Rehabilitation of Existing Foundation Building to Resist Lateral and Vertical Loads

Transcription

1 International Journal of Current Microbiology and Applied Sciences ISSN: Volume 3 Number 12 (2014) pp Original Research Article Rehabilitation of Existing Foundation Building to Resist Lateral and Vertical Loads El-Samny M. Kassem 1 and Abd El-Samee W. Nashaat 2 * 1 Civil Engineering Department, Al-Azhar University, Cairo, Egypt 2 Civil Engineering Dep. Beni- Suef University, Faculty of Engineering, Beni- Suef, Egypt *Corresponding author A B S T R A C T K eywo rd 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 and combination 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 vertical loads 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. The thickness of raft was 0.95 meters while the required one should be 1.30 meter. In addition, there is a great eccentricity on the raft due to lake of raft design that makes the stresses on soil reaches 5 kg/cm 2 at some areas while the allowable is 1.5 kg/cm 2. The increasing area and thickness as well as strengthening of the existing raft foundation are presented. In addition, new reinforced concrete shear walls inside the building connected to the foundations are chosen for strengthening the existing structure to resist lateral forces. Introduction There are many reasons to evaluate the structural safety and overall serviceability of existing building. Evaluation and repair of those buildings are also necessary because those buildings must meet cases as exceeding their design reference period, change in occupancy and bad design. Wensheng and Xilin (1997), presented a discussion of the important protecting outstanding historic buildings. The methodology for assessing the safety and resistance of historic buildings was proposed. The evaluation and repair of several historic buildings in the Shanghai Band area were introduced. Naderzadeh and Moinfar (2004), presented an analysis of earthquake resistance diagnosis carried out for some 350 buildings 950

2 in Tehran. Buildings were selected based on their age, usage, structure and distribution. The investigation covered Disaster Management Buildings, Emergency Response Organizations, hospitals, schools as well as residential buildings. Factors affecting seismic resistance of buildings in this 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 'Seismic Index Requirement' and the result was used to evaluate the level of building safety. The details of the diagnosis method implemented as well as the proposed strengthening methods are presented. Elsamny and El Samee (2013), presented some methods of strengthening existing foundation concrete buildings to resist lateral and vertical loads. A study case of an existing sweet factory in Cairo area was presented. Deterioration of some concrete elements due to old age has been found. The said condition of the foundation was due to washing floors with chemicals to remove sticky sweets. However, no adequate disposal system was found (wastewater collection). The analyses of the structural elements of that existing building showed that it is seismically unsafe. Retrofitting of existing damage and deteriorated foundation was done by adding new raft foundation and considering the old foundation as plain concrete. The addition of new shear and wing walls was undoubtedly the best method of strengthening the existing structure to improve seismic performance. The shear and wing walls were connected to the foundation. Urmson et al., (2013) presented buildings incorporating tilt-up construction examined from several perspectives using relevant case studies. The behavior of these buildings during the Canterbury Earthquakes was reviewed, and methods used to repair earthquake damage were then discussed. Specific aspects including grouted connections, bolted connections and panel reinforcing were examined in detail. Issues related to the design and constructions of new buildings which incorporate tilt-up construction were discussed. Experimental study Soil investigation The soil profile indicates that the soil condition consists of a filling material up to 2.00 meter depth from the ground surface followed by about 3.00 meter very hard brown clay (q u =1.50 kg/cm 2 ). The above is followed by 1.00 meter of medium clay soil (q u =0.80 kg/cm2), followed by soft brown clay up to depth. The above is followed by fine to medium sand up to meter depth (end of borings). The water table appears to exist at 3.5 meter depth. Building under construction Figure (1) shows the building under study and Figure (2) presents the general layout of the typical floor of the building found around Cairo greater area. The building consists of a basement, ground floor, and 11 typical floors. The following observations have been found; i-the building has been tilted to one side more than 10 % as shown in Figure (3). However, the inclination is due to the fact that the foundation design was incorrect. The thickness of raft was 0.95 meters while the required one should be 1.30 meter. 951

