How buildings twist during earthquakes
C.V.R. Murty
IN  your childhood, you must have sat on a rope swing — a wooden cradle tied with coir ropes to the sturdy branch of an old tree. The more modern versions of these swings can be seen today in the children’s parks in urban areas; they have a plastic cradle tied with steel chains to a steel framework.

UNDERSTANDING THE UNIVERSE 
WITH PROF YASH PAL
What is the reason for magnetic energy and gravitational force?

NEW PRODUCTS & DISCOVERIES
Building a better shuttle
BY now, the space shuttles can be considered the dinosaurs of the space age, as obsolete as a 386 computer. But they’re still flying, and when and if NASA lifts the moratorium it imposed after the shuttle Columbia broke apart on Feb. 1, the shuttles may fly for the rest of the decade.

How buildings twist during earthquakes
C.V.R. Murty

IN  your childhood, you must have sat on a rope swing — a wooden cradle tied with coir ropes to the sturdy branch of an old tree. The more modern versions of these swings can be seen today in the children’s parks in urban areas; they have a plastic cradle tied with steel chains to a steel framework. Consider a rope swing that is tied identically with two equal ropes. It swings equally, when you sit in the middle of the cradle. Buildings too are like these rope swings; just that they are inverted swings (Figure 1). The vertical walls and columns are like the ropes, and the floor is like the cradle. Buildings vibrate back and forth during earthquakes. Buildings with more than one storey are like rope swings with more than one cradle.

Thus, if you see from the sky, a building with identical vertical members and that too uniformly placed in the two horizontal directions, when shaken at its base in a certain direction, swings back and forth such that all points on the floor move horizontally by the same amount in the direction in which it is shaken (Figure 2).

Again, let us go back to the rope swings on the tree: if you sit at one end of the cradle, it twists (i.e., moves more on the side you are sitting). This also happens sometimes when more of your friends bunch together and sit on one side of the swing. Likewise, if the mass on the floor of a building is more on one side (for instance, one side of a building may have a storage or a library), then that side of the building moves more under ground movement (Figure 3). This building moves such that its floors displace horizontally as well as rotate about a vertical axis.

Once more, let us consider the rope swing on the tree. This time let the two ropes with which the cradle is tied to the branch of the tree be different in length. Such a swing also twists even if you sit in the middle (Figure 4a). Similarly, in buildings with unequal vertical members (i.e., columns and/or walls) also the floors twist about a vertical axis (Figure 4b) and displace horizontally. Likewise, buildings, which have walls only on two sides (or one side) and thin columns along the other, twist when shaken at the ground level (Figure 4c).

Buildings that are irregular shapes in plan tend to twist under earthquake shaking about a vertical axis. For example, in a propped overhanging building (Figure 5), the overhanging portion swings on the relatively slender columns under it. The floors twist about a vertical axis and also displace horizontally.

Twist in buildings, called torsion by engineers, makes different portions at the same floor level to move horizontally by different amounts. This induces more damage in the columns and walls on the side that moves more (Figure 6). Many buildings have been severely affected by this excessive torsional behaviour during past earthquakes. It is best to minimise (if not completely avoid) this twist by ensuring that buildings have symmetry in plan (i.e., uniformly distributed mass and uniformly placed vertical members). If this twist cannot be avoided, special calculations need to be done to account for additional shear forces in the design of buildings; the Indian seismic code (IS 1893, 2002) has provisions for such calculations. But, for sure, buildings with twist will perform poorly during strong earthquake shaking.

Authored by CVRMurty of the Indian Institute of Technology, Kanpur, for the Building Materials and Technology Promotion Council, New Delhi

This question cannot be answered simply or easily. It needs a fair amount of elaboration. Firstly let me clarify that magnetism and gravity belong to different classes of forces. I say this in spite of the fact that ultimately one might find a way of describing all forces through a single unified theory — we are not there yet.

The four classes of forces that seem to describe and govern most of the universe and its phenomena are 1) Gravitation, 2) Electro-magnetism, 3)the Weak force and 4) the Strong force.

Gravitation is the most familiar because things fall down when released from a height. This is also the force between any two masses merely because they have mass.

It is found that gravitation also affects light or radiation. Gravity describes the planetary motions and dominates when large masses are involved.

