NEESWood Capstone Test Structure

After the destruction caused by the 1995 Kobe earthquake the Japanese government took it upon themselves to construct the world’s largest seismic testing table, often referred to as a “shake table”. This testing facility, called Earth-Defense, was built to its enormous size out of necessity. Space to build new structures is a rare commodity in Japan and it was essential to be able to test large mid-rise (4 to 7 story) structures that maximize usable space while minimizing the building footprint. The Earth-Defense shake table is 50’ x 65’ and can support an astonishing 2.5 million pounds while “shaking” test buildings in three directions at once.

The NEESWood Capstone project shown in this video was conducted last summer to test the viability of wood framed mid-rise structures. Mid-rise structures are more traditionally constructed out of steel and concrete, but with the trend towards “green” construction it is becoming desirable to use renewable construction products like wood in larger commercial, residential and mixed use projects. The NEESWood Capstone project tested a seven story mixed use building consisting of a steel framed commercial (retail) main level and six stories of wood framed residential units. This test building was constructed in its entirety within the walls of Earth-Defense. The test building was constructed with many proprietary wood and steel products along with new NEESWood construction methodologies, all of which being beyond the scope of this article.

The portion of the results this test that was of most interest to me as an engineer was the “real life” forces experienced in the structure. As engineers in school we are handed exhaustive volumes of information that we are expected to accept as “the unquestionable truth”. There is an understanding that all of this information has been determined by hundreds of collective years of expert design experience, material testing and are always in a continuous state of refinement. As an engineering student I accepted that this was the adopted standard practice of my trade, but I always wondered how all the design theory I was being fed related to the real world. Hundreds of gauges were installed throughout the Capstone structure to test the forces actually experienced during an earthquake. It was quite satisfying as a design professional to see that the calculated anticipated forces at play in the structure were very close to those actually recorded.

For more detailed information on NEESWood Capstone project please follow this link.

Many older homes in the Denver area are built on shallow crawlspace foundations. Adding a second story to a home, often called a “Pop-Up”, is quite disruptive and often displaces the family living there. For this reason, home owners often consider constructing a full basement addition or digging under their existing crawlspace to add foundation walls below the existing crawlspace foundation (under-pinning) to create a full basement which then can be finished into living space.

When considering this option it is important to consider the impact that your excavation may have on your neighbor’s foundation. While on inspection this last winter I took the photo shown below. In this example a completely new home is being built between two existing houses. What concerned me is that there was no shoring installed to protect the adjacent existing homes. Shoring is a general term the measures taken to protect the soils supporting structures near a new excavation or to keep steeply cut soils from spalling out.

A vertically cut excavation in a historic Denver neighborhood without shoring.

Many home owners (and even quality professional contractors) do not fully understand how foundation loads are distributed through the soils beneath a house. Most homes are built on a spread footing foundation system. The load from a house travels through bearing soils at a 1:1 slope (45 degree angle). When an excavation is dug for a new or under-pinned foundation wall, additional soils must be removed so that workers can maneuver around what they are building. This is called “over excavation”. Even though your foundation may not be any closer to the property line than it was before often the over excavation will go completely to it. The illustration below shows how loaded soils can be disrupted during a deeper excavation.

Soil load transfer.

When loaded soils are disrupted there is a real chance that the soils suddenly collapse if precautions are not taken. If the scope of your project includes a deep excavation, a professional engineer (such as EVstudio) should be contacted for shoring design. Properly designed and installed shoring will prevent soils from collapsing and lawyers from being telephoned.

There are many different shoring types. The most common is the cantilevered concrete pile. Most of us have probably seen this type of shoring while stuck in traffic during highway construction projects. The photo below shows properly installed cantilevered concrete pile shoring installed at a residential basement addition project. This shoring protects not only your neighbor’s home, but the workers completing your project.

Cantilevered concrete pile shorting.

