Development of inelastic design procedures for stainless steel indeterminate structures

不锈钢优异的耐大气腐蚀性和良好的机械性能使其非常适合各种结构应用，特别是在恶劣的环境中，或者耐用性和低维护成本是关键设计标准的地方。阻碍不锈钢在建筑中更广泛应用的主要缺点是其高材料成本和价格波动。然而，考虑到项目的整个生命周期成本和可持续性，由于在项目生命周期结束时材料的回收或再利用潜力很大，因此当考虑到成本时，不锈钢更具吸引力。不锈钢结构的设计受到一些国际设计规范的保护，这些规范要么最近被引入，要么最近根据最近的实验测试进行了修订，从而表明近年来全世界对不锈钢的兴趣。尽管没有明确定义的屈服应力，所有当前的不锈钢设计标准都采用等效屈服应力，并假设不锈钢与碳钢一样具有双线性（弹性，完全塑性）行为，以保持与传统碳钢设计指南的一致性。鉴于不锈钢的高材料成本，提高现有设计指导的效率是有必要的。改进可以通过校准现有的设计程序来实现，其中一些是基于工程判断和有限的测试数据，针对额外的实验结果，或者通过设计更准确的设计方法来符合实际的材料响应。在任何情况下，更有效但更安全的设计规则都是可取的。大多数发表的关于不锈钢结构的研究文章都集中在单个构件的响应上。尽管不锈钢的延性优于普通结构钢，但由于相关实验数据不足，目前的任何结构设计规范都没有对不锈钢结构的塑性全局分析给出规定。在欧洲规范3：第1.4部分中，尽管在同一规范中规定了粗体元件的长细限制，但明确指出“没有给出塑性整体分析的规则”，不允许对延性材料制成的不确定结构进行塑性设计的争议是显而易见的。此外，由于缺乏不锈钢框架的相关实验数据，在任何不锈钢设计规范中都没有规定考虑不锈钢框架中的二阶效应的具体设计规定。当前设计指南的缺陷使不锈钢与其他材料相比处于劣势，从而阻碍了其在应用中的使用，如果设计标准没有由于当前知识的差距而对其设计施加严格的限制，它可能是首选的解决方案。该项目旨在通过对两跨连续梁、门式框架和先进的数值分析进行实验研究，研究不锈钢非定常结构的结构响应，并制定适当的设计规则。将产生适合数值模型验证的实验结果，并允许对不确定不锈钢结构的极限响应进行严格的研究。将评估当前设计程序的准确性（即不允许在不确定结构中进行塑性设计或部分力矩重新分配），并探索将塑性设计应用于不锈钢结构的可能性。据设想，拟议的项目将导致适合纳入en1993：第1.4部分的设计规则。

The excellent atmospheric corrosion resistance and favourable mechanical properties of stainless steel make it well suited for a range of structural applications, particularly in aggressive environments or where durability and low maintenance costs are crucial design criteria. The main disadvantage hindering the more widespread usage of stainless steel in construction is its high material cost and price volatility. However, life-cycle costing and sustainability considerations make stainless steels more attractive when cost is considered over the full life of the project, due to the high potential to recycle or reuse the material at the end of life of the project.The design of stainless steel structures is covered by a number of international design codes, which have either recently been introduced or or were recently amended in light of recent experimental tests, thus indicating the worldwide interest stainless steel has received in recent years. Despite the absence of a well-defined yield stress, all current design standards for stainless steel adopt an equivalent yield stress and assume bilinear (elastic, perfectly-plastic) behaviour for stainless steel as for carbon steel in an attempt to maintain consistency with traditional carbon steel design guidance.Given the high material cost of stainless steel, improving the efficiency of existing design guidance is warranted. Improvements can be made either by calibrating the existing design procedures, some of which are based on engineering judgment and limited test data, against additional experimental results, or by devising more accurate design approaches in line with actual material response. In any case more efficient yet safe design rules are desirable.The majority of published research articles on stainless steel structures focus on the response of individual members. Due to insufficient relevant experimental data, no rules are given for plastic global analysis of indeterminate stainless steel structures in any current structural design code, even though the ductility of stainless steel is superior to that of ordinary structural steel. The controversy of not allowing plastic design for an indeterminate structure made of a ductile material is obvious in Eurocode 3:Part 1.4 where it is explicitly stated that "No rules are given for plastic global analysis" even though a slenderness limit for stocky elements is specified in the same code. Moreover, because of the lack of relevant experimental data for stainless steel frames, no specific design provisions to account for second order effects in stainless steel frames are specified in any stainless steel design code. Deficiencies in current design guidance puts stainless steel at a disadvantage compared to other materials thereby hindering its use in applications where it might be the preferred solution, had the design standards not imposed strict restrictions to its design due to a gap in current knowledge.The proposed project aims at investigating the structural response of stainless steel indeterminate structures and developing appropriate design rules, by means of experimental studies on two-span continuous beams, as well as portal frames and advanced numerical analyses. Experimental results, suitable for the validation of numerical models, will be generated and will allow a rigorous study of the ultimate response of indeterminate stainless steel structures. The accuracy of current design procedures (i.e. not allowing for plastic design or partial moment redistribution in indeterminate structures) will be assessed and the possibility to apply plastic design to stainless steel structures will be explored. It is envisaged that the proposed project will lead to design rules suitable for incorporation in EN 1993: Part 1.4.