detailed technical assessment of mr. shiva poudel & mrs

Detailed Technical Assessment of

Mr. Shiva Poudel & Mrs. Indu Adhikari’s Residence

At Bansbari, Kathmandu

(September-2015)

Submitted by:

BK Shrestha & Builders P. Ltd.

Lagan, Ganabahal, Kathmandu

Detailed Technical Assessment of Mr. Shiva Poudel & Mrs Indu Adhikari’s Residence at Bansbari, Kathmandu, Nepal

1. INTRODUCTION

1.1 General Background

According to the relevant I. S. Codes and Nepalese Standard Code, Nepal is rated as a zone of high

seismic activity. The vulnerability and seismic risk is defined as extreme and Nepal is placed in zone

five (V) with the value of seismic co-efficient 0.36, the highest of all. Kathmandu lies about 75 km

from the highly active boundary between the Eurasian and Indian tectonic plates along the

Himalayan front, which has been the site of many large magnitude earthquakes within historical

times. Moreover, Kathmandu is sited on the deep alluvial deposits of Kathmandu Valley; such

deposits may also prone to amplify earthquake ground motions, making them more destructive, and

the deposits may also be prone to liquefaction during strong earthquake.

The earthquake risk zones for unreinforced masonry building for Nepal is provided by Nepal National

Building Codes (Error! Reference source not found.). The figure clearly illustrates that Kathmandu

valley is lying in Zone A with high level of seismic risk associated with unreinforced masonry building.

Figure 1 : Seismic Zones for Unreinforced Masonry Buildings (Source: NNBC 109: 1994)

The level of Risk associated with the Seismic Zones (Error! Reference source not found.) shows that

Kathmandu valley is lying in zone A where the risk level is high with potential for widespread

collapse and heavy damage to unreinforced masonry buildings. The zone wise risk factor associated

with masonry building is presented in Error! Reference source not found.


Table 1: Seismic Zones for Unreinforced Masonry Buildings (Source: NNBC 109: 1994)

Zone Zone Coefficient Risk

A Z ≥ 1.0 Widespread Collapse and Heavy Damage

B 0.8 ≥ Z > 1.0 Moderate Damage

C Z < 0.8 Minor Damage

On 25 April 2015, massive earthquake triggered Nepal which occurred at 11.56 NST with a local

magnitude of 7.8 Richter Scale with maximum Mercalli Intensity (MMI) of VIII which had potential to

damage severely the buildings, boundary wall and other structures. To date, more than 10,000

people were killed and injured more than 40,000. Epicenter of 25 April earthquake was at Barpak

village of Gorkha district. The seismic energy released at the depth of 15 km (approximately) which is

called Hypocenter. Following major earthquake on 25 April, continued aftershocks more than two

hundred in numbers occurred in the country ranging from 4 to 6.8 Richter Scale (local magnitude).

The latest aftershock hit Nepal with 6.8 Richter scale on 12 May 2015 whose epicenter was at

Sunkhani village of Dolakha district.

According to USGS, the temblor was caused by a sudden thrust, or release of deposited energy along

the major fault line where the Indian plate is slowly diving underneath the Eurasian Plate. Nepal

locates between these two plates, therefore, is always threat to vulnerable structures thereby to

human beings as well.

At the present scenario the buildings that were constructed in the past are very much susceptible to

the risk of earthquake because they were not constructed by considering the seismic load. These

kinds of seismically vulnerable buildings can turn in to the death trap for large no of people if not

access from the perspective of earthquake. Hence there is great need for seismic assessment of the

buildings.

BK Shrestha & Builders P. Ltd. Is Nepali registered, Kathmandu based, Construction Company which

has long experience in the field of seismic intervention work and major construction work as well.

The report describes the method and findings of the assessment, which was conducted on

September 11 and 15, 2015. Recommendations and conclusions are provided indicating safety of

building occupants.

