Description

The World Housing Encyclopedia (WHE) Report Database contains 130 reports on housing construction types in 43 seismically active countries. Each housing report is a detailed description of a housing type in a particular country. The description is prepared from a number of standard closed-ended questions and some narrative that have been provided by report authors. Each report has five major categories including architectural and structural features; Building Materials and Construction Process; Socio-economic Issues; Past Performance In Earthquakes, Seismic Features and Vulnerability; and Retrofit. All of the housing reports in this database have been contributed by volunteers. If you are interested in writing a housing report please contact the WHE Editorial Board.

About

The World Housing Encyclopedia (WHE) is a collection of resources related to housing construction practices in the seismically active areas of the world. The mission is to share experiences with different construction types and encourage the use of earthquake-resistant technologies worldwide. The technical activities of the WHE are steered by an international team of 22 professionals specializing in different aspects of seismic safety of buildings and structures. They bring relevant experience from 16 seismically active countries across the world. For more information about the World Housing Encyclopedia, visit http://www.world-housing.net/.

General Information

 

Report #:146
Building Type: Dhajji Dewari
Country: Pakistan and India
Author(s): Kubilay Hicyilmaz
Jitendra K Bothara
Maggie Stephenson
Last Updated:
Regions Where Found: Buildings of this construction type can be found in both the Pakistani and India sides of Kashmir. Similar forms of construction are found in Britain, France, Germany, Central America, South America, Turkey, Greece, Portugal and Italy and most likely other Eastern European countries. They are known as half-timber, colombage, Fachwerk, taquezal or bahareque, quincha, himisand Gaiola respectively with some minor variations as shown in Figure 5 to Figure 10. [Note that taquezal, bahareque and quincha are somewhat different from dhajji and quincha is closer to wattle and daub. This form of construction is also known as Brick nogged timber frame construction in India. According to an article by V.K.Joshi this building type is known as Kat-Ki-Kunni in the region of Kulu and Pherols in Uttarkashi in Uttaranchal in India (see Reference 4). This type of housing construction is commonly found in rural, sub-urban and urban areas. Typically these houses are found in the mountainous northern parts of Pakistan and India and a good example is shown in Figure 5 which was built in the 1930s at the time of the last great depression by a western funded research institution, for which some limited documentation was found on the web. A recent field trip by Arup engineers working in the region in August 2009 has confirmed that this particular Dhajji building is still in existence and is now being used as a museum. Other examples of this type of construction from around the world are shown in Figure 5 to Figure 10. This report concentrates on the types of dhajji dewari buildings as typically found in the northern parts of Pakistan and Pakistani Kashmir.
Summary:

Dhajji dewari (Persian for patch quilt wall) is a traditional ...

Length of time practiced: More than 200 years
Still Practiced: Yes
In practice as of:
Building Occupancy: Residential, unknown typeSingle dwellingMulti-unit, unknown type
Typical number of stories: 1-4
Terrain-Flat: Typically
Terrain-Sloped: 4
Comments: After the 8th October 2005 earthquake, this construction type has been adopted by many people for reconstructing their houses as


 

Features

 

 

