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IAPMO Officials Have Decided to Offer IRC Code Certifications for Helical Piles
by Bill Bonekemper
The International Association of Plumbing and Mechanical Officials (IAPMO) recently posted a draft of the Evaluation Criteria for Helical Piles for Use Under the IRC – EC 027-2017 on their website to invite public comment. The public comment deadline expired earlier this week, however you can
Does the U.S. helical pile industry really need another certification – especially one that is restricted to just the residential marketplace? Certainly, the twelve manufacturers who currently hold ER’s from ICC-ES will not need a residential-only code since their ER’s already cover that market. Possibly manufacturers that have not received an ICC-ES Evaluation Report might be interested, as the expense and time required will be considerably less..
When HPW learned of the IAPMO EC027-2017, we approached several helical pile manufacturers and engineers who have extensive experience in all facets of helical pile mechanics and foundation design to gather feedback and opinions about EC 027-2017. Their (anonymous) comments are listed below. Aside from the major question about our industry needing a residential-only code for helical piles, it is apparent from the comments that EC 027-2017 will require substantial changes before it can even be considered as a valid acceptance criteria for helical piles.
The title of the evaluation criteria specifically states the use of helical piles under the IRC. Helical piles are used as deep foundation and they are acknowledged in the IBC code. The IRC specifically excludes deep foundations and directs the user to IBC. If this criterion is accepted, does that mean that helical piles are to be used only for residential? Doesn’t that limit the sales of helical piles (if that’s the case, this will defeat the criteria purpose since the manufacturer will expect higher sale by obtaining an evaluation report)? Since this criterion is for IRC, how can a manufacturer obtain an evaluation report for helical piles to be used as deep foundation?
These issues should be addressed clearly and carefully, otherwise this criterion might create some problems in the future for helical pile manufacturers.
Section 4.0 Testing and Performance Requirements
This section mentions 18.104.22.168.2 and 22.214.171.124.1 of ASCE-7. These sections are vague and very general. Helical piles are manufactured product. The purpose of an evaluation report for a product is to confirm that the product is code compliant. This requires specific testing under specific standards, procedures and analysis so that the playing field is the same for every evaluation report seeker.
Section 4.3.1 Coupling Rigidity
What are the number of tests required? Is it the same number as mentioned in 126.96.36.199.2 of ASCE-7 for both specimens with couplers and without? If one test deviates more than 15% from the average, do we keep testing as stated in section 188.8.131.52.2? why a welded coupler is excluded from testing? Why not a threaded coupler? There are so many different couplers out there and the manufacturer will try to minimize the testing by claiming his or her coupler to develop no significant eccentricity. Also, how is the load is applied? There should be a clear procedure for all of this to make sure all different couplers are treated the same. after all, this is a criterion for all helical piles.
Section 4.3.2 Helix Capacity
In theory, this is logical that the largest helix will give the lowest capacity assuming all other factors are the same. However, testing has proven otherwise. Many larger diameter helices have performed better than smaller diameter helices, all other variable the same. This test is basically to determine the strength of the weld connection. Not all the welds are the same. Testing shall be conducted on all helix sizes. Also, what is the procedure for the test? How is the load applied? How do we determine the maximum capacity from this test? Why the factor of safety is 3? Why not 2 as it has been used by most manufacturers for decades?
Section 4.3.3 Validation of Torque Rating
Helical piles are very popular because of the correlation between Torque and capacity through the formula
Q = Kt x T. this section should be very clear about the determination of the rating torque since it is one very important key variable in predicting the helical pile capacity.
The way this section is written, does it mean that each helix size should be tested as many times as stated in section 184.108.40.206.2 of ASCE-7? What is the failure torque? Does it mean the test should continue until the specimen breaks? Is the rating torque, the failure torque? How do we apply section 220.127.116.11.2 of ASCE-7 in determining the rating torque? Is it the average torque of all helices tested? What is considered rational analysis for reducing the torque? How do we determine the factor that controls the torque capacity? If the weld breaks during torque testing, does it mean that the weld is the one that controls the test capacity? If so, what rational analysis should be used and how to reduce the torque? Who performs the rational analysis? The manufacturer! The testing agency or the evaluation agency! There are so many variables (weld, coupler, shaft, material specifications, etc.…) that can change and be a controlling factor during testing. How can you reduce the rating torque by just saying to use rational analysis? The torsion test is supposed to give us the rating torque from the test results. This approach of combining the test results with some rational analysis seems complicated and not validated. To avoid this complicated approach, and in order to capture all the possible variabilities in the material, torsion tests must come from many different heats and some statistical analysis of the test results must be used with at least 95% confidence level to obtain the rating torque of the product. Given the importance of the maximum installation torque for any helical pile product, the rating torque shall be based purely on testing with some confidence level included as stated above.
