Fairhaven-Pulte-Schertz, TX. Independent Engineer?

Posted on January 12, 2012 by admin

Case Study: Compliance and Professionalism

So, you’re a homeowner concerned about your foundation, your home’s structure, or perhaps your back yard retaining wall.  Your foundation is sinking.  Your walls are cracking.  And, you’re entertaining the idea of getting an unbiased opinion from an “independent” engineer regarding your concerns.    Well, you’re not alone.

Recently, I received a call from a homeowner.  They were seeking an unbiased engineering opinion of some foundation cracks they had recently noticed.  When they mentioned the subdivision name, it sounded vaguely familiar.  After a quick review of my records, I realized that I may have rendered several similar opinions in that subdivision over the past year or so.  To verify, I googled a few key words, clicked on some listings, and eventually found a letter from a builder to homeowners in Fairhaven- a Pulte community in Schertz, Texas.

If you are a resident of Fairhaven, then it’s likely you’ve already received or read Pulte’s Homeowner Letter dated January 3, 2012 as posted on their website www.fairhaventx.com .  The letter basically outlines how Pulte plans to handle homeowner concerns regarding certain homes in the Fairhaven community that have experienced settlement and foundation issues.  However, what struck me as oddly coincidental was the rather confusing statements made in the letter regarding retaining “independent” engineers. Here are two excerpts from the Pulte Letter:

  • “Based on our investigations to-date, it appears that there are a few homes experiencing unusual foundation cracking. Pulte has retained top engineers to help us analyze the situation with each home and assist in implementing a thorough corrective action. All repairs will be paid for by Pulte.”, and
  • “To ensure we properly analyze and repair each warranty issue, we have employed independent, structural and geotechnical engineers with years of experience dealing with Texas soils and home foundations.”

But, can a builder retain or employ “independent” engineers to analyze foundation problems for a particular homeowner or residence?   Or, put another way,  is it professionally ethical for a Texas licensed engineer to accept compensation exclusively from a builder,  yet provide simultaneously “independent” or “unbiased” opinions to both the builder and the homeowner?

Well, you don’t have to go too far to answer these perplexing questions.  You simply refer to the Texas Engineering Practice Act, Chapter 137, Compliance and Professionalism (www.tbpe.state.tx.us).  Engineers, like many other professionals, must maintain the interests and confidentiality of their clients.  In so doing, engineers “shall not accept compensation or benefits from more than one party for services pertaining to the same project or assignment”.  Put simply, unless authorized by the engineer’s client (Builder), an engineer  may not act in the interest of, or reveal any opinions or other information presumed confidential to any third party (homeowner) unless authorized to do so (paraphrased from Chapter 137).

 

This article is part of our continuing case study series in Engineering Ethics. This article is intended for educational purposes only.

 

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Austin Slab on Grade Foundation Stabilization: Structural vs. Non-Structural

Posted on December 8, 2010 by admin

Austin Slab on Grade Foundation Stabilization: Structural vs. Non-Structural

Stabilizing a slab on grade foundation system requires a design approach that mirrors its original design principle. Since shallow bearing foundation systems are designed as single units, they must be repaired as single units. At a minimum, the remedial structural design should uniformly stabilize the entire foundation system so it can resume resisting the soil, dead and live loads imposed upon it. A reliable, durable, and time tested method for uniformly stabilizing slab-on-grade foundation systems includes underpinning, where slab on grade foundation interior and exterior grade beams bear upon and span underpins (drilled and steel reinforced concrete piers, or DRCP’s). This is commonly known as “Full Pieringâ€�. DRCP’s convert the slab on grade foundation system from a shallow bearing structural element to one that bears on deep, yet stable soils. DTCP’s allow the engineer to specify and limit the vertical movement of the foundation system over its life, improve slab on grade foundation performance, and minimize foundation superstructure brittle material cracking.

“Partial Piering�, as it is commonly known, limits the number and placement location of underpins beneath a slab on grade foundation system. Partial piering restrains vertical movement near the part of the foundation system where the underpins are placed, and leaves the remaining portion of the foundation devoid of underpins to move unpredictably with the seasonal changes in soil moisture content. Over time, stress builds up between the restrained and unrestrained areas of the foundation system creating a hinge, or weakened area where the concrete can fracture and structurally fail.

