Seismic Behavior of Column Base Connections in Braced Steel Structures

本研究项目的主要目标是：(1)确定破坏原因，(2)制定合理实用的分析和设计模型，(3)制定与Northridge地震类似的钢结构柱基础连接的升级方案。柱基座是钢抗弯矩或支撑框架结构的重要组成部分。设计人员面临两个关键问题：(1)如何设计轴力、弯矩和剪力联合作用下的柱基座，以及(2)给定柱基座设计和细节设计时可指望的固定程度是多少？这两个问题都没有在现行的AISC LRFD钢结构手册中得到解决。在地震中观察到许多柱基破坏。这个问题没有得到解决，因为目前正在进行的SAC项目主要关注的是梁柱之间的弯矩连接问题。柱基连接问题的重要性已得到承认，但没有计划或正在进行研究。需要进行全面的研究工作，以了解柱基座连接的行为，并制定切合实际的设计和分析程序。这可以通过关注通过柱基座连接的“加载路径”来最好地完成。本研究的主要任务包括：建立并验证了基于有限元法的弯矩、剪力和轴力联合作用下柱基座解析模型；(2)明确柱基座性能差的原因，识别破坏模式，并从脆性破坏的可能性方面对其进行表征；(3)推广常用柱基座连接的模型，建立力的主导流道；制定一套简化的基础连接设计/分析模型，以反映受力流动的主要特征，为现有结构中可能存在缺陷的柱基础进行地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.