Question

Small paragraph/ some sources

final memo is required which summarizes the economy behind the use of spread footings. This memo MUST be based on contemporary issues dealing with spread footing design and construction methods. Cited publications must be 4. A d and attached to this memo. (20 pts) via

Answer 1

Spread footing foundation has a wider bottom portion compared to a load-bearing foundation; the wider bottom "spreads" the weight of the structure over a larger area for greater stability.

While traditional spot footings only have a single point of contact with the foundation, spread footings extend support continuously across the entire building layout.

Spread footings are used to support a foundation or set of piers below a building.

To add additional support, spread footings are constructed with concrete and reinforced with steel. Since spread footing transfers the weight of the building over a large area, spread footings have little risk of failure compared to spot footers.

Spread footing extends the life of a building by minimizing structural damage. Footings must be designed to carry the column loads and transmit them to the soil safely.

Spread footings may be circular, square, or rectangular.Spread footings work best for shallow foundations where the soil is well-compacted and stable. Also known as “T” footings (if the T is upside down), spread footings rest directly on the soil and are wider than the foundation wall by several inches. You determine the width and thickness according to the load it will bear above and the type of soil below. Most commonly used in residential applications, often, spread footings need not be reinforced to meet code, although you should use nominal reinforcement for flexure anyway. The lower the load-bearing capacity of the soil, the wider the spread footing needs to be to avoid dramatic settlement. Spread footings are also poured below the frost line. The footers make for a level and smooth line upon which the concrete foundations are then poured to form a continuous wall supporting the perimeter of the home.

Shallow spread footings require significantly less time to excavate and place than deep foundations consisting of drilled or driven piles. Shallow spread footings commonly are constructed using cast-in-place methods. Precast spread footings and newer hybrid systems that combine the installation of speed of precast with the economy of cast-in-place also are available.Precast units are fabricated offsite in a factory controlled environment, and then shipped to the project controlled environment, and then shipped to the project site. Consistent with the FHWA “Every Day Counts” initiative for Accelerated Bridge Construction, foundations are constructed concurrently with the site work. This enables contractors to reduce overall project time since the work is completed faster. The combined result of efficient design and speedier construction is a more economical solution for owners while placing fewer burdens on public funding.

The Spread footing is not suitable for every soil type.Large amount off concrete is also required but preparing such an amount of concrete is quite problematic .Also,there is quite a decent amount of work on running the concrete, so manpower required

Design

The design process involves necessary checks of limit states of the foundation design. A limit state is defined simply as a “failure mode.” For spread footings, AASHTO BDS requires the following limit state checks:

Service Limit States — Shallow spread footings should be checked for serviceability of the foundation, and also the structure it supports. While having a high probability of occurring, issues such as settlement, horizontal movements, overall stability and scour usually are not life threatening. With larger footings, service limit states are the controlling factor in the footing design.

Strength Limit States — Strength limit states govern the design based on structural safety and the potential loss of load carrying capacity. Structural capacity of a foundation is designed at this limit state using factored loads. Bearing capacity, limiting eccentricity (overturning), excessive loss of contact and sliding are checked at this limit state.

Extreme Event Limit States — AASHTO BDS defines the extreme event as a major environmental event. Although rare, these events include flooding, seismic activity and high winds, as well as situational occurrences such as vessel or vehicle collision, and other site-specific situations.