1. Materials and Process In Manufacturing;DeGarmo,1997
2. Zain F (2017) Different Types of Defects in Timber. http://civilblog.org/2017/05/30/different-types-defects-timber/.
3. Nondestructive evaluation techniques for timber bridges;Emerson,1998
4. Inspection of Timber Bridges Using Stress Wave Timing Nondestructive Evaluation Tools: A Guide For Use And Interpretation;Ross,1999