Fellenius, B.H., Basics of foundation design. Pile Buck International, Inc., Vero Beach, FL,. Electronic Edition, wm-greece.info, p. Order a hard copy . other requirements of the design of foundations,. • design the plain concrete footings, isolated footings for square and rectangular columns subjected to axial . of the factors which should be considered in the design or foundations for seismic loads. Foundation Design for Vertical and Lateral Loads. Failure of a structure.
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Instructional Materials Complementing FEMA P, Design Examples. Foundation Design - 3. Load Path and Transfer of Seismic Forces soil pressure. PDF | This book is intended primarily as a textbook for undergraduate and graduate level foundations engineering courses. It provides a. Example completes the analysis and design of shallow foundations for the strength of the soil may control foundation design where large amplitude.
Preservative-treated wooden beams, located just below movement between the post and concrete surface or floor. The post rotates about an axis below the Lateral soil resistance is assumed to increase linearly with depth ground surface. Reactive soil pressures are on both sides of the post. An because the support does not rotate. To prevent frost heaving of the iterative solution is required for the non-constrained case.
Vary d until an post, do not connect the surface support to the post. In areas of deep acceptable embedment is obtained. The rotation axis location is sensitive frost penetration, these surface collars are not recommended. Some solutions for y and 7b illustrate surface support. Calculate the lateral resultant, R s , with exceed the valid boundaries of the rotation axis equation; therefore, y the following: must be slightly less than d and yield positive moment and shear 4.
Sliding resistance on the post bottom is where neglected. This case also applies to foundations with concrete backfilled post holes, see paragraph 4.
In areas of deep frost penetration, R 5 reaction, kN lbf concrete backfilled foundations require special care or frost heaving may R s 5 lateral soil resistance, kN lbf be a problem, see paragraph 4.
Calculate embedment depth, required k cs 5 lateral sliding coefficient, concrete on soil, soil resisting moment, and soil force resultants with the following: see paragraph 4. Bottom collars lower the rotation axis, yet Vg 5 shear at ground surface, from engineering analysis, increase resisting moment. Collars sustain lateral bearing and frictional m ft forces.
Dimension changes require recalculating y. Without connection to the 4. Collars increase lateral support at the surface footing and when the sliding resistance between the collar and footing is by providing a wider bearing area, generally post hole diameter in width. No lateral resistance size and post depth.
Friction on the post bottom is neglected. In areas of is developed by the footing. Calculate the location of the rotation M r 5 z Q 6 Effective width, b , for paragraphs 4. When footings are mechanically connected to collars or when the sliding resistance between collar and 4.
The effective depth and soil resistance is increased. The lateral sliding resistance acts on the 4. Lateral and vertical allowable soil pressure.
Calculate the location of the rotation axis, soil 4. Site specific soil tests produce the most accurate resisting moment and soil force resultants with the following: allowable pressures when they include design load criteria and an acceptable safety factor.
In the absence of tests or building code M r 5 z Q 8 Q 4 restrictions, basic soil lateral pressure values may be presumed from Table 1. The presumed values from Table 1 may be increased for both depth and width adjustments. Lateral soil strength is assumed to increase hydrostatically with depth. S , should not be increased for depth. Presumed pressures from Table 1 determined by engineering analysis of wind, snow, live and dead load may be adjusted for the conditions of design that include wind load, combinations on the post-frame building.
Consider uplift, sliding, and isolated post location and deflection tolerance. Some building codes may overturning forces from wind loads. A downward post force provides 4. Lateral soil pressure lateral foundation sliding resistance from collar friction on concrete may be doubled for isolated posts that are spaced at least six times their footing or footing friction on soil.
If the post is rigidly anchored to the floor width apart. The increase is due to the expanded volume of soil support surface, sliding resistance is zero. The sliding resistance coefficient for for the post, as in deep footing cases. Coefficients for concrete 4.
Lateral soil pressure on soil are in Table 1. Lateral soil pressure may be increased one-third for wind forces acting alone or in combination with 5. Post foundations resist vertical upward and downward vertical loads. Wind increases are cumulative with other pressure forces, including overturning forces from wind and gravity loads from increases for both constrained and non-constrained cases.
