CALCULATION OF PILE CAPACITY - EXAMPLE

CALCULATION OF PILE CAPACITY - EXAMPLE

Data:

i) A Bore log furnishing the properties of the soil is given in Table-4

ii)        The pile founding level is considered at 20.0m depth from the ground level.

iii)      The pile cut off level is at 3.5m below the ground level.

iv)      The diameter of the pile is 550 mm.

v)        Concrete grade used : M20

11.1     PILE CAPACITY BASED ON SOIL SUPPORT

            The properties of the soil at depths are as under :

Depth in 'm'	'C' in kg/cm²	'f' in degree
3.5 to 5.0	0.50	28
5.0 to 10.0	0.50	31
10.0 to 16.0	0.0	34
16.0 to 19.0	0.5	29
19.0 to 25.0	0.0	36

            Since the pile founding level is at 20.0m depth, f value of 36° is considered to calculate the point resistance at the pile tip.

            From the formula 4.1

                        Ppu      =          Ap (P_D N_q + 0.5 g D N_g)

             For  f = 36°,      Nq   = 60 from fig.1 and Ng   = 56.3 from Table-1

D    = 0.55 m

L     = 16.5 m

g                 = 1.0 t/m3

For calculation of maximum effective overburden pressure P_D, fifteen times diameter is considered from pile cut off level as all the soil layers are silty soil with angle of internal friction (f) more than 28^0.

            P_D        =       15 x D x g   = 15 x 0.55 x 1.0 = 8.25 t/m²

            Ppu      =       p x 0.55²/4 [8.25 x 60 + ½ x 0.55 x 1.0 x 56.3]  = 120.0 t

            The frictional resistance of the soil is calculated using the formula 4.10

K  = 0.70,        d = 3/4 f

            Between depths 3.5 and 5.0 m

            Psu1   = [0.70 x (4.25 -3.5) x tan 21.0 + 0.5 x 5.0] p x 0.55 x 1.5    = 7.0 t

            Between depths 5.0 and 10.0 m

            Psu2   = [0.70 x (7.5 -3.5) x tan 23.25 + 0.5 x 5.0] p x 0.55 x 5.0    = 32.0 t

Between depths 10.0 and 16.0 m

Psu3   = [0.70 x 8.25 x tan 25.5 + 0] p x 0.55 x 6.0                            = 28.6 t

Between depths 16.0 and 19.0 m

Psu4   = [0.70 x 8.25 x tan 21.75 + 0.5 x 5.0] p x 0.55 x 3.0              = 24.9 t

Between depths 19.0 and 20.0 m

Psu5   = [0.70 x 8.25 x tan 27] p x 0.55 x 1.0                                     = 5.1 t

Psu     = Psu1 + Psu2 + Psu3 + Psu4 + Psu5

           =   7.0 + 32.0 + 28.6 + 24.9 + 5.1        = 97.6 t

            Wp     =   p/4 x 0.55² x 16.5 x 2.5       = 9.8 t

Ultimate Pile capacity Pu  =     Ppu + Psu - Wp  =  120.0 + 97.6 - 9.8  = 207.8 t

            Safe load on pile         P_all  =     207.8/2.5                   =          83.1 t

11.2     STRUCTURAL CAPACITY OF PILE

Considering concreting is done using tremie,

Allowable compressive stress in concrete s_c= 0.33 x 20  = 6.6 N/mm²

As the pile is wholely embedded in good soil, pile is designed as short column.

Allowable load on pile = A_p s_c -Wp = p/4 x 550² x 6.6 x10^-4 - 9.8   =  147.0 t

11.3     The safe load on the pile is least of the values obtained in 11.1 and 11.2 which is 83.1 t.

STABILISATION OF SOIL WITH ADDITIVES

Types of Additives Used The various additives used fall under the following categories:

(i) Cementing materials: Increase in strength of the soil is achieved by the cementing
action of the additive. Portland cement, line, fly-ash and sodium silicate are examples
of such additives.

(ii) Water-proofers: Bituminous materials prevent absorption of moisture. These may
be used if the natural moisture content of the soil is adequate for providing the
necessary strength. Some resins also fall in this category, but are very expensive.

(iii) Water-retainers: Calcium chloride and sodium chloride are examples of this category.

(iv) Water-repellents or retarders: Certain organic compounds such as stearates and
silicones tend to get absorbed by the clay particles in preference to water. Thus,
they tend to keep off water from the soil.

(v) Modifiers and other miscellaneous agents: Certain additives tend to decrease
the plasticity index and modify the plasticity characteristics. Lignin and
lignin-derivatives are used as dispersing agents for clays.

FEASIBILITY OF MICROPILES

Micropiles have specific advantages compared to more conventional support systems. In general, micropiles may be feasible under the following project-specific constraints:

1. • project has restricted access or is located in a remote area;
2. • required support system needs to be in close pile proximity to existing structures;
3. • ground and drilling conditions are difficult (e.g., karstic areas, uncontrolled fills,boulders);
4. • pile driving would result in soil liquefaction;
5. • vibration or noise needs to be minimized;
6. • hazardous or contaminated spoil material will be generated during construction; and
7. • adaptation of support system to existing structure is required.

