el-samny m. kassem and abd el-samee w. nashaat rehabilitation of existing foundation building to...

8/20/2019 El-Samny M. Kassem and Abd El-Samee W. Nashaat Rehabilitation of Existing Foundation Building to Resist

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I nt.J.Curr.M icrobiol.App.Sci (2014) 3(12): 950-961

950

Original Research Article

Rehabilitation of Existing Foundation Building to ResistLateral and Vertical Loads

El-Samny M. Kassem1 and Abd El-Samee W. Nashaat

2*

1Civil Engineering Department, Al-Azhar University, Cairo, Egypt2Civil Engineering Dep. Beni- Suef University, Faculty of Engineering, Beni- Suef, Egypt

*Corresponding author

A B S T R A C T

Introduction

There are many reasons to evaluate thestructural safety and overall serviceability of

existing building. Evaluation and repair ofthose buildings are also necessary because

those buildings must meet cases asexceeding their design reference period,

change in occupancy and bad design.

Wensheng and Xilin (1997), presented adiscussion of the important protecting

outstanding historic buildings. The

methodology for assessing the safety and

resistance of historic buildings was proposed. The evaluation and repair ofseveral historic buildings in the Shanghai

Band area were introduced.

Naderzadeh and Moinfar (2004), presentedan analysis of earthquake resistance

diagnosis carried out for some 350 buildings

International Journal of Current Microbiology and Applied SciencesI SSN: 2319-7706 Volume 3 Number 12 (2014) pp. 950-961

http://www.ijcmas.com

K e y w o r d s

Foundation,Tilted,

Existing,

Strengthening,

Shear wall

Some of the important causes of damage and collapse in concrete building can be

classified under general causes to facilitate analysis. These causes are overstress,

bad design, faulty construction, foundation failure, unexpected failure modes andcombination of causes. In the present work, a case study of an existing building

under construction found around Cairo greater area is presented. Methods of

strengthening the existing foundation of the buildings to resist lateral and verticalloads are presented. The building consists of a basement, ground floor, and 11

typical floors. The building has been tilted to one side more than 10%. However,

the inclination is due to the fact that the foundation design was incorrect. Thethickness of raft was 0.95 meters while the required one should be 1.30 meter. Inaddition, there is a great eccentricity on the raft due to lake of raft design that

makes the stresses on soil reaches 5 kg/cm2 at some areas while the allowable is 1.5kg/cm2. The increasing area and thickness as well as strengthening of the existingraft foundation are presented. In addition, new reinforced concrete shear walls

inside the building connected to the foundations are chosen for strengthening theexisting structure to resist lateral forces.


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in Tehran. Buildings were selected based ontheir age, usage, structure and distribution.

The investigation covered DisasterManagement Buildings, Emergency

Response Organizations, hospitals, schools

as well as residential buildings. Factorsaffecting seismic resistance of buildings inthis investigation included age, construction

quality, and ductility condition. Diagnosis of buildings took place in several steps: i-

Preparation, ii- Field survey, and iii-Diagnosis and judgment. The diagnosis

method used was Seismic Index Method.The calculated value of Seismic Index

Method was compared with the 'SeismicIndex Requirement' and the result was used

to evaluate the level of building safety. Thedetails of the diagnosis method implemented

as well as the proposed strengtheningmethods are presented.

Elsamny and El Samee (2013), presented

some methods of strengthening existingfoundation concrete buildings to resist

lateral and vertical loads. A study case of anexisting sweet factory in Cairo area was

presented. Deterioration of some concreteelements due to old age has been found. The

said condition of the foundation was due towashing floors with chemicals to remove

sticky sweets. However, no adequatedisposal system was found (wastewater

collection). The analyses of the structuralelements of that existing building showed

that it is seismically unsafe. Retrofitting ofexisting damage and deteriorated foundation

was done by adding new raft foundation andconsidering the old foundation as plain

concrete. The addition of new shear andwing walls was undoubtedly the best method

of strengthening the existing structure toimprove seismic performance. The shear and

wing walls were connected to thefoundation.

Urmson et al., (2013) presented buildings

incorporating tilt-up construction examinedfrom several perspectives using relevant

case studies. The behavior of these buildingsduring the Canterbury Earthquakes was

reviewed, and methods used to repair

earthquake damage were then discussed.Specific aspects including groutedconnections, bolted connections and panel

reinforcing were examined in detail. Issuesrelated to the design and constructions of

new buildings which incorporate tilt-upconstruction were discussed.

Experimental study

Soil investigation

The soil profile indicates that the soil

condition consists of a filling material up to2.00 meter depth from the ground surface

followed by about 3.00 meter very hard brown clay (qu=1.50 kg/cm

2). The above is

followed by 1.00 meter of medium clay soil(qu =0.80 kg/cm2), followed by soft brown

clay up to 10.00 depth. The above isfollowed by fine to medium sand up to

20.00 meter depth (end of borings). Thewater table appears to exist at 3.5 meter

depth.

Building under construction

Figure (1) shows the building under studyand Figure (2) presents the general layout of

the typical floor of the building foundaround Cairo greater area. The building

consists of a basement, ground floor, and 11typical floors. The following observations

have been found; i-The building has beentilted to one side more than 10 % as shown

in Figure (3). However, the inclination isdue to the fact that the foundation design

was incorrect. The thickness of raft was 0.95meters while the required one should be 1.30

meter.


