A box culvert is situated under heavy traffic load. The design details are not available for the said culvert. so what are the possible ways to calculate the load carrying capacity of that culvert without disturbing traffic movement.
we can continuously go on loading the structure and observe the mid-span deflection. The load at which the maximum permissible deflection is reached will be the the maximum serviceable load.
The best time would be night or early morning,if the site is within the city, when the traffic would not be disturbed.
you can go for NDT to determine the compressive strength of concrete and the density using the pundit test, this could be done inside the culvert without disturbing the traffic flow.