350 Summer Street is a 17-floor commercial high-rise in Boston, Massachusetts, built tight against an existing building. Moldtek handled the full structural steel detailing scope: 3,700 tons of main and secondary steel, plate girders, and davit support posts, and broke the tower into 91 sequenced packages so the model could be reviewed, released, and erected without stalling the site. The engagement ran to a 23.6-week schedule, and every connection where new steel met the existing structure was coordinated and field-verified before it went to fabrication.
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The complication on 350 Summer Street was never the height. It was the interface. The new tower goes up directly beside an existing building, and it ties into two existing levels — so the detailing had to reconcile new steel with existing columns, existing beams, and slab elevations that don’t line up cleanly.
The building rises directly beside an existing building, so clearances and access had to be coordinated rather than assumed.
New columns splice onto existing columns. Every splice location had to be field-verified before the connection could be finalized — a drawing-board guess here becomes a fabrication error later.
Level 2 carries both existing structure and new beams framing into existing beams, which made it the most coordination-heavy floor in the building.
Varying slab elevations around Level 2 meant connections couldn’t be copied floor-to-floor; they had to be worked out for the real geometry.
Joints between new framing and existing beams needed careful, case-by-case detailing rather than a typical detail.
The full frame was modelled to LOD 400 in Tekla Structures, so connections, copes and clearances were resolved in the model before a single drawing was issued.
Deliverables were packaged against the 91 erection sequences, letting the fabricator and erector work continuously while later sequences were still being detailed.
Moment and braced-frame connections were coordinated with the EOR and checked to AISC and AWS D1.1, keeping the connection-heavy core fabrication-ready.
Every sequence passed an internal “first time right” QC review for clash-free geometry before release, minimising site RFIs and rework.
Phases overlapped by design — connection design, shop drawings and erection drawings ran in parallel so the programme never waited on a full set.
The frame was detailed on Moldtek’s standard toolchain and delivered against US structural codes, so shop and field teams received drawings, models and CNC data ready to build.
Sequenced delivery kept fabrication and erection moving continuously, and the model-first QA gate kept the constrained site free of costly surprises.
All 3,700 tons detailed and released within the 23.6-week window that the erection schedule demanded.
Sequence-by-sequence release meant the fabricator and erector never waited on detailing to catch up.
Model-first detailing resolved the zero-clearance geometry up front, minimising site RFIs and rework.
| Project | 350 Summer Street |
|---|---|
| Location | Boston, Massachusetts, USA |
| Building type | Commercial high-rise |
| Scale | 17 floors + roof |
| Structural steel | 3,700 tons |
| Erection sequences | 91 |
| Delivery timeline | 23.6 weeks |
| Site condition | Built tight against an existing building (zero-clearance party line) |
| Moldtek scope | Full structural steel detailing — connection design coordination, fabrication & erection drawings, advance BOM and CNC data |
| Model accuracy | LOD 400 |
| Codes & standards | AISC, AWS D1.1, OSHA |
From constrained downtown high-rises to stadiums and industrial plants, Moldtek turns design intent into clash-free, fabrication-ready steel — on schedule.
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