| Report # | 116 |
| Report Date | 19-01-2005 |
| Country | INDIA |
| Housing Type | Unreinforced Masonry Building |
| Housing Sub-Type | Unreinforced Masonry Building : Brick masonry in mud/lime mortar, with vertical posts |
|
Author(s)
|
Amit Kumar, Jeewan Pundit |
|
Reviewer(s)
|
Ravi Sinha |
Important
This encyclopedia contains information contributed by various earthquake engineering professionals around the world. All opinions, findings, conclusions & recommendations expressed herein are those of the various participants, and do not necessarily reflect the views of the Earthquake Engineering Research Institute, the International Association for Earthquake Engineering, the Engineering Information Foundation, John A. Martin & Associates, Inc. or the participants' organizations.
Summary
This type of house is used for residential purposes. The building type under study has been picked the from central part of India (Madhya Pradesh), but it is found throughout India with small or large variations. Timber is primarily used for the frame structural elements but due to an accute shortage of timber, this construction type is not practiced anymore. Various components of the building change from place to place depending on climate, socio-economic conditions, availability of material, etc. Timber frames, placed in longitudinal and traverse directions, are filled with brick masonry walls. The floor structure is made of timber planks. Most of the buildings are found to be rectangular in shape with few openings. The roofing material is usually light when it is made from galvanized iron sheets. Seismic performance of a perfectly framed building is very satisfactory. Exisiting old structures, however, require maintenance and strengthening (Figure-1a,1b). It has been observed that nominal cost will be incurred for introducing earthquake resistant features.
1. General Information
Buildings of this construction type can be found in The typical building of this type is found through out India with small or large variations. The typical construction type has been taken from the Nimar region of Madhya Pradesh, which is prone to moderate earthquakes in seismic zone III (I.S. 1893:2002) but this construction type is spread uniformly over central and southern India. This type of housing construction is commonly found in both rural and urban areas.
These buildings are found in both rural and urban areas. The percentage of houses in urban areas is high. Only the affluent sector in rural areas possesses this type of housing in villages due to high construction costs.
This construction type has been in practice for less than 200 years ago.
Currently, this type of construction is not being practiced. Construction of this type of structure has slowed due to the absence of wood/timber, government policies for protecting forested areas, a developing economy and the availability of alternate building materials. Even now if a building of this type is constructed, it is found that it is not a perfectly framed structure. Many times the workmanship is not satisfactory.
Figure 1a: Typical Brick Building With Timber Frame | 
Figure 1b: Typical Brick Building With Timber Frame | 
Figure 2a: Change in Construction Material
|
Figure 2b: Change in Construction Material
| 
Figure 3: Discontinued Column and Beam Connection With Existing Part | 
Figure 4a: Details of Timber Frame
|
Figure 4b: Details of Timber Frame
| 
Figure 5a: Column and Beam Joint
| 
Figure 5b: Column and Beam Joint
|
Figure 6: Construction Details of First Floor
| 
Figure 7: Damage Pattern of Building
| 
Figure 8: Openings at Different Level
|
Figure 9a: Corner Separation
| 
Figure 9b: Corner Separation
| 
Figure 10: Damage to partition wall
|
Figure 11a: Gable Failure
| 
Figure 11b: Gable Failure
| 
Figure 12: Swaying of Columns
|
Figure 13: Heavy Roofing Elements
| 
Figure 14: No Proper Joints Between Rafters and Purlins | 
Figure 15: Houses Are Coved With Galvanized Iron Sheet |
Figure 16: Construction Details of Timber Frame Brick Building | 
Figure 17: Retrofitting Details of Brick House
| 
Figure 18: Graph of Time vs Occupancy Rate for residential houses |
Figure 19: 3-D sketch of structural elements
|
2. Architectural Aspects2.1 Siting
These buildings are typically found in flat terrain. They do no have common walls with adjacent buildings. When separated from adjacent buildings, the typical distance from a neighboring building is 5 meters.
2.2 Building Configuration
Most of the houses are rectangular in shape but sometimes depending upon functional requirements, plan irregularities are found. General shapes include rectangular with a high length-width ratio, T , L or U. Generally in semi-urban and rural areas, the old pattern of construction does not have an adequate ventilation system. In common, it is found that in each wall face, openings are limited to 5 - 8 %. Even the height of doors and windows are small at 6 feet and 2 feet respectively.
2.3 Functional Planning
Single family house and Multiple housing units. In a typical building of this type, there are no elevators and 1-2 fire-protected exit staircases. Generally this type of building consists of a single storey. The typical building has no escape route at the rear.
2.4 Modification to Building
It is found that comparatively older buildings are generally made with sufficient precision and good building skills. Extensions or modifications, however, are generally done without appropriate building construction techniques.
In urban areas, the outermost rooms are converted into shops or used for commercial purposes. It has been found that some modification and extension has been done with heterogeneous materials and structural systems. One example of such modification is the continuation of an existing brick wall with random rubble masonry (Figure-2a,2b,3). The older houses are made up with mud mortar but recently extensions are built with cement mortar. These type of modifications and alterations adversely affect the seismic performance.