moment end-plate beam to- column connections(CHECK LIST)

 failure modes for moment end-plate beam to-column connections are:
1. Flexural yielding of the end-plate material near the
tension flange bolts. This state in itself is not limiting,
but yielding results in rapid increases in tension
bolt forces and excessive rotation.
2. Shear yielding of the end-plate material. This limit
state is not usually observed, but shear in combination
with bending can result in reduced flexural capacity
and stiffness.
3. Bolt rupture because of direct load and prying force
effects. This limit state is obviously a brittle failure
mode and is the most critical limit state in an endplate
connection.
4. Failure of bolt, or slip of bolt in slip critical connections,
due to shear at the interface between the end
plate and column flange.
5. Plate bearing failure of end-plate or column flange
at bolts.
6. Rupture of beam tension flange to end-plate welds or
beam web tension region to end-plate welds.
7. Shear yielding of beam web to end-plate weld or of
beam web base metal.
8. Column web yielding opposite either the tension or
compression flanges of the connected beam.
9. Column web buckling opposite the compression flange
of the connected beam.
10. Column flange yielding in the vicinity of the tension
bolts. As with flexural yielding of the end plate, this
state in itself is not limiting but results in rapid
increases in tension bolt forces and excessive rotation.
11. Column web stiffener failure due to yielding, local
buckling or weld failure.
12. Column flange stiffener failure due to yielding or weld
failure.
13. Excessive rotation (flexibility) at the connection due
to end-plate and/or flange bending.
14. Column panel zone failure due to yielding or web plate
buckling.

Comparison of Rigid Jointed / Pin Jointed Framing System

RIGID JOINTED FRAME

Advantages

1.More free space (allows openings)

2.Less numbers of Members

3.More sway as compared to braced frame

      Disadvantages

1.The flanges only resist the moment. Stress diagram is triangular (less utilization of area)

2.Connections are difficult to fabricate

3.Bulky sections are required

BRACED FRAME

Advantages

1.Full cross sectional area is utilized as members are mainly axially 

loaded

2.Simple connections, simple behaviors (direct load transfer)

3.Lesser sway

4.Easy to analyze

5.Capable of resisting accidental loads, twisting etc.

6.Easy to modify

7.Aesthetically appealing

8.Economical

    Disadvantages

1.More number of members

2.Difficult to provided openings

3.Heavy bracing s are required for long spans

4.Loads need to act essentially on joints

5.Design load for the Bracing design is always debatable

 

structural and other benefits of using composite floors

The mainstructural and other benefits of using composite floors with profiled steel decking are:

• Savings in steel weight are typically 30% to 50% over non-composite construction
• Greater stiffness of composite beams results in shallower depths for the same span.Hence lower storey heights are adequate resulting in savings in cladding costs,reduction in wind loading and savings in foundation costs.
•  Faster rate of construction.

• The steel decking performs a number of roles, such as:

•  It supports loads during construction and acts as a working platform
•  It develops adequate composite action with concrete to resist the imposed loading
•  It transfers in-plane loading by diaphragm action to vertical bracing or shear walls
•  It stabilises the compression flanges of the beams against lateral buckling, until
• concrete hardens.
•  It reduces the volume of concrete in tension zone
•  It distributes shrinkage strains, thus preventing serious cracking of concrete.

Reinforcing the Beam-Column Joint

Reinforcing the Beam-Column Joint

 Diagonal cracking & crushing of concrete in joint region should be prevented to ensure good earthquake performance of RC frame buildings. Using large column

sizes is the most effective way of achieving this. In addition, closely spaced closed-loop steel ties are required around column bars (Figure 3) to hold together concrete in joint region and to resist shear forces. Intermediate column bars also are effective in confining the joint concrete and resisting horizontal shear forces.

Providing closed-loop ties in the joint requires some extra effort. Indian Standard IS:13920-1993
recommends continuing the transverse loops around the column bars through the joint region. In practice, this is achieved by preparing the cage of the reinforcement (both longitudinal bars and stirrups) of all beams at a floor level to be prepared on top of the beam formwork of that level and lowered into the cage (Figures 4a and 4b). However, this may not always be possible particularly when the beams are long and the entire reinforcement cage becomes heavy.

Concept of vibro stone columns ( GROUND IMPROVEMENT TEECHNIQUE

Concept of vibro stone columns

This technique introduces a coarse grained material as load bearing elements consisting of gravel or stone aggregate as a backfill medium.

The stone column and the in situ soil form an integrated system having low compressibility shear strength. The excess pore water pressure can dissipate through the stone column, which also acts as a vertical drain. The settlement expected for the treated soil is reduced while the rate of settlement is increased when compared with the untreated soils.

The following figure.2 illustrates the schematic of the installation procedure for Vibro Stone Columns. The grading of the stone usually falls into the range of 75mm to 12mm for Vibro Stone Columns

The above technique (vibro stone columns) ensures following applications:

Ø Improves bearing capacity of in-situ soils

Ø Mitigates liquefaction potential under the excitation of earthquake

Ø Reduces excessive settlements and minimises differential settlement.

Ø Allow rapid consolidation by providing radial drainage

Concept of vibro compaction

Vibro compaction is proposed as ground Improvement scheme to mitigate liquefaction potential of the loose to medium dense silty sands and to hence bearing capacity of the foundations up to 15T/m2

The basic principle behind the process is that particles of non-cohesive soils can be rearranged into a denser state by means of vibration. A schematic showing basic principle of Vibro compaction technique is presented in Figure 3

 

The above technique (vibro compaction) ensures following applications:

Ø Mitigates liquefaction potential under the excitation of earthquake

Ø Improves bearing capacity of in-situ soils

Ø Reduces excessive settlements and minimizes differential settlement