Fill annular space around the post with one of the following: 5. The vertical bearing area required to support gravity loads or vertical wind forces is: 4. P 5 vertical foundation load, kN lbf 4. Concrete backfill increases effective width b.
In addition to codes and other requirements, upward tapered sides of postholes increase the heaving potential.
Special design may be needed when the 4. It is essential that the timber is driven in the right direction and should not be driven into firm ground. As this can easily damage the pile.
Keeping the timber below the ground water level will protect the timber against decay and putrefaction. To protect and strengthen the tip of the pile, timber piles can be provided with toe cover. Pressure creosoting is the usual method of protecting timber piles. Usually of square see fig b , triangle, circle or octagonal section, they are produced in short length in one metre intervals between 3 and 13 meters.
They are pre-caste so that they can be easily connected together in order to reach to the required length fig a. This will not decrease the design load capacity. Reinforcement is necessary within the pile to help withstand both handling and driving stresses. Pre stressed concrete piles are also used and are becoming more popular than the ordinary pre cast as less reinforcement is required.
Figure a concrete pile connecting detail. They are made to accurate dimensional tolerances from high grade steels. Pre cast, reinforced concrete tubes, about 1 m long, are threaded on to a steel mandrel and driven into the ground after a concrete shoe has been placed at the front of the shells. Once the shells have been driven to specified depth the mandrel is withdrawn and reinforced concrete inserted in the core. Diameters vary from to mm.
Franki Pile: A steel tube is erected vertically over the place where the pile is to be driven, and about a metre depth of gravel is placed at the end of the tube. A drop hammer, to kg mass, compacts the aggregate into a solid plug which then penetrates the soil and takes the steel tube down with it.
When the required depth has been achieved the tube is raised slightly and the aggregate broken out. Dry concrete is now added and hammered until a bulb is formed. Reinforcement is placed in position and more dry concrete is placed and rammed until the pile top comes up to ground level.
Their relatively small cross-sectional area combined with their high strength makes penetration easier in firm soil. They can be easily cut off or joined by welding. If the pile is driven into a soil with low pH value, then there is a risk of corrosion, but risk of corrosion is not as great as one might think.
Although tar coating or cathodic protection can be employed in permanent works. It is common to allow for an amount of corrosion in design by simply over dimensioning the cross-sectional area of the steel pile. In this way the corrosion process can be prolonged up to 50 years. Normally the speed of corrosion is 0. As indicated earlier, part of a timber pile which is installed above ground water could be vulnerable to insect attack and decay. To avoid this, concrete or steel pile is used above the ground water level, whilst wood pile is installed under the ground water level see figure 1.
In the process of driving the pile into the ground, soil is moved radially as the pile shaft enters the ground. There may also be a component of movement of the soil in the vertical direction. Piles can be produced by casting concrete in the void. Some soils such as stiff clays are particularly amenable to the formation of piles in this way, since the bore hole walls do not requires temporary support except cloth to the ground surface.
In unstable ground, such as gravel the ground requires temporary support from casing or bentonite slurry. Alternatively the casing may be permanent, but driven into a hole which is bored as casing is advanced. A different technique, which is still essentially non-displacement, is to intrude, a grout or a concrete from an auger which is rotated into the granular soil, and hence produced a grouted column of soil. There are three non-displacement methods: The following are replacement piles: Also advantages and disadvantages of different pile materials is given in section 1.
Have a limited bearing capacity. Prefabricated concrete piles reinforced and pre stressed concrete piles. Relatively inexpensive. Construction procedure unaffected by ground water. Can be carried above ground level, for example, through water for marine structures. Replacement piles may be required. Lifting of previously driven piles, where the penetration at the toe have been sufficient to resist upward movements. Concrete cannot be inspected after completion.
Concrete may be weakened if artesian flow pipes up shaft of piles when tube is withdrawn. Cannot be used immediately after the installation.
