Construction Practice 2Lecturer: Peter Falconer

Construction Report: 2006An investigation of the construction processes used in commercial building.

P. PremkumarB. ConstructionStudent Number: 1213020

Collaboration with other students:The following students formed a group for site visits and sharing of photographs, drawings and documentation.

1. Praveen Premkumar 2. Qu Juan (Olivia)3. Wenjun Sun (Wendy)4. Man Moi Chin

Acknowledgements:We wish to thank the following people:Paul Stone, Regional Manager, Ebert Construction for permission to use this siteMark Ebert, Construction manager for providing documentationVladimir Milinovic and Dieter Helm, Project Managers for providing documentationHans Stoffel, Site Manager for allowing us to visit the site

We are especially grateful to Mathew Reed of URS New Zealand and Mike Conneally of Buller George Engineering for giving us a large amount of time and detailed explanations of the engineering

Job DescriptionProject location:

130 Anzac Street, Takapuna

Legal Description:

Lot Numbers: 1 & 2DP: 117066Intended Use: Residential

Client: Takapuna Procurements LtdContractor: Ebert Construction LtdArchitect: Francis Co Architects LtdStructural Engineers: Buller George Engineers LtdEnvironmental Engineers: URS New Zealand Ltd

Contents

1.1 Site History........................................................................................................................11.2 Site characteristics.............................................................................................................11.3 Geotechnical investigation................................................................................................21.4 Environmental investigation.............................................................................................3Leachate................................................................................................................................3Water tables...........................................................................................................................3Test Pits.................................................................................................................................3Landfill gas............................................................................................................................3

2.1 The piles............................................................................................................................5Pile layout..............................................................................................................................5Pile testing.............................................................................................................................6Pile caps.................................................................................................................................6

2.2 Ground beams...................................................................................................................72.3 Tanking.............................................................................................................................72.4 Landfill gas protection......................................................................................................7The gas collection system.....................................................................................................7The protection layer..............................................................................................................8

2.5 Ground slab.......................................................................................................................9

3.1 Bracing............................................................................................................................10Wind loads...........................................................................................................................10Seismic loads.......................................................................................................................10

3.2 Shear walls......................................................................................................................113.3 Floors...............................................................................................................................12Deck Floors.........................................................................................................................12

3.4 Columns and beams........................................................................................................133.5 Stairwell and lift shaft towers.........................................................................................13Vertical joints......................................................................................................................14Horizontal joints..................................................................................................................14Joint seals............................................................................................................................14

3.6 Exterior Claddings..........................................................................................................143.7 Fire resistance..................................................................................................................153.8 Roof.................................................................................................................................16

4. References...........................................................................................................................175. Appendix.............................................................................................................................18

1. Introduction...........................................................................................................................1

2. Part A. Foundations...............................................................................................................5

3. Part B. Structure and External fabric..................................................................................10

1. IntroductionThe development is located on the corner of Anzac Street and Fred Thomas Drive, Takapuna. The owners of the site, Takapuna Procurements Limited, are building 134 apartment units made up of 3 apartment blocks and a podium. The apartment blocks and podium will be built over a single level carpark. Ebert Construction Limited is the main contractor and it is a build only contract.

The site forms part of the closed Barry’s Point Landfill. The site is bounded by Anzac Street along the northern boundary and Fred Thomas Drive on the western side. There are existing developments on the southern and western boundaries.The depressed nature of the site means that the northern boundary along Anzac Street is approximately 8 metres higher than the southern boundary. The apartment blocks are laid out on three sides of the site perimeter with the podium providing a common recreational area in the centre.The development has a fairly long history. The original development was proposed in 1999. Since then the site was sold to the current owners and the design has undergone many changes. Building on the site started in October 2005. The particulars of the site have greatly influenced the final design of the structures.

1.1 Site HistoryThe site is approximately 700m from Lake Pupuke. This lake was formed by the explosive eruption of Pupuke volcano about 150000 years ago. Prior to this successive lava outflows created basalt layers around the volcano. These basalt layers were quarried and this quarry operated until the 1930’s. The quarry was then used as a landfill and the initial filling of the quarry took placed at the Anzac street end. Refuse is reported to have been placed in the quarry from 1930 onward. The landfill was closed in the 1960’s and since then the land has been developed and zoned for various purposes, predominately commercial and numerous developments have been built. This particular site remained occupied by the council and was used as a storage and maintenance depot until its sale. Most recently the site was used for storage of shipping containers and as a carpark. Since 1989 the redeveloped landfill area has been closely managed for both landfill gas and leachate.

