Foundation Presented by: Lewis Ayan Mond. Fakhruddin Zuhilman Ibrahim Fadli Foundation • The basis on which something is grounded • A lower support of a structure • The foundation of a building is the soil or rock on which it sits. • The footing is that portion of its structure that serves to transfer the weight of the building into the ground itself. • Most foundations extend underground, and the foundations of large buildings often penetrate to the bedrock. The design of foundations consists of 3 essential operations: • calculating the loads that must be transferred from the structure to the strata supporting it; • determining the exact character of subsurface conditions; groundwater conditions, to a depth of at least twice the width of the structure; and • designing a foundation structure that will safely transfer the loads from the structure to the foundation beds that have been found at the site. Variations in Site Conditions Subsurface conditions at any building site can be grouped into three main types: 1. Solid rock - may exist either at ground surface or so close to it that buildings may be founded directly upon it; 2. Bedrock - may exist beneath the surface but at such a depth that building loads may, if necessary, be transferred indirectly to it; 3. Bedrock - may be so far beneath the ground surface that it is neither practicable nor economical to transfer building loads to it, the loads having to be carried by the superincumbent soil. Material of Foundations Usually foundation is made from concrete Foundation formwork TYPES OF FOUNDATION Shallow foundation Spread Mat/Raft foundation foundation SHALLOW FOUNDATION SHALLOW FOUNDATION 1> Advantages • Cost (affordable) • Construction procedure (simple) • Material used (mostly concrete) • Workers (doesn‟t need experience) 2> Disadvantages • Settlement • Limit capacity „soil‟ structure • Irregular ground surface (slope, retaining wall) • Foundation subjected to pullout, tension, moment. SPREAD/PAD FOUNDATION • As a foot of a column/bearing wall (footer/footing) • Under the column and bearing wall located a layer of concrete slab. • Only column and bearing wall have their own individual footing. • Small area of footing • Used when surface soils are sufficiently strong and stiff to support the imposed loads. • For the good strength soil, pad foundation most suitable used to reduce cost & ease of construction. • The system: structural load spread out over a broad area under the building. Shape of spread/pad foundation • Square spread footing • Rectangular spread footing • Circular spread footing • Continuous spread footing • Combined footing • Ring spread footing Square spread footing • Located a single column & support at the center. • Concrete mix • Used to support an individual point load such as that due to a structural column. • Usually consist of a block or slab of uniform thickness. • Usually shallow, but deep foundation also can be used. Rectangular Spread footing • Footing with large area • Especially design for column/bearing wall which present large load at a moment. • Rectangle shape. Circular Spread footing • Circle shape from plan view but most to a cylinder with low high. • Used for light standard, flag poles, and power transmission lines. Continuous/Strip footing • Especially used for bearing wall which support large load. • Long area of footing • Not for all bearing wall but only for certain wall according to avoid from misspend. Combine footing • Shape: - rectangular - trapezoidal - cantilever • Design for more than one column • Column axis is located too close for each –other-need combine footing. • Ease of construction. Ring spread footing - continuous footings that have been wrapped into a circle - commonly used to support the walls above- ground circular storage tanks. - The contents of these tanks are spread evenly across the total base area and this weight is probably greater that the tank itself Mat/raft foundation 1) Definition: A foundation (usually on soft ground) consisting of an extended layer of reinforced concrete. • 1 layer concrete slab that strengthen with steel reinforced. • Used to spread the load from a structure over a large area. • Normally consist of concrete slab which extend over the entire loaded area. • Maybe stiffened by ribs or beams. • Advantage: reduce differential settlements • Often needed on soft/loose soil with low bearing capacity as they can spread the load over a larger area. To design mat foundation 1. Determine the capacity of the foundation 2. Determine the settlement of foundation 3. Determine the differential settlement 4. Determine the stress distribution beneath the foundation 5. Design the structural component of the mat foundation using the stress distribution obtain from 4. Mat/raft foundation Deep foundation • Deep foundations are those founding too deeply below the finished ground surface for their base bearing capacity to be affected by surface conditions, this is usually at depths >3 m below finished ground level. Caisson foundation • Similar in form to pile foundations, but are installed using a different method. • Caissons are created by auguring a deep hole into the ground, and then filing it with concrete. • Drilled either to bedrock or deep into the under laying soil • Special drilling bits are used to remove the soil for these “belled caissons” Diaphragm foundation • Diaphragm walls are underground structural elements commonly used for retention systems and permanent foundation walls. • Diaphragm walls are constructed using the slurry trench technique. The technique involves excavating a narrow trench. • Slurry trench excavations can be constructed in all types of soil. Diaphragm wall construction begins with the trench being excavated in discontinuous sections or “panels”. Panels are usually 8 to 20 feet long with widths varying from 2 to 5 feet. Diaphragm walls are commonly used in congested areas The picture above shows a Diaphragm wall excavation. Diaphragm walls are constructed using the slurry trench technique A grab used for excavation Once the excavation Diaphragm of a panel is complete, a wall steel reinforcement cage reinforcement is placed in the center of & concreting the panel. Concrete is poured in one continuous operation through one or more tremie pipes that extend to the bottom of the trench. The tremie pipes are extracted as the concrete rises; however, the discharge end of the tremie pipe always remains embedded in the fresh concrete. The