Question: What is the angle of the Leaning Tower of Pisa?

Leaning Tower of Pisa




The Leaning Tower of Pisa (Italian: Torre pendente di Pisa) or simply the Tower of Pisa (Torre di Pisa [ˈtorre di ˈpiːsa; ˈpiːza]) is the campanile, or freestanding bell tower, of the cathedral of the Italian city of Pisa, known worldwide for its unintended tilt. The tower is situated behind the Pisa Cathedral and is the third oldest structure in the city's Cathedral Square (Piazza del Duomo), after the cathedral and the Pisa Baptistry.
The tower's tilt began during construction in the 12th century, caused by an inadequate foundation on ground too soft on one side to properly support the structure's weight. The tilt increased in the decades before the structure was completed in the 14th century. It gradually increased until the structure was stabilized (and the tilt partially corrected) by efforts in the late 20th and early 21st centuries.
The height of the tower is 55.86 metres (183.27 feet) from the ground on the low side and 56.67 metres (185.93 feet) on the high side. The width of the walls at the base is 2.44m (8ft 0.06in). Its weight is estimated at 14,500 metric tons (16,000 short tons).[1] The tower has 296 or 294 steps; the seventh floor has two fewer steps on the north-facing staircase. In 1990 the tower leaned at an angle of 5.5 degrees,[2][3][4] but following remedial work between 1993 and 2001 this was reduced to 3.97 degrees,[5] reducing the overhang by 45cm at a cost of £200m.[6] It lost a further 4cm of tilt in the two decades to 2018.
Architect
There has been controversy about the real identity of the architect of the Leaning Tower of Pisa. For many years, the design was attributed to Guglielmo and Bonanno Pisano,[7] a well-known 12th-century resident artist of Pisa, known for his bronze casting, particularly in the Pisa Duomo. Pisano left Pisa in 1185 for Monreale, Sicily, only to come back and die in his home town. A piece of cast bearing his name was discovered at the foot of the tower in 1820, but this may be related to the bronze door in the façade of the cathedral that was destroyed in 1595. A 2001 study[8] seems to indicate Diotisalvi was the original architect, due to the time of construction and affinity with other Diotisalvi works, notably the bell tower of San Nicola and the Baptistery, both in Pisa.
Construction