1.2 Site characteristics The site is Business 9 zoned by the North Shore City Council. The site is depressed as shown in figure. The made up ground (Emmitt & Gorse, p. 57) is level and was covered in grass. The northern bank and part of the eastern boundary consists of fissured basalt. Springs emerge at the base of the northern bank and the water flows in a ground channel around the northern and eastern perimeters into a concrete channel near the bottom end of the eastern boundary. The site is very wet along the northern bank and extremely wet in the north western corner. This corner receives very little sun during summer and no sun during winter.

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The ground along the southern boundary has been covered with gravel/metal layers to provide an access road but the plastic nature of the soil is still very evident. The soil heaves a great deal around the tyre tracks of vehicles using the road. The soil consists of layers of clay and landfill material.

There are shrubs and two trees, an oak and a pohutakawa along the western bank. This is the area that receives the most sunlight. The basalt bank along the eastern boundary intrudes on the proposed development area and needed to be chopped further back. There is however an existing development, 124 Anzac Street, along this eastern boundary. Reinforced masonry retaining walls and a short section of piled retaining wall had to be built to support this existing development (see figure 1). These piles were driven to a depth of 4.5m and timber infill placed. Concrete was poured in place. This retaining wall supports the columns of the second storey floor of the existing development.

The site is permanently fenced with a large double gate providing easy access. The site is spacious with plenty of room for offices sheds, smoko, latrines and storage. There are two tower cranes installed on the site. Their positions are shown approximately in figure 1. There is an area of dead space shown which the tower cranes cannot service. The construction needed to be sequenced in a way that provided a mobile crane access to this area.

Asda Plaza 1 (Takapuna Bowling Alley) is the development along the southern boundary. This development enjoys a right of way over the site. An access road along this boundary had to be incorporated into the design of the development (see figure 1)All noisy construction work on the site can only take place between 7.30 am and 6 pm, Monday to Saturday.

1.3 Geotechnical investigationInitial geotechnical investigations carried out on the site was limited to depths of 6m. The results indicated landfill over clays, peat and silt. (See figure 2). The thickness of the landfill averaged 3m but varied from 1.9m to 5.3m. Since a multi-storey apartment development was envisaged piling was required. Further technical investigation was therefore undertaken in July 2002.In this investigation six machine drill holes were sunk to depths of 30 to 37m. The boreholes were spread out over the site. Three boreholes were completed cored except through the landfill material. The other three boreholes were done by wash boring to a depth of 28m followed by coring to the terminal depths.The report concluded that driven steel piles should be founded beyond 29.5m with capacity testing recommended to assess the pile capacity.

1.4 Environmental investigationThe company URS New Zealand Limited and its predecessors, Woodward Clyde (NZ) Limited and Murray North Limited have been involved with monitoring and controlling

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landfill gas and leachate at the Barry’s Point Landfill since 1989. In addition the past and present owners of this site envisaged many modifications to their central idea of a multi-storey apartment development. These modifications required much investigation. This was all done by URS New Zealand Limited. The company has therefore extensive data and understanding of the conditions in and around the site.

LeachateLeachate samples are slightly acidic with a low chemical oxygen demand. These results are consistent with aged refuse.

Water tablesWater table depths ranged from 0.8m to 2.3m across the site and the monitoring results indicate a ground water/leachate flow in a southerly direction. Water table depths remain consistent over time but are expected to vary once the development is complete.

Test PitsTest pitting was carried out in 2002 and again in 2004 to assess the contamination of the soils and the corrosion requirements for steel piles.The soil quality was better than expected and included household refuse and inorganic fill material. Subsequent chemical analysis of the soils showed some contamination. Contamination levels were sufficiently low allowing soil excavated to be suitable for disposal at the Redvale Landfill.Soil and groundwater corrosivity assessments were undertaken by a separate company, Les Boulton and Associates (M. Reed, personal communication, September 6, 2006). Soil chemistry, pH, and ground water/leachate chemistry showed moderate corrosion rates that required a sacrificial steel allowance of 0.05mm per year. (D. Coats, personal communication, 28 June 2005).

Landfill gasThe composition of landfill gas and its subsequent movement through and escape from the landfill material poses significant health and safety risks for the development. Methane and carbon dioxide may pass through cracks in the floor slab and accumulate in rooms inside the building. It was necessary to incorporate landfill gas protection measures into the design of the development.Landfill gas monitoring on the surrounding landfill ground have been undertaken since 1989, but on the site it has not been extensive. In 1994 six additional probes were installed on the site The monitoring results reveal that;

Refuse material within the site is continuing to biodegrade at a low rate. Methane concentrations vary considerably between test probes and with time. High levels of methane 90% by volume exist along the southern boundary with

Takapuna Bowling alley.

