In addition to the stresses, the deflection of a skyscraper increases with height. By welding and bolting the horizontal girders to steel columns, the rigidity of the joint (Figure 7.25c) is increased, which helps reduce the sway, Skyscraper designs often have columns on the outer perimeter, which are connected to the central core columns. The outer columns act like flanges to resist most of the wind load, while the inner columns carry most of the weight. In modern skyscrapers, computer-controlled masses of hundreds of tons, called tuned mass dampers, move to counter the building sway. Today skyscrapers are also designed to move with earthquakes rather then stress the building frames.