Section 4.3.4 Geotechnical Load-Bearing Capacity
Again, why use SF=3 for tension? For long time, a factor of safety of 2 has been used for both tension and compression.
Section 4.3.5 Full Scale Load Testing
Like we said about the rating torque, Kt is a very important variable that is used in determining the soil capacity of the helical pile. In this section, it seems Kt will be determined based on one single test per helix size. This approach seems not reasonable since the suggested total tests do not constitute a large enough sample. soil is a material that its properties are hard to accurately predict. Just conducting one single test is contradictory to section 18.104.22.168.2 of ASCE-7. that one test could represent the upper bound or lower bound (we don’t know) of that specific pile. Also, most helical piles used have many configurations (double, triple…). During installation, the multiple helices piles cause more soil disturbance than single ones. This might have effect on the pile capacity especially in tension. Since Kt is very important variable, as seen in the formula above, it shall be determined as accurately as possible. To do so, at least, each helix configuration must be tested per section 22.214.171.124.2 of ASCE-7. These soil tests must be conducted in at least the three common soils encountered, mainly Clay, Sand and bedrock because helical pile capacities change with soil type.Also, why should the pile be installed to at least 90% of the rating torque? A more common sense will be that all soil tests shall be conducted evenly at 25%, 50%, 75% and 100% of the rating torque. This is more representative of the production piles in the real world and therefore is better for determining the Kt value.
Finally, section 4.3.4 states that the Kt value obtained from the testing shall not exceed the maximum value obtained using the formula from Dr. Perko’s Book. First, what is the maximum value? For every shaft diameter, this formula will give us just one single value. Second, the Kt equation in Perko’s book was based on soil capacities that were all determined using net deflection equal to 10% of the average helix diameters. This method of obtaining the pile capacity from the Load-Deflection test results is very common. However, there are many methods used for the interpretation and analysis of the load test results, mainly, Davisson’s offset limit method, DeBerr’s method, Brinch- hansen’s method, Etc.… all of these methods, when used for the same load test, will give very different results.
Since this criterion proposes the use of Davisson’s method to obtain the soil capacity, which is then used to obtain the Kt value, how can this kt value be compared to a Kt value obtained from soil capacity based on the 10% average helix diameters?
I appreciate the fact that IAPMO is trying to partner with the helical industry. Their organization is well respected. However, I think they are taking a flawed approach with the current draft of their criteria. The IRC specifically excludes deep foundations and instead directs the user to the IBC. By attempting to pull deep foundations back into the auspices of the IRC, the acceptance criteria creates a new set of problems. If accepted, other deep foundation industries could try to make the case that helicals are only “residential” elements and not appropriate for other structures. If a manufacturer tries to get an IAPMO approval instead of the existing ICC-ES approval, are they limiting their potential sales? If a manufacturer gets an IAPMO report for residential, will they turn around and have to pay again to get an ICC report for IBC projects?
In the end, there are a lot of questions that need to be answered.
We support the IAPMO in their efforts to create a new document to be used as a standard in their evaluations. We certainly are in favor of having more product evaluation options available to our industry which is what this document is intending to create. We do, however, feel that the proposed document will need extensive revisions to resolve some issues. There are some areas that are ambiguous and some areas that are confusing. There are also areas that create additional conservatism that some will feel is unnecessary. There are even some guidelines that appear to have not been included that perhaps should have been. As it stands currently, it is not compatible with the current state of practice in our industry.
We would certainly recommend that IAPMO work with the industry at large to assist them in revising this document.
We plan on submitting comments to the IAPMO to reiterate these concerns directly to them before the end of the public comment period ending May 8th. We would encourage others to do the same.
