Archives for March 2012

Report #154: Assam-type House

by  Hemant B. Kaushik, K. S. Ravindra Babu    

Assam-type houses are commonly found in the northeastern states of India. Generally, it is a single storey house; however, two-storey houses are also found at some places. The main function or use of this construction type is multi-family housing. These are generally single dwelling units and do not have common walls with adjacent buildings. The house is made largely using wood-based materials. Performance of Assam-type houses has been extremely good in several past earthquakes in the region. Structural strengths that influence earthquake safety of the house include good configuration, light-weight materials used for walls and roofs, flexible connections between various wooden elements at different levels, etc. However, the houses are vulnerable to fire because of use of untreated wood-based materials. When built on hill slopes,unequal length of the vertical posts leads to unsymmetrical shaking that may damage the house.


Report # 146: Dhajji Dewari

by  Kubilây Hiçyılmaz, Jitendra Bothara, Maggie Stephenson    

Dhajji dewari (Persian for “patch quilt wall”) is a traditional building type found in the western Himalayas. Such houses are found in both the Pakistan and Indian Administered Kashmir. This form of construction is also referred to in the Indian Standard Codes as brick nogged timber frame construction. Dhajji most commonly (but not exclusively) consists of a braced timber frame. The spaces left between the bracing and/or frames is filled with a thin wall (single wythe) of stone or brick masonry traditionally laid into mud mortar. Completed walls are plastered in mud mortar. They are typically founded on shallow foundations made from stone masonry.

Dhajji buildings are typically 1-4 storeys tall and the roof may be a flat timber and mud roof, or a pitched roof with timber/metal sheeting. This building system is often used side-by-side or above timber laced masonry bearing-wall construction known as taq, bhater, unreinforced masonry and is also used extensively in combination with timber frame and board/plank construction or load bearing timber board construction.

The floors of these houses are made with timber beams that span between walls. Timber floor boards, which span over the floor beams, would traditionally be overlain by a layer of clay (or mud).
Dhajji buildings are typically used for housing, often of large extended families. In rural areas the lowest level may be used to shelter livestock. In urban areas they are more equivalent to town houses. With time these buildings are usually extended. This construction type was and is used extensively for commercial buildings, shops, workshops, bazaars.

Because the timber framing and/or bracing is first erected the masonry does not directly carry vertical loads. Although this construction type is not formally “engineered” and is a relatively basic construction system, well maintained ones performed reasonably well during the 8th October 2005 earthquake in both Pakistan and India.

The earthquake resistance of a dhajji building is developed in the following ways. Because of the weak mortar, the masonry infill panels quickly crack in-plane thereby absorbing energy through friction against the timber framing, and between the cracks in the fill material and the infill material and the hysteretic behaviour of the many mud layers. The timber frame and closely spaced bracing, which essentially remains elastic, prevents large cracks from propagating through the infill walls and provide robust boundary conditions for the infill material to arch against and thus resist out of plane inertial loads. Because the framing and/or bracing is often extensive and close together, particularly when rubble stone is used as the infill, it is possible for keep the masonry walls relatively thin. This helps to reduce the mass of the building and therefore the inertial forces that must be resisted during an earthquake. The “soft” behaviour of the system has the additional benefit of de-tuning the building from the energy rich content of earthquake excitation.

Good quality timber and experienced craftsmen are the vital components to ensure the proper detailing of the buildings timber components during construction, as well as resistance against premature decay. The technology to build such a house is simple. Builders have a large degree of control over the quality of the building materials they use because the materials are sourced locally from the natural environment and are not dependant on manufacturing processes. It is often the owner who is responsible for the selection and purchase of materials and therefore often he who decides on the timber quality to be used on a project. It is rare that the “Mistris” (term used in Kashmir to describe craftsmen such as carpenters and masons) have any significant say in the quality of the purchased materials.

These structures are environmental friendly and traditionally would not have incorporated any toxic products in their construction, apart from the natural fungal and insect resistant chemicals in the timber itself.


Report #161: Confined and Internally Reinforced Concrete Block Masonry Building

by Diego Velasquez Jofre, Lars Abrahamczyk, Jochen Schwarz

The February 1976 earthquake caused severe damage to housing and buildings in Guatemala. Because many adobe houses were destroyed during the earthquake, there was greater interest in building with reinforced concrete block masonry structures after the event. This building type can now be found throughout Guatemala. Reinforced concrete block masonry structures are primarily used for family housing, both in cities and in rural Guatemala. The main load-bearing elements are masonry walls with concrete block walls reinforced with vertical and horizontal reinforced concrete elements in addition to internal steel reinforcement bars placed in the hollow cores of the concrete blocks. After the 1976 earthquake several guidelines were published on the construction of masonry block buildings, but the first formal standard/code was established in 2000, the Recommended Structural Standards of Design for the Republic of Guatemala -AGIES. The main parameters for structural design are incorporated in chapter No. 9  Mamposteria Reforzada. Nowadays reinforced concrete block masonry houses are constructed all over the country by governmental institutions for low-income classes. Currently this type of structure is the most widely built in Guatemala.