Volume 5, Issue 1, January – 2020 International Journal of Innovative Science and Research Technology

ISSN No:-2456-2165

Condition Assessment and

Strengthening Measured for
Historical Building
Kirti Tiwari 1, Hima Shrestha2 and Ramesh Guragain3
1
Structural Engineer, National Society for Earthquake Technology-Nepal, Nepal
2
Director, Earthquake Engineering Research and Training, National Society for Earthquake Technology-Nepal, Nepal
3
Deputy Executive Director, National Society for Earthquake Technology-Nepal, Nepal

Abstract:- Charkhal is a historical building of Nepal, and steel I-sections. The sizes of openings are the same in
built of clay brick in mud mortar dated more than 105 two floors and placed in symmetrical position. The
years of age. This paper focuses on seismic vulnerability foundation of the building is in strip footing. The plinth
assessment and retrofit option of historic buildings level is considerably high above the ground level with a
charkha Adda carried by NSET just few years before provision for ventilation. The front view and footprint of
the Gorkha Earthquake, which got damage during the Charkhal Adda are shown below in fig. 1 and fig 2.
recent Gorkha earthquake 2015. The building is a
courtyard type; with a large number of openings in
their facade. The building is three stories with a total
height of 10.88m and largest dimension in the plan of
55.01m. The thickness of walls varies in the range of
0.8m to 0.35m with the greatest values attained at the
ground floor. The building floors are thick with jack
arch and steel I-sections. The foundation of the building
is in strip footing. The plinth level is considerably high
above the ground level with a provision for ventilation.
A complete geometric and structural survey of the
whole building was performed during the assessment of
building. The need for safety of the building lying at
high seismic zone in Nepal, the Seismic Vulnerability
Assessment out was carried out to improve the building
response in future earthquakes. The seismic
vulnerability of the building was assessed after the
following:(a) historical investigation about the building, Fig 1:- Front View of the Building
(b) detailed geometrical investigation, (c) identification
of materials by means of surveys and literature
indications, (d) Detailed Intrusive Tests, (f) Detail linear
static analysis of the building by means of a Finite
Element (FE) model. After these steps, the FE model
was used to assess the safety level of the building by
means of linear static analyses, and identifying a proper
retrofitting strategy for this building.

Keywords:- Historical Building; Seismic Vulnerability; FE

Modeling; Intrusive Test, Retrofit Option.

I. STRUCTURAL SYSTEM OF
CHARKHAL ADDA

The building is a courtyard type, having three stories

with a large number of openings in their facade. The
building contains long walls with rectangular shaped
courtyards. The main structural system for lateral load
resisting is thick un-reinforced masonry walls with about Fig 2: Building Foot Print
800mm thickness in the ground and first floors, and a
reduced thickness in the third floor of 0.56 to 0.35mm. The
walls are made of burnt clay brick, and un-burnt brick (in
some walls) in mud mortar. Floors are thick with jack arch

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 Volume 5, Issue 1, January – 2020 International Journal of Innovative Science and Research Technology
ISSN No:-2456-2165
II. FIELD INVESTIGATION BEFORE GORKHA
EARTHQUAKE

A number of site visits were conducted for visual

observation of the building. Detailed surveys of building
geometry and materials made it possible to detect
characteristic features such as type and configuration of
floors, and disposition of resistant masonry walls.

The structural behavior of existing masonry buildings

is often a complex issue due to the inevitable uncertainty
regarding geometry, typologies and mechanical properties
of materials. Observations of the building were conducted
and listed below: Fig 4:- Damages due to weathering of west wing outer wall

i. Inadequate number of the existing cross wall, which

makes the large size of the rooms, long unsupported
walls.
ii. The buildings were constructed with thick walls
800mm, in mud mortar.
iii. Most of floor/roof brick and steel I-beam in second
floor was found damaged due to leakage of water.

