STUDI EKSPERIMENTAL BUKAAN GANDA TERHADAP KAPASITAS LENTUR BALOK BETON BERTULANG

MOHAMAD MESRANTO

Abstract


Lubang pada penampang lateral balok beton digunakan untuk melewatkan jaringan utilitas pada bangunan bertingkat tinggi. Semakin banyak jaringan utilitas yang akan dilewatkan, akan semakin besar dimensi bukaan yang dibutuhkan. Balok beton bukaan ganda digunakan untuk mengakomodasi kebutuhan bukaan yang terlampau besar, sehingga bukaan ganda pada badan balok akan mengubah perilaku mekanik balok, mengakibatkan berkurangnya kekuatan dan kemampu layanan balok. Penelitian bertujuan untuk mengetahui perbandingan balok bukaan ganda terhadap balok utuh terhadap kuat lentur balok beton.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           


Studi eksperimental  tentang pengaruh bukaan ganda terhadap kapasitas lentur dibuat dua balok beton bertulang yang dibuat dari beton mutu normal dengan f’c = 35 MPa menggunkan acuan Standar Nasional Indonesia (SNI- 2843), sedangkan baja tulangan menggunkan D13 untuk tulangan lentur dan ᴓ8 untuk tulangan geser. Balok beton berukuran 200x 300x 3300 mm sedangkan lubang berukuran 80 mm arah vertikal dan 400 mm arah horizontal. Benda uji balok beton bertulang berjumlah 2 buah meliputi balok utuh (BUL) dan balok berlubang (BBL). Penempatan dua beban titik berada di seperempat bentang dengan bentang bersih sepanjang 2700 mm sedangkan dua lubang ganda ditempatkan 100 mm dari beban yang mengarah ketengah bentang. Rasio pembebanan  a/d = 2,53 menurut Chu-Kia Wang adalah daearah lentur geser, akan tetapi direncanakan retak lentur saja, sehingga di daerah bentang  geser diperkuat dengan tulangan geser (sengkang) dengan jarak 80 cm menjadikan   yang menunjukkan balok kuat terhadap geser agar retak yang terjadi membentuk retak lentur.


Hasil pengujian beton diperoleh f’c= 35,52 MPa untuk campuran balok utuh dan  f’c = 35,67 MPa untuk balok Berlubang, sedangkan mutu baja tulangan D13 adalah fy = 385,73 MPa dan mutu baja tulangan ᴓ8 adalah fy = 450 MPa.  Hasil penelitian menunjukan bahwa dengan adannya  dua lubang besar didaerah momen maksimal dengan rasio a/d=2,53 berpengaruh terhadap kuat lentur beton yang mengakibatkan  lendutan balok uji BBL yaitu 26,35 mm lebih besar dibandingkan BUL yaitu 11,60 mm pada saat beban sama-sama 60 kN, sehingga kuat lentur beton BBL mengalami penurunan dibandingkan BUL, akan tetapi lendutan balok uji BBL dibawah lubang lebih kecil dibandingkan dengan ditengah bentang, hal tersebut dikarenakan balok uji BBL didaerah lubang di beri perkuatan tulangan lentur, hal tersebut didukung dengan pola retak balok yang membentuk retak vertikal (retak lentur)  yang dominan ditengah bentang dibandingkan dibawah lubang, sehingga dengan adanya perkuatan tulangan lentur dibawah lubang membantu meminimalisir lendutan dan pola retak dibawah lubang.


Kata Kunci: Beton bertulang, Balok berlubang, Kuat lentur.


 The opening in the lateral cross section of concrete beam is used to skip the utility networks on high-rise buildings. The more utility that will be missed, the greater the required dimensions of the openings. Multiple openings concrete beams are used to accommodate the needs of the too large openings, so that multiple openings on the body of the beam will change the mechanical behavior of the beam, resulting in reduced strength and beam ability-service. The study aimed to determine the effect of the double openings toward concrete beam flexural strength.


Experimental study on the effect of double openings toward flexible capacity was made of two reinforced concrete beams which were made from normal strength concrete with fc= 35 Mpa by using the Indonesian National Standard reference (SNI- 2843), while the reinforcing steel used the D13 to flexible reinforcement  and ᴓ8 for flexural and moved reinforcement. Concrete beams measured 200x 300x 3300 mm while the openings was 80 mm vertically and 400 mm in the horizontal direction. The tested reinforced concrete beams amounted to 2 pieces including the whole beam (BUL) and the hollow beam (BBL). Placement of two load points were located on a quarter-span by clean span throughout 2700 mm while the two double holes were placed 100 mm from the load leading into the middle span. Loading ratio a/d = 2.53 according to Chu-Kia Wang is a moved flexible spot, however it was planned to be flexible cracked only, so that the moved span area was strengthened (stirrups) wioth the distance of 80cm, resulting ∅Vn > Vu showing the beam was strong against movement in order making the shear occurrence forms to be flexible shears only.


The concrete test result obtained fc = 35.52 MPa for mixed of whole beam and fc = 35.67 MPa for hollow beam, while for the quality of D13 reinforcement steel was fy= 385.73 MPa and the quality of reinforcement steel ᴓ8 was fy= 450 MPa. The result of the study showed that with two large holes in maximum moment area with ratio a/d = 2.53 affected to the flexibility strength of concrete, resulting the dent of BBL tested beam which was 26.35 mm larger than BUL 11.60 mm during the same load of 60 kN, so that the flexible strength of BBL concrete decreased compared to BUL, but the dent of tested BBL concrete under the openings was smaller than in the middle of span. it was because the tested BBL concrete in the openings area was strengthened by giving flexible reinforcement, it was supported by the concrete crack pattern which formed a vertical crack (flexible shear) which was dominant in the middle span than under the hole, so that with the strengthening of flexible reinforcement below the hole helped to minimize the dent and crack pattern under the hole.


Keywords: Reinforced concrete, beam openings, Flexibility strength.


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