The lateral displacement of the soil during driving is low steel section H or I section piles can be relatively easily spliced or bolted. Describe the main function of piles 2. In the introduction, it is stated that piles transfer load to the bearing ground. State how this is achieved. Piles are made out of different materials. In short state the advantages and disadvantages of these materials.
Piles can be referred as displacement and non-displacement piles. State the differences and the similarities of these piles 5. Piles can be classified as end-bearing piles cohesive or friction piles. Describe the differences and similarity of these piles. Piles can be classified as bored or driven state the differences. The first part gives brief summary on basic pile arrangements while part two deals with load distribution on individual piles.
Vertical piles can be designed to carry vertical loads as well as lateral loads. If required, vertical piles can be combined with raking piles to support horizontal and vertical forces. However if a group of piles is subjected to lateral load or eccentric vertical load or combination of vertical and lateral load which can cause moment force on the group which should be taken into account during calculation of load distribution.
In the second part of this section, piles are considered to be part of the structure and force distribution on individual piles is calculated accordingly. In the first part of this section, considering group of piles with limited number of piles subjected to vertical and lateral forces, forces acting centrally or eccentrically, we learn how these forces are distributed on individual piles.
The worked examples are intended to give easy follow through exercise that can help quick understanding of pile design both single and group of piles. In the second part, the comparison made between different methods used in pile design will enable students to appreciate the theoretical background of the methods while exercising pile designing.
The pile cap distributes the applied load to the individual piles which, in turn,. Figure 2. For some special cases, calculations can be carried out using the following methods… For a simple understanding of the method, let us assume that the following conditions are satisfied: U ……………………………………………3. In a group of piles, If all piles are of the same material, have same cross-sectional area and equal length L , then the value of k is the same for all piles in the group.
Further, let us assume that for each pile in the group, these movements are small and are caused by the component of the vertical load experienced by the pile. The formulae in the forthcoming sections which are used in the calculation of pile loads, are based on these assumptions. If Q the vertical force acting on the pile group is applied at the neutral axis of the pile group, then the force on a single pile will be as follows: If we assume that the moment MX and MZ generated by the force Q are acting on a group of pile, then the sum of forces acting on a single pile will be as follows: Example 3.
Determine the maximum and the minimum forces on the piles. Q is located 0. Calculate vertical load per pile: It carries a horizontal load applied to the surface of the cap of kN. The only vertical load exerted on the pile group is the weight of the pile cup. Determine the loads on the piles. Determine the magnitude of the vertical force: For a pile cape 4. Determine the location of the N. This can be achieved graphically.
On a millimetre paper, in scale, draw the pile cup. Taking the top of the pile cup draw the vertical component downward as shown in figure then taking the tip of the vertical component as reference point draw the horizontal component perpendicular to the vertical component. By joining the two components establish the resultant force R. Measure the distance from the N. A to the cutting point of R at the underside of the pile cup.
Using the following formula, calculate the load on each pile: Decide the location of the N. A of the vertical and the raking piles in plan position. Draw both N. Point c is where the moment M is zero. Y is the moment arm see fig. The horizontal force, H, imposes a torsional force on the vertical piles.
A of both the vertical and raking piles Example 3. Determine the forces acting on each pile. The raking piles lie at an angle of 4: First we determine the location of the neutral axis, N. A, of both the vertical piles and the raking piles.
From figure 3. A for the vertical piles is determined as follows: A for the raking piles: A Of the vertical piles. Draw both neutral axis till they cross each other at point c.
Pile inclination 4: A of raking piles from eo or from the N. Calculate the forces acting on each pile: With reference to figure 3. Determine the force on the piles shown in figure 3. The inclination on the raking piles is 5: NA for the raking piles: NA for the vertical piles: Establish moment arm Y Inclination 5: Calculate load distribution on individual piles: However during installation of piles slight changes in position do occur and piles may miss their designed locations.
The following example compares theoretical and the actual load distribution as a result of misalignment after pile installation. A, pile distance, ri, of each pile: During pile design, the following factors should be taken into consideration: These two methods are refereed as geotechnical and dynamic methods. This section too has worked examples showing the application of the formulae used in predicting the bearing capacity of piles made of different types of materials.
