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Full Scale Load Test Strengthened RCC Slab Panel Using Carbon Fiber Reinforced Polymer (CFRP)

1Mangesh Joshi, CEO,2Sanjay Rade, Head Technology,3Sagar S. Patil, Design EngineerSanrachana Structural Strengthening Pvt. Ltd. (SSSPL)

Abstract: The objective of the load test was to verify the structural performance of RCC slab, which was strength-ened using CFRP strengthening system as per the approved design. Load test was carried out on the slab panel of typical 4 m wide x 8 m long patch.

Due to change of use it was decided to put server and battery panel on RCC slab. Because of this total impose load on slab was around 750 Kg per sq.mt. Existing RCC slab was not designed for this higher loads. After checking different options it was decided to strengthen the slab using carbon fi-ber reinforced composites supplied by M/S SRMPL.(Specialty Reinforced Matrix Pvt. Ltd.). CFRP strengthening scheme was designed by using ACI codes and analysis was done us-ing FEM base software as per the required data.

The structural strengthening has been carried out using CFRP and their performance has been compared with that of the full scale load test.

Additional server room loading we have strengthened the slab for additional deficiency with CFRP. We check the of Slab and Beam for given loading in FEM base software,

Data taken for Design,

Grade of slab= M40 N/mm2

Grade of Steel = Fe 415 N/mm2

Depth of slab = 250 mm

Loading on slab

Self weight of Slab = 6.250 KN/m2

Live Load = 2KN/m2

Floor Finish = 1KN/m2

Other Finishes = 1.5KN/m2

Services = 0.5KN/m2

Waterproofing = 6KN/m2

IMPOSED LOAD = 7.5KN/m2

Test Parameters-The test parameters were set as per the input data re-

ceived from consultants as follows:

Design imposed load of 750 kg/m2.Note: Since the displacements are being measured in

the proposed load tests, the test shall be conforming to limit state of serviceability. However, as advised by consultant, the imposed test load considered as per IS456 clause 17.6 as follows.

Analysis Results

Strengthening Area

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Schematic Layupt for two way slab at Bottom

Plan

Schematic Layupt for two way Slab at Top

Typical Detail for Flexure Strengthening

Typical Detail for Shear Strengthening

Dead Load + 1.25 times imposed load Therefore actual imposed test load = 1.25 x 750 = 937.5 kg/m2.

Test Specimen

Load test was carried out on the strengthened slab panel

Site Photo

Slab Strengthening from Bottom

Flexure Strengthening of Beam

Shear Strengthening of Beam

of typical 4 m wide x 8 m long patch, which was mutually se-lected by the consultants as per the test arrangement given below.

In absence of the floor finish load, it was simulated con-sidering single layer of brick bat coba.

The design imposed load was applied by using standard bags of cement/sand mortar and micro concrete as follows:

Typical weight of single bag: - Micro concrete bag -25Kg / bag, standard cement/ sand mortar-40 Kgs / bag,

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Test load: 937.5 kg/m2Test patch: 4 m wide x 8 m longTherefore, total designed imposed load = 937.5 x 8 x 4 =

30,000 kg

Actually applied bags:

Total Micro Bags used – 624nos (24960 kg)Total Readymade cement sand mortar bags used – 202nos

(5050 kg)Total Actual Test Load: 24960 kg + 5050 kg =30,010 Kg

Test Equipments

The test facility consists of the following:Test specimen 4 m wide x 8 m long patch of slab clearly de-marcated.TC-1600 FD data acquisition system4 numbers of LSC 140 mm range linear displacement sen-sors.

Test Schedule

Proper precautions were exercised during testing i.e. area underneath the slab being tested was kept vacated to avoid any damages/injuries in case of any unfortunate event of failure. Load was applied gradually in such a way that rate of loading did not exceed 1m per hour. Proper care was ex-ercised in order to avoid impact while load application. The load was applied uniformly by suitably arranging the load bags in different layers.

Material Specification used in Project-STR wrap Strong UD 900Tensile Strength=575 MpaTensile Modulus=25 GpaTensile Strength (Gpa)= 2.43 GpaTensile Modulus (Gpa)= 83 GpaElongation=3.1 %Density=2.55 g/cm3

Experimental Setup

Syetem Arrangement Sensor Connectivity

Position of Sensor Loading of Bags

Structural Performance Test-

a) Displacement sensors were placed on the soffit of the slab panel to measure the displacements at predetermined locations as shown in annexure 1. Each sensor was checked and set to zero reading prior to testing. Initial readings at each sensor were recorded before loading and unloading b) Load was applied gradually. c) Displacement and re-sidual displacements at the predetermined locations were captured by the data acquisition system and the deflection values were calculated by using in-house software. d) The test specimen was loaded to 100% design load in specific intervals. Each load interval was maintained for specific time interval. And the displacements of the test specimen were measured at each interval. Each interval was considered upon completion of loading of single layer of load bags in the given test patch.

