SOFTWARE ICON GUIDE
Introduction to
Truss Loading
Course Workbook
EN
CONTENTS
Definitions …………………………………………………..
Chapter 1
Duration Factor ………………………………………….....
Chapter 2
PLF/PSF …………………………………………………….
Chapter 3
Calculating Reactions ……………………………………..
Chapter 4
Calculating Girder Reactions ………..……………………
Chapter 5
Calculate Area Reactions from Conventional Framing...
Chapter 6
Calculating #1 Hip Loads ………………………………….
Chapter 7
Loading #1 Hip with Add’l Span.…………………………..
Chapter 8
Girder that Carries Hip and Commons…………………...
Chapter 9
Cantilevered Hip .…………………………………………..
Chapter 10
Deflection ……………………………………………………
Chapter 11
Standard Attic Loads ………………………………………
Chapter 12
Dormer Condition …………………………………………..
Chapter 13
Floor Balcony ……………………………………………….
Chapter 14
Cantilevered Floor ………………………………………….
Chapter 15
Office Load ………………………………………………….
Chapter 16
Mechanical Load …………………………………………...
Chapter 17
Steeple/Cupola Load ………………………………………
Chapter 18
Wall Girder Load ……………………………………...........
Chapter 19
Loading Class Manual for intelliVIEW – Chapter 1
Definitions
Live Load - Loads which are not from the weight of things permanently attached to the building
such as; wind, snow, seismic, construction, and occupancy loads.
Dead Load - The weight of the structure or building itself is considered dead load. Examples
include the permanently applied loads from purlins, sheathing, roofing and ceiling materials,
and the weight of the truss itself. Since material weights are normally expressed on a poundsper-square foot basis, dead loads for sloped surfaces must be adjusted for the pitch of the
chord member.
Uniform Load - A load that is equally distributed over a given length or area and is expressed in
pounds per lineal foot (plf) or pounds per square foot (psf).
Triangular Load - A type of uniform load that increases or decreases at a steady rate along a
given length. Loads applied to a hip jack or loads resulting from snow drifting would be
considered a triangular load. These loads typically have either a starting or ending magnitude
of zero.
Concentrated or Point Load - Loads of a specific magnitude located at specific location. The
load resulting from a beam attached to the bottom chord of Truss would be an example of a
concentrated load.
Unbalanced Load - This term refers to the removal of load from a portion of the truss. An
unbalanced snow load check would analyze the truss with the live load removed or reduced
from a section of the truss, typically one side of the peak.
Attic Trusses are an example of a truss that is sensitive to unbalanced loading because they
have an area without webbing triangulation and as such require an unbalanced load check. The
unbalanced loads are generated by intelliVIEW automatically.
Floor Trusses with interior bearings, cantilevers, or balconies also require unbalanced load
checks. These loads are automatically generated by intelliVIEW.
Loading Class Manual for intelliVIEW – Chapter 2
Duration of Load Factor (Duration Factor)
This is an adjustment to the allowable stress in wood members based on the duration; total
length of time, the load causing the stress is applied to the member. The shorter the duration of
time that the load is applied, the higher the percentage increase in allowable stress.
Because of wood’s structural properties, it can support higher loads for shorter periods of time.
The Duration Factor approximates the total length of time that the maximum load is applied to
the structure during its life.
Factor Duration
2.00
2-Seconds
Typical Loads
Impact Load. This duration factor is to be used only with the engineer
of record’s prior approval, and never with connectors.
1.6
10 Minutes
Wind and Seismic Loads. Consult building codes as some areas require
1.33 duration factor for wind loads.
1.33
2-3 Days
Wind Loads. Consult building codes to determine if this duration factor
is applicable to your area.
1.25
7 Days
1.15
2 Months
Construction and Roof Live Loads. Short term live loads. Typically not
applicable for loads resulting from Snow.
Snow Load. Typically, snow in a climate that would not allow melting
for a period of time.
1.00
10 Years
Floor Live Load. This is the standard Duration Factor used where floor
live loading is applicable.
0.90
50 Years
Dead Load. Applies to conditions where all or the majority of the
applied load is dead load. A typical condition would be a member that
carries brick. Consult with engineer of record before using this duration
factor.
What do these values mean?
Think of a truss that has been designed using a duration factor of 1.15 which is generally
applied to snow loads. Live loads due to snow are typically at their highest shortly after a snow
storm. As soon as some of the snow melts or is blown off of the roof, the remaining reduced
load will be endured by the structure for an even longer period of time.
Multiple Duration Factors and Load Cases applied to the truss.
There are typically several instances where combinations of different load types can occur
simultaneously on a truss. Attic Trusses and Wall Girders are two common examples of where
multiple types of load and multiple duration factors need to be considered. These trusses are
analyzed with several load cases.
One load case includes all load types that can occur together. The Duration Factor associated
with the shortest duration load in the mix is used to check this case. Other load cases might
just include one type of live load plus dead load. These cases would each be checked using the
Duration Factor associated with the live load included with that case. iModel can calculate the
necessary load cases if you use the appropriate loading features of iDesign.
Loading Class Manual for intelliVIEW – Chapter 3
Pounds per Square Foot (PSF) / Pounds per Lineal Foot (PLF)
Most loads are entered in pounds per square foot (PSF).
How do PSF loads translate into pounds per lineal foot
(PLF) loads? How does one convert the pounds per
square foot to pounds per lineal foot?
The example roof section shows the sheathing on the top
and bottom chords of the trusses. The sheathing transfers
the applied loads from one truss to another. The top
chord load will be transferred to the adjacent top chords
and the bottom chord load will be transferred to the
adjacent bottom chords.
To calculate the PLF loading on the truss chords, multiply the PSF by the on center (O.C.)
spacing of the truss:
(PSF)(TRUSS SPACING)=PLF
In the above example, the trusses are spaced 2’ O.C. and the total load is 40 PSF.
