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Real Challenges for Civil Engineers No.01Engineering challenge
Introduce a Balcony slab to existing building
Client requirement Parapet wall around the balcony for
safety
Conventional Methods
Option 1Break the existing slab to the extent of anchorage
length of proposed slab reinforcement
Problems Encountered
1. Breaking of concrete slab and beam may weaken the
structure
2. No support for brick wall on top leads to develop cracks on
the wall
3. Difficulties in re-concreting
4. Other structures may affect due to vibration while concrete
breaking
5. Minimum 4 days will be taken to complete the task
6. Additional supports to be provided for the existing slab for
few days
7. Risk for the job
8. High cost incurred at the end of the job
Option 2Provide fabricated cantilevered angle iron frame to
support the slab
Problems Encountered
1. Problem in fixing of cantilevered frame to the beam
2. Unpleasant architectural appearance
3. Minimum 4 days will be taken to complete the task
4. Risk for the job
5. High cost incurred at the end of the job
New Method introduced by the HILTI with the development of
Technology
Drill holes to the existing concrete beam and fix reinforcement
with HILTI RE 500 bonding agent
Advantages1. No concrete breaking is required
2. No additional support needed to support existing concrete
3. No vibration and hence no chance to develop cracks
4. Maximum 2 days to complete the total task
5. Easy for concreting
6. Low cost ( less than Rs.150/- to fix Y10 bar at nominal
embedment depth )7. Application is so simple and no chance for
mistakes
8. No risk for the job
9. Pullout test will be done by HILTI Engineers before
concreting to ensure the strength
10. All technical support will be given by HILTI Engineers
11. Architecturally looks like originally cast slab
Method statement
1. Consult your structural Engineer for the design of cantilever
slab reinforcement
2. Call HILTI Engineer to get instruction for reinforcement
fixing
3. Drill holes to specified diameter and depth4. Clean holes
with blow out pump provided
5. Insert HILTI RE 500 chemical with the use of dispenser
provided ( No hand mixing)6. Insert the reinforcement bars and keep
8 hrs to cure
7. Arrange reinforcement as usual
8. Roughen the concrete surface and apply any bonding agent if
necessary and do the concreting as usual
Sample calculation
Assumptions :
Consider 1m strip of concrete
Concrete grade 25N/mm2
Slab thickness 200mm at support Structural Engineer recommend to
have Y10 @ 150 mm c/c
Moment develop at the support of new cantilever slab M = 20
kNm/m M = T * Z
where T = ultimate tension develop in the reinforcement at
support ( for 1m ) Z = lever arm = 0.775d = 0.775(200 25) =
135.6mmT = M/Z = 20 / 0.136 = 147 kN
Tension of single reinforcement = 147/ (1000/150) = 22 kNCheck
for concrete / bond failureAccording to the HILTI specifications
for embedment depth 180mmTension capacity of Y 10 bar with RE 500 =
19.7 x 180/90 x 1.03 x 0.9 = 36.5 > 22 kN SatisfactoryCheck for
steel failure Tension capacity of Y10 = 0.87fy.As = 0.87 X 460 X
78.5 = 31.4 kN
Hence application is satisfactory with Safety Factor of 31.4/22
= 1.4Hole diameter = 14mm Hole depth = 180 mm chemical consumption
= 18 mlTechnical Assistance Neelanga Sooriyarachchi B.Sc. Eng
(Hons);MBA; AMIE(SL)
Engineering Service Manager Mob 0717712968 Email .
[email protected]
KumaraB.Sc.Eng(Hons);CEng;MIE(SL);MSSE(SL);MBA
Technical ManagerMob. 0717772815 Email.
[email protected]
207, Nawala Road, Nugegoda
Te. 0114713352, 0114542320
Fax. 0114723208
Email. [email protected] Sales Engineers / Sales
ExecutivesChandima Samarasinghe Colombo Area
B.Sc. Eng ( Hons)
Te. 0717579369
Lalith Chaminda Colombo Area
B.Sc. Eng ( Elec)
Te. 0718540846
Nadun Ranatunga Colombo Area
Sales Executive
Te. 0713733107
Sampath Bandara Kurunegala, Kandy, Anuradapura, Batticaloa
Sales Executive
Te. 0713733106
Tuwan Burah Southern, UvaSales Executive
Te. 0717124687
Slab to introduce
Brick wall
Existing Beam
Existing Slab
Brick wall
