At the top looking at the 2nd tower, as the one shakes... Silhouette through archway?
At the top looking at the 2nd tower, as the one shakes... Silhouette through archway to show shake... second tower with frame of the first tower shaking, zoom to balls hanging on tower and they shake. Another shot of the shake etc.
From bottom, as the tower is shaken, zoom to CV of hanging heavy balls as the they shake with the tower..a kite perches itself precariously..note its posture..as the tower shakes.....
Ahmedabad is the home of India's textile industry. This bustling city of over half a million people in Western India, capital of Gujerat state is also the home of Mahatma Gandhi. The skyline of Ahmedabad is dotted with textile mills chimneys. The skyline of Ahmedabad is also dotted with some exquisite minarets of historic mosques built by Gujerat's early Muslim rulers. These mosques have one thing common their superb stone carving and Hindu influence of flowers. Two of the mosques have what is claimed to be architectural winder shaking towers (minarates). Thus if Europe has its Leaning Tower of Pisa in Italy, India has its Shaking Towers in Ahmedabad. At one of the mosques, Bibiji's mosque, and Englishman is reported to have demolished half of one of teh towers to find its secret of shaking. He failed, till recently an Indian architect had tried to find an answer in a article published some time ago in India's Science Today magazine.
Jums Masjid of Ahmedabad is amongst the biggest mosques of India. Its main prayer hall in lined with hundreds of beautifully carved stone pillars. The main dome is over 150 high built of stone and mortar. The Tripolia Gate (The Triple Gateway) is really the main entrance leading to the Jama mosque. It today bustles with heavy traffic.. not the large numbers of motor scooters, and scooter rikshawa.. following the high price of petrol. Even taxis are absent from the streets. Form stop this gate the Sultane of yesteryears saw colourful processions go from the Jama Masjid to the Palace or vice versa.
Yet another colourful mosque in Ahmedabad is the Mosque of Siddi Saiyad. Built in 1572, this mosque is fine example of Indo-saracenic architecture. It contains tracery windows which have become world famous for their workmanship. The earliest mosque of Ahmedabad is the mosque of Ahmed Shah, built by the founder of teh city in 1411 A.D.
Outside the Sidi Bashir's mosque in Ahmedabad, a board proclaims that it is a challenge to modern architecture. The mosque has tow minars, and if you go up one minar and shake it, the other too shakes. "This is a mystery", reads the board, "unknown to modern architects, a problem for research."
The phenomenon, of course, is unique. And ever the years the minars have come to be known as Shaking Minars. It is difficult to see or feel the tremors unless you go up the minars. the "guides" take you up. And visitors have always been fascinated by the experience.
Why do these minars shake while others do not? There have been various theories, or rather speculations. some think the stones of the minars are elastic in nature. Others speculate that there is hinglike device below which allows them to shake. But there has been hardly any scientific investigation.
In fact, there are two pairs of shaking minars in Ahmedabad. One is at the Bibiji's mosque at Gomptipur. These are also known as Rajpur-Haripur minars. One of these is broken. A part
THE height of the minar plays a great role in creating a visual impression Balconies are provided to allow people to rest as well as for the muazzin to stand outside. The top of the minars can be reached by a spiral staircase which starts from a certain height of the wall in the minar. A stringed staircase in the wall itself provides access to the spiral staircase.
The spiral staircase is clad with a circular stone cover. The spiral steps are fixed in this cladding. The cladding its. It is made up of two layers of stone, exterior and interior, joined with lime concrete. The wall also has the facing of stone on both the sides and lime concrete inside.
To understand why the minar shakes, we must analyze its various parts. First, let us study the minar at Bibiji's mosque at Rajpur-Hirpur. the mosque has a roja and a mosque proper. the central entry to the mosque has two minars, one on each side. And of the two minars, one is broken. The other one is complete and possess exquisite carvings.
These minars can approached (Fig. 5) through a staircase with eight straight steps through the wall. This leads to the spiral staircase which has 71 steps up to the top of the minar. The base of the lower portion of the minar, up to the height of about 4.25 metres, is solid along with the wall. The spiral staircase, which makes the minar hollow, starts here.
Looked from outside, the mosque wall has height of 8.9 metres, from the base to the terrace. Above that, the minar stands free. This forms a cantilever, like a rod (the freestanding part above the wall) tied to a wooden plank (the wall). The minar has three balconies the first at the right of 4 metres from the terrace of the wall, the second 3.75 metres above the first balcony and the third one 3.7 metres further up.
