Frequently Asked Questions

1. What wind loadings spectra should be used for designing steel masts against fatigue?
Some guidance is available in HERA Report R8-22 Fatigue in Welded Structures Workshop and Australian Standard AS3995-1994 Design of Steel Lattice Towers and Masts.
2. Can API line pipe be substituted with spiral welded pipe?
Spiral welded pipe can typically substitute for API line pipe. It can be made in NZ. This allows it to be customized to your particular requirements and lengths. The welds are typically 100% X-ray checked during the manufacturing process. Refer to http://www.steelpipe.co.nz/process.htm for more information.
3. What guidance is available for designing continuous composite steel beams?
Refer to NZ Steel Structures Standard NZS 3404: 1997 cl. 13.4.3.2. The region of the beam where the concrete will be subject to tension is referred to a the "negative moment region"
4. How are the lever-arms between compressive and tensile actions: e and e' , determined for partial composite sections in NZS3404:1997 cl.13.4.5.2 ?
Refer to Composite beam Seminar Notes HERA Report R4-49 pp.13.47 to 13.49
5. How can seismic movement joints be designed between simply supported steel beams and columns to allow movements of + / - 50 mm?
Holes are typically slotted into the web of the steel beam and a the hole in the cleat to the column set out so as to allow the beam to move the required distance without contacting the column face.
6. How durable are galvanised bolts when located on a wharf structure in the Auckland area?
If the bolts are assumed to have a galvanised zinc coating of 50 microns and are fully exposed to air above the splash-zone an assessment based on Metal Corrosivity Standards ISO 9223 and ISO 9224 would be as follows:

From ISO 9223 Classification of time of wetness: T5 Classification of pollution by sulphur: Po-P1 Classification of pollution by airborne salinity: S3 The estimated corrosivity category is C5.

From ISO 9224 Average corrosion rate (first 10 years) = 4 to 10 micrometers/year Average corrosion rate (steady state) = 4 to 10 micrometers/year

Assuming the zinc coating thickness is 50 micrometers, the bolts should be able to last for 5 to 10 years.
7. How should composite steel beams with solid pre-cast concrete planks be detailed and what shear stud capacities can be used?
Some useful references are:
Design of Composite Beam Using Pre-cast Concrete Slabs, SCI Publication:P287 ASI Steel Construction, Volume 37 Number 2, Sept 2003. DCB, No-55 and No-45.

The following are excerpts from SCI Publication: P287. Shear stud capacities need to be adjusted for concrete cylinder strength and reduction factors used in NZS 3404:1997.
8. Is a gap required between steel studs and building paper?
In most cases a gap is required so as to prevent moisture condensing at the contact between the stud and paper. NASH are developing technical guidelines. http://www.nash.asn.au/MAIN.HTM
9. What is a cost-effective of providing bearings for small bridges?
Neoprene strips can often be used without the need of progressing to the more expensive composite steel-rubber elastomeric bearings. Load-displacement data and range is available at Skellerup in accordance with BE 1/76.

Skellerup website www.skellerup.co.nz
Skellerup Elastomeric Bearings, Pads and Strips to BE 1/76, July 2001
10. Are there any references that give guidance on checking the buckling of steel cylindrical structures like storage tanks.
The following paper is available from the HERA library: "Stability of Stiffened Cylindrical Bins", Author: M.J. Blackler and P. Ansourian.
11. Where can information be found on current steel supply and fabrication rates for developing preliminary project estimates.
The Structural Steelwork Estimating Guide is available on-line for an annual subscription of $20. Go to SCNZ Estimating Guide
12. How much of a "part-turn" is required to fully tension high strength garde 8.8 bolts of varying lengths?
Refer to Steel Structures Standard NZS 3404:1997 Table 15.2.5.2 "Nut Rotation from Snug-tight Condition":