Construction of the tower occurred in three stages over 199 years. Work on the ground floor of the white marble campanile began on August 14, 1173 during a period of military success and prosperity. This ground floor is a blind arcade articulated by engaged columns with classical Corinthian capitals.
The tower began to sink after construction had progressed to the second floor in 1178. This was due to a mere three-metre foundation, set in weak, unstable subsoil, a design that was flawed from the beginning. Construction was subsequently halted for almost a century, because the Republic of Pisa was almost continually engaged in battles with Genoa, Lucca, and Florence. This allowed time for the underlying soil to settle. Otherwise, the tower would almost certainly have toppled.
In 1272, construction resumed under Giovanni di Simone, architect of the Camposanto. In an effort to compensate for the tilt, the engineers built upper floors with one side taller than the other. Because of this, the tower is curved.[9] Construction was halted again in 1284 when the Pisans were defeated by the Genoans in the Battle of Meloria.
The seventh floor was completed in 1319. The bell-chamber was finally added in 1372. It was built by Tommaso di Andrea Pisano, who succeeded in harmonizing the Gothic elements of the bell-chamber with the Romanesque style of the tower.[10] There are seven bells, one for each note of the musical major scale. The largest one was installed in 1655.
After a phase (1990–2001) of structural strengthening,[11] the tower is currently undergoing gradual surface restoration, in order to repair visible damage, mostly corrosion and blackening. These are particularly pronounced due to the tower's age and its exposure to wind and rain.[12]
Timeline
On January 5, 1172, Donna Berta di Bernardo, a widow and resident of the house of dell'Opera di Santa Maria, bequeathed sixty soldi to the Opera Campanilis petrarum Sancte Marie. The sum was then used toward the purchase of a few stones which still form the base of the bell tower.[13]
On August 9, 1173, the foundations of the tower were laid.
Nearly four centuries later Giorgio Vasari wrote: "Guglielmo, according to what is being said, in [this] year 1174 with Bonanno as sculptor, laid the foundations of the bell tower of the cathedral in Pisa."
On December 27, 1233, the worker Benenato, son of Gerardo Bottici, oversaw the continuation of the construction of the bell tower.[14]
On February 23, 1260, Guido Speziale, son of Giovanni, a worker on the cathedral Santa Maria Maggiore, was elected to oversee the building of the tower.[15]
On April 12, 1264, the master builder Giovanni di Simone and 23 workers went to the mountains close to Pisa to cut marble. The cut stones were given to Rainaldo Speziale, worker of St. Francesco.[16]
Giorgio Vasari indicated that Tommaso di Andrea Pisano was the designer of the belfry[17] between 1360 and 1370.
Builders
One possible known builder of Pisa Tower was Gerardo di Gerardo. His name appears as a witness to the above legacy of Berta di Bernardo as "Master Gerardo", and as a worker whose name was Gerardo. 
A more probable builder was Diotisalvi, because of the construction period and the structure's affinities with other buildings in Pisa, but he usually signed his works, and there is no signature by him in the bell tower. 
Giovanni di Simone was known to be heavily involved in the completion of the tower, under the direction of Giovanni Pisano, who at the time was master builder of the Opera di Santa Maria Maggiore. Di Simone could be the same Giovanni Pisano who completed the belfry tower. 
History following construction
Galileo Galilei is said to have dropped two cannonballs of different masses from the tower to demonstrate that their speed of descent was independent of their mass. However, the only primary source for this is the biography Racconto istorico della vita di Galileo Galilei (Historical Account of the Life of Galileo Galilei), written by Galileo's secretary Vincenzo Viviani and published in 1717, long after Viviani's death.[18][19]
During World War II, the Allies suspected that the Germans were using the tower as an observation post. A U.S. Army sergeant sent to confirm the presence of German troops in the tower was impressed by the beauty of the cathedral and its campanile, and thus refrained from ordering an artillery strike, sparing it from destruction.[20][21]
Numerous efforts have been made to restore the tower to a vertical orientation or at least keep it from falling over.  Most of these efforts failed; some worsened the tilt.  On February 27, 1964, the government of Italy requested aid in preventing the tower from toppling. It was, however, considered important to retain the current tilt, due to the role that this element played in promoting the tourism industry of Pisa.[22]
A multinational task force of engineers, mathematicians, and historians gathered on the Azores islands to discuss stabilisation methods. It was found that the tilt was increasing in combination with the softer foundations on the lower side. Many methods were proposed to stabilise the tower, including the addition of 800 tonnes of lead counterweights to the raised end of the base.[23]
The tower and the neighbouring cathedral, baptistery, and cemetery are included in the Piazza del Duomo UNESCO World Heritage Site, which was declared in 1987.[24]
The tower was closed to the public on January 7, 1990, after more than two decades of stabilisation studies and spurred by the abrupt collapse of the Civic Tower of Pavia in 1989. The bells were removed to relieve some weight, and cables were cinched around the third level and anchored several hundred meters away. Apartments and houses in the path of the tower were vacated for safety. The solution chosen to prevent the collapse of the tower was to slightly straighten it to a safer angle by removing 38 cubic metres (1,342 cubic feet) of soil from underneath the raised end. The tower was straightened by 45 centimetres (17.7 inches), returning to its 1838 position. After a decade of corrective reconstruction and stabilization efforts, the tower was reopened to the public on December 15, 2001 and was declared stable for at least another 300 years.[23] In total, 70 metric tons (77 short tons) of earth were removed.[25]
In May 2008, engineers announced that the tower had been stabilized such that it had stopped moving for the first time in its history. They stated that it would be stable for at least 200 years.[25]

