Flexure cracks in the top of a concrete deck would most likely be found in what area?

• A. At mid-span
• B. On the deck edge
• C. Above an intermediate support
• D. At a support bearing

Answer: (C)

When concrete is loaded in bending, cracks appear where the material is in tension. In a multi-span deck, the moment diagram shows hogging (negative moment) over supports and sagging (positive moment) at midspan. Over the supports, the top fibers are in tension, so flexure cracks tend to open on the top surface right above an intermediate support. At midspan the top is primarily in compression under positive moment, so top cracking is less likely there (the bottom fibers would crack instead). The deck edge involves boundary and shrinkage effects and isn’t the typical location for flexural cracks caused by bending. So the top surface above an intermediate support is where these cracks are most likely to be found.