St James Twin Chapel Spire

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St. James Twin Chapel Spire

A case study report in Structural Conversation submitted by Mariana Isa

towards the degree of Master of Science in the Conservation of Historic Buildings

at the University of Bath.

Department of Architecture and Civil Engineering.

Session 2005-2006


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Acknowledgement

The help, advice and support from the following are gratefully acknowledged:

Dr. Michael Forsyth

NokAli AmranDavid Stapleton

Teq Hud Hud

Juliane Eichner

Bath North East Somerset Archive

Haycombe Cemetery Office

Classmates of Msc. Conservation of Historic Buildings 2005-2006


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Synopsis

This report is a structural case study on the St. James Twin Chapel Spire, which was

dismantled due to its condition that was at severe risk of collapse if there had been a strong

gust of wind. This report covers the structural condition of the spire before it was dismantled

in 1978 based on documents found in the Bath City Archive.

This report consists of two sections. The first section includes a structural analysis and

diagnosis of the spires structural defects and the second section is a discussion on the

proposed intervention and the philosophy of conservation behind it.


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Contents

Page No.

Acknowledgement

List of Illustrations i

Synopsis ii

1.0 Introduction 1

2.0 Published Records 3

3.0 In situ Survey 4

4.0 Structural Analysis 5

4.1 Structural Description of the Spire 5

4.2 Structural Condition of the Spire 6

4.3 Wind Action onto the Spire 6

4.4 Defect 1: Crack at Base of the Original Anchor Block (F/G) 7

4.5 Defect 2: Crack at the Base of Tapered Octagon 9

5.0 Proposed Structural Intervention 11

5.1 Stone Treatment 11

5.2 Strengthening the Spire Post Stressed System 11

6.0 Philosophy of the Structural Repair Techniques Applied 13

7.0 Conclusion 14

Notes 15

Bibliography 16

Appendices

Appendix A Drawings

Appendix B Working Procedure Report


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i

List of Illustrations

Figure

No.

Title of Illustration Illustration Credit

1 The present St. James Twin Chapel. Author

2 Location map of St. James Twin Chapel in Bath. Author

3 Twin Chapel Spire before and after demolition in 1978. The CreasyPartnership

Guildford & Epsom

4 Stonework of the spire stored in the East Chapel. Markings

on the stones are still visible.

Author

5 A conceptual north-south section of the Twin Chapel Spire. Author

6 Cracks at the mid height of the Twin Chapel Spire Bath City

Archive

8 Wind action effect to level F/G and T/U. Author

9 Defect at base of the original anchor block (F/G). Bath City

Archive

10 Cause of structural defect at F/G. Author

11 Defect 2: Crack at the base of tapered octagon (T/U). Bath City

Archive

12 Cause of structural defect at T/U. Author

13 Proposed Intervention to restore the Twin Chapel Spire. Author


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St. James Cemetery Twin Chapel Spire

1


1.0 Introduction

Figure 1: The present St. James Twin Chapel.

1.0.1 St. James Twin Chapel in the middle of St. James Cemetery was opened in 1861 buthas now closed. It is located mile west of the Bath City Centre, on the south of the

Lower Bristol Road.

1.0.2 Built in 1860, the St. James Twin Chapel was a mortuary building designed by Baths

City Architect at that time, Charles Edward Davis1. The chapel is of medieval

architecture, consisting of two twin chapel complexes built using Coombe Down Stone.

The two chapels are placed on the West-East axis, separated by a twin-carriage porch-

way.


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1.0.3 A slender stone spire was placed above the twin carriage porch-way of the chapel.

Unfortunately, the spires structural condition was deemed to be dangerous and was

carefully dismantled in 1978 by the Bath City Council2.

1.0.4 During the spires demolition, all the stonework were measured, recorded andsubsequently numbered. The stonework are now stored in the two cemetery chapels for

future reuse3. The stump of the original spire is temporarily capped-off at the top of its

pedestal level, just above the ridge of the Twin Chapels roofs.

Figure 2:

Location map of St.

James Twin Chapel

in Bath.


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Figure 3: Twin Chapel Spire before and after demolition in 1978.

1.0.5 A grant aid of 37 500 had previously been offered to the City Council by the

Department of the Environment under Section 4 of the Historic Buildings and Ancient

Monuments Act 1953, as the Department of the Environment regarded the Twin Chapel

as an outstanding historic building4. However, the restoration project never came to

being due to funding difficulties5.

2.0 Published Records

2.0.1 There are little published records on the St. James Twin Chapel. However, as the

building was designed by the City Architect in 1860, Charles Edward Davis, original

scaled contract drawings and specifications still exist in the Bath City Council

Archives6. These drawings however are not available to the general public.