Copper roofing being installed on the Rotunda Roof @ Silver Rock Manor

We recently visited the construction site of the Silver Rock Manor, a high-end luxury residence that we designed in Evergreen, Colorado to see how the project was progressing. The project is coming along nicely and is scheduled for completion at the end of June! They were putting the copper roofing on the Rotunda roof the day we were out there.

Master Suite under construction @ Silver Rock Manor

Rear Deck under construction at the Silver Rock Manor

Adam has worked at Purrington Professional Engineering in Evergreen for the last 4.5 years. EVstudio has worked with Adam on a number of projects while he was with PPE and we're excited to have him on our team full time. Prior to PPE Adam worked with Jim (our director of structural engineering) at MNA. Adam graduated from Montana State with a degree in Construction Engineering.

EVstudio's Structural Engineers are working with Earthcore SIPs LLC to provide high quality SIP walls, floors, roofs and foundation walls to meet every client’s need.  EVstudio's role will be to provide structural engineering services for each project, provide detailed shop drawings and provide engineering reports for all of Earthcore's products. 

Earthcore manufactures SIP walls, floors and roofs using OSB or Magnum Board facings and a polyurethane foam core.  The polyurethane core provides insulation R-values of roughly 7.0 per inch of thickness, higher than commonly used polystyrene.  Earthcore uses Ecomate® foam which has a water based blowing agent. This eliminates all CFC and HFCs in the product which makes it one of the most environmentally friendly foams available.  In addition, the polyurethane bonds directly to the facing and wood plates providing a much stronger composite system without the use of additional adhesives.

Magnum Board can be used in lieu of OSB facings to create a panel that can be used below grade as foundation walls, exterior walls with no additional protection or siding needed and many other situations when something more than OSB is needed.

Magnum Board® products are:

• Virtually impervious to fire – are non-flammable and non-combustible
• Virtually impervious to water – can be fully submerged for long periods of time with no affect dimensionally whatsoever
• Unaffected by all insects – such as termites and carpenter ants
• A non nutrient for mold or mildew
• Are completely non toxic
• Homogenous construction to eliminate delaminating
• Available for almost every application required in construction for of your projects including Residential, Commercial and Industrial.

Earthcore also offers a variety of demising wall options for the multi-family or commercial project.  A choice between a magnesium board skin or a Blazeguard® coating can be made to reach a class A fire rating.

You can learn a lot more about SIPs by visiting Earthcore’s blog.

EVstudio attended the pre-construction meeting earlier this week and had our first chance to visit the train and observe the existing conditions.  The plan is simple; prepare the new site and place tracks, set the temporary bridge using a steel frame adjacent to the existing bridge and use a flat bed train car to span the 50ft between the bridge and embankment.  Each train car will be moved on a flat bed truck to a temporary storage area.

Flat bed train cars have been recycled as bridges for years.  Due to the width and length of the flat bed train car, the bridges are typically single lane bridges used for private roads or trails spanning 40 to 60 feet.   The flat bed train cars were originally designed to carry large loads such as tanks or other large equipment and therefore have no problem supporting lighter loads such as cars.

Your home may or may not have a sump pit.  If you have one be sure to check it every few months, especially when you may have heavy rain.  Most people forget about the sump pit leaving them open to a good chance of major problems.

When checking your sump pit check for the following items:

• Standing water more than 4"
• Properly working sump pump, it should turn on when the float is raised
• Discharge pipe properly attached with no leaks
• Discharge pipe exists the dwelling and extends at least 5ft away from the foundation
• Water entering sump pit, is it dripping or pouring in?

Around the Denver area many houses are built with an elevated structural floor.  When you are checking the sump pit be sure to check the conditions in the crawlspace.  Feel the soil to see if it feels soft below the vapor barrier.  Soft or muddy soil is a sign of high water content.  Also, check the floor joists for signs of rotation or buckling.  If the foundation wall is exposed look for cracks larger than 1/8" wide.

