Wind Analysis in Five Minutes

Posted on August 7th, 2012 in Wind

Summary

The source material outlines the process for setting up and performing a wind load analysis on a 3D building structure using a specialized wind analysis program, likely MasterSeries Wind, emphasizing the speed and automation of the process while addressing complex architectural features.

Structure and Initial Setup

The analysis is performed on a typical 3D building featuring complex geometry, including overhangs, balconies, wing walls, inset stories, and canopies. The building is defined as a steel structure, and the analysis uses the Eurocode method.

Key initial steps involve:

1. Choosing the direction of winds to consider.

2. Setting the four principal angles along with internal pressures.

3. Setting the angle to north to 0.

4. Applying globally reduced values.

5. Identifying inclined members (bracing) using view filters and applying the wind loading to them, excluding specific canopy members. These selected members take the wind loading on a global basis.

Defining Site Location and Wind Analysis Type

The location for the wind analysis is set by using a grid reference finder. A postcode is typed in, a point is marked (e.g., in a field), and the grid reference is copied and pasted into the wind settings. The identified location is Southwest Manchester, and the site is locked down. The analysis is defined as a standard once in 50 years wind analysis, utilizing the Eurocode method.

Creation of Wind Panels

The creation of wind panels is described as the "most difficult part" initially, as the structure starts with no wind panels. While manual creation is possible, it is deemed "slow and laborious" .

The "auto wall" feature automatically generates wind panels . However, the program initially treats the structure as full height and does not understand the inset stories or variations in story heights .

To address the inset stories and complex levels, a finer approach is used:

• The user applies a filter story-by-story, selecting geometry from just below to just above a specific level .

• Applying "auto" within these filtered views ensures the system correctly maps panels for inset stories, balconies, and the roof .

• The filter is noted as powerful because it removes other members from the view, clarifying the selection process .

• The system automatically identifies parapets as separate from the rest of the building, and also identifies small elements like a canopy from an overhang in an inset story .

Generating Loading Cases and Combinations

To manage the loading scenarios, the software allows for automatic generation of combinations, rather than manual creation . The user selects various load combinations, including:

• Dead plus live; live only; dead .

• Dead plus live plus wind (with either wind leading or live leading) .

• Dead plus wind favorable and unfavorable .

Electing to replace existing cases generates 181 loading cases . This large number is due to permutations involving:

• Internal suction and pressure .

• The different leading pressures .

• The repeat of the 610A and 610B loading cases .

All these loading cases and combinations are handled automatically in the analysis . For instance, in loading combinations, the system uses 'P1' (e.g., W1 pressure) and knows to use the 'P' for pressure in the analysis .

Reviewing Wind Loads

The wind loads applied to the structure can be visualized, showing that individual panels are "zoned up" .

When viewing the wind pressures (Q values are considered more applicable ):

• For the Manchester area, leading edge pressure on the structure for a specific direction is visible, looking around 0.8 to 0.9 .

• Small features, like a canopy, may exhibit a different wind pressure compared to normal surfaces, such as pressure on one side and suction in behind .

• The system can display CP values, showing, for example, 1.3 on the leading edges .

• Viewing different wind directions (W1 to W4) shows the leading pressures, positives, and suctions on the structure .

Internal Pressure and Suction Effects

The analysis allows consideration of internal pressure and suction effects .

• When considering the W1 direction with internal pressure, some external pressures are reduced while others are increased .

• Conversely, when considering the S values (internal suction), the pressures shift again: areas that previously increased due to pressure now decrease (sucked back in), and areas that decreased due to external suction now increase .

Application for Cladding Design

For designing the cladding, engineers may focus on the local maximum pressures and suctions . The results show:

• A maximum pressure of 0.7 around certain areas .

• Minimum values (negatives/suctions) showing 1.1 of suction on leading edges .

These tables of values for internal suction and pressure allow for the cladding to be designed more accurately .

Summary with Timestamps

The following table summarises the key steps, processes, and findings detailed in the source material regarding the wind load analysis of a 3D building structure, including the relevant timestamps and source citations.