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