Theory of gravitation associated with the name of Newton has been modified and refined by the General Theory of Relativity, though in the ordinary world the Newtonian gravitation is a fairly good approximation and suffices.

You have asked for the reason for the gravitational force. It is possible that the existence of mass might be fundamentally connected with this. In the study of astronomy and cosmology there are hints that some more fundamental particles might account for gravitation being what it is. So the simple answer to your question is that I do not quite know.

You must, of course, realise that it is like asking why should there be a universe like ours — why the sun and the earth, the stars and galaxies, why life and people? These are hard questions to answer, you would agree. You could almost say that one of the possible universes was the one we have, but there might be others with which we have no connection and where we would certainly be non-existent.

Coming now to what you call magnetic energy. Incidentally where there is force, energy is also implied because when force acts energy is changed. This comes from the very definition of these two terms. Magnetism and electricity were unified some time ago. There are very elegantly described by a single theory. Wherever there are electric currents they also have magnetic fields. Movement of a conductor through a magnetic field produces electric current. All this is fairly well understood and extensively utilised in our homes and industry in general. In this case also one might state that the why of electromagnetism is understood from basic principles and symmetries.

The universe seems to have a character in which, according to the current understanding, electromagnetism, the weak force responsible for phenomena like radioactivity and the strong force that is responsible for structure and phenomena at the nuclear level have to be what they are, more or less. We still have some ways to travel to include gravitation in the world of this interdependence and inevitability.

I am somewhat apologetic about giving the kind of answer I have given, but the fault lies with your irrepressible idle curiosity! I would suggest that we should try to confine our questions to things that we have ourselves discovered through our own observation and experimentation.

BY now, the space shuttles can be considered the dinosaurs of the space age, as obsolete as a 386 computer. But they’re still flying, and when and if NASA lifts the moratorium it imposed after the shuttle Columbia broke apart on Feb. 1, the shuttles may fly for the rest of the decade. When the space agency originally built a fleet of four shuttles, no one expected that the very same vehicles would still be on the launch pad more than 20 years later. Had NASA adhered to the once-a-month launch schedule that it once envisioned, the 100-flight proposed lifetime of each vehicle would have expired years ago.

But the $3 billion annual cost of the shuttle programme and the labour-intensive efforts required to maintain the vehicles after each bruising space flight has led to a much slower schedule. On average, there are only five shuttle flights per year. Even Discovery, the most flown shuttle, has taken only 30 trips.

In one respect, that’s fortunate because NASA has yet to choose a successor to the space shuttle. In the 1990s, the agency failed in two costly attempts to design and begin building next-generation, reusable spacecraft. On the other hand, the continued use of the shuttles is only a stopgap on the way toward truly 21st-century space vehicles.

Although the Columbia tragedy may force NASA to speed up development of the next-generation spacecraft, the agency is currently addressing the future of space flight with a conservative, two-pronged approach—one evolutionary and one more revolutionary.

The evolutionary approach, announced last November, calls for the construction of a spacecraft that would serve initially as an emergency escape vehicle for the crew of the International Space Station. NASA hopes that the first of these rescue vehicles, dubbed the Orbital Space Plane, will attach to the space station by 2010. But if the craft proves durable, a modified version would begin ferrying space-station crew to and from Earth by 2012. Science News

Scientists may have peeled away another layer of mystery about materials floating in deep space. Tiny multilayered balls called "carbon onions," produced in laboratory studies, appear to have the same light-absorption characteristics as dust particles in the regions between the stars.

"It’s the strongest evidence yet that cosmic dust has a multilayered onionlike carbon structure," said Manish Chhowalla, assistant professor of ceramic and materials engineering at Rutgers, The State University of New Jersey. Chhowalla used transmission electron microscopes to study radiation absorption of the laboratory-produced onions and found characteristics virtually identical to those reported by astrophysicists studying dust in deep space.

A carbon onion is a miniscule but intricate component of nanotechnology – the study of structures and devices on a scale that can approach one-millionth the width of a human hair. Discovered in 1992, carbon onions were considered difficult to produce in the laboratory until 2001 when Chhowalla, then at Cambridge University in the UK, was part of a group that discovered a way to synthesise sizable quantities of the nanoparticles in water.