This report is based on the best engineering judgment arrived at from the visual inspection during

site visits, prevailing practices of building construction in the Kathmandu valley, and conduction of

some necessary field tests at some critical sections of the existing structural elements of the building

and verifying the findings. All possible efforts have been made to provide an accurate and

authoritative seismic vulnerable assessment of the building.

1.2 Scope of Works The main objectives of assignment are:

• To carry out a structural inspection of buildings on the compound, aiming to establish the

seismic vulnerability of the building and appropriate structural remedial measures.

• To assess the building and its condition, to explore the structural layout and to determine

the integrity of the building through site observation, field investigations, a study of the

drawings.


• To carry out simple field tests as necessary to obtain brief notifications regarding structure

of building.

• To hold discussions with house owner regarding damages as a result of recent earthquake

on 25 April 2015 and aftershocks thereafter.

• To prepare a report on the findings, conclusions and recommendations arising from the

work carried out.

The following field tests have been carried out for the building:

1) Schmidt Hammer Test

This is also the non-destructive test in which the Schmidt hammer measures the rebound of a spring-

loaded mass impacting against the surface of the sample. The test hammer will hit the concrete at a

defined energy. Its rebound is dependent on the hardness of the concrete and is measured by the

test equipment. By reference to the conversion chart, the rebound value can be used to determine

the compressive strength. When conducting the test the hammer should be held at right angles to

the surface which in turn should be flat and smooth. The rebound reading will be affected by the

orientation of the hammer, when used in a vertical position (on the underside of a surface) gravity

will increase the rebound distance of the mass and vice versa for a test conducted on a floor slab.

This test method for testing concrete is governed by ASTM C805.

At several points of structural column at different location or grid have been chosen and marked to

carry out this test. Please refer attached test results herewith. This sample result has been assumed

as comprehensive representation of overall concrete quality of building.

Ferro or Re bar Scanner

Ferro Scanning enables easy location of steel reinforcement in concrete which locates steel

reinforcing to 180 mm deep and determine depth, diameter and condition of rebar. In our specific

case, the Ferro Scanning will highly enable us to further analyze the structure for detailed seismic

vulnerability evaluation test, which may require repair or retrofitting.

1.3 Categorization of the Buildings available in Kathmandu (Identification of

building typology)

Most buildings, especially residential buildings are constructed in a traditional manner in the

Kathmandu valley. In general, we can categorize the available buildings in Kathmandu Valley into the

following four types:

TYPE 1: Building constructed with reinforced concrete shear wall; relatively rare, and found only in

high rise commercial building.

TYPE 2: Residential building with reinforced cement concrete frame which is also called frame

structured building designed to resist lateral forces and more or less meet the seismic codeof

criteria.

TYPE 3: Residential building with confined brick masonry system: 230 x 230 mm RCC columns tied

with horizontal beams at plinth and every floor level.


TYPE 4: Residential building constructed in pure brick masonry system; is also known as load bearing

structure.

The assessed building can be categorized as TYPE 4.

1.4 Introduction of the Building

The building is located at Bansbari, approximately 1 km distance from Maharajgunj ring road

intersection. The building is two storeys high excluding basement of pure machine made brick

masonry structure (fair faced) with load bearing walls constructed in rich cement mortar. The

building is minor irregular in both orthogonal directions but can be neglected. Most of walls in the

first floor are vertically continued from the ground floor, being separated with RCC floor beam and

slab. The first floor has been covered with RC beam and pitched roof slab. The thickness of

peripheral wall is 370 mm thick including all finishes. The interior partition walls in ground floor and

first has been constructed of same thickness as of peripheral wall except in bathroom walls which is

a positive aspect in consideration of the seismic aspect for such a building of high importance.

The footprint area of the ground floor is 1260.20 sqft and the first floor is 1271.45 sqft. The building

posses floor beam and slab at each floor level. Most of roof slab are pitched roof being provided by

sloped beam. A single flight spiral type staircase is located near main entrance door of building.

