correspondance

Walter Wriston

Chief Executive Officer

Citicorp

601 Lexington Ave

New York, NY 10022

Dear Mr. Wriston,

I have recently become aware of a potentially serious issue regarding the steel connections of lateral bracing installed on the Citicorp Center project. After careful deliberation, calculation, and correspondence with Alan Davenport and my team, I have determined the extent of the situation warrants your attention and needs to be addressed.

As mentioned, the issue resides in the gusset plate connections that bolt to the diagonal framing members. These are installed to handle the lateral force of wind that acts perpendicularly to the face of the building. However when considering the quartering force, (wind blowing diagonally acting on two faces at the same time) my calculations show an unforeseen behavior. The chevron braces of the wind-affected side in this situation experience practically zero lateral load while the braces on the opposite side are put under nearly double the lateral load of what is considered a standard operation. My concern does not lie with the steel members themselves, but with the bolted connections that have to transfer these loads to the rest of the structure.

My drawings initially called for these connections to be secured with full-penetration welds. During the course of construction, Bethlehem Steel issued a proposal to substitute the welds required per the construction documents with high-strength bolts as a cost saving measure. This substitution was reviewed and approved by myself admittedly without the proper calculatory due diligence.

I propose amending this situation with a retrofitted connection at the joint each lateral member. This process involves welding a two inch thick by six foot long steel plate to the over 200 bolted lateral connections in the building. The work can be expedited with a carefully coordinated schedule that will minimize interference with the normal functions of the building. I also suggest we coordinate a team to service the mass damper, a team to monitor the stresses imposed on the structure in real time, and finally a team to provide frequent weather predictions to mitigate any situations that may arise before this repair is complete.

With a well coordinated execution and deliberate planning I feel this situation can be resolved expeditiously. I look forward to hearing back from you soon to discuss the next steps moving forward.

Sincerely,

William LeMessurier