Inelastic torsional seismic response of nominally symmetric reinforced concrete frame structures: Shaking table tests

• Seismic torsional response of a reinforced concrete frame structure is discussed.
• A symmetric structure exhibits torsion attributable to non-uniform yielding.
• The ratio of translational to torsional period is a key parameter in torsion.
• Accidental eccentricity is important to control non-structural damage.
• Accidental eccentricity can be disregarded for rare (design) earthquakes.

This paper discusses the torsional response of a scaled reinforced concrete frame structure subjected to several uniaxial shaking table tests. The tested structure is nominally symmetric in the direction of shaking and exhibits torsion attributable to non-uniform yielding of structural components and uncertainties in the building process. Asymmetric behavior is analyzed in terms of displacement, strain in reinforcing bars, energy dissipated at plastic hinges, and damage at section and frame levels. The results show that for low levels of seismic hazard, for which the structure is expected to perform basically within the elastic range, the accidental eccentricity is not a concern for the health of the structure, but it significantly increases the lateral displacement demand in the frames (about 30%) and this might cause significant damage to non-structural components. For high levels of seismic hazard the effects of accidental torsion become less important. These results underline the need to consider accidental eccentricity in evaluating the performance of a structure for very frequent or frequent earthquakes, and suggest that consideration of torsion may be neglected for performance levels associated with rare or very rare earthquakes.