Thursday 10 November

2.00- 3.30pm ConcurrentTechnicalSessions: 7

7 A Arawa Room Beams and Columns - Flexure, Shear and Torsion

78 Tiri Room Masonry and Strengthening

7. Confinement by Rectilinear Ties in Reinforced Concrete 56. Rehabilitation of Concrete Structures by Shotcrete UsingAlkali-Resistant Glass Fibers and Ultra-Rapid HardeningCement

Columns -* Sakai K., Sheikh S.A., Kakuta Y., Ohta T. * Hokkaido University, Japan

9. Hysteretic Restoring Force Characteristics of Unbonded

- Miyata S, Tottori S, Ushijima STrack and Structure Laboratory (RTRI) Tokyo, Japan

Prestressed Concrete Framed Structure under 61. The Use of Sprayed Concrete in the Strengthening ofEarthquake Risk BuildingsEarthquake Load

- Nishiyama M, Muguruma /-/, Watanabe FKyoto University, Japan

-Leuchars JSmith Leuchars, Auckland

10. Shear Design of Reinforced Concrete Members Based on 72.

the Plastic TheoryIn-Plane Bending of Single-Leaf Block Walls - *Symons MG, Amey DJ, Johnston R

- *Minami K, Kuramoto H, Wakabayashi M *South Australian Institute of Technology.*Department of Architecture, Osaka Institute of Technology,Japan 73. New Zealand Masonry Design and Construction Code

Review11. Research on Precast Concrete Members with Joints in

Torsion and the Provisions of Codes in Japan- Izumi M. Meijo University, Japan

4.00- 5.30pm Concurrent Technical Sessions: 8

8A Arawa Room Precast Building Systems

30. Fanshawe Street Building - A Precast Concrete Study- Silvester DB, Dickson ARBeca Carter Hollings & Ferner Ltd, Auckland

26. Precast Concrete Moment Resisting Framing System- O'Leary AJ, Mason JE, Monastra DPMorrison Cooper & Partners, Wellington

31. Precast Buildings Using Cruciform Columns-O'Grady CRO'Grady Mitchell, Auckland

- Barnard DP, Gaerty LCement & Concrete Association of New Zealand

88 Tiri Room Rehabilitation

57. Reliability of a Repairing Method for Cracked andDamaged Reinforced Concrete Slabs of Bridge Deck-* Sonoda K., Hiyashi H., Okino M., Matsui S.* Osaka City University, Japan

58. A Simple and Economic Method for Rehabilitation of Wharf Piles in Remote Tropical Areas- Robinson RA Contech Group Ltd, Auckland

59. Protection of Cracked Concrete Facade ElementsShowing Early Deterioration- *Geiker M, Rostam S*Izard Manufacturing Co Ltd, Wellsford, New Zealand

60. Replacement of Horizontal Prestressing on a MajorReservoir

11

- *Hopkins DC, Leslie PD *KATA Ltd, Wellington

PACIFIC CONCRETE CONFERENCE

PRECAST CRUCIFORM COLUMNS, H FRAMES AND PRECAST CONCRETE SHEAR

WALLS IN BUILDING CONSTRUCTION BY C.R. O'Grady of O'GRADY & MITCHELL CONSUL TING ENGINEERS AUCKLAND NEW ZEALAND

The Need for Development:

a) Because of the need for fairly high concentrations of steel in the beam/columnjoints for seismic design together with the requirement for high strength, wellvibrated concrete in these areas, it seemed to me logical to develop amethodology which would allow cruciform units to be produced in precastfactory conditions.

b) The high cost of bridging finance has put greater demands on quicker and moreefficient methods of construction while still ensuring top quality.

c) The demands put on the Building Industry due to the increased level of buildingactivity had necessitated the employment of less trained personnel who foundit increasingly difficult to cope with the exacting site demands.

d) The need to deny the acceptance of any denegration of standards, but ratherto devise a method where dense, well vibrated concrete can be placed aroundaccurately positioned steelwork particularly in beam/column joints which are atthe frontal edge of seismic attack.

