses. In these cases, enter the sum of the distances to the midpoints between each
neighboring truss or support.
Select Roof Pitch from one of the options or enter
a decimal, for example “6.25”.
Classification of buildings and Other Structures.
Select an option best described by the proposed occupancy i.e.
- Houses/All others. - All buildings and structures except those listed below.
- Public Buildings - buildings and structures where the primary occupancy is one,
which more than 300 people congregate in one area.
- Essential Service buildings - Buildings and structures designated as essential
service facilities, including but not limited to; v Hospital and other medical facilities
having surgery or emergency treatment areas. v Fire or rescue and police stations. v
Structures and equipment in government communication centers and other facilities required
for emergency response such as Power stations and other utilities required in an
emergency. v Structures having a critical national defense capabilities. v Designated
shelters for hurricanes.
- Farm low Hazard buildings - Buildings and structures that represent a low hazard
to human life. Buildings such as agricultural buildings, certain temporary facilities, and
minor storage buildings which, in the event of failure, provide a low hazard to human
life.
Select the “Continue” button to bring up the load details options
form.
Load Details
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Dead loads - These include those loads
imposed by permanent construction. They may include the weight of the roof covering,
ceiling materials and fixed service equipment. Select the appropriate roof covering and
the corresponding mass figure will appear in the adjacent text box. Enter an alternate
mass if desired. Select a ceiling construction from the options. As with the roof mass, an
alternate mass may be entered in the adjacent text box. Snow Load - If a snow load is required, the relevant ground snow
load figure should be inquired from a local building authority, and the slider bar may be
employed to enter the figure. If the above option is selected, “Roof
temperature” options will appear. These conditions should be representative of those
that are likely to exist during the life of the structure. |
Heated a little for example, refers to a structure that is kept from freezing.
The condition where the wind blows the snow from one side of the roof and allows
it to build up on the other side is automatically calculated. If however, a physical roof
obstruction such as a chimney might influence the design of the truss through the build-up
of snow, select the “Roof obstruction” check box.
Wind Load - Enter the Basic wind speed. The default
figure is 95 mph as required in Texas. Designers throughout the US commonly use 80 mph
which is the minimum, however lesser figures will not be accepted. Wall height - Enter the
height from the ground to top of wall, for example, given 8ft ceiling and 2ft of crawl
space enter 10ft. Hurricane coastline - Buildings to be constructed within 100 miles from
the designated hurricane coastline require special wind load consideration and check box
should be selected.
Click on Continue
The original input form will appear with added features. Note the load details.
With practice, it will be possible to make a good guess at what type of truss to
select depending on the figures shown in the “Load in Top Chord” and “Top
Chord Bending Moment” text boxes. From the Truss types list, choose the simplest
truss type i.e. Type 1 and check each of the truss members in turn.
If the default Top chord section is not adequate i.e. (denoted as No in the suitability box), opt for one of the
following scenarios;
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The basic cold-formed steel shapes referred to in the section
selection form conform to accepted International conventions. The web is the back of the
“C” shape and the flanges form the top and bottom of the “C”. The lips
complete the “C” to distinguish this section from the plain channel, which does
not have the lips. C-sections are most commonly used for truss members and wall studs.
Plain channels are not normally used for the structural members of roof trusses. The
dimensional measurements are derived from the outside surfaces of the section parts,
except for the bend radius, which is measured on the inside of the sections. |
As each of the sections are made the costs are reflected in the truss cost area.
It may be useful to try alternative section combinations to arrive at the best price or
simplest truss. Sometimes it may be best on the other hand, to select heavier gauges and
simpler designs if rough site handling or transport conditions are expected.
Company Info
The load data form may be activated from the top menu bar in the truss Load
Analysis Form by selecting ”File” and “Load” or from the Open screen
by selecting “Initialize”. Enter company details and prices.
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Select “File” from the menu and print the following;
- Design analysis.
- Computations.
- Fabrication details.
- Construction details.
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Tog-L-Loc
The number of fixings and choice of fixings may be nominated from the Menu bar.
Selection will be represented in the engineering calculations and the documentation.
EasySteel does however, strongly recommend BTM Tog-L-Loc fastening for best practice.
The truss design and computations should be reviewed and stamped by a
professional engineer prior to submittal to any building authority.
For further information please complete
information request form
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