The total height of the minar from the ground to the top is 22.4 metres. The height of the wall (Fig 3) is 8.9 metres and the freestanding minar is 13.5 metres. The freestanding minar, forming the cantilever from the wall, thus creates a ratio of 1 : 1-5 (8.9 metres of wall to the 13.5 metre of minar in air).
This is very important point. The cantilever is a projection from the solid base, providing a free area projected from the base, like the projections for the porticos, or the canopy. There is a partywall (joining wall), a type of construction in stone at a distance of 3 cm from the spiral connection with the wall.
The minars are hollow columns receding hardl 7.5 cm per 1.75 metres, the total taper being 0.25 metres at the height of 16.25 metres. The thickness of the wall at the base from where the spiral staircase starts is 76.5 cm and this recedes to 39 cm at the top. The diameter of the hollow section is 1.3 metres at the base and 1.16 metres at the top.
AT the top, where the steps end, there is a hollow space, high enough for a man to stand. From here one can go to the balcony. Standing outside in the balcony or inside at the corner at a fixed angle, one can push the minar using a little extra force. After a few seconds, a mild tremor starts and one can feel the minar shaking. When the pushing is stopped, the minar continues to shake with less vibration and then gradually stops shaking completely. The maximum tremor is felt at the top, at the third balcony, and it is the minimum at the base, where the spiral staircase starts.
We have noted that the maximum tremor is felt at the top, which is the free end projecting from the wall. This is because of the cantilever. The tremor then starts passing though the staircase and the stone cover round the column. Since the steps of the spiral staircase are joined to the cladding, the central part of the steps form a column. the steps act as the carriers of the force applied at the top of the minar. And so the minar shakes up to the base where the staircase starts.
The construction of the circular cladding is very useful in understanding the phenomenon of shaking. The cladding is made of a series of two stones, cut to size, and joined with lime mortar in between (Fig. 4). Moreover, where the spiral steps are joined to the cladding as shown in the figure, the steps replace the inner cladding stone. the steps are actually embedded in the cladding. Similarly, the balcony stones and the support stone of the balcony are embedded in the wall from outside. The mortar thus becomes a continuous element from the top to the bottom. When force is applied, the mortar absorbs the shock, and reduces its action, passing it to the next step. Otherwise, with the force applied, one of the outer stone pieces would have been displaced.
Now, the other free ends of the spiral steps meet at the centre, lying one above another. This forms a continuous column (Fig. 5). However, this is not a rigid column, filled with mortar. The column is a pivot, functioning as a medium passing the force coming from the top through the steps and the cladding. And since the ends are not rigidly held but just placed one above the other in a free column, the force received, though it does upset the end of the step, does not disturb or displace it. The steps carry the force, touching the cladding and through it to another step, to cladding again and to another step, making the minar continuously vibrate. As the free end of the minar is 1.5 times more than the wall, one experiences the tremor. This seems to be the adequate ratio.
The walls and the minars of the Jumma mosque were in the proportion of 1: 1.75 and they collapsed during the earthquake, because of the greater length of the free standing minar. If the free height were more than double the wall height, even a strong wind could shake the minars.
Another point to be noted is the less taper per unit height. Tapering means a decrease in the diameter of a given area. But the tapering here is not like the tapering in a chimney of a textile mill. In that case, the minar would not have shaken at all. the feasible relative height of the wall and the minar make it neither very rigid nor flexible. And when the force is applied, the effect on the steps would be simply a tremor which would pass through one another allowing it a little jerk and a negligible displacement which is not visible. this way the vibrations are passed down and they become minimum gradually with the last step remaining unaffected.
On the other hand, if the central column joining the steps had been continued as a single piece of stone, or even if it had been joined at two or three places, the shaking of the miars would have been impossible. Besides, a great effort would have been necessary in that case to shake the minar.
It is also interesting to note how the minars are joined to the wall. Hardly ??? of the portion of the total minar is joined with the wall and this penetrates into the edge of the wall. But the construction is continuous. And where the hollow portion of the minar starts, we find that only a little connection is available with the wall since the wall is pierced in the centre by steps. The wall is 1.24 metres thick. The hollow area with the steps inside the wall is 62 cm. The portion of the wall on either side of the steps is 31cm. The minar itself protrudes up to 2.45 metres from the wall, and is thus more than double in thickness than the wall (Fig. 4). As the major portion of the (1.35 metres) stands free and the wall thickness is less than half of the protrusion of the minar, naturally the wall can resist the tremors of the minar, though, being continuous with the minar, it does get a little affected.
This analysis leads us to the following important factors (i) the relation between the height of the wall and the height of the minar is 1 : 1.5; (ii) a uniform hollow minar; (iii) the mortar in between the double stone filling used in the construction of the minar result in stabilising the elastic effect; and (iv) the centre of the steps work as the column of the axis where the column is in pieces, instead of being continuous.
