Blog 2
The Jewel Tower

The Jewel Tower

Structure Information

The Jewel Tower is located in Westminster, London, England. The building was originally constructed between 1365 and 1366, with later additions constructed in the 1600’s and again in the 1700’s to serve the buildings changing purpose. A photo of the building today is shown in Figure 1 below.

Figure 1: Front view of the Jewel Tower

The Jewel Tower was originally built to securely store royal treasure within the private palace of Edward III. Its use has changed since its original construction. The succession of monarchs dictated the use of the Jewel Tower until its transition to containing the records office of the the House of Lords sometime before 1600. In 1869, the tower underwent another transition from a parliamentary office to a testing facility for the Board of Trade Standards Department, better known as Weights and Measures. The Department vacated the building in 1938, and the building is currently a monument and facility to display historic artifacts [1].

The Jewel Tower was designed by Henry Yevele, the most succesful master mason and architect of his time. Henry Yevele was the principal royal-appointed architect during the reign of Edward III, and the Jewel Tower was one of his many royal works during this time [2]. This indicates that the building was paid for by the monarchy of England. Other notable surviving works by Yevele include the naves of Westminster Abbey and Canterbury Cathedral.

Historical Significance

The Jewel Tower is a three-story L-shaped structure with a turet structure on the backside of the building. Each floor is comprised of a large rectangular room and a smaller room in the turret tower. Each floor is distinguishable by its ceiling vaulting. The ground floor of the Jewel Tower is the only floor with the original medieval rib vaults in place [3]. Although the Jewel Tower may not have been the first building of its time to employ the technique of ribbed arches and resulting ribbed vaults, it was constructed around the time of the forefront of the use of ribbed vaults leading to what we now know as Gothic architecture.  This structural engineering technique for constructing more efficient buildings with higher ceilings was not new, although the Jewel Tower may have helped architect Henry Yevele in perfecting his techniques for this type of vault used in his works Westminster Abbey and Canterbury Cathedral built after the Jewel Tower. Ribbed vaults were continually used in succeeding Gothic Architecture. Figures 2 and 3 below show a ribbed vault in the ceiling of the ground floor of the Jewel Tower and the ribbed vaults in the nave of Canterbury Cathedral, respectively. As previously mentioned, both were works of Henry Yevele–The Jewel Tower preceded Canterbury Cathedral.

Figure 2: Ribbed vaults in ground floor of the Jewel Tower [2]

Figure 3: Vaulting at Canterbury Cathedral [2]

 

 

 

 

 

 

 

 

 

 

 

 

 

It should be noted from the Figure 2 that there are extra ribs in the vaults. This forms a small fan. The vaulting at Canterbury Cathedral is full fan vaulting. Fan vaults are the most recently developed and most complex form of vaulting. The development of such vaulting was said to begin in 1351, only about 10 years earlier than the construction of the Jewel Tower. The development of fan vaulting is also attributed solely to England [4]. It can be concluded that the works of Yevele, especially the Jewel Tower, were a contributing factor to further development of fan vaulting. The motivation for the development of fan vaulting is mostly aesthetic, but the additional ribs did not compromise the structural safety of high vaults, and ultimately required less formwork [4].

The best existing example of a building with fan vaulting is Bath Abbey, shown in Figure 4.

Figure 4: Fan vaulting in nave of Bath Abbey, England [5].

 Cultural Significance

The Jewel Tower is associated with three distinct, successive functions: the royal keeping of jewels, the storage of the records of the House of Lords, and the Weights and Measurements office.

The Jewel Tower is one of four surviving buildings that made up the medieval palace of Westminster, which was the central residence for the English monarchy for the majority of the middle ages. The tower served Edward III through Henry VIII as a place to store royal treasures and things of great value. Figure 6 below shows the Jewel Tower in its original location as a part of Westminster Palace.

Figure 6: Jewel Tower in position of original construction as a part of Westminster Palace [2].

In 1512, the use of Westminster as a main royal residence was ended due to the destruction much of the Privy Palace in a fire. The function of the Jewel Tower as building of Parliament is arguably more significant than its function as royal jewel storage. This building was the safeguard to many documents sacred to England’s history. Finally, the function of the Jewel Tower as a testing facility of the Weights and Measurements office was short-lived, but the results of the decisions made by this office dictated trade policy for the British Empire [6].

There were no marked major historical events centered on this building, but its persistence to remain standing throughout fires, demolition, and 650 years of history makes this building special. The Jewel Tower as a historical whole embodies the transition of the British state from a monarchy to a Parliamentary Democracy to a highly developed imperial power [3].

