By Martin van den Hemel, Richmond Review,
10 Aug. 2011
________________
Even a moderately strong
earthquake could trigger liquefaction beneath Richmond Hospital's
aging north tower, and cause its foundation to sink and fail and lead to
"significant building damage and possible partial structural
collapse."
That's according to a
structural engineering report obtained through B.C. freedom of information laws
by journalist Stanley Tromp and provided to The Richmond Review.
Authored by Bush, Bohlman and Partners senior partner Clint Low, the March 3
report focused on the north tower, which was built in 1965 under the building codes of the era,
"when seismic design was not a governing consideration."
Richmond Hospital is somewhat unique, the report states, in that it faces two major
seismic considerations: its ability to resist lateral shaking during a quake, and the underlying soil's
ability to support the foundation during a high-energy ground-shaking event.
While the current practice
for large buildings involves densifying the ground to resist and prevent
liquefaction, that wasn't done at
the time the north tower was constructed nearly five decades ago.
Vancouver Coastal Health
Authority spokesperson Anna Marie D'Angelo said long-range plans call for the
north tower to be replaced, rather than upgraded.
"It will be a big
project and takes time to develop," she said.
D'Angelo said the health
authority does take the contents of the report seriously. She noted that the hospital's Westminster tower was
built in 1997 and complies
with modern earthquake standards.
Upgrading the north tower to
meet current building code requirements would cost upwards of $12 million, and
be a "significant and disruptive construction project," the report
said.
In conclusion, Low wrote:
"The soft soils underlying the hospital
are prone to liquefaction under moderate and strong earthquake ground shaking.
Liquefaction will lead to foundation failure and large horizontal ground
displacements causing significant building damage and possible partial
structure collapse. Liquefaction substantially increases the building seismic risk."
Added Low: "We rate the
building as high risk."
The current building code
requires a building to be able to withstand four times as much of the seismic
forces as in the 1960s, and
the north tower's superstructure and foundations are adequate for about 20 per
cent of the 2010 code's seismic demand.
Richmond Hospital's north tower isn't the only tall Richmond building constructed
during the late 1960s and early 1970s.
Simon Fraser University
research professor John Clague said the phenomenon of liquefaction wasn't well
known during that period. Asked earlier this year about the three tall towers
across from Richmond
Centre, Clague wrote that he didn't know whether their foundations were
constructed taking into consideration the possibility of liquefaction.
"Ground shaking is much
less of an issue than liquefaction...It is very important that the foundations
of these building be seated below the liquefiable sand layer that underlies Richmond. If not, there is a
problem."
__________________________