EFFECT OF COMPOSITE ACTION ON THE DYNAMIC BEHAVIOUR OF SPACE STRUCTURES

[yanburak]

EFFECT OF COMPOSITE ACTION ON THE DYNAMIC BEHAVIOUR OF SPACE STRUCTURES

In this work, the effect of introducing composite action in changing the dynamic
characteristics of space frames, in particular the natural frequencies and damping ratios
was presented. The study was expanded to determine the effect of composite action in
changing the response to dynamic excitations. The measured responses included the
lateral displacements and changes in the internal member force distribution under
shaking table vibrations.
Three aluminium space frame models of the square on square (SOS) configuration were
manufactured. The first model was non-composite, while composite action was applied
to the other two models with a top aluminium deck and a timber deck, respectively.
Two common cases of support conditions were used in connecting the models to the
loading frame, which was the platform of the shaking table.
Initial displacement method (snap test) was used to determine the frequency of vibration
and the damping ratio of test models in the vertical and horizontal directions using
logarithmic decrement method. All models were then exposed to shaking table
vibrations to determine the changes in dynamic responses between different models.
These tests were repeated for the three models after the successive removal of panels
from one direction to identify the changes to their characteristics and behaviour with
different aspect ratios.
The second part of the study was carried out numerically by using the finite element
package ABAQUS. It started by selecting a valid finite element model from nine
proposed models using experimental test results on physical structures. A parametric
study was conducted using the validated finite element model to expand the study to
include two common space frame configurations; the square on large square (SOLS)
and square on diagonal (SOD), and two other cases of support configurations, namely,
fully edge-supported and supports at corners and middle edges of models.
Based on the work done in this study, it can be concluded that composite action
changed the dynamic characteristics of space frames, which was clear in the increase of
their vibration frequencies in all directions as a result of the increase in stiffness.
Furthermore, the increase in stiffness resulted in a general reduction in the damping
ratio of space frames covered with aluminium deck, while the high friction with top
joints and the nature of timber as a good energy absorbent material resulted in a variable
effect on the damping ratio associated with the increase in aspect ratio.
The effect of composite action was clear in reducing the lateral displacement of
composite models by more than 50% compared to the non-composite case. Moreover,
composite action resulted in changing the distribution of internal forces in diagonal and
lower chord members such that forces became more concentrated at corners and edges
parallel to the direction

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