A. Walls' decays/damages from the exterior and internal

Damage of the external wall is due to wetness, erosion,
moss and wall cracks. The growth of plants and roots
damage the brick masonry. The interior of the building
generally is in a better state than the external walls: there
are some minor damages due to wetness, and erosion on the
interior walls. The mortar joints tend to be more exposed to
wind and rain at the top and so tend to deteriorate more,
Fig 5:- Growth of plant in external wall of west wing
weakening their seismic resistance. There are also some
vertical cracks in the west wing and east wing walls. Photo
documentation is included below:

Fig 3:- Weathering of west wing outer wall

Fig 6:- Erosion of brick/mortar in external wall of west
wing

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ISSN No:-2456-2165

Fig 7:- Deterioration of brick of west wing outer wall

Fig 10:- Damage portion of roof in second floor

B. Non-destructive and Intrusive Tests

Nondestructive and intrusive tests carried out to
determine the material properties of the building. In situ in-
plane shear test, micro tremor test, flat jack test and wood
drill tests conducted at the site.
Fig 8:- Erosion of brick/mortar in external wall of North
wing
 In Situ In-plane Shear Test
The test done at 16 locations at ground floor, 11
locations at first floor and 7 locations at second floor. The
average shear strength of brick masonry of the Charkhal
Building is 0.056 N/mm2 (ASTM Standard), 0.032 N/mm2
(IS Guidelines). Considering the uncertainty in the
coefficient of friction and workmanship during construction,
the value of 0.032 N/mm2 considered for analysis and
design.

Fig 11:- Shear Test in second floor wall of north wing

Fig 9:- Damage of outer wall in plan

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ISSN No:-2456-2165
and 1 location in the first floor. As far as possible,
measurements taken at four corners and near CG of second
floor of all four wings of the courtyard building. The
average fundamental frequency in East-West (X) direction
found to be 4.565 Hz, while in North-South (Y) direction
was 3.71 Hz respectively shown in Table 2. The
fundamental time period at X and Y-directions was found
to be 0.219 sec and 0.269 sec.

 Wood drill Test:

Besides inspecting the surface visually, the condition
of wooden members (beams, girders, rafters, posts,
windows, doors, etc.) tested with the help of decay
Fig 12: Shear Test in ground floor wall of south wing detection instrument, IML Resistograph PD Series. The
IML Resistograph System based on the principle of
 Micro Tremor Measurements measuring the drilling resistance.
Micro Tremor measurements taken to calibrate the
numerical analysis model. The Micro Tremor
measurements obtained at 15 locations in the second floor

Fig 13:- Conducting Wood Decay Test using IML Resistograph PD Series in Charkhal Adda

In this method of testing, a drilling needle with a amplitude graphs represent the higher intact of wood. The
diameter of 1.5 mm with a 3 mm cutting tip inserted into test carried out only on the exposed wood surface at about
wood under constant drive. While drilling, the resistance 35 different locations. Very few beams found damaged.
measured as a function of drilling depth of the needle. The The location of damaged wooden beams and the test results
data plotted on a scale of 1:1 simultaneously. The high shown in Figure 5.

West Wing
Fig 14:- Location of damage wooden beam and post in west wing of Charkhal

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Fig 15:- Resistograph of beams with irregular surface Fig 17:- Resistograph of intact beams

 Flat jack Test:

Double Flat Jack testing carried out at Charkhal
building. In this test, a small volume of masonry in a
structure is sandwiched between two jacks that react
against the masonry above and below. It is thus possible to
carry out a limited stress strain test on the masonry in-situ,
provided a correction factor is applied which takes into
account the characteristics of the jack and the ratio between
the area of the jack and that of the cut.

