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— Property Management Quarterly — November 2015
W
hat do you do when your
team is well into a con-
struction project and real-
ity fails to align with what
was planned? Is it possible
to change course and salvage a proj-
ect, thus avoiding a teardown and
starting over?
These are big, important ques-
tions, and exploring each of them
could constitute a thoughtful aca-
demic exercise. But when a concrete
producer contacted our firm about a
snag in construction, we didn’t have
time for academics. The producer
was well into a large, high profile
high-rise in downtown Denver, and
the second-floor parking deck was
unable to meet the required loads.
The project was 16M, a
340,000-square-foot, mixed-use
building on the southeast corner
of the 16th Street Mall and Market
Street in downtown Denver. The
site formerly was an Office Depot.
The vision for 16M was a 10-story
redevelopment including luxury
apartments, five floors of office
space and a full floor of restaurant
space – all of which was threatened
because of concrete that wasn’t
meeting compressive strength. The
structural engineer of record had
carefully analyzed the slab using the
lesser strength achieved and found
a small area that would not provide
adequate support as built.
No one on the project had antici-
pated this problem, because so
many steps were taken to ensure
a smooth build. Early tests showed
that the concrete should make
the required design strength. Yet
the material wasn’t performing
as expected. The
project team now
faced practical
(and potentially
costly) concerns
as to whether the
existing slab would
need to be torn
out and replaced,
which would be a
cumbersome, dis-
ruptive decision
that would have
delayed work on
the building.
When we
received the call,
most of the on-
the-ground project
team, who had years of experi-
ence in high-rise construction, saw
slab replacement as the presump-
tive option. However, I knew from
40-plus years of experience in mate-
rials testing that this choice came
with a very high price.
Another option was beam place-
ment below the problematic area.
But this option was expensive and
potentially unacceptable, as it would
limit clearance in the main drive
location of the belowground parking
lot.
Luckily, our materials testing
team’s experience spans many
sectors of development and con-
struction. Relying on our work with
departments of transportation and
road/bridge developers, we could
see a solution that had eluded 16M’s
project team. Commercial construc-
tion rarely needs this “fix,” because
primarily it is used to reinforce
roads and bridges, but we believed it
would work, and careful study bore
us out.
The answer was to use carbon
fiber to improve the strength of the
section in question. This could be
done with concrete as placed, pre-
venting the need for a teardown. The
carbon fiber material has been used
for more than two decades and pos-
sesses incredible strength compared
to steel. The Colorado Department
of Transportation occasionally uses
it on bridge repair and highway con-
struction projects.
The strong, thin layer of carbon
fibers, encapsulated in a resin film,
can be adhered with epoxy to the
surface of concrete, akin to putting
a cast on a broken arm. Proceeding
with reinforced post-tension con-
crete in this case would place tensile
reinforcement on the bottom of the
slab, providing a structurally sound
repair while also serving as a new
application of a unique solution.
Most importantly, the application
would compensate for the lesser
compressive strength, thus allowing
the concrete to stay in place. In addi-
tion, external tensile reinforcement
uses strong, flexible fibers that are
not subject to weathering – a key
consideration for structures such as
Management
Orville “Bud”
Werner II, PE
President,
CTL|Thompson
Materials
Engineers Inc.,
and Principal,
CTL|Thompson,
Denver
Photos courtesy CTL|Thompson
The parking lot project was at 16M, a 340,000-square-foot, mixed-use building on the
southeast corner of 16th and Market streets.