3. Structural Details3.1 Structural System
| Material | Type of Load-Bearing Structure | # | Subtypes | Most appropriate type |
| Masonry | Stone Masonry
Walls | 1 | Rubble stone (field stone) in mud/lime
mortar or without mortar (usually with
timber roof) | ☐ |
| 2 | Dressed stone masonry (in
lime/cement mortar) | ☐ |
| Adobe/ Earthen Walls | 3 | Mud walls | ☐ |
| 4 | Mud walls with horizontal wood elements | ☐ |
| 5 | Adobe block walls | ☐ |
| 6 | Rammed earth/Pise construction | ☐ |
Unreinforced masonry
walls | 7 | Brick masonry in mud/lime
mortar | ☐ |
| 8 | Brick masonry in mud/lime
mortar with vertical posts | ☑ |
| 9 | Brick masonry in lime/cement
mortar | ☐ |
| 10 | Concrete block masonry in
cement mortar | ☐ |
| Confined masonry | 11 | Clay brick/tile masonry, with
wooden posts and beams | ☐ |
| 12 | Clay brick masonry, with
concrete posts/tie columns
and beams | ☐ |
| 13 | Concrete blocks, tie columns
and beams | ☐ |
| Reinforced masonry | 14 | Stone masonry in cement
mortar | ☐ |
| 15 | Clay brick masonry in cement
mortar | ☐ |
| 16 | Concrete block masonry in
cement mortar | ☐ |
| Structural concrete | Moment resisting
frame | 17 | Flat slab structure | ☐ |
| 18 | Designed for gravity loads
only, with URM infill walls | ☐ |
| 19 | Designed for seismic effects,
with URM infill walls | ☐ |
| 20 | Designed for seismic effects,
with structural infill walls | ☐ |
| 21 | Dual system – Frame with
shear wall | ☐ |
| Structural wall | 22 | Moment frame with in-situ
shear walls | ☐ |
| 23 | Moment frame with precast
shear walls | ☐ |
| Precast concrete | 24 | Moment frame | ☐ |
| 25 | Prestressed moment frame
with shear walls | ☐ |
| 26 | Large panel precast walls | ☐ |
| 27 | Shear wall structure with
walls cast-in-situ | ☐ |
| 28 | Shear wall structure with
precast wall panel structure | ☐ |
| Steel | Moment-resisting
frame | 29 | With brick masonry partitions | ☐ |
| 30 | With cast in-situ concrete
walls | ☐ |
| 31 | With lightweight partitions | ☐ |
| Braced frame | 32 | Concentric connections in all
panels | ☐ |
| 33 | Eccentric connections in a
few panels | ☐ |
| Structural wall | 34 | Bolted plate | ☐ |
| 35 | Welded plate | ☐ |
| Timber | Load-bearing timber
frame | 36 | Thatch | ☐ |
| 37 | Walls with bamboo/reed mesh
and post (Wattle and Daub) | ☐ |
| 38 | Masonry with horizontal
beams/planks at intermediate
levels | ☐ |
| 39 | Post and beam frame (no
special connections) | ☐ |
| 40 | Wood frame (with special
connections) | ☐ |
| 41 | Stud-wall frame with
plywood/gypsum board
sheathing | ☐ |
| 42 | Wooden panel walls | ☐ |
| Other | Seismic protection systems | 43 | Building protected with base-isolation systems | ☐ |
| 44 | Building protected with
seismic dampers | ☐ |
| Hybrid systems | 45 | other (described below) | ☐ |
3.2 Gravity Load-Resisting System
The vertical load-resisting system is confined masonry wall system. The infill walls are made of brick masonry. These infill walls are the gravity load-bearing structures. The walls partially take the load of roofing elements.
3.3 Lateral Load-Resisting System
The lateral load-resisting system is timber frame load-bearing wall system. If the building is made with adequate engineering skills and techniques, it has sufficient lateral load resisting strength. The frames are made up of teak wood, which is considered to be very durable and free from insects and termite. The Figures 4a, 4b & 19 show the configuration of a frame. Generally the column and beams are placed longitudinally and transversely. In longitudinal direction, the columns are placed at the distance of 2 to 2.5 m centre to centre. The transverse columns are placed at the distance to 2.0 m centre to centre. The size of column varies from 0.25 m x 0.25 m to 0.35 m x 0.35 m. Beams run throughout the periphery of the house. In both directions, the beams are resting on column grids. The connectivity between the column and beam is found to be very good with proper joint system (Figure-5a,5b). The first floor is made up of timber plank (Figure-6). The thickness of wooden plank varies from 0.1m to 0.125 m. The wooden platform is covered with bamboo mat and finally plastered with mud. The thickness of mud plaster is limited to 0.05 m. The timber posts for the attic, which support the sloping roof extend from the timber rafters. The attic is used for storing grain and other household items. Sometimes it is used as a living room. It is generally observed that the gable portion of wall is not provided with a timber band. The sloping roof of the house is resting on the gable end, which is very vulnerable to lateral dynamic forces. Perfect timber framed buildings are very good at resisting earthquake forces. The evidence of the good performance of such building was shown in the Latur earthquake in 1993. The building may sway but will definitely avoid total collapse. The damage pattern of such building may be referred to in Figure-7. The damage to the building was due to heavy and thick external walls and roof. The walls are not attached to the timber frame. The only attachment is achieved by the inside and outside plastering. The roofing elements are partly resting on outer walls and partly on intermittent timber columns. These buildings do not require many resources for retrofitting and restrengthening.
