1.1 Historical Context
- Expert witness advice for previous building constructed on deep alluvial soils highly prone to settlement.
- Building suffered 700mm settlement including 100mm differential.
- Geotechnical modelling, assessment and reporting.
- Undertook structural design and construction for the replacement building.
1.2 The Structure
- 113m x 20m building consisting of a 30x20m office space with a mezzanine floor, and a 87m x 23m workshop area.
- Screw piles apx 27m depth with pile caps
- Ground beams, steel-fibre-reinforced floor slab
- Fixed-base steel portals, roof spans apx 24m. CFS purlins, tension cross-bracing
- Intermediary gravity columns
- Internal steel beams
- Precast shear walls
- Rib & timber infill floor with void, supported by steel beams and concrete walls
1.3 Modelling and Analysis
Concept design generally done by hand, excel, MEMDES and other rough tools.
Preliminary/Detailed design ETABS Model for office structure
- Define load cases
- Gravity and live loadings, auto-lateral loading for wind and seismic
- ULS combinations (gravity combos, wind and earthquake combinations in each direction)
- SLS combinations
- Preliminary definitions for all structural and foundation elements
- Material definitions
- Input concept members
- Auto-selections
- Steelwork analyses
- Built-in automatic assessment to NZS3404 (steel standard)
- Adjust preliminary member sizings
- Check members generally match concept design
- Iteration and optimization
- Adjust deflection limits
- Adjust steel parameters
- Concrete analyses
- ETABS automated reinforcement design to NZS3101
- Define as shell elements, define boundary conditions
- Specify wall geometry and thickness
- Assess in-plane and out-of-plane behaviour
- Check shear, flexural, and axial loadings
- Rib & timber infill acts as diaphragm
- Seismic analyses
- Seismic loadings to ASNZS 1170.5 (EQ loading standard)
- Response Spectrum Analysis
- Warehouse area designed by colleague in SPACE GASS
- Manipulation of interactive database to support coordination between ETABS, SPACE GASS models. Assessment of lateral load sharing, deflection comparison.
- SAP2000 Model for foundation
- Microsoft Excel for:
- Stairs, calculated as a beam
- Canopy elements
- Strut & tie analyses
- Concrete connections generally via Hilti Profis Anchor
- Steel connections generally via Steel Construction NZ Connections Guide
1.4 Construction
We completed the drawings while overseeing construction. That had a lot of complications as well. I took two months to stay in Whangarei during construction.
- Construction sequencing
- Constructability during design
- Challenges during construction
- Screw piles installed then capped
- Ground beam reinforcement laid, including starters to slabs and precast panels
- Ground beams poured. Slab reinforcement laid.
- Review precast panel prefabrication drawings. Precast panels delivered and propped.
- Ground slab poured.
- Review steelwork prefabrication drawings. Portal frame legs installed, followed by spliced portal beams.
- Gravity columns and beams supporting internal office structure installed.
- Various additional elements installed; roof purlins, tension bracing, additional supports to mezzanine floor.
- Mezzanine floor ribs, formwork then pour. Slab poured above.
- The workshop side had other elements as well, which I haven’t covered, such as wind beams for garage doors, and the canopy structure.
By the end of it all we were as glad as we were relieved to sign the final paperwork certifying construction. And last I checked the building hasn’t settled yet!