This ultimate load capacity can be determined by either: When the stage of full mobilisation of the base resistance is reached point D , the pile plunges downwards with out any farther increase of load, or small increases in load producing large settlements. The generic formulae used to predict soil resistance to pile load include empirical modifying factors which can be adjusted according to previous engineering experience of the influence on the accuracy of predictions of changes in soil type and other factors such as the time delay before load testing.
Fig II the load settlement response is composed of two separate components, the linear elastic shaft friction Rs and non-linear base resistance Rb. The concept of the separate evaluation of shaft friction and base resistance forms the bases of "static or soil mechanics" calculation of pile carrying capacity. The basic equations to be used for this are written as: All such formulae relate ultimate load capacity to pile set the vertical movement per blow of the driving hammer and assume that the driving resistance is equal to the load capacity to the pile under static loading they are based on an idealised representation of the action of the hammer on the pile in the last stage of its embedment.
The working load is usually determined by applying a suitable safety factor to the ultimate load calculated by the formula. However, the use of dynamic formula is highly criticised in some pile-design literatures.
Dynamic methods do not take into account the physical characteristics of the soil. This can lead to dangerous miss-interpretation of the results of dynamic formula calculation since they represent conditions at the time of driving. They do not take in to account the soil conditions which affect the long- term carrying capacity, reconsolidation, negative skin friction and group effects. In some cases where piles are driven in to the ground using hammer, pile capacity can be estimated by calculating the transfer of potential energy into dynamic energy.
When the hammer is lifted and thrown down, with some energy lose while driving the pile, potential energy is transferred into dynamic energy. For standard pile driving hammers and some standard piles with load capacity FRsp, , the working load for the pile can be determined using the relationship between bearing capacity of the pile, the design load capacity of the pile described by: And pile length not more than 20 m and geo-category 2.
Table Baring capacity of piles installed by hammering drop hammer activated by rope and friction hammer DROP HAMMER released by trigger winch cross-sectional area of pile cross-sectional area of pile fall height 0. Determine appropriate condition to halt hammering. Type of hammer Drop hammer activated by rope and friction winch. Class 2, GC 2, pile length 20 m solution: However considerable additional support is obtained form the bottom part.
In designing piles driven into friction material, the following formulas can be used ………………………… 5. The load is carried by cohesion between the soil and the pile shaft. Bearing capacity of the pile can be calculated using the following formula for pile installed in clay. The undrained shear strength of the soil, measured from the pile cut-off level is: Determine the ultimate load capacity of the pile. Pile cut-off level is 1. Average diameter: The comment type of steel piles have rolled H, X or circular cross-section pipe piles.
Pipe piles are normally, not necessarily filled with concrete after driving. Prior to driving the bottom end of the pipe pile usually is capped with a flat or a cone-shaped point welded to the pipe. Strength, relative ease of splicing and sometimes economy are some of the advantages cited in the selection of steel piles.
The highest draw back of steel piles is corrosion. Corrosive agents such as salt, acid, moisture and oxygen are common enemies of steel. Because of the corrosive effect salt water has on steel, steel piles have restricted use for marine installations. If steel pile is supported by soil with shear strength greater than 7kPa in its entire length then the design bearing capacity of the pile can be calculated using the following formulas.
Use both of them and select the lowest value of the two: Example 5. Treated against corrosion. Consider failure in the pile material. Cc of the soil is 18 kPa, favourable condition. S2 Steel BS solution: Concrete piles may be pre-cast or cast-in place. They may be are reinforced, pre-stressed or plain. Depending up on project type and specification, their shape and length are regulated at the prefab site.
Usually they came in square, octagonal or circular cross-section. The diameter and the length of the piles are mostly governed by handling stresses. In most cases they are limited to less than 25 m in length and 0.
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. If a concrete pile is supported by soil with undrained shear strength greater than 7 MPa in its entire length, the following formula can be used in determining the bearing capacity of the pile: In favourable condition.