Plaque in memory of Galileo Galilei's experiments
Lead counterweights, 1998

Surviving earthquakes
At least four strong earthquakes hit the region since 1280, but the apparently vulnerable Tower survived. The reason was not understood until a research group of 16 engineers investigated. The researchers concluded that the Tower was able to withstand the tremors because of dynamic soil-structure interaction (DSSI): the height and stiffness of the Tower together with the softness of the foundation soil influences the vibrational characteristics of the structure in such a way that the Tower does not resonate with earthquake ground motion. The same soft soil that caused the leaning, and brought the Tower to the verge of collapse helped it survive.[26]
Guinness World Records
Two German churches have challenged the tower's status as the world's most lop-sided building: the 15th-century square Leaning Tower of Suurhusen and the 14th-century bell tower in the town of Bad Frankenhausen.[27] Guinness World Records measured the Pisa and Suurhusen towers, finding the former's tilt to be 3.97 degrees.[5] In June 2010, Guinness World Records certified the Capital Gate building in Abu Dhabi, UAE as the "World's Furthest Leaning Man-made Tower";[28] it has an 18-degree slope, almost five times more than the Pisa Tower, but was deliberately engineered to slant. The Leaning Tower of Wanaka in New Zealand, also deliberately built, leans at 53 degrees to the ground.[29]
Technical information

Elevation of Piazza del Duomo: about 2 metres (6 feet, DMS)
Height from the ground floor: 55.863 metres (183ft 3 in), 8 stories
Height from the foundation floor: 58.36m (191ft 5.64in)
Outer diameter of base: 15.484 metres (50ft 9.6in)
Inner diameter of base: 7.368 metres (24ft 2.1in)
Angle of slant: 3.97 degrees[5] or 3.9 metres (12ft 10in) from the vertical[30]
Weight: 14,700 metric tons (16,200 short tons)
Thickness of walls at the base: 2.44 metres (8ft 0in)
Total number of bells: 7, tuned to musical scale, clockwise
1st bell: L'Assunta, cast in 1654 by Giovanni Pietro Orlandi, weight 3,620kg (7,981lb)
2nd bell: Il Crocifisso, cast in 1572 by Vincenzo Possenti, weight 2,462kg (5,428lb)
3rd bell: San Ranieri, cast in 1719–1721 by Giovanni Andrea Moreni, weight 1,448kg (3,192lb)
4th bell: La Terza (1st small one), cast in 1473, weight 300kg (661lb)
5th bell: La Pasquereccia or La Giustizia, cast in 1262 by Lotteringo, weight 1,014kg (2,235lb)
6th bell: Il Vespruccio (2nd small one), cast in the 14th century and again in 1501 by Nicola di Jacopo, weight 1,000kg (2,205lb)
7th bell: Dal Pozzo, cast in 1606 and again in 2004, weight 652kg (1,437lb)[31]
Number of steps to the top: 296[32]
About the 5th bell: The name Pasquareccia comes from Easter, because it used to ring on Easter day. However, this bell is older than the bell-chamber itself, and comes from the tower Vergata in Palazzo Pretorio in Pisa, where it was called La Giustizia (The Justice). The bell was tolled to announce executions of criminals and traitors, including Count Ugolino in 1289.[33]
A new bell was installed in the bell tower at the end of the 18th century to replace the broken Pasquareccia.

The circular shape and great height (currently 55.86m (183ft 3.21in) on the lowest side and 56.67m (185ft 11.10in) m on the highest) of the campanile were unusual for their time, and the crowning belfry is stylistically distinct from the rest of the construction. This belfry incorporates a 14cm (5.5in) correction for the inclined axis below. The siting of the campanile within the Piazza del Duomo diverges from the axial alignment of the cathedral and baptistery of the Piazza del Duomo.
Gallery

View looking up
Entrance door to the bell tower
External loggia
Inner staircase from sixth to seventh floor
Inner staircase from seventh to eighth (the top) floor
View from the top
Assunta bell
Pasquareccia bell
View, looking down from the top
Tourist in a common pose at Tower of Pisa, June 2009

See also
Leaning Temple of Huma—Only leaning temple in the world
List of leaning towers
Leaning Tower of Niles, a replica of the Tower of Pisa
Leaning Tower of Zaragoza, was a famous European leaning tower
Great Mosque of al-Nuri (Mosul), an ancient leaning tower that stood until 2017
Machang, Kelantan—home to another leaning tower
Round tower (disambiguation), for other types of round towers
The Greyfriars Tower—the remains of a Franciscan monastery in King's Lynn, nicknamed "The Leaning Tower of Lynn"
Torre delle Milizie, a tilting medieval tower in Rome
Tour de Pise, a rock dome in Antarctica, was named after this tower






—official site
 (Creative Commons–licensed photos, laser scans, panoramas), data from a University of Ferrara/CyArk research partnership, includes 3D scan data from Leaning Tower.
 at Structurae