The initial cost to underpin slab on grade foundation systems using DRCP’s can appear disproportionally high when compared to other non-engineered structural repair methods such as “partial pieringâ€�. Where soils are highly expansive, or when soils shear strengths are unusually low, the owner may decide that slab stabilization using DRCP’s is simply too costly. Cheaper structural repair alternatives to DRCP’s may have a lower initial cost and may appear to initially stabilize the foundation system, but over time, their life cycle costs often exceed typical DRCP life cycle costs. And since “partial pieringâ€� fails to uniformly stabilize a slab on grade foundation system over its entire expanse, this repair method is less reliable than DRCP’s and can cause further damage to an already weakened slab on grade foundation system.

Option 1: DRCP’s.

When properly engineered, DRCP’s are reliable, yet costly. For residential foundation systems, these underpins are strategically placed beneath the expanse of the foundation system, usually to depths exceeding eight feet to provide maximum support. Unlike the typical (and inexpensive) multiple segmented concrete pile components stacked atop one another like unstable kinder blocks, DRCP’s are poured in place, reinforced with vertical steel, and placed to bear on deep, yet stable soils, free from seasonal moisture variations. More importantly, and unlike segmented piles (which are often used in “Partial Pieringâ€�), DRCP’s provide superlative resistance to soil friction that tends to push the underpin up (float) or push the underpins from side-to-side (lateral). As such, DRCP’s provide a stable bearing surface for the damaged foundation system by limiting its ability to move vertically or horizontally. For a residence of like kind, quality, age and size, 30-40 reinforced concrete underpins drilled to depths exceeding ten feet and placed strategically under the interior and exterior perimeter beams of the foundation system may be expected. The depth, spacing, and number of DRCP’s are determined jointly by competent and experienced Geotechnical and Structural engineers.

Option 2: Non-Structural Repairs to Minimize Foundation Movement and Improve Performance.

Slab on grade foundation systems incorporate design criteria relating to climate, soil, and structure. Reinforced concrete foundation performance can be impacted by post-construction activities unrelated to its core design criteria. If rainfall is allowed to pond or collect adjacent to a structure built on expansive soil, the structure may be subjected to unscheduled distress caused by swelling bearing soils due to increased soil moisture content. Lot surfaces must be graded to drain away from the structure in accord with the International Residential Code R401.3. In accord with 304.100(a)(2) and section 7.3 of the ASCE Guidelines, the following summarizes the recommended non-structural remedial measures:

Roof Rain Gutter System (ASCE, section 7.34). Uncontrolled roof rainfall runoff can erode the ground surface along the foundation perimeter and provide a source of excessive and non-uniform water input to the foundation perimeter beam bearing soils. Variances in bearing soil moisture content distribution along the foundation perimeter can result in unscheduled foundation system vertical displacement and rotational movement. Rain gutters and downspouts should be placed along the entire house perimeter eave lines where the sloping roofline discharges rainfall runoff. The gutters will capture and convey roof rainfall runoff. The runoff is then discharged via downspouts into a ground surface swale, or into a subsurface solid pipe drain system. This type of gutter system will help to eliminate ground surface erosion, and prevent excess water accumulations near the foundation system.

Drainage Improvements (ASCE, section 7.35).

  • Surface Grading along the Foundation perimeter. For adjacent ground areas, a minimum slope of 5% (6â€� fall per 10’) away from the foundation should be provided for the first five feet all the way around. Swales shall have longitudinal slopes of at least 2% (6â€� per 25 ‘) if practical, and 1% (3â€� per 25’) minimum. Eroded surfaces should be replaced with vegetated surfaces. Gaps between concrete surfaces along the foundation system perimeter that allow surface water to infiltrate into the foundation bearing soils should be eliminated. Concrete surfaces that may allow water to flow towards the foundation system perimeter should be modified to direct water away from the foundation perimeter. Erosion Control. Ground cover should be placed in areas where ground surface erosion currently exists.
  • Surface Water Drainage Option A. The ground surface should be graded to slope to one or more subsurface solid drainpipe inlets. Cleanouts should be provided at 50 feet intervals for proper maintenance. Roof rainfall gutter downspouts may be connected to the subsurface solid pipe system provided the pipe has sufficient capacity to prevent a backwater condition. The pipe should have a minimum slope of 0.5 percent to the surface outfall. In any case, the ground surface slope along the foundation perimeter must comply with local code requirements.
  • Subsurface Water Drainage Option B. Subsurface water drains are appropriate to control surface water runoff. They may consist of a perforated pipe placed in an aggregate filled trench along with an optional filter fabric to prevent pipe stoppages. The pipe should have a minimum slope of 0.5 percent to the surface outfall. Cleanouts should be provided at 50 feet intervals for maintenance. In any case, the ground surface slope along the foundation perimeter must comply with local code requirements. Gutter downspouts should not be connected to a perforated pipe system.
  • Monitor foundation performance after completing all non-structural repair measures to assure their satisfactory implementation.

