Swimming Pool Structural Engineering - Custom Vs Generic

 Defective Infinity or Vanishing Edge Swimming Pool Expert Witness Paolo Benedetti discusses the importance of using project specific structural engineering and geotechnical reports.

Generic or Project Specific Engineering?

Generic structural engineering fills a void in the concrete swimming pool construction market by providing cost effective "ready made" and "off the shelf" engineering.  These plans are sufficient for most tract home pools with a flat yard and no surcharges.

Project specific engineering is structural engineering that has been designed FOR YOUR SPECIFIC PROJECT.  This means that the experts have consulted with each other and have designed something that will economically function on your site.

The Dangers of using Generic Engineering

The publishers of generic structural engineering provide a catalog or on-line listing of their various plans and construction details.  This allows the pool builder to select the products that they need & rapidly receive the plans.  Therein lies the whole problem...  the pool builder SELECTS  the engineering, the strengths and what is required.

Soil Conditions

Though the plans are engineered, each is contains details unique to the soil conditions.  Standard plans are designed to accommodate various types of expansive soils.  Many contain three to four various steel schedules, based upon the soil condition on the construction site.  Who determines the soils conditions on the site and the resulting strength of shell to use?   The pool builder, of course.

Without obtaining a soils report (aka: geotechnical report) prior to construction, then your pool builder will select the appropriate (or inappropriate) engineering.  There is ABSOLUTELY NO WAY to determine the soil conditions without a soils report.   

Site Conditions

Generic mail order plans also do not take into consideration the "site conditions" on a construction project.  The structural engineer has not reviewed the topography of the site to determine if any surcharges are present.  A surcharge is something that can potentially place stress upon the pool structure.  Surcharges can be nearby up slopes, down slopes, buildings, structures, lakes, retaining walls, surf, snow, wind or even seismic events.

Without a structural engineering review of the project plan, soils report, topographical map and site images, the responsibility of identifying these surcharges is left to the pool builder.  Even if they do identify potential surcharges, do you really want them determining the amount of surcharge?  Are you confident that they identified ALL of the potential surcharges?

Catch-All

Generic engineering is designed to be a catch-all for all geographic regions where the mail order engineering firm is licensed.  This means that the plans may include structural elements that are not required in your local.  This all translates to unneeded additional cost for the buyer.  The plans may also omit items that may be required by local code or ordinance.

Additionally, these plans are only designed to meet the MINIMUM standards.  Though industry standards often utilize 4,500 or even 5,000 PSI concrete, these generic plans oftentimes only specify 2,500 PSI concrete.  

Why?  Because most pool builders who are utilizing mail order plans are cost conscience.  5000 PSI concrete costs more.  Concrete exceeding 2500 PSI also requires that the placement of the concrete be inspected by a special deputy inspector, and in some regions, a quality assurance testing laboratory.  Again, additional costs.  But why wouldn't you want these workmanship guarantees and quality assurances?

Correctly Utilizing Generic Engineering

If you plan on utilizing generic mail order engineering, then there are some things that must occur:

1.  A soils report for the construction site must be provided to the structural engineer.  Test borings must occur in the proposed locations of construction.
2.  The structural engineer must be provided site images, a topographical map and proposed project layout.
3.  The structural engineer must provide a letter or notations on the plans that they actually reviewed the soils report & make reference to the Soils Engineering Report, date and author.
4.  The soils engineer, then must review the generic mail order structural engineering and write a letter stating that they have reviewed the structural engineering and that they agree that the plans meet or exceed the requirements for the site.
5.  The structural steel should be inspected by the structural engineer to verify that the plans were followed.  This can be an in person inspection or through digital photographs.   An "inspection letter" should be obtained, stating that the structural engineer has reviewed and approved the steel placement.
6.  Minimum concrete strengths should be 4,500 PSI.
7.  An inspector should be present during all gunite/shotcrete placement.  Samples should be sent to a testing lab to verify that you're getting what you paid for.

Why not use Project Specific Engineering?

Since project specific engineering requires that the same steps be followed as using generic engineering correctly, why not just obtain project specific engineering?

GOOD QUESTION !

Paolo Benedetti Aquatic Artist, Consultant & Construction Defect Expert Witness
"Creating water as art."™
Aquatic Technology Pool and Spa
©www.aquatictechnology.com

Consumer Mistakes when Buying a Swimming Pool

Many consumers approach construction projects like they are buying a consumer commodity.... which is the furthest from the truth.

