A102

Effectiveness of Repair Action in Recovering Steel Frames with Earthquake-induced Irregularity〇Kun-Sian LIN, Masahiro KURATA, Tafu KAWAMOTO, Shintaro MATSUO, Didier PETTINGA

Structural irregularity, such as irregular structuralarrangement, mass, and stiffness, increase vulnerability
in buildings, and modern seismic codes impose

design level and input to the shaking table sequentially,as shown in Table 1.
4-story SMRF

7.0 m

1. Introduction

seismic damage results in severe damage underaftershocks or future events. Therefore, identifying

3@3.4 mpenalties for them. Structural irregularity induced byand recovering regularity by rapid repair methods are

3.6 m

structural irregularity immediately after earthquakes
increasingly important.

2@5.0 mThis study first presents an overview of a full-scaleFig. 1 Floor plans and elevations, and photo of theshaking table test for a four-story steel frame. The

adopted 4-story SMRF

structural response identification, which determines thechanges in natural frequencies, modal shape, and story

Table 1. A list of the loading cases

stiffness of the 4-story building, was performedIDGround motion

according to the test results. The applicability and1JMA Kobe NS X dir. 16%

effectiveness of a simple repair method of retightening

2JMA Kobe NS Y dir. 16%

anchor rods for exposed column bases were3

OS-2 Y dir. 20%

investigated through tests and simulations.

4JMA Kobe NS X dir. 50%

5OS-2 XY dir. 50%

6

JMA Kobe NS XY dirs. 50% UD Z dir. 100%

2. E-defense shaking table testing of a steel frame
A full-scale shaking table test of a hospital facility
specimen was conducted.. The specimen comprises a

3. System identification results

four-story steel moment-resisting frame (SMRF) and a

The natural frequencies, modal shape, and story

three-story base-isolated steel frame. This study

stiffness of the 4-story SMRF were identified from theexamines the behavior and the damage of the 4-story

test results, as shown in Fig. 2. The story stiffness was

SMRF only. Fig. 1. shows the general floor plans andidentified directly with a method proposed for damage

elevations of the 4-story SMRF. The structural design

evaluation of a steel structure based on ambient

followed the building law of Japan with reserved

vibration measurements.

strength of 1.5 times the code minimum and adopted
the weak-base/strong-column design.

For story stiffness, the results become relatively
stable after 10 seconds. In ID1, the story stiffness

Two ground motions were scaled to six scales,remained unchanged, implying the structure is in theincluding elastic level, life safety level, and 1.5 times

elastic range. In ID6, the story stiffness decreased

the ground motions of ID5 and ID6 by 23% and 4%,

at around 13 seconds corresponded to the visualrespectively. It indicated that the simple repair methodobservation of column base fracture.

could rapidly revert the overall stiffness of the column

Vertical stiffness (kN/cm)

400

base and reduce the story drift after a strong earthquake

ID1such as ID4.

300
200

41F
2F
3F
4F

100
00400

510152025Time (s)

30

200

35

40

2
11F
2F
3F
4F

300

ID5 w/o re-tightening
ID5 w/ re-tightening
ID6 w/o re-tightening
ID6 w/ re-tightening

3StoryVertical stiffness (kN/cm)

significantly at the first floor. The reduction in stiffness

ID6X dir.

000.5

11.5
2
Story Drift (%)

2.53Fig. 4 Comparison of dynamic responses with and100

without retightening process

005

10152025Time (s)3035405. Conclusions
The study concluded several remarks as listed follows:

Fig. 2 Identification results of the mode shape and(1) System identification results indicated that thestory stiffness in ID1 and ID6

structural irregularity caused by damage enables to beidentified from the changes in structural characteristics.

4. Numerical simulation on repair(2) The irregularity of changes in mode shapes

A unique feature of the exposed-type column base iscorresponds to concentrated deformation at the lower

a simple repair option, where constructors retighten

floor resulting in severe damage in subsequent groundelongated anchor rods with ensured ductility bymotions as a failure of column bases.

specifications, as shown in Fig. 3.

(3) The simple repair method of the retightening
process of anchor rods was proven to be effective

Acceleration

through the test program and subsequent analyses for
low-rise buildings.
ReferenceRetightening processof anchor rods
MajorearthquakeTimeAftershocks

Fig. 3 Column base repair methodology1) Lin KS., Kurata M., Pettinga D., Suzuki Y., Matsuo
M., Perea T. (2023). Effectiveness of repairing
yielding anchor rods in exposed column bases insteel

structures.

Earthquake

Engineering&Structural Dynamics.
The numerical model of the four-story building was2) Lin KS., Kurata M., Kawamoto T., Matsuo S.,

developed using OpenSees framework to investigate

Pettinga D. Identification and reparation ofthe effectiveness of the repair method. Dynamic

earthquake-induced irregularity of steel frames withanalysis with and without the repair between eachweak-base/strong-column design. 10th European

inputted ground motion was performed. Fig. 4 showed

Workshop on the Seismic Behaviour of Irregularthat the repair reduced the maximum story drifts underand Complex Structures, Catania, 2023.10