Plan Shape Square, solidRectangular, solid
Additional comments on plan shape Length to width ratios are in the order or 2:1 or 3:1. High altitude multi-storey Dhajji is usually approximately square in plan and is typically three bays wide in each direction. If constructed on sloping terrain, these buildings are usually sat into relatively narrow man made terraces which imposes the adoption of a rectangular building plan layout for the building.
Typical plan length (meters) 10 to 20
Typical plan width (meters) 5 to 20
Typical story height (meters) 2.5 to 3.5
Type of Structural System Other
Additional comments on structural system The vertical load-resisting system is timber frame. Because the stone/brick masonry infill with mud mortar is placed into the frames after the building frame has been built it is not thought that the infill carries any of the vertical loads until the building settles, the timber frame deforms under permanent gravity loads with time and the timber shrinks as it dries out. It is thought that this compression of the infill panels is in part responsible for their stability during out of plane shaking. In the case that a building is extended upwards at a later date some degree of vertical loading of the complete infill wall system will occur. The lateral resistance of a Dhajji building comes from a combination of the extensively braced timber frame with stone/brick masonry infill laid in mud mortar. This combination of timber framing and masonry infill resists the earthquake loads in a composite way. Because of the weak mortar, the masonry infill panels quickly crack in-plane under lateral loads and thereby absorbing energy through friction between the infill material and hysteretic behaviour of the many mud layers that form the mortar between the stones/bricks and timber framing and bracing. The timber frame and closely spaced bracing, which essentially remains elastic, prevents any large cracks from propagating through the infill walls. The framing provides robust boundary conditions for the infill material to arch against and thus resist significant out of plane inertial loads. Because the framing and bracing is so extensive it is possible to build the walls out of relatively thin masonry panels. This helps to reduce the mass of the building and therefore the inertial forces that must be resisted by the building system during an earthquake.
Gravity load-bearing & lateral load-resisting systems In current days extensive use is made of nailing. The timber frame is extensively braced with stone/brick masonry infill traditionally laid in mud mortar. Typically after the construction of a shallow stone foundation the timber frame is built first. It is not thought that anchorage of the posts to the foundation will traditionally have been undertaken. Examples are shown in Figure 51, Figure 58, Figure 59, Figure 60, Figure 61 and Figure 64. During reconstruction efforts after the 2005 Pakistan earthquake connections between the posts and the foundation has been recommended in the ERRA guidelines (See Figure 55 and Figure 56 and Reference 3). It is most important to note ERRA and implementing partners recommended measures to make sure the plinth is stable and secure, not likely to collapse under the building. Also to make sure the building is not likely to walk off the plinth. Therefore the plinth area should have a small margin larger than the floor area of the building. The infill is added between the extensive bracing patterns adopted in building the building frames. There are no firm principles that are used to decide on the adopted bracing patterns. In other words, the location of the principle timber columns, the secondary frame members and the extent, location and configuration of the adopted bracing pattern depends entirely upon the choices of the home builder/carpenter. Examples of some idealised bracing patterns observed in the field after the 2005 Pakistan earthquake are shown in Figure 49 which also depend on the available timber. The infill fulfils functional (enclosure and partitioning) and structural requirements. 1. Because of the low infill panel strength and high flexibility of the timber frame, due to the generally loose timber connection, the in-plane wall panels crack in the very early stages of ground shaking. This softens the frame and has the effect of immediately decoupling the Dhajji buildings period of vibration from the likely predominant period range of an earthquake. This results in reduced inertial forces being imposed on the building. It is thought that the first phase of earthquake response is movement along the masonry-timber interfaces, before the masonry itself is stressed enough to begin to crack. In other words it is thought that there is much friction along these construction joints even before cracking of the masonry starts. 2. The cracking and sliding of masonry units along mortar joints increases the hysteretic damping levels in the building thereby reducing the earthquake loads. 3. During long duration earthquakes a few isolated infill panels may topple without jeopardizing the stability of the building as the timber frame essentially remains elastic and maintains a vertical load path and lateral stability to the building structure. 4. The closely spaced timber framing and bracing mitigates out-of-plane toppling of the infill walls by providing support point from which the masonry panels can retain their stability through arching action which ensures that the friction force is greater than the inertia force that wants to dislodge the infill pieces from the walls. It is important that long walls are regularly connected to perpendicular walls to avoid a global out-of-place failure of wall panels. Some infill failures do occur when the infill is poorly compacted because the masonry units are unable to develop proper arching action between the timber boundaries. Equally failures also seem to occur due to geometry such as inverted triangles with the long side at the top of a wall.
Typical wall densities in direction 1 10-15%
Typical wall densities in direction 2 5-10%
Additional comments on typical wall densities
Wall Openings Usually openings are well distributed in this type of building. Openings are in the range of 20% to 30% of the gross external wall area. However, if the building is constructed in slopping ground, the uphill long side and the short sides are usually solid wall with all the openings being concentrated on the downhill face of the building. On the downhill long side the openings can make up to 50% of the total wall area. The arrangement gives an unsymmetrical provision of the walls resulting in an increased torsional response of the building under earthquake excitation. The structural walls are evenly distributed internally of the building to ensure even lateral resistance to the seismic loads.
Is it typical for buildings of this type to have common walls with adjacent buildings? No
Modifications of buildings Dhajji buildings are characterized by informal and incremental construction by nature. Addition of new space is common and is driven by the need for more rooms and the availability of resources. It is common to build upwards, due to the small flat plots available to build on in mountainous settings. Where a subsequent level is added many years after the original construction it is thought that the additional floor will be built as if it were a completely separate house that happens to be placed on top of the existing house. In other words the timber columns will not be continuous through the storeys. Similar construction techniques have been found in some pagodas. Correspondence with R. Langenbach sheds the following light on to the subject: From what I have seen, commonly Dhajji frames are more often platform frames where each story is framed onto the top plate of the story below which distinguishes them from heavy timber frames or the early American balloon frames which were stud frames where the vertical timbers carried through two stories, and the floor joist plate was framed into the studs. More generally there are three common ways to extend these buildings: 1. Horizontally, extra rooms, using end wall as party wall. 2. Vertically by constructing a flat roof initially over the Dhajji, with light mud, this becomes the first floor. 3. Vertically by constructing the frame to the roof in the first place, but only filling in walls and occupying floors according to need and resources. Detailed surveys of existing multi-storey Dhajji buildings would be required to confirm how the buildings are stacked or interconnected. If these buildings are extended horizontally, the extensions will most likely share walls with the existing building.
Type of Foundation Shallow Foundation: Rubble stone, fieldstone strip footing
Additional comments on foundation Typically, these buildings have shallow dug foundations without any proactive drainage provisions around the timber frame base. It has been found that often people build a house first and only then do they think about the site preparation. This can only in part be explained through the need to provide safe shelter after the earthquake. Nowadays solid masonry (not concrete blocks or hollow clay tiles) or even nominally reinforced concrete may be used to form the shallow foundations. It is not thought that any positive anchorage will have been traditionally provided between the timber frame and the strip foundations. Foundations are typically most of the time stone. The plinth may be constructed up to several feet depending on site and location (slope or snow). There was some previous use of bolting to foundation prior to the earthquake. Nowadays, with the availability of long bolts it is envisaged that positive coupling between the timber frame and the strip foundations is being adopted more frequently as part of the reconstruction efforts undertaken after the 8 October 2005 earthquake.
Type of Floor System Earthen floor, unknownOther floor system
Additional comments on floor system In other words the timber columns are connected by primary timber beams. Secondary timber beams span between the primary beams with timber floor boards that are likely to be nailed to the secondary beams. In traditional dhajji buildings it will have been common for the timber floor to have overlain by a mud screed for levelling purposes. Important to note, that good quality timber boards are used in areas where timber is plentiful or people have money. In other conditions, scrap timber of various lengths and sections are simply laid on the beams and overlaid with a mud screed. In this version there is no fixing to the beams and therefore no diaphragm action, this built up floor simply shakes apart in an earthquake. Unfortunately this has proven to be very common in the post earthquake reconstruction. Traditional houses often had timber boards also used beneath the beams as a ceiling, new practice is likely to be plywood which is all to often actually a poor quality fibreboard rather than proper plywood. The mud screed serves the secondary purpose of fire protection to the structural timber floor. It is thought that the floors, although not rigid are sufficiently stiff to reasonable distribute lateral loads to the dhajji wall system in the case that the floor beams have been covered with wooden floor boards.
Type of Roof System Wooden beams or trusses with Wood-based sheets on rafters or purlinsheavy roof covering
Additional comments on roof system The roofing system consists of wooden trusses clad in corrugated iron either zinc galvanised or with a painted finish. The roofing system typically consists of timber A-frame trusses spanning between principal timber columns, though this is not always the case. Sometimes the timber trusses are found to span between primary beams rather than columns. The timber trusses are typically configured to form a gable roof or even better in a hipped roof configuration. The hipped roof has better all round stiffness compared to roofs pitched only in two directions. Hipped roofs also avoid the unrestrained gable masonry. 95% hipped in Pakistan except in very high areas close to the line of control. Note that some of the roofs are getting very elaborate with complex floor plans, dormer openings and variations within the hipped roof. The elaboration of the roof has also been a response to ERRAs restriction of single storey for all construction types, whereby people simply planned to use the roof space more for living, but constructed as habitable roof not as second or third storey. In April 2008 ERRA started to allow multi-storey timber in areas of traditional timber frame construction. Traditionally rough cut purlins were used to span between the roofs trusses on to which shingles were placed as the weather surface. Flat boards were also used as found in the region of Neelum. Shingles were typically for richer people. More recently the roof covering has been made of various types of sheeting such as metal, asbestos, cement or plastic corrugated sheets. The authors do not know of cases where clay tiles have been used on these types of buildings in Pakistan or India.
Additional comments section 2 In rural areas building are separated by many meters. If a building is extended then extensions will share common walls with the existing half. Dhajji buildings are more commonly found in rural areas. In urban areas and settlements along transportation corridors, wherever modern materials such as cement and steel are easily available and more affordable than they used to be, Dhajji buildings are largely being displaced by modern forms of construction. In rural areas, houses probably have a larger foot print but are likely to be only one to two stories high. In urban areas, and this is mainly in Srinagar, Indian Kashmir, there are many example of Dhajji buildings up to four stories high. After the 2005 earthquake in Pakistan there has been considerable uptake of the Dhajji construction method due to evidence of their relatively good structural performance under the earthquake and the fact that they are affordable unlike the more modern and much more expensive and complicated reinforced concrete construction methods that exist these days. One of the big issues for the siting of Dhajji buildings or any other type of such building is the necessity to construct back walls as part of the building to retain the higher ground and to construct high plinths at the downward slope of the building or under the veranda. Safe site selection is an important issue. However often families do not have much choice in deciding where they live. Typical sites 4 of 34 10/15/2012 10:20 AMare at risk from avalanches, landslides and are accessed with great difficulty because most are built away from the few existing roads in their mountainous setting. A short film prepared by the Pakistani Earthquake Rehabilitation and Reconstruction Authority (ERRA), set up after the 2005 earthquake, indicates that land ownership is recorded at the revenue department where records go back for 500 years. Traditionally land boundary records were kept on a map drawn on cloth called a ladha. The ownership records would typically name the father, the grandfather and the great grandfather and the fathers son on the records. Finally a unique field number should be available for every plot of land and that in Pakistan that records are maintained at the village level in patwar circles, district and provisional levels. Recent field experience by the authors indicates that the above description of landowner ship is not a national practice. It is thought that the majority of land is held by landlords with various agreements with tenants. Pakistan administered Kashmir has a high prevalence of owner occupancy but again that this is not a national practice. Increasingly marginal land is being used for settlement, both in rural and urban areas due to rising population. Growing rural population and settlement is increasing pressure on natural resources including ground water supply, forest cover and increased pollution by sewerage disposal. This in turn increases vulnerability to hazards and decreases resilience. When separated from adjacent buildings, the typical distance from a neighboring building is 0.5 meters.

