Asian Journal of Civil Engineering (2021) 22:443–460
https://doi.org/10.1007/s42107-020-00324-1
ORIGINAL PAPER
Analysis and seismic retrofitting of unreinforced masonry building:
a case study
Ishfaq Aziz1 · Raquib Ahsan1 · Md. Shadman Sakib2 · Shamontee Aziz3 · Md. Aminul Islam3 · Mehedi Ahmed Ansary1
Received: 14 July 2020 / Accepted: 2 November 2020 / Published online: 2 January 2021
© Springer Nature Switzerland AG 2021
Abstract
Unreinforced masonry structure (URM) consists of a major portion of existing structures in under-developed and developing
countries all over the world. Most of these URM structures are non-engineered which usually do not conform to local building codes and would be considered significantly deficient to international standards. So, seismic vulnerability assessment of
these URM structures is of major significance. The present paper addresses this issue with a systematic approach to assess
and analyze the structural vulnerability of a non-engineered URM building. Consequently, a complete retrofitting design
procedure is discussed followed by construction and field implementation. Initially, a detailed engineering assessment of the
whole structure was carried out which included site investigation, rigorous laboratory and in-situ tests, and development of
a 3D finite element model for structural analysis. Analysis showed that lateral shear stresses of the load-bearing walls were
higher than their acceptable limits when subjected to code specified loading. The flexural strengths of the RC beams were
also found to be inadequate. As a solution, the beams were retrofitted with U shaped reinforced concrete jackets, while two
alternative methods were proposed for the retrofitting of the load-bearing walls based on design requirement viz. Ferrocement overlay (for low stress) and Reinforced Concrete jacketing (for high stress). Stresses under most of the wall strip
footings were found to surpass the soil bearing capacity, so retrofitting was done by increasing footing widths to meet the
soil’s allowable bearing capacity. Finally, the implementation of the retrofitting design in the actual structure along with the
construction procedure has been presented. The present study is expected to provide a comprehensive guideline for engineers
to carry out seismic vulnerability assessment, structural retrofitting design, and the procedure of its implementation during
field construction in the concerned URM structure.
Keywords Unreinforced masonry · Ferro-cement · RC jacketing · Seismic retrofitting
Introduction
In under-developed and developing countries, masonry
structures comprise a good portion of the total buildings
built in the twentieth century. In the case of Bangladesh,
most of the unreinforced masonry (URM) structures still
standing today were built in the pre-independence period
* Shamontee Aziz
shamontee.aziz1@gmail.com
1
Department of Civil Engineering, Bangladesh University
of Engineering and Technology, Dhaka, Bangladesh
2
Department of Civil Engineering, University of Asia Pacific,
Dhaka, Bangladesh
3
BUET-Japan Institute of Disaster Prevention and Urban
Safety, Bangladesh University of Engineering
and Technology, Dhaka, Bangladesh
(1949–1971). No national seismic code existed during that
period. Owing to the tectonic framework and existence of
three major active fault lines within the country (Islam et al.
2016) and being one of the most densely populated regions
in the world, Bangladesh is in high seismic risk. At present
these masonry structures are used as government offices,
headquarters, factory units, religious centers, and residential
quarters, which increases the risk of damage and casualties
in case of a seismic event. So, proper engineering assessment of these structures along with required retrofitting and
rehabilitation is a dire need.
The load-bearing walls of the unreinforced masonry
structures are subjected to both gravity loading and lateral
loading. When subjected to strong earthquakes, tensile and
shearing stresses in the walls of masonry buildings may
cause severe damage to these structures. To reduce damage due to an earthquake, either the seismic capacity of the
13
Vol.:(0123456789)
444
structure needs to be increased by including additional shear
walls, infill walls, steel bracing, base isolation devices or by
other retrofitting measures (i.e. Ferro-cement, RC overlay,
RC jacketing etc.). The primary objective is to increase its
seismic resistance to a code specified level (for structures in
Bangladesh, the current code is BNBC 2020).
One common method of retrofitting of the masonry walls
is to apply Ferro-cement lamination composite, which, on
infilled masonry, changes the shear dominated failure to
flexure failure. The composite’s ductile strength depends on
the effective volume fraction, mesh type and its orientation
within the matrix (Prawel and Reinhorn 1982). According
to the studies by Reinhorn and Prawal (1985) the ferrocement overlay either fails by diagonal tension (ductile) or
de-attachment (bond failure). Besides, they found that bond
anchors have a dominant effect on the development of this
mechanism. Under static cyclic test, retrofitting with ferrocement overlay with wire meshes increased the in-plane lateral resistance by a factor of 1.5 (Abrams and Lynch 2001).
Bansal et al. (2008) found that wire mesh in ferrocement
oriented at 45° had the highest ultimate capacity compared
to other orientations. However, in respect of strength to cost
ratio wire mesh having 0° orientation had the most economically efficient outcome. Sen et al. (2019) also observed that
an effective mesh reinforcement of 0.16% increased the
lateral strength, initial stiffness, and energy dissipation
approximately two folds under lateral cyclic loading. A lime
base mortar reinforced with a carbon mesh was proposed
by Guerreiro et al. (2020) to reinforce masonry wall faces
which provided improved mechanical strength and avoided
unbalanced strength concentration on walls.
Another effective way of increasing the shear strength
of the load-bearing walls to the extent that flexural failure
consistently occurs is to apply a thin layer of cement plaster
over high strength steel reinforcement. This improves the
in-plane resistance of shear by a factor of 1.25–2.90 (Jabarov
et al. 1980; Sheppard and Tercelj 1980). There are also several case studies reported in professional literature where
reinforced plaster coatings were used to strengthen existing masonry structures (Guoliang 1980; Willie and Dean
1975). The out-of-plane resistance is substantially improved
as is the composite ductility. The improvement of strength
depends on the strengthening layer thickness, cement mortar strength, reinforcement quantity and means of bonding
with the retrofitted wall and the degree of masonry damage (ElGawady et al. 2004). Ghiasi et al. (2013) explained
different retrofitting options for URM foundation and their
applicability from a practical perspective. He adopted two
strategies for rehabilitation of the structure: one by physical
extension of the existing foundation and the other by the
improvement of subsoil layers. Apart from these, there have
13
Asian Journal of Civil Engineering (2021) 22:443–460
been several case studies leading to complete restoration of
historical masonry structure based on finite element analysis and laboratory experimental data (Hancilar et al. 2012;
Bozkurt et al. 2016; Sayin et al. 2019).
Over the years, there have been many studies on different
beam retrofitting techniques and the parameters governing
post-retrofitted performance. Surface roughness is a vital
determinant in retrofitted beam performance level (Cheong
and MacAlevey 2000). They observed a significant difference
in the behavior of the jacketed beam whose interface was
fully and partially roughened. Seleem et al. (2009) evaluated
the static response of beams retrofitted with U shaped RC
jackets in terms of strength, stiffness, and composite action.