As per field investigations, there are structural beams at each floor level as a result the building can

act monolithically in providing resistance to earthquakes as well as can act with a diaphragm effect

to seismic activity. In ground floor dining and kitchen and first floor backside, the distances from the

wall corners to the openings do not meet the code of minimum criteria. The minimum distance as

per the NBC code for any openings should be 600 mm from the wall corner or junction or ½ of the

opening. This is the main drawback of building however, the size of window can easily be modified

to reduced size later in future as there is no immediate threat for moderate earthquake. Further,

some strengthening work will be required in future for cantilevered portion at first floor, backside.

The front car port slab has been supported by two RCC columns which seems safe.

1.5 Existing Conditions

BUILDING HISTORY

Year Constructed: 1992

Maintenance: None

Renovation: None

Builders Information: None

Owner Information: Mr. Shiva Poudel & Mrs. Indu Adhikari


OVERALL DESCRIPTION

Number of Storeys: Two Storey

Height of Storeys

Ground floor: 9’ to 11’

First floor: 9’ to 11’

Horizontal Plan Configuration: Not symmetrical

Vertical Configuration: Symmetrical in most sections

Floor Area:

Ground floor: 12060.20 sft

First floor: 1271.45 sft

STRUCTURE

Type: Load Bearing Structure

Walls: 350 mm thick peripheral and interior wall, 120 mm thick in bathroom

partitions

Slenderness ratio: 7.7 which is less than 17. Therefore, the effective wall height/length to the

wall thickness in this building is within the seismic code standard.

Floors:

Ground floor: Marble in lobby and passage, tile in kitchen, dining and toilet, wooden

flooring in sitting area, guest room

First floor: RCC slab, wooden flooring in bed rooms, marble in lobby, passage and

staircase

Roof: RCC beam and pitched slab roof

CONDITION

Cracks: Minor thermal cracks were observed in first floor west side bed room, which

is easily repairable. In other parts no cracks were seen.

Water: Not observed during assessment

Termites: Not observed during assessment


Damp: Not observed during assessment

2 Findings and Recommendation (Please refer Annex)

• Total average grade of concrete as per test is 20 MPa, which was tested on external column of

car porch.

• In external column of car porch at ground floor , 8 nos of 12mm dia re-bars & 6mm dia stirrups

6”c/c .

• In staircase slab 12 mm dia re-bar @ 6 “spacing is found at slab bottom.

• In beam in front of main door at ground floor Grid 3 B-C, 4 no re-bar of 12 mm dia & spacing of

3 “ is found , stirrups of 6mm @ 6 “c/c.

• On first floor, in beam above staircase Grid 3-4 B-C, two nos 12 mm dia with 6mm stirrups @

6”c/c.

• On first floor beam in front of bed room Grid E 2-3 , two nos of 12 mm dia with 6mm stirrups

spacing @ 6 “ c/c.

3 Final conclusion

Overall, the building is safe for habitants in respect of structural soundness as a result of rapid visual

assessment of building and test results.

This shall be remarkably notified that, the timing, location and intensity of seismic events cannot be

predicted accurately, some uncertainties remain regarding the actual consequences of a particular

earthquake shaking.


ANNEX-I

(Non Destructive Test-I) Re-Bound Hammer

PROJECT : Residential Building

Floor : Ground

Knowledge Factor

: 1.00

C.F. 0.73

Elemen

t : Column Grid : A5

S.N.

Rebound

Number

Mean

Value

Compressive

Strength Adopted Value Remarks

1 25

25.111111

1 18.43 20

2 26

3 24

4 20

Discarde

d

5 22

6 29

7 24

8 26

9 33

Discarde

d

10 25

11 25

12 20

Discarde

d

The Grade of concrete is as per rebound hammer test is found to be 20 MPa ( M 20 ).


ANNEX-II

(Non Destructive Test-II) Re-bar Locator / Scanner


ANNEX-III


PHOTOGRAPHS

Photographs showing preparation Photographs showing re bar scanning test

of schimdt hammer test at porch column at ground floor beam


Photographs showing conduction of rebar scanning in staircase slab

detailed technical assessment of mr. shiva poudel & mrs

Documents