Risk refers to the idea that there are variables in any managerial situation that need to be recognized and in some cases reacted to. Technical risk in your project can come from design performance questions (I-35W bridge), materials (properties, regulatory reactions, costs), and manufacturing processes (tolerances, time, cost). In any project, it is important to identify the variables that are significant and understand how they might vary, what the impact of any variation in an important variable is and what can be done to modify the variation and/or react to an unfavorable variation that occurs. Finally, there needs to be responsibility for identifying an unfavorable variation that occurs and initiation of appropriate remedial action.
Your plan should briefly (a few tables with explanation) identify the key technical risks, the actions being taken to mitigate the risks and the individual responsible for identifying and responding to each significant risk factor as needed. To conduct this task, become familiar with failure mode effects analysis (FMEA) and do the analysis on your design.