0 0.05 0.1 0.150

0.5

1

1.5

2

2.5

Maximum Story Drift Ratio [rad]

Sa

(T1, 5

%)

[g

]

The Effect of Exposed Base Plates on the Seismic Response of Steel Moment Resisting Frames

1. Develop a comprehensive dataset for exposed column base plate connections 2. Develop and calibrate a simulation model to replicate the behavior of exposed column base plate connections subjected to earthquake loading 3. Perform statistical analyses of calibrated parameters and base plate connection details 4. Determine the effect of base plate connections on the global seismic performance of steel moment resisting frames

Natural Sciences and Engineering Research Council of Canada – Undergraduate Student Research Award

Exposed column bases transfer gravity and seismic loads from a structure into its foundations. Field observations from earthquake damage have confirmed that these connections may be significantly flexible under applied moments even when they are designed as fixed.

The damage evaluation of exposed column bases subjected to earthquakes has lead to a classification of their failure modes (see Fig. 2)

Objective: Investigate exposed column bases with an anchor bolt yielding critical design. This failure mode may improve the seismic performance of steel moment frames due to the “self-centering” ability of the exposed column base.

In order to model the behavior of exposed column bases, data from previous experiments was collected. This database includes:

An analytical model was developed and calibrated with every specimen in the database in order to determine the following input model parameters:

Maryia Markhvida Supervisor: Prof. Dimitrios G. Lignos

Department of Civil Engineering and Applied Mechanics , McGill University

Figure 1: Typical base plate connection configuration (Source: Aviram et al. 2010)

Figure 2: Possible failure modes (Source: Gomez, 2009)

a) b) c)

d) e)

column weld tearing grout damage anchor bolt failure

concrete spalling base plate deformation

Exposed Based Plate Loading Conditions Base Plate Specifications Concrete Foundation and Grout Layer Details Anchor Rod Specifications Connection Weld Details Classification of Exposed Base Plate Failure Modes Fully Digitized Moment Rotation Histories

Rotational Stiffness, Ke

Yield Moment, My

Post-Yield Stiffness, Kp

Capping Deformation, θc

Post-Capping Stiffness, Kc

Ultimate Deformation, θu

Unloading Moment, Μunl

Prof. Taichiro Okazaki and Dr. T. Yamanishi (TIT). The financial support from NSERC and the SURE program is greatly appreciated.

Figure 3: Calibration examples (Data from Takamatsu, 2005; Choi, 2003)

Rotational Stiffness: Yield Moment:

Figure 4: Parameter comparison with existing equations (Equations from Hitaka, 2005; Takamatsu, 2005)

Gravity Frame Moment-Resisting Frame

Base Plate Connection Modeling

Once the statistical analysis is completed, the developed column base model will be implemented into the Open Source simulation platform OpenSees, in order to assess the collapse risk of steel moment-resisting frames subjected to earthquake loading (see Fig. 5).

Figure 5: Collapse evaluation of low rise steel moment resisting frames