(40 PSF)(2’ O.C.)= 80 PLF
Let’s break the load down to determine where it is actually distributed on the truss. The total
top chord load = 30 PSF and the total bottom chord load = 10 PSF. Using what you have learned
calculate the Top and Bottom chord PLF.
(____ Total Top Chord PSF)(____’ O.C.)= ____ Total Top Chord PLF
(____ Total Bottom Chord PSF)(____’ O.C.)= ____ Total Bottom Chord PLF
Loading Class Manual for intelliVIEW – Chapter 4
Calculating Simple Truss Reactions
Now that you understand PSF and PLF and how those loads apply to a truss, the next step is to
calculate simple reactions. The formula shown below illustrates how to calculate a simple
reaction. This formula applies to all non-girder trusses at any spacing.
Note: when the trusses are spaced 2’ O.C., the spacing and the 2 Supports cancel each other.
Therefore, to calculate the reaction of a 10’ overall span non-girder truss at 2’0” O.C. using a 40
PSF total load, you would multiply 10’ by 40 PSF, which results in what reaction?
Calculating Uniform Load
A girder is a truss that supports other framing members such as; roof trusses, floor trusses,
conventional framing, or a combination of framing. Let’s now take a look at calculating the
supported PLF load applied to a girder’s bottom chord and the resulting girder reactions.
Remember that for this example the supported trusses are non-girder trusses.
Building on what you have learned, we will use the reaction from the previous example to
calculate the PLF to be applied to the girder bottom chord. As you’ll recall, the reaction = 400
pounds.
We could apply 200 PLF to the bottom chord of
the girder.
However, this load would be
conservative compared to the load calculated by
iDesign.
We calculated the load based on ½ of the
supported span. This applies the entire load to the
girder’s bottom chord. However, some of that load
is distributed to the girder’s top chord. When we
add the full load from ½ of the supported truss
plus the full 2’ of PLF to the top chord, the result is
more load than what is actually there.
Let’s take a look at how iDesign calculates the load.
Substituting the actual span and load, you can calculate a load as iDesign does. The difference
shown in this example is due to rounding.
Loading Class Manual for intelliVIEW – Chapter 5
Calculate Simple Girder Reactions
Many designers take advantage of the Load Transfer feature available in iModel to transfer
loads to girders. In addition to transferring the load, there are safeguards to alert you of
possible missed loads. While the loads generated by iModel are accurate, it is a good practice to
double check the results.
A relatively easy way to double check is to calculate the reactions of the girder using the
supported load area.
Review the diagram above. Each of the colored squares represents 1 square foot. We know
that half of the 10’ span will be supported by the girder. In addition half of the 2’ distance
between the girder and the adjacent truss will be supported by the girder. Looking closer, we
see that half of the load supported by the girder is distributed to each bearing (the reactions).
Using the formula below, we can calculate the girder reactions.
Total Area = 120 ft²
Total PSF = 40
The result will be close but also conservative because we did not deduct the width of the
bearings.
Loading Class Manual for intelliVIEW – Chapter 6
Calculate Area Reactions from Conventional Framing
Now that you understand how to calculate a reaction using load areas, let’s calculate the
reaction from a conventionally framed beam supporting conventional framing. Once we have
calculated the load we will apply it to the girder. The total job load is 40 PSF and the rest of the
information is shown below.
Using the formula from the last example to calculate the load, we find the reaction = 1000 lbs.
Using iDesign’s Loading Tools, we can verify our calculation and apply the load to the truss.
1. Take the girder into iDesign (if the job is already on your computer)
2. Select the Loading icon
3. Select the Add Concentrated Loads icon
4. Select the Header tab and enter data into the appropriate fields.
5. Select the Apply button
6. Read the yellow prompt at the bottom of the screen (Header location?).
7. Use your mouse cursor to select the peak of truss.
8. Read the yellow prompt at the bottom of the screen (Select the piece that load gets
applied to).
9. Use your mouse cursor to select the top chord just to the right or left of the peak.
Loading Class Manual for intelliVIEW – Chapter 7
Calculate #1 Hip Reactions Using Load Area Method
Continuing with the same base load case (right), we can calculate the reactions of a #1 Hip
Truss using load areas. The same formula, used in the last example, can be used to calculate
the girder reactions.
TC LL
20 PSF
TC DL
10 PSF
BC LL
0 PSF
BC DL
10 PSF
TOT. LD
40 PSF
The total supported area is illustrated below left. There will be two load areas that will need to
be calculated. The first area, shown below right in gray, defines the space between the girder
and adjacent common truss. The second area, shown below right in yellow, defines the area
occupied by the by the jacks. The sum of these two areas will determine the approximate Hip
Girder reactions.
Starting with the supported jacks, this area is trapezoidal;
Area of the Trapezoid = 𝑑 �
𝑏+𝑏1
d=setback = 7’
2
�
b=span of #1 hip = 30’
b1=span of #1 hip – setback (d) = 23’
Area of Trapezoid = 7 �
30+23
2
� = 185.5 𝑓𝑡²
Next, calculate the rectangular area;
Area of the Rectangle =
(𝑤)(𝑙)
L = distance from the #1 hip to the adjacent common truss = 2’
W = span of the #1 hip = 32’
Area of the Rectangle =
(2)(32) = 64 𝑓𝑡²
Once the two load areas are known, the girder reactions can be calculated.
(185.5 + 64)(40)
= 2495 𝑙𝑏𝑠
4
Now let’s see how the manually calculated reactions compare to those calculated by iModel
using the Loading Tools in iDesign. Create a Hip Truss in iDesign or load it from iModel and then
perform the following steps:
1. Select the Loading icon
.
