It simply means that your original design would not hold up the required load, i.e., the bridge would fail. Use a serif typeface such as Times New Roman except for the section headings, which should be a sans serif such as Arial. Check the typefaces for this web page. Draw the shear and bending moment diagrams for one of your trusses. Point out that the maximum stress is located at the midpoint.
Normal stress is much more important than shear stress.
Therefore, point out that bridge should be tall in center where moment is maximum and zero height at ends where the moment is zero. Compare roof and road trusses and discuss zero-force members. Try not to include zero-force members or use small area. Abstract, Table of Contents, Introduction, Objective, Procedure, Results, Discussion, Conclusions, References, and Appendix. Start Roman numerals with Introduction and end with Conclusions.