ASCE 7-16 Wind Changes

The ASCE 7-16 Minimum Design Loads for Buildings and Other Structures was released in the Summer of 2017, and some jurisdictions are starting to reference this standard. MecaStack has a built in calculator for ASCE 7 wind loads on the stack, but Meca also offers a program called MecaWind which calculates wind loads on any type of structure per ASCE 7-05 / 10 / 16. In the course of updating MecaWind to include ASCE 7-16, we have become quite familiar with the ASCE 7-16 standard and wanted to summarize some of the major changes.

Summary of ASCE 7-16 Changes:

The new ASCE 7-16 standard offered many changes to the ASCE 7-10. MecaWind includes ASCE 7-05, ASCE 7-10 and ASCE 7-16, and includes all of the changes in the new standard. I wanted to take a minute to explain some of the major changes that occurred in ASCE 7-16.

• Addition of a new Classification: “Partially Open Building”
• Wind Maps for Hawaiian Islands added
• New Wind map for Risk Category IV added
• Wind Speeds in non-hurricane regions decreased, and contours in Northeast USA revised
• Now a new parameter “Ke” added to account for reduced wind pressures at higher altitudes.
• Edge zone side dimension ‘a’ has been reduced for very large buildings with low sloped roofs.
• Transverse Frame criteria has been added
• Criteria for Rooftop Equipment has been revised and expanded
• Significant changes for Bins, Silos and Tanks
• Solar Panel criteria for Rooftop mounted panels added
• Flat and Sloped Roofs <= 60 ft saw an increase in component and cladding pressures; however, for h < 30 ft in Exposure B also saw some reductions.
• Gabled & Hipped Roofs <= 60 ft have significantly revised figures for Components and Cladding pressures that cover a wider range of slopes.
• Criteria on loads on Canopies has been added
• Components and Cladding Ch 30 Pt 2 completely revised the tables.
• Components and Cladding Ch 30 Pt 4 now refers to Ch 30 Pt 2 when h <= 60 ft.

Although most of these changes are not relevant to stacks, we have incorporated all of these changes into our MecaWind software. 

How does ASCE 7-16 Change for Stacks:

MecaStack includes the comprehensive stack design code ASME STS-1 ‘Steel Stack Design’. In this standard, the ASCE 7-05 wind load calculations are used, which were based upon an Allowable Stress Wind Speed. Recently the ASME STS-1 standard was revised to allow Ultimate Wind Speeds to be entered per ASCE 7-10. The revision was made by simply converting the ASCE 7-10 Wind Speed (Ultimate) to an equivalent ASCE 7-05 Wind Speed (Allowable). From that point on the calculations are the same as they would have been using ASCE 7-05. The STS committee has not yet determined what they will do with ASCE 7-16, but it seems that eventually the committee will have to revise the STS standard to use Ultimate wind speeds, since that is going to the basis for ASCE 7 from now on it appears.

There aren’t many changes in ASCE 7-16 that impact stacks. There are some revisions to the wind maps, and there is the possibility to consider a reduction in wind pressures at higher altitudes due to the air being less dense. It is unclear if STS will allow for this reduction within the Stack code.