 

Building Materials and Construction Process

 

 

Description of Building Materials


Structural Element Building Material (s)Comment (s)
Wall/Frame Timber posts with timber braces (nailing has been found in older buildings). Rubble or cut stone dressed in mud mortar. Mud mortar may be strengthened by the addition of lime and/or the addition of natural fibres (pine needles, goats/horse hairs) to avoid shrinkage of the mortar but more likely the render. Properties of the mud infill are not known. The level of hysteretic behaviour of the mortar during seismic actions is not known but unlike sand cement mortar it is expected that the mud mortar will retain some degree of ductility, a bit like malleable clay, and therefore be able to continuously keep creating new bonds and its energy absorption capabilities. Clearly research is required to scientifically quantify the value of the mortar in absorbing energy. Brick/stone in mud mortar. Failure occurs along infill material pieces through the weak mortar therefore the strength of the infill material is largely irrelevant (though it should not just crumble). Energy is absorbed by breaking the bond between the mud mortar and the infill material. Further energy is lost in the friction between all the infill components. Geometric shape of the infill is thought to influence the performance of the infill wall as shown in Figure 6 3. Wedge shaped fill may pop out when under compression cycle.
Foundations Stone masonrySemi dressed or rubble stone masonry (dry or mud mortar). More recently with uses of sand cement mortar and or reinforced concrete bands and anchor bolts are becoming more prevalent. Foundation failure thought to be rarely a controlling factor. Foundation adequacy is more determined by foundation depth and quality of stone wall construction. Where failures occur it is never due to the failure of the stone strength or mortar strength. Regular use of bonding stones, adequate wall height to thickness proportions are controlling factors.
Floors Floor compacted and levelled earth screed Shingle (i.e. wood roof tiles) connected to timber purlins often made from full timber boards or planks In more recent times extensive use of corrugated galvanised iron (CGI) sheets are being made. Gauge of the metal decking is thought to be very thin, making the longevity of many of the recently constructed roofs highly questionable.Available CGI sheets are generally available in 8 or 10feet lengths. 12ft long sheets are rarely available. Available sheets widths are 32, 36 and 42 wide Typical dimensions of available CGI sheets are shown in Table 6 4. CGI sheets used for roofs have a gauge of around 26 (0.476mm) giving a weight of 3.662kg/m2. Range of available sheet thickness is Typically 3 rows of purlins are used for 8feet long CGI sheets and 4 rows for the 10 and 12 feet long sheets. CGI sheets may typically extend approximately for 4inches beyond the eve boarding. Purlins are typically around 2.5 inches x 2 inches CGI sheets are typically connected to the purlins with 2 to 3 inch long nails every 2 to 3 corrugations. These nails are in the order of 4-5mm thick. Overlap between CGI sheets is typically 1.5 to 2 corrugations
Roof Same as floors
Other Timber beams overlain with wooden planks Timber framing, with joinery and timber dowels and wedgesThe size of the timber sections is an issue as they are only 5 x 5, 4 x 4, 4 x 2 inches, not like large European or American timber sections with dowel and peg joints. Principle frame of beams, columns and braces are mostly made from softwood. Timber connections do not appear to make any use of timber dowels or pegs apart from the Kashmiri joint which uses a locking peg. The most readily available timber in the region is shown in Table 6 3 (See Reference 31). Deodar is a species of Cedar and shares has properties of being rot resistant, fine grained and of reasonable strength. It is native to the Himalayan Region - and of cultural significance in Kashmir. The Wikipedia entry explains that "Deodar" is a "Sanskrit word, (Sanskrit: devdar), which means, "divine wood". Clearly the longevity of dhajji buildings will in some part depend on the effort that has been made during the construction to ensure that timber members remain dry. Using timber sections with good quality rot and fungal decay are to be preferentially selected for use on those members that are in contact with the ground or part of an external wall, in other words to members that are going to be exposed to moisture. The quality of Cedar is also illustrated by the observation that in North America, cedar is used for wooden roof shingles. It is also used for cedar closets and cedar chests for wool clothing storage because of its bug (moth) repellant qualities. How timber is handled until it is dry is not known to the authors at present. However, construction of dhajji houses using green wood will no doubt have its own problems, especially in cases where significant levels of shrinkage occurs as a relatively wet timber frame dries and becomes accustomed to the environment (principally temperature and moisture levels) it eventually finds its self in. It is important to stress that the selection of timber is a skilled art and must take into account the following principles: Visual strength grading (a function of the presence of knot area ratio and their disposition along a piece of timber). Slope of grain relative to the longitudinal axis of the piece Rate of growth (As an average width of the annual rings) Fissures Wanes Degree of distortion (bow spring, twist and cup) Resin and bark pockets Insect damage In an ideal work the visual grading of timber will be supplemented by machine grading of timber which does require testing equipment. Another aspect of dhajji construction is how the sapwood and heartwood are used. Sapwood which is found on the outside of trees is where the tree movement of sap and storage of sap occurs. In other words it is sugar rich and is the trees food. Because of this simple fact, sapwood is attractive to many decay organisms. On the other hand the heart wood is the older part of the tree and is known to be generally rot resistant. Typically sapwood will take days or weeks to dry after being exposed to rain, whereas heartwood may dry within an hour or two after being exposed to sun light. Many bugs and insects will bore in the sapwood and lay their eggs in this outer timber layer which is another reason why care needs to be taken when selecting timber for construction purposes. Sapwood also does not hold paint well. In fact it holds any moisture that may have entered a painted timber section through cracks and it is because of this reason that even apparently painted sections are found to be completely rotten after a few years of being exposed to the elements, typically as found in window frames. Anecdotal evidence indicates that heart wood can outlast sapwoods by 10 to 20 times. This is a sound argument to make use of Sapwood strategically, concentrating on the wood that will be most exposed to the moisture. This also emphasise the need to use mature trees in a responsible manner. Whilst the purpose of this report is not to be a report on timber grading but the importance of this craft to the construction of dhajji buildings cannot be over emphasised. Without proper selection of timber many houses will simply not last for any length of time and will require expensive rebuilding in an unreasonably short time. This will impose further pressure on already dwindling forest resources in the region and can safely be considered to be false economy. It is likely that the poor will not rebuild, they will simply live in buildings that have lost their strength and are in poor condition, therefore at high risk from future earthquakes.

Design Process


Who is involved with the design process? BuilderOwner
Roles of those involved in the design process
Expertise of those involved in the design process Generally design and construction expertise exists in the local communities to some degree. However their skill level is low and fundamental issues such as timber selection, curing, joinery are not much appreciated or understood. It could be said that the craft of the master carpenter or joiner in the sense of the master builder from a European perspective is not commonly found in the regions where dhajji buildings are still being built. Dhajji construction would benefit from a better understanding of the merits of traditional joinered connections vs. the performance of nailed connections. Unfortunately the engineering, architectural and technical community will have very limited knowledge of the construction type simply because education courses around the world do not teach traditional construction methods as a rule. Basically as a generalisation engineers/technicians do not have knowledge of this type of construction. The construction method will not feature in any conventional engineering courses which tend to focus on reinforced concrete, steel and masonry construction, even when those modern forms of construction are not afforded by local people. This is changing, and some progress has been made in mainstreaming dhajji, for engineers, sub engineers and architects since the 2005 earthquake.