The test result indicated a vital effect of the presence of stirrup in the concreting jackets in the enhancement of both stiffness and ultimate load capacity of the retrofitted beam. RC
jacketed beams showed significant improvement in flexure
capacity and mechanical behavior, compared to ordinary
reinforced beams of the same dimension, even though the
cores of the jacketed beams were damaged (Altun 2004).
Shehata et al. (2009) investigated the impact of the shear
stud in strengthening existing beams by adding high strength
concrete layers. As per studies by Raval and Dave (2012),
the use of shear connectors and bonding agents paired with
micro-concrete is much more efficient compared to other
jacketing alternatives in enhancing the performance level
of beams. Chaturvedi and Patel (2016) observed improved
behavior of RC jacketed beams in terms of deflection and
strength. Besides, Gorai and Maiti (2016) presented various
techniques for strengthening damaged structures.
Although the studies conducted by different researchers
present various building retrofitting procedures, there is no
comprehensive reference on unreinforced masonry structures rehabilitation—covering all the activities from vulnerability assessment, retrofit design, to field implementation
with elaborate -construction procedure. To bridge this gap,
the paper aims to be a complete reference set to seismic vulnerability assessment, analysis, retrofit design and post-operative appraisal for non-engineered unreinforced masonry
structures. Initially, a condition assessment survey was conducted to assess the as-built condition of the structure. The
required parameters for Detailed Engineering Assessment
(DEA) were determined by conducting in-situ and laboratory tests. Then, finite element analysis of the structure was
performed to analyze its response to seismic loading under
the current state. Based on the numerical analysis results,
laboratory tests and findings of past researches, retrofitting
schemes were designed for all the load-bearing members
which were found inadequate. Finally, the constructions of
the newly retrofitted portions of the whole structure were
carried out all of which are explained in this paper.
Asian Journal of Civil Engineering (2021) 22:443–460
445
Methodology
Building features
A visual inspection of an unreinforced masonry building
having a plan dimension of 31 m × 10.7 m (102′ × 35′) was
carried out to observe its existing condition. The office
building was constructed in 1960 and has two parts separated by an expansion joint. Whereas, the northern part of
the building is two storied with an identical plan in both
the stories, the southern part is four storied (Grid A to C of
Fig. 6b). Some building features are summarized in Table 1.
Visual observation
Initial measurements of the building were taken to prepare
as-built drawings. During field survey and assessment of
existing condition, various structural members of the building were found in good condition. No visible signs of cracks
or distress were found in the beams, load-bearing walls
and slabs. However, some of the walls on the ground floor
appeared to be moist and the partition walls were found to be
deteriorating due to the loss of the mortars’ binding capacity.
Figure 1 shows the load-bearing brick columns, which may
be susceptible to short column failure under seismic loading.
Data collection and testing
The concrete’s strength in the existing beams and slabs has
been assessed by extracting cylindrical concrete core samples and performing their compressive strength test according to ASTM C42. The diameter of the concrete core sample
was 68 mm with minimum length/diameter ratio of 1.0. The
core strength test results are summarized in Table 2. Combined failure was obtained in all the cases which represents
the failure of both mortar and brick aggregate that was used
in the concrete.
The compressive strength test on two samples of brick
was done as per ASTM C67 and their compressive strengths
were found to be 20.75 MPa and 17.51 MPa. Brick shear test
(Table 3) was performed on masonry wall to estimate allowable shear strength Fv, which in turn was used to calculate
Table 1 Building features of the
studied building
Fig. 1 Load bearing brick columns
allowable compressive stress f’mand modulus of elasticity
(Em) of masonry using the proposed equation of Bangladesh National Building Code (BNBC 1993). Minimum shear
stress was found to be on the safe side. The compressive
strength of masonry and modulus of elasticity of brick were
7.5 MPa and 5625 MPa, respectively. Mortar grade was M2
having mix proportion of 1:4 (BNBC 1993). These values
have been used for the structural analysis in the present
study.
The slab thickness was measured by drilling a small portion of the slab, as shown in Fig. 2. Schematic diagrams of
the beams are shown in Fig. 3. The beams, along with the
slabs were scanned, using an electro-magnetic rebar scanner,
for checking the presence of reinforcement.
Scan reports shown in Fig. 4, reveal that the first floor
beams (400 mm × 300 mm) have four tension rebars. The
second floor beams having a 500 mm × 300 mm cross section, show five rebars in the tension zone. According to the
scans, the rebars of the slab were spaced at 150 mm (6″) c/c
in both directions. As the determination of rebar diameter
using scanner imaging is not quite reliable (Selek 2015), a
Building features
Description
Floor system
Floor area
Foundation system
Load-bearing wall thickness
Floor height
Construction material
Beam supported RC slab
332 m2 (3570 sqft) per floor (northern and southern part together)
Wall foundation
375 mm in the ground floor, 250 mm in the other stories
Ground floor: 4.47 m (14.66 ft), Other floors: 3.20 m (10.50 ft)
Brick masonry with cement mortar and reinforced concrete
13
446
Asian Journal of Civil Engineering (2021) 22:443–460
Table 2 Core strength test
results
Sl. no
Location
Sample identification
Crushing strength
MPa (psi)
Type of failure
1
2
3
4
5
6
7
GF
GF
1st floor
1st floor
1st floor
1st floor
1st floor
GF Roof, C-1
GF Roof, C-2
1st floor roof C-1
1st floor roof C-2
1st floor roof C-3
1st floor Beam-1: C-1
1st floor Beam-5: C-2
11.4 (1605)
11.9 (1730)
12.1 (1750)
8.1 (1170)
24.5 (3550)
21.8 (3160)
17.7 (2570)
Combined
Combined
Combined
Combined
Combined
Combined
Combined
Table 3 Experimental data of brick shear test on masonry wall
No Location
Shear Stress, σ Area, A1 Load, P
MPa (psi)
mm2 (in2) kN (lb)
1
10.34 (1500)
858 (1.33) 8.87 (1995)
6.89 (1000)
858 (1.33) 5.92 (1330)
2
GF Interior wall
(G/1–2)
GF Exterior Wall
(K/1–2)
rebar diameter of 16 mm for beams and 10 mm for slab were
assumed as a conservative estimate to assess their capacity.
The standard penetration test (SPT) was performed
(Fig. 5) to obtain an approximate bearing capacity and
dynamic soil resistance measure. SPT value suggests that the
upper soil (up to 6.0 m depth) corresponds to very stiff cohesive soil suitable for moderate load bearing structures (Terzaghi et al. 1967). The groundwater level was at − 5.75 m
EGL. Soil test results are shown in Tables 4 and 5.
Finite element modeling
Fig. 2 Measurement of slab thickness
Fig. 3 Schematic diagram of
floor beams, a 1st floor, b 2nd
floor
13
For the detailed engineering assessment of the building,
finite element modeling was conducted using ETABS 16.2.