A funny little anecdote about the perception of the construction of the Jewel Tower has perpetuated throughout history. Edward III built the Jewel Tower and its moat (maximum medieval security) encroaching on the grounds of the Benedictine Abbey, to the great dismay of the monks who resided there. According to the record-keeping ‘Black Book’ of Westminster, the monks blamed the land grab on William Usshborne, keeper of the royal Privy Palace. Upon completed construction, Usshborne stocked the new moat with freshwater fish and is said to have died choking on a pike which was caught there. The monks saw this as a perfect example of divine retribution [2]. Although no workers were recorded to have died in the construction of this building or its history of use, the death of William Usshborne by moat fish could be considered the human cost of this building.

The Jewel Tower today functions as I believe it should–a testament to its history that is open to the public.

Structural Art

The Jewel Tower demonstrates some degree of structural art in a very discrete manor. The Jewel Tower is a blocky, rectangular structure. Its frame seems to be based on post-and-lintel construction, making it fairly easy to see how the load is transferred through the structure. Even though the facades are not open or light, the structure is somewhat transparent in its load-bearing manner. Another way that the Jewel Tower demonstrates structural art is there are no added elements of decoration. It is a plain building which has a form that communicates its function.

Even with the previous aspects considered, I would not consider the Jewel Tower an example of structural art. The stone masonry construction is far too heavy and imposing to fit in to David Billington’s efficiency criterion to describe structural art. With the developing trend of gothic architecture, this structure could have used much less material to go much further. In addition, the rectangular, blocky nature of the facade and plan of the Jewel Tower was far less technically advanced than structures that were being built during the same time period. This was likely a product of its function as a safe place for royal valuables.

Structural Analysis

The service function of the Jewel Tower dictated its design and final form. The tower was meant to be fortified in order to protect the royal treasury. Consequently, the Jewel Tower was made a three-story building, each level being more secure than the preceding level. The turet structure was built to house the spiral staircase and also in part for added security. The structure is L-shaped in plan and is an example of medieval masonry construction. The process of masonry construction involves building from the ground up. The Jewel Tower has a stone masonry foundation that is slightly larger in plan than the building itself. A portion of the foundation can be seen on the left side of Figure 7 due to the moat that surrounded the building when it was constructed.

Figure 7: Stone masonry foundation of the Jewel Tower

The stone foundation was supported by timber piles which are still on display in the Jewel Tower today, as shown in Figure 8.

Figure 8: Original timber foundations on display in the Jewel Tower

From the foundation, the Jewel Tower would have been built by laying each stone individually and securing the stones together with mortar. Timber formwork was used to keep the exterior of the structure stable until the mortar cured. The Jewel Tower is built using Kentish ragstone. The interior-facing walls of the L-shape of the building are built using roughly coursed rubble masonry whereas the remainder of the walls are rectangular-shaped ashlar masonry. All surviving windows and doors were 18th century additions to the Jewel Tower. The windows and doors are framed in three-hinged arches using Portland Limestone [3]. There is also a stone section at the crown of the building which   The moat as seen in Figure 7 is contained in two ashlar masonry walls. The interior of the building is a little more interesting than the exterior. The main rooms on each floor are approximately 25 x 13 ft and the turet rooms are 13 x 10 ft [3]. The rib vaulting used as the ceiling for the ground floor is the only ceiling that is original to the Jewel Tower. The vault incorporates tiercerons, which are intermediate ribs between the diagonal and transverse ribs, which forms a small fan. The plan view of the rib vaulting in the ground floor can be seen in Figure 9 below.

Figure 9: Plan of ground floor showing vault forms [7]

The view looking up at the vaulted ceiling is shown in Figure 10 below.

Figure 10: Interior view of rib vaulting [3]

The walls and floor of the second story were built before the vault in the ground floor. The self weight of the second story and above rests on the lateral stone walls. The construction of this vaulted ceiling required careful coordination between the mason and the carpenter. Timber formwork was used to to stabilize the stone as the ribs were constructed and the intermediate panel sections were installed.

The structural system employed for the structure as a whole is a simple gravity-load controlled system. The load on the building has only to do with the self-weight of the stone and potential static load of occupents or materials inside the building. The ceilings of the second and first floor have varying structural systems in place to support the weight of the slab above and load on the slab. The ceiling of the second floor has a timber truss structure that transmits the self-weight of the stone roof to the outer lateral walls. The first floor has a timber joist and girder system that transmits the self-weight of the slab above it to the outer lateral walls. The load-bearing system of the ground floor is the same as the system used in the first floor. The load on the wider plan stone foundation and original wooden piles is a function of the density of the stone and the height of the building. This would yield a differential area load on the foundation as shown below, assuming that the density of stone is 170 lb/ft^3 [8] and one storey is roughly 15 feet high. The self-weight of the roof and the floor slabs rest on the lateral stone walls. Figure 11 below shows the structural system of the overall structure.

Differential area load = (170 lb/ft^3)(15 ft)=2550 lb/ft^2

Figure 11: Load path of structure as a whole

The more interesting structural system is the interior rib vaulting in the ground floor ceiling. The ribbed vaults are composed of arch ribs and panels. From this point on, this analysis will consider one rib vault, which spans half of the square footage of the main large room on the ground floor plan shown in Figure 9 above. Crossed ribs arise from the four supports at each corner of the vault which act as engaged columns and intersect each other at the keystone. The vault only has to support its own self-weight.