3 Figure.1 Building under study Figure.2 The general layout of the typical floor 952

4 Figure.3 Building inclination Figure.4 Building model 953

5 Figure.5 B.M.D. (m11) for old foundation Figure.6 B.M.D. (m22) for old foundation 954

6 Figure.7 Raft foundation strengthening by increasing area (plan) 955

7 Figure.8 Raft foundation strengthening by increasing thickness (section 1-1) Figure.9 Location of anchors 956

8 Figure.10 Detail (1) implanting dowels in concrete Figure.11 Raft foundation strengthening increasing thickness (section b-b) 957

9 Figure.12 B.M.D (m11) for the strengthened foundation Figure.13 B.M.D. (m11) for the strengthened foundation 958

10 Figure.14 Proposed added shear walls Figure.15 Details (II-II) connection between shear walls and columns 959

11 In addition, there is a great eccentricity on the raft due to lake of raft design that makes the stresses on soil reaches 5 kg/cm 2 at some areas while the allowable is 1.5 kg/cm 2. ii- The building has no structural system to resist any lateral load (no shear and/or wing walls). The foundation is found to be of raft type at 2.50 meter depth. Raft foundation strengthening technique Strengthening of the existing foundation was done by increasing the foundation thickness as well as area. By using SAP2000 version 17 (linear and nonlinear static and dynamic analysis and design of three dimensional structures) the analysis and design of the foundation has been done. Figure (4) shows the 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: Figure.16 Anchorage of added shear wall 960 I- Increasing the foundation area by 1.2 m from three sides according to design as shown in Figure (7). Increase foundation area is done to ensure that the 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) in old foundation concrete sides. Calculation has been done to determinate the number and the length of shear connectors. III- Shear connectors are placed to ensure almost complete connection between the old foundation and added reinforced concrete foundation. IV - Shear connectors are placed as follows:- A. holes are carried out in the old foundation with diameter 18 mm. The minimum horizontal and vertical distances between holes are 0.25m and

12 0.30 m respectively as shown in Figure (8). The holes have been cleaned by compression of air B. Grouting is carried out by epoxy. Steel reinforcement bars with diameter of 16 mm by the required length leaving at least 1.0 m are placed as shown in Figures (9 & 10). V- Concrete cover has been removed from the three sides and upper surface of the old foundation reinforced concrete. VI- Increasing thickness of foundation by 0.35 m is done. Implant additional reinforcement mesh 15 cm top and bottom as shown in Figures (8-11). Figures (12 & 13) show the bending moments for the strengthened foundation. 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 or strengthened by added shear walls in order that the structure's strength for seismic force and lateral force can be significantly improved. The new structural elements in an existing building change the dynamic behavior of the whole space structure considerably during an earthquake. Figure (14) shows the added shear wall that connected with foundation. The added shear walls were monolithic to the existing columns as shown in Figures (15 & 16). The web thickness of the shear wall was 30 cm and the vertical reinforcement were 15 cm and the horizontal reinforcement were 15 as shown in Figures (15 & 16). The dowels with diameter of 16 mm by the required length leaving at least 0.60 m were 20 cm deep in columns. In Conclusion, from previous experimental study and obtained results, it can be 961 concluded the followings; Strengthening the existing raft foundation is done by increasing area as well as thickness. And also 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 Retrofitting and strengthening of Existing Building Foundation. Int. J. Engineering Stud., 5(1), Kevadkar, M.D. and kodag, P.B Lateral Load Analysis of R.C.C. Building. Int. J. Modern Engineering Res. 3(3), Naderzadeh, A. and Moinfar, A.A Earthquake resistance diagnosis and strengthening Techniques for existing buildings in Tehran"13 th World Conference on Earthquake Engineering Vancouver, B.C., Canada August 1-6, 2004 Paper No Urmson, C.R., Reay, A.M. and Toulmin, S.H Lessons learnt from the performance of buildings incorporating tilt-up construction in the Canterbury Earthquakes. Alan Reay Consultants Ltd., Christchurch, New Zealand NZSEE Conference. Weng, Y.K, Stefano, P., Rajesh, D., Henri, P.G. and Charles, R Seismic Performance of Reinforced Concrete Buildings in the September 2010 Darfield (Canterbury) Earthquake. Bullet. New Zealand Soci. Earthquake Engineering, 43(4), Wensheng, L. and Xilin, L Evaluation and repair of historic building structures in the Shanghi Band area". First international Civil Engineering (Egypt - China - Canada) Dec Cairo -Egypt, pp