Australian Standard – Commentary. AEES member and past president John Wilson has produced a publication titled “AS Summary This paper provides a short guide and worked examples illustrating the use of AS Structural design actions Part 4. Download AS _Earthquake Actions in Australia_pdf.
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Earlier this year CSIR Summary This paper provides a short guide and worked examples illustrating the use of AS Earthquake actions in Australia.
The examples assume that at least a static analysis has been selected, and therefore, sets out the data required to calculate the base shear. Many structures do not require this level of design effort as there are conditions for which no further work is required by the Standard.
The key to understanding AS This approach arises from the ax knowledge we have of earthquake risk in Australia coupled with the very low levels of earthquake risk we do currently expect. Process of designing for earthquake actions Earthquake actions are determined by considering the site hazard and the type and configuration of the structure.
The Standard also provides the means for reducing earthquake loads on a structure by achieving set levels of ductility. Materials design 1170.4 then provide detailing to enable the selected structural ductility to be achieved.
The aim is to avoid collapse. This requires the structure and indeed the whole building to be able to deform with the earthquake and absorb energy without vertical supports giving way.
Therefore, it is not expected that a structure subject to the design earthquake would be undamaged, but rather that the damage had not progressed to collapse. For Australian conditions, where we have scant knowledge of the earthquake activity, we design for a lateral equivalent static load, unless the structure is particularly vulnerable to dynamic effects.
The standard also sets out minimum detailing requirements that aim to provide buildings with a reasonable level of ductility.
AS Earthquake actions in Australia Worked examples_百度文库
In the event that a structure is subject to an earthquake, the ductility provided greatly improves its performance, regardless of the actual magnitude of the earthquake and the actual design actions. Analysis of the structure is not covered.
General principles Part 1: Permanent, imposed and other actions Part 2: Wind actions Part 3: Snow and ice actions Part 4: Earthquake actions in Australia AS As with all the parts of the series, Part 0 provides the annual probabilities of exceedance or, for buildings covered by the BCA, refers the user to those provided in the BCA.
Quick paths to an exit A you are designing one of the following structures, you can exit quickly to a simplified solution or even out of the Earthquake Standard altogether: Hazard at the site Once the appropriate annual probability of exceedance has been determined, AS The loads on the structure are then calculated based on this value. The site hazard is determined from Section 3 of the Standard.
The value of Z can be read from a Table or, for locations away from major centres of population, determined from the maps. This value is then multiplied by the probability factor kp xs determine the site hazard value kpZ for the appropriate annual probability of exceedance.
Influence of site sub-soil conditions The site sub-soil conditions are grouped into 5 categories Class Ae, Be, Ce, De or Ee ranging from hard rock to very soft materials. The soil type is determined by a 11700.4 investigation for taller longer period structures. The material in which the structure is laterally coupled to the ground provides the site class.
Generally, for short structures that are not of high importance, simply knowing whether the structure sits on rock or in soils of some depth eg.
Selecting the analysis method Once the annual probability of exceedance, the hazard value for the site, the sub-soil conditions and the building height are known, the required design effort can be determined using Table 2. This 1107.4 assumes that at least a static analysis has been selected, and therefore, the remaining data required to calculate the base shear has to be determined. The Table below shows how for many structures, there are points at which no further work is required. Section 6 sets out the method including the spectral shape factor, the structural ductility and performance factors, the natural period of vibration of the structure, etc.
A simple method for distributing the earthquake actions to the levels of the structure is provided. This is required for the highest hazard levels and tallest structures. Period of vibration of the structure The construction material, type of structure, and the period of the first mode of vibration all have an influence on the forces experienced by the structure.
In cases where a static or dynamic analysis is required, the first mode natural period of vibration of the structure is calculated T1. It is calculated by a simple 11704. given in Section 6 of the Standard.
AS 1170.4_Earthquake Actions in Australia_2007.pdf
The equation is based essentially on the height of the structure, but includes an adjustment for material type. The method of calculation given is the most reliable method available other than carrying out a full dynamic analysis and even then there are inherent modeling inaccuracies.
Determining the period of an existing structure, however, is a simple exercise involving measuring its vibrations. Spectral shape factor site hazard spectrum The period is then used to determine the spectral shape factor Ch T1 for the building on the site. For dynamic analysis, the effects of a number of periods of vibration may be summed to determine the action effects in the members and, therefore, a number of spectral shape factors may be used in the analysis.
Mu the Greek letter represents the structural ductility while Sp, the structural performance factor, is an adjustment made to calibrate the known performance of structure types to the calculated ductility. For the lowest values i. Detailing rules to achieve these levels of ductility can be highly complex.
Once the value of Mu is selected the structure must then be detailed to achieve that selected ductility.
The ductility is achieved by applying the detailing provided in the materials design Standards currently in use. In order to achieve the ductility assumed in design of the structure, it is essential that stiff elements should not impose themselves on the behavior of the seismic force resisting system. If they do, the structure will not exhibit the ductility required of it and will therefore attract a much higher load than that for which it is designed.
The Standard assumes that structures are irregular as the vast majority of structures in Australia fail to achieve regularity. Calculating the base shear For the vast majority of structures low height, normal importance on firm or shallow soils the next step is to estimate if the load is likely to be less than the wind load.
The base shear may be understood to be the percentage of the weight of the building to be applied laterally eg. Once the horizontal design action is calculated from the above information and the seismic weight of the structure, analysis can be carried out. The materials design Standards are then used to design the members for the required resistance including achieving the ductility assumed in determining the loads. Finally, the parts of the structure must be tied together and individually designed to perform.
Inter-storey drifts should be checked to ensure that parts such as stiff walls do not interfere with the seismic force resisting system. Walls will usually require a check of the resistance to face loading. The analysis and materials design is where AS The Australian Standard provides for simplified analysis methods based on the low level of hazard.
Also, as a result of the lower earthquake loads expected, the detailing required is minimal compared to that for such countries as New Zealand. Therefore, the materials design Standards are much simpler than those required in high hazard areas.
Worked examples To illustrate the use of the Standard, following are some examples of the design required for various site conditions. This will result in more effort in detailing to achieve the higher Mu assumed. A similar approach to reducing loads assuming a higher Mu value could be used where Z is high. The use of annual probabilities in the examples is based on recommendations to be proposed for adoption in the BCA at the time of adoption of the new Standard: General principles provides the link between the limit states actions imposed on the structure and the design of materials for resistance.
This was a group of loading experts from across the APEC region that met to create a means of establishing inter-changeability between the loading codes of different nations. The motivation for this move is the GATT agreement and the reduction of technical barriers to trade. The basic aim is to state the design event in terms of the annual probability of the action being exceeded.
The load is then defined for any annual probability of exceedance so that the design event is independent of the technical definition of the loads. One of the fundamental principles of this approach is the removal of hidden factors through the provision of an umbrella document that defines the loading and resistance levels for design using the design event approach.
This led to the development of Part 0.