3.4 Building Dimensions
The typical plan dimensions of these buildings are: lengths between 5 and 5 meters, and widths between 3.5 and 3.5 meters. The building is 1 storey high. The typical span of the roofing/flooring system is 2 meters. Typical Plan Dimensions:The length and width change depending on requirements and certain governing factors. These factors include:
(1) Occupancy rate
(2) Economy background
(3) Availability of resources like materials, manpower and money
(4) Caste system
(5) Rural or Urban area
Typical Story Height: Story height can range from 3.5 to 4.0 meters with a 1.0 to 1.5 meter high attic.
Typical Span: The span between columns ranges from 1.75 to 2.5 meters, centre to centre. The typical storey height in such buildings is 3.5 meters. The typical structural wall density is up to 20 %. 15-20% For medium size buildings, the wall density ranges from 15 to 20 %.
Longitudinal Direction: 20-25 %.
Transverse Direction: 15-20 %.
3.5 Floor and Roof System
| Material | Description of floor/roof system | Most appropriate floor | Most appropriate roof |
| Masonry | Vaulted | ☐ | ☐ |
Composite system of concrete joists and
masonry panels | ☐ | ☐ |
| Structural concrete | Solid slabs (cast-in-place) | ☐ | ☐ |
| Waffle slabs (cast-in-place) | ☐ | ☐ |
| Flat slabs (cast-in-place) | ☐ | ☐ |
| Precast joist system | ☐ | ☐ |
| Hollow core slab (precast) | ☐ | ☐ |
| Solid slabs (precast) | ☐ | ☐ |
Beams and planks (precast) with concrete
topping (cast-in-situ) | ☐ | ☐ |
| Slabs (post-tensioned) | ☐ | ☐ |
| Steel | Composite steel deck with concrete slab
(cast-in-situ) | ☐ | ☐ |
| Timber | Rammed earth with ballast and concrete or
plaster finishing | ☐ | ☐ |
| Wood planks or beams with ballast and concrete or plaster finishing | ☑ | ☐ |
| Thatched roof supported on wood purlins | ☐ | ☑ |
| Wood shingle roof | ☐ | ☑ |
| Wood planks or beams that support clay tiles | ☐ | |
Wood planks or beams supporting natural
stones slates | ☐ | ☐ |
Wood planks or beams that support slate,
metal, asbestos-cement or plastic corrugated
sheets or tiles | ☐ | ☑ |
Wood plank, plywood or manufactured wood
panels on joists supported by beams or walls | ☐ | ☑ |
| Other | Described below | ☑ | ☑ |
(e.g. is floor/roof considered to be a rigid or a flexible diaphragm?).
3.6 Foundation
| Type | Description | Most appropriate type |
| Shallow foundation | Wall or column embedded in
soil, without footing | ☑ |
Rubble stone, fieldstone
isolated footing | ☑ |
Rubble stone, fieldstone strip
footing | ☑ |
Reinforced-concrete isolated
footing | ☐ |
Reinforced-concrete strip
footing | ☐ |
| Mat foundation | ☐ |
| No foundation | ☐ |
| Deep foundation | Reinforced-concrete bearing
piles | ☐ |
Reinforced-concrete skin
friction piles | ☐ |
| Steel bearing piles | ☐ |
| Steel skin friction piles | ☐ |
| Wood piles | ☐ |
| Cast-in-place concrete piers | ☐ |
| Caissons | ☐ |
| Other | Described below | ☐ |
4. Socio-Economic Aspects4.1 Number of Housing Units and Inhabitants
Each building typically has less than 10 housing unit(s). 2 units in each building.
The number of housing units in a building is usually limited to 2 but, the number of housing units in a building changes from house to house. Generally economic factors play a major role in the number of units per building. Richer people may occupy multiple housing units while this is less likely for the poor. The number of inhabitants in a building during the day or business hours is less than 5 persons. The number of inhabitants during the evening and night is 5-10 persons. In semi-urban to rural areas, the male members are going to agricultural fields for cultivation. The graph shows the variation in occupancy of typical building. See the graph in Figure-18.
4.2 Patterns of Occupancy
The building may be occupied by a single family or a joint family.
4.3 Economic Level of Inhabitants
| Income class | Most appropriate type |
| a) very low-income class (very poor) | ☐ |
| b) low-income class (poor) | ☑ |
| c) middle-income class | ☑ |
| d) high-income class (rich) | ☐ |
The House Price is in Indian Rupees (US$ 1 = IN Rs. 45.00)
Economic Level:
For Poor Class the Housing Price Unit is 100000 and the Annual Income is 25000.
