CEDAR RAPIDS — Just one-half inch separates the foundation wall of trucking company CRST International Inc.’s new 11-story office tower, CRST Center, going up downtown and the city’s 12-foot-tall concrete flood wall that will stand directly in front of it.However, David Hayek, senior project manager for contractor Ryan Companies US Inc., said the building’s columns under the ground tie in to the concrete footing of the city flood wall to provide additional support for the office tower via building pilings under the flood wall footing.Hence, a complication: Who pays for what?The total project is about a $40 million one, and in August the City Council agreed to pay up to $3.95 million for its part.