Post on 19-May-2015
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