wall engineering ltd. calgary ab, t2m 2p9 canada building ... · building science & restoration...

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

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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 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#: 10110.0004 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:

..c

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


WaIl#: 10110.0004

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