Structural Design for Vertical and Horizontal Enlargement
To alter the existing building’s structural system, several issues existed: (1) determining which of the permitted building codes, old or new, should govern the modifications; (2) choosing the appropriate structural design criteria; and (3) deciding how to engineer and construct the building’s new lateral load. A new lateral-force-resisting system was installed after the front wall was removed to maintain two such systems in each direction. In order to leave the space the entire space open, a moment frame system was designed to connect to the metal floor deck by puddle welds for diaphragm shear force transfer at each floor. To resist possible bow actions, steel straps welded to the moment frames were bolted into the brick walls to create sufficient bond to the sidewalls. The moment frame was discontinued at the second floor due to the beam interfering with the front stair opening. To transfer the shear forces securely, horizontal braces were designed at the second floor in between the moment frames. The steel moment frame ended at the basement on a concrete shear wall, which safely dissipates the lateral forces into the ground.