2.0.2 A detailed measured drawing of the spire and photographs of the Twin Chapel before

the spire was dismantled in 1978 were obtained from the Bath Council Archive,

showing the form, details and structural defects of the spire. The drawing and

photographs are used as primary reference to the spires original design for this report.

Pedestal

Level

Original

Spire


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2.0.3 The most comprehensive document found on the spires structural history is the

Feasibility Study on the Restoration of The Twin Chapel Spire Report by Creasy

Partnership Guildford and Epsom, published by the Departmental of Environmental

Services of Bath City Council. This report contains detailed description of the spires

characteristic features, structural analysis, structural calculations and technical details

of the proposed spire restoration in 1985. Detailed recordings of the original spire

together with its drawings are also included.

2.0.4 It has been noted that a structural report on the Twin Chapel Spire was submitted by

David Mclaughlin, a Msc. Conservation of Historic Buildings student at the University

of Bath in 2005. However, this report was not used as reference.

3.0 In situ Survey3.0.1 The first site visit was on 12 November 2005 to investigate whether the Twin Chapel

was suitable for the assignment. The buildings cemetery compound was found to be

well looked after and the chapel is locked at all times to keep safe the spires original

stonework.

3.0.2 The second visit on the 20December 2005 was accompanied by a representative fromHaycombe Cemetery Office. Investigation into the chapel found the whole buildings

structure to be in a sound condition. There were hardly wall cracks or timber rafter

decay.

3.0.3 The long effects of storage onto the spires stored stonework have appeared to be mildwith little sign of severe chemical erosion from the local atmosphere. The markings on

the stones are still visible.


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Figure 4: Stonework of the spire stored in the East Chapel. Markings on the stones are still visible.

3.0.4 As a whole, the Twin Chapel building is thought to be well maintained despite the factthat it has been closed for a few decades.


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4.0 Structural Analysis4.1 Structural Description of the Spire

Figure 6: A conceptual north-south section of

the Twin Chapel Spire.

4.1.1 The spire of St. James Twin Chapel

was a tapered octagon structure,

hollow at its stem and solid at its

apex. The spire rose to a height of

86ft (27 metres) above the ground.

The vertical axis of the spire was

placed at the middle-point of the

longitudinal axis of the twin chapel

complex7.

4.1.2 The base of the spires pedestal is

formed in cross section as a solid

cruciform. Part of the pedestals base

is carried in suspension, below the

pitch of the porch-way roof and

above the carriage way, by a system

of Wrought Iron Beams. The pedestal

emerges through the roof into an

exposed extension of a similar

cruciform cross section, carrying a 4-

column unit of an open bell

chamber8.

4.1.3 The bell chamber supports the lower

stem of the tapered octagon spire. The

lower stem is the first unit above the

base of the spire which is formed as a

hollow octagon. The stem itself is

parallel sided but with four diagonal

open latticed panels. These four

latticed panels are what support theupper portion of the tapered octagon

9.


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Figure 7: Cracks at the mid height

of the Twin Chapel Spire.

Figure 8: Wind action effectto level F/G and T/U.

4.2 Structural Condition of the Spire

4.2.1 A structural inspection of the spire, carried out in

1978 revealed two major structural cracks at the mid

height of the spire (Figure 7). Scaffolding waserected around the spire to its full height to help

investigation.

4.2.2 In general, the original spire was found to be in good

condition, but the structure was inclined to sway in

high winds and there were significant external

damage to several areas of the stonework. Both

defectswere found to be inherent in the construction

of the spire10.

4.2.3 The decision was to take down the spire to its

pedestal level, capping off the exposed stone with a

temporary covering of lead, and to make a detailed

record of the dismantled stonework11.

4.3 Wind Action onto the Spire

4.3.1 The city of Bath is located within a moderate zone of

wind intensity. The maximum basic wind speed

which will blow continuously for a gust duration of

3 seconds is 42 m/sec over a period of 50 years12

.

4.3.2 National Code Recommendations suggested that the

spire would safely resist an equivalent static pressure

of 25 psf (0.5N/m2)

13.

4.3.3 As a whole, the spire was quite stable under average

intensities of wind pressure, but liable to suffer

damage from high pressure gusts which are repeated

over a long term. High gusting had induced

corresponding fluctuations in uplift and eventually

rocked the spire and generated hammer blows on the

windward side of the stonework14.

