Load test for hollow core slabs

This could be found in the ACI318, Chapter 20,”Strength Evaluation of Existing Structures” Section 20.3 “Load Test Procedure”. Based on this reference, the total test load, including the dead load already in place, shall not be less than “0.85 [(1.4D + 1.7L)] – un-factored weight” of the slab where D is the total un-factored dead load and L is the total un-factored live load.

The following steps should be carried out on site:
• Calibrated dial gauges should be fixed at the bottom of the slab to measure the expected deflection. Five (5) gauges should be used to monitor the deflection in the case of loading.
• The gauges should be set to an initial reading.
• Special precautions should be made to prevent any vibrations in the testing area.
• Test load provided by the contractor should be uniformly distributed on the slab according to the intensities indicated in the cases of loading.
• Test load should be applied in four (4) approximately equal increments.
• Response measurements should be recorded after completion of each Increment
• After completion of four (4) loading increments, the slab should be kept loaded for 24 hours after which deflection readings and response measurement should be taken.
• The slab will be unloaded. Final response measurements should be done after unloading directly then after 24 hrs from removal of test load in order to indicate residual deflection.

the measured maximum deflections shall satisfy one of the following two conditions:
• ?max ? L2 / 20,000h
• ?rmax ? ?max / 4

?max: is the maximum deflection in mm
?rmax: is the maximum residual deflection in mm

L2: is shorter of:
(a) Distance between centers of supports in mm.
( Clear distance between supports plus thickness of member in mm.

h: is the thickness of the slab in mm.

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