Create Wind Definition & Assign Wind Load for Bridge (AASHTO 2012)

Here are some pointers.

Since you already know the intensity of pressure, you can directly feed that data into the intensity vs height data from inside Definitions > Wind Definitions. For details on how to do this, you may go to Help > About STAAD.Pro and browse to the section of the online help as marked below.

The software would then calculate the wind loading on the structure and you will be able to see these generated loads after you run the analysis.

When you say wind component on live load, do you mean wind load acting on the moving vehicles ? If so that is not something that you can generate automatically in STAAD.Pro. The software can generate moving loads on the structure automatically but any lateral load due to wind on the vehicles has to be added manually to the appropriate load cases.  

Here are some pointers.

Since you already know the intensity of pressure, you can directly feed that data into the intensity vs height data from inside Definitions > Wind Definitions. For details on how to do this, you may go to Help > About STAAD.Pro and browse to the section of the online help as marked below.

The software would then calculate the wind loading on the structure and you will be able to see these generated loads after you run the analysis.

When you say wind component on live load, do you mean wind load acting on the moving vehicles ? If so that is not something that you can generate automatically in STAAD.Pro. The software can generate moving loads on the structure automatically but any lateral load due to wind on the vehicles has to be added manually to the appropriate load cases.  

Sorry if the instructions were not clear enough. Within the Reference Materials in that same help page, the last item is the Wind Load tab. If you click on that you will find details on how to apply the load. That page also refers to section 5.32.12 of the technical Reference which explains the command syntax.

Here is a list of steps for your ready reference

Once the wind definition is complete, add a new load case from within Load Case Details.
Select the newly defined load case and click on the Add button.
The Add New : Load items dialog box will pop up.
Choose the Wind Load option from with that box and define the inputs as explained in the above help documentation and click on Add.

By default the software considers the structure to be made of closed panels and would calculate the wind load at each node based on the influence area for each node. The load will be applied at each node on the face of the structure that is loaded by the wind. On the other hand if you choose the Open Structure option when applying the wind load, the software would calculate the wind load as an udl on the individual members.