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Carbon dioxide levels are much lower than normally expected; <11% by volume. Horizontal migration of landfill gas into the site from other parts of the Barry’s Point

Landfill is uncertain but appears to be low. In addition the landfill gas production rate of the site was modelled using the US Environmental Protection Agency landfill gas emission model. Based on the inputs chosen the model predicts an overall landfill gas emission rate of 2.8m3 per hour and a methane gas emission rate of 1.3 m3 per hour. This is equivalent to about 400 ml of gas per hour per square metre.Despite the age of the landfill on the site and the low emission rates the concentrations of landfill gases in the ground remain high. In February 2005 URS New Zealand prepared a report in support of the resource consent application. The report recommended that certain passive landfill gas protection measures had to be included in the design of the development to prevent the risks of explosion, asphyxiation and ill health. The protection measures incorporated into the design are

Maintain the existing ventilation trench along the southern side of the site Install a subsoil venting system beneath the carpark floor slab Seal the ground surface under the carpark floor slab and any ground level structures

using an airtight membrane to prevent the entry of landfill gas. Elevate all residential areas above ground to allow natural ventilation beneath these

structures Underground services must be vented and sealed to prevent gas migrating along

service lines or service trenches Incorporate gas monitoring points

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2. Part A. FoundationsThe landfill material and the subsoil layer beneath did not have the bearing capacity to support the load of the building. A piled foundation had to be used. The geotechnical investigation of the site identified a load bearing sandstone layer at a depth of 29.5m. This depth is considered to be long (Mitchell p. 87&85).

2.1 The pilesDue to the length and rock layer into which the piles had to be driven it was necessary to use steel piles. The proximity of two schools, the residential apartments across Anzac Street and the adjoining developments led the structural engineers to initially specify screw piles in the design. These piles do not cause much noise or vibration during installation. Due to the long lead times (9 weeks) for importing these from Australia it was necessary to change the design and to use standard 300 MPA grade universal columns (UC) with much shorter lead times ( 2weeks). The UC’s were driven into the ground and into the sandstone layer with an embedment depth of 2m. They are classified as end bearing piles because the ends of the piles rest on the load bearing stratum and they transfer their loads onto this layer. The feet of the piles were not fitted with any shoes. Shorter 15m sections were first driven into the ground. When these lengths were almost fully driven additional lengths were weld to their tops. The sections had to be vertically aligned before welding. The piles were driven using a 7 tonne hydraulic hammer falling through 1.5mThe development needed 122 piles. The piles design took into account future steel loss due to corrosion. Different UC sizes were used 150, 200, 250 and 310mm. The piles were arranged either singly or in groups. The smaller section piles were predominantly used to support the podium and the single storey office and foyer buildings.Groups of piles or pile clusters were used where the bearing capacity needed was greatest. There were groups of 2, 3 and 4 piles.The piling was done by Hauraki Piling Ltd and was the single largest expense incurred for the development.

Pile layoutThe structure and piles are arranged in a rectangular grid. There are several advantages to this, (some of these are listed in Foster, 1994, Part 1):

The structural calculations are easier Loads on the structure are transmitted evenly to the foundations. This minimises

differential settlement. Structural columns and beams can be of the same size. This allows repeated use of

moulds and formwork It minimises the variation in rebar sizes Traffic flow and car park spacing can be optimised

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Pile testingAn independent company Tonkin and Taylor undertook dynamic testing of the piles. Dynamic tests give a better indication of the long term pile capacity compared with a test done at the end of the pile driving (Hauraki Piling, 2006). Dynamic test are done by striking the pile with the hydraulic hammer used in the pile driving rig. Transducers and accelerometers are bolted to the pile and “as the pile is struck the equipment means the force and the acceleration of the pile” (Emmitt & Gorse, 2006, p.106). The information is then processed with a Pile Driving Analyser (PDA). A sample of 21 piles was tested and all individual piles tested exceed the calculated ultimate bearing capacities. Several piles were installed out of vertical including one 2 pile cluster where the piles were inclined toward each other. The raked installed of some piles is attributed to buried obstructions.

During pile driving compressive stress is set up in the pile and the length of the pile shortens slightly. The length does recover when driving it stopped. The pile tests also revealed that the maximum permissible compressive driving stresses within two of the smaller section piles (150 and 200 mm sections) piles reached 290MPa. This exceeded the calculated maximum of 270 MPA for 300 MPa grade steel. The over-stress was attributed to the significant skin friction and the difficulty of delivering small blows using this particular hydraulic hammer. No damage to the piles was observed. The maximum stress recorded during testing of the large 310mm piles was 252 MPa which is less than the maximum permissible.