Fig 16:- Resistograph of decayed beams

Fig 18:- Flat Jack Test in Charkhal Adda

Testing is carried out as per ASTM Standards (ASTM and the initial distance between gauge points are measured.
C1196 and ASTM C1197) by using two flat jack palates of By pressuring the flat jacks, loads applied to the wall
size R-6-16 (0.15” X 6” X 16”). Two slots of size 6.5” x 17” specimen. With a pressure increase in the flat jacks, the
are prepared which are 18.5” apart (5 layers of brick) and distance between gauge point pairs decreases. By gradually
gauge point pairs are selected to measure the deflection of increasing the pressure, the pressure and deformation
the masonry units. Flat jacks then introduced into both slots,

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recorded and stress-strain curve developed. The pressure  Brick Test Result
increased until failure in the masonry specimen occurs. Twelve brick samples taken from the building wall
from different locations, with compressive strength and
Figure 9 shows the stress-strain curve of masonry water absorption tests carried out at Central Material
obtained from the flat jack testing. From the flat jack test, Testing Laboratory, Institute of Engineering. The average
the following results obtained. breaking strength of brick found between 16.97 kg/cm2 to
59.23 kg/cm2 and water absorption of 12 samples are
Average Modulus of Elasticity of Masonry = 200 MPa 13.35% to 30.22%. The tests found that the brick
Average Compressive Strength of Masonry (Ultimate) = compressive strength was very low.
0.6 N/mm2

C. Investigation of members:

Fig 19:- Compressive Strength Test of Brick Unit

 Foundation Inspection: Foundation is made of brick masonry and there is no plinth

To explore the foundation details of the building, band in walls. The depth of the foundation is 6’10”.
excavation carried out on the south wing of the building.

Fig 20:- Foundation Investigation in Charkhal Adda

Fig 21:- Foundation Section of Charkhal Adda at inspected locations

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 Floor/Roof detail identification: north wings were damaged due to the corrosion of the I-
The floor system is fitted with steel I-sections and steel beam and leakage of water. In order to check the
considered flexible diaphragms. Despite the heavy dead corrosion portion, the investigation conducted on different
load, the floor does not provide any kind of seismic- portions of the west, north and south wings. About 50% of
resistant function. Most of the roof/floor in the west and the flange portion found to feature corrosion.

Fig 22:- Floor/Roof detail exploration in west wing of Charkhal Adda

 Investigation of the Brick Masonry Wall

Status of bricks and mortar are important parameters to determine the status of the building. The wall is constructed using
burnt clay brick with mud mortar. The average thickness of mortar is 10mm.

Fig 23:- Brick Lay Pattern in opening of wall

III. STRUCTURAL ANALYSIS OF Only symmetrical portion considered while modeling

CHARKHAL ADDA BUILDING the building. While taking the advantage of symmetry, only
a portion of the actual structure need to model, so that it
A 3D finite element model using the ANSYS code reduce the analysis run time and memory required. Model
v.12.0 approached the structural analysis of the Charkhal consists of 10,406 nodes, 31490 Solid185 elements,
Adda. The masonry walls were discretized with Solid185 corresponding to 597 DOFs.
elements is eight node iso-parametric brick element type
with three degrees of freedom: translations in the nodal Symmetry boundary conditions are applied to the
X,Y and Z direction, have plasticity, hyper elasticity, stress north face of the bay to simulate the existence of adjacent
stiffening,creep,large deflection and large strain bays. A fully rigid boundary condition, which prevents
capabilities. It also has mixed formation capability for translation and rotation in all three directions, applied to the
simulating the deformations of nearly incompressible base of each foundation.
elasto-plastic materials and fully incompressible hyper
elastic materials. The brick floors and I steel beam were not Finally, model result is also check with Etabs model.
considered in the model and their own weights were
applied on the bearing walls by means of vertical
concentrated loads.

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Fig 24:- Symmetrical portion considered while modeling

(Ansys)

Fig 26:- Finite element model of the Charkhal Adda (Ansys

and Etabs)

A. Seismic Analysis
The seismic analysis is a part of the detailed
evaluation of an existing building. The steps involve in
developing a computational model of the building include
applying the external forces, calculating the internal forces
in the members of the building, identifying deformations
and capacity of the members and building, and finally
interpreting the results. The structural analysis is carried out
with the help of the available drawings and ETABS
2013/Ansys, a structural analysis and design software. IS
1893:2002; criteria for earthquake resistant design of
structures is used to determine the base shear in the
building.

