Beams are typically heat cambered by standing the beam up on its flange and supporting it at each end, with the supports reasonably close to each end of the beam. Heat is placed in the beam web in the shape of a "V", and the heated area extends to include the flange. The length of the "V" is typically is at least half the depth of the beam, and the "V" width depends on the beam size, the beam length, the amount of camber, and the number of heated "V"s along the length of the beam. You might want to try a "V" at 15 feet, 30 feet, and 45 feet for starters, and if that doesn't produce the desired camber, you can add more "V"s between those points. If you add more "V"s, you might want to reduce their depth and width, but that will depend on how much camber you have prior to adding them. You have to be very careful not to heat too much of a "V" area because the beam web will start to buckle. Also, your heat should not exceed 1100 degrees F. The amount of camber can be checked by pulling a string from one end to the other of the beam and measuring the difference in the middle. The end result will be a beam that has NO LESS than the required camber, with a nice continuous curve. You can't just put a "V" in the center and camber the beam. Without a continuous curve, the beam will not serve the full intent of its design requirements.