The 1.1 Material The pultruded BFRP plate

The
well-known advantages of the FRP composites such as lightweight, corrosion
resistance, UV resistance, and low conductivity, promote it replace the steel
connections (plates and bolts). An experimental study was conducted at the
University of Southeast to study the behaviour of double shear lap, multi-bolted
connections fabricated completely from Basalt fibre-reinforced polymer (BFRP)
composite material (i.e., BFRP plates and bolts). Furthermore, this research
investigates the effect of several parameters such as number of bolts (4, 6, 8,
and 10), bolt type (SS, BFRP, and HSFRP), bolt arrangement, bolt diameter (6,
8, and 12 mm), hole patterns, the connection techniques (bonded, bolted,
bonded-bolted, injected), and effect of external BFRP layer on the behaviour of
BFRP connections.

This chapter (through following
sections) will present in detail the connection fabrication and configuration,
test set-up, instrumentations, experimental program and results of static
tests.

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1.1  Material

The pultruded BFRP plate which was
used in this investigation, was produced by GMV company Nanjing-China. The
pultruded BFRP plate is orthotropic and consists of unidirectional basalt
roving and three layers of bidirectional fibres; the first in top surface, the
second in the bottom surface and the third is in the middle. The three layers
were bounded with Sanyu L-500 resin.

Firstly, the basalt roving were
collected together as shown in Fig. 3-1a, submerged into resin and exposure to
heat. Afterward, they were extracted from a special mould for plates with the
required width and thickness as shown in Fig. 3-1b. The tensile and shear
strength of the resin are 30 MPa and 10 MPa respectively. Table 3-1 shows the
mechanical properties of the basalt fibres. The ratio of fibres to the resin
was 47% to 53%

High rigidity and low elongation at
break make Basalt fibres a popular choice for scientist and engineers to
replace steel and carbon fibres. Basalt fibres are characterized with
non-combustible, good resistance to alkaline and acids, and high chemical
stability. BFRP can be used in very low temperature and high temperature. It is
very cheap compared with carbon fibres and featured with high strength compared
to glass fibres. The most important feature for basalt that it is
environmentally friendly and non-hazardous materials. Thus, this study uses
BFRP as the main FRP material to help in promoting its application in the
practice. The bolts types used in this
investigation were stainless steel bolts (SS), BFRP bolts and hybrid steel-FRP
(HSFRP) bolts with three different diameters, M6, M8, and M12 (i.e., 6, 8, and
12 mm). The BFRP bolts were fabricated by using pultruded BFRP bars which were
cut into small pieces and then the bolts shank and the threaded part were
sculptured. For the fabrication of the HSFRP bolts, a small diameter stainless
steel bar was used as a core during the pultrusion process of the BFRP bars
(i.e., inner core made of stainless steel and surrounded by BFRP). Fig.3-2
shows the three types of the bolts. 3.3 Connection specimens

3.3.1 Connection fabrication

In
this study, the connections consisted of rectangular plates cut from large
plates with dimensions of 6000 x 120 x 7 mm (i.e., length x width x thickness)
on a table saw as shown in Fig. 3-3a. The plates were cut according to the
required length and width with an accuracy of ±2 mm. After cutting the plates,
bolts’ holes were drilled at the required distances and with the required
diameter using the drilling machine as shown in Fig. 3-3b. Three specimens were
prepared for each configuration. A total of 114 specimens were prepared and
tested under static tension load till failure. 3.3.2 Experimental Program

In
order to provide full understanding to the behaviour of the bolted connections,
six parameters were tested in this investigation which believed to have a
significant effect on the connection strength and behaviour. These parameters
are

1.     number
of bolts (4,6,8,10 bolts),

2.     bolts
type (SS, BFRP, HSFRP),

3.     bolt
arrangement,

4.     bolt
diameter (6,8,12 mm),

5.     bolt
pattern

6.     Connection
techniques (bolted, bonded, bolted-bonded, injected bolts).

In
addition, the effect of adding an additional layer of BFRP to the plate
surfaces in the transverse direction to the applied load.

The
plate thickness was kept constant for all specimens and equal to 7 mm. Edge
distance and pitch distance was constant according to the hole diameter, 5d and
4d respectively.

The
connection consists of BFRP main plate and two outer cover BFRP plates
connected through bolts. The geometric parameters were selected according to
EUROCOMP code (Clarke, 1996) and previous
studies (Hassan, 1995,
Abd-El-Naby and Hollaway, 1993,
Prabhakaran, Razzaq and Devara, 1996,
Wu, Feng and Bai, 2014), which stipulates the following:

1)     the
edge distance (e) shall not be less than three times the hole diameter,

2)     the
side distance (s) shall not be less than two times the hole diameter,

3)     the
pitch distance (P) shall not be less than three times the hole diameter, and

4)     The
hole clearance equal to 5% of the bolt diameter.

It
worth to mention that a finger tight was applied to all bolts. Also, all joints
had the same total length of 940 mm. The constant parameters of the connection
geometry which were used for all specimens, were summarized in Table 3-2. The
following sections provide complete details on each of the investigated
parameters.

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