Problems:

1. Basic Code philosophy is based on an idealized symmetrical building. Thus ifwe are to fully embrace this philosophy we should strive to affect symmetrywhere possible.

2. The problem of reliable jointing of columns and the best position for thesejoints.

3. The design of beam/column joints.

4. The need to devise a positive method of locking the peripheral hull beams intothe floor diagram.

5. Our fire codes presuppose a 900mm spandrel at each floor of a multi-storiedbuilding or an effective spandrel with either a l ½ HR or 2 HR FRR.

6. The problem of concurrency in Columns.

Solution:

It became clear to me that working in a controlled shop environment, where both reinforcing and concrete, can be placed in steel moulds and finished to a high degree of accuracy, was infinitely preferable to the site environment. Further, we can utilize higher strength, well vibrated concrete, to maximise quality and design effectiveness, as the completed unit will be cured in optimum conditions.

The immediate problem to address is the size and to check crane capacities at various jib lengths. the viability and cost effectiveness of the design.

345

weight of the completed units and This is the salient consideration in

Note: On subsequent jobs we have revised the technique. We now use Conbextra G.P. which is far more fluid allowing us to pump the face joint and all jointers through the inlet port of one jointer with each jointer sealed when a steady flow is achieved from the outlet ports. However, timing is of the essence and specially trained staff only must be used.

The column rebar extensions are checked on site arrival. We allow a tolerance of 0 to -10mm with bar lengths specified at 5mm from the centre line of the jointer. Bar lengths below this tolerance are cause for rejection. Bars overlength are cut by side grinder. We do not permit gas cutting.

It must be noted that precast design places more demands on the consultant.

First: Detailing: Considerable time must be allocated to the design and detailing of workable details. All units must be fully dimensioned and tolerances specified.

Secondly: Supervision: Much more supervision, both in the precast yard and on site, is required. Indeed with a new contractor it is almost a teaching mode.

Encouraged by the success of this project, we developed the methodology on two further buildings in Grafton. (Refer Appendix 7 A).

A bigger challenge was Equiticorp House, an eleven storey building (2 basements and 9 office floors). (Refer Appendix 3). The building is 630m2 (6,800 sq. ft.) in plan floorarea. The lifts and amenities area were positioned external to the main office area. This area was steel framed with metal floors and pin-jointed beams and columns braced back to the building proper. This had a torsional effect on the building. We adopted quite large spans with 4 internal columns and 8 external columns. Although the perimeter or Hull Frames were quite stiff (Cols 1200 x 500 Beams l 000 x 400) we had to enlist the central frames to asist against seismic attack, particularly in the lower floor levels. To this end, we designed a new shell beam 700mm x 400mm with solid halved ends to the outer spans. We poured the 4 internal columns which were cruciform to induce more stiffness to these frames. These did not impede progress as the Column Formers were used through a number of floors. Floor to floor turn around averaged 6 working days.

DUCTILE PRECAST CANTILEVER SHEAR WALLS

Design is an on-going process. Confinement steel was again becoming a problem. So, with the next major job in Queen Street, Mayfair House, (2 Basements; 9 Office Floors), we investigated a Ductile Shear Wall design: i.e. Precast Cantilever Shear Walls jointed with NMB splices with pin-jointed external and internal beams.

Erection progress was startling with 2 floors being erected in 6 days before precast delivery let us down.

The owner was very pleased with the overall result and immediately commissioned another building (Parkview). This building was of similar height but different in plan form and structural pattern. This building also went well (Refer Appendix 78).

Comparing the efficacy of both systems I believe that, although it is hard to generalise, for buildings in excess of l O floors, Ductile Shear walls are more efficient. Further, the lesson from the results of observed earthquakes, support this assertion.

347

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