2. Select the Add Load Case icon
3. Select the Hip Loading tab.
4. Select the Display LL DL or TL icon
shown below.
to check your results which should match those
To check the reaction:
1. Select the Engineer Icon
2. Select Run Analysis
3. Hold your mouse cursor over a bearing to view
the bearing information.
The Max Reaction = 2489.69 lbs which very close to your
manually calculated reaction which was 2495 lbs.
When the girder exists on a layout, the loads from the supported trusses are automatically
transferred to the girder truss. Also, the uniform loads is reduced appropriately to produce
competitive designs.
Loading Class Manual for intelliVIEW – Chapter 8
Loading #1 Hip Girder that Supports Additional Trusses
The
girder
truss
labeled HG5 (right) is
supporting #1 Hip
framing (end and
corner jacks) to one
face and 32’ standard
trusses to the other.
We will calculate the
load applied to the
girder using the tools
available in iDesign
and also look at Load
Transfer from iModel.
Using iDesign to Manually Load Girder
Assuming that HG5 has been created, either as a New Truss in iDesign or as a truss loaded from
iModel, and is displayed in the iDesign window, we can proceed to apply the loads.
1. Select the Loading icon
2. Select the Add Load case icon
3. Select the Hip Loading tab from the dialog box.
4. By default the input field’s entries match the current truss. It is a good practice to check
the entries to ensure they match your specific conditions.
5. After reviewing the entries, select the Hip Girder button.
6. Input the supported span, review the other options to ensure they match your specific
needs.
7. Select OK to apply the setting and close the dialog box
8. Select the Apply Button to apply the loads to the girder
9. Select the Done button to close the Add Load case dialog box.
Loads applied to the bottom chord include, concentrated loads from the hip jacks, PLF load
from the 32’ common trusses, end jacks, and ceiling load. Top chord loads include, normal
roof load and, PLF from the end jacks. When reviewing the diagram below, red represents
live loads and green represents dead loads.
Same Girder Using Load
Transfer to Apply Loads
Assuming that this girder was created
as part of a layout, we can take
advantage of Load Transfer which is an
automatic process that applies
concentrated loads to the girder that
are derived from the reactions of the
supported trusses.
Loading Class Manual for intelliVIEW - Chapter 9
Girder that carries Hip Condition and Commons
In this next lesson, we will examine loading the HG9 girder (above) using tools available in
TrusCAD as well as Load Transfer using Layout. The HG9 itself is not a #1 Hip Girder, however it
does support a Hip Condition consisting of a #1 hip girder, common trusses and jacks. The
supported hip condition, in this case, is considered to be a full hip condition as it has corner
jacks at both ends.
Loading from iDesign
Assuming the truss has been created from scratch in iDesign, we are ready to add the loads.
1. Select Loading Icon
2. Select Add Load Case
3. Select the Hip Loading tab from the Add Loads dialog box. Even though this girder is not
a #1 hip, we still use Hip Condition to apply the loads.
4. Set Jack Types to No Jacks (A below). Setting this field to No Jacks tells intelliVIEW that it
is not a #1 hip and that 1’ of PLF is to be added to ones face.
5. Select the Hip Girder Button (B above)
A. Check this box to indicate that the
girder is carrying a #1 hip truss.
B. Type of #1 Hip controls how the
concentrated load is calculated. It
is important to select the proper
type.
C. Location where the #1 hip
connects to the girder as
measured from the end of the
girder.
D. Indicates which end of the girder
to locate the load from the #1 hip.
E. Once all fields are set properly,
select the OK button to close the dialog box.
6. Select the Apply button and then the Done button to apply the load to the girder.
Applied Loads:
1. Bottom chord triangulated load, located at left end of truss, is the load generated from
the supported end jacks
2. 4371# concentrated load represents the load placed on the girder from the #1 hip
girder.
3. 928.8 PLF bottom chord load represents the load placed on the girder from the 32’
common trusses.
Example 2
In this next example, girder truss HG9A is supporting a 32’ hip condition, like the last girder.
The differences in the two examples are that this time there is no offset in the setback of #1 hip
MHG and girder MHG is a mono hip instead of being a full hip.
Loading from iDesign
Assuming the truss has been created from scratch in iDesign, we are ready to add the loads.
1. Select Loading Icon
2. Select Add Load Case
3. Select the Hip Loading tab from the Add Loads dialog box. Even though this girder is not
a #1 hip, we still use Hip Condition to apply the loads.
4. Set Jack Types to No Jacks (A below). Setting this field to No Jacks tells intelliVIEW that
it is not a #1 hip and that 1’ of PLF is to be added to ones face.
5. Select the Hip Girder Button (B above)
F. Check this box to indicate that the
girder is carrying a #1 hip truss.
G. Type of #1 Hip controls how the
concentrated load is calculated. It is
important to select the proper type.
H. Location where the #1 hip connects
to the girder as measured from the
end of the girder.
I. Indicates which end of the girder to
locate the load from the #1 hip.
J. Once all fields are set properly,
select the OK button to close the dialog box.
6. Select the Apply button and then the Done button to apply the load to the girder.
Applied Loads:
1. Bottom chord carries normal PLF load from the left heel to the concentrated load.
2. 4789# concentrated load represents the load placed on the girder from the #1 hip
girder. Notice, this load is higher than in the first example due to the framing
configuration used.
3. 928.8 PLF bottom chord load represents the load placed on the girder from the 32’
common trusses.
Loading Class Manual for intelliVIEW – Chapter 10
Working with a Cantilevered Hip Condition
The diagram to the left illustrates a corner set that is
cantilevered 3’ and has a 1’ overhang. The trusses labeled CJ1,
CJ3 and CJ5 will require additional support (bearing) at the end
of their overhangs. This support member is referred to as a
Structural Sub-fascia. In turn the structural sub-fascia is
supported by the hip jack (HJ10) and another truss. During this
lesson we will our discussion to loading the hip jack (HJ10).