The slabs were modelled as shell element. The load-bearing
walls were modelled as a membrane. The material type of
the walls was ‘Masonry’, directional symmetry of which was
isotropic. Element dimensions were taken from the as-built
drawing. Average compressive strength of 13.8 MPa (2 ksi)
was considered for the reinforced concrete in RC members.
The minimum yield strength (275.79 MPa) and tensile
strength (482.63 MPa) of the 40-grade rebar were assumed
for analysis. The modulus of elasticity of the masonry material was taken as 5625 MPa (determined as per the guideline
of BNBC 2020), and the same for RC members (shell and
beam √
elements) was 17,580 MPa which is equal to
�
57,000 fc� , (f c in psi). As the extreme ends of the reinforced
Asian Journal of Civil Engineering (2021) 22:443–460
447
Fig. 4 Rebar scans of GF beam E1-E2 [a lateral, b bottom] and c slab
Fig. 5 Standard penetration test
on site
Table 4 Soil property: borelog-1
Depth (m)
Soil property BH-1
Table 5 Soil property: borelog-2
1.0–6.0
6.0–9.0
Stiff to very stiff silty clay (High plasticity)
Medium stiff to stiff, clayey silt with fine
sand (Medium compressible)
Medium dense, silty fine sand, trace mica
Depth (m)
Soil property BH-2
1.0–6.0
6.0–9.0
9.0–15.0
Medium stiff to very stiff silty clay (High plasticity)
Stiff, clayey silt with fine sand (Medium compressible)
Medium dense, silty fine sand, trace mica
9.0–15.0
13
448
Asian Journal of Civil Engineering (2021) 22:443–460
concrete beams rested on masonry walls, they tend to behave
like simply supported beams. Therefore, they are assigned
hinge restraints in FE model. Hinges were also assigned at
the bottom nodes of the load-bearing walls as supports.
Seismic loading parameters e.g. zone coefficient
(Z = 0.15), strength reduction factor (R = 6.0), importance
coefficient (I = 1.0), exposure category A (urban–suburban
area), wind load (V = 210 km/h), are as per BNBC 1993
are applicable for the present site. The site coefficient was
considered 1.0 as the soil is stiff clay at the foundation level.
The building was analyzed for gravity loads (dead and
live loads) as well as code specified lateral loads. The loading was based on Bangladesh National Building Code
(BNBC 1993,2020) where the design basis earthquake has
10% probability with a return period of 50 years. Seismic
loads were applied at the center of the mass of the diaphragms at each story. The surface area method was used for
the wind load analysis and maximum wind load deflection
h
limit 500
was considered acceptable for the wind effect only.
The loading used in the finite element analysis is shown in
Table 6. The 3D model and the plan view of the structure is
shown in Fig. 6. However, since retrofitting design was to be
done for vertical extension of the northern part, a model consisting of four stories on both the northern and the southern
part was later prepared and analyzed, the image of which is
not presented in this paper.
Table 6 Super-imposed static loads
Loading type
Code specified
load (kN/m2)
Live load (office building)
Live load on porch
Live load on stairs
Internal partition wall load
Floor finish
2.87
0.48
4.80
1.44
1.44
Fig. 6 Complete finite element
model of URM building, a 3D
model, b typical plan
13
Sensitivity analysis
Sensitivity analysis was carried out on the finite element
model to choose the optimum size and number of mesh for
which results obtained will be reliable and accurate to the
desired degree and at the same time, it will require optimum
time to run and execute the analysis of the model. Coarser
mesh produced lower stresses in the walls as compared to
finer mesh. So, optimum mesh sizes were selected by trial
and error considering two vital factors:
1. Analysis run time
2. Results having similar accuracy compared to those with
finer mesh size
An illustration of a small part of the wall in elevation 1
is depicted in Table 7. The number of wall divisions was
set to be 40, 128, 512 and 1152 and maximum shear stress
(Dead + EQ) was investigated for each case. It was observed
that the change in stress decreases as the number of shell
elements increases, and it has a value of only 1.4% when
the number of elements is changed from 512 to 1152. Afterwards, no further divisions of the shell elements were made
since, for further refining of mesh, the change in results will
be negligible, but it will require a significantly longer time
to analyze the model.
For verification of the accuracy of the modeling procedure, results of the FE analysis were checked by calculations
performed manually. To present in this paper, a small model
of one story URM building was created following the same
procedure as the main model. Properties of the model and
comparisons of the FEA results with the manual calculations
are shown in Appendix A (Fig. 18 and Table 21). It shows
that the results obtained from FE analysis matches with the
manual calculations which further justifies the use of FEM
results in the current study.
Asian Journal of Civil Engineering (2021) 22:443–460
Table 7 Sensitivity analysis of
the structure
Table 8 Slenderness ratio of the
building
449
Number of shell elements
Maximum shear stress for
10-inch wall
% change in stress
Image of a wall
40
93
128
100
512
106.5
1152
108
–
7.53%
6.5%
1.41%
Story details
Effective height inch (m) Effective thickness inch
(m)
Slenderness ratio
Comment
Ground floor
1st–3rd floor
175.5 (4.46)
115.5 (2.93)
11.7
11.55
Satisfied
Satisfied
Results and discussion
Adequacy check of load‑bearing walls
The structural system of the building is primarily an unreinforced masonry system resting on wall foundations. According to the BNBC 1993 guideline, Working Stress Design
(WSD) method was used to assess the structural adequacy
of the masonry elements of the structure.
Slenderness ratio check
Table 8 shows the existing slenderness ratio of the walls.
According to the BNBC 1993, masonry walls’ slenderness
ratio shall not exceed 20 and this ratio for all the walls of this
structure fall within the prescribed limit. From this, it can
be stated that the existing thickness of the walls is adequate.
Maximum compressive stress (Fa) check
In unreinforced masonry structures, load-bearing walls are
by far the most vulnerable element to seismic loading. These
elements are primarily designed to carry vertical loads by
compression. Allowable limit of axial compressive stress,
Fa (Eq. 1; Eq. 4.3.1 BNBC 1993) was calculated to be
1.38 MPa (200 psi). As shown in Table 9, the load bearing
walls satisfy the vertical compressive stress requirement due
to service load combination (Dead + Live).
[
( � )3 ]
f �m
h
,
1−
Fa =
(1)
5
42t
15 (0.38)
10 (0.25)
Table 9 Maximum axial compressive stress generated in FEM model
for load-bearing walls
Wall
designation
Generated Maximum compres- Remarks
(limit state)
sive stress
MPa (psi)
1A-1L
1D-1 K
2A-2B
2C-2 K
A1-A2
B1-B2
C1-C2
C4-C5
G1-G2
K1-K2
0.52–0.59* (75–85*)
0.52–0.59* (75–85*)
0.69* (100*)
0.69* (100*)
0.62 (90)
0.83 (120)
0.52 (75)
0.21* (30*)
0.34 (50)
0.41 (60)
Satisfied
Satisfied
Satisfied
Satisfied
Satisfied
Satisfied
Satisfied
Satisfied
Satisfied
Satisfied
*In very small portions of the wall surface, the stress values have
been found to be much greater than the maximum values presented in
the table. For example, the point of the wall at which a beam rests the
compressive stress is above 120 psi. At such resting points of beams,
compressive stress reached up to a maximum of 300.6 psi (67% of
which is the allowable compressive stress. So, these points of stress
concentration are to be considered while retrofitting of the structure
where h’ is the effective height of the wall and t is the
masonry wall’s effective thickness.