The load path for the general structure begins with the self-weight of the stone roof. The weight transfers as a surface load to a line load on each of the inclined timber joists in the ceiling truss structure of the second floor. The line load is transferred as point loads on to the center girder and the lateral exterior wall. The point loads from each joist on the center girder are transferred as a point load on to the exterior wall at each end of the girder. The weight of the slab (floor) of the second floor is transferred as a surface load to each joist in the structure of the ceiling of the first floor. There is a line load on each joist which is transferred as point loads to the lateral exterior walls. The same system is in place between the first and ground floor. All loads in the lateral walls are transferred to the stone foundation which are then transferred to timber pile foundations to the soil. The load path of the overall structure is shown in Figure 12 below.

Figure 12: Load path of overall structure

The general load path of a ribbed vault is displayed using the model shown below in Figure 13.

Figure 13: Load path of a ribbed vault [9]

The load path starts at the key stone and transfers through the ribs to the supports. The horizontal thrust and vertical load are transferred to the lateral stone walls.

The ribbed vaults can be analyzed by finding the tributary area of each rib and calculating the self-weight of the vault. The self-weight can be calculated using the density of the stone and the thickness of the vault. Assuming a thickness of 0.5 ft, the self-weight is found using the following calculations.

Vault self-weight=(170 lb/ft^3)(0.5 ft)=85 lb/ft^2

Using the geometry of the plan view shown in Figure 14, the tributary area for each rib can be calculated.

Figure 14: Plan view of the rib vaulting

The rib vault covers half the square footage of the ground floor main room. The square footage of the bay of the vault is given by the following equation.

Bay square footage=(25 ft x 13 ft)/2=162.5 ft^2

The four column supports are located at the corners of the plan view. By geometric symmetry, each column takes the same amount of load. One quarter of the bay is shown with dimensions assigned in Figure 15.

Figure 15: Tributary area layout for one column support

Tributary Area for rib 1: At1=(0.5*6.25 ft*2.17 ft)+(1/3)((0.5*6.25 ft*6.5 ft)-(0.5*6.25 ft*2.17 ft))=11.29 ft^2

Tributary Area for rib 2: At2=(6.25 ft*6.5 ft)-(11.29 ft^2+11.28 ft^2)=18.10 ft^2

Tributary Area for rib 3: At3=(0.5*2.08 ft*6.5 ft)+(1/3)*((0.5*6.25 ft*6.5 ft)-(0.5*2.08 ft*6.5 ft))=11.28 ft^2

Multiply the tributary area of each rib by the self-weight of the vault to find load transmitted to column by each rib:

Rib 1: Load to column = (11.29 ft^2)*(85 lb/ft^2)=959.65 lb

Rib 2: Load to column = (18.10 ft^2)*(85 lb/ft^2)=1538.50 lb

Rib 3: Load to column = (11.28 ft^2)*(85 lb/ft^2)=958.80 lb

Total load to column = (959.65+1538.50+958.80) lb = 3456.95 lb = 3.46 kips

Note that rib vault is in total compression.

Therefore the horizontal thrust generated at the base of the column taken by the lateral wall is given by the equation below, assuming that the pointed arches that make up the rib vault direct the load more vertically and minimize horizontal thrust. Therefore the load travels to the lateral walls at an assumed angle of 70 degrees

Horizontal thrust=3.46 kips (cos(70))=1.18 kips

Vertical load is given by the following equation.

Vertical load = 3.46 kips (sin(70))=3.25 kips

The lateral stone wall must be strong enough to resist 1.18 kips horizontally, and an additional 3.25 kips is transferred to the foundation vertically at each of the eight columns.

Personal Response

I never really thought about how the principles of construction have remained relatively constant for over six centuries. Somehow aa building which was built in the 1300’s is still standing and still has some of its original features. Studying a building with this much history makes you think about how constant civil engineering has been and always will be as time moves forward.

References

[1] http://www.english-heritage.org.uk/visit/places/jewel-tower/history/

[2] http://www.countrylife.co.uk/out-and-about/theatre-film-music/great-british-architects-henry-yevele-died-1400-24443

[3] http://www.english-heritage.org.uk/visit/places/jewel-tower/history/description/

[4] https://www.britannica.com/technology/fan-vault

[5] https://visitbath.co.uk/listings/single/bath-abbey

[6] http://www.english-heritage.org.uk/visit/places/jewel-tower/history/significance/

[7] http://www.english-heritage.org.uk/content/visit/places-to-visit/history-research-plans/jewel-tower-phased-plan

[8] https://www.simetric.co.uk/si_materials.htm

[9] https://www.sciencedirect.com/science/article/pii/S0141029617301864