THE UNIVERSITY OF AUCKLAND CLOCK TOWER EAST WING: A NEW LEASE OF LIFE

A. MARTEDDU1; R. A. ROGERS1; T. ALMEIDA2; P. HARTLEY3; N. BULLER4

1 BBR Contech, Auckland, New Zealand 2 Structure Design Ltd, Auckland, New Zealand

3 Salmond Reed Architects, Auckland, New Zealand 4 The University of Auckland, Auckland, New Zealand

SUMMARY The Clock Tower is arguably the most iconic building at the University of Auckland. It was originally constructed in 1923-1926 and is listed by Heritage New Zealand as a Historic Place Category 1. A seismic upgrade project was undertaken in 2015-2018 which focused on the East Wing building that is adjacent to the tower. The design and construction processes employed were developed through close collaboration between the project and heritage architects, structural engineer and contractors. A key driver for the project was to ensure that the heritage character of the building was not adversely affected by the seismic upgrade works. INTRODUCTION Brief Description The former Arts building at 22 Princes Street, Auckland, consists of the main block – also known as the Clock Tower – and a connecting student wing to the rear – also known as the East Wing – that used to house the Student’s Club for Auckland University College (now the University of Auckland) Council. These two buildings are interconnected via an open cloister (see Figure 1).

Figure 1. View of the Clock Tower from the East, with the Student Wing at Left (A P Godber Collection)

The East Wing building (see Figure 2) is two storeys, with a reinforced concrete suspended floor and a timber-framed/trussed roof. The perimeter walls are reinforced concrete clad in heavy limestone masonry. The lateral seismic resisting system is provided predominantly by the reinforced concrete walls around the perimeter of the building.

Figure 2. Aerial View of the East Wing Building from South The building is supported on shallow strip footings and pad thickenings under the main walls bearing onto weathered volcanic ash and tuff of the Auckland Volcanic Field. The cloister between the Clock Tower and the East Wing has a reinforced concrete roof bearing on unreinforced stone masonry piers. A parapet, approximately 1.0m above the concrete deck, is also unreinforced and topped with a large capping stone. At the southern end, the cloister roof is connected to the main block structure. Construction of the Building Since construction, many alterations to the internal layouts of the building have been undertaken, as shown in Table 1 below.

Table 1. Summarised Chronology of Construction Dates (Heritage New Zealand, n.d.) 1852 – 1923 Early history of the site

Site of Albert Barracks and gardens of the former Government House

1923 – 1926 Original Construction

Construction of Arts Building, with student wing

– 1968 Modification

Internal modifications

– 1986 Modification

Internal modifications

1985 – 1989 Modification

Tower strengthened

The University of Auckland drawing archive also documents first floor alterations c1978 and significant alterations at the ground and first floor c2004. Prior to 1978 most of the internal partition walls were removed presumably as part of undocumented refurbishments. Client Key Drivers and Objectives A seismic risk review carried out in November 2013 identified that several areas of the building did not meet the requirements of the Building Act 2004 and the building would likely be

earthquake-prone. Failure to comply within the allocated time frame would result in the building being vacated. The key drivers of this project were: • Existing use – mostly office space identified as Importance Level IL2. The earthquake

rating was calculated as 16%NBS(IL2). • Proposed use – teaching spaces identified as Importance Level IL3. Consideration was

given to upgrading to 100%NBS(IL3) but because of the building heritage rating, this level of upgrade would require a significant degree of compromise to its heritage appearance. As a result, a scheme for improving the seismic performance of the building was designed to achieve not less than 67%NBS(IL3).

• The refurbishment provided an opportunity to restore some of the building’s significant historical features and the new revised layout is more in alignment with the original design.

• The building was subject to several leaks and cracking to the stone cladding. These were addressed during the refurbishment.

• The associated risk with the seismic performance of the structurally connected Clock Tower and East Wing buildings. The cloister link provides the main access and egress route for two of the Clock Tower lecture theatres. In keeping with the Clock Tower previous seismic upgrade, the southern cloisters were to be upgraded to 100%NBS(IL3).

