Konkrit pra-tegasan telah menjadi kaedah pembinaan yang penting dan lazim
digunakan dalam kejuruteraan jambatan. Rasuk jambatan pra-tegasan pra-tuang
mempunyai kelebihan dalam mengawal retakan dan pemesongan berbanding dengan
konkrit bertetulang konvensional, dengan itu rasuk jambatan yang lebih panjang boleh
dicapai. Dalam industri konkrit pra-tuang, standard rasuk jambatan pra-tegasan
pra-tuang standard kini dihasil menggunakan konkrit kekuatan biasa sehingga 50 MPa.
Dengan kemajuan dalam teknologi konkrit, applikasi konkrit kekuatan tinggi dalam
konkrit pra-tegasan mungkin dapat memberi kelebihan kepada industri. Oleh itu adalah
penting untuk mengetahui peratusan penambahan dalam kapasiti seksyen rasuk apabila
rasuk jambatan pra-tegasan direka bentuk dengan konkrit kekuatan tinggi. Kesan
konkrit kekuatan tinggi pada peratusan pengurangan dawai pra-tegasan juga dikaji.
Sebanyak 15 standard rasuk jambatan pra-tegasan standard model yang terdiri daripada
rasuk-I, rasuk-Y, rasuk-M, rasuk-U, rasuk-T terbalik dan rasuk-PRT dengan pelbagai
kedalaman dan rentang telah dikaji. Reka bentuk dan analisis dilakukan menurut
standard BS 5400. Tegasan dalam konkrit dan pemesongan diperiksa agar mematuhi
had kebolehkhidmatan. Didapati bahawa konkrit kekuatan tinggi boleh meningkatkan
kapasiti momen rasuk pra-tegasan. Namun begitu, standard rasuk jambatan sekarang
didapati tidak sesuai dilaksanakan dengan konkrit kekuatan tinggi kerana rasuk direka
bentuk untuk kekuatan konkrit sehingga 50 MPa sahaja. Penambahbaikan dalam
kapasiti momen dihadkan oleh tegasan dalam dawai pra-tegasan. Untuk kapasiti ricih,
didapati peratusan peningkatannya agak rendah dan boleh diabaikan. Keputusan yang
sama ditunjukkan pada pengurangan keluasan dawai pra-tegasan yang diperlukan.
Seksyen rasuk dan pra-tegasan perlu direka bentuk semula agar dapat menggunakan
sepenuhnya kebaikan konkrit kekuatan tinggi.
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Prestressed concrete has become an important and commonly used construction
method in bridge engineering. Precast prestressed bridge beam has advantage of better
cracking and deflection control compared with conventional reinforced concrete,
therefore longer span bridge beam can be achieved. The current standard precast
prestressed bridge beam produced in precast concrete industry uses normal strength
concrete up to 50 MPa. With the advancement of concrete technology, application of
high strength concrete in prestressed concrete might able to bring advantage to the
industry. This study was carried out to investigate the percentage increase in beam
section capacity when prestressed bridge beam is designed with high strength concrete.
The effect of high strength concrete on the prestress strands reduction is also examined.
A total of 15 standard prestressed bridge beam models consisting of I-beams, Y-beams,
M-beams, U-beams, inverted T-beams and PRT-beams with various depth and span
have been studied. Design and analysis were carried out according to BS 5400 standard.
The stresses in concrete and deflections were checked to comply with the serviceability
limit. It is found that high strength concrete is able to increase the moment capacity of
prestressed beam. The percentage increase is dependent on the sectional shape and
prestress design. However, current standard bridge beam is found unsuitable to be used
together with high strength concrete as the current beams are designed for concrete
strength up to 50 MPa. The improvement in beam capacity is limited by the stresses in
prestress strands. For shear capacity, it was found that the percentage increment is low
and negligible. The result showed the same case for the reduction in strand area required
where the percentage of reduction in strand area required is limited by the stresses in
prestress strands. The beam section and layout of prestressing strands need to be
redesigned in order to make full use of the benefit of high strength concrete.
Effect of high strength concrete on capacity of prestressed beam for bridge construction / Thai Kim Sing