Bridge & Infrastructure Scanning in San Francisco, CA

San Francisco's bridge inventory divides three ways, and each part gets scanned for a different reason. Caltrans owns the state highway structures: the Bay Bridge west span and its approach viaducts over SoMa, the Central Viaduct carrying US 101, the Bayshore Viaduct carrying I-80, the elevated I-280, and the Alemany interchange. The Golden Gate Bridge at the north end belongs to its own district. And the city owns the movable bridges over the creek channels, all of them Strauss designs and all of them old: the Third Street bridge across Mission Creek, a 1933 heel-trunnion bascule renamed for Lefty O'Doul; the Fourth Street bridge, the Peter R. Maloney, a rare surviving vertical overhead counterweight bascule; and the Third Street bridge across Islais Creek, the Levon Nishkian, a double-leaf bascule of 1945.

What survey-grade scanning gives an engineer on those structures is specific. Vertical and horizontal clearance is computed across the full travelled width from a measured deck and soffit surface rather than from a few centerline shots, so the controlling low point is found instead of assumed. Structural as-builts capture deck, soffit, girders, bents, abutments, bearings, and expansion joints, and on a bascule the counterweight pit, trunnions, and machinery deck that no drawing set still describes correctly. Scour, settlement, and deflection get a baseline epoch that a later scan is differenced against, surface to surface. All of it runs off a control network observed with GNSS and total station and adjusted by least squares with independent checks, on NAD83 State Plane and NAVD88, and here on CCSF-CS13 and CCSF-VD13, which is a NAVD88 realization rather than an offset from it.

Field time is the constraint on a bridge, not office time. A scan position takes minutes, so a night lane closure or a window between vessel openings is usually enough, and any dimension nobody thought to ask for comes out of the archived cloud instead of a second closure. Deliverables are the registered cloud in E57 or RCP, clearance envelopes, scan-to-CAD sections and elevations in DWG or DXF, surface models, and epoch comparison exhibits. City-owned bridges funded through the federal Highway Bridge Program and Caltrans Local Assistance carry their own documentation expectations, and we scope to them. See infrastructure scanning, San Francisco 3D scanning, and deformation monitoring.