Time-dependent effects on critical buckling load of pultruded column

It is well known that the performance of pultruded structural elements is influenced by the viscoelastic behavior of the based-polymer material that are not affected by aging effects. In what concerns buckling of pultruded columns, creep causes a time-dependent decrease of the critical load or, in other words, a time-dependent induced buckling due to the evolution in time of the lateral deformations due to initial imperfections or load eccentricity. The numerical and experimental analyses have been carried out on pultruded column that have been used in a large all-GFRP (Glass Fiber Reinforced Polymers) structure built in L'Aquila, Italy. The critical load is firstly evaluated using the well known Euler formulas; secondly, the long-term critical load is evaluated, - on the base of the same formulas - adopting a reduced value for the elastic constants, taking into account the creep behavior of the material. Finally, a geometrically non linear analysis of the column is carried on, taking into account creep deformations and transversal deformability. A possible application of the numerical computations is to find a value of the constant applied load that causes the time-dependent buckling of the column for limited load duration that can be analyzed in an experimental campaign, in order to compare the results and to define the parameters of viscoelastic law.