For Middle Class the Housing Price Unit is 200000 and the Annual Income is 40000.
| Ratio of housing unit price to annual income | Most appropriate type |
| 5:1 or worse | ☑ |
| 4:1 | ☐ |
| 3:1 | ☐ |
| 1:1 or better | ☐ |
What is a typical source of
financing for buildings of this
type? | Most appropriate type |
| Owner financed | ☑ |
| Personal savings | ☑ |
Informal network: friends and
relatives | ☐ |
Small lending institutions / micro-
finance institutions | ☐ |
| Commercial banks/mortgages | ☐ |
| Employers | ☐ |
| Investment pools | ☐ |
| Government-owned housing | ☐ |
| Combination (explain below) | ☐ |
| other (explain below) | ☐ |
The rural house owners use money from their own savings and if not, they borrow money from small local money lenders. There are many times when illiterate rural people are cheated by those moneylenders. Now the government is providing many encouraging housing loan facilities to all groups of society with lower interest rates. In each housing unit, there are 1 bathroom(s) without toilet(s), 1 toilet(s) only and no bathroom(s) including toilet(s).
In urban areas, the houses are built with one bathroom and one latrine.
In the semi-urban and rural areas, the older houses were not provided with latrines and bathrooms. They use opens field for toilet and natural water bodies like rivers, ponds or wells for bathing. Newly constructed houses provide at least one latrine and one bathroom. .
4.4 Ownership
The type of ownership or occupancy is individual ownership.
Type of ownership or
occupancy? | Most appropriate type |
| Renting | ☐ |
| outright ownership | ☐ |
Ownership with debt (mortgage
or other) | ☐ |
| Individual ownership | ☑ |
Ownership by a group or pool of
persons | ☐ |
| Long-term lease | ☐ |
| other (explain below) | ☐ |
5. Seismic Vulnerability5.1 Structural and Architectural Features
Structural/
Architectural
Feature | Statement | Most appropriate type |
| True | False | N/A |
| Lateral load path | The structure contains a complete load path for seismic
force effects from any horizontal direction that serves
to transfer inertial forces from the building to the
foundation. | ☑ | ☐ | ☐ |
Building
Configuration | The building is regular with regards to both the plan
and the elevation. | ☑ | ☐ | ☐ |
| Roof construction | The roof diaphragm is considered to be rigid and it is
expected that the roof structure will maintain its
integrity, i.e. shape and form, during an earthquake of
intensity expected in this area. | ☐ | ☑ | ☐ |
| Floor construction | The floor diaphragm(s) are considered to be rigid and it
is expected that the floor structure(s) will maintain its
integrity during an earthquake of intensity expected in
this area. | ☐ | ☑ | ☐ |
Foundation
performance | There is no evidence of excessive foundation movement
(e.g. settlement) that would affect the integrity or
performance of the structure in an earthquake. | ☐ | ☐ | ☑ |
Wall and frame
structures-
redundancy | The number of lines of walls or frames in each principal
direction is greater than or equal to 2. | ☑ | ☐ | ☐ |
| Wall proportions | Height-to-thickness ratio of the shear walls at each floor level is:
Less than 25 (concrete walls);
Less than 30 (reinforced masonry walls);
Less than 13 (unreinforced masonry walls); | ☑ | ☐ | ☐ |
Foundation-wall
connection | Vertical load-bearing elements (columns, walls)
are attached to the foundations; concrete
columns and walls are doweled into the
foundation. | ☑ | ☐ | ☐ |
Wall-roof
connections | Exterior walls are anchored for out-of-plane seismic
effects at each diaphragm level with metal anchors or
straps | ☐ | ☑ | ☐ |
| Wall openings | The total width of door and window openings in a wall
is:
For brick masonry construction in cement mortar : less
than ½ of the distance between the adjacent cross
walls;
For adobe masonry, stone masonry and brick masonry
in mud mortar: less than 1/3 of the distance between
the adjacent cross
walls;
For precast concrete wall structures: less than 3/4 of
the length of a perimeter wall. | ☑ | ☐ | ☐ |
| Quality of building materials | Quality of building materials is considered to be
adequate per the requirements of national codes and
standards (an estimate). | ☐ | ☑ | ☐ |
| Quality of workmanship | Quality of workmanship (based on visual inspection of
few typical buildings) is considered to be good (per
local construction standards). | ☐ | ☑ | ☐ |
| Maintenance | Buildings of this type are generally well maintained and there
are no visible signs of deterioration of building
elements (concrete, steel, timber) | ☐ | ☑ | ☐ |
| Other | | ☑ | ☐ | ☐ |
5.2 Seismic Features
| Structural Element | Seismic Deficiency | Earthquake Resilient Features | Earthquake Damage Patterns |
| Wall | --Mud mortar
--No sufficient bearing for opening
--The openings are at different levels (Figure-8). | --Wall as partition wall (Figure-4a)
--Comparatively light in weight than conventional load bearing brick walls (Thickness ranges from 0.35 to 0.45 m | --Corner separation (Figure-9a,9b)
--Damage to partition wall (Figure-10)
--Overturning of walls
--Deep cracking in walls
--Gable failure (Figure-11a,11b). |
| Frame (columns, beams) | --Connection with wall is not sufficient
--Column and beam bracings are not adequate (Figure-3)
--Lack of proper linkage between columns and beams
--Loose connection. | --Ductile beam and column thus better resistance to earthquake forces
--Sometimes braces are present which links column and beams (Figure-4b). | --Swaying of columns (Figure-12)
--Excessive deflection in beams
--Joint failure of beams and columns(Figure-12)
--Collapse of frame structure. |
| Roof and floors | --Heavy roofing elements(Figure-13)
--No proper joints between rafters and purlins (Figure-14)
--Poor linkage between roofing elements and wall. | --Many houses are coved with galvanized iron sheet, which is light in weight, thus reducing seismic forces on building (Figure-15). | --Collapse of roof (Figure-10)
--Displacement of roof covering tiles
--Joint failure of purlins and rafter. |
| Other | | | |
The structural system connectivity for a good timber frame brick building is perfect at its wooden joints but most of the time it has been found that poorly constructed buildings are missing such important parameters. In this regard, the survey was conducted and found that about 85 % of the buildings in the study area do not have adequate structural connectivity.