 Modeling Output for Existing Building:

Initially, the existing building is modeled and in-plane
stresses along with out-of-plane moments are studied. From
the analysis, large amounts of out-of-plane moments are
produced on the walls due to the large wall span. The in-
plane stress and moment diagrams obtained from analysis
are shown in Figures below.
Fig 25:- Whole building in ETABS

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Fig 27:- Compressive stress in wall (In plane stress (S22)) (Y-direction)

Fig 28:- Out-of-plane horizontal bending moment diagram obtained from analysis

Fig 29:- Out-of-plane vertical bending moment diagram obtained from analysis

To reduce the out-of-plane moments, some cross walls are added on the building. To tie the walls and make floors rigid,
bracings are introduced

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Fig 30:- Diagram showing normal stress (Sx) in building during earthquake in X direction before addition of cross wall.

Fig 31:- Diagram showing normal stress (Sx) in building during earthquake in X direction after addition of cross wall.

Fig 32:- Diagram showing normal stress (Sz) in building during earthquake in X direction

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Fig 33:- Diagram showing normal stress (Sx) in building during earthquake in Neg-X direction

Fig 34:- Diagram showing normal stress (Sz) in building during earthquake in Neg-X direction

Fig 35:- Diagram showing normal stress (Sz) in building during earthquake in Z direction

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Fig 36:- Diagram showing normal stress (Sx) in building during earthquake in Z direction

Fig 37:- Diagram showing normal stress (SZ) in building during earthquake in Neg-Z direction

Fig 38:- Diagram showing normal stress (SX) in building during earthquake in Neg-Z direction

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The maximum value of tensile stress is seen in figures park service cultural resources, heritage preservation
(denoted by red colour).The portions around the openings services.
and wall corner were found to be highly vulnerable in all [8]. ASTM C1197-04 [2013] “Standard Test Method for
cases. From analysis it found that tensile stress decrease to In Situ Deformability Properties Using Flat Jack
some extent after addition of cross wall. Measurements”, ASTM International, 100 Barr
Harbor Drive, PO Box C700, West Conshohocken,
IV. RESULT AND DISCUSSION OF ASSESSMENT US
[9]. ASTM C1196-09 (2013) “Standard Test Method for
 The global behavior of building depends on the semi In Situ Compressive Stress Within Unit Masonry
rigid or loosely connected floor and unreinforced Estimated Using Flat Jack Measurements”, ASTM
masonry walls. The vulnerability of Charkhal Adda is International, 100 Barr Harbor Drive, PO Box C700,
mostly due to the absence of adequate connections West Conshohocken, US
between the walls and the floor/roof of the building, [10]. ASTM C1531-09 (2011) “ Standard Test Methods for
deterioration of load bearing walls due to weathering In Situ Measurement of Masonry Mortar Joint Shear
effects, lack of proper maintenance, water leakage from Strength Index”, ASTM International, 100 Barr
roof, growth of grass in load bearing walls and rusting Harbor Drive, PO Box C700, West Conshohocken,
of steel beams that support the brick floor. US
 The large sizes of the rooms without cross walls, [11]. RILEM MDT.D.4 [2004] “In-situ Stress Tests based
loosely connected floor, and unreinforced masonry wall on the Flat Jck”, RILEM TC 177-MDT: Masonry
are the main drawbacks of this building. Durability and On-site Testing, Material and
 Some structural modifications, floor stiffening and wall Structures, Vol. 37.
strengthening are required to enhance the building [12]. RILEM MDT.D.5 [2004] “In-situ Stress-strain
performance. Behavior Tests Based on the Flat Jack”, RILEM TC
 The portions around the openings and wall corner found 177-MDT: Masonry Durability and On-site Testing,
to be highly vulnerable. Material and Structures, Vol. 37.
 From the analysis results, large amounts of out-of-plane
moments produced on the walls.
 From analysis, both in-plane and out-of-plane tensile
failure are still observed on the walls.

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