wall engineering ltd. calgary ab, t2m 2p9 canada building ... · building science & restoration...
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L14L ENGINEERING LTD.
Wall Engineering Ltd. Building Science & Restoration
408 - 32 Avenue NW Calgary AB, T2M 2P9 Canada www.wallengineering.ca
March 13, 2017
Riverside Tower Condominium Corporation C/o Connelly & Company Property Management #204, 2723 37 Ave NE Calgary AB, T1Y 5R8 Attn: Mr. Marty Connelly Email: [email protected]
Dear Mr. Connelly,
RE: Riverside Tower - 145 Point Drive NW, Calgary Parkade Post Tensioning System Update
WalI#: 10110.0004
In response to your request, Wall Engineering Ltd. performed update testing of the post-
tensioning system at the above referenced property in February 2017. The primary intent of the
testing is to monitor any changes in tension deficiencies within the existing test sample. Test
results obtained and recommendations provided in this report are based on limited sampling in
select areas. The following provides a summary of our findings.
1,0 BACKGROUND INFORMATION
Unbonded post-tensioned strand systems are a common form of structural reinforcing that
was widely used throughout the 1970's to 1980's. The system relies on high strength steel
strands to reinforce a thin concrete slab and each strand is comprised of seven (7) steel wires
encased in grease and plastic sheathing. The structural strength of this system relies on the
draped profile installed during original placement of the strands, which sinusoidally extends
over each of the columns/beams. Once the slab has cured, the strands are hydraulically
tensioned, which straightens the draped profile (i.e. lifting the concrete slab) and engaging
the slab to achieve the structural design capacity.
Each strand that is embedded within the concrete incorporates steel anchors at the end of
the slab. These anchors can be susceptible to moisture ingress depending on the degree of
exposure and quality of waterproofing during original construction. Post construction
moisture ingress can also occur through deficient waterproofing. The deterioration process
includes the emulsification or breakdown of grease, surface corrosion of wires,
pitting/sectional steel loss, stress corrosion cracking of the individual wires and in many
cases fracture of one or more of the wires (loss of tension/tension deficiency). The rate of
Wall Engineering Ltd. Riverside Tower 145 Point Drive NW, Calgary
Wall#: 10110.0004
Page 1 of4
408 - 32 Avenue NW
Building Science & Restoration Calgary, AB T2M 2P9
£ C £ERhC ID
"Helping You Find Solutions" Canada -- www.wplleneineerjne.ca
strand deterioration has been documented to vary from structure to structure depending on
the quantity and composition of the water, type of grease, and degree of strand exposure.
Strand fractures (breakage) reduce the load carrying capacity of the structure and either
replacement or supplementary support systems may be required should a sufficient number
of strands deteriorate to the point of fracture.
Strand damage may also occur due to improper handling during original construction,
strand slippage from the anchors, brittle wire cracking and coring/drilling post
construction.
2,() l'RFVU)IJSl' FIST RESULTS
Previous test reports by Morrison Hershfield. dated May 9, 2016 were provided for our
review. The report indicates that tension testing was completed on 468 strands and that 5
cables are currently displaying signs of tension deficiency.
3.0 CURRENT UPDATE TEST RESULTS
The post-tensioned strands previously exposed were penetration tested to confirm if the
strands within the sample remain under tension. Penetration testing was completed on 468
strands at 123 existing inspection recesses distributed throughout the parkade structure.
Three (3) fully tension deficient strands, located on levels 1, 3, & 4 and two (2) partially
tension deficient strands on level 1 were detected within the tested sample.
4.() DISCUSSION
Although, the three fully tension deficient strands have reduced the local structural capacity
of the floor slabs, based on the location and type of strands, the reduced capacity will have a
minimal effect on the overall structural performance. It is our opinion that replacement of
the fully tension deficient strands is not required at this time. There does not appear to be
any significant change in strand tension deficiencies at this time within the test sample.
Based on the current test results and past programs performed to date, there is a risk that
corrosion related strand deterioration and breakage may occur in the future in this facility.
Based on our site review, we estimate that between 10 to 15 strands have already been
removed and replaced. Monitoring of strand tension at inspection recesses will provide
updated information regarding the ongoing condition of the sample.
Wall Engineering Ltd. Riverside Tower - 145 Point Drive NW, Calgary
Wall#: 10110.0004 Page 2 of4
408 - 32 Avenue NW Building Science & Restoration Calgary, AB T2M 2P9 ' "Helping You Find Solutions" Canada www.walleneineerina.ca
The size of the strand test sample is intended to be statistically representative of general
conditions throughout the building, however the number of strands being monitored
represents a very small portion of the total number of strands in the building. With any
program based on selective sampling, there is a potential that conditions in areas not tested
to date may vary in comparison to the test sample. Similarly, there is also a risk that strand
breakage may be occurring in an area not tested to date, which presents a safety concern if
a significant loss in structural capacity remains undetected,
5.0 RECOMMENDATIONS
4.1 STRAND TENSION MONITORING PROGRAM
In order to assess ongoing strand condition, we recommend that strand tension monitoring
be completed annually. The next update testing program should be performed in February
2018.
Monitoring Allowance
$3,800
4.2 STRAND EXTRACTION AND REPLACEMENT
The Board may wish to consider replacing the tension deficient cables. Replacement would
permit visual review of the tension deficient strands and attempt to determine the possible
cause(s) of the tension loss. This program may be deferred to a later date.
Extraction and Replacement Allowance $35,000 to $40,000
6.0 ADDITIONAL CONSIDERATIONS
Given the number of strands contained within the post-tensioning system on all floors of the
building, coupled with the repair history and current testing results, we recommend that the
Board accumulate funds to potentially address future post-tensioning system deficiencies.
We recommend that the Board retain approximately $15,000 to $20,000 per year for select
strand replacement, maintaining waterproofing assemblies and expanding the post-
tensioning sample size.
Wall Engineering Ltd. Riverside Tower - 145 Point Drive NW, Calgary
Wall#: 10110.0004 Page 3 of4
408 - 32 Avenue NW Building Science & Restoration
Calgary, AB T2M 2P9 Helping You Find SolutionsENM~ RG LTO.
Canada www.wpjleneineerine.ca
7.0 CLOSURE
Performing regular penetration testing of strands exposed at existing recesses allows
detection of strand tension loss, and assessment of any reduction in potential load carrying
capacity of the structural slabs. Please note that all fees and costs presented above do not
incorporate GST.
Trusting this letter meets your present requirements, we respectfully remain at your service.
Please contact the undersigned if you have any questions or concerns.
Yours truly, Wall Engineering Ltd. APEGA Permit to Practice P11659
Reviewed By:
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u- co o
Elie Filion, B.A.Sc., P.Eng. Kris, Wall, B.Sc., P.Eng. Project Engineer Principal
Building Science & Restoration
Building Science and Restoration
Wall Engineering Ltd. Riverside Tower - 145 Point Drive NW, Calgary
WaIl#: 10110.0004
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