Objective of the Test

The RCC slab was strengthened for additional load of 750 kg/m2 by using carbon fiber reinforced system. Thus, with the load test, the structural performance of the strength-ened slab was thoroughly verified as per Clause No. 17.6 of IS:456 2000.

CONCRETE: STRUCTURAL PERFORMANCE

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Conclusion

- As per the Indian standard IS456: clause 17.6.3 the de-flection due to imposed load only shall be recorded. If within 24Hr of removal of the imposed load the structure does not recover at least 75% of the deflection under su-

perimposed load, the test may be repeated after a lapse of 72Hr. If the recovery is less than 80%, the structure shall be deemed to be unacceptable. In the load test it was found that within 24 hours of removal of the imposed load, much more than 75% of the recovery observed in the structure as described in the graphs presented above.

- As per the Indian standard IS456: clause 17.6.3.1 If the maximum deflection in mm, shown during 24hr under load is less than 40l2 / D, where l is the effective span in m and D the overall depth of the section in mm, it is not necessary for the recovery to be measured and the recovery provisions of clause 17.6.3 shall not apply. In the load test, the recovery of the structure took place with the generous margin as mentioned above. Moreover, the recovery requirements are not really applicable as the maximum deflection observed in the slab panel = 8.008 mm, which is less than 40*l2/D as described below

- The test slab was subjected to a load equal to full dead load of it plus 1.25 times the imposed load for a period of 24 hours and then the imposed load were removed. It was found that the maximum deflection during 24 hour load period is 8.008 mm which is less than the limit value of i.e. 10.24 mm. Also the average recovery observed in the load test is much higher than 75%. Thus, the strengthened structure suitably meets the IS

code requirements as per clause 17.6.3 of IS 456:2000.

References

1. KATSUMATA, H., KOBAYASHI, K., MORITA, S. and MATSUZA, Y. Japanese state of the art on seismic retrofit by fibre wrapping for building structures: Technologies and research development ac-tivities, Fourth international symposium on fibre reinforced polymer reinforcement for reinforced concrete structures, ACI International, SP 188-74, 1999, pp. 865-878.

2. MANCARTI, G. D. Strengthening of California steel bridges by pre-stressing, Transportation Research Record No.950, Transportation Research Board,1984, 3-187.

3. DUNKER, K. F., KLAIBER, F. W., BECK, B. L. and SANDERS, W. W. Jr. Strengthening of existing single span steel beam and concrete deck bridges, Report No. ISUERI- Ames-85231, Civil Eng, Iowa State University, Ames, 1984, pp.102.

4. SWAMY, R. S., JONES, R. and BLOXHAM, J. W. Structural behaviour of reinforced concrete beams strengthened by epoxy bonded steel plates, The Structural Engineer, 65A(2), 1987, pp. 59-68.

5. MEIER, U. Carbon fibre-reinforced polymers: Modern material in bridge engineering, Structural Engineering International, 1, 1992, pp. 7-11.

6. MUKHERJEE A. Repair and rehabilitation of structures- Strategies with nonmetallic fibres. Proceedings of the 1st National workshop on ageing and restoration of structures, IIT Kharagpur, 2001,13, pp. 1-12.

7. GIBSON, R. F. Principles of composite material mechanics. McGraw Hill International edition, Engineering mechanics series, 1994.

8. Maitra, S. R. ~2001!. ‘‘Fiber-reinforced polymer composites in the rehabilitation and strengthening of reinforced concrete columns.’’ M.Tech. thesis, Dept. of Civil Engineering, Indian Institute of Tech-nology, Bombay, Mumbai, India.

9. Manfredi, G., and Realfonzo, R. ~2001!. ‘‘Models of concrete con-fined by fiber composites.’’ Proc., 5th Int. Symp. on Fiber-Reinforced Polymer Reinforcement for Concrete Structures (FRPRCS–5), C. Burgoyne, ed., Thomas Telford, London, 865–874. w

Conclusion

CONCRETE: STRUCTURAL PERFORMANCE