 

You're not buying a TV at Walmart

A swimming pool is a personal item - one that should be designed around the buyer, their lifestyle, how they entertain and the intricacies of the building site.  Unlike consumer commodities like tv's, the quality, design and performance varies by the designer or contractor.  In construction, it is the buried components that determine the long term performance of your project - and the cost of operation.

Not getting educated

Picking companies from the Internet or yellow pages based upon a pretty website or large ad is absolutely wrong.  Most pool construction companies employ a team of salesmen, who's job it is to "sell you a pool."  They are not interested in educating you as to the correct way to build a pool.

They are only interested in signing that contract.

Do your research BEFORE you talk to the first company.  The Internet is full of information, but don't believe everything on the Internet.  Create a list of criteria that you'll use to select your contractor.

Over reaching

It is foolish to call swimming pool contractors and request a "free quote."  You cannot make rational comparisons between different designs and specifications.  Since most swimming pools are built utilizing the lowest quality workmanship & materials without any written criteria or construction specifications, how can you possibly compare bids?

Since the salesman is out to SELL you a pool he is interested in "churning out" a plan or project scheme as fast as possible.  The quality of the design and project specifications are going to be reflect in the "FREE" effort they expended!  You get what you pay for!

Lack of Due Diligence

Everyone is willing to provide you with a list of references.  They are NEVER going to give you the list of people that they pissed off.  But how do you find these people???  Through due diligence and legwork.

Check the local Better Business Bureau.  They will not be able to give you references, but their records may represent a trend.  Where there is smoke there is fire.

Check the local court records.  Many are available for review on-line.  The builder may have been a plaintiff (suing to get paid) or a defendant (sued by an upset customer).  Contact the other party, learn what went wrong, why there was a dispute, why it ended up in court, and if the issues were resolved.  TAKE THE COMMENTS WITH A GRAIN OF SALT.  Remember, you cannot always please everyone.  Some consumers are unreasonable.  What you are looking for is a PATTERN of upset consumers in their wake.

Check the Contractors Licensing Board - Not every state requires that contractors be licensed.  Those that do, usually have records visible on-line.  Search other licensed states, as some builders that had licenses revoked in other states merely move to another state.  If a contractor has had any complaints or actions against their license - again, it illustrates that they cannot resolve issues before they get out of hand.

Check out on-line reference websites: The Franklin Report, Yelp, Angie's List and others.  Again, take what you read with a grain of salt.  Remember, you are looking for a pattern of happy or unhappy customers.

Review building permits issued in surrounding communities.  Most building departments have searchable on-line databases.  Search for the last 4-5 years of permits.  Contact these owners.  Most will be happy to provide a candid review of the contractor.

Price Point Decision Making

Warning: The prices are going to be all over the map.  Trying to compare apples, to oranges, to grapes, to lemons will only result in a brain full of fruit salad.  How do you make sense of it all?

It is best to obtain a design package (sometimes called a "bid package").  The entire project will be defined with schematics of the plumbing, high & low voltage electrical and lighting.  It will include illustrations of the minute details that are unique to your project.  It will also include construction and workmanship specifications.

Utilizing a "bid package" allows all possible contenders to provide a quote based upon the same exact set of criteria.  Stand your ground - ensure that they realize that substitutions are NOT ALLOWED.  This will ensure that the design does not get altered and that the performance is not degraded.  It also ensures that you are comparing APPLES TO APPLES !

REMEMBER: 
YOU GET WHAT YOU PAY FOR!  
IF SOMETHING IS TOO GOOD TO BE TRUE - IT IS!

On-line Quotation or Consulting Services

You cannot design a pool or provide a quotation on-line.  Just like I cannot paint your house or change your car's oil over the phone.

It is impossible for anyone to validate any assumptions that they make over wires.  They must visit your site, sit down with you, understand your budget and needs.  They have to get to know YOU!

Prices are lower in a down economy or in the off season

 Labor expenses, overhead, insurances, fuel, concrete, steel and everything else that goes into the construction of a pool is constantly increasing in price.  

There is no better time than RIGHT NOW to build a pool.  Why?  Because next year those items are going to cost even more!

