So many people jammed onto the Golden Gate Bridge for its 50th anniversary party that worried engineers did rapid calculations to make sure the span could support the weight, officials said. "The bridge flattened out, its whole arch disappeared," said Gary Giacomini, president of the bridge district board. "The bridge had the greatest load factor in its 50-year life." Officials estimate that 250,000 people crowded onto the bridge deck Sunday morning for a walk across the span. More than 500,000 others packed the bridge approaches, but were denied access by concerned authorities. At bridge district headquarters, meanwhile, engineers determined that the bridge was indeed capable of supporting the weight. Built to be flexible, the bridge can move 15 feet vertically and more than 27 feet from side to side, allowing for changes in weight or the powerful wind that often howls through the mile-wide channel that connects the Pacific and San Francisco Bay.