Under deflection, where will a split occur in a glulam beam with a top restraint bolt?

• A. Area near bottom bolt connection
• B. Mid-span of the beam
• C. Area at and around top bolt connection
• D. Area at the lateral restraint clip

Answer: (C)

Splitting in a glulam beam under deflection tends to start where there is a local concentration of stress caused by fasteners and restraint. A top restraint bolt creates a localized constraint at the top of the section, turning the bolt hole area into a notch that concentrates compressive and shear stresses as the beam deflects. The top fibers are already under compression from bending, and the restraint around the bolt amplifies that stress around the hole, making crack initiation more likely there and along the grain. From that high-stress region, a split can propagate along the grain as the wood fibers separate. In contrast, the mid-span lacks a concentrated restraint, the bottom side is more about tension, and a lateral restraint clip doesn’t produce the same localized stress concentration at the critical face to start a crack.