Pile capsWhen the piles were driven to the required set (embedded 2m into the sandstone) the excess exposed lengths were cut and the soil cleared around the pile heads. The soil is cleared according to the design of the pile cap intended for the particular pile or pile cluster. Shear studs 19mm were welded at 150mm centres along the flanges of the UC to a depth of about 1100mm. The purpose of these studs is to create a strong bond between the concrete pile caps and the UC. The steel and concrete will then act together to resist shear stress developed under load (Emmitt & Gorse, p.314).Reinforcement cages made from deformed mild steel bars are placed over the pile heads. These reinforcement cages varied according to the size of the pile or pile cluster. The reinforcement was tied into horizontal reinforcement cages bars intended for the ground beams. The vertical column reinforcement was also added. This is done to provide structural continuity between the elements.Wooden formwork is built around this arrangement of steel and concrete is poured to create the pile caps. Different types of piles caps are created for the different sized piles and pile clusters.

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2.2 Ground beamsDue to the length of the piles and the weakness of the upper soil layers it is necessary to link all the pile caps together using reinforced ground beams. “Linking the piles together is always done if there are less than three piles under a load” (Foster, 1994, Part 2, p.86). The reasons for linking them together with ground beams are

It stops the sideways displacement and rotation of the piles. It provides a margin of safety when there are less than three piles under a load It is cheaper than installing three piles under a load.

The ground beams are made from reinforced concrete. The ground beam elevations change to accommodate the penetrations through the beams. These penetrations are required for the drainage pipes, gas ventilation pipes. PVC sleeves running between the reinforcing bars are placed inside the formwork. These are held in place by placing the reinforcing ties and stirrups up hard against the PVC.The size and RL of these beams varied across the site. The ground beams across the podium were 100mm lower than those beneath the apartment blocks except in one area where they where 400 and 500mm lower. This reduction was to allow for drainage pipes to pass above the ground beams.The largest beams 700 x400mm were those beneath the shear walls of the apartment blocks and the stairwell/lift shaft towers. The beams were smaller elsewhere. Double row of starter bars were placed in the reinforcement cages of most of the ground beams. The double rows was required to tied in the ground slabs of the adjoining rectangular cells .The ground beams under the shear walls had triple rows of starter bars the inner most row was tied into the ground slab while the two outer rows were part of the wall reinforcement.

2.3 TankingThe lift pits were approximately1500mm below FFl. The water table was higher than this and near the northern bank the water table was less than 500mm below ground. To stop water penetration into the lift pit the lift pit walls were waterproofed.

2.4 Landfill gas protection.Two of the landfill gas protection measures mentioned earlier is incorporated into the foundations. The first is a passive landfill gas collection system placed in the foundations and the second is the sealing of the ground between the ground beams.

The gas collection systemThis system is placed in the soil between the ground beams, in an approximately 500mm deep layer called the ventilation layer. The following description of the system should be read in conjunction with drawing number G-010 Version 0 in the appendix.

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An array of slotted PVC pipes 65mm called laterals are placed horizontally, the green network of pipes (fresh air intake) allow fresh air into the soil and the red network of pipes (gas collection) collect the landfill gases. Both sets of laterals are connected to a main PVC pipe 150mm. These mains are connected to stacks running to the roof. The gas collection stack has a wind driven cowl attached to the opening. This causes a vacuum to be produced inside the gas collection pipesThe mains are laid at a grade with an allowance for subsidence; there is condensate collection drains placed at the low points. The fresh air main is slotted while the gas collection main is solid. This is done to maintain the vacuum to all the laterals. The fresh air main is designed as a ring main running around the perimeter of the development. This done to prevent any obstruction in the main from cutting off the fresh air supplied to the rest of the laterals.The presence of the ground beams caused some difficulties. The laterals and mains must pass through the ground beams. To avoid the horizontal reinforcement bars in the ground beams the system had to be placed 200 mm lower than originally planned. The ground beams created a rectangular grid of cells. A ventilation layer was created within each cell with one fresh air lateral and one collection lateral. Since the cells are in rectangular alignment the length of a pair of laterals was increased to serve more than one cell. To place the laterals the ground in each cell had to be prepared as follows:

A layer of soil is removed Shallow trenches are dug to accommodate the laterals A metal layer is placed over the ground surface and lines the trenches A geotextile fabric is placed over the metal layer. The laterals are placed A thick layer of scoria is the placed on top of the geotextile and fills the entire cell The top of the scoria is then covered with the protection layer which seals off the top

of each cell

The protection layerThe surface of each cell beneath the carpark is sealed off using a multiple layers of geotextile and gas proof membranes. There are two types of protection layers The areas that are not elevated above the carpark such as the ground floor offices, foyers stairwells storage rooms and lift shafts are sealed off using a flexible polypropylene membrane sandwiched between two layers of geotextile. The polypropylene is 750 microns thick. It is thicker and tougher than the polyethene. It is also much more expensive it is for this reason it was not used over the entire area. The edges of this protection layer are sealed using a 38x3mm aluminium strip attached with Ramset drive pins at 200mm centres.