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Figure.1 Building under study

Figure.2 The general layout of the typical floor


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Figure.3 Building inclination

Figure.4 Building model


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Figure.5 B.M.D. (m11) for old foundation

Figure.6 B.M.D. (m22) for old foundation


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Figure.7 Raft foundation strengthening by increasing area (plan)


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Figure.8 Raft foundation strengthening by increasing thickness (section 1-1)

Figure.9 Location of anchors


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Figure.10 Detail (1) implanting dowels in concrete

Figure.11 Raft foundation strengthening increasing thickness (section b-b)


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Figure.12 B.M.D (m11) for the strengthened foundation

Figure.13 B.M.D. (m11) for the strengthened foundation


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Figure.14 Proposed added shear walls

Figure.15 Details (II-II) connection between shear walls and columns


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Figure.16 Anchorage of added shear wall

In addition, there is a great eccentricity on

the raft due to lake of raft design that makesthe stresses on soil reaches 5 kg/cm

2 at some

areas while the allowable is 1.5 kg/cm2

. ii-The building has no structural system to

resist any lateral load (no shear and/or wingwalls). The foundation is found to be of raft

type at 2.50 meter depth.

Raft foundation strengthening technique

Strengthening of the existing foundation wasdone by increasing the foundation thickness

as well as area. By using SAP2000 version

17 (linear and nonlinear static and dynamicanalysis and design of three dimensionalstructures) the analysis and design of the

foundation has been done. Figure (4) showsthe building model. Figures (5 & 6) show

the bending moments for the old foundation.Increasing area as well as thickness of the

new raft foundation is presented as follows:

I- Increasing the foundation area by 1.2 m

from three sides according to design asshown in Figure (7). Increase

foundation area is done to ensure thatthe vertical stress on soil doesn't

exceed the allowable stress 1.5 kg/cm

2 with any eccentricity on the raft.

II- Implant shear connectors (dowels) inold foundation concrete sides.

Calculation has been done todeterminate the number and the length

of shear connectors.III- Shear connectors are placed to ensure

almost complete connection between

the old foundation and addedreinforced concrete foundation.IV - Shear connectors are placed as

follows:-A. holes are carried out in the old

foundation with diameter 18 mm. Theminimum horizontal and vertical

distances between holes are 0.25m and


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0.30 m respectively as shown inFigure (8). The holes have been

cleaned by compression of airB. Grouting is carried out by epoxy. Steel

reinforcement bars with diameter of 16

mm by the required length leaving atleast 1.0 m are placed as shown inFigures (9 & 10).

V- Concrete cover has been removed fromthe three sides and upper surface of the

old foundation reinforced concrete.VI- Increasing thickness of foundation by

0.35 m is done. Implant additionalreinforcement mesh Ø16mm @ 15 cm

top and bottom as shown in Figures (8- 11). Figures (12 & 13) show the

bending moments for the strengthenedfoundation.

Adding a new shear wall to resist lateral

forces

Shear walls provide the most significant part

of the earthquake resistance of the building.However, a severely damaged or poorly

designed building must be repaired orstrengthened by added shear walls in order

that the structure's strength for seismic forceand lateral force can be significantly

improved. The new structural elements in anexisting building change the dynamic

behavior of the whole space structureconsiderably during an earthquake. Figure

(14) shows the added shear wall thatconnected with foundation. The added shear

walls were monolithic to the existingcolumns as shown in Figures (15 & 16). The

web thickness of the shear wall was 30 cmand the vertical reinforcement were Ø16 @

15 cm and the horizontal reinforcement wereØ12 @ 15 as shown in Figures (15 & 16).

The dowels with diameter of 16 mm by therequired length leaving at least 0.60 m were20 cm deep in columns.

In Conclusion, from previous experimental

study and obtained results, it can be

concluded the followings; Strengthening theexisting raft foundation is done by

increasing area as well as thickness. Andalso new reinforced concrete shear walls

were added to strengthening the existing

structure to improved seismic performance.

References

Elsamny, M.K. and El Samee, W.N. 2013.

Retrofitting and strengthening ofExisting Building Foundation. Int. J.

Engineering Stud., 5(1), 111-128.Kevadkar, M.D. and kodag, P.B. 2013.

Lateral Load Analysis of R.C.C.Building. Int. J. Modern Engineering

Res. 3(3), 1428-1434. Naderzadeh, A. and Moinfar, A.A. 2004.

Earthquake resistance diagnosis andstrengthening Techniques for existing

buildings in Tehran"13th World

Conference on Earthquake

Engineering Vancouver, B.C., CanadaAugust 1-6, 2004 Paper No. 912.

Urmson, C.R., Reay, A.M. and Toulmin,S.H. 2013. Lessons learnt from the

performance of buildingsincorporating tilt-up construction in

the Canterbury Earthquakes. AlanReay Consultants Ltd., Christchurch,

New Zealand. 2013 NZSEEConference.

Weng, Y.K, Stefano, P., Rajesh, D., Henri,P.G. and Charles, R. 2010. Seismic

Performance of Reinforced ConcreteBuildings in the September 2010

Darfield (Canterbury) Earthquake.Bullet. New Zealand Soci. Earthquake

Engineering, 43(4), 340-350.Wensheng, L. and Xilin, L. 1997.

Evaluation and repair of historic building structures in the Shanghi

Band area". First international CivilEngineering (Egypt - China - Canada)

Dec 18 - 20 Cairo -Egypt, pp 227 -237.

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