Applying the load can be done either in iDesign or by using Load
Transfer from iModel.
Loading using iDesign
Assuming that the truss has been created and is loaded into iDesign
1. Select the Loading icon
2. Select the Add Load case icon
3. Select the HipJack tab and the Add Loads dialog box opens
4. By default, intelliVIEW populate the
data fields, based on the truss being
loaded. It recommended that you
verify that these entries are correct
before proceeding.
5. Select the Apply button to load the
truss and then select the Done button
to close the dialog window.
6. The image (right) displays the
resultant loads.
From iModel
When the cantilevered hip jack is created in
layout, the loads can be generated
automatically using the Structural Fascia
option.
The structural fascia, shown right, supports
the corner jack CJ1, CJ3, and CJ5. The fascia
is supported by the Hip Jack HJ10, the end
jack CJ7, and the #1 hip girder truss.
Loading Class Manual for intelliVIEW – Chapter 11
Deflection
Deflection is the movement of a member that results when load is applied. Every material
deflects under load. There are several types of deflection that occur on a truss or between
individual trusses. The following are some types of Deflection:
1. Live Load Deflection
2. Dead Load Deflection
3. Total Load Deflection
4. Vertical Deflection
5. Horizontal Deflection
6. Mid-panel Deflection
7. Nodal Deflection (at joints)
8. Relative Deflection
9. Differential Deflection
10. Creep
The following examples depict several types of deflection and how they occur on the truss.
Relative Deflection
After studying the example above, you can assume that Relative Deflection is a measure of the
deflection of one deflected node relative to an adjacent deflected node.
Horizontal Deflection
All trusses incur a certain amount of Horizontal Deflection. Certain truss shapes, such as the
Scissor Truss above, are more prone to horizontal deflection than other trusses. There is a
maximum allowable defection, and when exceeded, intelliVIEW displays a warning on the
screen.
Differential Deflection
The two Hip Trusses above demonstrate Differential Deflection which can be explained as the
difference in deflection of two adjacent trusses. The deflected distance between the #1 Hip
and H9 is substantial. This is a condition that, although quite common, has the potential to
cause problems in the field. The #1 Hip is multi-ply and some of the chords have been
increased, resulting in a decrease in the deflection. H9 works without increasing the ply or
lumber sizes; however, there is a higher degree of deflection. A similar condition is created
when the adjacent truss (trusses in the same run) are different in shape i.e. Scissor Truss next to
a Common Truss, or a full span truss next to a stubbed truss. Here are a few suggestions to
reduce deflection:
1. Change web configuration
2. Increase chord sizes
3. Change truss profile (i.e. increase the depth of a flat truss or increase the difference
between the top and bottom chord pitches of a scissors or vaulted type truss)
4. Decrease the on center spacing of the truss
5. A combination of the above.
Deflection Settings in intelliVIEW
intelliVIEW provides settings that allow the designer to control the allowable amount of
deflection. The deflection settings are located in the User Deflection Limits and can be
accessed by selecting the Analysis tab in Job Settings, or the Misc tab from Engineer Options in
iDesign (shown below).
Select the Deflection button to open the Deflection Limits dialog box (shown below).
A toggle allows you to set the deflection limits for roof or floor trusses separately. Also, from
this dialog box you can set the deflection limits for the; top chord, bottom chord, cantilever,
and overhang for the Live Loads or Total Loads.
Span/Defln
The TC, BC, Cantilever, and Overhang fields contain several standard deflection values in the
drop-down menus. You may also manually enter a value into the fields. Each of these fields
has a minimum value set. If you specify a deflection limit that is less than the minimum,
intelliVIEW automatically defaults to the minimum. The chart below shows the Minimum L/D
Deflection Limits for different situations.
Absolute (in.)
The Absolute value allows you to specify the maximum amount of deflection, in inches, which a
truss can deflect. For example, a truss might meet the standard deflection limits but not the
Absolute limit. When this occurs, intelliVIEW generates a warning.
Plaster Ceiling Applied
The Plaster Ceiling option instructs intelliVIEW to use deflection limits of L/360 for Live Load
and L/240 for Total Load. These limits are reflected in the Deflection Limits Dialog box after the
Plaster Ceiling Applied option has been selected.
The following list contains typical deflection limits:
1. Roof (no plaster)
2. Roof Overhangs
3. Floor or Roof w/ Plaster
Live = L / 240
Live = L / 180
Live = L / 360
Total = L / 180
Total = L / 120
Total = L / 240
What does L/240 and L/180 mean?
The L is equivalent to the length (truss span) in inches and is divided by the denominator to
determine the allowable maximum deflection. For example, if you have a 40’ roof span and
wanted to calculate the maximum deflection allowed for Live Load, you can use the following
formula. (X = allowable deflection) The result indicates that the truss is allowed to deflect 2”
under Live Load.
L/240 = X = (40) (12) / 240 = 2”
Similarly, to calculate the allowable maximum Total Load Deflection, use the formula below:
(X = allowable deflection)
L/180 = X = (40) (12) / 180 = 2.66”
The difference between the allowable Total Load Deflection and the allowable Live Load
Deflection equals the Dead Load Deflection; therefore, the maximum allowable Dead Load
Deflection for this example is 0.66”.
Creep
Creep is a permanent Dead Load Deflection that is a result of wood deflecting, or creeping,
under a sustained load over a given time. To compensate, you can adjust the Dead Load
Increase Factor. For example, if you select 1.5, the Dead Load Deflection is increased by 50%
and then added to the Live Load Deflection to obtain the Total Load Deflection (DLD x creep
factor) + LLD = TLD. Remember, you cannot enter a limit in the deflection fields that is larger
than 999, so this is an alternative method to add a higher limit when a higher stiffness factor is
desired (i.e. girders of any type).
