the effect of soil type on isolated footing during …placed. thus, entire building space frame can...

© 2017 IJNRD | Volume 2, Issue 6 June 2017 | ISSN: 2456-4184

IJNRD1706012 International Journal of Novel Research and Development (www.ijnrd.org) 67

THE EFFECT OF SOIL TYPE ON ISOLATED FOOTING

DURING EARTHQUAKE 1TARUN TIWARI

1Mtech S.E, P.G. STUDENT, STRUCTURAL ENGINEERING, GRAPHIC ERA UNIVERSITY,UTTARAKHAND,INDIA

ABSTRACT: Recent earthquakes in India show that not only non-engineered but also engineered buildings in our country are susceptible

even to moderate earthquakes and the most susceptible structural element is FOUNDATION thus an attempt is made through the paper titled

“EFFECT OF SOIL TYPE ON ISOLATED FOOTING DURING EATHQUAKE” for evaluating seismic performance of the footing on

different soil type. Building is modelled through commercial software STAAD PRO. As we are very aware that it’s an easy task to design

foundation for lateral forces such as Live Load and Dead Load as the magnitude of these loads can easily be estimated but the problems

arises when the foundation is designed for seismic or earthquake loads as it can occur at any x, y and z direction and also with unknown

magnitude. Thus by using software STAAD PRO aims in finding better technique to make out the sensitivity of footing rested on different

soil type.

Keyword:- Live Load, Dead Load, Siesmic Load, STAAD PRO.

1. INTRODUCTION

The intensity of shock due to an earthquake could vary locally at any place due to variation in soil conditions. Earthquake response of systems

would be affected by different types of foundation system in addition to variation of ground motion due to various types of soils. Considering the

effects in a gross manner, the standard gives guidelines for arriving at design seismic coefficients i.e. (Sa/g)based on stiffness of base soil

Fig. 1: Siesmic Zones of India

1.1 Design criteria for foundation

The structure shall not be founded on such loose soils which will subside or liquefy during an earthquake, resulting in large differential

settlements (I.S.4326:1993)

For the design of foundations, the provisions of (I.S. 1904:1986) in conjunctions with (I.S. 1893:1984) shall generally be followed.

The subgrade below the entire area of the building shall preferably be of the same type of the soil. Wherever this is not possible, a suitably

located separation or crumple section shall be provided. Loose fine sand, soft silt and expansive clays should be avoided. If unavoidable, the

building shall rest either on a rigid raft foundation or on piles taken to a firm stratum. However, for light constructions the following measures

may be taken to improve the soil on which the foundation of the building may rest:

a) Sand piling, and

b) Soil stabilization.



2. METHOD ADOPTED

In this project a detailed design of four-storeyed office building having a regular layout, which can be divided into a number of similar

vertical frames, has been considered to illustrate the analysis and design of a frame. Frame in considered for analysis and design for further

designing the foundation. A standard computer program on a personnel computer has been carried out for the analysis. The design is carried out

according to IS 13920:1993 following the IS 456:2000 and SP 16:1980.

Fig-2: Typical plan of the building

2.1. Premelinary Data For Frame

The floor plan of a typical public-cum-office building is shown. The plan is regular in nature in the sense that it has all columns equally

placed. Thus, entire building space frame can be divided into a number of vertical frames. An interior frame as shown is considered for analysis

and design. Following are some of the salient feature of the frame

Type of structure Multi-storey rigid jointed frame

2 zone 4

3 Layout As shown in Figure 2

4 Number of stories Four (G+ 3) as shown in Figure

5 Ground storey height 4.0 m

6 Floor-to-Floor height 3.35 m

7 External walls 250 mm thick including plaster

8 Internal walls 150 mm thick including plaster

9 Live load 3.5 KN/m2

10 Materials M 20 and Fe 415

11 Seismic analysis Equivalent static method

12 Design philosophy Limit state method conforming to IS 456:1978

13 Ductility design IS 13920: 1993

Fig-3: Detail of Frame

2.2.Types of loads taken into considearation

DEAD LOAD (DL):-DEAD LOAD is defined as the the load on a structure due to its own weight (self-weight). It also added other loads if some

permanent structure is added to that structure.

LIVE LOAD (LL):-LIVE LOAD Or IMPOSED LOAD is defined as the load on the structure due to moving weight. The LIVE LOAD varies

according to the type of building. For example generally for a Office building the LIVE LOAD is taken as 3.5kn/m2.

SEISMIC LOAD (SL):-SEISMIC LOAD can be calculated taking the view of acceleration response of the ground to the super structure.

According to the severity of earthquake intensity they are divided into 4 zones.

