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Structural Rehabilation & Retrofitting
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REMOVAL OF COLUMNS BY EXTERNAL POST TENSIONING TECHNIQUE TO INCREASE SPANS

At one of the commercial complex (cellar  + 5 floors) constructed  abutting a National Highway – a prime location, the column spacing was only 4 m c/c.  Due to this close spacing of columns there were no takers for the structure as the column spacing is too less to accommodate any commercial activity such as show room/office/supermarket. 

   

The clients have consulted Varshitha to check the possibility to remove alternate columns atleast in one direction and crease the column spacing to 8.0 m.  In normal cases, the best option would be to provide Steel Girders below the beam to a length of 8 me and then remove the intermediate column.  This option is not only cost incentive but also will reduce the available head room atleast by 500 mm. 

   

The option of external post tensioning was considered and checked structurally and found suitable and feasible.  However, due to redistribution of column loads, the balance columns have to take the additional loads of the columns being removed.  Hence balance columns and their foundations were checked for these additional loads and found to be satisfying the requirement.

 

There a total of 7 columns in one row and there are 4 such rows (excluding 2 end rows).  The alternate columns viz., 2nd, 4th and 6th were marked for removal.  The following procedure was adopted for execution of the work  :

   

SCHEMATIC SHOWING THE SEQUENCE OF ACTIVITIES

 


 

   

STEP 1: All the existing plaster on the beams was removed and shear connectors fixed to the sides of the beam.


STEP 2: Reinforcement was fabricated and fixed as per design tied to the shear connectors.

  After  reinf. & cable laying

STEP 3: Core holes were made adjacent to the beams in the slab at regular intervals to enable pouring of Micro concrete for the beams encasement.

  After concreting

STEP 4: Three Nos Mono strands on each side of the beam (encased in 20 mm HDPE pipe) were threaded on either side of the beam.  The profile is such maintained that it at top at the columns being retained and at the lowest point at the columns being removed.

  Stressing in progress
   

STEP 5  Micro concrete encasement (to a thickness of 125 mm on each side of the beam) was carried out using the core holes drilled in the slab adjacent to the beams to the complete length of the beam approximately 24 m in single pour.

STEP 6 Once the concrete has gained enough strength, First stage stressing to 10.0 Tons in each strand was carried out.

  Column being removed
   

STEP 7 Once the 1st  stage stressing is completed, the columns identified were supported by suitable cribs and jacks on all 4 sides.  Now the columns were chipped off using electrically operated chippers.

 

STEP 8 Now the supports are removed and 2nd stage stressing to 14.5 Tons in each strand is carried out.

  Alternate Columns removed
   

DISMANTLING OF STRUCTURES BY HIGH REACH BOOM PULVERIZING .  (Oct, 2011)

 

Varshitha in the financial year 2011-11 has diversified into High Reach Demolition of structures using Jaw crusher/Pulverisor.  This is one of the best way of demolition of structures safely.  Varshitha has launched its High Reach Boom crushing in the month of September 2011 and has completed 2 projects in Hyderabad.

 

The first project involves dismantling of 3rd floor roof slab standing about 45 ft above ground level.  The total area of slab is about 500 sqm with 300 mm thick PT slab and PT beams of 1200mm and 1800 mm width.  This was necessary by the client for under construction building as they wanted to raise the level of the slab by 4 ft to suit the revised architectural requirements.   Since the columns are not to be dismantled, it was important that the stresses of PT cables are not transferred to columns during dismantling of Beams/slab.  To enable this, firstly the PT cables are disconnected at the column end by core drilling and the beams were fully supported.  Back propping was also carried out to lower slabs as the debris is expected to fall on the lower slab.  Sand cushion was provided on the lower slab to minimize damage to the slab due to falling debris.  Since the operation is by pulverizing the concrete, only small pieces of concrete are expected to fall on the slab and not large chunks.  The complete slab was dismantled in just 30 working hours of the High reach boom.  The in accessible end rear beam was dismantled using conventional electrical chipping.

 

The second project involves dismantling of 3 buildings of Ground + 1 floors constructed on 1000 mm raft concrete.  These three buildings are part of multiple residential towers being constructed.  Though the construction of other towers is in progress, there was a change of architectural and internal layout planning  in these 3 buildings.  The structures include 300 mm thick flat slab supported on 300-400 mm wide long columns ranging from 1.5 to 4.0 m.  The total concrete to be dismantled is about 1500  cum.  Further the client was planning to use the same raft for revised construction plan, the structure has to be dismantled carefully without inducing vibrations or damage to the raft.  In view of it either use of pneumatic breakers or Hydraulic excavated mounted breakers are ruled out. 

The best available option for speedy execution – Concrete Pulverizing/crushing was adopted by the client and the complete job was completed in just 100 working hours of the crusher and additional ¾ days for removal of the debris from the site.

 
 

 

 

 

 

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Structural Rehabilation & Retrofitting
 
1. Innovative way of dismantling retaining wall by use of Post Tensioning Technique
2. Restoration of a Failed Bridge
3. Jaw Crusher Demolition of Towers
4. High Reach Demolition 4th Floor P T Slab Demolished
5. Stabilization of Vertical Pit Faces Using P T Technique
6. Removal of Columns by External Post Tensioning Technique to Increase Spans
7. Structural Rehabilation & Retrofitting
8. Removal and Recasting columns in a under construction building
9. Restoration of a National Highway Bridge under distress
10. Restoration of Bridge damaged by poor expansion joint maintenance
11. Restoration of a Heritage building at Hyderabad Public School
12. Restoration of Bridge damaged by Earth Quake at Andaman
13. Restoration of Fire Damaged Building, Hyderabad
Concrete Sawing & Core Driling
Bearing Replacement & Bridge Lifting