Electronic Blueprint update; CPD for Architects, Engineers and Builders

In a major training initiative, Electronic Blueprint Updates will provide the focus for coordinated Continuous Professional Development Training programs by Distance Leaning techniques for practising Architects, Engineers and Builders in conjunction with the following organisations:

• Archicentre.
• ACEA NSW, Victoria & Tasmania.
• MBA (NSW).

Distance Learning is a program of training carried out in the convenience and comfort of your own home or office. Should you require more information of any of the matters raised herein, please refer to our website www.electronicblueprint.com.au or contact us by email info@electronicblueprint.com.au.

Non-structured Distance Learning
Architects, Engineers and Builders may select Distance Learning Packages from a comprehensive list to suit their particular needs. The training is carried out at the convenience of the participant, an assignment is submitted and assessed, the Certificate of Completion is issued and the CPD points assigned.

Structured Distance Learning Program
Every two months, a coordinated Distance Learning Package consisting of several related topics will be offered. Each package will include an Electronic Update, which summarises the content, and several voiced-over presentations, as follows:

• Specification, detailing and problem solving for Architects.
• Structural, civil and/or mechanical/electrical design for Engineers.
• Problems, solutions, and site control for Builders.

Further Assistance
For more help on any subject, participants may contact the tutor by email. The tutor will respond within 48 hours. On completion of the presentation, participants may complete a short assignment and email it to the tutor. The purpose of the assignment is to provide focus for the presentation, and to enable participants to apply the information to practical situations. The tutor will assess it, provide comments and forward a certificate by return email.

Architects - Considerations in the Selection of Retaining Wall Systems
This article introduces the training module intended to give an understanding of the architectural design and construction considerations for retaining walls associated with building projects. While the structural design remains the responsibility of the engineer, there are important practical limitations and specifications that must be considered by Architects.

It covers low to medium height retaining walls in common use in the building industry, including:

• Mass Gravity Retaining Walls.
• Crib Walls.
• Segmental Concrete Gravity Retaining Walls.
• Segmental Concrete Reinforced Soils Systems.
• Reinforced Concrete Masonry Cantilever Retaining Walls.
• Cantilever Post Retaining Walls.

Soil Pressure
The following discourse is a very simplified description of the function and behaviour of retaining walls. If unrestrained, a soil embankment will slump to its angle of repose. Some soils, such as clays, have cohesion that enables vertical and near-vertical faces to remain partially intact, but even these may slump under the softening influence of ground water.

Retaining Walls - Geometry To Achieve Stability
The retaining structure must have sufficient weight (including the weight of any soil "captured within") to resist excessive rotation and sliding. The soil "captured within" includes:

• The reinforced soil block of a reinforced soil system.
• The fill contained by the cribs of a crib wall system.
• The fill on the heel of a reinforced masonry cantilever wall.

A very rough guide for good quality soils of low cohesion, without water pressure, is as follows:
THE WIDTH SHOULD APPROXIMATE 0.6 TO 0.8 TIMES THE HEIGHT.

Rock Outcrops
If massive rock formations are present immediately behind the structure, these will restrict the volume of soil which can be mobilized against the wall, and thus reduce the force. The magnitude of the reduced force may be determined by considering a steeper theoretical wedge, which is restricted between a vertical line at the rear of the retaining wall and the rock face.

Water Pressure
If water is trapped behind the retaining structure, it exerts an additional hydraulic pressure. This occurs when:

• Rain water or ground water is permitted to infiltrate into the fill behind a retaining wall,
• Water mains or sewers in the vicinity of a retaining wall burst or leak, or
• There is rapid draw-down of the water level in front of a wall (e.g. a sea wall) leaving water trapped behind.

The presence of ground water also reduces the adhesion and bearing resistance.

Sloping Retaining Wall
If the interface between the retained soil and the retaining structure slopes (into the embankment) the weight of the soil wedge causing movement is reduced, and the resulting active pressure is reduced.

Global Slip
Retaining walls and embankments must be stable for global slip failure around all potential slip surfaces or circles. Terracing of a site, using multiple retaining walls, will not necessarily reduce the tendency for global sip failure around a surfaces encompassing all or some of the retaining walls.

Engineers - AS 4678 Earth Retaining Structures
This article introduces the training module intended to give an understanding of AS 4678 Earth retaining structures, and an insight into its use to design practical retaining walls in Australia. It is legitimate for engineers and builders to ask the simple question - If we have been designing and building retaining walls for thousands of years, why do we now need a new standard?

