1) is obtained, which indicates the condition of the bridge is safe and feasible to operate."> 1) is obtained, which indicates the condition of the bridge is safe and feasible to operate.">
Uji Kelayakan Balok Prategang Berdasarkan Analisis Perilaku Frekuensi dan Lendutan Balok Hasil Pengujian Laboratorium
WAHYU SETYANINGSIH, Prof. Ir. Henricus Priyosulistyo, M.Sc., Ph.D.
2024 | Skripsi | TEKNIK SIPIL
Salah
satu parameter yang dapat menentukan syarat kelayakan jembatan secara teoritis
maupun eksperimen adalah nilai frekuensi alami jembatan. Laju kerusakan
struktur jembatan dapat dideteksi dengan perubahan nilai frekuensi alami
jembatan. Semakin tinggi tingkat kerusakan dan beban yang dipikul maka nilai
frekuensi alami jembatan umumnya semakin rendah. Namun, dengan adanya gaya
prategang pada tendon struktur jembatan beton prategang, nilai frekuensi alami
tidak mengalami penurunan yang signifikan antara sebelum dan setelah dilakukan
pengujian. Tujuan penelitian ini adalah menilai kapasitas jembatan prategang
dengan mengetahui perilaku frekuensi dan lendutan jembatan
beton prategang terhadap pengujian laboratorium.
Pengujian
mengacu pada SNI
1725:2016 terkait beban hidup berupa beban lajur “D” terbagi rata “BTR” dan uji
evaluasi batas lendutan. Sedangkan beban terpusat ditambahkan guna mencapai
batas izin lendutan maksimum pada jembatan, menggunakan hydraulic actuator.
Parameter lendutan diukur dengan alat LVDT yang diletakkan pada 1/3,
½, dan 2/3 bentang. Saat pengujian, getaran pada jembatan
direkam menggunakan alat accelerometer. Secara teoritis, penilaian beban
ditentukan menggunakan metode load rating factor yang mengacu pada
Pedoman Penentuan Nilai Sisa Kapasitas Jembatan (2011). Metode ini berfungsi
memperkirakan kapasitas dan mengetahui faktor keamanan struktur jembatan.
Berdasarkan hasil pengujian laboratorium dan pengolahan data, diperoleh
frekuensi balok sebelum dibebani sebesar
20,5 Hz dan setelah dibebani (seluruh beban diunload) sebesar 19,57 Hz.
Meskipun selisih nilai frekuensi tersebut tidak signifikan, penurunan nilai
frekuensi menandakan adanya retak halus pada balok. Retak terjadi ketika balok
diberi beban actuator 4,5 ton yang mencapai lendutan 5 mm. Hal tersebut
dibuktikan dengan perbandingan massa dan frekuensi dengan asumsi nilai kekakuan
yang sama. Ketika diberi beban actuator, microcrack terbuka,
setelah release beban actuator
microcrack kembali tertutup oleh pengaruh gaya prategang. Dari hasil
perhitungan load rating pada jembatan, diperoleh rating factor
(RF) sebesar 1,16 (>1), yang menandakan kondisi jembatan aman dan layak
beroperasi.
One of the parameters that can
determine the eligibility requirements of the bridge theoretically and
experimentally is the natural frequency value of the bridge. The rate of damage
to the bridge structure can be detected by changes in the natural frequency
value of the bridge. The higher the level of damage and the load carried, the
lower the natural frequency value of the bridge generally. However, in the
presence of prestressing forces on the tendons of the prestressed concrete
bridge structure, the natural frequency value does not experience a significant
decrease between before and after testing.
The purpose of this research is to
assess the capacity of prestressed bridges by knowing the frequency and
deflection behavior of prestressed concrete bridges against laboratory
tests. Testing refers to SNI 1725: 2016
related to live loads in the form of "D" lane loads divided equally
"BTR" and deflection limit evaluation tests. While the centralized load
is added to achieve the maximum deflection permit limit on the bridge, using a
hydraulic actuator. Deflection parameters were measured with LVDT devices
placed at 1/3, ½, and 2/3 of the span. During the test, the vibration of the
bridge was recorded using an accelerometer. Theoretically, the load assessment is
determined using the load rating factor method which refers to the Guidelines
for Determining the Residual Value of Bridge Capacity (2011). This method
serves to estimate the capacity and determine the safety factor of the bridge
structure.
Based on the results of laboratory
testing and data processing, the beam frequency before loading was 20.5 Hz and
after loading (all loads were unloaded) was 19.57 Hz. Although the difference
in frequency value is not significant, the decrease in frequency value indicates
the presence of fine cracks in the beam. The cracking occurred when the beam
was loaded with a 4.5-ton actuator that reached a deflection of 5 mm. This is
evidenced by the comparison of mass and frequency assuming the same stiffness
value. When given an actuator load, the microcrack is open, after releasing the
actuator load the microcrack is closed again by the influence of the
prestressing force. From the calculation of the load rating on the bridge, a
rating factor (RF) of 1.16 (>1) is obtained, which indicates the condition
of the bridge is safe and feasible to operate.
Kata Kunci : Prategang, Frekuensi, Lendutan, Microcrack, Rating factor