The protection layer under the carpark floor slab consists of two layers of 250 micron polyethylene sandwiched between two layers of geotextile. The edges of this protection layer end on the top edges of the ground beams.

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The top edges of the ground beams had to be cleaned and dried using hot air. A bituminous paint was applied to waterproof the beams and butyl tape sealed the plastic membranes to this waterproofed strip. The upper geotextile layer then overlaid this seal.

The concrete slabs poured over these two types of edge sealing would then permanently seal the membranes into the concrete.

Two types of gas monitor probes were created; one was 3000mm deep and the other 200mm deep. The shallow probe monitors the ventilation layer while the deeper probe monitors the landfill material and is referred to as a standard probe. The probes were usually placed in pairs and spread of through the carpark. There are 6 sets of probes and two standard probes.This passive gas collection system was designed to remove 2m3 of gas per hour. These probes passed through the protection layers and therefore a third type of sealing detail was necessary.

2.5 Ground slabThe development consists of three separate apartment blocks and a podium level. These are all elevated above a carpark area. The apartment blocks and the podium are structurally separated by seismic joints.The reinforced concrete carpark floor slab is however continuous throughout the carpark. This means that the floor slab beneath each apartment block is connected to the carpark slab beneath the podium. Saw cuts 40x2mm provides crack control joints. The slab around each column has diamond shaped crack control joints. The carpark floor slab contains a great deal more reinforcement than that required for a drive on slab. D16 bars at 300 centres each way are used. The starter bars from each ground beam are also tied into the slab reinforcementThe large amount of reinforcement used is due to seismic design requirements. Any energy generated by the movement of the building during seismic events must be returned to the ground via the ground slab. It acts as a structural diaphragm (M. Conneally, personal communication, 11 September 2006).

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3. Part B. Structure and External fabricThis development consists of three separate apartment blocks and a podium. This section will report only on the structural details of Block A.Block A is made of reinforced concrete. Alternatives were considered, but were ruled out (M. Conneally, personal communication, 11September 2006). For economy and safety it was decided to use a framed concrete structure consisting of columns, beams and in situ cast shear walls at the flank ends of the building. The floors and beams are precast. The stairwell/lift shaft tower is built of precast concrete panels. The external fabric is independent of the structure and it is attached either to the timber infill walls or the concrete frame

3.1 BracingIn designing the structure the engineer took account of earthquake and wind loads. These loads will exert horizontal forces on the building and these forces may be exerted from any direction. In this development it was sufficient to consider only to two main directions; the longitudinal direction which is the long axis or length of block A and the transverse or lateral direction at right angles to the long axis. If the structure of Block A is strong enough to resist the maximum anticipated loads in these two directions then horizontal loads from all other directions would then be accounted for.

Wind loadsFrom a structural engineering view the building can be regarded as a ‘beam’ cantilevered from the ground (M. Conneally, personal communication, 11 September, 2006). Wind loads along either the longitudinal or the lateral directions will cause the ‘beam’ to bend. In the longitudinal direction the ‘beam’ has great depth and wind loads are transferred to many rigid columns and beams which provide sufficient stiffness to resist any bending. In the lateral direction wind loads on the cladding, glazing and floors are transferred to only two rows of columns. It was therefore necessary to provide extra stiffness to limit the lateral bending of the ‘beam’. This was done by constructing reinforced concrete shear walls at either end of the building. (Foster, 1994, Part 2, p. 172).

Seismic loadsDuring seismic events the ground will move both vertically and horizontally. In general the vertical movement will be small compared to the horizontal movements (Millais, 2006 p. 18). The precise nature of the load is unclear but the effect will be horizontal loads similar to wind loads. Again it is the beam and columns in the longitudinal direction that will provide the necessary bracing, while the shear walls will provide bracing in the lateral direction. The structural engineer must provide the structural joints with sufficient ductility and shear strength. The way that this is done by:

providing sufficient longitudinal reinforcement and anchorage

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providing sufficient transverse reinforcement and anchorage providing sufficient strength to the piles, pile caps and their connections.

3.2 Shear wallsThe shear walls form the flank end of the building. Horizontal loads are resisted by the depth and stiffness of the shear walls but these loads have the effect of causing the wall to lift at one end and compress at the other end. This tendency to overturn is resisted by the piles and the ground beam joining these piles. The corners of the walls must resist a greater loading so 3 pile clusters are placed under the corners of the walls with individual piles placed at intermediate points. Door openings are centralised and at ground level the large 700x400mm ground beams compensate for these openings.At each floor level two columns are incorporated into the shear walls . Gaps were left in the shear wall shuttering. Plywood formwork was created around column enforcements placed in these gaps. Reinforcing bars were tied into the shear wall sections using threaded inserts cast into the 200mm face of the wall. The shear walls were poured in 3 m sections using steel shuttering made for the project. The shear walls have a double layer of D16 reinforcing bars at 300 centres each way. D16 Starter bars are incorporated at each floor level. The starter bars are placed in the centre of the two layers and these are bent in toward the floor when the shear wall- floor joints are made.Because the lift shaft and stairwells are external to the building the shear walls needed to have door openings built in at each level. These opening tend to weaken the shear wall and to overcome this and to provide load path continuity substantial additional reinforcement is used above the door openings as shown in the appendix, drawing S322. These sections of wall are known as coupling beams.