If you allow water to collect in the sump pit it will eventually rise to a level where the water then collects in the perimeter drain.  Once water collects in the perimeter drain the foundation is at great risk to move if swelling soil is present.  Also, you are exposing your house to potentially flooding during a heavy rain.

Helical piers are typically used when repairing failed shallow foundations.  The helical piers are a deep foundation system that can be placed alongside existing foundations with very little interference.

However, helical piers are also used for new construction as an alternative to typical straight shaft drilled piers.  EVstudio recently designed a new foundation using helical piers due to high water table and swelling soil.  With a small surface area on the steel shaft the helical pier is very stable is highly expansive soil.  We have also recently used helical piers for an addition to a home.  There was no soils report, but the house was on drilled piers.  A drill rig for new drilled piers could not gain access to the backyard, so helical piers installed using smaller machinery was recommended.

The real advantage helical piers have is their use for repairing moving foundations.  The entire existing structure can be underpinned using helical piers that are bolted to the bottom of the foundation.  Once the structure is underpinned the moving soil below the footing can be removed, establishing a void space separating the structure from any future movement.

PROS
Fast Installation
Can be Proof Tested
Negligible Uplift Pressure from Swelling Soil
High Tensile Resistance
Moderate to Small Equipment Needed

CONS
Specialized System
Concerns with Corrosion

Learn more about different types of foundations

All of the issues were purged from the home in their entirety, and the happy couple moved in recently and had me over to see how it all came together in the end. We stood by them every step of the way and while the road for them was long and wrought with many difficult decisions (like, to bulldoze the home or keep going), they are happy to have persevered and are now enjoying their entirely re-built (and vermin free) home. Did I mention that they also had to let their first contractor go - well, that story is for another post.

A Raft Slab-on-Grade foundation can be as simple as a 4” thick slab with no reinforcement and a shallow perimeter rib to an 8” thick slab heavily reinforced with deep ribs spaced roughly 10’o.c.  The wide range of concrete thicknesses and reinforcement is a function of many things such as soil type, loads, exterior finishes, allowable deflections, climate, and many more factors.  The primarily factor that influences the slab thickness, reinforcement and rib sizes of a slab-on-grade foundation is the soil type.

If the soil is a sandy material with non-swelling fines to allow good compaction then the slab-on-grade foundation will be evenly supported, and has a low risk of soil movement.  This raft foundation will just need the minimum slab, ribs and reinforcement.

If the soil has swelling material that is susceptible to changes in moisture content then the raft must be designed to resist this movement.  The use of reinforced ribs is an economical way to strengthen the slab.  Ribs are below the slab and are spaced evenly to create a grid or waffle appearance.  This is done in lieu of thickening the entire slab because you gain more strength with depth and will typically use less concrete and steel reinforcement to achieve the same design capacities.

Raft foundations have been used for residential structures, commercial structures and heavy construction structures.  The reason for the wide range of uses is simply because the raft slab-on-grade foundation is simple to construct and one of the most cost effective foundations.  Typically, little earthwork is needed, sites are leveled, ribs are trenched, reinforcement placed and then concrete is placed.  Also, since the raft foundation is just reinforced concrete, access to plumbing can be achieved by removing sections of the slab and then patching as needed.  If the slab is post tensioned then accessing the plumbing is much more difficult.

But the raft foundation has its problems as well.  On sites with high risk of soil movement the slab can become expensive if deep ribs and heavy reinforcement is needed.  That is when a post tensioned slab may become cost effective.  In addition, the control of visible cracks in the slab can be difficult.  Concrete shrinks as it cures and if control joints are not placed appropriately or sufficient reinforcement is not used the owners may be upset with visible cracks.  Cracks caused by shrinkage do not indicate failure, but can be an eye sore and a difficult conversation with the owner.

PROS
Cost effective
Common Construction
Low Tech
Sections may be removed to Access Plumbing

CONS
Limited Design Capacity
Does not respond well to Soil Movement

Learn more about different foundation types.