Thursday, 9 December, 2021

Building Quake-Resistant Structures


Dinesh Choudhary

On Saturday, 25 April 2015 at 11.56 a.m., a 7.8 magnitude earthquake devastated human lives and structures in many parts of the country. It not only flattened several houses near its epicentre but also destroyed many earthquake-resistant reinforced cement concrete (RCC) structures in the Kathmandu Valley, which were far from the epicentre. Why were the earthquake-resistant RCC structure destroyed? Why are many of them still being damaged?
Let us scrutinise some facts about our earthquake-resistance building construction and the cost spent on these structures in our country, especially in the Kathmandu Valley.

The reinforced cement concrete (RCC) buildings are one of the best earthquake-resistant structures in which we use cement, concrete and rebar (steel reinforcement). The bond between the rebar as tension force observing and resisting element and concrete as compression force observing and resisting elements should have of high quality. For that, the engineering codes and science only permit clean rustle rebar having good qualities of internal materials and material used for concrete mortars made of cement, sand, coarse aggregate and water should have of standard quality.

Our construction methods compel us to purchase and use rusted rebar on which we directly pour low-quality concrete mortar without cleaning the rusted surface of rebar. A three-storey, 1000 sqft RCC building costs nearly Rs 10 million. If it collapses due to earthquakes or other disasters, it may kill people living in it and surviving families and others may be forced to take shelters at other places.

After observing various earthquakes in Turkey, Japan, India, and other countries, researcher H.S.Gadiyar had declared: the earthquake in Turkey saw thousands of multi-storey buildings collapsing like a pack of cards, while very old structures like mosques suffered a little damage. Although much more severe and regular earthquakes are witnessed in Japan, building collapses are rather rare there. In places where buildings collapsed, corrosion is a major factor.

Any lack of bonding in the RCC structures means failure of structures, which may collapse in different modes. With rusted rebar accelerating the corrosion mechanism, it expands the volume of rust day-by-day by getting moist air or water through remaining or cracked passages in the concrete. After some time, an increase of rust volume in the rebar cracks the concrete layers and loosens the bond between rebar and concrete. The earthquake of 2015 had already shown us how the RCC structures failed. Many structures that were rattled by the tremor are currently in a loose bond while the bond of many RCC structures after the earthquake are getting loose.

To protect the RCC from the bonding problem, I had filed a petition on the issue at the Supreme Court. Responding to my petition, the Supreme Court ordered on April 2, 2018, eight government bodies including the Prime Minister's Office to maintain international law and standards in the engineering of construction technology as our present quality and rules of engineering do not meet international standards.
Earlier, responding to my application, the CIAA (Commission for Investigation of Abuse of Authority) has directed the Prime Minister's office to control the use of rusted rebar in construction as it decreases the strength of the structures.

After observing sluggish progress on the Apex Court's verdict, I submitted a proposal to change the existing housing code to the Development and Technology Committee of the House of Representatives on August 10,2020 AD.
Another glaring question regarding house construction is - why should a common citizen of Nepal spend Rs. 10 million to construct a non-earthquake-resistant? Why was the Apex Court order not implemented? Why was the instruction issued by the powerful CIAA ignored? Why is the House Committee passive on the issue?

Our historical Bhimsen Dharhara, Kathmandu has also been constructed using some rusted rebar. The authority has not yet managed to keep the rebar in clean storehouses. The clean rebar is stored in open spaces under the open sky where all harmful atmospheric agencies like water, moist air, dust etc come in contact with the surface of the clean rebar which transforms them into rusted rebar. We, consumers, do not know the simple science of rust and thus have to pay prices for our ignorance.

When rebar touches water and air combination agencies like those that moist air, rust is formed. So keeping rebar at storehouses minimises the risk of rusting and if some rust appears at the site, one should clean all rusted rebar with a proper tool like sandblasting, wire brush etc. After cleaning, you should pour the qualitative concrete on a clean surface of the rebar.
One must look at and learn from Dharhara. There is no programme, which may help transfer simple skills from intellectuals to consumers in a scientific way. One can put all consumer-level training on behalf of open intellectual persons. It would be advisable that the concerned authority should install an attention board covering all valuable information regarding construction materials and their usage at construction sites.

Whenever a Technology Transfer Training programme aimed at boosting the knowledge and skills of experts to consumers is held scientifically, consumers are bound to ask some questions: what is the role played by rebar, cement and sand, coarse aggregate, water in making a structure strong enough to survive big quakes? How can they be used appropriately?

Such a training is required as it ensures a perfect bond between consumers and building experts. If such information is passed from the learned people to the simple citizen and the concerned agencies, all confusion and conflicts will vanish and a good qualitative bond among them will develop. Then we start observing the primary behaviour of rebar, cement, sand, aggregate etc. and government agencies will be bound to arrange proper storehouses for clean rebar. Consumers will also start caring about clean rebar.

If some rust appears on the surface of the rebar, one must ask a technician of higher grades like engineers to clean the rust from the rebar. The masons must clean the rusted surface before pouring concrete mortar on them.
Because of the requirement, the engineers will cast a qualitative concrete to cover the surfaces of fresh and clean rebar so that rebar will not develop rust on them.

The owner of the house must observe construction materials to ensure that they are of good qualities like fresh-clean rebar and qualitative concrete and good management of casting, directions, and another engineering process. When a house owner feels that the structures of houses are earthquake resistant he/she should not worry much about running out of the house when an earthquake strikes.

(The author is an engineer and advocate)