The main objectives of this project were:

• Teaching – refurbish the building to provide four new 50-seat size seminar rooms for teaching, crush space for group learning, and associated bathroom facilities, increasing the University’s ability to meet modern teaching demands.

• Historical – reinstate historical features of the building which include returning the roof to more durable clay tiles, attention to the cracks in the stone cladding and to water ingress, reinstate and refurbish the timber window and door joinery, and to visually reinstate the fireplaces on both ground and first floors.

HERITAGE Heritage Status and Notable Features The Old Arts Building is listed as a Historic Place Category 1 since 1st September 1983. Category 1 is defined as “places of special or outstanding historical or cultural heritage significance or value” (Heritage New Zealand Pouhere Taonga Act 2014, pt 4, s 65). The construction of the East Wing (see Figure 3) is integral to the main Clock Tower building, comprising of reinforced concrete elements encased in Oamaru stone.

Figure 3. Original Drawing of the East Wing First Floor Plan

CONTINUES TO CLOCK TOWER

The concrete provides the structural frame around which the stonework functions as weathering surface incorporating decorative architectural detailing. The duality of modern 1920s concrete construction concealed beneath an elaborate masonry skin represents the last decade of style over function in New Zealand during the twentieth century. In comparison with overseas developments, the design of the Lippincott Clock Tower and East Wing contrasts starkly with the Bauhaus buildings constructed in Dessau, Germany during the same period.

Lessons Learned from the Clock Tower The main Clock Tower building has exhibited long-standing problems of corroding reinforcement within the concrete frame, causing damage beneath and within the Oamaru stone, and past repair projects informed the potential for similar conditions of the East Wing building prior to the commencement of this refurbishment project. The design of the seismic upgrade addressed both the structural behaviour of the concrete and stonework elements, whilst localised cracking of individual stones alluded to damage in the concealed concrete through expansion of corroding embedded steel bars. Accessing the deeply embedded steel reinforcement has required more significant intervention than the scheme of seismic strengthening, but both aspects have required the involvement of skilled stonemasons. In this respect, both traditional conservation repair and the modern approach to the structural upgrade have partnered a sensitive approach to the building in recognition of its heritage status. DESIGN Critical Structural Weaknesses The following areas of the East Wing building were initially identified with a seismic performance falling below the 34%NBS(IL2) threshold or with potential for a more comprehensive seismic retrofit that would target improving the seismic performance above the 67%NBS(IL2) threshold:

• first-floor diaphragm connection to perimeter walls;

• roof level diaphragm capacity and structural connections to wall elements;

• stability of cloister parapets;

• existing cloister stone piers flexural and shear capacity;

• shear and flexural capacity of existing perimeter walls and associated foundation beams. Investigations Extensive physical inspections and some intrusive investigations were carried out during the design phase. These included the verification of geotechnical conditions, key elements and details and material testing. Specifically, concrete scanning and core testing were conducted and have identified unexpected as-built differences from the original drawings. No evidence was found of reinforcement in the spandrels immediately above the windows and in the lower segment of the gables or of interlocking/keying connecting the stone and reinforced concrete. Larger horizontal and vertical spacing for the wall reinforcement was also observed and extremely low concrete compressive strengths and significant variance between samples were noted in the test results, most likely because the concrete was hand mixed on site and placed with poor compaction.

An inspection of the timber roof structure was also carried out. Leaking box gutters were found and progressing decay was identified where the timber trusses were in contact with the masonry walls. At these locations, it was found that the masonry walls conducted water through to the timber trusses, raising the timber moisture content to levels usually associated with the onset of decay. These investigations were fundamental to identify differences between the available drawings and what had been built. Additionally, they provided an appropriate degree of confidence in the assumptions that were made. Improvement of Seismic Performance The major structural works proposed for the East Wing building and southern cloisters are summarised below. The strengthening schemes were designed to achieve at least 67%NBS(IL3) and 100%NBS(IL3), respectively, in terms of the expected performance for life safety (NZSEE, 2006).

