Page 2 - Open-Access-September-2020

TECHNICAL PAPER

Officials (AASHTO) beam prestressed and reinforced with stress relaxation for the BFRP tendons was proposed based
[16]
carbon fiber-reinforced polymer (CFRP) tendons distributed in on experimental results, and a polynomial-based equation was
different layers was tested in which the failure was initiated obtained to express the relationship between the prestress ratio,
[3]
by rupturing of the prestressing CFRP tendons in the form of relaxation, and mechanical properties of the BFRP tendons.
sequential progressive failure. It was recommended to provide Due to their mechanical properties being different from that
the CFRP tendons in different layers along the depth of the of steel bars, such as higher tensile strength and lower elastic
beam cross-section to effectively address the issues related to modulus, the BFRP reinforcements are predestined for use in
brittle failure exhibited by the CFRP reinforcement . structures in which the ultimate limit state is rather decisive than
[3]
the serviceability limit state . Nonetheless, the flexural design
[17]
The BFRP composite has a tensile strength of about twice the philosophy for the BFRP-prestressed concrete (PSC) beams is yet
tensile strength of steel, however, a modulus of elasticity of arguable, if under- or over-reinforced section to be preferred.
about 40-50 GPa as compared to a typical 200 GPa for the steel,
which makes the elastic lengthening of the basalt bar much The aim of this present investigation is to study a design
more pronounced than that of the steel counterpart . The approach for the BFRP-prestressed concrete beams in flexure,
[4]
moment capacity of the prestressed concrete member with the as a partially prestressed under-reinforced section with multiple
BFRP tendons was studied and it was noted that the bending layers of tendons, using the unified design approach and the
[5]
moment and shear force distribution along the span significantly strain compatibility method, and to assess the flexural behavior
affected the failure mode. The basalt fibers with polyester resin from the experimentally obtained results and the finite element
were found to have a tensile strength of 19.3% more than the (FE) analysis.
glass fibers with epoxy resin ; therefore, basalt fibers could
[6]
possibly be used instead of the glass fibers. The use of the BFRP 3. DESIGN SPECIFICATIONS
bars as internal reinforcements for concrete members can be
promising while designing the beam for concrete crushing The beam was designed as an under-reinforced section, partially
[7]
prestressed with two layers of tendons, following the flexural
which can satisfy the serviceability requirements for deflection design philosophy provided in the ACI 440.1R 2006 . The
[1]
and crack width . The BFRP has been the most recently flexural design based on the traditional strain compatibility
[1]
introduced FRP composite material utilized as reinforcements method and the unified design approach is presented
[18]
[8]
and prestressing tendons for concrete . As compared to steel subsequently. The beam had dimensions of 200, 300, and
cables, the prestress losses in the BFRP are less , and grouting 2000 mm for the width, depth, and length, respectively. Because
[9]
has a significant effect in increasing the ultimate capacity and the FRP-reinforced concrete members have a relatively lower
reducing the deformability of the BFRP-reinforced concrete . stiffness upon cracking, the deflection after cracking becomes
[10]
Basalt FRP is a high-performance material with 20% higher greater in magnitude, and consequently the permissible
strength, about same cost, and more chemical stability as deflection under service loads may control the design. However,
compared to glass FRP, and lower cost as compared to carbon the recommended minimum depth (thickness) for the design
FRP . The possibility of utilizing the BFRP bars as internal of beams with the FRP is provided as L/10 for simply-supported
[11]
[1]
reinforcements for concrete beams was investigated and beam , where ‘L’ is the beam span, and this results in 180 mm
[12]
it was stated that prestressing should be used to keep the in the current study which is lesser than the provided overall
deflection within the acceptable limit due to the low flexural depth (thickness) of 300 mm. The designed beams were
prestressed by a prestressing force of 60% (33.66 kN) of the
rigidity of the basalt bars as compared to the conventional ultimate tensile strength of the BFRP tendon. The tension
steel reinforcement. Regarding the shear strength of the BFRP- reinforcements consisted of two prestressing tendons placed in
reinforced concrete beams, it is usually less than that of steel- two different layers (Figure 1) and two non-prestressing tendons
reinforced beams due to the lower dowel actions. Therefore, all with BFRP composite rods of 8 mm diameter. The shear
[13]
the BFRP-prestressed concrete beams without stirrups are reinforcements were made from steel rebars of 6 mm diameter
susceptible to failure under shear forces. with 125 mm center-to-center spacing near the supports and

It was stated that the BFRP reinforcements are relatively lighter 200 mm center-to-center spacing for the middle-third of the
and stronger than conventional steel with less embodied beam span. The longitudinal section and cross-sections of the
[14]
energy emissions and possessing a better environment impact beam are shown in Figure 1, wherein the cross-sections are
profile because reduced energy resources and materials shown for the same location (A-A') but in different test stages
are required for its production. The effect of the degree of of loading applied, such as (a) before failure, (b) after the first
prestressing of the basalt tendons on the performance in rupture of the lowest prestressing tendon (farthest from the
neutral axis), and (c) after the rupture of the second prestressing
flexure was studied , and it was concluded that increasing
[15]
the prestressing force reduced the average deflection, crack tendon in the next layer closer to the neutral axis.
width, and number of cracks in the BFRP-prestressed beam The mechanical properties of concrete, used in the laboratory
as compared to the non-prestressed beam. The coefficient of tests, and the BFRP reinforcing bar, are presented in Table 1.

20 THE INDIAN CONCRETE JOURNAL | JANUARY 2021