civil engineering

There's no way to answer your question as currently presented. Could you provide a little more information, such as:

• what size rods?
• what is their material of construction?
• what will they be supporting?
• how long will they have to support whatever it is they are supporting?

The more information you can provide about what you are trying to do, the higher the likelihood that someone here will be able to help you.

Really you only need the maximum compressive and lateral loads, maximum moments, points of support, shape and length of the rods, material composition, and required safety factors. From this information you could calculate the necessary size of the rods.