• Construct new internal reinforced concrete blockwork masonry walls to improve the lateral load resisting capacity of the building and reduce the flexural and shear demand on the existing perimeter walls;

• Construct new reinforced concrete strip footings for the new walls and widen the existing footings around the building external perimeter with the construction of new reinforced concrete footings drilled and epoxied to existing. This will reduce the toppling demands and soil bearing pressures on the existing footings;

• Increase the in-plane capacity of the existing shear walls and reinforce with bonded post-tensioning;

• Increase the in-plane shear capacity of the first-floor diaphragm and reinforce its connection to the perimeter walls with the application of an externally bonded fibre-reinforced polymer (FRP) system;

• Construct a new plywood diaphragm at ceiling level and improve the structural connections of the ceiling and roof structure to the existing walls;

• Upgrade the gable end walls structural connections to the ceiling diaphragm and roof structure and install new roof plane diagonal bracing;

• Create a new seismic joint at roof level between the East Wing building and the southern cloisters;

• Reinforce cloister stone piers with bonded post-tensioning concealed within cored cavities;

• Rebond all capping stones to parapets and gables and secure the external facing stone to the internal reinforced concrete superstructure with Helifix ResiTies. This mechanical pinning and remedial tying system will prevent detachment from the wall at high levels of seismic shaking.

Seismic Analysis Procedure and Design Parameters The East Wing building structure satisfied the criteria for an equivalent static method of analysis, as defined in NZS 1170.5:2004 (Standards New Zealand, 2016). A three-dimensional analysis was carried out using a structural ductility factor of µ = 2.0 to determine rocking actions due to earthquakes (Kelly, 2009). Strengthening of the existing shear wall flexural capacity with bonded post-tensioning tie rods was achieved by (1) applying a pre-tension load to resist µ = 2.0 seismic actions and (2) limiting tie rod forces to below yield stress for µ = 1.0 seismic actions. An analysis with µ = 1.0 has also been used to determine design actions for floor diaphragms, the shear strength of walls, and to ensure there were no potential brittle mechanisms such as shear failure in walls.

CONSTRUCTION Strengthening with Post-Tensioned Bars Target: to increase the in-plane capacity of the existing reinforced concrete shear walls and cloister stone piers. The construction methodology involved core drilling 65mm diameter vertical holes from the top of parapet or roof gable down to foundation level, up to 12m deep. Tight tolerance on verticality was achieved while drilling straight down by accurately levelling the rig using a steel frame and an anchor installed into the existing structure. A total core drilling length of 635m was completed. A wet coring process was used due to restrictions on acceptable levels and hours of noise in the University of Auckland’s campus. Where drilling occurred through Oamaru stone masonry, typically at the cloister piers, 16mm diameter stainless steel Macalloy S650 bars were used. The bar end extended into the existing reinforced concrete footing and was embedded in a minimum of 1m of Mape-Antique I, a cement-free lime-based injection slurry. This product was specified because its elastic and mechanical properties are compatible with those of the materials originally used, have the capacity to eliminate the risk of condensation and avoid an alkali-aggregate reaction. Stainless steel bars were used for long-term durability since the lime-based products do not provide effective corrosion protection. However, setting and hardening times for lime-based mortars are longer than for cement-based grouts. In addition, geo socks were used as a grout retainer to prevent loss of grout as the existing substrate was extremely porous. Since the bottom anchorage relied on bar bonding length only, on-site testing was carried out to demonstrate that adequate structural bonding and pull-out capacity were achieved for the levels of post-tensioning required. The Contractor allowed for 28 days in the construction methodology for the product to cure and achieve its full properties prior to the application of an initial post-tensioning force of 26kN to the bar (see Figure 4). Core cavities were then pressure filled with Mape-Antique I over the core full height.

