Seismic Behavior of Column Base Connections in Braced Steel Structures

本研究项目的主要目标是：(1)确定破坏的原因，(2)建立合理实用的分析和设计模型，(3)针对类似于北岭地震中观察到的钢结构中的柱基连接，制定升级方案。柱基是钢结构抗弯或支撑框架结构的重要组成部分。设计人员面临着两个关键问题：(1)如何设计轴力、弯矩和剪力组合的柱基；(2)对于给定的柱基设计和细部设计，可以指望多大程度的固定？这两个问题在目前的鞍钢LRFD钢结构手册中都没有涉及。地震中观察到了大量的柱基破坏。这个问题没有得到解决，因为目前正在进行的SAC计划主要关注梁柱弯矩连接的问题。柱基连接问题的重要性已经得到认可，但目前还没有计划或正在进行的研究。需要进行全面的研究工作，以了解柱基连接的性能，并制定现实的设计和分析程序。这可以通过关注通过柱基连接的“加载路径”来最好地实现。本研究的主要工作包括：建立柱脚在弯矩、剪力和轴力共同作用下的有限元分析模型，并进行验证。为了找出柱基性能差的原因，识别破坏模式，并根据柱基的脆性破坏潜力对其进行表征，(3)推广常用柱基连接的模型，建立主要的力流动路径，建立反映力流主要特征的简化基础连接设计/分析模型，为现有结构中潜在缺陷的柱基抗震评估和升级制定实用的细节和设计程序。

The principal objectives of this research project are: (1) to determine the causes of damage, (2) to formulate rational and practical analysis and design model, (3) and to develop upgrading schemes, for column base connections in steel structures similar to those observed in Northridge earthquake.Column bases are an essential element of steel moment-resisting or braced frame structures. The designers face two critical issues: (1) How to design a column base for combined axial, moment and shear forces, and (2) What degree of fixity can be counted upon for a given column base design and detailing? Neither of these two issues is addressed in the current AISC LRFD Manual for Steel Construction.Numerous column base failures were observed in earthquakes.This problem is not addressed as the currently in progress SAC Program is primarily focusing on the problem of beam-to-column moment connections. The importance of the problem of column base connections is recognized but no study is either planned or under way.A comprehensive research effort is needed to understand the behavior of column base connections and formulate realistic design and analysis procedures. This can be best accomplished by focusing on the "load path" through the column base connections.1. The principal tasks of this research include: formulation and verification of a FEM-based analytical model of the column base under combined moment, shear and axial force, (2.) to pin-point the causes of poor column base performance, identify the failure modes, and characterize them in terms of the potential for brittle failure, (3) to generalize the model for commonly used column base connections and establish the dominant flow path of forces, to formulate a simplified base connection design/analysis model that captures the principal characteristics of the force flow, to formulate practical details and design procedures for seismic evaluation and upgrading of potentially deficient column bases in existing structures.