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ABSTRAK
EFEK RESIDUAL STRESS TERHADAP KINERJA ELEMEN
LINK PADA STRUKTUR RANGKA BAJA BERPENGAKU
EKSENTRIK
Oleh
KURDI
NIM: 35013004
(Program Studi Doktor Teknik Sipil)
Efek tegangan sisa terhadap kinerja elemen link pada struktur rangka baja
berpengaku eksentrik penahan gaya lateral seperti beban gempa diteliti. Pengujian
secara eksperimen dilakukan dengan dua tahapan. Tahap pertama, sebanyak
delapan sampel dari elemen link diukur tegangan sisa dalam arah transversal,
longitudinal maupun normal. Besaran dan distribusi tegangan sisa diukur secara
eksperimental dengan cara Neutron Diffraction Method menggunakan alat DN1
PSTBM BATAN. Verifikasi secara numerik dengan uncouple transient thermal
static structural analysis dilakukan. Parameter geometri link seperti parameter
kondisi tumpuan saat pengelasan, luas daerah k, tebal pelat badan, jumlah lasan
dan jarak pengaku diteliti dalam penelitian ini. Selanjutnya, hubungan besaran
tegangan sisa dengan parameter dominan diusulkan untuk perbaikan kinerja dari
elemen link.
Tahap kedua sebanyak tiga link pendek yang telah diukur tegangan sisa diuji
menggunakan beban siklik sesuai denga pola pembebanan AISC 341-10. Satu link
merupakan link standar yang didesain sesuai AISC 341-10 dan dua link
modifikasi pada pelat pengaku badan. Perilaku elemen link dipelajari terutama
pengaruh tegangan sisa terhadap kinerja link. Hasil pengukuran menunjukkan
bahwa di dan sekitar area pengelasan antara pelat pengaku dengan pelat badan
serta pelat sayap atau yang biasa dinamakan daerah k menghasilkan tegangan sisa
tarik yang tinggi dan menjadi awal dimulainya crack saat beban luar diberikan.
Pemahaman yang baik mengenai besaran dan distribusi tegangan sisa saat desain
dan proses pengelasan dari elemen link terutama di daerah k, dapat meningkatkan
kinerja elemen link karena fraktur di daerah k dapat diperlambat, sehingga syarat
kapasitas inelastik sesuai AISC 341-10 dapat dicapai.
Temuan dari hasil elemen link modifikasi menghasilkan peningkatan parameter
kinerja link yaitu nilai daktilitas sebesar 30,90%, rotasi plastis sebesar 14,29%,
nilai overstrength sebesar 10,00% serta energi disipasi sebesar 41,56%
dibandingkan dengan link standar. Hasil pengujian eksperimental juga
menunjukkan bahwa nilai overstrength SNI 1729-2015 dan AISC 341-2010 tidak
cukup konservatif (tidak aman) terhadap nilai overstrength pengujian. Hal ini
menyebabkan desain elemen di luar link menjadi tidak aman sehingga harus
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diperkuat. Dari hasil penelitian ini, nilai overstrength untuk desain kekuatan
elemen di luar link (bresing, kolom, balok diluar link), diusulkan untuk dinaikkan
15% dari nilai overstrength SNI 1729-2015 dan AISC 341-2010.
Kata Kunci : tegangan sisa, link pendek, metode difraksi neutron, sruktur rangka
baja berpengaku eksentrik, daerah k.
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ABSTRACT
RESIDUAL STRESS EFFECT ON LINK ELEMENT OF
ECCENTRICALLY BRACED FRAME
By
KURDI
NIM: 35013004
(Doctoral Program of Civil Engineering)
This study determined the residual stress effects on the link element performance
of eccentrically braced frame as lateral force shields for earthquake loads.
Experimental tests were conducted in two stages. In the first stage, residual
stresses were measured in eight samples of the link elements in transversal,
longitudinal and normal directions. The magnitude and distribution of residual
stresses were measured experimentally by Neutron Diffraction Method using the
DN1 PSTBM BATAN tool. Verification was performed numerically using the
uncouple transient thermal static structural analysis. The study takes into account
the link geometry parameters, for example, the support condition during welding,
the extent of k area, the thickness of web plate, the number of welding and the
distance of stiffeners. Furthermore, the relationship between the magnitude of
residual stress with the dominant parameters was suggested for improvements of
link element performance.
In the second stage, the three shear links that had prior measurement of residual
stresses were tested using the cyclic loading as in the AISC 341-10 loading
pattern. The first link is the standard link designed as is the loading pattern of
AISC 341-10, whereas the other two links are modified links on the web plate
stiffeners. The behaviour of link element was studied with emphasis on the
influence of residual stresses to the link performance. The results of
measurements showed that the area on and around the welding area between the
stiffeners plate with the web and flange plates, or is commonly known as the k
area, generated high residual tensile stresses, hence initiated cracks during
external loading.
A good understanding on the magnitude and distribution of residual stresses
during the design and welding processes of the link element, particularly on the k
area, may increase the link performance as fractures on the k area may be
hampered, therefore could meet the requirements for inelastic capacity as set
forth in AISC 341-10.
Findings from the modified links resulted in overall increases of the parameters of
link performance, namely the ductility (30.90%), plastic rotation (14.29%),
overstrength value (10.00%) and dissipation energy (41.56%), compared to the
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standard link. The results of experimental tests also showed that the overstrength
values of SNI 1729-2015 and AISC 341-2010 were unlikely to be conservative
(unsafe) compared to the overstrength values in the tests. This has caused the
design of element outside of the link to be unsafe, therefore it has to be
strengthened. The research results of the overstrength value for the design of
resistance in the element outside of the link (bracing, column, beam outside of the
link) was suggested to increase 15% from the overstrength value of SNI 1729-
2015 and AISC 341-2010.
Keywords: residual stress, shear link, neutron diffraction method, eccentrically
braced steel frame structure, k area.