Figure 4 – Jack Set Up for Vertical Post-Tensioning

In the East Wing building, drilling generally occurred through reinforced concrete. High tensile alloy steel bars with corrosion protection were initially specified and the core was to be fully grouted over its full height with a high performance, non-shrink cementitious grout. However, due to limited tolerance and to reduce the risk of contamination, stainless steel bars, geo socks and cement-free lime-based products were used here also. An initial post-tensioning force of 80kN was applied to 25mm diameter stainless steel Macalloy S1030 bars. Anchor plates embedded in the new foundation tie beams were used due to the higher post-tensioning requirements. (see Figure 5). A top anchor plate and an anchor block containing additional spiral reinforcing steel (see Figure 6) were used to control the maximum permissible bearing stresses into the unreinforced stone (Ingham, 2011).

Figures 5 and 6. Bar Anchorage at Foundation Level (above) and Top of Gable (right)

A total of 104 stainless steel Macalloy bars were installed in the cores and these were pressure filled with 2143L of Mape-Antique I slurry. The concealment of the new steel tension bars has not visually impacted on the main East Wing building, but the requirement for wet drilling through the interface of the concrete and stone wall construction has introduced water into the fabric of the building. This technical necessity has required preventative measures of drying out and poulticing of internal wall surfaces to extract soluble salts mobilised by the localised saturation of concrete and mortar. Dry drilling would have alleviated this detrimental impact upon the heritage fabric, and this aspect requires careful consideration in future projects involving seismic upgrading. However, dry drilling must be balanced against additional noise, dust and longer construction times. Horizontal drilling was also required at the roof level of the cloisters to bind the slab into the piers. An aluminium frame was specifically made to hang from the parapet and support the drilling rig (see Figure 7). Pattress plates fabricated to fit with the construction era of the building were recessed into the stone and used as anchor plates for the post-tensioned bars. These were carefully set out to align with the stone joints and remain visible to celebrate the strengthening of the building (see Figure 8).

Figures 7 and 8. Rig Set Up for Horizontal Drilling (left) and Cloister Pattress Plates (right)

Strengthening with FRP System Target: to increase the in-plane shear capacity of the first-floor diaphragm and to reinforce its connection to the perimeter walls. The first-floor diaphragm slab was checked to account for the limited ability of the diaphragm to transfer forces and due to the very thin concrete topping with a low level of steel reinforcement (see Figure 9). To find the internal design actions, diaphragms were analysed separately using the truss method (Scarry, 2014).

Figure 9. Original First Floor Slab Details of

Reinforcement

The first-floor diaphragm was found to have inadequate strength in tension. An externally bonded FRP system was proposed to strengthen the slab and reinforce the connection to the perimeter walls. The existing concrete substrate strength is an important parameter for bond-critical applications of FRP systems and careful surface preparation is required to achieve an adequate adhesive bond between the FRP system and the concrete (American Concrete Institute, 2008). An extensive survey of the first-floor slab was carried out to map existing loose, spalled and cracked concrete. This included a hammer test of all areas (see Figure 10). The substrate also contained corrosion-related deterioration of reinforcing steel likely induced by the presence of unwashed beach sand in the original concrete mix. This could compromise the structural integrity of the externally applied FRP system and the substrate was repaired to meet the system requirements (American Concrete Institute, 2008). A total quantity of 8m3 of Sikafloor Level-30, a high performance cementitious, self-levelling and fast drying cementitious screed mixed with Sika Pea Metal aggregate was used to reinstate 15 to 60mm thickness of structural topping slab (see Figure 11).

Figure 10. Hammer Test Survey

Figure 11. Substrate Repair

Additional FRP strips were installed to supplement the corroded reinforcing steel. FRP strips designed for diaphragm action were also considered as a supplement to corroded mesh as required, to avoid duplicates (see Figure 12). A total of 650m2 of wet-lay SikaWrap-600 C unidirectional carbon fibre fabric strips was installed on the main slab (see Figure 13).

