Bolster retrofitting extends the crossbeam below the girders, preventing the girder from slipping off sideways during an earthquake. Girders support the road surface, so it is important that they remain in place during an earthquake.
On some bridges, we will fill in gaps between existng columns with a support wall. The support wall will better hold the bridge in place during a severe earthquake.
Two types of seismic improvements are shown here: a column jacket, which prevents the bridge column from crumbling apart during an earthquake, and girder stops, which prevent girders from sliding or tipping over.