The horizontal joints between the shear walls and the floors were made when the topping was poured over the Dycore slabs. Starter bars were approximately 1000mm long emerged at the top of each section of shear wall. A layer of 665 mesh was placed on top of the Dycore and propped up on short plastic spacers. The starter bars were then bent over the bottom layer of mesh. A second layer of 665 mesh was placed over this and tied to the starter bars. A horizontal D12 bar was placed parallel to the shear walls

The topping was thickened to 100mm for a distance of 4200mm from the joint with the shear walls. This was achieved by lowering the Dycore slabs closest to the wall.The Dycore slabs did not butt up against the shear was. A 15mm thick timber infill is used because the Dycore slabs are considered too brittle. During wind or seismic loads the floors act as diaphragms and transfer the horizontal loads as well as the weight off the building to the shear walls through these shear wall-floor joints. For this reason it is necessary to use the more ductile reinforced concrete joint created by the timber infill.

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3.3 FloorsThe upper floors are all construction using precast prestressed Dycore slabs.The slabs are delivered to the site and placed in position using the tower crane. Each slab is marked on the top face with al large sprayed on label. These labels identify the slab type. The Slabs are placed in position and span the space from beam to beam. In block A the span was 14.9m. The slabs are placed in position using a layout plan because certain slabs have notched cut-outs to fit around the column reinforcing. Certain slabs also have shallow cut outs on the longitudinal edges. Two slabs with identical cut-outs are placed together in order to create a sufficiently wide projection through the floor.The Dycore slabs are placed on 50mm wide McDowell seating strips placed on the beam edges before the slabs are lowered in place. These seating strips are essential without them the friction between the Dycore and the beam would be too great and the slabs could not be manipulated into position without damaging the slabs.The top surface of the Dycore is quite rough to accept the concrete topping. A 665 mesh is placed on top of the slabs with short plastic chairs providing a standoff. The topping is 65mm thick except near the shear wall joints where the it is 100mm thick.Dycore slabs provide a quick economical construction method but it has one major disadvantage- the prestressing cables. These cables are made from braided steel wires and run down the length of the slab. On average three cables fit in the concrete between the hollow cores. Once the topping is placed on the Dycore slabs the position off these stressing cables becomes unknown and any service penetrations through the floor must be very carefully measured and checked before they are cut.

Deck FloorsDeck floors for level one were cast with the topping slab. This is because the first floor has a 75 unispan slabs on either side of the building. These unispan slabs form part of the carpark roof. Reinforcing bars and wooden formwork had to be built on top of the unispan slabs.These slabs share a common beam with the Dycore slabs but span across to a second beam on either side of the building as shown in the figure.These deck floors were 160 mm lower than the Dycore topping. The topping was continued onto the unispan slabs, these slabs received a 75mm toping with 665 mesh. The deck floors are on average 1000mm wide. The deck floors on the 2nd, 3rd, 4th and 5th levels are all cantilevered precast floor units. These are hoisted into position with the tower crane. Special lifting inserts are cast into all the precast concrete sections because the panels cannot be hoisted using the reinforcing bars. D12 starter bars at 300 centres 1.5 times the width of the precast floor emerges from the precast deck floor units. These are tied into the reinforcing bars placed at the tops of the beams. The deck floor units have a 70mm seating on the beam edge and are supported by falsework while being cast in place. There are different types of precast floor units some are external balcony floors and others are cantilevered sections of the apartment floors.

