Short Course on Seismic Design of Reinforced and Confined Masonry Buildings

February 17-21, 2014, IIT Gandhinagar, India

Analysis of Confined Masonry Buildings: Part 1

Dr. Svetlana BrzevBCIT, Vancouver, Canada

IIT Gandhinagar, India

Acknowledgments

Coauthors: Juan José Pérez-Gavilán E, UNAM Mexico Kiran Rangwani, IIT Gandhinagar, India

EERI Confined Masonry Network – authors of the confined masonry guide: Roberto Meli and others

Topics

Part 1: Simplified Method (Svetlana Brzev)

Part 2: Wide Column Model (J.J. Perez Gavilan)

The Simplified Method (SM)

Based on an idealized distribution of lateral seismic forces in regular shear wall structures with rigid diaphragms.

Shear strength of all walls at any floor level is required to exceed the seismic demand (applied shear force due to earthquake ground shaking)

Assumptions

1.It is assumed that all walls at each floor level fail simultaneously.

2.The walls have shear-dominant behaviour (the effect of bending is ignored).

3.The method assumes rigid diaphragm behaviour.

4.The method ignores torsional effects.

Theoretical Background

The goal:Shear strength of all walls at any floor level (VR ) should exceed the seismic shear force demand (Vx) at the same level

Seismic Shear Force Demand

Interstorey shear force Vx

ix QV

Seismic Force Distribution to Individual WallsWall shear demand Vjx

Seismic Force Distribution to Individual Walls

xN

jjx

jxxjxjx V

k

kDkV

1

j

jAEjjx H

AFGk

N

jjAEj

jAE

xjx

AF

AFVV j

1

Wall resistance VRj

Storey Shear Resistance

Seismic loadAp

Aw

Wall cross-section Aj

Storey Shear Resistance

1AEF when 33.1L

H

2

33.1

H

LFAE when 33.1

L

H

AEjsRj FAfV

Wall Density Index (d)One of the key indicators of seismic resistance

p

w

A

Ad

Seismic loadAp

Aw

Wall Density Index Derivations

Goal: resistance greater than demand

ws

N

jjsR AfAfV

1

ThB WAV pT nwAW

s

h

f

wnAd

BR VV

Wall Density Index – IndiaAllowable shear stress

(N/mm2)Floor weight

(kN/m2)Number of storeys Seismic Zone

III IV V

0.3

6.0

1 1.6 2.4 3.6

2 3.2 4.8 7.2

3 4.8 7.2 10.8

0.4

1 1.2 1.8 2.7

2 2.4 3.6 5.4

3 3.6 5.4 8.1

0.5

1 1.0 1.5 2.2

2 2.0 2.9 4.4

3 2.9 4.4 6.5

0.3

8.0

1 2.2 3.2 4.8

2 4.3 6.4 9.6

3 6.5 9.6 14.4

0.4

1 1.6 2.4 3.6

2 3.2 4.8 7.2

3 4.8 7.2 10.8

0.5

1 1.3 2.0 2.9

2 2.6 3.9 5.8

3 3.9 5.8 8.7

Assumptions

1. =2.5 for confined masonry (currently not addressed

by IS 1893) 

2. = 2.5 assuming the fundamental period range from 0.1 to 0.4 sec

3. Importance factor =1 assuming regular importance

4. Allowable masonry shear stress (fs): from 0.3 to 0.5

N/mm2

5. Floor weight (w) – two values: 6.0 kN/m2 (light-weight floor structure) and 8.0 kN/m2 (heavy-weight floor structure e.g. RC slab).

Further Reading

Attached writeup (document) on the Simplified Method

Seismic Design Guide for Low-Rise Confined Masonry Buildings, EERI, 2011

www.confinedmasonry.org