Bridge Load Testing as Per IRC SP 51

Abstract

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Introduction

I. INTRODUCTION

Load testing is mainly used for assessing the flexural  capacity of bridge. It is used to assess the condition and safety of bridge. The situations in which the testing is carried out if there is excessive creep deflection, materials defect, structural detoriation, uncertainities in current built in conditions , bomb or fire damage, or structural strength unknown. The load testing is used to check whether maximum deflection and percentage recovery are within permissible limits or not. If the bridge fails to meet the criteria, the bridge is no longer used.

II. OBJECTIVES OF LOAD TESTING

The overall goal of conducting load tests on the Bridge is to :

1. Quantify its response to various loading conditions.
2. Measuring roadway-surface deflections due to various live loads.
3. Deriving stresses from measured deflections via analytical models, and comparing analytical results with design standard.
4. Testing may be carried out to assist the design in the following circumstances:

a. Where adequate analysis models are not available

b. Where large number of similar components are used

c. To check assumptions made in the design

III. METHODS OF MEASUREMENT

Deflections, Inclinations and Strains are measured with following instruments.

IV. PROCEDURE OF LOAD TESTING

1. The test was carried out as per IRC SP 51 -2015 ( IRC – Indian Road Congress Special Publication)
2. Instruments assembled at desired location such as, Dial Gauge , Strain Gauges , Digital Thermometer , Data Acquisition System.
3. Visual inspection of bridge is done. In Visual Inspection, Bearing and expansion joints were checked. Both must be in their functional and working condition. The traffic was closed for further testing and whitewash is applied to the superstructure for monitoring of cracks.
4. Dial Gauges were placed on magnetic stands. They were placed firm on scaffolding platforms with steel plates , so that magnetic stands are firmly located. Dial gauges were mounted just by touching the soffit of structure.
5. Glass plate of size 50x50x5mm shall be fixed to structure at location of Dial Gauges For Positioning.
6. Before Loading The precautions should be taken:

a. All staging provided shall be stable and safe.

b. Staging for instruments and observers shall be independent.

c. Staging for instruments shall be rigid.

7. As per IRC SP 51, Loading Operation Stages from  0% , 25% , 50% , 75% , 100% of test load in 5 stages , which shall be completed in 4 hrs. At the starting of Bridge load test 25% of load on bridge is taken, out of total 120MT which is 30MT, then 50% then 75% then 100%. We had to increment the load at the interval of every 1 hr. during this the deflection were recorded at each stage of loading.

8. After completing loading, we had to keep it retained for 24 hrs and observe.

9. After 24 hrs, Structure shall be unloaded at same stage of loading i.e. 100% , 75% , 50% , 25% , 0% ,But unloading shall be done in same way of loading , load shall be removed at 1 hr of interval from 100% to 75% to 50% , as well as deflection is rewarded at each stage.

10. Measurements were recorded at every hour of loading and unloading.

11. Data was collected by visual observation before and after loading and there will be interpretation of results.

V. DATA COLLECTION

A. Visual Inspection

In visual inspection test , all visual defects were measured, mapped, and plotted. Bearings were checked. Bearing were ensured for their functional condition. Expansion joints were in working condition. Expansion joints gaps shall be ensured through their functional condition. The traffic was closed. All the vegetations on site was removed .Then whitewash was applied to the soffit of superstructure for better monitoring of cracks. Digital caliper was used for measurement of cracks.

B. Temprature Correction

The temperature readings are taken without applying the load . at every one hour of interval temperature readings are noted and how much deflection is caused due to temperature is noted.

TABLE I

Initial  Loading,  Dial Gauge Reading (Load 0.00 MT ) for 24.00 hr

C. Initial Stage of Loading

After taking temperature reading, the load is applied on bridge in 5 stages. Starting from 0%, the load is applied at every one hour of interval upto 0%, 25%, 50%, 75%, 100%.

TABLE II

Initial  Loading,  Dial Gauge Reading (Load 0.00 MT to 120.00MT)

D. 24 hour Retention of Load (100%)

After Initial stage of loading, the loading is retained for 24 hours. Again, the readings are taken at every 1 hour of interval for 24 hours while retaining the load.

TABLE III

100% Loading Dial Gauge Reading (Load 120.00MT) for 0.00hr. to 24.00hr

E. Initial Stage of Unloading

After 24 hours of loading, the structure shall be unloaded as same 5 stages. Starting from 100%, the bridge is unloaded at every 1 hour of interval upto 100%, 75%, 50%, 25%, 0%.

TABLE IV

Initial  Unloading,  Dial Gauge Reading (Load 120.00 MT to 0.00MT)

F. 24 Hour Retention of Load (0%)

After removal of load , once more the deflections are measured at every 1 hour of interval for 24 hours.

TABLE V

0% Unloading Dial Gauge Reading (Load 00.00MT) for 0.00hr. to 24.00hr

G. Uninstallation of Instruments

After noting final deflection for the bridge, the instruments and scaffolding were safely removed from the site.

