Seismic Analysis and Fragility Assessment of Masonry Infilled Steel

Frame Structure by means of Incremental Dynamic Analysis (IDA)

and Cloud MethodMSc Civil Engineering (with Seismic Design)

Biao Song

Supervisor: Prof Dina D’Ayala

Over the past few decades, a large number of masonry infilled frame

structures have been built in seismic-prone regions around the world

with the advantages such as light weight, fast installation and cost

efficiency. During the past earthquakes, these structures have

constituted a significant part of high risk constructions in urban and rural

areas. However, based on traditional design, the masonry infills in steel

frames are considered as non-structural components and their influence

in providing stiffness and strength to the whole system is ignored by

engineers.

Therefore, this study aims to investigate the seismic behaviour of low-

rise and mid-rise steel frames with masonry infill walls by means of

Incremental Dynamic Analysis (IDA) and Nonlinear Time History

Analysis (NLTHA) based Cloud Analysis.

Methodology

Introduction & Main Aim

Design & Modelling

10 groups of models with different geometric properties have been

designed using ETABS 2015. In each group, the followings have been

considered:

Design codes: gravity design code (low code) and seismic design

code (high code);

Structural systems: moment resisting frame (MRF) and concentrically

braced frame (CBF).

Then, these models have been realised and analysed in SeismoStruct

(v.7) by considering the presence of masonry infills.

Selection of Earthquake Records

IDA & Cloud Analysis Results

Fragility Analysis ResultsBased on IDA Results

Based on Cloud Analysis Results

Selection of Damage Threshold

Damage States

Model 10 (MRF)Slight Moderate Extensive Complete

HAZUS 0.4 % 0.8 % 2 % 5.33 %

Manually defined

from SPO0.91 % 2.09 % 3.66 % 4.8 %

Discussion and Conclusion

Masonry infills can increase the lateral stiffness and strength of the

steel frame structures in a large extent and therefore the fragility

performance of them can be improved.

Considering the equivalent lateral loads in design stage (seismic

code) can enhance the lateral resistance, ultimate capacity and then

fragility performance of steel frame structures.

The steel grades only affect the strength of the steel frame structures.

The fragility curves have high sensitivity to the capacity of the whole

steel frame structure and the values of damage thresholds selected.

Design in ETABS 2015

Modelling and

analysing

models with

and without

masonry infills

in

SeismoStruct

(v.7)