1842 Damage Caused by Nearby Structures and Lifelines

Weak or poorly designed facilities will often cause damage to nearby structures during earthquakes. The intelligent planning of adjacent lifelines (called colocation) is a good way to minimize disruptions to lifelines during earthquakes and other disasters.

When buildings, bridges, and other structures are built too closely together, one problem is pounding. This is particularly a problem for connectors on highway interchanges that are sometimes in such close proximity that the column of a higher structure will go through the lower bridge deck. Buildings are often built too closely together causing pounding and moderate structural damage during earthquakes. Pounding can cause serious damage since impact loads of very short duration can carry a very large force. However, pounding may also be beneficial when it prevents resonance.

More serious damage occurs when a poorly designed structure collapses onto an otherwise seismically resistant structure. There are no benefits from this interaction.

Piers 352 and 353 on the Route 3 Expressway in Kobe, Japan, supported the superstructure on steel hammerhead piers. The columns were 2 m by 1.5 m by 8.8 m in height, supported on pile foundations, and built using the 1964 specifications. The piers were 8.8 m tall and on pile foundations. The superstructure consisted of 30-m-long, steel simply supported plate girders, one end fixed and the other end on elastomeric expansion bearings. During the 1995 Kobe Earthquake, the bridge was damaged when a collapsing building fell against the expressway. The building (shown in Figure 18.68) applied a lateral load to the superstructure. This resulted in buckling of the vertical stiffeners on the girder webs, bearing damage, and also some damage to the bottom of Pier 353. The main damage was separation of a metal plate that was installed to protect the steel column from traffic collisions. However, because there was a collapsed building leaning against the bridge, it was felt to be expedient to provide shoring to the piers after the earthquake. The ability of the superstructure to move laterally over the piers helped to prevent more serious damage from occurring to the substructure.

FIGURE 18.68 Collapsed building leaning against the Kobe Route 3 Expressway. (Photo courtesy of Hanshin Expressway Public Corporation.)
FIGURE 18.69 Washed-out abutment fill caused by water pipe break.

A lifeline can often cause problems to other nearby lifelines during earthquakes. The Balboa Boulevard Overcrossing is a three-span (actually two spans with a 22-ft-long bin-type abutment between Abutment 1 and Bent 2) cast-in-place prestressed concrete bridge (except for a concrete slab for the bin-type abutment) on Highway 118 near Northridge, CA. The superstructure is 283 ft long and 117 ft wide. Bent 3 is a three-column bent on a spread footing. The columns are 5-ft octagonal sections with a large flare. The abutments and wingwalls are on piles. During the 1994 Northridge Earthquake the Balboa Boulevard Overcrossing experienced minor spalling of the concrete cover at the top of the columns during the earthquake. The shaking broke a small-diameter water line under Abutment 1 that washed out the backfill behind the abutment. Figure 18.69 shows the collapsed slab for the bin-type abutment and the cast-in-drilled-hole (CIDH) pile supporting Abutment 1. The grade beam that supports the wingwall is on the left.

These are just a few of the many secondary causes of damage during large earthquakes. What typifies this kind of damage is that its prevention may not rely on structural issues. In fact, the best solution is to find a better site during the planning of the structure. There is little the engineer can do once the structure straddles an active fault or is within a few feet of a vulnerable structure.

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