5.3 Overall Seismic Vulnerability Rating
The overall rating of the seismic vulnerability of the housing type is C: MEDIUM (i.e., moderate seismic performance), the lower bound (i.e., the worst possible) is B: MEDIUM-HIGH (i.e., poor seismic performance), and the upper bound (i.e., the best possible) is D: MEDIUM-LOW (i.e., good seismic performance).
| Vulnerability | high | medium-high | medium | medium-low | low | very low |
| | very poor | poor | moderate | good | very good | excellent |
Vulnerability
Class | A | B | C | D | E | F |
| ☐ | ☐ | ☐ | ☐ | ☐ | ☐ |
5.4 History of Past Earthquakes
| Date | Epicenter, region | Magnitude | Max. Intensity |
| 1988 | Eastern Nepal between Udaipur and Dharan (Bihar-Nepal Earthquake) | 6.6 | IX |
| 1993 | Killari (Maharashtra ) | 6.4 | IX |
| 1997 | Kosma Ghat (Jabalpur) | 6 | VII |
In the Bihar Nepal Earthquake (1988), with isoseismal areas of IX, nearly 75 % of these buildings experienced moderate to severe damage ranging from wide cracks to partial collapse. More damages were reported due to liquefaction than ground shaking.
In Killari earthquake (1993), typical timber framed brick buildings at Intensity VII to IX, performed satisfactorily. The damage varied from minor cracks to swaying of the timber frame without partial or complete collapse.
In Jabalpur earthquake(1997), similar building types performed differently in various places. Although the statistical data for damage of this building type is not available, the range of damage varies from unaffected to complete collapse.
6. Construction6.1 Building Materials
| Structural element | Building material | Characteristic strength | Mix proportions/dimensions | Comments |
| Walls | Brick | N/A | N/A | |
| Foundation | Rubble Stone with Mud mortar. | N/A | N/A | |
| Frames (beams & columns) | Timber (Teak Wood). | N/A | N/A | |
| Roof and floor(s) | Timber planks (Teak). | N/A | N/A | GROUND FLOOR: Mud Plaster.
FIRST FLOOR: Wooden planks. |
6.2 Builder
Builders live in this type of construction.
6.3 Construction Process, Problems and Phasing
The building is constructed by local artisans and skilled and unskilled manpower with locally available material and tools. The typical house of two rooms for single family may take nearly four to six weeks of time.
FOUNDATION: For brick wall construction, a spread footing foundation is generally practiced. The depth of foundation is about 0.60 m. The foundation is made up of random rubble masonry with mud mortar. The thickness of the footings varies from 0.60 to 0.75 m. In many cases, the width of the foundation continues above the plinth level and gradually tapers down to the wall thickness. The timber columns are erected and placed during the foundation construction phase.
TIMBER FRAME AND WALL CONSTRUCTION: The timber frame is erected before masonry work. All necessary bracings are done. Once the frame is erected, then brick work starts. The brick may be burnt or sun dried. The characteristics and quality of brick has been discussed in section 7.1. Major construction work is done by the family members. Only specific technical jobs, are done by skilled or semi-skilled masons or carpenters.
WALL CONSTRUCTION: The walls are constructed after erection of timber frame. Generally mud mortars are used for the brick masonry work. The english bond systemis applied for walling but many times this feature is missing in rural construction. There are no provisions for waterproofing the walls. (Figure-16). ROOFING SYSTEM: The roof has two tiers. A flat roof is constructed just above the ground floor. The flat roof is made up of timber. The details are shown in Figure-16. The roof above the attic, which is exposed to the outside, is covered with galvanized iron sheets or clay tiles. The construction of this type of housing takes place incrementally over time. Typically, the building is originally not designed for its final constructed size.
6.4 Design and Construction Expertise
In general, no formal engineering design is practiced for the construction of these houses. The building is constructed by local skilled or semi skilled workers, which have little knowledge of engineered construction. They follow rules-of-thumb for construction. In semi-urban and rural areas, civil engineers do not play a role in the design and construction of these buildings. These days, due to a lack of wood for building material, the rate of construction of these buildings has declined.