The best pool designers and contractors are still busy, even in a down economy.  They are not going to "work for wages."  It ends up becoming a losing proposition in the long run, and the smart ones know that.  And you don't want to hire the dumb ones that will work for wages.  They just won't have the resources to perform system tweaks later on or perform warranty repairs.

Failing to Review and Understand the Contracts

A contract is a two-way street.  It should clearly define everything that you are to receive.  It should outline the contractor's obligations.  Anything that was promised during a sales presentation should be included in writing.

Ensure that a dispute resolution process is included.  Know what your obligations are: paying invoices within XX days of receipt; providing a soils/geotechnical report; marking property lines, boundaries and easements; obtaining planning department or HOA approval; providing trash disposal, dumpsters, electricity or toilet facilities; repairing fences, sprinklers, sidewalks and driveways, upgrading the electrical or gas meter... the list goes on and on.

Not obtaining proper structural or mechanical designs

Most swimming pools are design and specified by the salesman.  They have little or no knowledge of structural engineering, proper filtration, circulation or hydraulic designs, mechanical systems, water chemistry management, state of the art controls and automation or alternative energies.

Most select plumbing sized based upon a guess and not sound hydraulic design calculations.  When properly sized, the response from most potential bidders is "the pipes are way too big," "who specified these huge pipes?," "way overkill."  In reality the plumbing should be specified based upon the science of hydraulics (physics), which these contractors and salesmen apparently do not understand.  When you hear these responses, you should have one reaction... cross them off of your list.

Do they require a soils report?
Where do they obtain their structural engineering?  
Does the structural engineer actually review YOUR project plans, site/topographical map AND the soils report, prior to defining the strength of the pool shell and placement of the steel?  
 Will the engineer sign on the plans that they have reviewed those documents?  

This is very important because:
a) it ensures the consumer that the contractor forwarded those documents for review
b) you'll know that the document were actually read by the engineer
c) many contractors just buy random structural engineering on-line or mail-order (based on their best guess)
d) you are guaranteed that your pool is going to be built to withstand the forces from your soil and your site conditions.

Thorough plans prevent surprises

Having a thoroughly thought out set of plans with defined specifications ensures that there are not future surprises.

The plans should also include any infrastructure required for future projects.  Getting water, gas, sewer & electrical routed under the hardscapes & plantings now, will be less expensive than tearing it all up to install them at a later time when that outdoor kitchen, shower, cabana, guesthouse, garage or barn is built.  Maybe incorporating future connections for alternative energies may be something of interest. 

The safety components of the project, from fencing & gates, door alarms, pool covers or an integrated anti-drowning alarm system should be a part of the plans and contract.  You don't want to miss the final inspection because those items were left off for you to handle.

Best Advice

1) Hire a well respected designer or consultant to design your dream backyard, before you start construction.  
2) Hire the best contractor that you can afford.  
3) And if you are not hiring the BEST AVAILABLE, then come to the realization NOW that everything will not be PERFECT.  Nor should you expect or demand perfection from those lesser contractors.


Paolo Benedetti - Aquatic Artist
"Creating water as art."™
Aquatic Technology Pool and Spa
©www.aquatictechnology.com