Due to this construction, all the parts of the high minar can be stable against graviation under normal circumstances, in wind storms, heavy rain, etc. But when a heavy and equal pressure comes from below, it may become unstable and many break.
NOW let us take the minars at the Sidi Bashir's mosque at Sarangpur. The two minars shake in such a way that when one minar is shaken, the other also shakes.
Here the total height of the minars from the ground level up to the wall of the mosque is 8 metres, while the height of the minars above it is 12 metres. Thus again the proportional relation is 1: 1.5. the minars are joined by an arch and there is no wall extending on either side. The centre of the wall is pierced by the steps and the wall ends at a distance a little bit ahead that the extreme end of the minar connecting the wall (Fig. 6).
Originally there was a continuous wall on both sides of the minars. But in the 18th century, the Marathas had blown away the wall as well as some other parts. The wall ends have been repaired, creating and artificial terrace on both the sides. This allows the movement to reach the spiral staircase through the steps in the wall.
The arch is as thick as the wall - 1.25 metres. Of this, the steps occupy 0.65 metre in the centre. Up to the top of the wall the steps approach diagonally. Unlike in the Gomtipur minars, here the steps are not up to the height of the wall. Nor does the spiral staircase start from the wall. Instead, it starts from the level of the terrace. The steps, however, are similar in construction to the Gomtipur mosque, separated from the middle and embedded in the wall and forming a column in the centre. They also have similar balconies, step information and lime-mortar filling in between the two layers f circular cladding. Thus they also become elastic and shock resisting.
But how does one minar shake when the other is shaken? The following points are relevant here: (i) the wall on both sides of the mosque is broken down and the hollow arch is the only medium connecting both minars; (ii) the thickness of the arch is 1.25 metres and a flat terrace works as a bridge between the minars from the middle; (iii) the steps in the hollow wall reaching the top of the terrace make a diagonal and fork on one side with which the minar is connected, and (iv) the minars are connected to the wall at a portion 30 cm thick with the 65 cm thick middle portion creating a hollow diagonal which makes the connection of the minars light instead of holding them firmly with the ground. The force applied to the minars from the top, therefore, does not go directly to the ground but due to the hollow porion below, which makes a fork, returns back and affects the other minar through the arch. As shown in Fig. 6, force is applied to the minars parallel to the wall from south to north or from north to south. The whole structure gets momentum and the area below is pushed towards the easterly side with a twist because of the tie. The force then passes to the opposite minar through the tie and move it to the west side.
The direction in which the force is applied is very important. If this force is not parallel to the wall of the mosque, there would be difficulty in shaking as the wall would not be helpful to the movement. As there are no restrictions on the side of the wall, and the minars being similar to those we have studied earlier, they vibrate in an elliptical way in the first minar from south to north or from north to south and this makes the other minar shake due to the twist.
The effect of the tremor cannot be noticed easily just after the force is applied. If the minar shakes slowly, the motion passes below through the diagonal, the arch and the terrace and then affects the minar slowly, so the second minar gets vibrations (Fig. 6). An experiment was done to find out the direction of shaking of both the minars. A lemon tied to a piece of thread was suspended from the inner part of the top of the wall. It was found that the minar which is shaken, moves north south or south north, while the other one which shakes due to the twist shakes east west or west east (Fig 6). This proves that the shaking of both the minars is not in the same direction.
The important point here is that even if the vibrations pass though the terrace, it does not shake. Analysis has shown that the terrace is joined to the minars as well as the arch wall from both the sides. Thus the deflection due to the force applied is negligible in the terrace. The vibrations in the second minar are comparatively less than in the first one and diminish slowly. Due to the force, the lower part buckles and affects the other end which has free minar so that it is forced to shake in the opposite direction. It is also ??? that the second minar continues to shake for some time after the first minar stops shaking. It shows that the force which shakes the second minar works independently once it is set into motion.
These minars are a precious treasure. They shown an achievement in construction though they were never designed to shake. Lime tends to become weak after about 150 years. Then it starts disintegrating which helped these minars shake. That is why the phenomenon was noted very late. The first reference to the shaking phenomenon is found in the book Mirat-i-Ahmedi written by Ali Muhammedkhan is the second half of the 18th centry. Anyway, the minars should not be allowed to be shaken much. For, there is every danger of the lime getting slowly disintegrated and developing cracks. The stone pieces may then be disturbed and displaced.
The is said that the minars of one of the important mosques at Isphahan in Iran also shake. The reasons might be similar.