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3.4 Columns and beamsColumns are constructed on top of a pile or a pile group. The columns are 600x600mm with 12 vertical HD 32 bars arranged in a square in side the columns. These bars have a 1200 overlap when joined and are tied together with groups of 3HR10 ties at 150 centres. Inside the beam column joints the vertical bars are tied together with groups of 4HR12 ties evenly spaced inside the joint: 8 groups are used at level 1, 2, and 3 while 7 groups are used at levels 4 and 5.Steel column formwork was specifically made for the project. The formwork has a working deck. The column schedule drawing did not explicitly state the height to which the carpark columns should be poured. It was left for the site foreman to interpret other detail drawings. This caused a problem and the columns on grid lines A1 and A4 were poured too high. This created at least a 3 day delay because the 30MPA concrete had to be chipped away from the rebar to lower the column height so that the beams could be placed in position. This had a secondary effect because now the rebars were too long and these had to be cut and re-bent. This re-bending had to be achieved with heat and the radius of bending could not be controlled. The overall effect is to weaken the steel in the vicinity of the bend.Precast beams were used again this was more economic and allowed faster construction beam spans varied from 6600mm to 9900mm. All beams had the same depth. The shorter span beams could therefore have been shallower but this would have complicated the construction and would not have been aeasthically pleasing.The beams had 2 HD32 bars emerging from the base and their ends were bent upwards. The beams did not always seat on the top of the columns. A large amount of reinforcing was added to the tops of the beams. Each beam had approximately 4 rows of HR10 hook bars emerging at the top, spaced at approximately 100mm centres. 4 HD 20 bars were placed horizontally in these hook bars. These bars were passed through the column reinforcing and there were at least 1500mm laps on either side of the columns. On top of this HR10 stirrups were placed to tie the HD bars together horizontally. The joints between the Dycore and the beams were created by breaking out the top cover from alternate hollow cores in the Dycore. HR 12 hairpins were placed inside the cores and tied to the horizontal HD20 bars on top of the beams.The beam/column joints were boxed using Formply. When the Dycore topping was poured all beam/columns and beam/Dycore joints were filled at the same time to creating a monolithic reinforced structural element.

3.5 Stairwell and lift shaft towersThe stairwell and lift shaft are placed in towers on the north and south side of block A. These structures are made of precast concrete wall sections with precast stairs and flooring. Each level in these structures is connected to the corresponding level in Block A by means of a light precast bridging floor. The narrow walls sections are storey high 150mm thick reinforced concrete. The wider panels are half storey height.

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Vertical jointsThe panels are stacked vertically with butt joints between adjacent panels. Weld plates are cast into the shear wall and the precast panels. These weld plates are 16mm thick and rebated to ensure that the connection is flush with the concrete surface. Steel cleats are then weld onto the plates to create the vertical connections between the adjacent panels and between the shear wall and an adjacent panel. The plates, welds and cleats are then cleaned and painted with a primer to prevent rust.

Horizontal jointsThe horizontal connections are more complicated. Starter bars from one panel insert into 35mm channels cast into the adjoining panel. Two holes are drilled from the interior side of the panel into each channel. These holes enable the channels to be filled with grout and in this way the horizontal connections are made permanent. The ground floor panels rest on the ground beams so the starter bars from the ground beams insert into these initial panel. The starter bar positions are measured and these measurements are passed to the precast panel manufacturer. All subsequent panels and their associated starter bars and channels are controlled by the precast panel manufacturer.It is essential that the lift shaft and stairwell walls are perpendicular to one another. It is therefore important that the ground floor panels were accurately set out since all subsequent panel positions are based on these initial ground floor panels.The gaps in the horizontal joints are created by resting the panels on high density plastic spacers. These spacers are then either grouted or sealed in place. The ground floor joints are grouted and all the rest are sealed.

Joint sealsNon-rigid joint seals are used. All panel-panel joints and all shear wall-panel joints are filled with a solid closed cell foam rod. The joints varied in width so that rods of different diameters were used. The rods are placed in the centre of the joint. Soft flexible sealant was then applied which seals the remaining gap. Two different types of sealant are used, one for interior use and the other for exterior use. Both sealants are coloured to match the grey colour of the concrete. The interior sealant is an intumescent fire resistant sealant with a 4 hour fire resistance rating. The exterior sealant is not fire rated but must withstand the exposure to the sun, rain and wind.

3.6 Exterior CladdingsThe exterior claddings of both Block A and the stairwell/lift tower have not yet been fixed to the structure. The placing of the timber framed infill walls started on 23 September 2006. The following details are base on an examination of the relevant architectural and structural drawings.The façade of Block A is made up of exposed precast concrete panels, glazing, composite Alucabond panels, and fibre-cement panels. Timber framed infill walls are placed between the floor and roof slabs at each floor level. These infill walls create the external walls onto

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which the cavity based cladding and windows are fixed. The stairwell/lift shaft tower has a strip of glass curtain walling.The precast panels are placed vertically between apartments and at the flank ends of the building. Precast concrete spandrel panels are fixed to the cantilevered balcony slabs. These precast panels act as walls between apartments and provide privacy. The panels rest on high density plastic spacers paced on the balcony floors. The panels are fixed to the structure using bolted cleats. They also joined to the balcony soffits by means of 3 HD 12 hairpin lugs grouted into the voids between the upper deck floors.

