ارزیابی مقاومت طراحی برای بتن و اعضای کامپوزیت فولاد و بتن
Abstract
1- Introduction
2- Target reliability index and design resistance
3- Reliability analysis
4- Applications
5- Conclusions
References
Abstract
This study evaluates the performance of the design equations given in the Australian/New Zealand bridge and steel structures design standards AS 5100.6, AS 4100 and NZS 3404.1 based on reliability analysis. For this evaluation, the following two methods were utilised: (i) a capacity factor calibration method to meet the target reliability level when there are a limited number of steel yield strength tests; and (ii) an inverse reliability analysis method to calculate the required minimum number of steel yield strength tests to achieve the target reliability level when using capacity factors provided in the design standards. The methods were applied to steel and composite members including I-beams, hollow section columns, CFST columns, and composite beams. To ensure the adoptability of imported steel for these members, structural steel that conforms to European, Korean, Japanese, American, Chinese and Australasian manufacturing standards were considered in the analyses. The results showed that, for an infinite range of manufacturing data, the capacity factors were insensitive to the different manufacturing tolerances. Furthermore, when a limited number of mechanical tests were available, a much larger number of results were needed to achieve the target capacity factor for composite members in comparison with non-composite members. Finally, when considering hollow sections used as columns, the current design equations were unable to deliver the target reliability levels for any of the manufacturing standards used internationally.
Introduction
Structural steel is an international commodity that is commonly shipped thousands of miles from where it is produced to wherever there is a market. The members of the industry association worldsteel represent around 85% of world crude steel production. Fig. 1(a) presents the annual crude steel production data from worldsteel members in Australia, China, Japan, UK and USA between 1980 and 2016 [1]. As can be seen from Fig. 1(a), whilst Australia, Japan, UK and USA have broadly maintained their output, steel production in China has increased remarkably over this 36-year period. As can be seen from Fig. 1(b), China accounted for 50% of world steel production in 2016, amounting to an output of 808.4 Mt. It is therefore important for designers in the Asia-Pacific region to be able to gain access to the vast supply of Chinese made steel. For an Asia-Pacific country who wishes to adopt the Eurocodes as their national design standard, an immediate problem is that the normative references in Eurocode 3 [2] and 4 [3] list harmonised European product and execution standards (hENs). Two options exist for designers in these countries: source steel products from mills that manufacture to hENs; or deem steel products manufactured to other standards to be equivalent in performance to hENs. Whilst the former option may be considered attractive, sourcing can be problematical and CE Marking is not mandatory in countries outside the European Economic Area where the Construction Products Regulation [4] is enforced. As a consequence of this, the latter option of accepting equivalent steel products is commonly used. In Singapore and Hong Kong, two guides have been developed to enable designers to use alternative steel products that are deemed to have equivalent performance to hENs [5,6]. Provided that an alternative steel product is manufactured to a national standard recognized by these two guides, the steel mill is required to supply: a factory production control (FPC) certificate issued by a notified body; and a test certificate for each batch of steel product delivered to the project issued by an independent third-party inspection agency (the latter is consistent with the level of traceability required by EN 1090-2 [7] for grade S355JR and S355J0 steel in EXC2, EXC3 and EXC4 structures). Depending on the alternative steel product satisfying certain requirements [8], three product classes are defined with different partial factor values, viz. Class 1 with γM0 = 1.0 (i.e. deemed to be directly equivalent to hENs, so the recommended value in Eurocode 3 and 4 is used); Class 2 with γM0 = 1.1; and Class 3 with fyd = 170 MPa for steel thicknesses not N16 mm (an identical value is given for unidentified steel in Australasia).