Construction Process


Who typically builds this construction type? OwnerBuilder
Roles of those involved in the building process The builders usually live in the house they build. There is no concept of a builder in the general sense. House owners are involved in the construction right from the beginning until the completion and occupation of a house. This construction system is mostly an informal construction process whereby the building owner manages the project and procures the materials. The skilled craftsman (Mistri), who may be employed by the home owner for more specialist aspects of construction, plays a pivotal role in the building development process. The Mistri help the building owner in various ways such as: Architectural advice Informal quantity estimation Time estimates General procurement advice Quality control Execution of the works Informal building training to the home owners who will typically be doing significant amounts of the construction will also be provided by the Mistri. In Kashmir trades are carried out generally by distinct families. Masons, carpenters, metal workers. House owners may salvage or procure timber, but they do not carry out the main tasks of construction themselves. Even the poor consult and hire the designated mistris. House owner members may assist the mistri, but he is responsible on site. Even skilled mistris are not high in social status. In North West Frontier Province there is less social stratification and more owner building.
Expertise of those involved in building process It is basically owner built construction. Locally known labour contractor cum mason (Mistri) are invited and entrusted with the labour contract or wage contract. Construction is carried out under the advice and consultation of the Mistri. After the 2005 earthquake necessity has dictated that a large degree of people have taken on the roles of carpenter and builder to rebuild their homes. Unfortunately many of these builders will not possess a natural aptitude to the building profession and this is reflected in some of the construction practices being observed. A rush time is never good for quality control, even the good carpenters take short cuts, to maximise profit, or under pressure from house owners, costs are far higher due to timber supply, labour supply and transport costs. It should stabilise again. Also note the very lowest income households used dhajji and recycled less than optimum quality timber.
Construction process and phasing Construction material is procured by the building owner with help from the Mistri. Small tools such as saw, hammers and chisels are used for the entire construction process. The entire construction process is labour intensive and is usually carried out as per the availability of resources and funding. Plinth first, basic frame, roof, cover, then infill, it can take weeks or years. For example in some cases a temporary light mud flat roof is constructed until the owner can afford a pitched one. The design is typically worked out during the construction. There is no history of planning buildings by the preparation of construction drawings and specifications. Provisions in the design to be able to readily accept future changes and additions will rarely be considered during the initial construction process. The construction of this type of housing takes place incrementally over time. Typically, the building is originally not designed for its final constructed size. To ensure a proper foundation to a dhajji building it is important that proper foundations are built using one of the methods below: Stone masonry with regular through stones Brick masonry with proper bonding pattern Reinforced concrete strip footing with proper placement of reinforcement by ensuring proper cover is maintained to the rebar during the concreting, adequate concrete strength, placement and compaction of the concrete is required. Profile of reinforced concrete plinth to throw off water, Height of all options above are to be built above ground level by at least one foot. Commonly recent the advice given to people is that the building should be anchored to the foundation. This is sensible advice for resisting wind loads and is in line with most modern earthquake codes for buildings. However, it is not clear if creating a solid connection with the foundations is beneficial during seismic actions as long as the building has a sufficiently large and stable base to sit on (i.e. prevented from falling of a ledge or similar). It could be argued that the ability for the building to move about on its foundations is a form of natural base isolation thereby reducing the level of seismic forces that are seen by the building. To allow this to happen the timber walls would need to be robustly interconnected at their lowest level to minimise differential movement across the building. Clearly this merits detailed research. Where possible the core wood should be used for members that connect to the foundation or are exposed to the outside. Sap wood should not be used for important locations of the timber frames. The base plate is required to be sufficiently large to be able to receive all vertical posts. It is important to make the base plate from high quality timber as it is close to the ground. Interconnection of the perpendicular wall and base plates is important to ensure the building acts like a box. Doing so ensures that the walls do not just separate during an earthquake. Do not place the base plate directly on to the ground, concrete, or bricks. If placed onto concrete or bricks it is important to use a damp course layer to stop moisture travelling into the timber frame. At corners, using overlapping connections will enhance the general robustness of the frame and reduces the exposure of vulnerable end grain. The principle members of the walls consist of timber posts and ring beams at floor/roof level. Figure 6 15 to Figure 6 18 show a range of timber carpentry details that should be used to help built robust frames. The quality of these joints is dependant on the carpenter knowing when to choose a certain type of joint over another. It is believed that poorly prepared timber to timber connections will result in premature failure of the timber frames. Key to preparing these connections is having a clean and proper work area, a feature that is seldom given any consideration. Looking at Figure 6 4 to Figure 6 7 and Figure 6 10 it is clear that much work is done on the ground, a weak position from which to build. Equally important as a good work surface is the availability of good quality tools. Typically a carpenter will need a saw, hammer, chisel, set square and a drill to prepare good quality timber connections. The use of blunt tools results in poor quality finishes to any joinery making it harder for the joints to function as they might have been envisaged. The importance of building good quality connections is even obvious in that the skilled people who make these connections are called Joiners in English, a skill that society has long recognised as being important and thus given appropriate linguistic recognition. Figure 6 17 shows a series of sketches on various connections, principally how to splice timber pieces together. There is a general issue about complex joint connections as compared to simple nailed connections, or splice pieces. Joints are reductive making small pieces of timber which may break, and also making the frame potentially very stiff as compared to the ductility of nailed connections which can loosen if done the way they are here. Japanese evaluation of timber frame construction recommends it is not preferable to develop timber joints. Dhajji construction would benefit from a holistic review of suitable timber connections in seismic applications Whilst many might see installing the infill material as a step in the construction process that can be executed without too much attention to detail the authors believe that this is not the case. The following points are thought to be important to ensure the reliable behaviour of the infill frames during seismic actions: It is important that infill material is packed tightly against the main timber frame and the bracing in order to ensure that arching action can be developed in order for the infill material to be able to resist out of plane forces. Do not use round stones or wedge shaped stones as these will pop out when the infill panels are squeezed during the compression cycles of the seismic loading (See Section 6.2.3). Do not use too much mortar as it is likely to be soft and thus not provide the support to develop arching action between the infill and the timber frame and bracing. Research is required to determine optimum mud mortar thickness to be used as a function of panel size. Avoid shrinkage of mud, test in advance and add other materials or prepare better. Also leave to shrink before plastering, and plaster in a few rounds to catch all small holes to be filled. Where a dhajji building is two storeys or more it is important that the floor framing is built in such away that it has either enough room to move about without loosing bearing contact or that the connections are strong enough to resist the seismic forces at the connections. The assumption is that the joints are the weakest parts of timber frames with failures always occurring at the joints simply because it is at these locations that the gross timber sections have been cut down to enable the connections to be made in the first place (unless metal inserts have been used skilfully). Probably because of timber supply and manual work, timber posts are never more than one storey. From field surveys, all timber frame construction is platform frame type, with each floor constructed as a box and the boxes separate and stacked. Each storey has a separate base plate and wall plate, with close spaced timbers in between. The roof keeps the house dry and therefore plays an important part in ensuring that the frame is protected from moisture increasing the durability of a house. A few simple connections are shown in Figure 6 19 and Figure 6 20. As ever it is important that these connections are carried out with great care. Especially for single storey dhajji building the roof is the only thing that holds the various walls stitched together. Therefore, it is important that connections between the roof trusses and the walls are able to withstand significant levels of load reversal. Unfortunately when people construct a ceiling they dont fix it on top of the walls / posts to contribute to the diaphragm action. Instead they simply fix it in between the posts. Clearly this is an area where strategic strengthening could significantly help improve the performance of dhajji buildings. The use of pegs and proper joinery will go a long way to ensuring good the appropriate load paths are an inherent feature of the dhajji building. Strategic use of metal strapping or similar is also thought to contribute towards the strength of the connections.
Construction issues

Building Codes and Standards


Is this construction type address by codes/standards? Yes
Applicable codes or standards This construction type is addressed by the codes/standards of the country. Pakistan does not have any formal engineering codes/standard on this building type as up to the year 2009. However, the ERRA guidelines do provide basic guidance on dhajji construction (See Reference 3). We understand that there are efforts to incorporate dhajji in the code. The main problem is the lobby who do not want timber standards endorsed as they see it as timber construction promoted and deforestation. Indian standard cover this building type but with name brick nogged timber framed construction as can be found in Reference 5.
Process for building code enforcement

Building Permits and Development Control Rules


Are building permits required? No
Is this typically informal construction? Yes
Is this construction typically authorized as per development control rules? No
Additional comments on building permits and development control rules Traditionally this form of construction was not formally recognised or checked. Theoretically, all the buildings constructed in urban areas require building permits, though these are hardly exercised. In rural areas, both Pakistan and India, building permits are not thought to have been ever enforced. There are generally no standards or planning or building control systems for housing in rural areas. However, after the 2005 Pakistan earthquake, and although dhajji construction was initially restricted, its use became later acknowledged as a reasonable means by which the earthquake affected people could start rebuilding their homes. The dhajji construction method is now even recognised in the ERRA guidelines (See Reference 3). Compliance with the guidelines formed the basis by which affected people were able to claim some limited government monies to help with their reconstruction costs.