The cavity based fibre cement panels and the Alucabond panels are fixed to the structure using stainless steel nails or screws and proprietary fixings. Since the air pressure within the cavity is the same as on the face of the cladding the air barrier must be able to resist the full wind pressures. It should also resist fatigue due to positive and negative pumping actions of the wind. Since the building is designed to for a high urban wind zone a rigid air barrier must first fixed to timber infill walls. Fibre cement panels 4.5mm thick (Eterpan) are first fixed to the timber walls to provide a rigid air barrier (RAB). The vertical joints between RAB boards have a small gap 2mm which is sealed before the battens forming the cavity are fixed to the RAB. Horizontal gaps between the RAB boards are at interfloor levels. These gaps will accommodate any differential movement between the timber infill wall and the concrete. These joints are 12mm wide and sealed with silicone. It is unclear from the drawings whether any flashings will be used in this joint. Outer panels of either 9mm fibre cement (Eterpan) or composite aluminium panels (Alucabond) are then fixed over the cavity.Spandrel precast concrete panels are fixed to beams below balcony soffits. Spandrel glazing is used in the stairwell/lift shaft tower. The sliding doors and windows are placed in the precast panels, shear walls or timber infill walls. The head, jamb and cill details of some of these are shown in the appendix.

3.7 Fire resistanceThe fire resistance of the concrete structure is determined by the type of aggregate used and the concrete cover provided for the steel reinforcement. The aggregate used is 19mm stone and this will produce some spalling of the concrete (Foster 1994, Part 2, p 346). The concrete cover provided for the reinforcement varies. The greater the cover the greater is the fire resistance. The concrete cover specified by the structural engineers varied from 30 to 40mm. the floors having the lowest cover at 30mm. The prestressing cables of the Dycore floor slabs have a similar amount of concrete cover. The structure has a 60/06/60 FFR while the precast balcony walls and floors all have a minimum 30/30/30 FRR.The roof beams and rafters are steel and will be coated with intumescent paint. The fire rating was unavailable. The cantilevered balcony floors and vertical precast panels act as fire aprons on the exterior of the building.

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3.8 RoofThe roofs of both Block A and the stairwell/lift tower have not been constructed. The details described below are based on an examination of the relevant architectural and structural drawings. The roof of the stairwell/lift tower is a monopitch timber frame clad with Nuraply on H3.2 treated plywood. This roof is separated from the shear wall by a proprietary seismic joint.

Block A has a hipped roof clad with Coloursteel corrugated sheeting. The roof framing is made of steel. The rafters are universal beams supported on columns with parallel flange channels forming the eave beams. The proprietary roll formed Dimond Hi-span purlins are to be used. The rafters at both ends of the roof are to be braced with R32 rods, 2 braces in each bay. The purlins are braced and are to be placed at 500 – 1200mm centres. The roof framing will be bolted together using cleats and M20 bolts. The rafters are fixed to the columns using M20 bolts cast into the tops of the columns. These stiff joints provide lateral bracing for the roof frame.The use of large eave beams and rod bracing provides bracing against longitudinal wind pressures which tend to tilt the rafters (Foster, 1994, Part 2, p 294).

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4. References

Abbott, P. (2002). Final Report: 130 Anzac Street: Additional Assessment for Proposed Basement Excavation. Auckland: URS New Zealand.

Buller George. (2006). Structural Engineering Specification: Apartment Development, 130 Anzac St., Takapuna. Auckland: Buller George Engineers Ltd.

Chan, Y. (2002). Anzac Street Apartments, Geotechnical Investigation, Assessment of Depth to Rock. Auckland: Riley Consultants Ltd.

Emmitt, S. & Gorse, A. (2006). Barry’s Advanced Construction of Buildings. Oxford, UK: Blackwell Publishing.

Foster, J. S. (1994). Mitchell’s Structure & Fabric (Parts 1-2). Harlow, England: Longman Scientific & Technical.

Hauraki Piling. (2006). Report: Apartment Development, Anzac St. Takapuna, Dynamic Pile Testing. Auckland: Tonkin & Taylor Ltd.

Landfill Gas Primer: An overview for Environmental Health Professionals. (Dec 28, 2001). Retrieved 23 September, 2006 from http://www.atsdr.cdc.gov/HAC/landfill/html/intro.html retrieved 9 September 2006

Millais, M. (2005). Building Structures: from concepts to design. (2nd ed.). New York: Spon Press.

Reed, M. (2005). For Consent: 130 Anzac Street Development, Assessment of Environmental Effects. Auckland: URS New Zealand.

Volcanic Field. (n.d.). Retrieved 23 September, 2006 from http://www.arc.govt.nz/arc/environment/hazards/volcanoes-of-auckland/volcanic-field.cfm#pupuke

Woodward – Clyde. (1999). Report: Landfill Gas Control and Utility Services for the proposed Residential Development at 130 Anzac Street. Auckland: Woodward Clyde (NZ) Ltd.

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5. Appendix

Drawings, photographs and sketches

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