In Truss Studio™, the Bearings dialog does more than define where a truss is supported—it directly influences how loads are generated, particularly wind loads on the bottom chord. Adjusting bearing location or type can change how the software interprets exposed versus supported regions, which in turn determines whether (and where) wind pressures are applied to the bottom side of the truss. This behavior aligns with broader engineering principles found in ASCE 7-22 and ANSI/TPI 1-2022, which state that wind can act on both sides of a structure and that support assumptions govern load paths and reactions. However, in order to guarantee code compliance, designers must verify that modeled conditions reflect real-world exposure and that required loads are present. [For all images, See PDF or View in Full Issue.]
Why This Matters
Designers often expect wind to act on the underside of trusses in exposed conditions such as overhangs, cantilevers, or open floors. However, in Truss Studio:
- Small bearing changes can add or remove bottom chord wind loads
- Missing loads may not trigger obvious warnings
- Support assumptions affect load generation, reactions, and load combinations.
Understanding this interaction helps ensure that:
- The model reflects real structural behavior
- Critical wind cases are not unintentionally omitted
- The Truss Design Drawing (TDD) accurately represents design conditions.
What Truss Studio Does
Truss Studio uses bearing definitions to interpret the context of the truss within surrounding structure.
Key behaviors:
- Marking a bearing as Overhang Support defines which regions are treated as interior vs. exposed
- Exposure interpretation controls where wind loads are applied to the bottom chord
- Changing the bearing Overhang Support can:
- Suppress or activate bottom chord wind loads
- Alter load distribution and reactions
- Change generated load combinations.
Observed behavior:
- Marking all bearings as Overhang Support can remove bottom chord wind loads
- Unsupported overhangs or cantilevers can trigger wind loads on the underside
- In some cases, expected wind loads may not be generated automatically and require manual input.
The Bearings dialog in Truss Studio does not simply define how and where a truss is supported. Bearings define how the software models exposure and load paths via the Overhang Support checkbox.
Load and Design Standards in Context (ASCE 7-22 & ANSI/TPI 1-2022)
Wind Loading (ASCE 7-22)
- Wind pressures can act on both top and bottom chord surfaces
- Underside pressure develops when airflow occurs beneath a member
- Relevant conditions include:
- Overhangs and canopies
- Elevated floors
- Cantilevered elements.
Elements exposed on either or both sides of the truss must be designed for uplift and downward pressures unless otherwise specified by the Engineer of Record (EOR).
Load Path Principles (TPI 1-2022 Section 6.1.1)
- Small changes in bearing type and location can significantly affect:
- Internal forces
- Reactions
- Load distribution
- Therefore, it is important that the truss designer builds the truss and applies the correct bearing definitions as accurately as possible.
Load Combinations (ASCE 7-22 Chapter 2)
- Structures must be evaluated under multiple combinations of Dead, Live, Wind, Snow, etc. Loads to simulate both “everyday” scenarios and worst-case scenarios.
- Wind plays a very important role, as it can govern:
- Uplift conditions
- Lateral Load transfers (shear blocking)
- Recommendations for hangers, tiedowns, and nailing patterns/spacing for truss to sheathing connections.
- Partial or unbalanced loading may control design. Wind loads can play a major role in these scenarios.
Bearing & Reaction Behavior (TPI 1-2022 Section 7)
- Bearing assumptions affect:
- Reaction magnitude and distribution
- Local stresses and force transfer.
- Partial or offset bearings can introduce:
- Eccentric loading
- Bending and shear effects.
Crushing at Bearings
- Bearing stress depends on:
- Reaction force ÷ contact area
- Local crushing can govern design even if the truss is otherwise adequate
- Designer-defined limits may be necessary where supports are constrained.
How They Relate (Critical Connection)
[For table, See PDF or View in Full Issue]
Practical Scenarios
1. Trusses with Overhang Support turned on in the Bearings dialog.
In the Bearings dialog, checking the Overhang Support button on or off will enable or suppress wind loading on the bottom chord. To do this, you must have at least (2) bearings active. By highlighting one of the end bearings and checking the Overhang Support button on, Studio will effectively ignore that bearing for wind load application purposes and apply wind load to the bottom of the truss until it reaches the next bearing. The “next” bearing is respective of the direction of the wind load as stated in the “Load Combinations” section of the “Applied Loads View” window.
The picture above shows a good example of this. Here, the Overhang Support is turned on for the left end bearing. Due to this, wind load is applied (starting left and moving right) to the bottom chord until it reaches the next bearing.
2. Cantilevered Trusses
Cantilevered sections often require bottom chord wind loads due to full exposure. Trusses with at least one cantilevered end will also have wind load applied to the underside of the cantilevered portion of the truss. To do this, use the “X-Location” section of the Bearings dialog to move an end bearing over by whichever distance most accurately represents the final product. Use the dropdown menu to the immediate left of this input distance to set where this is measured from and which part of the bearing this distance is measured to.
For instance, inputs of “LL” and “5-00-00” will result in the bearings placed 5 ft from the left edge of the truss, with the left edge of the bearings against the 5 ft line. Possible inputs for this dropdown are LL, LC, LR, RL, RC, and RR. The first letter, ‘L’ or ‘R’, represents the side from which the x-location will be measured, such as “4 ft from the left side” or “2 ft 6 inches from the right side”. The second letter dictates where the bearing will be placed with respect to the input distance. For example, if the bearing is placed at an “X-location” of 5 ft, then ‘L’ means the left edge of the bearings will be at the 5 ft line; ‘C’ means the vertical centerline of the bearing will be located at 5 ft; and ‘R’ means the right edge of the bearing will be at 5 ft.
3. Elevated Floor Systems
For an elevated building, whose underside is assumed to be fully exposed to wind, checking the Overhang Support button on for all bearings but one will get Studio to apply wind load to the entire bottom side of the truss, as shown in the picture above.
Connection to Standards
ASCE 7-22 recently added elevated building wind load requirements to their standard. This is currently in development as a new feature in Studio. For any questions on this, please reach out to our engineering team.
TDD Impacts
Depending on your Bearings dialog inputs, some changes may occur to the truss design drawing (TDD). These changes are reflective of the unique load situation. When any uplift wind pressures have been applied to the bottom chord of the truss, a note (shown highlighted in the picture below) should populate in the “Loads Summary” section of the TDD. Note: A missing bottom chord wind load note may indicate missing loads on the truss, so make sure to double-check.
Practical Guidance for Designers
Pay Close Attention to:
- Cantilevered designs
- Overhangs
- Elevated or open-floor systems
- Unexpected missing wind loads
Adjust:
- Bearing location
- Bearing type (wall, hanger, etc.)
- Overhang Support settings
Notes and Limitations
- Some expected wind loads may not be automatically created. Designers should always double-check.
- Bearing inputs do not affect snow load generation.
- Standards require consideration of exposure to wind loads, but:
- The software does not determine compliance. It is the responsibility of the truss designers to model and load the truss in a way that accurately reflects the final product and situation.
Contact your Simpson Strong-Tie Representative or email CSHelp@strongtie.com for more information.