Building Maintenance and Condition


Typical problems associated with this type of construction
Who typically maintains buildings of this type? Owner(s)No one
Additional comments on maintenance and building condition Generally home owners may not be aware of maintenance issues and the degree to which maintenance is undertaken depends mainly on the practical abilities of the individual home owners and their priorities to look after the fabric of their houses. It is commonly known that poorly maintained buildings will lead to severe timber rotting which will completely undermine the buildings construction form and inherent seismic resistance. This is a major issue arising out of the inadequate plinths used for dhajji houses, along with poor grade timber and limited use of preservative. Secondly lack of protection from site moisture due to back walls being built against the ground. A number of measures are proposed to improve site drainage, timber preservation, and wall protection. This include very simple measures like making sure the roof extends outward more, use of a gutter and rainwater harvesting, constructing a veranda, apart from intrusive repairs and replacement.

Construction Economics


Unit construction cost The concept of a construction cost in the strict sense of $/m2 or similar does not mean much for this building type as this construction type is not based on cash economics. It is an informal construction where building owners collect materials over the years and many materials come from local sources. Typically large cash flow required for the construction phase is not required. Costing construction is based on square foot cost for the building or cubic foot for the timber. It is not thought that banks or other lending institutions make money available for people building in dhajji. There is no funding by banks for other construction techniques either, so marginalisation is not an issue. There is effectively no housing mortgage system. Banking is well developed, but housing finance is not. The cost of dhajji house is from $2000 upwards depending on timber availability. Skilled labour cost is currently minimum $6 per day. Both at 2009 prices. This policy of not funding people who build in dhajji further marginalises the construction form and send the somewhat signal that the building system must be inherently unsafe as otherwise funding for dhajji construction would be freely available. It needs to be stressed that western sense of banking is probably not yet widely established in the regions of India and Pakistan where these buildings are typically used anyway. The decision by ERRA to provide financial assistance equally for dhajji and for reinforced and confined masonry gave people an equal choice and helped ensure a regeneration of dhajji as it was perceived as a safe, cost effective and fast solution in the boom of reconstruction after the earthquake.
Labor requirements
Additional comments section 3

 

Socio-Economic Issues

 

 

Patterns of occupancy Each building typically has 1 housing unit(s). With the passing of time these houses can become home to a relatively large number of people from an extended family. Typically extensions are built with the growth of the family or the house is divided in two when the male offspring of the owners each inherit a part. The number of inhabitants in a building during the day or business hours is less than 5. The number of inhabitants during the evening and night is 5-10. One family is likely to have on average 7 people per family as quoted in Pakistan after the 2005 earthquake. During the day/business hours these houses will typically be home to babies, very small children, most women of the household from teenage girls upwards, sick people and grandparents. Children of school age and working men will typically be at school or work. School children will return earlier in the day than working adults. In the evenings and night time these buildings will have the largest number of inhabitants. As these buildings are mainly family homes they will likely have their highest occupancy level during school holidays, weekends and in particular during the cold and wet and dark winter months.
Number of inhabitants in a typical building of this construction type during the day <5
Number of inhabitants in a typical building of this construction type during the evening/night 5-10
Additional comments on number of inhabitants One family is likely to have on average 7 people per family as quoted in Pakistan after the 2005 earthquake.
Economic level of inhabitants Low-income class (poor)Middle-income class
Additional comments on economic level of inhabitants Most of the dhajji buildings belong to subsistence farmers and small business owners. Their economy is based on subsistence farming, labour work, or remittance (money sent back to home by family members working in other parts of the country. Construction of dhajji also depends on geography and the locally available construction materials. In some locations wealth household also build in dhajji albeit in a more elaborate manner.
Typical Source of Financing Owner financedPersonal savingsInformal network: friends or relatives
Additional comments on financing The ratio of the housing unit price to their annual income is typically not available. The typical source for financing the purchase of these buildings is owner financed through personal savings and loans from a network of friends and relatives. Often the extended family will provide assistance in the form of labour to construct such houses. Dowries may include furniture to help set up homes For example a person on a low income is earning ~3000 PKR per month. Middle income is ~30 000 PKR per month. A house will cost from 150-500,000 PKR current costs (year 2006/7 prices). A lot depends on the cost to the owner of timber, he may have his own trees, or good relations with the forestry dept. In effect these houses are built by the building owners with the help of friends and extended family. The only source of technical input will come from local craftsmen who are known as Mistris (a term used in Pakistan and India to describe a craftsman or master craftsman in Urdu/Hindi). These Mistris play a pivotal role in the overall construction process of dhajji houses. The house owner will typically collect the construction material over a number of years. Cash will be required for procurement of materials such as some wood (traditionally locally available); iron sheets, nails, metal straps etc that needs to be brought from larger towns, transportation of these items to the construction site and for the payment of the Mistris as recognised skilled craftsmen. A local set up of band sawing is usually set up at site to cut timber to size and helps the Mistri .in his work Traditionally, many of the people who built dhajji will not have had bank accounts. However, after the 8th October 2005 earthquake this was being changed as the government of Pakistan only provided financial assistance to those who achieved compliance with the reconstruction guidelines provided by ERRA and who had bank accounts for the money to be placed into. This resulted in an increased uptake of formal banking in the region. All affected households were required to and supported to open bank accounts in order to manage the direct and efficient disbursement of funds. Financial assistance was in 4 tranches, 25,000PKR initial, 75,000 mobilisation, 25,000 at plinth inspection, 50,000 at lintel inspection. Tranche 3 and 4 were contingent on compliance with ERRA standards. Currently it is not known if this will lead to banks providing financial services to anybody who wants to build in dhajji or any other type of building in the future in Pakistan. One issue with dhajji is that there are no codes in Pakistan according to which a dhajji house should be built or assessed. However, the ERRA guidance has provided basic guidance for dhajji construction as part of their compliance catalogue.
Type of Ownership Own outright
Additional comments on ownership It in not thought that mortgages or even micro loans have typically been made available to people who have built their houses in dhajji. In the North West Frontier Province the land may be owned by a landlord, the house may be owned by the landlord or by a tenant who constructs it.
Is earthquake insurance for this construction type typically available? No
What does earthquake insurance typically cover/cost The concept of a dhajji building that has been seismically strengthened does not exist to date and insurance is probably not available or sought after by building owners anyway. Therefore it is somewhat of an irrelevant issue to the current realities of people building in dhajji. The concept of formal insurance, in general, is not part of the rural culture in the area where such buildings are typically found. However, people from these parts of India and Pakistan will have the informal insurance system consisting of the extended family coping mechanisms.
Are premium discounts or higher coverages available for seismically strengthened buildings or new buildings built to incorporate seismically resistant features? No
Additional comments on premium discounts
Additional comments section 4

 

Earthquakes

 

 

