In bolts of 6,8, and 12 mm diameter were

In
order to understand the effect of bolts’ diameter on the connection behaviour,
SS, BFRP, and HSFRP bolts of 6,8, and 12 mm diameter were used as shown in fig.
3-6 and table 3-5.

3.6.4.1
Load-Displacement

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Fig.
3-23 shows the recorded load-displacement curves for SS, BFRP, HSFRP bolted
specimens with different bolts diameter and number to give the same total
cross-sectional area of bolts. As mentioned in bolts’ number parameter, in the
first stage for all diameters, there was an increase in the displacement due to
the clearance between the bolts and the hole. After that, the slope of the
load-displacement curve increased due to the full contact of bolts with the
holes till reaching the ultimate load. SS bolted specimens showed linear
behaviour for all diameters till ultimate load, unlike bearing failure in BFRP
curves was more observed for all diameters at approximately from 35 to 50% of
the ultimate load.

It
can be seen from fig. 3-23 that SS, and BFRP bolted specimens had approximately
the same ultimate load when maintaining the total cross-sectional area of the
bolts but changing the diameter. Unlike HSFRP bolted specimens, as can been in
fig. 3-23c, 12 mm diameter was higher than 8 and 6 mm, and 8 mm diameter was
the lowest.

In
addition, SS bolted specimens had similar stiffness with changing the diameter,
however for BFRP and HSFRP specimens there was differences in the stiffness
with varying the diameters and increasing the load as shown in fig. 3-23(b, c).

It
worth to mention that after reaching the ultimate load, it was noticed that
changing the diameter of bolts did not affect the HSFRP specimens’ behaviour,
specimens with HSFRP bolts did not lose all of their strength suddenly like
specimens with SS. However, it showed a ductile behaviour and gradual
degradation which can be attributed to the damage of the HSFRP bolts which
reduce the intensity of the shear out failure as discussed in Ch 2.

3.6.4.2
Comparison of failure load.

The
bearing failure started with resin cracks and fibres micro-buckling near the
bolts’ holes at 30-50% of the ultimate load which appeared as nonlinearity in
the load-displacement curve before the ultimate load with hearing low sounds of
cracking, and as mentioned this was more obvious in BFRP bolted joints as seen
in Fig. 3-23b.

Table
3-5 shows the failure load of each specimens. The average failure loads of SS,
BFRP and HSFRP bolted joints with different bolts’ diameter are compared in
Fig. 3-24. It is clear that there was no significant differences in the
ultimate load for SS and BFRP bolted specimens with changing the bolt diameter.
In term of SS bolted specimens, the failure load decreased by 2.14%, and 5.56%
when the bolt diameter changed from 12 mm to 8 mm and 6 mm respectively. For
specimens with BFRP bolts, the decrease in the failure load for 8 mm and 6 mm
was 3.85% and 8.5% respectively.

However,
for HSFRP bolted specimens 6 mm diameter bolts was higher than 8 mm diameter.
The ultimate load was decreased by 14.5% and 7.12% when changing the bolt
diameter from 12 mm to 8 mm and 6 mm respectively.

It can be concluded that replacing bolts
with smaller ones with the same total cross-section area of the bolts will not
scientifically affect the capacity and failure mode of the bolted connections.

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