Maximum shear stress Fv check
In a seismic event, load-bearing walls are subjected to
repetitive in plane and/or out of plane horizontal loading.
Due to not having any reinforcing element, they have little
13
450
Asian Journal of Civil Engineering (2021) 22:443–460
resistance to horizontal shear stress. The allowable limit
of shear stress of unreinforced masonry was calculated to
be 0.069 MPa (10 psi) (Eq. 2; Eq. 4.3.5, BNBC 1993 and
Eq. 6.7.6, BNBC 2020).
√
Fv = 0.025 f � m < 0.40 N∕mm2 .
(2)
Table 10 shows the generated shear stress on the masonry
wall for service load combination (Dead + Live) and lateral
loading (Dead + Earthquake). According to the criteria of
BNBC 1993, most of the wall sections are found to be vulnerable to failure under horizontal shear. On the other hand,
all the walls fail to satisfy the limits of horizontal shear prescribed by BNBC 2020. This is because the seismic forces
calculated as per BNBC 2020 were much higher than those
calculated as per BNBC 1993 owing to the difference of the
Response Reduction Factor (R). For load-bearing unreinforced masonry structure R is 1.5 in BNBC 2020, which is
much less than that of BNBC 1993 (R = 5). So, the allowable limit of shear stresses due to dead and seismic forces of
BNBC 2020 is exceeded for all the walls as shown in Fig. 7.
Figure 7 shows the typical floor plan view of the adequate
and inadequate walls for both the loading criteria of BNBC
1993 and 2020. This indicates the necessity of measures to
ensure the adequacy of the walls. Thus, retrofitting of the
walls was done, considering the forces of higher magnitudes
(Seismic forces of BNBC 2020).
At some small locations of the walls (asterisk marked),
actual maximum stress was found to be much greater than
the tabulated maximum values. This may have happened
due to stress concentration at locations where beams rest on
walls or at sharp corners (i.e. Window/door frames). These
were discarded as they covered a negligible portion of the
wall surface and were not representative of the actual maximum stress.
Table 10 Maximum shear stress generated in FEM model for load-bearing walls
Wall designation
Maximum shear
stress D + L
MPa (psi)
Remarks (limit state)
Maximum shear
stress D + EQ
MPa (psi)
BNBC 1993
Remarks (limit state)
Maximum shear
stress D + EQ
MPa (psi)
BNBC 2020
Remarks
(limit state)
1A-1L
1D-1 K
2A-2B
2C-2 K
A1-A2
B1-B2
C1-C2
C4-C5
G1-G2
K1-K2
0.07* (10*)
0.01* (2*)
0.10 (14)
0.04* (6*)
0.20 (29)
0.21 (30)
0.14 (20)
0.06* (8*)
0.09 (13)
0.03* (5*)
Satisfied
Satisfied
Not Satisfied
Satisfied
Not Satisfied
Not Satisfied
Not Satisfied
Satisfied
Not Satisfied
Satisfied
0.14 (21)
0.03* (5*)
0.19 (27)
0.19* (28*)
0.15 (22)
0.16 (23)
0.19 (28)
0.06* (8*)
0.15 (22)
0.10 (15)
Not Satisfied
Satisfied
Not Satisfied
Not Satisfied
Not Satisfied
Not Satisfied
Not Satisfied
Satisfied
Not Satisfied
Not Satisfied
0.76 (110)
0.09 (13)
0.90 (130)
0.57 (83)
0.37 (54)
0.39 (56)
0.50 (73)
0.16* (23*)
0.43 (63)
0.31 (45)
Not Satisfied
Not Satisfied
Not Satisfied
Not Satisfied
Not Satisfied
Not Satisfied
Not Satisfied
Not Satisfied
Not Satisfied
Not Satisfied
Fig. 7 Wall condition in typical floor plan, a BNBC 1993 EQ loading condition, b BNBC 2020 EQ loading condition
13
Asian Journal of Civil Engineering (2021) 22:443–460
Table 11 Analysis result of
beam (1st floor)
Table 12 Analysis result of
beam (2nd floor)
Beam designation
451
Steel requirement (mm2)
Comment
Compression
Tension
1D-2D
1E-2E
1F-2F
1H-2H
1I-2I
1J-2 J
Overstressed
Overstressed
Overstressed
Overstressed
Overstressed
Overstressed
Overstressed
Overstressed
Overstressed
Overstressed
Overstressed
Overstressed
Beam designation
Steel requirement (mm2)
1D-2D
1E-2E
1F-2F
1H-2H
1I-2I
1J-2 J
Compression
Tension
2845
2860
3011
2393
2587
2691
1865
1883
2057
1345
1569
1688
Failure – Inadequate section
Failure – Inadequate section
Failure – Inadequate section
Failure – Inadequate section
Failure – Inadequate section
Failure – Inadequate section
Comment
Failure – Inadequate reinforcement
Failure – Inadequate reinforcement
Failure – Inadequate reinforcement
Failure – Inadequate reinforcement
Failure – Inadequate reinforcement
Failure – Inadequate reinforcement
Adequacy check of reinforced concrete members
Adequacy check of beams
The dimensions of all the beams of first floor (Ground floor
roof) and second floor (first floor roof) are, respectively,
400 mm × 300 mm and 500 mm × 300 mm. The Ferro-scan
test determined the number and location of longitudinal
bars in the beams but gave a vague idea about the exact
diameter of the rebar. So, conservatively 16 mm diameter
reinforcement bars were assumed as longitudinal bars for
beam adequacy check. None of the beams were adequate to
withstand the service load moment, as shown in Tables 11
and 12. The inadequacy of all the beams was due to the
combination ‘1.4DL + 1.7LL’.
Fig. 8 Foundation excavation. a Exterior wall footing, b Interior wall
footing
Adequacy check of columns and slabs
Adequacy check of wall foundation
The RCC column design assumed a minimum of 1% rebar.
The columns were found to be adequate as per FEM analysis, and the governing combination was ‘1.4DL + 1.7LL’.
According to the analysis, 10 mm bars placed 150 mm
apart are adequate. The slabs’ scan reports suggest that
rebars are spaced at around 140 mm c/c along the short
direction of the slabs, which conforms to the slabs’ structural requirement. The maximum deflection of the slabs and
the minimum slab thickness were checked and found to be
within the limit prescribed by the code.
The foundation system of the building consists of a masonry
strip foundation. Figure 8 shows the excavated foundation
of an exterior and an interior wall, which have a depth of
approximately 0.94 m and 1.0 m, respectively. From the bore
log, the top layer was found to be medium-stiff to very stiff
silty clay with an average SPT value of nearly 6.
