METHODOLOGY FOR LOAD TEST ON BRIDGE [ SUPERSTRUCTURE]

 

METHODOLOGY FOR LOAD TEST ON

BRIDGE [ SUPERSTRUCTURE]

1. Scope:

  The work shall consist of Preparation of load test on new constructed structures for deflection on designed load as per IRC.

2. References:

   IRC – SP 51:Clause No. 5.0 and IRC – SP 37: Clause No. 6.6.2.

3.  Equipments:

 Movable loads arrangement for loading, Dial gauge of accuracy 0.0 1mm, Total/Auto level station with leveling staff- tripod , 7.5 KV DG set with single phase power supply and light mask for proper lighting arrangement.

4.  Tools:

   Measuring steel tape, line rope, temperature and humidity sensors. All size spanners.

5. Responsibility:

 Responsibility of Implementation of this procedure lies with Site engineer and in charge of structures with QC person.

6. Materials:

 Load as per IRC Class – A / 70 R loading, Steel towers (Scaffolding) for dial gauge fixing at bottom of slab/girder, Hard wooden blocks for base arrangement, lubricant oil,

7. Procedure:

DEFLECTION MEASUREMENT: 

   Vertical deflections on the bridge (up to 2 5mm) will be measured by Displacement Dial Gauges, having least count of 0.01mm, fixed on firm supports. Dial Gauges are positioned along the longitudinal & transverse alignment of the bridge. Displacement Dial Gauges are placed in longitudinal direction along the mid point of Girder bottom . There will be 12 nos of gauges, 4 nos will be placed at mid span (one each for a girder). Similarly 4 nos each on both end of girder bear bearing.. Dial gauges are supported by firm scaffolding beneath the bridge so as to avoid any disturbance to the dial gauges.

  POSITION OF LOAD FOR TESTING:

The method of loading adopted is point load reaction method. Loading is according to the IRC standard .

 LOADING & UNLOADING SEQUENCE: The test load is applied in six stages viz; 30 %, 50%, 70%, 80 % , 90% and 100% of load. Unloading is also carried out in the same sequence.

 MEASUREMENT OF DEFLECTIONS: Deflections are measured by Displacement Dial Gauges of 25mm (Min.) having least count of 0.01mm.

CORRECTION FOR TEMPERATURE: Temperature measurement is done at the bottom of the test span or adjoining span. The temperature is measured by probe/thermometer. Appropriate correction is made for the temperature variation.

Testing steps by step: Displacement Dial Gauges are fixed at place and deflection is measured prior to loading for 24hrs at regular one hour interval for compensating for temperature correction. Next day loading is started and simultaneously deflection is measured. First increment of (0.3W) is maintained for 1 or 2 hrs and next stage of loading is applied and will be maintained up to 2 hrs , and similar procedure is adopted till 100 percent load is applied. This 100 perecent load is retained for next 24 hrs, and deflection reading will be noted for each one hour. After 24 hrs of retainment of 100 % load, unloading is started immediately by removing load in the reversal sequence as was been loaded. Rebound readings are measured.

  ACCEPTANCE CRITERIA

IRC  SP 37: Clause No. 6.6.2  & IRC SP 51 Clause no 5.

The load for rating should be taken as the least of: -

(i)         The loading causing deflection of 1 / 1500 of the span in any of the main girders for simply supported spans or as per design load.

(ii)        The load causing tension cracks of width more than 0.3mm in any of the girders for normal cases and 0.2mm for structures exposed to very severe and adverse conditions.

(iii)      The load causing appearance of visible new diagonal cracks of width more than 0.3mm for normal cases and 0.2mm for structures exposed to very severe and adverse conditions or opening/widening of existing cracks close to the supports in concrete girders.

(iv)       The load at which recovery of deflection on removal of load is not less than 75% for R.C.C. structures and composite structures and 85 % for prestressed concrete structures as given in table below

(v)        PSC and RCC superstructures are given in Table below:

Sr. No.	Types of Bridges	Duration of Retention of Test Load (Hrs.)	Minimum percentage recovery of Deflection at 24hrs. after removal of Test Load
1.	Reinforced Concrete	24	75
2.	Pre-stressed Concrete	24	85
3.	Steel	24	85
4.	Composite	24	75

8. Reports and measurements :‑

 All measurements will be noted down in formats with loading and deflection for final analysis.

9. Safety Requirements:

1. The work area shall be properly barricaded. Care shall be taken during testing; the sensors shall not be disturbed.
2. Any labour, if being used in the job for surveying shall be screened and trained.
3. All workmen at work area shall wear PPE^·s and reflective jackets, safety belts.
4. During night work  lighting shall be provided.