Real Challenges for Civil Engineers – No.02

Client requirement – Build up another floor on top of existing slab

Engineering challenge – Introduce starter bars for columns or walls

Conventional Method –

Break the existing beam to the extent of anchorage length of proposed column or wall reinforcement

Problems Encountered

1. Breaking of concrete slab and beam may weaken the structure2. Other structures may affect due to vibration while concrete breaking3. Minimum 4 days will be taken to complete the task4. Risk for the job5. High cost and time incurred at the end of the job

Existing Beam

Existing Slab

New column or wall

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 OR HILTI HY 150 bonding agent

Advantages

1. No concrete breaking is required2. No vibration hence no chance to develop cracks3. Maximum 1 day to complete the total task4. Low cost ( less than Rs.150/- to fix Y10 bar at nominal embedment depth )5. Application is so simple and no chance for mistakes – Zero human errors6. No risk for the job7. Pullout test will be done by HILTI Engineers before concreting to ensure the strength 8. All technical support will be given by HILTI Engineers

Method statement

1. Consult your structural Engineer for the design of column or wall reinforcement2. Calculate the stress to be developed in the reinforcement due to moment3. Call HILTI Engineer to get instruction for reinforcement fixing4. Drill holes to specified diameter and depth5. Clean holes with blow out pump provided6. Insert HILTI RE 500 OR HILTI HY 150 chemical with the use of dispenser

provided ( No hand mixing)7. Insert the reinforcement bars and keep 8 hrs for RE 500 OR 40 minutes for

HY 150 to cure8. Arrange reinforcement as usual9. Roughen the concrete surface and apply any bonding agent if necessary and do

the concreting as usual

Sample calculation

Assumptions : Concrete grade 25N/mm2 Existing column size 270 X 270 mm and clear cover 30mm Similar size column to be on top Moment develop at the support of new column M = 20 kNm

M = T * Z where T = ultimate tension develop in the reinforcement at the connection Z = lever arm = 0.775d = 0.775(270 – 30) = 186 mm T = M/Z = 20 / 0.186 = 107.5 kN ( for 2 bars of the column )

Check for concrete / bond failure

Assume 2Y16 to be introduced with HILTI RE 500 as bonding agent and embedment depth of 300mm

150mm

270mm

According to the HILTI specifications for embedment depth of 300mm

Tension capacity of 2Y16 bar with RE 500 = 2 X 43.7 x 300/150 x 1.00 x 0.8 = 139.8 > 107.5 kN

Hence application is satisfactory with Safety Factor of 139.8/107.5 = 1.3

Check for steel failure Ultimate tension capacity of 2y16 steel bars = 2 X 0.87 fyAs = 2 X 0.87 X 460 X 201 = 160.9 kN > 107.5 kN Satisfactory

Hole diameter = 22mm Hole depth = 300mm chemical consumption = 70 ml

Existing bars

New bars to introduce

Technical Assistance Neelanga Sooriyarachchi B.Sc. Eng (Hons);MBA; AMIE(SL) Engineering Service Manager0717712968

T.D.Wijitha KumaraB.Sc.Eng(Hons);CEng;MIE(SL);MSSE(SL);MBATechnical Manager0717772815

Office207, Nawala Road, NugegodaTe. 0114713352, 0114542320Fax. 0114723208Email. hunterhc@eol.lk

Product of Hilti Engineering Division

Hilti Sales Engineers / Sales Executives

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