www.sefindia.org

[jaswant_n_arlekar]

Dear SEFI Members:


Please see the attached article about the load testing for Cable Stayed Bridge, which is a part of a 90° segment of SCLR Extension at Mumbai. I don't have more information about this test, but it is supposed to start today.


Summary of IRC-SP51 Guidelines for Load Testing of Bridges
1. Full scale load testing of bridge superstructure to assess the behaviour of bridge by the application of design live load, to confirm the elastic performance of the superstructure. Also called as proof load test.
2. Evaluates only the flexural behaviour of the superstructure. Shear capacity is not evaluated due to absence of reliable methods for the same. Does not evaluate the ultimate load carrying capacity.
3. The procedure does not include loads of environmental origin, e.g., flood, wind, temperature or earthquake.
4. Test is to be conducted on representative sections of the superstructure, which may be normal or known to be defective. The observed results are to be correlated with the analytical models for further assessment and evaluation of the bridge.
5. The code prescribes a loading protocol.
5.1. Loading steps: 0%-50%-75%-90%-100% to be completed within 24 hours
5.2. 100% load to be retained for 24 hours
5.3. Unloading steps: 100%-90%-75%-50%-0% to be completed in 24 hours
5.4. All post testing measurements to be completed in 24 hours of full unloading.
6. The code also touches upon without details on the physical scaled model testing, and dynamic testing, but with very little guidance.  
7. Acceptance criteria is given in terms of recovery of deflection after 24 hours of removal of the applied love load, and crack widths.


Summary of IRC-SP37 Guidelines for Evaluation of Load Carrying Capacity of Bridges
1. Applicable for all bridges designed using IRC Codes. Not applicable for old bridges, where materials differ as compared to modern IRC codes.
2. The guideline gives procedures for inspection and analysis of bridges based on the structural condition, materials and loads. Actual testing is one of the methods for evaluating the capacity of the bridges.
3. Analytical methods are to be used to estimate the actual load-carrying capacity, which will incorporate the in-situ conditions of configuration, material strengths, section properties, loading (including traffic), and any distress conditions. This is suitable when all details are available.
4. Load testing method is suitable when construction details are not available.
5. The guideline recommends a rating system for the bridges, where, after collecting all the information about the bridge, the bridge is evaluated by structural analysis to safely sustain the desired load rating. If the response of the bridge is not satisfactory, it is evaluated for the next lower-class loading, until the response is more than 90% of the acceptable response, and that load rating (70R, Class A, etc.) is assigned for the bridge. This is not based on actual testing of the bridge.
6. Load testing for rating and posting is prescribed when all documentation for analytical evaluation is not available. Mobile test vehicles which simulate the effects of various class loading are recommended in place of static loads.
7. Acceptance criteria is given in terms of deflection and cracks and recovery of deflection after removal of load. IRC Codes have excluded testing for environmental effects like wind, earthquake, etc. due to unavailability of reliable testing procedures.


Thank you, and with best regards,
Jaswant N. Arlekar