BALOK SEDERHANA (CONTOH SOAL DAN PENYELESAIANNYA)

Contoh soal

Hitung reaksi perletakkan, perhitungan bidang momen, bidang lintang, bidang normal dan gambar MDN jika sudut P2 adalah 45°!
Penyelesaian.
P2x = P2 . cos 45°
= √2 . ½ √2
= 1 KN
P2y = P2 . sin 45
= √2 . ½ √2
= 1 KN
Reaksi perletakkan
∑MA = - RB . 4 + P1 . 1 + P2x . 0 + P2y . 2 = 0
= - RB . 4 + 2 . 1 + 1 . 0 + 1 . 2
= - RB . 4 + 2 + 2
RB . 4 = -4
RB = 1 KN

∑MB = RA . 4 – P1 . 3 + P2x . 0 – P2y . 2 = 0
= RA . 4 – 2 . 3 + 0 – 1 . 2
= RA . 4 – 8
RA = 2 KN

∑Fx = 0
HA – P2x = 0
HA – 1 = 0
HA = 1 KN

Kontrol
∑Fy = 0
RA + RB – P1 – P2y = 0
2 + 1 – 2 – 1 =0
= 0..................ok!
Perhitungan Bidang Momen
Dari kiri ke kanan
MA = 0
MC = +RA . 1 = +2 . 1 = 2 KNm
MD = +RA . 2 – P1 . 1 = +2 . 2 – 2 . 1 = 4 – 2 = 2 KNm
MB = +RA . 4 – P1 . 3 – P2y . 2 = 8 – 6 – 2 = 0........OK!
Perhitungan bidang lintang
DA kiri = 0
DA kanan = +RA = +2
DC kiri = +RA = +2
DC kanan = +RA – P1 = +2 – 2 = 0
DD kiri = +RA – P1 = +2 – 2=0
DD kanan = +RA – P1 – P2y = +2 – 2 – 1 = -1
DB kiri = +RA – P1 – P2y = +2 – 2 – 1 = -1
DB kanan = + RA – P1 – P2y + RB = +2 – 2 – 1 + 1 =0...........OK!
Perhitungan bidang normal
NAD = -1KN (tekan)
Gambar MDN