Soil-Structured Interaction,Thessaloniki, Greece Ref no: 111

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SOIL STRUCTURED INTERACTED ANALYSIS

MS ARIADNE TSAMBALI

UNIVERSITY OF WESTMINSTER, 35 MARYLEBONE RD. LONDON, NW1-5LS, U.K,

tsambani@hotmail.com

EXTENDED ABSTRACT

This research investigates the Soil – Structured Interaction Modeling, under any significant

loading.

The effect of the dynamic loading on the structures depends upon the type of the structure, number

of levels, and type of foundations, construction method.

This displacements produced due to the dynamic loading may result in severe damage of the

structure.

In evaluating the response of structure to earthquakes, it is normally important to understand the

sub-soil conditions of each structure during the earthquake, as explained wholly on this paper.

1. INTRODUCTION This research investigates the Soil – Structured Interaction Modeling, under any significant

loading.

The effect of the dynamic loading on the structures depends upon the type of the structure, number

of levels, and type of foundations, construction method.

This displacements produced due to the dynamic loading may result in severe damage of the

structure.

In evaluating the response of structure to earthquakes, it is normally important to understand the

sub-soil conditions of each structure during the earthquake, as explained wholly on this paper.

The structural response to any dynamic load is varying with time.

If the time variation of loading is fully known, it will be referred to herein as a prescribed dynamic

loading; and the analysis of the response of any specified structural system to a prescribed

dynamic loading is defined as a deterministic analysis.

Also, the structural response to a dynamic load, is also time varying, or dynamic.

If the time variation of loading is fully known, it will be referred to herein as a prescribed dynamic

loading; and the analysis of the response of any specified structural system to a prescribed

dynamic loading is defined as a deterministic analysis.

In general, structural response to any dynamic loading is expressed basically in terms of the

displacements of the structure.

2. METHODS AND MATERIALS Type of Structure, such as: Plane 82 on ANSYS 5.4 Finite Element Software (structural solid

element type) was used as the best type of element, to describe solid materials such as a soil,

concrete or steel. A plane 82 element was believed to model closely, the deformation behaviour of

these materials and contains sufficient numbers of nodes for accuracy while not requiring

excessive time to obtain solutions.

The model was developed using key points, which were afterwards united to create areas. The

different areas were assigned different material properties corresponding to concrete, steel or soil.

Once all, the areas have been defined, the size of the mesh, to be used is determined, by us.

In this way, we will define a finer mesh around the foundation and a broad mesh towards, the

boundaries of the problem in order to obtain more, accurate results where they are needed. The

meshing should be, carried out in such a way that we guaranty the continuity between the

foundation and the structure and between the foundation and the ground.

The different elements corresponding to concrete, steel or soil will be assigned their particular

material properties, such as modulus of elasticity, shear modulus, density and Poisson’s ratio. The

properties, defined for our particular problem, illustrated on Table 1.1.

TABLE 1.1 Material properties for structure and ground used in the analysis.

3. RESULTS

The frequencies, obtained for all three cases have been analyzed and illustrated in Tables.

In 1st case, the effects, of adjacent structures on the behaviour of an individual structure have been

studied comparing the results of the isolated five floors shear frame building with those obtained

for the case of three adjacent buildings and for the case of an underground structure. The

comparison between the three cases shows that the three buildings system will tend to vibrate

more than the isolated five-floor building. This is probably due to the fact that those buildings are

located quite close to each other and there will be a coupling effect between them. This coupling

effect will determine that the three buildings will behave as a single one with the same height but

increased weight and therefore more prone to movements.

Material

Parameter

Concrete

Foundation

Steel

Structural

Members

Stiff Clay Soft Clay

Young’s

Modulus, E

18.5GPa 205Gpa 140Mpa 14Mpa

Density 2400Kg/m³ 7820Kg/m³ 1950Kg/m³ 1700Kg/m³

Poisson’s

Ratio v 0.15 0.27 0.35 0.35

Shear

Modulus 8.04GPa 80 GPa 51.85 MPa 5.185 MPa

When comparing the results of the building with those for the building adjacent to an underground

structure we can observe that the frequencies of the underground structure are less from those into

the three buildings. This is because the soil is very stiff and our structure is very heavy.

The weight of the building prevents the building from moving and therefore the system will tend

to vibrate less.

In the case of the mode4, mode 5, and mode6, we can see that the frequencies are increased. This

is because the stiff underground concrete structure will prevent the building from moving and

therefore the system will tend to vibrate less.