1. Zone I and II are combined as zone II.



2. Zone III.

3. Zone IV.

4. Zone V.

2.3. Design Procedure of building using STAAD

STEP 1

Fig-4: Geometry of building

Here the building of lenth 40.7m, width 11.5m and height 14.05m are taken into account the building is modelled in the commercial

software which shows the position of nodes at the right hand side of designed building in above picture.

STEP 2

Fig-5: Properties of components of building

Then the properties of colums, beams and slabs are provided which are shown at the right hand side of the above picture the render view of

this is shown below.

Fig-6: Render view of building showing beam, columns and slabs



STEP 3

After providing the section properties the supports are given to the structure here we have taken fixed support into consideration.

Fig-7: Support properties assigned to building

STEP 4

Now the loads are assigned to the building including load combinations suggested as per IS 1893

Fig-8: Showing earthquake force on building

Fig-9: Dead loads applied in the building



Fig-10: Live Loads applied in the building also with load combination

After assigning the loads and completing all others procedures analysis is run. So as to get the desired result.

-Obtained result in staad

-Beam Forces.

Fig-11: Beam forces in beams.

Bea

m

Load/load

combination

Nod

e

Fx(kN) Fy(Kn) Fz(kN) Mx(kN) My(kN) Mz(kN)

Min

MZ

13 7 Generated

Indian code

General

Structure 4

11 969.03 2.899 101.53 -1.1 -330.47 5.64

Min

MZ

141 1Seismic Load 61 -392.78 0.245 -111.81 0.046 -306.44 0.203

Min

MZ

233 10 Generated

Indian code

General

Structure 7

62 -0.069 273.281 -5.933 -1.261 6.734 309.26

Min

MZ

233 9 Generated

Indian code

General

Structure 6

122 2.11 -273.21 -5.931 1.293 6.724 309.17

Min

MZ

282 10 Generated

Indian code

General

Structure 7

122 -140.72 -6.544 181.82 -1.015 -308.99 -11.079

Min

MZ

142 9 Generated

Indian code

General

Structure 6

62 -140.51 -6.53 -181.74 1.025 308.95 -11.037



Min

MZ

432 10 Generated

Indian code

General

Structure7

185 -41.694 -4.254 -34.637 28.375 -82.288 -22.365

Min

MZ

12 9 Generated

Indian code

General

Structure 6

5 -43.421 -4.247 -35.596 -28.342 84.365 -22.395

Min

MZ

141 9 Generated

Indian code

General

Structure 6

61 -246.79 -2.762 -170.08 0.087 462.71 -3.395

Min

MZ

281 10 Generated

Indian code

General

Structure 7

121 -247.04 -2.782 170.14 -0.081 -462.85 -3.964

Min

MZ

233 10 Generated

Indian code

General

Structure7

62 -0.069 273.281 -5.9330 -1.261 6.374 392.26

Min

MZ

233 12 Generated

Indian code

General

Structure9

122 -0.0477

259.502 -5.933 1.267 - 6.874 301.46

Table:1- Components of forces

2.4. Bending moment and shear force diagram.

Here the member no.13 BMD and SFD are shown as it withstand maximum value of loads

Fig:12- Showing Member 13

Fig:13- Bending Moment Diagram of member 13



Fig: 14- Shear Force Diagram of member 13

2.5. Foundation design using staad foundation

STEP 1

First of all after data is being analysed in staad without an error the building is then exported to staad foundation for design. The exported

data to staad foundation will somehow represent (as shown in fig.) showing the position of various column.

Fig:15-Showing the foundation plan representing the column position at the right hand side

Fig:17- Showing the loads and factors for which the foundation is designed



Fig:18- Showing the max. column reaction from 61 member

STEP 2

Now the job is created here we have adopted the pile foundation thus the job created will be of pile using design code INDIAN.

The load envelope created is for (SIESMIC+DEAD) as are main motive is to design foundation for Siesmic loads.

Fig:19- Pile job Created with load envelope represented on right side

STEP 3

After creating the pile job the design parameter are assigned.

Fig:20- Design Parameters for foundation



Strength of Concrete 25 N/mm2

Unit weight of Concrete 25 kN/m3

Yield strength of Steel 415 N/mm2

Side Cover 50 mm

Bottom Cover 50 mm

Pile in Pile Cap 75 mm

Initial thickness 300 mm

Min. Bar size 12

Max. Bar size 40

Table- 2:Design Parameters adopted for Foundation Design

STEP 4

Now pile layout is defined by hit and trial method.

