How to repair cracked floor joist?

<p><span class="_Tgc">Set a hydraulic jack and post under the beam, and jack up the <strong>joists</strong> about 1/8 in. a day until they&#039;re level. Jacking them up too fast may cause <strong>cracks</strong> in the walls and <strong>floors</strong> overhead. If a <strong>crack</strong> or sag is isolated to one area, the sister <strong>joist</strong> should extend at least 3 ft. on both sides of the problem area.</span></p>