In 2nd case, the presence of a softer more, compressible soil greatly reduces the frequency

response in the analysis. The decreasing soil stiffness assumed, for the two-layered models are

reflected in a reduction in the mode frequencies. Thus, the building will vibrate more when; the

founding soil is layered and with different stiffness, than when then building is based on

homogeneous strata. The presence of a softer, more compressible soil greatly reduces the

frequency response in the analysis. Energy dissipation is greater in the case of softer materials.

For the piles case, the piles will act as, an anchorage but their efficiency will be less, than if the

soil was uniform. It is quite clear from the result that piles will act as; anchors of the structure in

the ground and therefore, the movements will be reduced when piles are used as founding media.

The anchorage, potential is slightly reduced in the case in which, a steeply dipping layer of

reduced Geotechnical properties is found, underneath the building. The frequencies, obtained in

this case, are lower than those for piles drilled or driven in a homogeneous soil are.

In 3rd case, the presence of a softer more, compressible soil greatly reduces the frequency

response in the analysis. The decreasing soil stiffness assumed, for the two-layered models are

reflected in a reduction in the mode frequencies. Thus, the building will vibrate more when; the

founding soil is layered and with different stiffness, than when then building is based on

homogeneous strata. The presence of a softer, more compressible soil greatly reduces the

frequency response in the analysis. Energy dissipation is greater in the case of softer materials.

For the piles case, the piles will act as, an anchorage but their efficiency will be less, than if the

soil was uniform. The presence of a softer more, compressible soil greatly reduces the frequency

response in the analysis.

The presence of a softer, more compressible soil greatly reduces the frequency response in the

analysis

4. DISCUSSION

As, the main purpose of this report is the investigation of the different factors as influencing, the

dynamic behavior of a soil-structure interaction system, we will divide the discussion on the same

points as we presented the problem.

The modes of shape obtained, from the analysis have been printed and are below with the

corresponding frequencies, for each of them.

The frequencies, obtained for the first case analyzed are illustrated in Table 4.1

Table 4.1 Effects of height and width of the buildings and of the area of influence.

Frequencies for the different

modes

Mode 1

Mode 2 Mode 3

1st floor (3.5m high, 5m wide)

Area of influence 25m

laterally, 17.5m with depth

0.1764 0.3128 0.6611

One floor (5m high, 10m wide)

Area of influence 50m

laterally, 25m with depth

0 0.961E-04 0.24E-03

Five floors (20m high, 5m

wide)

Area of influence 25m

laterally, 17.5m with depth

0.7247 0.2864 0.5586

Five floors (27.5m high, 10m

wide)

Area of influence 50m

laterally, 25m with depth

0 0.468E-04 0.860E-04

Frequencies for the different

modes

Mode 4

Mode 5 Mode 6

1st floor (3.5m high, 5m wide)

Area of influence 25m

laterally, 17.5m with depth

4.715 4.773 6.342

One floor (5m high, 10m wide)

Area of influence 50m

laterally, 25m with depth

0.340 0.537 1.306

Five floors (20m high,

5m wide).

Area of influence 25m

laterally, 17.5m with depth

4.715 6.341 0.072476

Five floors (27.5m high,

10m wide).

Area of influence 50m

laterally, 25m with depth

0.76982 0.2518 0.5160

The frequencies, obtained for the second case analyzed are illustrated in Table 4.2

Table 4.2. Frequencies for effects of adjacent buildings

Table 4.2. Frequencies for effects of adjacent buildings

The frequencies, obtained for the third case analyzed are illustrated in Table 4.3

Frequencies for the different

modes

Mode 1

Mode 2 Mode 3

Three buildings located 10m

apart from

Each other

0.0728 0.0752 0.1167

Three buildings located 20m

apart from each other

0.264E-04 0.361E-04 0.726E-04

Adjacent underground

structure

0 0.801E-05 0.6580

Frequencies for the different

modes

Mode 4

Mode 5 Mode 6

Three buildings located 10m

apart from

Each other

0.2935 0.4233 0.520

Three buildings located 20m

apart from each other

0.072 0.725 0.0862

Adjacent underground

structure

0.7566 1.473 2.919

Frequencies for the different

modes

Mode 1

Mode 2 Mode 3

Five floors and piled

foundations

With L=5, H=5h

0.933E-05 0.121E-04 0.144E-04

The frequencies, obtained for the forth case analyzed are illustrated in Table 4.4

Table 4.4. Frequencies for effects of ground conditions

The presence of a softer, more compressible soil greatly reduces the frequency response in the

analysis.