finished wall after Reinforcement excavation PILES Long, slender members that transmit foundation loads through soil strata of low bearing capacity to deeper soil or rock strata having a high bearing capacity. End bearing piles End bearing piles are those which terminate in hard, relatively impenetrable material such as rock or very dense sand and gravel. Friction piles • Friction piles obtain a greater part of their carrying capacity by skin friction or adhesion. This tends to occur when piles do not reach an impenetrable stratum but are driven for some distance into a penetrable soil. Settlement reducing piles Settlement reducing piles are usually incorporated beneath the central part of a raft foundation in order to reduce differential settlement to an acceptable level. Such piles act to reinforce the soil beneath the raft and help to prevent dishing of the raft in the centre. Tension piles • Structures such as tall chimneys, transmission towers and jetties can be subject to large overturning moments and so piles are often used to resist the resulting uplift forces at the foundations. In such cases the resulting forces are transmitted to the soil along the embedded length of the pile. Piles in fill • Piles that pass through layers of moderately- to poorly- compacted fill will be affected by negative skin friction, which produces a downward drag along the pile shaft and therefore an additional load on the pile. This occurs as the fill consolidates under its own weight. TYPES OF PILES • Steel piles • Concrete piles • Timber piles (wood piles) Steel piles • Steel piles withstand driving pressure well and very reliable end bearing members. • Pipe piles are normally, not necessarily filled with concrete after driving. • Strength, relative ease of splicing and economy are some of the advantages cited in the selection. • Corrosion (salt, acid, moisture and oxygen) > restricted use for marine installations. Steel piles Concrete piles • Much more resistance against corrosive elements • Concrete is available in most parts of the world than steel. • Concrete piles may be pre-cast or cast-in place. Pre-cast concrete piles Formed, cast to specified lengths and shapes and cured at pre casting stations before driven in to the ground. Their shape and length are regulated at the prefab site. Usually came in square, octagonal or circular cross-section. The diameter and the length of the piles are mostly governed by handling stresses. Limited to less than 25 m in length and 0.5 m in diameter. Some times it is required to cut off and splice to adjust for different length. Where part of pile is above ground level, the pile may serve as column. Cast-In-Place Concrete Piles • Made at the construction • Steel shell is grounded to the soil to as container to allow the concrete filled in it • Not contribute load capacity to the pile Timber piles (wood piles) • Timber piles are frequently used as cohesion piles and for pilling under embankments. • Made from tree trunks with the branches and bark removed. • Normally wood piles are installed by driving. Typically the pile has a natural taper with top cross-section of twice or more than that of the bottom. • To avoid splitting in the wood, wood piles are sometimes driven with steel bands tied at the top or at the bottom end Can be form of >>>>>>> Shrinkage Expansion Cause Cause Settlement Heave When dry conditions prevail, soils consistently lose moisture and shrink. When moisture levels are high, the opposite is true, and soils swell It will most likely manifest itself in the form of visible cracks in the foundation walls, exterior brick walls, or interior sheetrock or plaster walls. Officially, any structure movement is known as differential settlement. Causes • Poor drainage • Moisture around the foundation • Transpiration • Plumbing leaks • Bad Design • Faulty Construction • Extraordinary Loads Poor drainage Yard and gutter downspouts discharging at the base of the foundation are among other causes Moisture Moisture around the foundation can cause the soils to become over- saturated and lose the strength to support weight. When this happens, structures “settle” or sink into the ground Transpiration During an active season, roots extending beneath and around the footings of the house can remove moisture from the soil, causing it to become desiccated. Again, where expansive soils exist this removal of moisture will cause soil shrinkage and settlement. Plumbing leaks Home‟s pipes Poor Construction • Material used • Construction workers Bad design • Failure to take into account the loads the structure will be called upon to carry, • erroneous theories, • inaccurate data, • ignorance of the effects of repeated or impulsive stresses • improper choice of materials or misunderstanding of their properties. Faulty Construction • The use of salty sand to make concrete, • Bad riveting or even improper tightening torque of nuts, • bad welds, Extraordinary loads • Extraordinary loads are often natural, such as repeated heavy snowfalls, or • the shaking of an earthquake, or • the winds of a hurricane. A building that is intended to stand for some years should be able to meet these challenges. Earthquakes The picture on the right shows a building which has lost the ground floor. This house will probably have to be demolished. Do New Houses Have Foundation Failure? Unfortunately, for many homeowners, problems may develop relatively soon after the house has been completed. While older homes experience some settling over time, serious foundation failures occur more frequently in homes less than ten years old. When the ground shakes, lose particles (i.e. soil) moves in a fashion similar to a liquid (i.e. water). When the soil (which is lose) surrounding it is shaken the foundation in effect sinks. This is often uneven and the building may topple. Bulging floors, Cracked walls Doors that won't close The problem occurs when only part of the foundation heaves or settles, causing cracks and other damage. This differential movement is largely caused by differences in soil moisture. Settlement cracks are nearly always vertical. Exterior Warning Signs : Wall Rotation Separation around garage door, windows and/or walls Cracked bricks Broken and/or cracked foundation Displaced Moldings Interior Warning Signs Misaligned Doors and Windows Cracked sheetrock Cracks in Floor Cracked walls Cracked foundation Misaligned Doors and Windows Thanks!
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