This program calculates the wind pressures on a structure where the wind force will vary with height. Analysis is performed per 1994 UBC Section 16 Division II, Section 1613 -> 1618, which uses Ce, Cq, qs, and I to calculate wind pressures at different heights on a structure.

 

The user can enter floor to floor heights for the program to use in calculating the wind pressures, and enter tributary widths for the calculation of total story shears at each level.

 

 

 

Basic Usage

 

This program performs a simple tabular summary of wind pressures, and basic usage consists of entering the wind pressure criteria, selecting the number of stories, and entering the floor to floor heights and exposed widths.

 

Basic usage follows these steps :

 

 

Example

The data entry for this example is shown in the screen captures that accompany the Data Entry Tabs and Results & Graphics Tabs sections to follow.

 

 

 

Data Entry Tabs

This set of tabs provides entries for all input in this calculation. While you are entering data and switching between these tabs you can view the desired resulting information on the tabs on the right-hand side of the screen (calculated values, sketches, diagrams, etc.). A recalculation is performed after any entry data is changed. After each data entry you can view the results on the right-hand set of tabs.

 

General Tab

 

 

Exposure

Enter the type of exposure the structure will be exposed to per section 1994 UBC section 1614. Exposure B is for terrain that has buildings, forest, or surface irregularities 20 feet or more in height, covering at least 20 percent of the area within one mile of the structure. Exposure C is for terrain that is generally open, extending ½ mile or more from the site in any full quadrant. Exposure D is for wind speeds in excess of 80mph (129 km/h) and has terrain that is flat and unobstructed facing large bodies of water. Please see the UBC for more in-depth descriptions.

 

Cq = Pressure Coefficient

This factor, which varies from 0.5 to 3.0, can be obtained from UBC Table 16-H. It pertains to the general composition of the structure that the wind load will be applied to.

 

I:Importance Factor

Enter the  "I"  factor from UBC Table 16-J.

 

Basic Wind Speed

From UBC section 1616 and 1994 UBC Figure 16-1.

 

Qs = Wind Stagnation Pressure

This value is read directly from UBC Table 16-F, which is stored internally. Based directly on the user defined Basic Wind Speed.

 

 

Force Table Tab

This table is the actual analysis of the wind forces on the structure. The calculated Design Pressure for each level height will be applied over the Exposed Width to yield the total lateral force per level. This lateral force will be added down the height of the structure, level by level, to calculate the Story Shear. Similarly, the lateral force will be multiplied by the appropriate lever arms to give the  Story Moments .

 

 

Level

This is the story label for the level. It will be numbered automatically from the highest floor downward. The table is automatically sorted in order of highest to lowest "Height".

 

Height

The user should enter the height of each level above the base for the analysis. This height will be used to recall the various Exposure Coefficients from the internally stored UBC Table 16-H.

 

Exposed Width

Enter the width of the structure to which the Design Pressure should be applied, for calculating the shear force per level.

 

Add, Change, Delete Buttons

These buttons control your modifications to the table of story information. Pressing Add or Change displays another window where you can specify the floor information. Here is what it looks like :

 

 

 

Results & Graphics Tabs

This set of tabs provides the calculated values resulting from your input on the "Data Entry Tabs". Because a recalculation is performed with each data entry, the information on these tabs always reflects the accurate and current results, problem sketch, or stress/deflection diagram.

 

Results Tab

This table provides a table of the calculated values for each floor level.

 

 

Level

This is the story label for the level. It will be numbered automatically from the highest floor downward. The table is automatically sorted in order of highest to lowest "Height".

 

Ce

Based upon the Level Height above the base and the Height/Gust/Exposure factors the user has entered, this value is read from the internally stored UBC Table 16-H.

 

Cq

This value is automatically inserted from the previous input.

 

Design Pressure

For each level, the design pressure is determined by calculating UBC Formula 18-1 for the values entered. This design pressure is then applied to the Exposed Width to calculate the lateral force being applied at each level.

 

Lateral Force

This is the product of the Design Pressure * Exposed Width * Height Between Floors above & below, and is the force applied to each level for calculating Story Shear and Story Moment.

 

Story Shear

The Story Shear at each level is calculated by adding the Lateral Forces  at and above the current level.

 

Story Moment

The Story Moment at each level is the summation of all the lateral forces above the current level times their moment arms.

 

Base Totals

This are the total shear and overturning moment at the base of the structure.

 

 

Sketch Tab

This tab provides a sketch of the beam with loads and resulting values shown. Using the [Print Sketch] button will print the sketch in large scale on a single sheet of paper.

 

 

 

Design Pressure List

This tab shows the calculated wind pressure for the entire height of the structure you have entered. The total height is divided into 400 increments and the pressures give.  To calculate the total force per level the individual pressures are totalled for 1/2 the level height above and below.

 

 

 

Sample Printout