Past Earthquakes in the country which affected buildings of this type


YearEarthquake Epicenter Richter Magnitude Maximum Intensity
1555Kashmir
1842Kunnar
1855Shrinigar,Kashmir
1878Abbottabad, Pakistan
1905Kangra, Himachal Pradesh
1974Pattan
1981Karakoram, Darel, Tangir, Khanbari valley
1991Uttarkashi, Uttarkashad
1999Chamoli, Uttarkhand
2005Bagh, Muzzafarabad, Poonch (Kashmir), Abbottabad, Battagram, Kohistan, Mansehra, Shangla (NWFP)
> 7.0 Mw
7.5 Mw
6.3 Mw
6.7 Mw
7.8 MwIX
6.2 Mw
6.2
6.8 MwIX
6.4 MwVIII
7.6 MwX to XII

Past Earthquakes


Damage patterns observed in past earthquakes for this construction type From the available literature it is not known to the authors on when and how dhajji construction was introduced to northern Pakistan and India. Was it a construction method developed locally, in isolation from outside influences, as a direct response to observations by the local population that well built dhajji buildings performed well in past earthquakes or was it simply a construction method that was developed due to local economic conditions where timber and other construction materials were in relative short supply? Alternatively was dhajji introduced from another region? If dhajji was a local response to a past earthquake event what event was the triggering event that led its construction form? Dhajji may have evolved from economy and in response to optimising the characteristics of stone and mud as well as timber. If one looks at Leepa Valley, the east end has 100% timber houses; the west end has 100% dhajji, within few kilometres of each other within the same community. In between there are combinations, the explanation we found is that more timber is available in the east, and less timber and better stone in the west. It also seems to depend on a number of local conditions, height of snow, quality of stone, etc... Fully timber houses are considered locally the best for earthquakes with interlocked corners. In areas of stone construction people know timber bracing makes it stronger and less liable to damage. It is an economical way to use stone also as the wall thickness is smaller, the technique allows all materials to be used sparingly and in small and random pieces.
Additional comments on earthquake damage patterns Complete destruction of any building Rotten timber frame leading to rapid collapse of the building Retaining wall failure during earthquake leads to partial or full collapse of the house. Rotting of the timber frame base leading to failure at the base of the building and then subsequent collapse. Leads to collapse of the building do to loss of strength in the timber frame House falls off the foundations leading to local damage or in the case of more severe drops complete collapse of the building. Lack of tying of the timber frame base in both principle directions allows walls to move independently leading to differential movement and thus damage. Local torsion effects are introduced and timber members and their connections perform poorly in torsion leading to failure of the building frame Separation of framing from one another. Separation of wall panels and loss of mutual support leading to out-of-plane failure of walls. Out-of-plane failure of the masonry infill. Larger panels also suffer from greater amounts of shrinkage in both the mud mortar and the timber framing which may both work to loosen the support to the bracing Out-of-plane failure of the masonry infill Failure of the roof ring beam and thus prop to the walls. This will then lead to failure of the walls. Failure of the roof ring beam and thus prop to the walls. This will then lead to failure of the walls Ring beam falls apart due to high force demand and/or inadequate connection capacity Loss of support to walls leading to wall collapse Tension failure of roof truss bottom chord splice Gabel wall infill fails out of plane.

Structural and Architectural Features for Seismic Resistance


The main reference publication used in developing the statements used in this table is FEMA 310 “Handbook for the Seismic Evaluation of Buildings-A Pre-standard”, Federal Emergency Management Agency, Washington, D.C., 1998.

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.
Structural/Architectural Feature Statement Seismic Resistance
Lateral load pathThe 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.TRUE
Building Configuration-VerticalThe building is regular with regards to the elevation. (Specify in 5.4.1)TRUE
Building Configuration-HorizontalThe building is regular with regards to the plan. (Specify in 5.4.2)TRUE
Roof ConstructionThe 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.FALSE
Floor ConstructionThe 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.FALSE
Foundation PerformanceThere is no evidence of excessive foundation movement (e.g. settlement) that would affect the integrity or performance of the structure in an earthquake. TRUE
Wall and Frame Structures-RedundancyThe number of lines of walls or frames in each principal direction is greater than or equal to 2.TRUE
Wall ProportionsHeight-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);N/A
Foundation-Wall ConnectionVertical load-bearing elements (columns, walls) are attached to the foundations; concrete columns and walls are doweled into the foundation.FALSE
Wall-Roof ConnectionsExterior walls are anchored for out-of-plane seismic effects at each diaphragm level with metal anchors or straps. TRUE
Wall OpeningsN/A
Quality of Building MaterialsQuality of building materials is considered to be adequate per the requirements of national codes and standards (an estimate). N/A
Quality of WorkmanshipQuality of workmanship (based on visual inspection of a few typical buildings) is considered to be good (per local construction standards).TRUE
MaintenanceBuildings of this type are generally well maintained and there are no visible signs of deterioration of building elements (concrete, steel, timber).TRUE