6.5 Building Codes and Standards
This construction type is addressed by the codes/standards of the country. Title of the code or standard: --IS 13828-1993: Indian standard guidelines for improving earthquake resistance of low strength masonry buildings --IS 1893-2002: Indian standard guidelines for earthquake resistant design of structures --IS 4326-1993: Indian standard code of practice for earthquake resistant design and construction of buildings.
Year the first code/standard addressing this type of construction issued: N/A
National building code, material codes and seismic codes/standards: N/A
When was the most recent code/standard addressing this construction type issued? N/A.
The building code enforcement for this type of construction is very poor. The building bylaws in rural and semi-urban areas are not properly enforced.
6.6 Building Permits and Development Control Rules
This type of construction is an informal, and authorized as per development control rules. Building permits are not required to build this housing type.
6.7 Building Maintenance
Typically, the building of this housing type is maintained by Owner(s).
6.8 Construction Economics
The unit cost of construction without considering the cost of land and interior fitting comes out to be Indian Rs. 1500 to Rs. 2000 (USD35 to USD 45) per square meter depending upon the place and material available. If the size of a house is considered to be 12 m X 3 m, the time required to complete the house will take 35 days provided all resources are supplied to the site without interruption. The requirement of manpower will be as follows:
Labour = 38
Mason = 26
Carpenter = 5.
7. Insurance
Earthquake insurance for this construction type is typically not available. For seismically strengthened existing buildings or new buildings incorporating seismically resilient features, an insurance premium discount or more complete coverage is not available. Not available.
8. Strengthening
8.1 Description of Seismic Strengthening Provisions
Strengthening of Existing Construction :
| Seismic Deficiency | Description of Seismic Strengthening provisions used |
| Poor column and beam connection | Knee, horizontal and vertical bracing (Figure-17) |
| Poor roofing elements | Replacing the decayed wooden elements with good quality wooden members |
| Heavyweight roofing | Replacing heavy roofing material with galvanized iron sheet (Figure-17) |
| Plinth, lintel and roof band absence | Strengthening with wire mesh (Figure-17). |
| Poor brick mortar | Plastering with rich cement mortar with waterproofing compounds |
| Poor waterproofing | Plastering with rich cement mortar with waterproofing compounds |
Strengthening of New Construction :
| Seismic Deficiency | Description of Seismic Strengthening provisions used |
| Absence of lintel bands | Provide plinth, lintel and roof bands (Figure-17) |
| Heavy roofing material like country clay tiles | Lightweight roofing materials such as galvanized iron sheet |
| Discontinuous columns | Firm column and beam connection |
| Local bricks are made up of black cotton soil which contains many mineral lumps | Good quality bricks to be used |
| Black cotton soil mortar | Cement mortar in place of mud mortar |
| Absence of building codes practices | Good practice of building codes |
| No proper bonding techniques are applied in field | Proper bonding of walls |
METHOD FOR RETROFITTING / STRENGTHENING
Process Overview:
(A) Removal of Excess Heavy Roof Covering
(B) Insertion of a Timber Frame
(C) Strengthening the Timber Frame
(D) Seismic Bandage
(E) Roof Strengthening
(F) Pointing of Poor Mortar Brick Walls
(G) GI Sheet of Tile Roof Fixing
(A) Removal of Excess Heavy Roof Covering i.e Tiles, Timber Planks, GI Sheets, Clay Tiles, Etc.
Earthquake induced seismic forces are directly proportional to the mass of structural elements; the larger the mass, the larger are the seismic forces to be resisted by the structure. Therefore, the weight of the roof must be reduced to the greatest possible extent. The following procedure has to be adopted:
1. Removal of clay tiles or GI roofing sheets carefully without altering the existing load path of system.
2. Careful removal of roofing and truss materials; the roofing elements should not be repositioned until all other retrofitting work at and above eave level has been completed.
3. Placement of the wooden purlins and rafters (50-75 diameter) at a spacing of 250 mm center to center. The purlins must be placed firmly within proper grooves in the rafters. The rafters are fixedly placed on a wooden "Eaves Band" with a steel strap, placed all around the top of wall.
(B) Insertion of a Timber Frame.
The existing frame structure has its own strength and acts perfectly well during ground shaking. The load bearing brick walls perform comparatively poorly, so effort should be spent to convert the load bearing structure from the brick walls to frame. It is observed that this rural construction type is partially framed so less effort is required to convert a house into a fully framed structure.
The loads coming from the super-structure to the foundation should be studied. Colums should be inserted in the necessary locations using a proper foundation construction technique that ensures the loads can transfer from the structure to the ground. The eaves band must be positioned on the wall properly by making grooves and inserting the column.
(C) Strengthening the Timber Frame.
The strengthening is done by bracing the frame and wooden members. It includes installation of timber band, knee bracing as well as diagonal and horizontal bracing of timber frame.
(i) Installation of Timber Band.
The top most portion of the wall should be dismantled just below the eaves level and the timber band should be installed at this level; the parapet wall should be reconstructed using the same material. The timber band is to be also provided at gable tops.
(ii) Knee Bracing of a Timber Frame.