Vanishing Edge Pools

Paolo Benedetti discusses the intricacies and complexities of vanishing, infinity, negative, knife edge, perimeter overflow, slot overflow, disappearing edge or flooded edge pools...
What ever you want to call them, a vanishing edge pool is a pool wherein one (or more) sides of the pool are slightly lower than the operating water level. The most generic term for these edge effect pools is "a water in-transit pool."
While strikingly beautiful, they are actually quite hydraulically & structurally complex. Because they are oftentimes built on a mountaintop or the edge of a cliff, they require a geo-technical investigation and appropriate structural engineering.
Hydraulics
The hydraulic design of these types of pools is very complex. In fact, these pools require 2 separate filtration systems. The primary system is utilized to filter, heat, and sanitize the main pool - just like a regular swimming pool. The second system, draws water from the surge tank and returns it to the upper pool. A significant quantity of water may be required to raise the level of the pool, to create the "spill over" effect. The catch basin may be attached to the main pool or it may be remote holding tank. These 2 systems are in addition to the pumps & piping required for the spa jets, water feature(s), pool cleaner, and solar panels.
The volume of the plumbing needs to be calculated on some styles of these pools, as some rely on gravity drain lines to return water to the holding tank - lines that must be filled each time the system starts. The surge tanks need to be adequately sized to accommodate bathers' displacement, wind displacement, and storage of the "water in-transit" necessary to raise the main pool to the appropriate level to create the edge effects.
The with proper pipe sizing, the primary filtration pump can be as small as 3/4 HP. Depending on the project requirements, the secondary edge pump may need to be as large as a 3 to 10 HP. This is usually due to the quantity of water required to both raise the water level in the main pool and overcome the surface tension of the weir materials.
Small pumps or large pumps - Confused yet?
Don't worry, most swimming pool contractors and designers are confused as well.  The vanishing edge system (effects pump) requirements are determined by the linear feet of edge to be flooded, the edge tolerances (materials highs to lows & installation perfection), pipes to fill and flow rates required to ensure that the gravity gutters & pipes are scoured (water moving fast enough to carry away any debris).
Those that don't understand these complexities oftentimes under design or go for the overkill.  Either way the property owner loses... a system that does not operate correctly or one that consumes way more energy than is remotely required.
Taking the easy way out - edge filtration
Many pool builders & designers in a effort to "save the client money" (and make more money for themselves), eliminate the secondary filtration system. They may either delete the entire secondary system or just it's filter tanks.
By eliminating the filter tanks, they cause this system to blow the debris that collects in the catch basin back into the main pool. Since the edge is a giant weir, a majority of the debris in the main pool ends up in the catch basin.
Imagine what will happen every time the edge pump comes on.... a cloud of dirt and fine debris will be blown into the main pool, clouding the water. Just what a client desires when showing off their pool to guests or hosting a party! I know of a pool builder who routinely deletes the edge filtration system from projects that we design. I know, because I get the call once the project has been completed - complaining that I created a "faulty design." After viewing the finished project, it becomes readily apparent what the cause is... Yet this builder continues to build in this manner. I am sure he will only change his ways after a client's lawsuit.
If the secondary system is eliminated entirely, then the main pool filtration system will be forced to draw it's water from the catch basin. This forces the pool builder to install a pump that is significantly larger than what would normally be required... remember that the primary filter pump can be a mere 3/4 HP vs 3-10 HP for the edge system.
Though there was an initial savings of about $5,000 by eliminating the edge system, the electricity costs over the life of the project will grossly exceed any savings. This is stepping over dollars to collect pennies!
Auto-fill
An electronic automatic fill device is another requirement. Many pool builders & designers rely on inexpensive mechanical toilet float style auto-fills. While they are functional, they are the wrong choice for a water in-transit pool. But, hey they can save $200! If there was no wind and no one ever swam in the pool (and therefore were no waves), these mechanical auto-fills would work okay. The problem is, these pools are dynamic. Wind causes waves, swimmers displace water & create surges, and some plumbing lines for the edge system may need to fill when the system activates. These variables cause the mechanical auto-fill to surge, turning on & off with the wave action. The repetitive hissing sounds from the auto-fill is annoying enough. Add the rythmic water hammer on the plumbing system within the residence, and you have enough to cause most homeowners to immediately voice their complaints.
An electronic auto-fill has a built-in delay, thereby ignoring minor bather surges, waves, or fluctuations in the water level. This eliminates the annoying hissing & resultant water hammering in the plumbing. It also has a fail-safe timer, that prevents it from becoming stuck in the "on" mode for ever.
Back flow prevention
Another requirement, is the need for failsafe back flow prevention (in addition to check valves) on EVERY plumbing line that returns to the upper pool from the surge tank. When a check valve fails (and they WILL fail - not IF they will fail, but when!), the back flow prevention device will prevent the back siphoning of the upper vessel into the catch basin. On a hillside, dumping 30,000-50,000 gallons of water down the slope will be catastrophic for the foundation of the pool, the hillside or the living room of the downhill neighbors! Imagine all of that water and mud sliding into the neighbors backyard, followed shortly by the swimming pool?!
