Foundations

6. What are several (at least 3) of the items from Thallon's design checklist that you should keep in mind when assessing existing foundations?

1. Place the bottom of the footing below the frostline on solid, undisturbed material that is free of organic material. (Local codes will prescribe frost line depth.) 2. Use a continuous horizontal rebar in the footing and at the top of foundation walls (joint reinforcing may be allowable in concrete block walls.) Tie the footing and wall together with vertical rebar. 3.Use pressure treated of other decay resistant wood in contrast with concrete. Use a moisture barrier between all concrete and untreated wood. 4. Tie wood members to the foundation with bolts or straps embedded in the foundation. Anchoring requirements in hurricane and severe earthquake zones should be verified with local codes. 5. Provide adequate drainage around the foundation. Slope backfill away from the building and keep soil 6" below all wood.

3. How does climate affect the selection of the basic foundation types (Thallon posits 3 types) you may use for a building?

1. Slab-On-Grade Foundations: are used mostly in warm climates, where living is close to the ground and the frost line is close to the surface. The footing is usually shallow, and the ground floor is a concrete slab. Many slab-on-grade systems allow the concrete footing, foundation, and subfloor to be poured at the same time 2.Crawl Spaces: Found in all climates but predominately in temperate regions. In this system, the insulated wooden ground floor is supported above grade on a foundation wall made of concrete or concrete block. The resulting crawl space introduces an accessible zone for ductwork, plumbing, and other utilities and allows for simple remodeling. 3: Basements: The dominate foundation system in the coldest parts f the country where frost lines mandate deep footings in any case. Like crawl spaces, basements are accessible, and in addition they provide a large habitable space. Basement foundation systems are usually constructed of concrete or concrete block foundation walls. Drainage and waterproofing are particularly critical with basement systems.

1. What are the two primary functions of foundations in Thallon's Graphic Guide to Construction?

1.It supports the building structurally by keeping it level, minimizing settling, preventing uplift from the forces of frost or expansive soils and resisting horizontal forces such as winds and earthquakes. 2. A foundation system keeps the wooden parts of the building above ground and away from the organisms and moisture that both eat wood and cause it to decay.

9. What are the performance requirements of the foundation? (In other words, what must a foundation DO for a building or a building inhabitant?)

A foundation supports many different types of loads. 1. Dead Load: The sum of weight of the total building and all it components. 2. Live Load: Sum of the weights of the inhabitants. 3. Wind Loads: Lateral, downward, and uplift forces to a foundation. A primary objective of the foundation is to minimize differential settlemetn by loading the soil in such a way that equal settlement occurs under various parts of the building.

8. Generally, what are more desirable soil types to support a building? What are problematic soil types for construction?

All foundations settle to some extent as the soil beneath them adjusts to the load. Foundations on bedrock settle a negligible amount. Foundations on certain types of clay may settle to an alarming degree.

10. What materials do you expect to see in foundation construction? (from reading + your observations in assignment #1!)

Concrete, rebar, brick, other masonry.

12. How does the 'grain' of a soil, or its component particulate, make the soil more or less suitable to building?

Different types of particulates that compose the soil have different properties. (Ie Sand, Gravel, Clay)The distribution of particle sizes and types of soils is important to know when designing a foundation because it is helpful in predicting the loadbearing capacity of the soil, its stability, and its drainage characteristics.

11. What type of settlement is detrimental to buildings? What type is generally of little consequence?

Differential Settlement: Occurs when the various columns and load-bearing walls of the building settle by substantially different amounts. The frame of the building may become distorted, floors may slope, walls and glass may crack, and doors and windows may refuse to work properly. Uniform Settlement is of little consequence: Settlement occurs at roughly the same rate from one side of the building to the other *A primary objective in foundation design is to minimize differential settlement by loading the soil in such a way that equal settlement occurs under the various parts of the building. This is not difficult in situations where all parts of the building rest on the same kind of soil.

5. What other factors should influence the selection of a foundation type, besides climate?

Each foundation system has many variations and it is important to select the one best suited to the climate., the soil type, the site, and the building program. With all foundations you should investigate the local soil type. Soil types, along with their bearing capacities, are often described in local soil profiles based on Information form the USGS.

16. What is a footing vs a foundation?

Footings: Part of the foundation that transfers the building's loads- its weight in materials, contents, occupants, and snow directly to the ground. They are typically made of concrete with rebar reinforcement that has been poured into an excavated trench. The purpose of footings is to support the foundation and prevent settling. Footing size depends largely on soil type and the building's weight. Foundations: The function of a foundation is to transfer the structural loads from a building safely into the ground. The foundation reaches through the unstable surface to underlying soil that is free of organic matter and unreachable by winter frost (below the frost line.)

17. What are some ways that foundations deal with sloping sites?

Foundations on sloping sites, viewed in a cross section through the building. The broken line indicates the outline of the superstructure. Wall footings are stepped to maintain the necessary distance between the bottom of the footing and the surface of the ground. Separate column foundations, whether caissons, as shown here, or column footings, are often connected with reinforced concrete tie beams to reduce differential movement between the columns. A grade beam differs from a tie beam by being reinforced to distribute the continuous load from a bearing wall to separate foundations.

14. Discuss the stability of clay soils. Do the properties of clay make it a good soil to support foundations?

Rocks, gravels, sands, an many silts tend to be stable soils (they have a much better loadbearing capacity) Many clays however are dimensionally unstable under changing subsurface moisture conditions. Clay may swell considerably as it absorbs water and shrinks as it dries. When wet clay is put under pressure water can be squeezed out of it with a corresponding reduction in volume.

13. What two characteristics of soil affect the soil's suitability for building?

Stability Characteristics: The stability of a soil is it ability to retain its engineering properties under the varying conditions that may occur during the lifetime of the building. Drainage Characteristics: Important in determining how water will flow on and under building sites and around building substructures.

2. Which building system is most likely to determine the longevity of the building? Why?

The Foundation. If the foundation does not support the building adequately, cracks and openings will occur over time. Even in the most finely crafted structures. No amount of repair on the structure above the foundation will compensate for an inadequate foundation; once a foundation starts to move significantly, it will continue to move. We now have developed the knowledge to design and construct durable foundations, so there is no reason to invest in a modern building that is not fully supported on a foundation that will endure for the life of the structure.

7. What are some issues you can imagine coming across if a foundation was poorly designed and/or constructed? (for example if the designer and/or contractor weren't familiar with Thallon's recommendations as presented in the checklist?)

The frame of the building may become distorted, floors may slope, walls and glass may crack, and doors and windows may refuse to work properly. Foundation walls need to be carefully dampproffed and drained to avoid flooding with groundwater and to prevent the buildup of water pressure in the surrounding soil that could cause it to cave in.