Crack 1

(F/G)

Crack 2(T/U)


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4.4 Defect 1: Crack at Base of the Original Anchor Block (F/G)

Figure 9: Defect at base of the original anchor block (F/G).

4.4.1 External cracking appeared at level F/G at the base of the original anchor block. It was

assumed that this defect (Figure 9) was due to the considerable oscillation caused by

wind action against the height of the spire, and worsen by the ineffective stone anchor

which was suspended internally from the apex by an iron finial crossed by two linked

iron bars15

. It is likely that the architect used this pendulum device in an attempt to

counteract the effect of wind sway by holding down the head of the spire.

4.4.2 This dead-weight anchor block, resting on the internal base at level F (Figure 10) was

not heavy enough to hold down the spire. Its influence was particularly insignificant atthe positions where it most needed. The size of the kentledge provided was only 2%

of that required to stabilize the most sensitive components of the structure16

.

4.4.3 In a high gust wind, the suspended anchor block is liable to lift and swing against the

internal faces of the spire with corresponding damage to the stones at both the support

level at the apex of the spire.

Crack at F/G


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Figure 10: Cause of structural defect at F/G.


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4.5 Defect 2: Crack at the Base of Tapered Octagon (T/U)

Figure 11: Defect 2: Crack at the base of tapered octagon (T/U).

4.5.1 There was a severe horizontal crack through the stonework of both the solid and latticeface where the base of tapered octagon is. The crack was most significant on the north

east of the structure and probably accords with the direction of the prevailing wind.

4.5.2 A flat band of iron to encircle the structure at the base of the octagon was introduced to

restrain the outward thrust on the stonework of the open belfry from the weight of the

spire above. This precautionary measure was not adequate to prevent a fracture of the

stones at T/U.

4.5.3 Level T/U at the base of the tapered octagon is a position of exceptional sensitivity and

is particularly vulnerable to above average wind gusts. The four latticed panels of the

lower stem, supporting the tapered octagons are relatively weak in diagonal tension and

provide only a fraction of the desirable efficiency. A stabilising component was

inserted horizontally at the mid height of the lower stem to stiffen it17.

Crack at T/U


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4.5.4 The bell chamber is arranged as 4 wide panels on the square sides of the octagonal

cross-sections without any form of restraint on the diagonals. In its present form the

efficiency of the bell chamber unit is very low and largely indeterminate. Improvements

to ensure that the 4 columns act together as a fully braced frame is possible by inserting

a horizontal cross frame at mid height.

Figure 12: Cause of structural defect at T/U.


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5.0 Proposed Structural Interventions

5.0.1 In 1985, two methods were proposed to restore the spire back to its original position

and improve its structural stability. The proposed structural intervention included

treatment of stonework and strengthening the spire by introducing a full height system

of central anchor rods which are post stressed from the existing base18.

5.1 Stone Treatment

5.1.1 The spires restoration report states that at least 80% of the stone from the original spire

can be re-used after relatively minor treatments.

5.1.2 The proposed guidelines for the spires stone treatment are as follows:

i. Natural erosion of the stone face and corners are to be accepted. Stones

which may have been used in positions of face bedding are to be avoided

in the process of restoration.

ii. The removal of structural defects (rusting from previous fitments,

cracks, blemishes and spalling) will only involve those threatening the

stability of the restored spire. This will involve squaring up of the

existing stone block and importing additional material to match.

iii. The stonework of the spire, including the base and pedestal are to beface cleaned. All traces of old mortar are to be removed for the stability

of the structure, especially in the position of the anchorage seating.

5.1.3 The existing metal cross which surmounts the spire can be reused. However, the

existing apex seating was found to be very narrow and appears to have been damaged

by erosion and relaxation in the anchorage. The top anchorage was redesigned to avoid

these troubles. A limited amount of new stonework will probably be required in this

sensitive position.

5.2 Strengthening the Spire Post Stressed System

5.2.1 The dead weight of the stonework towards the spires apex was insufficient to hold

down the structure against the above average wind gusting. The loose anchor block

which was originally inserted at mid height to stabilise the structure, was also

inadequate for this purpose, both in weight and the insecurity of the anchorage within

the main stonework19.


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6.0 Philosophy of Structural Intervention Techniques6.0.1 The restoration of the spire is measured against English Heritages principles of

conservation; minimal intervention, like for like, do nothing, preserve as found,

sympathetic and reversibility.

6.0.2 The spire has a significant historical and structural value to the community, hence, its

reconstruction is deemed substantial.

6.0.3 It is fortunate that the spires stonework was carefully marked during the demolition

and is still securely kept. This, together with the availability of the spires measured and

original contract drawings, allows the spire to be restored to its original formrighteously - conservation wise.