Table 4.4. Frequencies for effects of ground conditions

Table 4.4. Frequencies for effects of ground conditions

The frequencies, obtained for the fifth case analyzed are illustrated in Table 4.5

Table 4.5. Frequencies for effects of ground conditions

Frequencies for the different

modes

Mode 1

Mode 2 Mode 3

Five floors 0.775E-05 0.108E-04 0.132E-04

Pile foundations and soil

layering 0.139E-04 0.180E-04 0.214E-04

Five floors and piled foundations

With L=10, H=10h 0.265E-05 0.720E-05 0.983E-05

Frequencies for the different

modes

Mode 4

Mode 5 Mode 6

Five floors and piled

foundations,

With L=5, H=5h

1.041 1.431 1.732

Five floors and piled

foundations,

With L=10, H=10h

0.0326 0.065 0.0818

Frequencies for the different

modes

Mode 1

Mode 2 Mode 3

Five floors 0.775E-05 0.108E-04 0.132E-04

Pile foundations and soil

layering 0.139E-04 0.180E-04 0.214E-04

Table 4.5. Frequencies for effects of ground conditions

In the second case, the effects, of adjacent structures on the behaviour of an individual structure

have been studied comparing the results of the isolated five floors shear frame building with those

obtained for the case of three adjacent buildings and for the case of an underground structure.

The frequencies obtained in the analysis are presented in Table 4.2.

A comparison between the three cases show that the three buildings system will tend to vibrate

more than the isolated five-floor building.

This is probably due to the fact that those buildings are located quite close to each other and there

will be a coupling effect between them.

This coupling effect will determine that the three buildings will behave as a single one with the

same height but increased weight and therefore more prone to movements.

When comparing the results of the building with those for the building adjacent to an underground

structure we can observe that the frequencies of the undeground structure are less from those into

the three buildings.

This is because the soil is very stiff and our structure is very heavy.

The weight of the building prevents the building from moving and therefore the system will tend

to vibrate less.

In the case of the mode4, mode 5, and mode6, we can see that the frequencies are increased.

This is because the stiff underground concrete structure will prevent the building from moving and

therefore the system will tend to vibrate less.

In the third case, the frequencies, for systems founded, on piles have been compared with that of a

single five floors building.

Table 4.3 illustrates, the values obtained for the different, cases and mode shapes.

It is quite clear from the result that piles will act as; anchors of the structure in the ground and

therefore, the movements will be reduced when piles are used as founding media.

Frequencies for the different

modes

Mode 4

Mode 5 Mode 6

Five floors 0.646 1.357 1.721

Pile foundations and soil

layering 0.242E-04 0.268E-04 0.1145

The anchorage, potential is slightly reduced in the case in which, a steeply dipping layer of

reduced Geotechnical properties is found, underneath the building.

The frequencies, obtained in this case, are lower than those for piles drilled or driven in a

homogeneous soil are.

Mode 3 however shows that the piles will break under those deformations.

In the forth case, the presence of a softer more, compressible soil greatly reduces, the frequency

response in the analysis.

The decreasing soil stiffness assumed, for the two-layered models are reflected in a reduction in

the mode frequencies (See Table 4.4).

Thus, the building will vibrate more when; the founding soil is layered and with different stiffness,

than when then building is based on homogeneous strata.

The presence of a softer, more compressible soil greatly reduces the frequency response in the

analysis.

Energy dissipation is greater in the case of softer materials.

For the piles case, the piles will act as, an anchorage but their efficiency will be less, than if the

soil was uniform.

In the fifth case, the presence of a softer more, compressible soil greatly reduces, the frequency

response in the analysis.

The decreasing soil stiffness assumed, for the two-layered models are reflected in a reduction in

the mode frequencies (See Table 4.5).

Thus, the building will vibrate more when; the founding soil is layered and with different stiffness,

than when then building is based on homogeneous strata.

The presence of a softer, more compressible soil greatly reduces the frequency response in the

analysis.

Energy dissipation is greater in the case of softer materials.

For the piles case, the piles will act as, an anchorage but their efficiency will be less, than if the

soil was uniform.

coupled, effect on the soil and on the structure, under any dynamic loading is of vital importance, when

designing buildings, particularly in seismic areas.

Different, factors have been observed to influence, the behaviour of the soil-structure interaction

systems.

Several, dynamic analysis-affecting structures have been carried out, with changing structures,

areas of influence, ground conditions and types of foundations.

Stiff underground structures, will add restraints to the movement of a building, which will suffer

more vibration, if high structures are located close to it.