Knee bracing should be introduced at top of each timber post to reduce the likelihood of lateral sway and to strengthen timber frame against a possible earthquake. Two bracings are required for corner posts and four bracings are required for inside posts in a bidirectional column-beam system. There are several possible types of knee bracing, depending on the availability of construction materials (steel or timber). The length of the knee bracing should be approximately 60 cm. When steel bracing is employed, rolled steel angles with a minimum size of 35 X 3 mm should be used. For timber bracing, a timber plank of 30x80-mm cross-section may be used.
SEE THE REMAINING SECTIONS (c-iii, d,e,f,g) IN SECTIONS 10.4 & 10.6.
8.2 Seismic Strengthening Adopted
Has seismic strengthening described in the above table been performed in design and construction practice, and if so, to what extent?
This seismic strengthening procedure has been described based on post-earthquake rehabilitation of the Killari earthquake, earthquake retrofitting techniques adopted for earthquake prone areas of Nimar and Indian standard codes. No retrofitting programmes have been initiated before earthquake occurrence for this type of construction.
Was the work done as a mitigation effort on an undamaged building, or as repair following an earthquake?
In India, mitigative measures have only been instituted in large scale after earthquakes. Examples can be sited after the Killari earthquake in Maharashtra, India, where this type of construction, namely Khan construction, was retrofitted and strengthened.
8.3 Construction and Performance of Seismic Strengthening
Was the construction inspected in the same manner as the new construction?
Yes
BELOW ARE ADDITIONAL SECTIONS (c-iii, d) FOR THE METHOD OF RETROFITTING/STRENGTHENING DISCUSSION STARTED SECTION 10.1:
(iii) Diagonal and Horizontal Bracing of the Timber Frame.
As an alternative to knee bracing, bracing of a timber frame by means of either diagonal bracing elements or horizontal struts is recommended. The purpose of providing diagonal and horizontal bracing is:
1. To prevent swaying of a timber frame during an earthquake and
2. To prevent tilting of the wall to the inside of the house and/or to reduce the effective wall height.
Bracing of the core house area, particularly all the bedrooms, is of the highest priority. Consequently, diagonal or horizontal bracing should be provided inside first, and then on the outside of the house.
For diagonal bracing applications, a minimum of two bracings should be installed in adjacent spans with alternate directions. Alternatively, "X" bracing can be installed within one frame span. Timber planks used for diagonal or horizontal bracing should be at least 30x80 mm in cross section.
(D) Seismic Bandage.
To ensure integral action of the walls during an earthquake, installation of seismic bandage at the lintel level is recommended for UCR stone masonry as well as for BB and solid concrete block masonry walls. Seismic bandage is an alternative to a reinforced concrete (RC) band at the eave level, and it should be provided whenever it is not feasible to install a RC band at the eaves level by dismantling a portion of the parapet. When the masonry work is not in good condition, bandage can be provided, without dismantling a portion of wall.
Seismic bandage can be installed, whenever: a) the height of the wall (from the ground level to eaves level) is over 3 m, and/or b) the distance between the top of the openings (windows) and the eaves level is at least 1m. In such a case, seismic bandage should be installed at the lintel level.
Construction of seismic bandage should be carried out as per the following procedure:
· Clean a 80 cm wide horizontal strip of the exterior wall face all around the building, starting at the lintel level.
· Remove the plaster from the wall surface. Rake the joints between the stones to a depth of approximately 20 mm. Surface should be cleaned with a wire brush until all vegetation and dust particles are removed.
· Provide an opening for a shear key (approximately size 15 x15) by removing one stone from the wall below the roof level. Shear keys should be spaced horizontally every 2 m.
· Two pairs of "U" shaped stirrups (6mm diameter mild steel bars) should be inserted in each shear key. Four longitudinal bars of 8 mm diameter TOR steel should be placed in the corners of the "U" stirrups.
· Fill the space in the shear keys with micro-concrete (1:2:4 mix, maximum 6 mm diameter aggregate).
· Affix a 60 cm wide strip of welded wire mesh reinforcement of 2 - 3 mm diameter @ 25 - 50 mm c/c spacing (i.e. Wire mesh of size 25 x 25 x 2 mm or 50 x 50 x 3 mm or with intermediate diameter and appropriate spacing) to the walls at the roof level by means of long nails. The mesh should also be connected to the shear key reinforcement with the binding wire.
· Provide a 10 mm wide gap between the mesh and the wall.
· Overlap the mesh to ensure the continuity of reinforcement. The overlapping length should be approximately 60 cm.
· Wet the wall surface by sprinkling water. Apply a 15mm thick layer of 1:3 cement-sand mortar to cover the mesh.
· After one hour, apply another layer of 1:3 cement-sand mortar of the same thickness (15mm).
· Cure the belt continuously for 14 days by sprinkling water.
· For a house having more than one room, seismic bandage should be provided along with tie bars as shown in figure 17
SEE THE REMAINING SECTIONS (e,f,g) IN SECTION 10.6.
Who performed the construction seismic retrofit measures: a contractor, or owner/user? Was an architect or engineer involved?
The house was constructed by the contractor with overall supervision of engineers deployed for the redevelopment and rehabilitation.
What was the performance of retrofitted buildings of this type in subsequent earthquakes?
