Wind Assessment Standards for Australian Residential Projects (Pt. 2)

Learn how to design wind bracing system to Australian Standards - AS 4055 Wind Loads for Housing and AS 1684.2 Residential Timber Frame Construction

About this event

Using the correct wind classification is critical in ensuring a building is designed to comply with the applicable local building standards. In Australia, the two standards that apply are the AS 4055: 2021: Residential Wind Actions and the AS/NZS 1170.2:2021: Structural design actions, Part 2: Wind actions.

However, calculating wind loads for a residential building can be difficult and time-consuming. The parameters that go into wind calculations such as topographic parameters, shielding parameters, and terrain categories are often obtained based on guesstimates and may result in potentially unsafe or costly outcomes during or after the build.

Join Qiming Liu, ClearCalcs' Structural Engineer, on Wednesday, June 28th, 2023, from 12 pm to 1 pm Australian Eastern Standard Time (AEST) in this 2-webinar series on Wind Assessments Standards for residential buildings in Australia.

In the second part of the series, Qiming will give an overview of the wind bracing design workflow to the AS 4055: 2021 and AS 1684.2 requirements. We will discuss the different site characteristics involved in the analysis, the affected building and what to do when your design fall outside the design limitations such as geometric limits, wind loads, torsional irregularities, large openings, etc.

In this webinar, we will cover:

• An overview of the workflow for designing a bracing system -- Determining the "wind class" of your structure (AS 4055) -- Determining total bracing requirements (AS 4055 / 1684.2 - overlaps them both) -- Deciding upon the specific bracing type and how to lay it out (AS 1684.2)
• Site-specific characteristics for wind assessment
• Limitations to the wind bracing system design (geometric limits, wind loads, torsional irregularities, large openings, etc.)
• How to use ClearCalcs Wind Bracing Calculator & a worked example in ClearCalcs

Resources

• PowerPoint Presentation
• SR337 Design guidance of specifically designed bracing systems in light timber-framed residential buildings (2015)
• AS 1684.2:2021 Appendix D Examples - Foundation bearing area, distribution of bracing and shear force

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Webinar Summary

The presenter, Qiming Liu, discusses the different wind assessment standards and provides an overview of wind bracing for residential houses. The webinar aims to educate participants on how to determine wind class and calculate wind forces for structural design.

The presenter explains that AS 4055 and AS 1170.2 both consider environmental factors that impact wind speed, such as shielding, topography, and terrain. AS 4055 is specifically for residential houses, while AS 1170.2 can be applied to buildings less than 200 meters. The presenter also mentions the limitations of each standard and the simplified assumptions used in AS 4055.

The presenter then explains the seven-step design process for wall and subfloor bracings, which includes determining wind classification, calculating wind forces, designing the bracing system, and checking connections. They also briefly mention roof bracing, including pitched and gable roof bracings, as well as trust roofs, which require reference to another code for design details.

After determining the wind classification and calculating the horizontal racking force, the next step is to determine the wind pressures using table lookups in the standard. The wind pressures depend on the surface type of the roof, whether it's vertical or sloped. Once the wind pressures are determined, the total racking force can be calculated by multiplying them. The code also mentions the use of nominal wall bracings, which are internal linings of the building that can already take some of the racking force.

The presenter continues to explain the wind bracing requirements for residential houses, discussing the capacity and specifications for cross bracing and sheet bracing. They also mention the height modification and the option to increase capacity if using a different framing group. Additionally, they highlight the importance of evenly distributing the bracings and provide spacing requirements based on wind classes.

The presenter continues by discussing the spacing requirements for wind bracing, depending on the wind class and whether it is for a single or upper floor of a two-story building. They also mention the need to consider selling depths and provide proper connections for the bracing. The presenter concludes by introducing ClearCalcs' wind bracing calculator and encourages users to provide feedback for future improvements.

The presenter demonstrates how to use the ClearCalcs platform to design wind bracing for a residential building. They input the building configuration, wind class, roof pitch, and other parameters to calculate the area of elevation and wind pressures. The platform provides a summary of the design, including utilization percentages and recommendations for adjusting the design if necessary.

During the Q&A session of the webinar, participants raised questions about mixing bracing systems and the potential issues that may arise from using elements of different stiffness. The presenter mentioned that there are no restrictions in AS1684.2 regarding mixing systems or taps, but further investigation is needed to understand any potential torsional effects. Additionally, a participant shared their experience with using different bracing systems in New Zealand and how they maintained equal bracing demand across the building to ensure better performance.

The participants discuss the possibility of using a design program that allows for breaking up a building into separate compartments for bracing purposes, but they note that this approach may not comply with the codes. They also mention the importance of considering factors like frictional drag and the length of the building when designing the bracing system. The webinar concludes with a reminder to reach out with any further questions or feature requests for the calculator.