6.0.4 The existence of 80% of the spires original stonework enables the retention of its

historic authenticity. Replacement of blemished stones with the same material is a like

for like intervention.

6.0.5 The spires major problem was the structural design itself. If reconstructed to the exact

original, the spire is expected to encounter the same complications. The proposal to

strengthen the structure by inserting iron anchor rods, is not a minimal or reversible

structural intervention. The new anchor rods will change the spires load path onto the

masonry beneath it. The complications that this proposal would create for the masonry

structure must be taken account of. The tendency for the iron rods to rust must also be

noted.

6.0.6 It is difficult to comprehend the reasoning behind the spires demolition before thestructure had broken down in 1978. The question whether the proposed anchoring to

conserve the spire could have taken place before demolition arises. Measures should

have been taken to restrain it from breaking down, not to bring it down before the

structure fails. If the structure has managed to stand against time, it gives an indication

that it is capable of standing even longer. Calculations are sometimes unreliable in

cases such as this.


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6.0.7 The decision to dismantle the spire does not comply with any of the conservationprinciples. It seems that this decision was heavily influenced by the lack of existing

funds.

6.0.8 The decision to record the stones and store the spires stonework however, opens the

possibility for future restoration when technology has advanced and funds have

expanded.

7.0 Conclusion

7.0.1 The assumption that the spire was a dangerous structure and was demolished before itactually failed is unaccountable. If the spire has found a way of standing for several

decades, an explanation on why it has stood must be looked into. If analysis suggests

that the spire does not work, the analysis is at fault, not the structure.

A structure only falls down when it has exhausted all possible ways of standing up.

Walleys Theorem

7.0.2 However, it is understood that the stonework was dismantled as a precaution measureto avoid damage, in-case the structure does fall down. Limited funding implies that

there is no guarantee that the structure will be able to undergo restoration in near future.


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Notes

1. Bath City Archive Records2. The Creasy Partnership Guildford & Epsom (1985), p 43. Honeycombe Cemetery Office Records4. The Creasy Partnership Guildford & Epsom (1985), p 45. Honeycombe Cemetery Office Records6. Bath City Archive Records7. The Creasy Partnership Guildford & Epsom (1985), p 58. The Creasy Partnership Guildford & Epsom (1985), p 59. The Creasy Partnership Guildford & Epsom (1985), p 510. Honeycombe Cemetery Office Records11. The Creasy Partnership Guildford & Epsom (1985), p 412. The Creasy Partnership Guildford & Epsom (1985), p 613. The Creasy Partnership Guildford & Epsom (1985), p 614. The Creasy Partnership Guildford & Epsom (1985), p 715. The Creasy Partnership Guildford & Epsom (1985), p 816. The Creasy Partnership Guildford & Epsom (1985), p 917. The Creasy Partnership Guildford & Epsom (1985), p 1118. The Creasy Partnership Guildford & Epsom (1985), p 1119. The Creasy Partnership Guildford & Epsom (1985), p 12


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Bibliography

1. Beckmann, Poul. Structural Aspects of Building Conservation. Mcgraw-Hill Book

Company, London, 1995.

2. Brebbia, C.A. Structural Studies of Historical Buildings IV: Dynamics, Repairs &Restoration Volume II, Computational Mechanics Publication, Southampton, 1991.

3. Brebbia, C.A. Structural Studies of Historical Buildings IV: Dynamics, Repairs &

Restoration Volume IV, Computational Mechanics Publication, Southampton, 1995.

4. Bussel, Michael. Lecture Notes for Msc. Conservation of Historic Buildings at

University of Bath (19.10.05), session 2005-2006.

5. Courtenay, Lynn. T. The Engineering of Medieval Cathedrals Volume 1. AshgatePublications, Aldershot, 1997.

6. DAyala, Dina. Damage, Appraisal and Repair of Historic Structures. Lecture

Notes for Msc. Conservation of Historic Buildings at University of Bath, session

2005-2006.

7. Fidler, John. Stone: Stone Building Materials, Construction and Associated

Component System: Their Decay and Treatment Volume 2. English Heritage, 2002.

8. The Creasy Partnership Guildford & Epsom. St. James Cemetery Bath Twin ChapelSpire Feasibility Study Restoration of the Spire. Department of Environmental

Services, 1985.

Website Resources

1. http://www.bathnes.gov.uk/BathNES/lifeandleisure/cemeteriesandcrematorium/

cemlist.htm.List of Cemeteries in Bath (Accessed (29.11.2005)

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