OAKLAND -- A simple welding mistake led to small bolts that sheared on the new Bay Bridge's bike and pedestrian path railing last year and the bolts were subsequently replaced in early 2013, bridge spokesman Andrew Gordon said Wednesday.

The undetermined number of broken fasteners were discovered where the railing is bolted onto the deck on one side of a series of expansion joints, or small spaces that allow the structure to expand and contract with the temperature.

The contractor mistakenly welded decorative caps directly onto deck plates rather than the tops of the bolts, which are threaded through oval grooves that allow the path to move but keep the railing in place, Gordon said. As the structure heated and cooled, the bolts' movements were restricted and sheared under the unintended load.

Inspectors discovered the glitch last year and the contractor subsequently replaced all the bolts. The decorative caps were eliminated, Gordon said.

Unlike the high-strength steel anchor rods elsewhere on the bridge that snapped in early March due to hydrogen embrittlement, the steel used to make the small bolts that secure the railing to the pathway is not in question, Gordon.

"This was not a steel problem," Gordon said of the pathway repairs. "It was a minor welding mistake and it has been corrected."

Contact Lisa Vorderbrueggen at 925-945-4773, lvorderbrueggen@bayareanewsgroup.com, politicswithlisav.blogspot.com or Twitter.com/lvorderbrueggen.