Northrop

The College wanted to provide a new learning centre for the arts. Northrop Structures was engaged to provide innovative design solutions for this largely underground $16 million performance space which was surrounded by heritage buildings. The project was completed in 2015.

The project includes a 3 storey underground structure containing: a 300 seat drama theatre, large ensemble classrooms and support spaces. As all of these facilities were required to be located within a very compact area of the campus surrounded by heritage buildings. The project also comprised of a delicate extension to a heritage building which included a 2 storey above ground concrete framed structure accommodating large adaptable classrooms. A new formal entry to the adjacent Chapel consisted of high-end exposed architectural steelwork, and off-form sculpture concrete walls.

We looked to solutions that complemented the restricted site and the large single span over the underground auditorium structure. We considered different building techniques and initially provided two structural concept schemes: Steel trusses and deep post-tensioned roof beams and slabs. The large 17m clear spans were further complicated due to transfer loads and floor vibration, due to rhythmic activities. We advised the design team on the constraints and structural opportunities for both concepts. Through collaborating with the design team these concepts were thoroughly tested and ultimately we adopted a post-tensioned concrete solution due to transport and erection constraints and it mitigated risk in relation to site tolerances and provided cost efficiencies. 

The early works included underpinning the existing O-Regan building to accommodate a new building foyer and back-of-house facilities. Both temporary and permanent pile underpinning and steel needle beams allowed for the construction of the 3 storey basement structure to be built adjacent to a heritage building.  We strategically placed piles to support the underpinning which could be incorporated into the permanent soldier piled shoring wall. As drawings for the existing building were not available a hands-on approach was needed during the Construction Phase. Unforeseen site issues were often solved through being pro-active and holding regular site meetings with the Contractor to problem solve issues as they arose. This collaborative approach ultimately meant the contractor keeping to their construction program.

Ground anchored soldier bored piers were utilised for the large excavation in soft rock. Due to the expansive open nature of the performance space both permanent and temporary ground anchors were adopted. We identified that further specialist geotechnical advice was required to assess the potential impacts of the proposed development on the adjacent Chapel structure. This meant working with the geotechnical specialist and providing them with input parameters, including the Chapel surcharge loads and recommending horizontal movement criteria for the shoring wall. This allowed the specialist consultant to produce a geotechnical finite-element model that accurately predicted the expected movements along the shoring wall. We also provided a performance brief to the early works contract which identified hazards and outlined a monitoring plan to de-leverage risk associated with the precarious excavation. The risk associated with this excavation were further reduced by working closely with the ground anchor sub-contractor and reviewing the detailed design, as well as nominating a strict ground anchor testing regime.

Due to the fractured nature of the soft rock ongoing seepage into the excavation through jointing in the rock-mass and along strata boundaries were a potential issue. We worked closely with both the Architect and Hydraulic Engineer to provide drainage recommendations and detailing to ensure an appropriate amenity of the below ground portions of the structure