The presence of a weaker, less stiff soil at foundation level provides, important information on the

effect of local ground conditions upon dynamic excitation transmitted to structures.

This research investigates the Soil – Structured Interaction Modeling, under any significant

loading.

The effect of the dynamic loading on the structures depends upon the type of the structure, number

of levels, and type of foundations, construction method.

This displacements produced due to the dynamic loading may result in severe damage of the

structure.

In evaluating the response of structure to earthquakes, it is normally important to understand the

sub-soil conditions of each structure during the earthquake, as explained wholly on this paper.

There are many types of dynamic loading that a structure can occurs during its life span.

The effect of the dynamic loading on the structures depends upon the type of the structure, number

of levels, and type of foundations, construction method.

The displacements produced due to the dynamic loading may result in severe damage of the

structure.

In evaluating the response of structure to earthquakes, it is normally important to understand the

sub-soil conditions of each structure during the earthquake.

If the time variation of loading is fully known, it will be referred to herein as a prescribed dynamic

loading; and the analysis of the response of any specified structural system to a prescribed

dynamic loading is defined as a deterministic analysis.

Also, the structural response to a dynamic load, is also time varying, or dynamic.

If the time variation of loading is fully known, it will be referred to herein as a prescribed dynamic

loading; and the analysis of the response of any specified structural system to a prescribed

dynamic loading is defined as a deterministic analysis.

In general, structural response to any dynamic loading is expressed basically in terms of the

displacements of the structure.

Earthquakes constitute the single most important source of dynamic loads on structures and

foundations.

Non-periodic loading may be, either short-duration ‘impulsive’ loading or long-duration general

forms of loads. Earthquakes constitute the single most important source of dynamic loads on

structures and foundations. Due to ground motion during an earthquake, footings may settle,

buildings may tilt, soils may liquefy and lose ability to support structures, and light structures may

float.

Non-periodic loading may be either short-duration ‘impulsive’ loading or long-duration general

forms of loads

5. CONCLUSION

Different factors have been observed to influence the behaviour of the system soil-structured

interacted. In evaluating the response of structure to earthquakes, it is normally important to

understand the sub-soil conditions of each structure during the earthquake.

There are many types of dynamic loading that a structure can occurs during its life span.

Earthquakes constitute the single most important source of dynamic loads on structures and

foundations. The effect of the dynamic loading on the structures depends upon the type of the

structure, number of levels, and type of foundations, construction method. The displacements

produced due to the dynamic loading may result in severe damage of the structure. In general,

structural response to any dynamic loading is expressed basically in terms of the displacements of

the structure. Several, dynamic analysis-affecting structures have been carried out, with changing

structures, areas of influence, ground conditions and types of foundations.

Stiff underground structures, will add restraints to the movement of a building, which will suffer

more vibration, if high structures are located close to it. The comparison between the three cases

shows that the three buildings system will tend to vibrate more than the isolated five-floor

building. This is probably due to the fact that those buildings are located quite close to each other

and there will be a coupling effect between them.

This research investigates the Soil – Structured Interaction Modeling, under any significant

loading. Model has been carried out. We carried out a dynamic analysis of all factors influencing

the structures. They used different type of structures, they estimated different areas of influence,

they estimated the underground conditions, they tabulated all the types of foundations and we

observed that on stiff underground structures, will add restraints to the movement of a building,

which will suffer more vibration, if high structures are located close to it.

REFERENCES

1. Wolf, John P., (1985). Dynamic Soil Structure Interaction, Prentice Hall, Englewood Cliffs, New Jersey, 2. Prakash S., (1981). Soil Dynamics, Mc Graw-Hill. 3. The Institution of Structural Engineers, March 1989, ‘Soil-Structure Interaction-The real behavior’. 4. Buchholdt,(1999). Structural dynamics for engineers. 5. Curtins, (2000). Design on Foundation, Blackwell, 6. British Code of Practice for Foundations BS8004:2000 7. British Code of Practice for Reinforced Concrete BS8110:2000 8. British Code of Practice for Steelwork BS5950:2001 9. Reynold, (1997). Concrete Design Following the BS8110, Practice. Ε & FN Spon. 10, Abbas-Al Hussaini, College Handnotes, 1998, Finite Element Analysis. 11. J. Armishaw, College Handnotes, 1998, Pile Design. 12. E. Moosavejad, College Handnotes, 1998, Dynamics on Structures 13. Craig, (1995). Soil Mechanics, Longman, Sutton. 14. Glough, (1998). Dynamics of Structures, McGraw Hill.