First, read the English article below.

Move the bookcase out of the way. Use a yardstick to mark the center of the stud with a vertical line. If this is impossible, you can attach your brackets at the top, into a center stud. For tall shelves, this is the best place to secure a bookcase into a stud because it is the least noticeable place. You can also use door chain latches in place of L brackets if you want to move the shelf regularly. Install the chain on the wall and the slide on the top of the shelf.  Drill the other side of the L bracket into the wall with washers and three-inch wood screws. Drill until the screw head is almost even with the bracket, but avoid stripping the screw. If you can’t find a stud, you should install wall anchors before you drive screws into drywall or masonry. Drill a pilot hole into the wall and push the wall anchor in. Then, align the brackets and drill with three-inch screws. Place an L bracket between the wall and the side of your shelf, where it will hit a stud. Repeat the same procedure on either side of the shelf. 

Now, please write a short abstract for it in Indonesian. Abstract:
Keluarkan buku-buku dari rak. Gunakan pencari tiang kerangka untuk mencari tiang kerangka pada tembok Anda. Tempatkan lagi rak buku Anda ke posisi semula, pada posisi tepat di antara tiang-tiang kerangka. Gunakan tangga sampai Anda berada pada posisi yang nyaman untuk mengerjakan bagian atas rak buku Anda. Gunakan besi siku berbentuk “L” sehingga besi menempel pada tembok dan rak buku. Pasang besi siku “L” pada bagian atas rak buku dengan bor tanpa kabel dan baut yang lebih panjang daripada ketebalan rak buku. Mintalah bantuan teman Anda untuk menahan rak buku apabila rak buku agak miring ke depan. Ulangi pada kedua sisi rak buku.