Vibration Serviceability of Two-Story Office Building: A Finite Element Modeling

In this work, a finite element model (FEM); built and solved in Abaqus environment, was developed to study the structural vibration levels and frequencies induced by human activity; i.e. walking, in two-level steel structure office units. The three-dimensional model considers two units assembled side by side. The developed geometrical model consists of beams and trusses elements generated using structure proposed dimensions. The structure is composed of multiple materials i.e. hot rolled rectangular bars, C steel channels, and floors\slabs made from cement. Elastic properties were only considered in the material model, while material damping was idealized as viscous damping using Rayleigh model. The model treated all joints; bolts or welds, to be rigid, therefore tie constraints were applied at all connections and joints. Fixed-free boundary conditions were considered for structure columns while other points presenting foundation support were constrained in the vertical direction only. Walking-induced forces were described based on multiple parameters; mainly human body mass, and pacing frequency, which are directly related to walking characteristics; specifically, step size and walking speed. Two load models were considered, first, a simple force model considering the walking induced force as a concentrated harmonic force applied at a fixed point. The second, a moving concentrated load applied along a predefined path. The structure natural frequencies and mode shapes were extracted first, and then dynamic explicit analysis to determine the vibration levels (acceleration) was performed. The finite element results are compared to simplified model described in design guide 11 by AISC. The estimated vibration levels using finite element analysis were found to be exceeding the comfort zone (ISO 2631-2), while calculations based on design guide 11 found to be at the boundary of the described limits.