Whole of the world is now considered as prone to earthquakes. Depending on the frequency and severity every location and piece of land falls into one of the 5 seismic zones. Thus all buildings that we need constructed need be resistant to quake. Tall buildings are dangerous in quakes and therefore should be avoided. Cement is one of the most serious emitter of GHG and under the present environmental conditions, its use need to be reduced drastically. This is possible since cement is preferable to lime in case of tall buildings. The construction can be greener when cement use is minimized. Construction with less cement and limited to, say, four-storey hight can rightly be called Safer and Greener construction in real sense. The Confined Masonry Construction developed by countries susceptible to earthquakes can conveniently be followed with slaked lime masonry for the purpose.
Many South American and European countries (especially those having vast experience of earthquakes) have developed some practices and regulations for construction to minimize likely damage to the structures in case of occurrence of earthquake. In India Disaster Management Cell at the Central Government level has initiated certain guidelines for the purpose. Guidelines as provided by some European and South American countries have been compiled in a small publication by National Information Center for Earthquake Engineering (NICEE) Kanpur. While actual implementation stage some modifications to these guidelines may have to be incorporated to suit local specifications as approved (if any) by local authorities.
Since India was so far considered to be (except some pockets in north-east and North-West) earthquake-free no general guidelines for construction have been drawn. Only local people (near the earthquake sites) developed their own ways to face the disasters when occurred. Generally they maintained single or double storey with light weight construction with local materials. This was found to be adequate for their purposes. After independence as the earthquakes started being experienced in other areas like Maharashtra and Uttar Pradesh the question of safer construction in earthquake-prone areas came as a National necessity.
As touted, cement is best building material and it lasts long as well (if constructed properly). That is why mainly RCC (columns and beams framed) structures are erected everywhere even as a quake-resistant structure. The cement (as against lime, its previous incarnation) is considered to be the best for multi-storied structures. Buildings of up to 100 stories tall have been constructed with cement in various places all over the world. Currently billions of tons of cement is being manufactured and used annually for construction purposes throughout the world. Rather its quantity of use is being considered as an important parameter for measuring ‘Development Index’ of Nations.
Cement appears to be a substance which is ‘unfriendly’ to Nature. Problems with use of Cement for construction are serious ones regarding environmental pollution and Green House Gas (GHG) emission. During manufacturing, GHG emission is at the rate of 11 tons of CO2 emitted per 30 tons of cement manufactured. It is a huge amount by any standard. It has been indicated by concerned laboratories that currently the atmosphere contains CO2 to the extent of 354 PPM. Cement appears to be one of the main abettor to the GHG emission which needs to be reduced to sustain safety of atmosphere to life on Earth. Therefore, use of cement in construction needs be discouraged. In addition, while using one ton of cement per month for an year, for creating or maintaining construction assets including roads, heat is generated and passed on to the
The buildings in earthquake prone areas therefore should not be very tall, rarely more than 3-4 storey high and therefore do not need lifts for vertical transportation of persons. As now entire world is earthquake prone with only variation in frequency and severity, this rule must apply all over the country. This gives another advantage that RC columns need not be very large and with110 X110 mm cross sections may prove adequate. It also becomes clear that the walls between columns can be of half-brick thickness and therefore the resulting construction will be a lightweight one. What we shall get thereby is known as ‘Confined Masonry Construction’ as developed in countries facing frequent and severe earthquake threats since in the past.
At every level, wall density must not be less than 2% for design ground acceleration 0.2g but 0.3g. The wall density is defined as the ratio of cross sectional
In any wall on ground floors the total length of openings (in that wall) must not exceed 50% of the length of that wall. This percentage will not exceed 42% in second floor while on subsequent upper floors it will not exceed 33 % of the length of the wall.
Needs of construction in Zones I and II can be considered as similar to that for Zone III. Zone I and Zone II, both have design ground acceleration below 0.2g, similar to Zone III.
Countries experienced in facing the earthquakes of high frequency as well as large intensity have created over the years certain guidelines for architects and for engineers regarding the Confined Masonry construction. They have been shown in attached appendices; Appendix – B1 and Appendix – B2.
As an effective measure against severe damage, it is suggested that the plan of a structure is more or less rectangular in shape whose length does not exceed twice the width. This will give more or less equal resistance all around to earthquakes in most situations.
Some details useful while planning the confined masonry buildings are given in Appendix – C attached. A simple plan is shown in figure-1, an elevation and a view is indicated in figure-2 whereas figure 3 depicts a sample view of a two-storey building in the appendix. Figure -1 also lets us know the way the main reinforcement bars of tie-columns are to be tied with the tie-beams. They must be taken in the beams at least for a distance of 50 times their diameter. It is suggested that the staircases should form entirely separate portion in the building for safety in case of disaster.
Details useful for construction have been provided in Appendix – D attached. Figure one indicates the extent of masonry that may be completed in a day’s work. Figure two shows the joint between the tie-columns and the confined masonry with adequate details. In figure three, foundation details of tie-columns can be seen. Figure four details the reinforcement required for the lintels on the openings that are provided in the walls,
The Architectural and Engineering Guidelines mentioned above as well as all the figures provided in Appendices C and D are copied from NICEE Pamphlet “Earthquake-resistant Confined Masonry Construction” (Dec 2007).
Reinforcement for tie-columns as suggested are for (top) two floors of the building. In case taller buildings are proposed the main steel reinforcement, may be changed to bigger size bars to strengthen the lower columns. The size of columns, however, needs no increase. With floor panels of about 25 meter sq supported by at least four tie-columns, more than 12 mm longitudinal bars may not be needed as main reinforcement. This will ensure lot of economy due to saving in cement and steel.
The foundation for walls need be taken to hard murum base in the ground since the structure is not very tall and therefore heavy. In the foundation trenches over a lean concrete layer of about 15 cms depth, the rubble walls can come up to plinth level ending in with plinth beam around the room floors. Tie-columns need be founded in the rubble masonry at the same time.
In the buildings steel as well as cement is minimum and hence its mass is restricted. The construction will be greener since cement used is very small in quantity. Lime being the primary material used for masonry purposes, use of cement mortar will be also dispensed with. Thin walls, columns and beams with not very tall construction, the structure will be (comparatively) very light and therefore in case of earthquakes, the damage is likely to be limited. Therefore the building will also be more safe. By using the guidelines offered by NICEE as well as Disaster Management Cell of the Government of India we can have all our buildings more environment-friendly and safer.
- New Building Material’ – by Prof M D Apte published in Nov ’07 issue of NBMCW
- Advertisments on National TV by Disaster Management Cell of Govt of India
- Earthquake-resistant Confined Masonry Construction- pamphlet by NICEE Kanpur