There are indeed several study materials and resources available for bridge engineering in the civil engineering optional subject. These materials can be extremely helpful in gaining a comprehensive understanding of bridge engineering principles, design, and construction. Here are some key resources that you can consider:

1. Textbooks:
- "Bridge Engineering" by Jim Zhao and Demetrios Tonias: This textbook provides a thorough introduction to bridge engineering, covering topics such as bridge types, design considerations, and construction techniques.
- "Bridge Engineering Handbook" edited by Wai-Fah Chen and Lian Duan: This comprehensive handbook covers all aspects of bridge engineering, including design, analysis, and maintenance.

2. Online Courses:
- NPTEL Online Courses: NPTEL offers a range of online courses on bridge engineering, providing lectures, assignments, and assessments. These courses are offered by reputed institutions and are available for free.
- Coursera: Coursera also offers online courses on bridge engineering, taught by industry experts and academics. These courses typically require a fee for enrollment.

3. Journals and Research Papers:
- Journal of Bridge Engineering: This journal publishes research papers, case studies, and technical notes related to bridge engineering. It is a valuable resource for staying updated with the latest developments in the field.
- Conference Proceedings: Proceedings of conferences such as the International Bridge Conference and the International Association for Bridge and Structural Engineering (IABSE) symposia often provide valuable insights into bridge engineering research and practice.

4. Previous Year Question Papers:
- Solving previous year question papers from the civil engineering optional subject can help you familiarize yourself with the exam pattern and the types of questions asked. This practice will also help you assess your preparation level and identify areas that need further improvement.

It is important to note that while these resources can be highly beneficial, it is equally important to refer to the syllabus provided by the UPSC for the civil engineering optional subject. This will ensure that you focus on the relevant topics and allocate your study time effectively.