Loading Class Manual for intelliVIEW – Chapter 12
Standard Attic Loads
The truss shown above is known as an Attic Truss or a Room-In Attic. This type of truss carries a
combination of Roof and Floor loading. It is also considered to be an indeterminate structure as
it has a non-triangulated web area, which interrupts the normal flow of forces thru the truss.
Proper analysis of an attic requires multiple load cases with multiple duration factors.
Attic Trusses are used for various conditions and are defined as either Habitable or
Uninhabitable. The classification as habitable or uninhabitable determines the amount of load
that must be applied to the open room area. Excerpts from, “ANSI/TPI 1-2002 Appendix B (Nonmandatory) RECOMMENDED MINIMUM DESIGN LOADS” (shown below) explain the
differences.
An Attic Truss that is Habitable is required to have the following loads to be applied to the room
area. These loads are in addition to the standard live and dead loads that have been added per
the job Settings. Note: Magnitude of the loads could vary based on specific conditions.
40 PSF Live Floor Load
10 PSF Dead Floor Load
10 PSF Dead Ceiling Load
If the Attic Truss is Uninhabitable (used for Light Storage) then the following loads should be
applied to the room area. These loads are in addition to the standard bottom chord dead Loads
applied per the Job Settings.
20 PSF Live Load
5 PSF Dead Load as a minimum
The Light Storage loading guide shown above can be applied to any truss.
Whether the Attic Truss was created in layout or iDesign, the following dialog appears to assist
applying the loads. Enter the appropriate loads in the fields provided and then click the OK
button.
While several load cases are created, two are shown below:
Full Load Case
Unbalanced Load Case 1
In addition to applying the proper loads, consideration must be given to the bottom chord size
used in the Attic Truss. The size of the bottom chord is based to limit the deflection in the
room. The following guideline is based on an L/D ratio not to exceed 24, which means the
room width should not exceed twice the depth of the bottom chord.
Bottom Chord Size
2x6
2x8
2x10
2x12
Maximum Clear Room Size (no interior bearing)
11’0”
14’6”
18’6”
22’6”
Loading Class Manual for intelliVIEW – Chapter 13
Attic Dormer Loads
A dormer condition, shown below, requires special loading considerations. There is typically a
girder attic truss on either side of the dormer area. Each girder carries half of the dormer width
and half the distance to the adjacent framing. For the purposes of this example, the width of
the dormer is given to be 8’.
From the framing sections, shown above, we can see that the dormer Attic Girders carry a
combination of both conventional framing and prefabricated trusses. The walls and trusses on
each side of the girders have been omitted in these figures for clarity.
The dormer width is 8’0” and there is a standard attic truss 2’0” from each girder on the
opposite side of the dormer. Each girder attic truss supports one half of the dormer width, 4’0”
of load to one face and one half of the distance to the adjacent truss, 1’0” of load to the
opposite face.
Adjusting the loads can be done in 5 steps:
1) Adjust the On Center spacing of the girder to increase the standard loads.
2) Extend the bottom chord room load to account for the additional accessible dormer
floor.
3) Calculate and add the dead load from the supported knee walls.
4) Calculate and add the load resulting from the ceiling and overhangs of the trusses above
the dormer.
5) Copy and modify Full Load case to create Unballanced Load Cases.
Step 1
There are 2 methods to adjust On Center Spacing. Each method is acceptable and it is up to the
designer determine which they prefer.
Method One
1. Select the word Truss from the Main Menu at the top of the screen in iDesign.
2.
3.
4.
5.
6.
Select Truss Properties from the menu to access the Properties for Truss dialog box.
Select the Load Type button to access the Loading Options dialog box.
Change the entry in the Spacing field to 5.
Select the OK button at the bottom of the Loading Options dialog box.
Select the OK button at the bottom of the Properties for Truss dialog box.
Method Two
1. Select the Loading icon
in iDesign.
2. Select the Modify Loadcase icon from the Loading Toolbar to access the Modify
Loadcase dialog box.
3. Select the Spacing tab.
4. Enter 5 in the Change current spacing to field.
5. Select the OK button to make the change and close the dialog box.
Either method produces the resultant loads shown below.
Step 2
Next we are going to extend the existing floor load confined to the room area to the right heel
of the girder. In our example the floor extends to only the right end of the truss. Other dormer
conditions may require the floor to be extended to both ends. The following steps should be
adjusted to meet the specifics of your condition. The Attic Std. Ld. Load case should be visible in
the Current field before proceeding.
1. Select the Display LL and DL icon from the Loading Toolbar. The Live and Dead Loads are
combined allowing them to be modified at the same time.
2. Select the Modify Uniform Loads icon from the Loading Toolbar.
3. Select the Uniform Floor Load on the Loading Diagram to access the Uniform Loads
dialog box. The selected load changes color for visual verification.
4. Select the Apply and Change Location button.
5. The highlighted prompt at the bottom of the screen indicates that intelliVIEW is waiting
for a new start location for the selected Uniform Load (Uniform load start location?)
Press the <Enter> key to use the original start point.
6. The highlighted prompt at the bottom of the screen changes (Uniform load end
location?). Using the mouse select a point at the right end of the truss (i.e. the right
edge of the right heel).
Step 3
Calculate the triangulated Load resulting from the dormer knee wall and apply that load to the
girder. The knee wall varies in height from 0’0” at the start point to 8’0” at the end point (see
below).
The triangulated Load is calculated to be 0.0 PLF at the Start Point and 110 PLF at the End Point.
110 PLF is arrived at by multiplying the height of the wall, 8’0” at the end point by 13.75 PSF.
1. Select the Add Uniform Loads icon from the Loading Toolbar, to access the Uniform
Loads dialog box.
2. Set the fields as shown
3. Select the Apply button. The highlighted prompt at the bottom of the screen indicates
the next step: Uniform load start location?.
