A search for expertise has stretched across the country in the effort to repair the Delaware River Turnpike Bridge.

The New Jersey Turnpike Authority and the Pennsylvania Turnpike Commission have hired four construction firms, eight engineering contractors, and two national engineering experts, including the man who first publicly identified welds as a factor that caused a crack in a beam in the bridge, to assist in the repair work. That crack prompted closure of the bridge Jan. 20, and it is expected to remain closed to traffic until at least April.

Karl Frank, professor emeritus at the University of Texas at Austin, looked at photos of the crack at the behest of the Inquirer and said plug welds, a now-obsolete technique used to fill unneeded holes drilled into a beam, created a structural weakness. Now, Frank has been brought on as a consultant.

Robert J. Connor, a civil-engineering professor at Purdue University, was also retained.

"At the end of the day, it was trying to bring in the best of the best from a national perspective in here," said Brad Heigel, the Pennsylvania Turnpike Commission's chief engineer.

The faulty welds likely weakened the beam, but engineers believe a sudden, heavy load may have created a critical moment for the compromised truss. They are investigating trucking records to determine whether a vehicle that exceeded the bridge's permitted weight crossed around the time the crack was discovered.

All told, the New Jersey Turnpike Authority approved more than $9 million in bridge-related contracts in January. The Pennsylvania Turnpike Commission is also managing contracts for the project, and approved a contract not to exceed $1 million with Modjeski & Masters, a Philadelphia engineering firm.

The first step in making repairs, jacking the cracked beam back into position, has yet to begin. The process of hoisting the damaged beam  into position, a distance of about half an inch, could take days. How the bridge's trusses react to that step will determine what repairs are needed, officials said.