Additional comments on structural and architectural features for seismic resistance The dhajji structural system generally contains a complete load path for seismic forces in any horizontal direction that transfers inertial forces from the upper portions of the building to its foundation. These buildings are generally regular with regards plan and elevation unless it has been built on a steep slope. On sloping ground the downhill wall will typically have more openings than the uphill wall(s). The roof diaphragm is not considered to be rigid. Usually there is no in-plane bracing at the bottom chord level of the roof trusses or bracing in the vertical plane joining adjacent trusses or in the inclined plane of the roof as shown in Figure 74. The simplest roof construction method that gives stiffness in both orthogonal directions is by the adoption of a hipped roof. It is thought that improvements to the roof diaphragm could be made by the introduction of roof bracing as shown in Figure 75, Figure 77 and Figure 78. Traditionally dhajji buildings will have been clad in timber shingles which would not offer any additional in-plane roof stiffness. The use of plastic, asbestos or metal roof sheeting more recently will offer some roof stiffness depending on how frequently the sheets are connected to the roof purlins, the degree of overlap between the sheets, the gauge of the roof sheeting and probably most importantly the general level of craftsmanship. Sometimes there will be a ceiling made of various board type materials and in certain instances the ceiling will be made from timber boards which will be able to contribute towards the diaphragm capacity. The floor diaphragm(s) are generally not considered to be rigid unless the floor boards have been extensively nailed to the floor beams. As dhajji buildings have a good distribution of walls in both orthogonal directions it is not thought that the flexibility of the floor(s) or the roof will have a negative impact on the seismic performance of the building. This does assume that walls are regularly supported by orthogonal walls that are structurally interconnected. However the roof often slides off, as it is not adequately fixed to the walls if at all. A second issue is that the roof and ceiling could help retrain the walls, especially the longer walls, but may not be able to do so if it is not well connected to the walls. Generally there is no evidence of excessive foundation movement (e.g., settlement) that would affect the integrity or performance of the building in an earthquake where such buildings have been built on safe ground. dhajji buildings are relatively light and are not expected to impart significant inertial forces that would need to be resisted by the ground under the building. However a number of buildings have had their built up plinth collapse causing damage to the buildings. At least two walls or frames are available in each principal orthogonal direction of the building structure. In dhajji typically all walls have the dual function of resisting vertical and lateral loads. Traditionally it is not thought that the vertical load-bearing timber columns that make up the walls will have been anchored into the foundation. From our experience the lowest timbers have always been raised off the ground and have been built with a continuous base plate. More recently, especially after the 2005 Pakistan earthquake the use of anchor bolts has been widely promoted. A few examples of foundation connection details are shown in Figure 53, Figure 55, Figure 56, Figure 57, Figure 58, Figure 59 and Figure 78. Exterior and interior walls should be anchored into the roof and at every floor level by the way the timber frame is built. In reality the degree of connectivity is very much dependant on the ability of the carpenter to build such joints. Traditionally metal anchors or straps to help resist seismic forces will not have been provided. More recently the use of metal strapping to strengthen connections is gaining more widespread usage. Unfortunately the use of nails and metal strapping is also being used as a substitute for proper carpentry. Examples of the walls and their connectivity are shown in Figure 59, Figure 60, Figure 61, Figure 62, Figure 63, Figure 64, Figure 65 and Figure 66. Equally the reconstruction rush following the earthquake has meant that nailing is seen to be a quick form of making connections as labour costs are high and nailing is fast. The quality of modern workmanship (based on visual inspection of some typical buildings) is very variable but it can be said to be generally of poor quality. It is clear that buildings such as those shown in Figure 1, Figure 2 are the exception in that they will have been built by highly skilled craftsmen who would have ensured a good fit and detailing of the timber frame with careful placement of the masonry infill between the timbers Since the earthquake many houses have been constructed by people who were not previously carpenters which will account for some of the post disaster construction quality issues. It is hoped that when the market slows down again, real carpenters will prevail. Traditionally dhajji houses were built without codes and standards. Even today there are only a few written guidelines available for people to follow. Even with the few available guidelines most of the people who build these houses are not formally trained and many have a very limited amount of schooling making written training material of little direct value as many cant read the material that is available. However, Rules of thumb do exist and these are typically passed on in the form of oral instructions. The technical support provided through the earthquake reconstruction programme included collecting and promoting good practice and training principles as well as improving joints and workmanship. Most information materials are based on photographs and physical models and out of necessity did not rely on literacy. In addition there is an issue for the clients to also appreciate the value and importance of joints and workmanship, and be willing to pay for it. Buildings of this type are generally maintained but there are often visible signs of deterioration of the timber framing. (Figure 51, Figure 59, Figure 67, Figure 68, Figure 73, Figure 34, Figure 35, Figure 38, Figure 74, Figure 75, Figure 76, Figure 77, Figure 78. Typically the timber is not well maintained, protected or treated enough. One of the main problems is the exposure to the rear of the building. There are many examples of deterioration. People also plan for a short life span so there are often many buildings in an advanced stage of decay. This is a wasteful use of valuable natural resources. It is important to extend the lifespan of the building, by increasing the durability and thereby reducing vulnerability. It is not expected that the floors or roof will maintain their shape due to their flexible nature. However the building is thought to maintain its integrity due to the many walls that support one another. In other words the various timber walls work together to give the building a box like characteristic. However very poor people may only be able to afford one large room which lacks the supporting walls to buttress their only room making them more vulnerable. The location of opening is not thought to be too important because the basic structural system is braced walls that also brace one another. However a concentration of the openings on one side of the house, as found on houses built on sloping ground, leads to an increased torsional response. The low mass of the building and the many walls mean that the torsion force are low and well distributed throughout the building walls. Clearly a systematic approach for locating the openings will help contribute toward better seismic performance of dhajji buildings. Metal straps are not seen in old dhajji buildings. Floors and roofs have been well tied with the walls through good quality timber joinery. However the use of metal straps and in particular the use of nails is a frequent modern occurrence in building dhajji houses. It is not uncommon to use cut strips of galvanised iron for such applications. It is also noted that where the galvanised sheets have been cut the bare steel will be exposed and it is unlikely that these cut locations will be sealed with an appropriate corrosion barrier. The maintenance of a dhajji building depends on the value and importance each occupier / building owner places on the long term value of good building maintenance. Likewise it must not be forgotten that good structural and architectural detailing will ensure that the base building design is inherently of good quality making sure that water is prevented from getting to the timber as much as possible and therefore compromising the longevity of the building frame.
Vertical irregularities typically found in this construction type Torsion eccentricity
Horizontal irregularities typically found in this construction type No irregularities
Seismic deficiency in walls Wall principle posts do not align with roof trusses or second floor principal beams Walls posts are not properly connected to the timber base plate When more than 1 storey it is not clear if the columns are continuous between the floors Perpendicular walls are not properly interconnected Bracing too few resulting in large infill panels Extensive use of nailing in more recent dhajji constructions will stiffen the timber frame up considerably. it is not clear if this is a good development as a stiffer frame will attract larger seismic forces. There are very many bracing patterns there is no real engineering evidence that quantifies the performance between various wall bracing patterns adopted. The extensive cross bracing feels like a formal engineering solution but is more likely to be stiff and thus attract larger seismic forces. The random looking bracing patterns with many odd sized brace sections looks looser and may provide better energy absorption and period elongation opportunities to the building. Detailed Engineering analysis required to evaluate this scientifically. Poorly built infill large stones that have limited planes over which energy can be lost. Limited opportunity to absorb energy by yielding the mortar material Round stones used for the infill material which will pop out when squeezed. Infill made from mass concrete which will fail as a rigid body Infill poorly built with lots of gaps masonry will not be able to arch properly
Earthquake-resilient features in walls Alignment of principle structural members ensure a simple load path and direct load distribution Proper use of timber to timber connections ensures reversible load paths. Use of proper strapping keeps the wall posts connected to the same ring beam which reduces differential demands on the walls Continuity of main timber columns ensures load path continuity but having discontinuous columns may provide a form of limited seismic isolation as long as the upper columns cannot get dislodged - Engineering study required to gain a better understanding of this. Proper connection of orthogonal wall lines from the start High level of bracing ensures small masonry panels giving the masonry many lines to arch against and the bracing helps prevent crack propagation in the infill Tightly build Use of bricks or well prepared stones laid tightly to ensure good bond between each stone/brick and one another, the timber frame and the timber bracing
Seismic deficiency in frames
Earthquake-resilient features in frame
Seismic deficiency in roof and floors Roof trusses do not align with principle posts introducing significant torsion in to the roof level ring beam Ring beam too small Ring beam splices in the wrong locations and or of poor quality Roof trusses not aligned with timber posts Roof truss not braced vertically between trusses Roof truss not braced horizontally to provide good horizontal roof level diaphragm Roof truss poorly connected to roof ring beam Truss bottom chord has poor quality splice Pitched roof have stiffness and strength in one direction only Floor beams only rest on top of first floor ring beams providing limited support to the walls Loosely laid floor boards that do not help distribute loads between walls If floors are not well tied together but the timber framing has very generous overlaps then it might be possible that there is a degree of natural isolation between the floors more engineering analysis is required to gain a better understanding of this construction type
Earthquake resilient features in roof and floors Ring beam helps distribute lateral forces evenly between all the columns and walls. Ring beam provides the point at which lateral support is provided to walls preventing them from failing out-of-plane Roof trusses aligned with wall posts. Hipped roof provided rather than roof with gable end. Horizontal bracing provided to connect walls. Good quality connections (that can handle load reversals) between the roof trusses and the roof ring beam Continuous bottom chord preferably made from one member alone Hipped roofs have stiffness in both orthogonal directions Floor beams detailed with sufficient overlap and locking with main beams to be able to take reversible loads Well connected floor boards providing a strong and stiff floor diaphragm
Seismic deficiency in foundation Land on which the building is built is unsafe (see Section 9). Foundations may not have been provided (or not raised enough) placing the timber frame in direct contact with the ground. On hilly sites slopes are sometimes retained by the back wall of the house. General deficiency: drainage not provided to the foundations away from the building Built directly on to the ground leading to rapid rotting of the timber frame Timber base ring beam anchored to the foundations Traditionally anchorage will not have been provided between the timber frame and the foundation Base beam not connected perpendicular to the wall direction
Earthquake-resilient features in foundation Proper strip footing provides solid foundation for the timber framing. Build well detailed retaining wall away from the house (also ensures water seepage through the retaining wall does not entre the house directly Stone foundation extends away from the building ensuring that timber stays as dry as possible Timber base built on top of a stone base or where reinforced concrete is used for the foundations a damp proof course should be used to prevent water making the timber frame wet through capillary action in the end grain. Fixity to the foundations ensures building does not fall of its base, especially if the house has been built on a slope where the downhill side of the building is raised much more than the back of the house Lack of anchorage may have provided some form of natural base isolation to the building. This needs detailed engineering investigation. Provision of timber ties for internal cross walls help tie the walls together if done at the outset