4. Select the Start Point indicated in the image above. This is the point where the left side
of the knee wall intersects with the top chord. The highlighted prompt changes:
Uniform load end location?.
5. Select the End Point noted in the image above.
6. The Triangulated Load appears on the Loading Diagram and the Uniform Loads dialog
box opens.
7. Select the Done button to close the dialog box.
Step 4
The last load to be calculated and added is the Uniform Load from the bottom chord (ceiling)
and the overhang of the 8’0” trusses that are supported by the knee walls. The elevation view
shown at the beginning of this lesson will help you better understand where the loads
originated. Using the following given loads and equations we can calculate the load to be
applied.
Top Chord Live Load
= 20 PSF
Top Chord Dead Load
= 10 PSF
Bottom Chord Dead Load = 10 PSF
Overhang Soffit Load
= 2 PSF
Truss Spacing = 2’0” O.C.
Starting with the bottom chord load, we can calculate the PLF of the supported trusses.
𝑂𝑣𝑒𝑟𝑎𝑙𝑙𝑆𝑝𝑎𝑛
8
�
� (𝑃𝑆𝐹 ) = 𝑃𝐿𝐹 = � � (10) = 40 𝑃𝐿𝐹
2
2
Using the same process as in step #3, the calculated load is applied to the truss.
Use the following formula to calculate the PLF from the 1’0” overhang (the overhang span is not
divided by 2 because there is no other support, so the full load is supported by the knee wall):
(𝑂𝑣𝑒𝑟ℎ𝑎𝑛𝑔 𝐿𝑒𝑛𝑔𝑡ℎ)(𝑇𝑜𝑡𝑎𝑙𝑇𝐶𝑃𝑆𝐹 + 𝑆𝑂𝑓𝑓𝑖𝑡𝑃𝑆𝐹 ) = 𝑃𝐿𝐹
(1)(32) = 32 𝑃𝐿𝐹
Follow the same steps above the load from the overhang is applied to the top chord of the
truss.
Step 5
Now that this load case has been modified we will copy it to a new load case in order to create
the other required load cases. Let’s start by reviewing the current Attic Dead Load Ld. Load
case (below). To display the load case, use the pull-down arrow in the Current field to open the
load case list and select the Attic Dead Load Ld. Load case.
As you can see this load case has no roof Live Load and its Duration Factor is 1.00. You can also
see that the Dead Loads from the knee wall and the dormer trusses have not been added and
that the floor Dead and Live Loads have not been extended. Under these circumstances, it is
easier to copy the modified Attic Std. Ld. Load case and then edit the copy to delete the
appropriate loads.
Start by making the Attic Std. Ld. load case Current.
Next, copy the load case:
1. Select the Copy Load Case icon from the Loading Toolbar
2. Enter a New Description for the load case. I used “Dead and Floor Load”.
3. Select the OK button to create the new load case and close the dialog box.
First, let’s change the Duration Factor:
1. Make the new load case active
2. Select the Modify Load Case icon
3. Select the Duration Factor tab, change both fields to 1.00, then select the OK button to
apply the change and close the dialog box.
Next, we will delete the Roof Live Loads which are the Uniform Loads shown in red:
1. Select the Delete icon
which is located on the CAD Tool Bar.
2. Verify that Uniform Loads or Uniform&Concentrated is visible in the Select Filter at the
top of the screen.
3. Select the 100 plf load and the 20 plf load top chord loads and then press <Enter>.
4. If prompted, “Delete the load from ALL load cases?”, select the No button.
The Loading Diagram for the Dead & Floor Load load case is shown below.
Verify that the modified load case is correct before proceeding.
The unbalanced load cases must also be modified to account for the extra load added as a
result of the dormer. You should review each existing unbalanced load case to determine how
the Top Chord Live Load has been distributed. Copy the modified Attic Std. Ld. Load case and
then modify the loads to create the new unbalanced load case. Repeat for each existing
unbalanced load cases.
As a final step, you can delete the original dead and unbalanced load cases. This step is
optional as leaving those load cases does not negatively affect the design of the Attic Girder.
Loading Class Manual for intelliVIEW – Chapter 14
Balcony Floor Load Condition
The floor truss below has a Balcony Condition at the right end, and there is no wall supported
on the end of the balcony. When this type of floor truss is analyzed, the Unbalanced Floor
Loading for Cantilevers dialog box, which is shown below, opens so that you can properly load
the floor truss.
This floor truss requires multiple load cases and intelliVIEW creates the required load cases
based on the information you have entered. The generated load cases are shown below.
Floor Total Load
Unbalanced case # 1
Unbalanced case #2
Unbalanced case #3
Unbalanced case #4
Unbalanced case #5
Unbalanced case #6
Loading Class Manual for intelliVIEW – Chapter 15
Cantilevered Floor Load Condition
The floor truss below has a cantilevered condition on the right end. In this example, there is an
8’ wall that supports a 28’ roof truss with a 2’ overhang at the right end of the cantilever
condition. When this type of floor truss is analyzed, the Unbalanced Floor Loading for
Cantilevers dialog box, shown below, appears allowing you to create the proper load cases.
This floor truss requires multiple Load cases and intelliVIEW creates the load cases, including
the appropriate duration factors, based on the information you have entered. The generated
load cases are displayed below.
Floor Total Load
Unbalanced case #1
Unbalanced case #2
Loading Class Manual for intelliVIEW – Chapter 16
Office Floor Load Condition
intelliVIEW offers two tools to apply Office Loads to a floor truss, shown below. Both tools are
located in the Add Load case tools on the Loading toolbar of iDesign.
When Auto Office Is selected, intelliVIEW creates several load cases based on the information
that has been entered. The actual number of created load cases depends on the span of the
truss.