VI.  RESULTS

As per IRC SP 51, the percentage recovery is calculated for bridge after removal of load for 24 hours. The data of temperature correction, total deflection and total recovery is determined.

As per IS SP 51, clause 8.3.1, page no.17 :

Initial value- deflections before commencement of loading= R1

Deflections at one hour, after placement of 100 percent test load = R2

Deflections at 24 hours after placement of 100% test load= R3

Deflection measurements immediately after removal of test load = R4

Deflection measurements at 24 hours after removal of test load = R5

Total deflection = R3 - R1

Total recovery of deflection after 24 hours after removal of test load = R3-R5

Percentage recovery of deflection 24 hours after removal of test load= (R3-R5/R3-R1)*100

(Where this value exceeds 100% it shall be restricted to 100%)

TABLE VI

Percentage recovery of deflections after retention of test load for 24 hours  (G –V)

TABLE VII

Summery Sheet of Total Deflection and Total Recovery

TABLE VIII

Maximum Permissible deflection of girders

TABLE IX

Theoretical Deflection vs Actual Deflection, After 24 hours of Loading of 100% of loading i.e.(120.00 Metric Ton)

Conclusion

VII. CONCLUSION Following are the acceptance criteria as per IRC SP 51-2015 and conclusions of test conducted on said bridge. 1) Criteria-I: Deflection Recovery: (Clause no. 6.8.2 page no. 12) The percentage recovery of deflections for various types of bridges after retention of test load for 24 hours shall be: Types of Bridges Minimum percentage Recovery of Deflection at 24 hours after Removal of Test Load 1.Reinforced Concrete 75 2.Prestressed Concrete 85 3.Steel 85 4.Composite 75 Minimum Percentage recovery as per IRC SP 51 Conclusion: The percentage recovery of deflection of all dial gauges is more than 75% which is within the acceptance criteria of IRCSP 51 – 2015. 2) Criteria-II: (Clause no. 6.8.1 page no. 12) Maximum Permissible deflection as per Design should not be more than (Span/800) = (16200/800) = 20.25 mm Conclusion: The maximum deflection of tested bridge is observed 2.05 mm at Girder No. 4, which is less than Permissible deflection as per Design, which is within the acceptance criteria 3) Criteria-III: (Clause no. 6.8.3 page no. 12), The Structure shall not show any cracks more than 0.3mm for moderate exposure, spelling or deflections which are incompatible with safety requirements. Conclusion: Observed Crack width in the tested bridge is less than 0.3mm, which is within the acceptance criteria. Tested bridge passed all the criteria, Hence it is concluded that the bridge is safe and ready for service.

References

[1] B. Bakht and S. G. Pinjarkar,Dynamic Testing of Highway Bridges- A Review of Dynamic testing highway bridges . Structures Research Report SRR-89-01. Ontario Ministry of Transportation , Downsview , Canada , (1989) [2] MOUSSA A. ISSA, MOHSEN A. SHAHAWY, Dynamic and static test of prestressed girder bridge, STRUCTURAL RESEARCH CENTER, MS 80 FLORIDA DEPARTMENT OF TRANSPORTATION TALLAHASSEE, FLORIDA, May (1993) [3] Andrzej S. Nowak and Vijay K. Saraf, Department of civil and environmental engineering university of Michigan,Load testing of bridges,(October 1996) [4] L.Fryba, M.Pirner et al. 17th July, Load test and model analysis of bridges. (1999), [5] T.J. Wipf, B.M. Phares, F.W. Klaiber, D.L. Wood, DEVELOPMENT OF BRIDGE LOAD TESTING PROCESS FOR LOAD EVALUATION, April (2003) [6] Slovak University of Technology, Department of Surveying Radlinskeho 11, SK-813 68 Bratislava, Slovakia, Loading testing of highway bridges in Slovakia, (2003) [7] Osman Hag-Elsafi, Jonathan Kunin, Sreenivas Alampalli, Court street bridge monitoring and load test. Transportation research and development bureau New York State Departmengt of Transporatation. (2006) [8] JICA STUDY TEAM Oriental Consultants CO., LTD. CHODI CO., LTD, The study on capacity development in bridge rehabitation planning, maintenance and management based on 29 bridges of national highway network in COSTA RIKA(2007) [9] Jiamei Zhao, Tao Liu, Yuliang Wang, Static test analysis of a bridge structurenin civil engineering,(2010) [10] Travis R. Brackus, Paul J. Barr, et al. Live Load and Shear Connection Testing of full-scale precast bridge panels. March(2013), [11] Petra Bujnakova ,JozefJost ,and MatusFarbak,Load testing of highway bridge, (2018) [12] IRC SP 51 : General Guidelines on load testing on bridges, published by Indian Road Congress - First Revision - January (2015) [13] IRC SP 37 : Guideline for Evaluation for Load capacity of Bridges -First revision – November (2010) [14] IRC SP 112 : Code for Practice of Concrete road bridges , Indian Road Congress , November (2011)

Copyright

Copyright © 2022 Harsh N. Mahale, Prof. Ravindra N. Patil, Vrushali R. Bagul, Megha L. Badade. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.