Concrete beams. Live load coefficients for deflections

We believe that not all the live load should be considered when obtaining the active deflection because, if it does get to act, it would be for such a short period of time that it cannot affect the deflection in an immediate manner.

If we explore the live load, part of it always present (quasi-permanent), such as fixed installations, furniture, objects…

The Spanish code provides a coefficient of 0.30, which supports our opinion to consider 25% (0.25) of the live load that produces the differed deflection, and is a constant load in time.

On the other hand, when assessing how much live load has produced the instantaneous deflection, it has been proven that it is difficult for the total live load value (2 kN/m2) to have to have been applied. In our opinion, the deflection should be estimated for the frequent live load, taken in the Spanish code as 0.5, which we have also taken to be 50% (0.5).

Studies have shown that, statistically, the loads in residential homes do not exceed 0.8 kN/m2. 50% of 2 kN/m2 is 1 kN/m2, which seems more than reasonable. To summarise, only 50% of the live load really appears and produces an instantaneous deflection and only 25% remains and produces differed deflection. This is our approach regarding the default values.

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