Using the Office tool gives you more control. VIEW creates a single load case based on your
input. Example load cases generated using the Auto Office tool is shown below.
Auto Office Ld1
Auto Office Ld2
Auto Office Ld3
Auto Office Ld4
Auto Office Ld5
Loading Class Manual for intelliVIEW – Chapter 17
Adding a Mechanical Load to a Truss
The need to add Mechanical loads to trusses is common. The following examples go through
the steps to add a HVAC (Heating Ventilation and Air Conditioning) load to a truss. HVAC units
may rest on the top of the bottom chord or be suspended from either the top or bottom chord
with mechanical fasteners. These units are often air handlers for AC units or massive exhaust
fans in restaurants weighing up to a few thousand pounds.
Example 1
Load the truss into iDesign that will have the Mechanical Load applied.
1. Select the Loading Icon
2. Select Add Concentrated Loads
3. Select the Mechanical loads tab.
A. Enter the Width of mechanical units between the support points in feet.
B. Enter the Total Weight of mechanical unit.
C. Supported by how many truss(es), the number of trusses that will share this load.
𝑩 𝑊𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑡ℎ𝑒 𝑈𝑛𝑖𝑡 𝑥 2
Resulting Point Load applied at each location = � 𝑪
D. Select the Apply button.
# 𝑜𝑓 𝑆𝑢𝑝𝑝𝑟𝑡𝑖𝑛𝑔 𝑡𝑟𝑢𝑠𝑠
�
5. intelliVIEW prompts
truss.
6. intelliVIEW prompts
truss.
. In this example pick the Peak of the
. Select the Bottom Chord of the
Two (2) 200 lbs point loads offset by 2 foot to either side of the center of the truss are applied
to the Bottom Chord of the truss.
7. Select the Done button, to continue designing the truss.
Example 2
An alternative method is to use a CAD line to locate the center of the mechanical load.
1. Add a CAD Line at the Center of mechanical load location
2. Continue to add the mechanical Load following step 1 through 7 above with one
exception. In step 5 select the intersection of the bottom chord and the CAD line as the
center of the mechanical load instead of the peak of the truss. Results are shown
below.
Loading Class Manual for intelliVIEW – Chapter 18
Steeple/Cupola Loading
Steeples and Cupolas are unique structures that special analysis of the supporting trusses. The
design process begins by contacting the EOR (Engineer of Record) or the AOR (Architect of
Record) to acquire the steeple/cupola specifications. Information found in the specifications
may include the following.
-
Wind data based on the specified building code and design criteria.
The height above ground that the base of the steeple/cupola will be.
Steeple/Cupola maximum weight
The geometry of the steeple/cupola, including the number of sections and the shape
and size of each section.
The surface material of the steeple/cupola
How the steeple/cupola will be connected to the trusses.
These factors are used to calculate the steeple/cupola loads that will be applied to the trusses.
Once all the design specs are collected, the information can be forwarded onto your Alpine
Engineer for the load calculation if needed. Once you have received the loads to be applied,
you can create the appropriate load cases. There are five typical load cases that need to be
created. Below are two methods to apply the loads. Both methods are acceptable and you
should consult your Alpine engineer which is appropriate for your specific conditions.
Method 1
Load the truss that will be supporting the steeple/cupola is into iDesign.
Select the Loading icon
.
Make sure STD.AUTO.LOAD is the Current load case
.
Select Copy Load Case
from the Loading toolbar. The following dialog box appears:
Enter a New Description in the field for the first load case. The label can be to your preference,
but you may want to keep it. For our purposes, this first load case will be labeled Steeple 1.
Click OK to create the new load case.
The new load case is created. Check that the new load case is displayed in the Current field.
.
Note: In method 1, we will copy the STD.AUTO.LOAD load case four more times. These new
load cases will then be modified adding the steeple/cupola load. Each time the load case is
copied a New Description must be entered. (i.e. Steeple 1, Steeple 2, Steeple 3, Steeple 4, and
Steeple 5).
First Load Case (Steeple 1)
The first Load Case will account for the Gravity Loads of the Steeple/Cupola. The 200 pound
point loads you, see below are the actual weight of the steeple/cupola divided by the number
of trusses that support it.
To add the point loads:
1. Select Add Point Load
appears:
from the Loading Toolbar. The following dialog box
2. Add in the appropriate information for your situation and select Apply.
3. intelliVIEW prompts for you to enter the Concentrated Load location. Using your cursor,
select the location where the concentrated load is to be applied. Hint: you may want to
use reference lines for assistance.
4. Once the point load has been added, the above dialog box reappears.
5. Repeat steps 2 thru 4 until all concentrated loads have been added.
6. Select “Done” to close the dialog box.
Second Load Case (Steeple 2)
The second load case accounts for the maximum downward reaction of the steeple/cupola
resulting from the wind overturning moment that is parallel to the ridge. In our example, the
1400 pound concentrated loads shown below have been calculated as the maximum downward
reaction. Use the same steps as the first load case, add the point loads. Remember to Set the
Current load case field to “Steeple 2” before beginning.
Third Load Case (Steeple 3)
The third load case accounts for the maximum uplift reaction resulting from the wind
overturning moment that is parallel to the ridge. In our example the -1000 pound concentrated
loads shown below have been calculated as the maximum uplift reaction. Use the same steps
as the first load case, add the point loads. Remember to Set the Current load case field to
“Steeple 3” before beginning.
Next the snow load will need to be deleted:
1. Go to the Loading Icon
.
2. Make sure that Uniform
Loads
is
selected
in
the
Select
Filter
.
3. Select Delete
from the toolbar. Highlight the top chord uniform live, remembering
that live loads are displayed on screen in the color red and then select Enter. Finished
load case is shown below.