To determine the bearing capacity of the soil, the unconfined compression test was performed. The unconfined compression stress was found to be 414 kPa and so the cohesion
was 207 kPa. Using the bearing capacity equation of Terzaghi (1943) and taking Terzaghi’s bearing capacity factor
Nc = 5.7 (Das 2007), the ultimate bearing capacity was found
13
452
Asian Journal of Civil Engineering (2021) 22:443–460
Table 13 Analysis result of beam (1st floor)
Beam designation
Maximum bending Governing bending moment – kN-m
BNBC 1993
moment – kN-m
BNBC 1993
Maximum bending Governing bending moment – kN-m
BNBC 2020
moment – kN-m
BNBC 2020
1D-2D
1E-2E
1F-2F
1H-2H
1I-2I
1J-2 J
389.42
393.77
412.86
332.77
356.38
366.31
349.84
353.75
370.98
298.73
320.03
328.99
412.86
370.98
Table 14 Analysis result of beam (2nd floor)
Beam designation
Maximum bend- Governing bending moment – kN-m
(BNBC 1993)
ing moment –
kN-m
(BNBC 1993)
Maximum bending moment – kN-m
(BNBC 2020)
Governing bending moment – kN-m
(BNBC 2020)
1D-2D
1E-2E
1F-2F
1H-2H
1I-2I
1J-2 J
400.17
402.38
423.84
336.09
363.64
378.38
423.84
359.20
361.16
380.52
301.37
326.22
339.52
380.52
Table 15 Retrofitting solution
for 1st floor beam considering
different material strength
Description
Code
Moment (kN-m)
b (mm)
d (mm)
fy (MPa)
fc′ (MPa)
Rebars
1st floor beam
BNBC 1993
BNBC 2020
412.86
370.98
500
500
500
500
500
500
13.79
13.79
5#7
4#7
Table 16 Retrofitting solution
for 2nd floor beam considering
different materials
Description
Code
Moment (kN-m)
b (mm)
d (mm)
fy(MPa)
fc′ (MPa)
Rebars
2nd floor beam
BNBC 1993
BNBC 2020
423.84
380.52
500
500
600
600
500
500
13.79
13.79
4#7
3#7
to be 1.16 MPa. Since the structure is expected to be vertically extended up to 4 stories after retrofitting, a factor of
safety on the higher side was taken and it was equal to 4.0.
So, the allowable bearing capacity of the soil was 0.29 MPa.
To check the footing’s adequacy, vertical reactions, Fz
at the supports (along the base of the wall) for un-factored
gravity loads were extracted from a full four story finite element model due to the vertical extension to take place after
retrofitting. With these, the additional load of the 3-inch RC
jacket and wall footing below grade were added to find the
total vertical load per unit length of the wall footing. Then
it was converted to stress and compared to the allowable
capacity. It was finally found that most parts of the provided
foundation were inadequate against bearing capacity failure.
13
Retrofitting of structural members
Retrofitting of RC beams
As previously stated, the beams were inadequate to withstand moments generated by service load. Hence retrofitting was required. In this case, U shaped RC jackets were
used for retrofitting of RC beams. This was chosen as among
other available options (externally bonded steels plates,
fiber-reinforced plastic (FRP), carbon fiber reinforced polymer (CFRP)) are prone to premature de-lamination failure,
due to mismatch of tensile strength and stiffness with that of
RC elements. These are also quite labor-intensive and costly.
Tables 13 and 14 show the governing moments in all the
Asian Journal of Civil Engineering (2021) 22:443–460
beams which were used to determine the additional required
reinforcement in the retrofitting process.
RC jacketing is done by extension of the existing beam
cross section, with a new layer of high strength concrete
reinforced with both shear and flexural reinforcement of
500 MPa. Shear reinforcement was designed as per intermediate moment-resisting frame (IMRF) requirement.
Tables 15 and 16 present the specifications of the retrofitting
design of beams. For the retrofit design, the effective slab
thickness of 100 mm was considered. Retrofitted extension
of depth and width was taken to be 100 mm. So, the new
dimensions of first floor and second floor retrofitted beams
became 600 mm × 500 mm and 700 mm × 500 mm, respectively. This enlargement of beam width, by 66.7%, will also
reduce the induced compressive stress on the wall at resting
points of beams which exceeded the allowable limits (note
of Table 9).
The existing reinforcement was considered to be 40 grade
16 mm diameter rebar. Only 50% of their area was considered to be effective in resisting flexural tension as these were
not at the same effective depth as the newly retrofitted bar.
For retrofitting of beams the concrete mix ratio was chosen
as 1:1.2:1.7. 5 mm down stone chips were used as coarse
aggregate and 100% Sylhet sand (Fineness Modulus = 2.4)
was used as fine aggregates. Super plasticizer was used as
an admixture. The beams’ compression zones mostly consist
of the old concrete with a compressive strength of 13.8 MPa
whereas the newly cast concrete ( f ′ c=35 MPa) was mostly
in the tension zone expected to undergo flexural cracking.
So, the concrete will contribute only to compression and
thus the compressive strength was considered as 13.8 MPa
in retrofitting design.
To facilitate the retrofitting work, at first the existing
plaster was removed, and old concrete was thoroughly
chiseled (fully roughened surface). Air blower was used
to remove dust and clean off any loose debris. U shaped
stirrups (10 mm diameter bars @ 100 mm c/c at supports
and 150 mm c/c at mid span) were drilled (75 mm) into
the existing slab, securing it by epoxy. Longitudinal bars
were placed as per design requirement. To ensure composite action between the concrete interfaces 10 mm diameter
@ 150 mm c/c shear keys (one end hooked) were embedded alternatively (staggered pattern) into the existing beam.
Embedded length was 75 mm. Surface bonding reagent was
applied to bind the new concrete with the existing surface.
Steel shuttering and propping were set in place. For concreting, 150 mm diameter holes were drilled into the top
slab. Concrete strength for beam was 35 MPa which was
confirmed by cylinder test with 28 days curing. Figures 9
and 10 present the beam cross section of the beam with the
details of the flexural design. Figures 11 and 12 show the
long section of the beam along with shear reinforcement.
453
Fig. 9 Retrofitted beam of 1st floor (dimensions in mm)
Fig. 10 Retrofitted beam of 2nd floor (dimensions in mm)
Retrofitting of masonry walls
Two alternative retrofitting methods of the masonry loadbearing walls were proposed viz. by ferrocement overlay and
by reinforced concrete jacketing. However, due to the shear
strength requirement of the structure for higher seismic loading of BNBC 2020, thicker ferrocement overlay with more
wire meshes was required which is cumbersome for practical
construction. For this reason, reinforced concrete jacketing
was done for retrofitting of all the walls in the existing building. Both the methods are still described in this section with
short details of the procedure.
