ON THE EFFECTS OF CIRCULAR BOLT PATTERNS ON THE ...

6.5 Bolt-Force Variation Under Cyclic Loading
The bolt force history of Model Tp½-Bd1¼-d30 is presented in Figure 6-12 (a and b). These results
show that in the models with relatively thin end-plate and large bolt diameter the effect of circular bolt
pattern is minimal. Also, it should be noted that the bolts in this model are not yielded, while the model
undergo major pinching (see Figure 6-1(a)). This behavior is due to the excessive bending of the
relatively thin end-plate.
A close examination of the bolt forces of Model Tp1-Bd1¼-d30-SQR presented in Figure 6-13(b) show
that two of the near bolts (Bolts-2 and Bolts-3) are yielded at the end of the 1.5% story drift and far bolts
(Bolts-4) are fully yielded at the end of the 2% story drift. While in the same model with circular bolt
pattern (see Figure 6-13(a)), it takes 3% drift to fully yield the near bolts and lose the pre-tensioning force
while the far bolts (Bolts-4) are still maintaining a portion of their pre-tensioning force. It should be noted
that in the Model Tp1-Bd1¼, far bolts (Bolt-1) takes no force in the connection with square bolt pattern,
while the same bolts engage in taking additional load at the early stage of loading, and they lose their pre-
tensioning force during 2% story drift (compare Figure 6-13(a), and Figure 6-13(b)).
Similar behavior was observed when the bolt forces of the Model Tp1½-Bd1¼-d30 were examined.
Bolts-2, Bolts-3, and Bolts-4 are completely yielded with square bolt pattern, while Bolts-1, Bolts-2 and
Bolts-3 are maintaining a sufficient amount of the pre-tensioning force in circular bolt pattern (compare
Figure 6-14(a), and Figure 6-14(b)).
The same behavior was also observed when the bolt force history of the Model Tp¾-Bd¾-d30 with
circular and square bolt patterns were compared; see Figure 6-17(a and b). The circular bolt pattern
delays the yielding of the bolts and increases the bolt force in far bolt (Bolts-1).
The bolt-force history of the Models Tp½-Bd½-d30 and Tp1½-Bd½-d30 are presented in Figure 6-14(a
and b) and Figure 6-15(a and b). These models with small bolt diameter are prone to yielding of the bolts
during early stage of loading. Thus, the entire bolts are fully yielded after the connection is subjected to
the first cyclic load.
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