No such case is apparent.
BELOW ARE ADDITIONAL SECTIONS (e,f,g) FOR THE METHOD OF RETROFITTING/STRENGTHENING DISCUSSION STARTED SECTIONS 10.1 & 10.4:
(E) Roof Strengthening.
a. Weld or clamp suitable diagonal bracing members in the vertical as well as horizontal planes to brace roof truss frames.
b. Improve the roof truss anchors that conect to the supporting walls to eliminate the roof thrust on the walls.
c. Integrate roof and floor systems that consist of prefabricated units like RC rectangular/T/channel units or wooden poles/joists carrying brick tiles. Timber elements could be connected by nails to diagonal planks and spiked to an all around wooden frame at the ends.
(F) Pointing Exterior Walls.
Joints of the brickwork must be raked out to a depth of 20 mm (3/4 inches) and the surface of the wall must be washed, cleaned and kept wet for two days before pointing. The mortar materials should be either a mix of cement and sand or a mix of kankar lime, surkhi and sand. The materials of mortar shall be dry mixed first by measuring with boxes to have the required proportion as specified (1:2 or1:3 for cement sand mortar, 1:1 for Lime surkhi (Crushed burnt brick bats) mortar of kankar lime); only then can the mortar be thoroughly mixed by adding water slowly and gradually.
Mortar shall then be applied in the joints slightly in excess. If there is any extra mortar, it should be removed and the surface finished. Mortar shall not spread over the face of bricks, and the edges of bricks shall be clearly defined to give a neat appearance. After pointing the surface shall be kept wet for seven days.
(G) GI Sheet or Tile Roofing.
It is observed that a suitable connection between the roof structure and the walls is absent in most of these houses. A GI sheet, when improperly supported directly on the roof band, requires a cut in a portion of the band. (A cut in the band is also required to embed the rafters or purlins.)However, such a cut in the band is not permitted. Instead, one or two courses of burnt brick masonry should be provided to connect the GI sheet roofing. On the front side, bolts can be embedded in the burnt brick masonry over the band and the GI sheet should preferably be held by a flat 30x3 mm which in turn should be embedded in the end of parapet walls. Alternatively, on the front side, a purlin can be used along the inside or outside of the band and J bolts can be connected through this purlin (which is flat on top) to hold the GI sheets in place.
Reference(s)- A Manual of earthquake resistant non-engineered construction Indian society of earthquake technology
IAEE
Indian Society of Earthquake Technology, University of Roorkee, Roorkee 1989
- Earthquake Protection
Coburn,A. and Spence,R.
John Wiley & Sons, London, UK 1992
- Reducing Human casualties in Building Collapse: Method of Optimising disaster plans to reduce injury levels
Coburn,A.W, Pomonis,A., Sakai,S. and Spence,R.J.S.
The Martin Centre for architectural and urban studeis, University of Cambridge, UK 1992
- The September 29, 1993 M6.4 Killari Maharashtra earthquake in central India
Earthquake Engineering Research Institute (EERI)
EERI special earthquake report, USA 1994
- Some observations on engineering aspects of the Jabalpur earthquake of 22 May 1997
Earthquake Engineering Research Institute (EERI)
EERI special earthquake report, USA 1997
- Learning from earthquakes: The Chamoli, India, earthquake of March 29 1999
Earthquake Engineering Research Institute (EERI)
EERI special earthquake report, USA 1999
- Development of project for retrofitting of building for Khandwa region, Madhya Pradesh
Kumar,A.
Disaster Management Institute, Bhopal, India 2002
- Seismic Retrofitting of Non-Engineered Buildings of Earthquake Prone Area of Madhya Pradesh
Kumar,A. and Parmar,A.K.S.
International Symposium on Seismology, Earthquake Hazard Assessment and Risk Management, Kathmandu, Nepal 2002
- Financial Assessment for Retrofitting of Brick Buildings
Kumar,A, and Bose,P.R.
Fourth International Conference on Seismology and Earthquake Engineering (SEE-4), Tehran, Iran 2003
- Strategies for Earthquake Mitigation through Retrofitting of Non Engineered Buildings for Nimar Region of Madhya Pradesh
Kumar,A., Bose,P.R. and Parmar,A.K.S.
UNDP Newsletter, Orissa, April 2003
- Seismic retrofitting of vernacular mud houses of earthquake prone area of Madhya Pradesh
Kumar,A.Parmar,A.K.S. and Bose,P.R.
National Architectural Conference, 1-2 November, 2003 2003
Author(s)- Amit Kumar
Assistant Director, Disaster Management Institute
Paryavaran Parisar E-5 Arera Colony, Bhopal 462016, INDIA
Email:Amitverma7@hotmail.com FAX: (91-755) 46 7981
- Jeewan Pundit
Postgraduate Student, School of Planning and Architecture
Indraprashtha Marg, Delhi 100001, INDIA
Reviewer(s)- Ravi Sinha
Professor
Civil Engineering Department, Indian Institute of Technology Bombay
Mumbai 400 076, INDIA
Email:rsinha@civil.iitb.ac.in FAX: (91-22) 2572-3480, 2576-7302
