Inelastic analysis-based design optimization of eccentrically braced steel frames

本研究旨在发展偏心支撑钢框架在地震作用下基于弹塑性分析的优化设计方法。他说，偏心支撑框架(EBF)的最先进的设计方法是能力设计方法，即根据规范指定的力调整杆件的大小，而所有其他构件则根据完全屈服和应变硬化的杆件产生的力进行比例调整。这种能力设计方法有四个主要缺点：1)它是由手工计算而不是由计算机实现的；2)它不能可靠地确定支撑开间中柱的内力；3)它不能考虑失稳效应；4)它不能识别杆件外部的弹塑性行为。他说，能力设计方法的这些缺点只能通过采用基于弹塑性分析的设计程序来克服。抗震设计有两种弹塑性分析方法，即非线性动力时程分析和Pushover分析。这些方法都不是没有陷阱的。考虑到Pushover分析的相对简单性，该建议将采用Pushover分析作为评估EBF抗震需求的主要工具，并在必要时采用时程分析来验证设计方案。考虑到使用非弹性分析的设计过程所需的巨大计算工作量，专门为EBF开发的计算机辅助工具确实是可取的。因此，将结构重量和地震破坏降至最低将是设计目标。能力设计理念将通过对钢构件的塑性需求施加约束来实现。例如，框架构件在连接之外的屈服将被禁止，或者如果不可避免的话将被严格控制。他说，拟议的研究工作不仅将把设计工程师从繁重的手工计算中解放出来，还将显著提高由拟议方法学设计的EBF的性能。

The objective of the proposed research is to develop an inelastic analysis-based design optimization methodology for eccentrically braced steel frames under earthquake loading.      The state-of-the-art design method for eccentrically braced frames (EBFs) is the capacity design approach, where the links are sized for code-specified forces while all other members are proportioned for the forces generated by the fully yielded and strain hardened links. The capacity design approach has four main shortcomings: 1) it is implemented by hand calculations instead of by computers; 2) it is unable to determine, with confidence, the internal forces for the columns in braced bays; 3) it cannot account for instability effect; and 4) it cannot identify inelastic behaviors outside the links.      These shortcomings of the capacity design approach can only be possibly overcome by employing an inelastic analysis-based design procedure. There exist two inelastic analysis methods for seismic design, i.e., nonlinear dynamic time history analysis and pushover analysis. None of these methods are pitfall free. Considering the relative simplicity of pushover analysis, this proposal will adopt pushover analysis as the main tool to evaluate seismic demands for EBFs, while the time history analysis is employed to verify the design solutions if necessary. In light of the tremendous computational efforts required for a design process using an inelastic analysis, a computer-aided tool specially developed for EBFs is indeed desirable.      Minimization of both structural weight and earthquake damage will be the design objective. The capacity design concept will be realized by imposing constraints on the plasticity demand for steel members. For example, yielding in the frame members outside the links will be prohibited, or strictly controlled if unavoidable.      The proposed research work will not only liberate design engineers from arduous hand calculations but also significantly improve the performance of the EBFs designed by the proposed methodology.