Fig:21- Pile Layout Values assigned to foundation

Pile arrangement for support 61(due to max. Column reaction)

Pile Capacity 500kN vertical

Pile Diameter 0.5m

Spacing 1.5m

Edge Distance 0.5m

Pile Arrangement 2 pile caps

Table:3- Pile layout values for support no. 61

STEP 4

Design it

Fig-22: Detail drawing of Pile cap



3. RESULTS

Comparison of pile cap design when soil type is changed from Hard soil to medium and soft soil

Key Points HARD SOIL MEDIUM SOIL SOFT SOIL

Width of Pile cap 0.47m 0.55m 0.55m

Diameter of pile 0.50m 0.50m 0.50m

Longitudinal reinf. #16@440mm #16@260mm #16 @ 260mm

Transverse reinf. #6@45mm #8@70mm #8@70mm

Table:4- Data for pile design for each soil type

4. CONCLUSION

When thinking about the dispersion of effects of an earthquake, many people think of it like dropping a pebble in a lake. The pebble hits the

water and it creates a uniform ripple effect getting weaker as it travels from the center. The earth’s surface, however, is not uniform like the water

in this comparison. During an earthquake one area can experience over ten times the effects as a neighboring area that is the same distance from

the fault line. This is because of what are called “site effects”. Site effects are variations that occur in the geologic conditions of a particular

location. There are two main conditions that account for these variations: The softness of the soil or rock, and the total thickness of the sediment

above the bedrock. The softer and thicker the sediment is, the greater the effects of an earthquake will be amplified.

As seismic waves travel though the ground, they travel faster through hard rock than soft soil. As a result, when the waves move from hard

rock to soft soil, the amplitude (largeness) of the waves needs to increase to be able to carry the same amount of energy, creating stronger

shaking. This same principle accounts for the site effects of sediment thickness. The deeper the sediment above bedrock, the more soft soil there

is for seismic waves to travel through, therefore creating stronger amplifications.

As we have discussed above the softer the soil greater is the shaking or amplifications produced by earthquake. This causes shear in footing

as we are aware that shear is one of the predominant factor in beam design but not in case of slab design. Since in foundation design one of the

major factor is wide shear thus foundation is considered by beam design but not as slab design. Thus the transverse and longitudinal

reinforcement are provided with less spacing in soft and medium soil than hard rock as foundation constructed in loose soil or soft soil are highly

susceptible to earthquake waves than in hard soil.

Thus concluded that soil type available in the foundation site influence the staibility of foundation when subjected to earthquake waves

5. REFERENCES

[1] Kahn, L.W., “Shotcrete Retrofit for Unreinforced Bick Masonry”, Eighth World Conference on Earthquake Engineering, Vol. 1, San

Francisco, 1984.

[2] FEMA 172, NEHRP Handbook for Seismic Rehabilitation of Existing Buildings, Building Seismic Safety Council, Washington, 1992.

[3] EERI, “Erzincan, Turkey Earthquake Reconnaissance Report”, Earthquake Spectra, Supplement to Vol. 9, 1993.

[4] IS 13935, Repair and Seismic Strengthening of Buildings-Guidelines, Bureau of Indian Standards, New Delhi, 1993.

[5] EERI, “Northirdge Earthquake Reconnaissance Report, Vol. 2”, Earthquake Spectra, Supplement C to Vol. 11, 1996.

[6] Agarwal, P., “ Experimental Study of Seismic Strengthening and Retrofitting sMeasures in Masonry Building”, Ph.D. Thesis ,

Department of Earthquake Engineering, IIT Roorkee, 1999.

[7] Thakkar, S.K. and P., “Seismic Evaluation of Earthquake Resistant and Retrofitting Measures of Stone Masonry Houses”, Paper No.

110, Twelfth World Conference on Earthquake Engineering, New Zealand, 2000.

[8] IAEE, Guidelines for Earthquake Resistance Non- engineered Construction, ACC Limited Thane 2001.

[9] Agarwal, P. and Thakkar, S.K., “Study of Adequacy of Earthquake Resistance and Retrofitting Measures of Stone Masonry Buildings”,

Research Highlights in Earth Systems Science, DST Special Vol. 2 on Seismicity pp. 327-335, O.P. Verma (Ed.),Indian Geological

Congress, August, 2001.

BIOGRAPHIES

My Name is Tarun Tiwari, I am a Btech(hons.) Civil Engineering of Graphic Era University Dehradun,

Currently I am pursuing my Masters of technology from Structural Engineering and living in

Dehradun,Uttarakhand .If you would like to know more about me contact me through my email

[email protected]

https://wsrb.wordpress.com/2012/06/11/the-modified-mercalli-intensity-scale-for-insurance-underwriting/

http://www.wsrb.com/wsrbweb/products/wsrb-property-edge-risk-mapping.aspx

http://www.wsrb.com/wsrbweb/products/wsrb-property-edge-risk-mapping.aspx

https://wsrb.wordpress.com/2012/06/26/soil-liquefaction-for-insurance-underwriting/

the effect of soil type on isolated footing during …placed. thus, entire building space frame can...

Documents