WINDOWS Magazine Spring 2017 | Page 34

WINDOWS | TECHNICAL AWA TECHNICAL COMMITTEE INSTALLATION PROJECT RUSSELL HARRIS Technical Manager, Australian Window Association Following the successful launch of the AWA installation videos, work continues on this project to develop appropriate training and technical manuals. The Technical Committee recently reached another key milestone with the completion of the draft handbook which will be published later this year. The Technical Committee’s focus will now turn to the development of course content for the training modules. AS 1530.8 Public Comment on Draft Australian Standard (AS) 1530.8 Parts 1 and 2 Methods for fire tests on building materials, components and structures recently closed. In response to a number of changes in the draft standard, the Technical Committee formed a working group of R&D specialists to review and comment on the proposed changes. This work culminated in an AWA submission to Standards Australia on behalf of all members. There is no indication at this time from Standards Australia as to when this revision will be published. AS 2047 Amendment 2 of Australian Standard (AS) 2047 Windows and external glazed doors in buildings was recently published. The pertinent changes in this amendment are: • Correction of unit-of-measure for the Charpy Impact Test. • Update references to AS 4420.1. DOCUMENT NO. 201706/01 VERSION 1 RELEASED JUNE 2017 KEY MESSAGE WIND LOADS FOR RESIDENTIAL AND COMMERCIAL BUILDINGS Clause 2.3.1 Housing • Clause 2.3.2 Residential and Commercial WIND SPEED AND WIND PRESSURE All buildings are subject to the elements of extreme weather which includes high wind speeds. Wind loads on buildings can be substantial and in many cases will act as one of the most significant forces that the building will be subjected to. Wind speed and wind pressure are closely related, but are not the same. Wind load is considered to be a dynamic force as it varies greatly in intensity over time. As wind flows around a building, it exerts high pressure on the windward face and low pressure (suction) on the leeward face. Leading edges (corners) experience the greatest force due to wind acceleration. Wind speed is an expression of the velocity of the air moving past a stationary object. It is most commonly measured in metres per second (m/s). Site wind speeds are derived from recorded regional wind speed data, the local effects of terrain (height, topography and shielding) and the relevant annual probability of exceedance. Site wind speeds are the predicted speed of wind over the building site, and are determined without consideration of the effects of the building itself (ie calculated as if the building does not exist). Wind pressure is the force per unit area exerted over a structure by moving air. The pressure varies with the velocity of the air (both wind speed and direction) and the aerodynamic shape and orientation of the structure. Different parts of the same building experience different wind pressures given the same site wind speed. Differential wind pressure is the difference in pressure between the inside and outside of a building surface (for example, a window). Pressure is measured in pascals (Pa). Figure 1 KEY MESSAGES The AWA has recently published a Key Message to provide information and guidance on wind loads for commercial and residential buildings (image 01). The Key Message discusses relevant aspects of wind loading such as: • Regulatory requirements of the National Construction Code (NCC) and Australian Standard (AS) 2047 Windows and external glazed doors in buildings. The purpose of this Key Message is to provide general information about wind load requirements for windows in residential and commercial buildings. ABOUT WIND LOADS Public Comment on Draft Australian Standard (AS) 2688 Timber and composite doors closed in early June. The AWA sought comments from members which were considered by the Technical Committee prior to a submission to Standards Australia on behalf of all members. An important note is that the draft standard now includes an option for voluntary testing to AS 4420.1 in an informative appendix. There is no indication at this time from Standards Australia as to when this revision will be published. • Wind speed and pressure. AS 2047:2014 sets out the performance criteria for all windows in all buildings. These requirements fall into two categories based on building type and purpose: • AS 2688 Airflow over a House REGULATORY REQUIREMENTS • Determination of Wind Actions according to Australia/New Zealand Standard (AS/NZS) 1170.2 Structural Design Actions – Part 2 Wind Actions. • Responsibilities for determining wind loads under Australian Standard (AS) 2047 Windows and external glazed doors in buildings. The National Construction Code (NCC) prescribes that a building must perform adequately under all reasonably expected design actions and withstand extreme or frequently repeated design actions, including the effects of wind loads. The NCC references Australian/New Zealand Standard (AS/NZS) 1170.2 Structural Design Actions – Part 2 Wind Actions as the primary engineering standard used in the des