3D time history analysis of RC structures versus common methods with attention to the modeling of floor slabs and near versus far-fault earthquakes

![CDATA[Commercial software such as ETABS and SAP, commonly used for the analysis of apartment building, assume the slabs as rigid or semi-rigid members and only roughly allow for the slab’s flexural stiffness using the concept of effective width. These assumptions when further simplified adopting a 2D frame method that ignores the torsional effects may produce results that are very different to the full 3D finite element modeling in particular when time-history nonlinear dynamic behaviour is sought. The errors could be larger in near-fault earthquakes that often excite higher vibration modes. Recent major earthquakes (Northridge 1994. Kobe 1995, Chi-chi 1999 and Bam 2003, etc.) have shown that many near-fault ground motions possess prominent acceleration pulses that result in different structural responses for common medium to high-rise buildings. Incorrect incorporation of the flexural stiffness of slabs can in some cases underestimate the lateral stiffness. It is shown in the current paper that in a wall-frame structure subjected to near-fault earthquakes, the full 3D time history modeling can significantly vary the analysis results and as such is an important consideration in design.]]