Ferrocement overlay One of the economically feasible retrofitting methods is ferrocement retrofitting. Ferro-cement
is an orthotropic composite material having a high strength
cement mortar matrix reinforced with steel wires in the form
13
454
Asian Journal of Civil Engineering (2021) 22:443–460
Fig. 11 Longitudinal section of retrofitted beam of 1st floor (dimensions in mm)
Fig. 12 Longitudinal section of retrofitted beam of 2nd floor (dimensions in mm)
of a mesh (horizontal/diagonal). It improves ductile strength
and in-plane inelastic deformation capacity making the retrofitted structure more resilient against seismic forces. As it
is cost effective and less labor intensive, it is economically
feasible for developing countries.
The direct tensile strength is dependent on the bonding
between the existing masonry and composite layer, the reinforcement distribution within the matrix, its orientation with
respect to the load direction (Prawel and Reinhorn 1982) and
volume fraction Vf .Vf is the ratio of volume of mesh reinforcement to the volume of composite layer (reinforcement
mesh and matrix). For ferro-cement reinforced with square/
rectangular mesh, the volume fraction and effective area
of reinforcement were calculated using following equation
mentioned in the Eq. 3 (BNBC1993, Appendix D)
Vf =
N𝜋db2
4h
(
)
1
1
+
,
Dt Dl
(3)
where Dt and Dl are center to center spacing of wires aligned
transversely and longitudinally in reinforcement mesh; db is
the diameter of the wire mesh; h is the thickness of the composite layer (reinforcement mesh and matrix) and N is the
number of layers of reinforcements. Effective area of reinforcement (Asi) per layer of mesh reinforcement in resisting
direct tensile stress in a cracked ferro-cement section can be
estimated (Eq. 4; BNBC 1993, Eq. 12.4.2, Rahman 2002).
13
Asi = 𝜂Vf Ac ,
(4)
where 𝜂 is global efficiency factor of mesh reinforcement
and Ac is cross-sectional area of the ferro-cement overlay.
From this effective reinforcement area (Asi ) nominal tensile
resistance was determined (Eq. 5; BNBC 1993, Eq. 12.4.3).
Allowable tensile stress of the wire mesh was taken to be
60% of the yield strength fy (BNBC 1993, Art. 12.4.3.2).
Nn = 0.6Asi fy ,
(5)
Detailing of the ferrocement design is summarized in
Table 17.
Reinforced concrete retrofitting The construction of a ferrocement section consisting of more than two wire mesh layers is practically cumbersome. Therefore, for high stresses
where two wire meshes are not sufficient reinforced concrete
jacketing of the walls can serve as a potential alternative for
retrofitting. However, in this case the total shear force is to
be taken by the RC section which follows from the results
of the assessment of Najafgholipour et al. (2018) about the
in-plane shear behavior of URM walls. It was found that
for URM walls strengthened with steel fiber-reinforced concrete overlay (SFRC) surface layer, in-plane response of the
retrofitted walls is controlled mostly by the retrofitting layer.
Therefore, the masonry strength was neglected in shear
strength calculation of the retrofitted walls.
Asian Journal of Civil Engineering (2021) 22:443–460
Table 17 Detailed design
of ferro-cement retrofitting
of the walls (for BNBC 1993
loading)
455
Wall
Maximum A.G.S
shear
stress
MPa (psi)
Description
Thickness
Vf
Capacity
Nn (psi)
1A-1L
2A-2B
2C-2K
A1-A2
B1-B2
C1-C2
G1-G2
K1-K2
0.145 (21) 18 gauge
0.186 (27)
0.193 (28)
0.152 (22)
0.159 (23)
0.193 (28)
0.152 (22)
0.103 (15) 18 gauge
External side: 2-layer wire mesh
19 mm
2.03%
31.39
External side:1-layer wire mesh
16 mm
1.21%
15.70
Table 18 Material properties of retrofitting materials
Material properties
Yield strength of steel deformed bar
Compressive strength of concrete
Concrete mix ratio
Coarse aggregate
Fine aggregate
Admixture
Table 19 Reinforced concrete
overlay design requirement (for
BNBC 2020 loading)
500 MPa
34.5 MPa
1:1.2:1.7
5 mm down stone chips
100% Sylhet sand as fine
aggregate
Super plasticizer
The design of the RC section is similar to that of the
reinforced concrete shear wall. Three-inch (3″) shear wall
was proposed and the total shear is taken by the concrete
(Vc ) and the steel (Vs ). This strengthening method leads to
significant improvement in the shear resistance of the jacketed walls (Churilov and Jovanoska 2013). Moreover, a new
RC layer is capable of withstanding additional compressive
load too, for which the stresses at resting points of beams
on the walls will further decrease. Material properties and
detailing of the reinforcement are shown in Tables 18 and
Wall
Maximum Maximum shear, Reinforcement
shear stress Vu N/mm (lb/in) detailing
MPa (psi)
1A-1L
2A-2B
2C-2K
A1-A2
B1-B2
C1-C2
C4-C5
G1-G2
K1-K2
0.759 (110)
0.897 (130)
0.572 (83)
0.372 (54)
0.386 (56)
0.503 (73)
0.159 (23)
0.434 (63)
0.310 (45)
192.69 (1100)
227.72 (1300)
145.39 (830)
94.59 (540)
98.1 (560)
127.88 (730)
40.29 (230)
110.36 (630)
78.83 (450)
Final design details
#3 @ 187.5 mm c/c #3 @ 6-inch c/c i.e 10 mm @ 150 mm c/c
#3 @ 187.5 mm c/c Vertical and Horizontal direction
#3 @ 262.5 mm c/c
#3 @ 462.5 mm c/c
#3 @ 437.5 mm c/c
#3 @ 312.5 mm c/c
#3 @ 2525 mm c/c
#3 @ 375 mm c/c
#3 @ 612.5 mm c/c
Fig. 13 Detailing of reinforced concrete wall retrofit
13
456
Asian Journal of Civil Engineering (2021) 22:443–460
Retrofitting of footing
Fig. 14 Rebars installed with shear connectors for RC jacketing of
masonry walls
19. Detailing of the reinforced concrete retrofitted wall is
shown in Fig. 13 and installation of the rebars with shear
keys are demonstrated in Fig. 14. The steel reinforcement
was arranged as a vertical and horizontal square mesh of
10 mm diameter bars, spaced at 150 mm c/c (Fig. 13). 8 mm
diameter shear keys were installed spanning 1000 mm in
both directions. They are affixed 75 mm into the surface of
the existing masonry wall by epoxy resin. Before concrete
casting, surface bonding reagent was applied to bind the
new concrete with the existing surface. The placement and
spacing of the shear keys (in case of RC jacketing) should
be such that those are to be inserted in mortar joints of the
masonry walls and not in bricks to prevent cracks in the
bricks. It can be noticed from Fig. 14 that, shear keys are
installed within mortar to avoid the initiation and propagation of cracks within the bricks.