Congratulations on a well written criteria for evaluation of Helical Piles for use under the IRC. Helical piles are being used extensively in residential construction and criteria addressing their manufacture, design, and installation are extremely important. It is a benefit to the helical pile industry and the public that IAPMO offer evaluation of helical piles as an alternative to ICC-ES. Such competition promotes fair evaluation, cost competitiveness, and gives manufacturers and designers a choice.
The IRC doesn’t cover any deep foundation system, only footing foundations. The IRC refers to the IBC when deep foundations are required which the IBC addresses. Therefore, there’s no need to add helical piles to the IRC which is a prescriptive code.
How do you get approval for something or from someone who doesn’t regulate it?? If the IRC let’s in one deep foundation system, they must let them all in. Deep foundation systems must be engineered. There’s too many variables for them not to. I assume for them to say they are compliant with the IRC, ICC will have to include helical piles or deep foundation systems in the IRC for them to state this. I don’t see ICC doing this.
They reference 3 sections of the IRC in the second paragraph of Section 1.1:
IRC Section R403.1 – This section only covers shallow footings (shallow foundation). I suppose they are wanting ICC to add helical piles to this section.
IRC Section R104.11 – This section states that the provisions of the code are not intended to prevent or prohibit and material, design or method of construction not specifically prescribed by the IRC. (The IBC has basically the same wording in the same section number.) However in the IRC, it goes on to say, “Compliance with the specific performance-based provisions of the International Codes shall be an alternative to the specific requirements of the IRC”. What they are saying is that if something isn’t addressed in the IRC the applicable International Code (in the case of deep foundations, the IBC) will govern. This is why the building officials revert back to the IBC when deep foundations are being used.
IRC Section R301 – Section R301.1.1 Alternative Provision. This states, “Where engineered design is used in conjunction with these standards, the design shall comply with the International Building Code”. Section R301.1.3 states, ”Engineered design in accordance with the IBC is permitted for the buildings and structures, and parts thereof, included in the scope of this code.
They don’t address side load brackets at all. I assume they are wanting recognition for new construction piles only and limited to 30 kips??
Torque rating is coming from lab tests and not field verification tests. You have eccentricity and bending moments that play a factor in the torque capacity while installing helical piles in the field. Several manufacturers could achieve the same torque capacities in the field that they achieved in the lab.
They are only requiring 3 full scale load tests in any type of soil the manufacturer chooses. This isn’t a large enough test sample. Helical piles have high load capacities in medium dense sand, dense sand and when bearing on rock. Manufacturers will test in these soil types to achieve their ratings. When the piles are installed in clay areas, the geotechnical capacity of the pile will be less. If they were going to test in only one soil type, it should be a clay soil which would provide the most conservative results that would work anywhere.
These are just my initial comments. It’s a weak acceptance criteria in my opinion and they will have a hard time getting the piles accepted for compliance to the IRC.
1. Code reference is the International Residential Code (IRC), not the IBC.
2. Limited to residential occupancies
3. 30 kip allowable axial loading, maximum
4. Seismic Design Category – A, B, and C – similar to AC358
5. Lateral capacity outside scope of EC 027-2017
6. From what I can infer from a quick read, the sample sizes for various tests are less.
7. Torque correlation factor minimums not pre-determined as they are in AC358. Perko’s torque correlation equation is used.
8. Field test appears to be done with single helix plate only. Each helix diameter needs to be tested at least once. Minimum tests per shaft size is three. It’s not clear if the minimum is three tests for tension, and three tests for compression; or if three tests total for both tension and compression combined.
9. Any soil type allowed for field tests.
10. Some tests have requirements similar to AC358
11. Section 5.3 limits the allowable stress is limited to 32 ksi.
12. Factor of safety of 2 used for compression when soil data is available; or 3 when torque correlation alone is used. Exception to FS = 3 is decks and small additions
13. Factor of safety of 3 used for tension
My initial reaction is the industry wants one or the other, not both. What’s intriguing about IAPMO EC 027-2017 is that it appears to be simpler than AC358, i.e. less testing/calculations, etc.
In my opinion, a major disadvantage is EC 027-2017 is just for residential construction. I don’t believe the helical pile industry wants to be restricted to just residential.
Some will use EC 027-2017 because it probably will result in less time and cost to get an evaluation.