Seismic Vulnerability Rating


For information about how seismic vulnerability ratings were selected see the Seismic Vulnerability Guidelines

High vulnerabilty Medium vulnerabilityLow vulnerability
ABCDEF
Seismic vulnerability class |- o -|

Additional comments section 5

Retrofit Information

 

 

Description of Seismic Strengthening Provisions


Structural Deficiency Seismic Strengthening
Foundations may not have been provided (or not raised enough) placing the timber frame in direct contact with the ground. General deficiency: drainage not provided to the foundations away from the building Slowly install at least a stone base under the timber frame to help spread the load a little and possibly more importantly try and keep the timber frame dry. Install stone/gravel drains away from the building thereby ensuring the timber frame stays as dry as possible.
Built directly on to the ground leading to rapid rotting of the timber frame. Or built directly on to masonry or concrete base. Slowly install at least a stone base under the timber frame to help spread the load a little and possibly more importantly try and keep the timber frame dry. Try and insert a damp proof course to prevent moisture traveling up to the timber frame. Treat timber with preservatives if possible.
Traditionally anchorage will not have been provided between the timber frame and the foundation Lack of anchorage may have provided some form of natural base isolation to the building. The common fix may be detrimental and requires engineering analysis to guide the design direction. If there is no fixing make sure the base is large enough, not too high and that it is stable
Base beam not connected perpendicular to the wall direction Retrospectively install steel ties/straps to connect perpendicular walls so that the walls become self supporting and do not pull apart.
Wall principle posts do not align with roof trusses or second floor principal beams Install posts under the roof truss locations to provide direct load path this will likely require local demolition of a dhajji wall. New post is to be connected to the ground beam and roof beam.

Additional comments on seismic strengthening provisions Strengthening of Existing Construction : Walls posts are not properly connected to the timber base plate - Insert metal straps, working in tension, if possible. Use appropriate rust protection for the metal straps. Use additional timber splices (probably nailed on) to connect disconnected members. Perpendicular walls are not properly interconnected - Use timber or metal splices to inter connect perpendicular frames. Bracing too few resulting in large infill panels - Systematically dismantle a panel and rebuild with a denser bracing pattern filled with more brick shaped stones or plain bricks laid in mortar. Round stones used for the infill material which will pop out when squeezed. - Systematically dismantle and rebuild infill wall with cut stone or bricks. Strengthening of New Construction : Land on which the building is built is unsafe. - Move to a safe site or mitigate by undertaking ground improvements (rock anchoring, cutting back slopes, building appropriate structural retaining walls) On hilly sites slopes are sometimes retained by the back wall of the house - Build well detailed retaining wall away from the house (also ensures water seepage through the retaining wall does not enter the house directly If a retaining wall is part of the house ensure the wall is adequately engineered to resist the forces from the building as well as the retained ground and that there is good external drainage to guide water away from the house. Timber base ring beam anchored to the foundations - Fixity to the foundations ensures building does not fall of its base, especially if the house has been built on a slope where the downhill side of the building is raised much more than the back of the house When more than one storey columns are rarely continuous from floor to floor. Always a platform frame and each storey is constructed as a separate box. - are rarely continuous from floor to floor. Always a platform frame and each storey is constructed as a separate box. Continuity of main timber columns ensures load path continuity but having discontinuous columns may provide a form of limited seismic isolation as long as the upper columns cannot get dislodged. Engineering study required to gain a better understanding of this. As a minimum ensure that the tendons connecting the upper post to the lower frame is long so that it is a good shear key. Where it is know that shear keys are not provided alternative ways to ensure upper columns do not dislodge and fall down need to be investigated, such as extending the size of the seat on to which disconnected timber columns may be bearing. Poorly built infill large stones that have limited planes over which energy can be lost. Limited opportunity to absorb energy by yielding the mortar material - Systematically dismantle an infill panel and rebuild with bricks or well prepared stones laid tightly to ensure good bond between each stone/brick and one another, the timber frame and the timber bracing Infill made from mass concrete which will fail as a rigid body - Rather than looking at the building as a dhajji building it might be better to reclassify the building as a reinforced concrete building and follow retrofitting guidelines for this form of construction. If not, dismantle the large mass concrete wall, install adequate levels of bracing an infill material. Limit the panel size above which to replace?. It is often more harm than good to remove infill as there is a lot of movement due to demolition. Clearly research is required. Infill poorly built with lots of gaps masonry will not be able to arch properly - Remove plaster, remove large chunks of weak mortar and rebuild locally, fill large gaps with stone or brick ensuring that the infill material can arch.
Has seismic strengthening described in the above table been performed? Because these buildings are low tech compared to modern forms of construction they are adjusted and tweaked constantly. It could be said that these buildings are constantly being modified but it is not thought that the modifications will be due to seismic considerations. In reality the buildings will be improved, expanded as needed and as resources become available to the family units.
Was the work done as a mitigation effort on an undamaged building or as a repair following earthquake damages? Much of the reconstruction in Pakistan will have been to build dhajji houses from scratch. The extent to which seismic retrofitting is being carried out to dhajji buildings is not really known. After the 2005 EQ many people strengthened their houses by diagonal bracing, particularly at corners, face nailed flat boards, After EQ 2005 the common other improvements were propping, replacing stones with concrete, Houses constructed after EQ 2005 have also been improved if constructed rapidly and substandard. After 2009 EQ people fixed wire mesh to the inside of their walls, at the top 2 ft of the walls, to protect from falling stones.
Was the construction inspected in the same manner as new construction? There is no formal construction inspection system in place. Building quality is nearly completely dependant on the individual home owner and the skills they can bring to the building construction. However after the 2005 earthquake the post earthquake reconstruction was managed with financial assistance which was linked to stage inspections. Likewise the strengthening of substandard houses.
Who performed the construction: a contractor or owner/user? Was an architect or engineer involved? The training structure included engineers, architects, sub engineers, who were responsible for maintaining consistency in the promotion of standards for dhajji, including practical training by carpenters, information and explanations The home owner will procure materials and do most of the construction with the help of the nuclear and extended family. Local master craftsmen will be employed occasionally for the more complicated parts of the building. People with formal education in construction (architects and engineers) as a rule would state that these buildings are old fashioned, dangerous and should be continued with. Such views are based on not understanding the construction method and incomplete training.
What has been the performance of retrofitted buildings of this type in subsequent earthquakes? New and old dhajji performed well in the 2009 earthquake, except where people had used sand cement plaster which fell off in complete sheets.
Additional comments section 6

 

References

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Authors




Name Title Affiliation Location Email
Kubilay Hicyilmaz Senior Engineer Dubai, Ove Arup & Partners 17th Floor Burjuman Business Tower, Trade Centre Road, Bur Dubai, Dubai PO BOX 212416, UNITED ARAB EMIRATES kubilay.hicyilmaz@arup.com
Jitendra K Bothara Senior Seismic Engineer Beca Carter Hollings & Ferner 77 Thorndon Quay, Wellington, NEW ZEALAND jitendra.bothara@gmail.com
Maggie Stephenson Technical Advisor UN - Habitat Hse 6, Street 20, F 7/2, Islamabad , PAKISTAN maggie@unhabitatpk.org

Reviewers



Name Title Affiliation Location Email
Randolph Langenbach Building Conservation Consultant Conservationtech Consulting Oakland CA 94618, USA rl@conservationtech.com
Dominik Lang Dr.-Ing. NORSAR Kjeller 2027, NORWAY dominik@norsar.no