Austin Slab on Grade Foundation Stabilization

 

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Hurricane Ike: Destructive Power Perfected

Posted on December 8, 2010 by admin

The 2008 Atlantic hurricane season was the third most costly on record. With damages exceeding $29 billion in the United States alone, it was the fourth busiest year since 1944 and the only year on record in which a major hurricane existed in every month from July through November in the North Atlantic. Of the sixteen named storms during the 2008 hurricane season, Ike was the most powerful. At one point, the diameter of Ike’s tropical storm and hurricane force winds were 600 and 240 miles, respectively, making Ike the largest Atlantic hurricane ever recorded. As the most destructive storm in the Atlantic basin in 2008, Ike made its landfall along the north end of Galveston Island on September 13, 2008 as a Category 2 hurricane.

Ike produced a storm surge of over twelve feet from Galveston Island eastward into southern Louisiana. Bearing the brunt of the surge, the Bolivar Peninsula saw the most extensive property damage, followed by the Galveston Island, Port Arthur, and Houston areas. As is typical for slow moving cyclones, Ike exacted widespread property damage and flooding as it tracked a northwesterly heading through Galveston Bay, about fourteen nautical miles east of downtown Houston, Texas.

As Ike moved slowly through the Houston area, it rendered much of the city’s power grid inoperable. Flooding and wind damage to various buildings and structures were both indiscriminate and wide spread throughout the affected metropolitan area. Ike’s massive size coupled with its record strength delivered a potent combination of torrential rains driven by wind gusts of up to 80-90 mph, placing excessive loads onto many building roof systems along its path, including urban and suburban dwellings. Ike is registered as the most destructive hurricane in Texas history.

Hurricane Ike had a large circulation center with an expansive wind field. Ike’s accumulated cyclone energy (ACE) was the highest registered of any 2008 hurricane. With an integrated kinetic energy exceeding any Atlantic storm on record, Ike neither strengthened nor weakened in the three hours preceding its landfall. Indeed, Ike’s winds persisted at tropical storm and hurricane force velocities near its center for no less than nine hours after its landfall. As Ike moved along its northwesterly inland path on September 13, 2008, the tropical cyclone delivered a potent combination of torrential rains driven by sustained winds of about 69 mph, and wind gusts of up to 90 mph onto many buildings. The nexus of high wind velocities and intense rainfall over an extended time period provided both the means and opportunity for wind caused roof system damage and wind driven moisture intrusion into previously water tight building envelopes and building interiors.

Ike’s relatively long post-landfall duration visited unrelenting wind pressure and rainfall onto building surfaces, including their roof covering systems. Battered by the wind, and saturated by heavy rain, many building roof coverings, wall materials, and metal carport materials either displaced, deflected, or detached completely. Decoupled and displaced asphalt roof covering components subsequently exposed underlying wood roof layers to hydraulically loaded wind driven rain. Wind driven rain impacted unprotected wood material surfaces, pushing moisture into the previously water tight roof component gaps and spaces. Once breached, roof systems and building surfaces allowed the free flow of rainwater into the vulnerable building interior spaces below. This wind driven water intrusion caused exterior and interior material damage both above and below building roof planes.

Ike eventually weakened to a tropical storm by by September 13, 2008 just east of Palestine, Texas, and then became extratropical when it interacted with a front about 12 hours later while moving northeastward through northern Arkansas and southern Missouri. The vigorous extratropical low moved quickly northeastward, producing hurricane-force wind gusts across the Ohio Valley on the afternoon of September 14, 2008. Thereafter, the low weakened and moved across southern Ontario and southern Québec and was absorbed by another area of low pressure near the St. Lawrence River by September 15, 2008.

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