EARTHQUAKE RESISTANT BUILDING CONSTRUCTION (ERBC)

It is a session of FAQ on ERBC

Brought-out by the Shelter Promotion Center,

with the objective of promoting ERBC

• What is shear wall concept in building construction practice?
  In this concept the walls are not only designed to resist gravity / vertical loads (due to its self-weight and other living / moving loads), but they are also designed for lateral loads of earthquakes / cyclones. The walls are structurally integrated with roofs / floors (diaphragms) and other lateral walls running across at right angles, thereby giving the three dimensional stability for the building structures.

• How can it be proved that shear wall structural system of 3-dimensions can effectively withstand the earthquake forces?
• The simple example to prove it is, a railway compartment or a bus coach, which will be subjected to lot of vibrations and base excitations (like artificial earthquakes) during their service period. They are built of so-called stiffened plate system. That means, it is made of a simple steel tin plate stiffened (strengthened / reinforced) by a grid of steel structural angles or channels. Similarly, in shear wall system, it is made of concrete or masonry wall panels, which are reinforced, with a grid of steel rods. Hence, a shear wall system can effectively withstand earthquake forces.

• Are there any other criteria to prove that shear wall systems are comparatively more stable to withstand earthquakes?
• Yes, shear wall structural systems are more stable. Because, their supporting area (total cross-sectional area of all shear walls) with reference to total plan area of building, is comparatively more, unlike in the case of RCC framed structures. The best example to illustrate this stability criteria is to refer great pyramids of Egypt. Pyramids have been tallest, largest and heaviest man-made structures on the earth standing undisturbed, withstanding all types of natural hazards like cyclones and earthquakes of moderate to severe magnitudes, for more than four thousand years. Because, pyramids have got largest base. Hence, they are most stable! Thus shear wall structures are more stable when compared to slender RCC framed structures of beams and columns.

• How are the shear wall structures superior to the conventional construction practices of load bearing masonry structures and / or Reinforced Cement Concrete (RCC) framed structure(of concrete beams, columns and slabs)?
  - The load bearing masonry is very brittle material. Due to different kinds of stresses such as shear, tension, torsion, etc., caused by the earthquakes, the conventional unreinforced brick masonry collapses instantly during the unpredictable and sudden earthquakes!
  - The RCC framed structures are slender, when compared to shear wall concept of box like three-dimensional structures. Though it is possible to design the earthquake resistant RCC frame, it requires extraordinary skills at design, detailing and construction levels, which can not be anticipated in all construction projects!
  - On the other hand even moderately designed shear wall structures not only more stable, but also comparatively quite ductile. In safety terms it means that, during very severe earthquakes they will not suddenly collapse causing death of people. They give enough indicative warnings such as widening structural cracks, yielding rods, etc., offering most precious moments for people to run out off structures, before they totally collapse.

• Are the shear wall building structures time tested and with stood the earthquakes anywhere in the world?

Yes, very much! After the post-earthquake surveys for over three decades, American earthquake experts have reported that, "not a single concrete building containing shear walls has collapsed and no lives were lost in the shear wall buildings, during a dozen moderate to severe earthquakes through out the world starting with the Skopje earthquake of 1963 through the Armenian earthquake of 1988".

* How to build shear wall building structures?

Unlike RCC framed structures, which are to be built of columns, beams and slabs, the shear walls are to be ideally built of RCC walls and slabs. Though constructing RCC slabs are conventional, casting RCC walls are not! RCC walls are relatively quite costlier and it requires a special system of formwork, calling for more investment. In this context, Reinforced Hollow Concrete Block Masonry (RHCBM) construction technique is an optimal solution, both from the angles of cost effectiveness and structural safety.

* What is RHCBM technique?

RHCBM walls are constructed by reinforcing the hollow concrete block masonry, by taking advantage of hollow spaces and shapes of the hollow blocks. It requires continuous steel rods (reinforcement) both in the vertical and horizontal directions at structurally critical locations of the wall panels, packed with the fresh grout concrete in the hollow spaces of masonry blocks.

* Where is RHCBM technique used?

In many parts of USA and other seismically prone countries of the world, this construction technique is popularly being utilised.

* Is there any research work done on this technology and is it being utilised in India also?

The Structural Engineering Research Centre, Madras, (SERC) has recently completed a sponsored research project, "Development of disaster resistant building construction system with RHCBM and compared it with conventional construction systems". SERC proved that RHCBM is not only structurally efficient construction technique, but also cost effective construction system. In some of the construction projects of India, RHCBM technique is being utilised from the angle of ease of construction. But it requires good awareness to popularise that, RHCBM is an effective earthquake resistant construction system without involving additional costs and any special skills, materials, equipment, machinery, etc..

* How to design such RHCBM building structures?

The design technology is simple. It can be found from the technical literature of US and some other countries. In India SERC may provide such design training. Engineers can easily follow it and quite easily execute it on the field.

* Are there any simple guidelines for the design ?

• It is advisable to provide minimum 12mm rod in every corner of a wall panel and at every free end of the wall panel.
• At a spacing of maximum 1.2m, minimum one rod of 8mm is to be provided.
• Similarly reinforcement is to be provided all around any openings such as windows and doors.
• Horizontal reinforcement is to be provided at floor level, sill (window bottom) level, lintel (window top) level, and roof levels in each storey.
• In moderate earthquake zones it may be sufficient to grout only the hollow spaces where reinforcement is being provided.
• However in severe earthquake zones it is advisable to grout all the hollow spaces in the entire wall panels and increase the quantity of reinforcement provision.

* Where can we get the design advice / guidance?

• We at the Shelter Promotion Center (SPC), a non-profit / service oriented organisation, brought out this useful semi-technical information, to promote the disaster resistant construction in all developing countries. We would like to dedicate this web site for the victims of Gujrath earthquake(2001).
• All the above information is compiled from the two decades of engineering experience / knowledge / technical wisdom of Mr. N.G.BHAGAVAN, Scientist, Structural Engineering Research Centre, Madras, India.
• Mr. BHAGAVAN is a highly qualified engineer with M.Tech. (high distinction) of Indian Institute of Technology, Madras (I.I.T.-M.). He published more than twenty technical papers in various international / national seminars and technical journals, on important aspects of civil engineering.
• As he got moved by the devastating destruction during the Latur / Killari earthquake (1993), he took the initiative to successfully get a sponsored project on "Development of disaster resistant building construction system", from the Ministry of Urban Development, Govt. of India and successfully completed the same by 1999. He gave lectures about this construction system at the international and national seminars, training programmes of HUDCO, Tamilnadu PWD, TWAD board, and other organisations. About ten technical papers are published on this subject.
• All the above information is compiled from his lectures and papers.
• If you may like to contact Mr. Bhagavan for any technical / engineering guidance, he is magnanimous to respond to you at:

Address:

Mr. N.G.BHAGAVAN, Sr. Scientist / Asst. Director

Structural Engineering Research Centre

C.S.I.R. Campus, Taramani

C H E N N A I - 600113, India

E-mail: guru.bhagavan@rediffmail.com

Phone: 044-4851683

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