From the adequacy check of wall foundations, major portion of the existing wall footing was found to be inadequate
against bearing capacity failure. This called for a cost effective and viable retrofitting option. Lateral extension of the
entire strip of the foundation is such an option.
In this case, the required amount of extension of the footing width, to comply with the allowable bearing capacity of
0.29 MPa, has been determined. Table 20 shows the required
extension for each wall footing.
Figure 15 shows the details of retrofitted strip footing.
The vertical reinforcement of the walls (of RC jacket) was
continued to the foundation on one side. On the other side,
horizontal extensions were done in two steps of 152 mm
each, one at the plinth level and the other at depth of 787 mm
from plinth level. Here, 12 mm diameter L shaped bars, as
temperature and shrinkage reinforcement, were placed vertically along with straight horizontal bars at an equal spacing
of 250 mm in both directions. The retrofit stripes were cast
using reinforced concrete, merged with the external 75 mm
thick retrofitted RC jacket above EGL.
At the footings base, 2–12 mm diameter horizontal rebar
were used as corner reinforcement. These were set along the
length of the strip foundation with shear key holding them
in place. 12 mm diameter shear key at 250 mm spacing were
used with an embedded length of 75 mm. The shear keys
were drilled in and fixed by epoxy.
Table 20 Required horizontal extension of strip footing
Elevation Wall
Extension
Load per
unit length on each
side
(kN/m)
(mm)
Governing extension
(mm)
1
188.3
177.1
283.6
250.0
189.4
192.8
205.8
171.2
164.4
225 mm on each side
2
A
B
C
G
K
1A-1L
1L-1K
2A-2B
2C-2K
A1-A2
B1-B2
C1-C2
G1-G2
K1-k2
13
60.9
42.4
219.9
163.8
62.8
68.4
90.2
32.5
21.2
Fig. 15 Strip footing detailing
Asian Journal of Civil Engineering (2021) 22:443–460
457
Consequently, the self-weight of the beam was transferred
to the floor slab. Sufficient propping was done to support the
dead weight of the floor slab along with the beam. Furthermore, to minimize the risk, the total retrofitting procedure
(i.e. shuttering arrangement, rebar placement, concreting)
was completed within a minimal time frame.
Conclusion and recommendation
Fig. 16 14.5 feet high bamboo propping system with horizontal bracing
To summarize, we can conclude that a case study has been
presented here where a masonry building was selected for
the study. The detailed engineering assessment of the building was conducted as per the national building code which
was followed by the retrofitting of the whole structure as
required. The following points from the whole study are
primarily outlined.
• The stresses on the load-bearing walls were investi-
Challenges faced during retroftting process
Difficulty in propping
The standard height of steel props available in the market is
10–12 feet in height. However, the clear height of the ground
floor was 14.5 feet. This posed a challenge to create a reliable support base before the retrofitting work commenced.
To solve this, a robust system of makeshift bamboo propping
was used as shown in Fig. 16. Since these 14.5′ long bamboo
props are prone to buckling, as safeguards, horizontal bracings were used in regular intervals to make a strong support
matrix for the floor slab.
Difficulty in beam retrofitting
In beam retrofitting, the beams’ support points were completely removed from the adjacent masonry load-bearing
walls, causing them to hover in midair, as shown in Fig. 17.
gated for the seismic loading of both the versions of the
national building code (BNBC 1993 and BNBC 2020)
and it was found that the stress due to the loading of
BNBC 2020 was much higher than that of BNBC 1993
due to a low response modification factor, R for masonry
load-bearing walls in BNBC 2020 compared to the 1993
version.
• Alternative methods of retrofitting were proposed for the
load-bearing walls where it was also recommended that
for higher stresses the ferrocement jacketing was not feasible for construction due to the requirement of more than
two layers of wire mesh. For these cases, reinforced concrete jacketing of the masonry load-bearing walls turns
out to be a handy solution to withstand high shear stress
due to lateral load and at the same time it will contribute
in resisting the gravity loading along with the existing
wall.
• To increase the flexural strength of an inadequate beam,
a retrofitting strategy by reinforced concrete jacketing
Fig. 17 Beam supports removed
from the adjacent wall
13
458
has been practically implemented and comprehensively
demonstrated in this paper.
• The base-widths of the wall footings were increased to
reduce the stress under each footing and keep it below
the bearing capacity of the soil.
• In case of newly cast concrete in walls, beams and footings for retrofitting, shear keys were installed in all members to ensure load transfer between the existing and the
newly built structural portions.
Thus, this study is expected to provide an elaborate and
detail guideline for the structural assessment of old masonry
structures along with a comprehensive retrofitting design
procedure of all the structural components involved.
Asian Journal of Civil Engineering (2021) 22:443–460
Appendix A
Verification of FEM results with manual
calculations
The model shown in this section is of a simple one story
URM building consisting of load bearing masonry walls on
four sides (Fig. 18). The properties of the structural members of the model and the obtained results compared with
manual calculations (Table 21) are depicted in this section.
Concrete slab dimensions = 10 ft by 10 ft by 6 inch,
Area = 100 sft, Unit weight = 150 lb∕ft3
Compliance with ethical standards
Conflict of interest On behalf of all authors, the corresponding author
states that there is no conflict of interest.
Fig. 18 One story URM building model for comparison of results
13
Masonry wall dimensions = 10 ft by 10 ft by 12 inch,
Unit weight = 135 lb∕ft3
Live Load on slab = 60 psf.
Asian Journal of Civil Engineering (2021) 22:443–460
Table 21 Comparison of
results of FEM with manual
calculations
459
Parameter
By manual calculation
From FE results
Total live load
60 psf × 100 sft = 6 kips
Total compressive stress on bottom of walls
due to dead loads
1. Slab weight = (6/12)× 150 lb/ft3 = 75
psf
Slab weight on one wall = (75psf ×
100sft)/4 = 1875 lbs
which is equal to 1875/(wall cross sectional area)
1875
= (10×12)×12
= 1.302 lb/in2 compressive
stress
2. Compressive stress due to wall selfweight
= 10ft × 135 lb/ft3 = 1350 lb/
ft2 = 9.375 lb/in2
Total compressive stress at wall bottom is
= 1.302 + 9.375 = 10.68 lb/in2
Sum of base
reactions for
live load = 6
kips
10.75 lb/in2
(shown in
Fig. 18)
References
Abrams, D. P., & Lynch, J. M. (2001). Flexural behavior of retrofitted masonry piers. Illinois: KEERC-MAE Joint Seminar on Risk
Mitigation for Regions of Moderate Seismicity.
Altun, F. (2004). An experimental study of the jacketed reinforced
concrete beams under bending. Construction and Building Material, 18, 611–618.
ASTM International C 42/C42M. (2013). Standard method for obtaining and testing drilled cores and sawed beams of concrete.
ASTM International C 67/C 67M. (2013). Standard test methods for
sampling and testing brick and structural clay tile.