Figures 12 and 13. First Floor FRP System Partial Plan (left) and On-Site Installation (right)

The diaphragm connection to the perimeter walls was also strengthened with FRP strips. An epoxy curved fillet radius of 65-75mm was specified at re-entrant corners around the slab/wall interface to prevent stress concentrations and voids between the FRP system and the concrete. Unidirectional glass fibre fabric was installed using 230m2 of SikaWrap Hex-100G strips and 900No. SikaWrap FX-50 C carbon fibre ropes were also anchored into the wall to enhance the floor to wall connection and ensure adequate shear transfer. Temperature, humidity, and surface moisture at the time of installation can affect the performance of the FRP system. To overcome the bad weather conditions and effects of wet drilling, auxiliary heat sources were used to raise the ambient and concrete surface temperatures. A final screed was placed to protect the FRP system and to ensure a correct levelling of the slab. Sikafloor Level-30 mixed with HD polystyrene pearls with a maximum density of 1160kg/m3 was selected due to its lightweight properties. The floor capacity was assessed for the additional loading and pour was limited to a maximum thickness of 47mm at mid-span. Close coordination with both project and heritage architects was maintained to integrate the fillet and edge detail into the architectural finishes without any heritage impact. PROJECT LEARNINGS AND UPDATE Improving the seismic performance of the Clock Tower East Wing involved a significantly higher degree of consideration into the strengthening strategy than would be required for most other existing buildings. While a cost-benefit study was important to identify suitable strengthening targets and methodologies, some of these compromised the building’s heritage appearance and were subject to restricted discretionary consent by the Territorial Authorities. Close collaboration

between the client, project consultants, contractors and other stakeholders was vital to systematically explore and pursue solutions that went beyond more traditional approaches in recognition of the building heritage status. This project also highlighted the importance of carrying out inspections and investigations into the existing structure. There is often limited or incomplete documentation available and differences between available drawings and what has been built. Investigations were essential to develop an appropriate degree of confidence in the assumptions that were made or to develop further the design when required. The client’s key drivers and objectives were integrated into the design and construction of the full range of interventions adopted for this building. The final product will be a modern building with increased efficiency that may continue to be used safely for the functions of the University of Auckland while preserving its intrinsic heritage values. The construction site establishment occurred 23rd October 2017 and practical completion target is set as the 21st December 2018. ACKNOWLEDGEMENTS The authors would like to acknowledge the contributions of Architectus, as project architect; Greenstone Group, as project manager; Argon Construction, as the main contractor; and the wider project team for working collaboratively and finding solutions to ensure the project is a success. REFERENCES American Concrete Institute, (2008), “Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures” (ACI 440.2R-08). A P Godber Collection, Alexander Turnbull Library: APG-1862-1/2-G. Heritage New Zealand (n.d.) “Old Arts Building, University of Auckland List Entry Information”, from http://www.heritage.org.nz/the-list/details/25 Heritage New Zealand Pouhere Taonga Act 2014. Ingham, J., (2011), “Assessment and Improvement of Unreinforced Masonry Buildings for Earthquake Resistance”. Auckland: Faculty of Engineering, The University of Auckland. Kelly, T. E., (2009), “Tentative Seismic Design Guidelines for Rocking Structures”, Bulletin of the New Zealand Society for Earthquake Engineering, Vol. 42, No. 4, December, pp. 239-274. New Zealand Society for Earthquake Engineering, (2006), “Assessment and Improvement of the Structural Performance in Buildings in Earthquakes”. New Zealand Society for Earthquake Engineering. Scarry, J.M., (2014), “Floor Diaphragms – Seismic Bulwark or Achilles Heel”, Towards integrated seismic design. Auckland, New Zealand. 21-23 March. Wellington: New Zealand Society for Earthquake Engineering. Standards New Zealand, (2016), “Structural design actions Part 5: Earthquake actions – New Zealand” (NZS 1170.5:2004). Standards New Zealand.