Complexities
Because these style of swimming pools are frequently built on the top of mountains or on the edge of cliffs, their structural engineering oftentimes requires drilled caissons or other complex foundation design. This complex structural engineering requires specialized training, construction practices, and independent testing lab inspections & material samplings/testings. The complexity of these concrete structures is similar to that of building a bridge overpass - beyond the licensing, training & expertise of most swimming pool contractors.
While these projects can be quite lucrative for a swimming pool contractor, the failure of such a vessel will result in major lawsuits. Many swimming pool contractors have attempted to build such complex pools, thinking that they are easy, only to make every possible mistake. If they are not an expert in such vessels and their intricacies & nuances, do you really want to be their learning curve??
Even if they have built "a few" of these type of vessels, due to the significant quantity of possible mistakes, do you want them making "just one" on your project? While the rewards of a properly executed project are astounding, the opposite results are disastrous!
I saw a pretty picture...
I recently heard of a California Horticulture contractor who attempted to copy a detail from one of our projects (Yes, another landscape contractor who ventured into pool design & construction - a realm they really do not understand). They attempted to place the spa along the vanishing edge, and have it appear that the spa was spilling over the horizon just like the pool. The problem, is that they did not understand the hydraulics & mechanical systems of creating such an effect.
Remember, that when the main pool filtration system is on, it draws water from the main pool skimmers & returns filtered/treated water to both the pool & spa? Because the spa also spills over the backside & into the catch basin, the water level in the main pool drops & the level in the catch basin rises.... eventually to the point where water spills out of the catch basin & down the hillside. Though they were able to "patch" a fix through creative programming of the automatic valving - it is a matter of time before an automatic valve fails to turn or a switch is accidentally left in the wrong position ...and the downhill neighbors get 50,000 gallons of free water! Greed won, brains lost!
This is just another example of how good intentions go bad.... biting off more that one can chew. Because someone has a mastery of an art, the execution of their craft appears easy to an outsider... because they know what they are doing! But by trying to execute a project for which they do not have an understanding or the expertise, is a time bomb waiting to explode. There is absolutely no acceptable excuse for these types of mistakes, especially when there are design consultants (like myself), classes (like the Genesis 3 courses) and reference literature available.
A vanishing edge on every hillside - not!
Just because a site is sloping lot, overlooks a body of water, canyon, or precipice, does not automatically qualify a project for a vanishing edge pool. I have actually talked clients out of a vanishing edge pool, when the lines of sight were not correct or when soils reports indicated that a majority of their budget would be required for foundations instead. Sometimes, a vanishing edge pool just "isn't right" for the site. A pool does not have to be a vanishing edge to be perfect for a view or hillside lot.
Exponential Cost
Lastly, property owners should not expect the cost of a vanishing edge pool to be comparable to a similar sized pool on a flat lot. There is a lot of additional finish work that needs to be completed. There is the secondary edge filtration system and complex structural engineering & foundations. The entire weir wall is a "free standing" wall, that requires additional steel, special form work, and unique talents of the shotcrete crew. There are the additional finish materials & labor for the catch basin & the backside of the weir wall (remember it is usually the length of the pool & 4-6 feet high!). Often times the outside of the catch basin also needs to finished. There is the added cost of constructing an equipment pad on a hillside (it should be placed at or below the level of the catch basin, which oftentimes requires footings, retaining walls, and access steps.). There is the matter of where to drain the overflow/rain water, without eroding the hillside.
Get shoehorned into a Yugo
In an effort to bring these expensive pools into the realm of mainstream affordability, some fiberglass & vinyl liner pool builders have attempted to build such vessels. I proffer that they are almost always lacking the proper geo-technical reports, structural engineering, and lack the proper details to prevent eventual catastrophic failure. These are usually package pools that are meant for flat parcels, being modified (by Tim Allen types) to wedge into a particular budget. The ones that I have reviewed always had a seam that was "bootleg" sealed or an under water joint that was critical in remaining waterproof. Again - if you cannot afford to do it right, DON'T DO IT! We'd all love to drive a Bentley or Maybach, but are resolved to drive a Ford or Chevy, because that's what we can afford. Just because a client wants a vanishing edge pool and cannot afford one done properly, does not mean that a builder should whore himself to create a modified vanishing edge pool from a kit!
How in the hell do they fasten a vinyl liner pool to the hillside? It is impossible to structurally tie the vinyl to a foundation or to contain a leak. They are just too fragile and susceptible to rips/tears to be placed in such a location.
Get Help
It's all about knowing what you are doing, how to execute it and knowing when to hire assistance when you don't!
You only pay for quality ONCE!

Paolo Benedetti - Aquatic Artist
"Creating water as art."™
Aquatic Technology Pool & Spa
©www.aquatictechnology.com