I'd just like to inject my two cents about Tipping Mar's contributions to project's sustainability features, which includes resilience--a very important factor in a project's longevity and service potential--and green concrete mixes, to dramatically lower GHG emissions. As the seismic consultant to SFPUC, Tipping Mar implemented our extremely cost-effective innovative post-tensioned lateral system that returns a building to plumb after a seismic event--this means no permanent deformations after a very large earthquake, the kind that render a building uninhabitable until it is repaired, often to the tune of millions of dollars. In addition, our design solution (1) added a thirteenth story to an originally 12-story building owing to lowered floor-to-ceiling heights (equating to higher density, not to mention greater usable real estate); (2) trimmed the construction schedule owing to our optimized link-beam design that, in conjunction with our PT lateral system, reduced steel reinforcement by 50 percent; (3) saved the project $10 million in direct costs; and (4) decreased the project's carbon footprint by 7.4 million pounds of carbon dioxide emissions, owing to Tipping Mar's work with Central Concrete to design six different low-concrete specs used throughout the building.
For in-depth information, read Engineering News Record's cover feature on Tipping Mar and SFPUC:
http://enr.construction.com/buildings/sustainability/2012/0220-65279tensioning-eases-stress.asp 