Bansal, P.P., Kumar, M., & Kaushik, S.K. (2008). Effect of wire mesh
orientation on strength of beam retrofitted using ferro-cement
jackets. International Journal of Engineering, 2(1), 8-19.
Bangladesh National Buidling Code, BNBC. (1993). Housing and
Building Research Institute and Bangladesh Standard and Testing Institute, Bangladesh, 2, Part 6.
Bangladesh National Buidling Code, BNBC. (2020). Housing and
Building Research Institute and Bangladesh Standard and Testing Institute, Bangladesh, 2, Part 6.
Bozkurt, T. S., Sayin, B., Akcay, C., Yildizlar, B., & Karacay, N.
(2016). Restoration of historical masonry structures based on
laboratory experiments. Journal of Building Engineering, 7,
343–360.
Chaturvedi, A., & Patel, R. D. (2016). Retrofitting of RCC beam using
Jacketing Method. i-manager’s Journal on Structural Engineering, 5(1), 20–25. https://doi.org/10.26634/jste.5.1.6053.
Cheong, H. K., & MacAlavey, N. (2000). Experimental behavior of
jacketed reinforced concrete beams. ACSE Journal of Structural
Engineering, 6(6), 692–699.
Churilov, S., & Jovanoska, E. D. (2013). In-plane shear behaviour of
unreinforced and jacketed brick masonry walls. Soil Dynamics and
Earthquake Engineering, 50, 85–105. https://doi.org/10.1016/j.
soildyn.2013.03.006.
Das, B. M. (2015). Principles of foundation engineering, 7 edn. Cengage learning, 138-139.
ElGawady, M., Lestuzzi, P., & Badoux, M. (2004). A review of conventional seismic retrofitting techniques for URM. Paper presented
at 13th International Brick and Block Masonry Conference, 4–7
July 2004, Amsterdam.
Ghiasi, V., Valipour, M. R., Mohammadirad, A. R., & Baharipour,
S. (2013). Method of retrofitting the foundation of unreinforced
masonry buildings. Electronic Journal of Geotechnical Engineering, 18, 5747–5758.
Gorai, S., & Maiti, P. R. (2016). Advanced retrofitting techniques for
reinforced concrete structures: a state-of-the-art review. i-manager’s Journal on Structural Engineering, 5(1), 36–48. https://doi.
org/10.26634/jste.5.1.6055.
Guerreiro, J., Ferreira, J. G., Proença, J., & Gago, A. (2020). Experimental and numerical analysis of the behaviour of masonry walls
strengthened with CFRP reinforced render. Asian Journal of Civil
Engineering, 21(2), 331–349.
Guoliang, J. (1980). ‘Damage in Tianjin during Tangshan earthquake’,
the 1976 Tangshan China earthquake. Berkeley: Earthquake Engineering Center.
Hancilar, U., Çaktı, E., & Erdik, M. (2012). Earthquake performance
assessment and rehabilitation of two historical unreinforced
masonry buildings. Bulletin of Earthquake Engineering, 10(1),
307–330.
Herak, M. (2011). Overview of recent ambient noise measurements
in Croatia in free-field and in buildings. Geofizika, 28(1), 21–40.
Islam, R., Islam, M. S., & Islam, M. S. (2016). ‘Earthquake risk in
Bangladesh: Causes, Vulnerability, preparedness and strategies
for mitigation. ARPN Journal of Earth Science, 5, 75–90.
Jabarov, M., Kozharinov, S., & Lunyov, A. (1980). Strengthening of
damaged masonry by reinforced mortar layers. Paper presented
at 7th World Conference on earthquake Engineering, Istanbul,
3, 73–80.
Najafgholipour, M. A., Dehghan, S. M., & Kamrava, A. R. (2018).
In-plane shear behavior of masonry walls strengthened with steel
fiber-reinforced concrete overlay. Asian Journal of Civil Engineering, 19(5), 553–570.
Prawel, S. P., & Reinhorn, A. (1982). Properties in Flexure of Under
Reinforced Ferrocement Panels in Two-Way bending. Journal of
Ferrocement, 12(3), 237–250.
Rahman & Habibur, A.K.M. (2002). Strengthening of distressed
RC slabs by using ferrocement overlay, M.Engineering Thesis,
Department of Civil Engineering, BUET, Dhaka, August, pp.
7–21
Raval, S.S., & Dave, U.V. (2012).Effectiveness of various methods
of jacketing for RC beams’, Paper presented at Chemical, Civil
13
460
and Mechanical Tracks of the 3rd Nirma University International
Conference on Engineering (NUiCONE), 230–239.
Reinhorn, A. M., Prawel, S. P., & Jia, Z. H. (1985). Experimental
study of ferrocement as a seismic retrofit material for masonry
walls. Journal of ferrocement, 15(3), 247–260.
Sayin, B., Yildizlar, B., Akcay, C., & Gunes, B. (2019). Seismic retrofitting of historical masonry building with insufficient seismic
resistance using conventional and non-conventional techniques.
Engineering Failure Analysis, 97, 454–463.
Seleem, M.H., El-Ghandour, N.A., Sallam H.E.M, & Abdin E.M.
(2009). Upgrading of RC beams using U-shape RC jackets. Paper
presented at Al-Azhar Engineering 7th International Conference.
7–10 April 2003. Egypt.
Selek, I. (2015). ‘Reliability of non-destructive testing methods for
detecting steel rebar in existing concrete structures’, M.Sc. Thesis, Architectural Building and Planning, Eindhoven University
of Technology, October, Eindhoven.
Sen, D., Torihata, Y., Alwashali, H., Tafheem, Z., & Maeda, M. (2019).
Investigation of the ferro-cement infilled masonry wall under
cyclic lateral loading. Paper presented at 2019 Pacific Conference
13
Asian Journal of Civil Engineering (2021) 22:443–460
on Earthquake Engineering, 4–6 April 2019, Auckland, New
Zealand.
Shehata, I., Shehata, L., Santos, E., & Simoes, M. (2009). Strengthening of reinforced concrete beams inflexure by partial jacketing.
Material and Structure, 42, 495–504.
Sheppard, P., & Tercelj, S. (1980). The effect of repair and strengthening methods for masonry walls. Paper presented at 7th World Conference on earthquake Engineering, Istanbul, vol. 6, pp. 255–262.
Steckler, M. S., Mondal, D. R., Akhter, H. S., Seeber, L., Feng, L.,
Gale, J., et al. (2016). Locked and loading megathrust linked to
active subduction beneath the Indo-Burman Ranges. Nature Geoscience, 9, 615–618.
Terzaghi, K., Peck, R. B., & Mesri, G. (1967). Soil mechanics in engineering practice. New York: Wiley.
Willie, L.A. & Dean, R.G. (1975). ‘Seismic Failures and Subsequent
Performance After Repair’, Proceedings, ASCE National Structural Engineering Convention, April 1975, New Orleans.
Publisher’s Note Springer Nature remains neutral with regard to
jurisdictional claims in published maps and institutional affiliations.