Length < 4x diameter: 2/6 = 1/3 turn
4x dia. < Length < 8x diameter: 3/6 = 1/2 turn
8x dia. < Length < 12x diameter: 4/6 = 2/3 turn
12x dia < Length < 16x diameter: 5/6 = 5/6 turn
16x dia.< Length < 20x diameter: 6/6 = 1 turn
13. Where can a list of contact details for New Zealand steel fabricators and suppliers be found?
A list is available at the Steel Construction Industry-New Zealand site on the following page: SCNZ Members Pages
14. Can the high strength bolts in Moment End Plate (MEP) and Moment End Plate Splice (MEPS) connections not be fully tensioned?
No. The tensioning ensures the fatigue performance and rotational stiffness of the joint is properly developed. Fatigue failures have occurred in such connections where bolts have not been adequately tensioned during construction.
15. What are the reinforcement integrity criteria for Speedfloor slabs subject to fire?
Refer to Design and Construction Bulletin No. 71 clause A5.3
16. What information is available for the fire design of concrete-filled steel hollow-section columns?
Refer to HERA Design and Construction Bulletin No. 58, pp. 25-30, 32-33. There are also references to relevant papers listed there.
17. Can Property Class 4.6 mild steel bolts or Property Class 8.8 high strength bolts be welded to mild steel plate?
Property Class 4.6 bolts may be welded if normal care is taken in accordance with AS/NZS 1554 with regards to selection of consumables, preheat and other welding variables. The chemical composition of the bolts will need to be known.

Property Class 8.8 bolts should never be welded unless specialist advice and supervision is sought and followed.
18. Where can a list of Certified Coatings Inspectors be found?
A list can be found at the CBIP web page: http://www.hera.org.nz/cbip/Certified%20Personnel.htm
19. How are local hollow tube face stresses accounted for when designing attached cleats subject to bending or tension?
Design procedures and background to these issues are covered in:
Syam, A., Chapman, B., "Design of Structural Hollow Section Connections", 1st Edition, Australian Institute of Steel Construction, Sections 5 & 6
Packer, J., Henderson, J., "Hollow Structural Section Connections and Trusses".
Both are available through the HERA Information Centre
20. Do Duragal sections have the same amount of galvanising as hot dipped galvanised members?
Duragal sections have a thinner layer of zinc than normal hot dipped galvanised sections. Time to first maintenance is therefore less. It is also easier to weld through.
21. What recommendations are there for stiffness of lateral restraints to flexural and compression members?
In most cases restraints will provide adequate stiffness if designed to provide adequate strength. Typically restraint forces are assumed to be approximately 2.5% of the axial compressive load being restrained. However where there are concerns as to the adequacy of the restraint stiffness reference can be made to the following resources:
HERA Design Guide Volume 1 Section 4.5
Jeffers, E., "Use of Braced Strut Behaviour to Assess BS5400 Provisions of Beam Restraint", The Structural Engineer, Vol.70, No.17, Sep 1992
22. Can Mill Test Certificates be used to select steels out of a shipment of a lower grade designation to achieve the requirements of a higher grade designation?
Mill Test Certificates cannot be used directly but may be used in conjunction with statistical adjustment.

Material grades are defined in standards so that high levels of confidence can be had by designers and constructors that the material used will meet the demands placed on it. Mill test certificates are not intended to be used for identifying reliable properties of a steel, but indicating statistical compliance within a production grade.

For example a review of tensile yield stress shown on mill certificates provided for a batch of steel pipes to API 5L B (PSL1) / ASTM A53B ERW Steel pipes gave an average yield of 376 MPa for the 12 samples with a standard deviation of the sample of 35 MPa. The designer wished to know whether this batch of steel could be used to satisfy Grade 350 requirements.

The maximum yield was 449 MPa and the minimum yield 335 MPa. For this set of tests a 95% confidence limit would therefore be 306 MPa and 99.7% confidence limit of 271 MPa. Assuming that steel supplied in accordance with a materials supply Grade such as API 5L is required to have a 99.7% confidence limit the material will meet the set limits. (95% confidence limits are also often used in materials specifications however it is not clear whether this is the case for steel pipe). For API 5L B a minimum yield of 241MPa is required. The sample 99.7% confidence limit of 271 MPa is therefore quite consistent with steel selected from a 241 MPa steel grade.

To be confident of selecting a steel out of a grade based on a mill test certificate, with a yield strength greater than the grade specified 99.7% minimum, the variability within a particular heat of steel about the test certificate result would need to be known. Typically this would be less than that of the total grade as the chemical composition and processing within a heat is more consistent than the chemical composition and processing across all the heats. However this variance is only known by the steel maker.

One strategy for therefore selecting some steel from this particular example of API 5L B stock , with levels of confidence consistent with the design standards, on the basis of the steel mill certificates presented, is therefore to take the approach that a yield strength of 271 MPa may be relied on with a high level of confidence.

If you were to require that only steels with mill test certificates of 390 MPa or more were used then a yield strength of 285 MPa could be used with a similar level of confidence.