Work on developing AS 4678 began in 1991 by the Standards Australia Technical Committee CE/32. Obtaining a consensus position on each of the principal points proved to be difficult, but not impossible. Some of the more difficult questions included:

• Should the document be a "guide" giving non-mandatory advice, or should it be a "standard", setting mandatory rules? The result - AS 4678 does both.
• Should the document deal with all competing earth retaining systems, or should it be restricted to one (say reinforced soils). The result - AS 4678 deals with all systems.
• Should the document embrace the modern design approach (limit state design) or rely on the older method (working stress design). The result - AS 4678 adopts limit state design.
• Should the document incorporate loading rules consistent with Australian loading standards AS 1170. The result - AS 4678 adopts (with minor modifications) the rules of AS 1170.
  The resulting Australian Standard, AS 4678 Earth retaining structures was published in 2002, and has been amended once during the subsequent period. The main innovations of AS 4678 are set out below.
• AS 4678 is compatible with the other major structural standards - AS 1170 (Loads), AS 3600 (Concrete), AS 3700 (Masonry), AS 4100 (Steel) and AS 1720 (Timber).
• AS 4678 identifies the time-dependent properties, such as reinforcement corrosion, geogrid deterioration and creep, and drainage clogging. It provides a practical means for accounting for the changes in these components
• AS 4678 is based on a common reliability for each of the major retaining wall systems.
• AS 4678 provides for a variable reliability, depending on the consequence of failure.
• Each failure mode may be assessed independently by limit state analysis.
• Permanent loads, imposed loads, earthquake, wind and hydraulic loads can be combined in a realistic way that reflects their various frequencies of occurrence.
• Partial material factors are consistent with confidence associated with each component.
• AS 4678 provides rules for site investigation, construction tolerances and performance monitoring.
  Although AS 4678 has made considerable improvements in design methodology, the design of safe/economic retaining walls still relies heavily on the selection of realistic soil properties.
• The design of retaining walls for cohesionless soils (e.g. sands, gravels, sandy silts etc., with a high friction angle around 35o), is considered to be both economical and safe, if correctly constructed.
• On the other hand, the design of economical retaining walls for cohesive soils (e.g. clays, silts etc with a high friction angle below 30o), is difficult. The selection of appropriate values for characteristic friction angle and cohesion for clay soils requires particular attention.
  AS 4678 is currently being reviewed, with the following major changes to be considered.
• It is planned to align the load factors in AS 4678 with the those published in the recently revised loading standard, AS/NZS 1170-2002, Parts 0, 1, 2 and 3.
• The design of earth-retaining structures for earthquake loads will be revised to align with draft AS 1170.4-2006.
• A major investigation and calibration of the standard is planned, with particular attention to problems of forward sliding in cohesive soils.
• An investigation of connection strength in reinforced soil structures (RSS) is also planned.

It is expected that these initiatives will lead to a more consistent approach for both cohesive and cohesionless soils.

Builders - BCA 2007
This article provides a discourse on "How to Cope with Insufficient Detail on Drawings" in the context of the BCA (Building Code of Australia). It forms part of a more comprehensive training package on the use and changes in BCA 2007, adopted from 1st May 2007.

How should a Builder proceed when there is insufficient or inadequate detail on the contract drawings and specifications? The most obvious option it to seek the appropriate information from the designer, but the following options are also available.

Method 1 - BCA Acceptable Construction Practice
This option involves reading the required detail directly from the BCA. The problem is that only a limited number of simple applications are available.

Method 2 - BCA Acceptable Construction Manuals (Australian Standards etc.)
These provide more comprehensive designs than are normally available in the BCA, although the standards are usually complex and often may be difficult to interpret. Most Australian Standards provide design rules, for use and interpretation by designers, and these are often lacking in the construction detail necessary on site. On the other hand, Industry Manuals may provide more construction-friendly details, although only a small number of such manuals have the status of "Acceptable Construction Manuals", as defined in the BCA.

Method 3 - Manufacturer's Details
Manufacturer's details, when available, provide information applicable to a limited range of particular products. Builders should ensure that the details meet the particular requirements of Australian Building Regulations and Australian Standards, particularly if the product is manufactured or developed overseas. Failure to acquire such assurance could result in installations that do not meet local requirements, and may be liable to rejection. One possibility is to assess the details under the BCA Alternative Solutions option.

Method 4 - Standard Details and Specifications
Industry Associations and organizations such as Electronic Blueprint provide details of specific forms of construction, often free of charge. To download free Electronic Blueprint construction specifications and details, access www.electronicblueprint.com.au Similar to the situation for Manufacturer's Details, Builders should obtain assurance that the details meet the particular requirements of Australian Building Regulations and Australian Standards, including (if necessary) assessment under the BCA Alternative Solutions option.

Method 5 - Common Practice
Tradesmen have a wealth of practical experience, but are often unaware of the detailed requirements of particular parts of the BCA or relevant Australian Standards. The Builder must assume responsibility for the work of the trades working under their direction.

Example
Problem: Determine the required size of steel lintel to span 3.3 m while supporting brick veneer.

Solution: The table shows that each of the first three methods provides a different size of lintel.

Caution: The designer (Architect, Engineer or Builder as appropriate) must select with care and be prepared to take responsibility for the choice. To ensure protection to the designer, the providers of Standard Details and Specifications must present all options, and allow designers to choose freely.