Fourth Load Case (Steeple 4)
The fourth load case accounts for the maximum unbalanced wind load with snow left to right
that is perpendicular to the ridge. In our example, the 1400 and -1000 pound concentrated
loads shown below have been calculated to reflect these loads. Notice that the snow load is
only applied to the top chord from the left end to the peak. Use the same steps as the first load
case, add the point loads. Remember to Set the Current load case field to “Steeple 4” before
beginning.
Fifth Load Case (Steeple 5)
The fifth load case accounts for the maximum unbalanced wind load with snow right to left that
is perpendicular to the ridge. In our example, the -1000 and 1400 pound concentrated loads
shown below have been calculated to reflect these loads. Notice that the snow load is only
applied to the top chord from the peak to the right end of the truss. Use the same steps as the
first load case, add the point loads. Remember to Set the Current load case field to “Steeple 4”
before beginning.
Method 2
NOTE
For adding the load cases In Method 1, we copied the STD.AUTO.LOAD load case for each of the
five load cases that were created and changed the New Description each time (i.e. Steeple 1, 2,
3, 4, and 5). In Method 2, we will copy different load cases which are listed below. You will use
the same steps from above to copy the load cases.
-
First Load Case (Steeple 1) – Is copied from the STD.AUTO.LOAD load case.
Second Load Case (Steeple 2) – Is copied from the worst case downward MWFRS case
parallel to the ridge.
Third Load Case (Steeple 3) – Will be copied from the worst case uplift MWFRS case
parallel to the ridge.
Fourth Load Case (Steeple 4) – Is copied from the worst case uplift MWFRS case that is
perpendicular to the ridge and from the right side of the truss.
Fifth Load Case (Steeple 5) – Is copied from the worst case uplift MWFRS case that is
perpendicular to the ridge and from the left side of the truss.
If you have questions on which load cases to copy for the 2nd, 3rd, 4th, and 5th load cases, contact
your Alpine Engineer for assistance. Once the new load cases are created, examples on how to
modify them are listed below.
First Load Case (Steeple 1)
The first Load Case is based on the Gravity Load from the Steeple/Cupola. The +200 pound
point loads you see below will be based off the actual weight of the steeple/cupola divided by
the number of trusses it will be resting on. To apply the point loads, use the same steps from
Suggestion 1 for applying point loads. An example of the first load case is shown below.
Second Load Case (Steeple 2)
The second load case is based on the maximum downward reaction coming from the wind
overturning moment that is parallel to the ridge. The +1400 pound point loads that are shown
below are calculated from the wind point load + steeple point load. Use the same steps from
the first load case to add the point loads.
Third Load Case (Steeple 3)
The third load case is based on the maximum uplift reaction coming from the wind overturning
moment that is also parallel to the ridge. The -1000 pound point loads that are shown below
are calculated from the wind point load – the steeple point load. Use the same steps from the
first load case to add the point loads in this load case.
Fourth Load Case (Steeple 4)
The fourth load case is created for the maximum unbalanced wind load. This load is based on
wind that is perpendicular to the ridge. The +1400 and -1000 point loads are from the previous
load cases and they are applied to complete the unbalanced load for the steeple. Refer to the
previous steps on how to add point loads for this load case. An example of load case 4 is shown
below.
Fifth Load Case (Steeple 5)
The fifth load case is the exact load as number 4 except for reversed. The point loads and the
wind uplift are flipped. This is done to create the unbalanced load for the opposite side of the
truss from load case 4. Refer to the previous steps on how to add point loads for this situation.
An example of load case number five is shown below.
Loading Class Manual for intelliVIEW – Chapter 19
WALL GIRDER LOADING
A truss is defined as a Wall Girder when its loads result from a composite of Floor, Wall, and
Roof loads with differing duration factors. The diagram below illustrates the Wall Girder truss
we will be using as our example and the loads being applied.
About Bracing:
Before we begin loading our girder, it is important to discuss bracing the top chord of the Wall
Girder. In this example, the conventionally framed Rafters provide top chord bracing. If there
were no rafters or trusses to brace the top chord, the Wall Girder would either have to be the
same height as the Floor Trusses or the same height as the bearing wall so that the roof trusses
would rest directly on the top chord of the Wall Girder. Both ways would provide the required
bracing. Specific design conditions will dictate how the top chord will be braced.
Adding Loads:
First, either transfer the wall girder truss from layout or create it from scratch in iDesign.
The loads will be applied in several steps:
- Step 1 will be to apply the loads from the upper roof and wall.
- Step 2 will be to apply the loads resulting from the lower roof.
- Step 3 will apply the supported floor loads.
Step 1:
Follow the steps shown below to calculate and apply the load from the 8’0” high bearing wall
which is supporting a 28’0” truss with a 4’0” cantilever and a 1’4” overhang.
Note: Do not select either of the buttons labeled ‘Done’ or’ OK’ until all of the loads have been
applied, i.e. after Step 3 is completed.
The loading diagram below displays the loads that were calculated and applied to the truss
when you selected Apply.
Step 2:
Next, we are going to add the load from the 10’0” conventionally framed Rafters and Ceiling
Joists. Because the Apply button was selected in the previous step, the Add Loads dialog box is
still active. Change the information fields as shown below and then select the Apply button.
Selecting the Apply button results in the loads to calculate and add to the existing loads. The
current load diagram is shown below.
Step 3:
The last load to be added results from the 16’0” Floor Trusses that are supported by the bottom
chord of the wall girder. Change the information fields and loading criterion as shown below
and select the Apply button.
Since this is the last load to be added to the load case, you can select the ‘Done’ button to close
the dialog box. Selecting the apply button again will result in the same load being applied a
second time. The resulting complete load case is shown below.
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North Bldg, 4th Floor
Glenview, IL 60025
(800) 521-9790
alpineitw.com
©2016 Alpine, a division of ITW Building Components Group Inc. Form M1026-R 6/17