An alternative approach is to make an assessment of the variability within a given heat of the steel supplied. A minimum of ten samples should be selected and tested from the stock to be used and the distribution of the yield strengths about the mill test certificate result determined. This could then be used to identify a minimum mill test certificate value for which a high level of confidence could be had of the steel meeting the minimum limits assumed in the design standards.

Obviously this all gets into probability assessments. This is the reason material grades are defined in standards so that high levels of confidence can be had by the designer and constructor that the material used will meet the demands placed on it.

Mill test certificates are not intended to be used for identifying reliable properties of a steel, but indicating statistical compliance within a production grade.
23. What design guidelines are available for floor vibration assessments?
The following are available through the HERA Information Centre and represent current practice:

Murray, T. et al, "Floor Vibrations Due to Human Activity, Steel Design Guide 11", American & Canadian Insititute of Steel Constrction, 1997

"ATC Design Guide 1: Minimising Floor Vibration", Applied Technology Council, California, 1999

Khwaounjoo, Y., "Report and User's Manual for NZFI_Vib1 Program", HERA Report R4-112, May 2002
24. Does aluminium in contact with galvanised zinc coated steel require any special treatment to avoid accelerated corrosion due to galvanic action?
According to Aluminium Structures Standard AS/NZS 1664.1:1997 Clause 6.6.2 no special treatment is required between the galvanised zinc coating and the aluminium as both are very close on the periodic table.

Galvanised connectors should be used to fix the aluminium to the galvanised steel so that zinc coating of the fastener is in contact with the base steel.
25. What clearances and edge distances should be used with M42 bolts?
Here is a link to a website which contain impact wrenches for M42 bolts. Look at the torque table to determine appropriate wrench and then look for that wrench product details. The product detail contains dimensions that should enable you to work out clearances.
http://www.rodcraft.com/en/druckluft_auswahl1.html
http://www.rodcraft.com/en/duopact.html
Here is another impact wrench website which has wrenches for M42 bolts and gives distance from centre to side.
http://www.atlascopco.com/tools
26. How should Grade 300E and 500E reinforcing steel be welded?
Welding procedures and advice are found at the following webpage: http://www.steelreinforcing.co.nz/product_tech/scope.ptm#welding
27. How much thread should there be left protruding above the top of a nut after tightening?
The New Zealand Steel Structures Standard, NZS 3404:1997 Clause 14.3.6.1.2 requires one clear thread above the nut and at least one thread run out beneath the nut after tightening.
28. How can requirements be determined for steelwork in various locations around New Zealand including at the coast?
AS/NZS 2312:2002 "Guide to the protection of structural steel against atmospheric corrosion by the use of protective coatings" and Amendment 1:2004, provides a step by step method for assessing corrosivity of the environment and recommending generic coatings systems. Times to first major maintenance of each system are also given.
All major paint manufacturers can supply coatings products in conformity with this standard.
29. What sizes and grades of steel hollow sections and pipes are available in New Zealand for structural purposes in accordance with AS1163?
A detailed listing is available at the Smorgan Steel web page: http://www.smorgonsteel.com.au/tubemills/

In summary they offer:
CHS C350L0: 26.9 to 508 dia
CHS & PIPE C250LO: 21.3 to 165 dia
RHS C350L0/C450L0: 50 x 25 to 400 x 300 SHS C350L0/C450L0: 13 x 13 to
400 x 400
30. How can requirements be determined for steelwork in various locations around New Zealand including at the coast?
AS/NZS 2312:2002 "Guide to the protection of structural steel against atmospheric corrosion by the use of protective coatings" and Amendment 1:2004, provides a step by step method for assessing corrosivity of the environment and recommending generic coatings systems. Times to first major maintenance of each system are also given.
All major paint manufacturers can supply coatings products in conformity with this standard.
31. Where to source weathering steel bolts and plates and what are the properties of these bolts?
The weathering steel bolts and plates are produced in Japan, USA and the UK and they can be sourced from local distributor such as New Zealand Steel. Weathering steel bolts have the same strength and properties of normal galvanised property class 8.8 HSFG bolts AS/NZS 1252:1996. Bolts from the USA are specified as ASTM A325m Type 3 (equivalent to property class 8.8 bolt) and ASTM A490 (equivalent to property class 10.9 bolt). More weathering steel information can be found in HERA Report R4-97:2005, New Zealand Weathering Steel Guide for Bridges.