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A REVIEW OF THE LITERATURE CURRENTLY AVAILABLE ON THE STABILITY OF MASONRY BUILDINGS AGAINST

ACCIDENTAL DAMAGE

LOK FAT WILLIAM LAI OVE ARUP & PARTNERS

CONSULTING ENGINEERS 13 FITZROY STREET

LONDON W1P 6BQ

ABSTRACT

The aim of this paper is threefo1d:

1. to summarise the historical background to the development of design requirements against accidental damage;

2 . to review research work on the stability and behaviour of masonry buildings when subjected to gaseous explosions and other accidental loadings; and

3 . to present the Building Regulations and code requirements and their differences.

INTRODUCTION

Following the Ronan Point disaster explosion in a bathroom on the progressive collapse of part of the attention of the public was drawn to accidental damage.

on the 16th May 1968 when a gas eighteenth floor triggered the multi-storey block of flats, the the adequacy of buildings against

In the subsequent years there has been extensi ve research and discussion about the robustness and stability of buildings . Most of the available published information relates to masonry and large panel structures as these were first conceived to be more susceptible to damage than other forms of construction.

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HISTORICAL BACKGROUND TO THE DEVELOPMENT OF DESIGN REQUIREMENTS

System building grew up in Bri tain and the Continent in the post-war housing drive to speed up construction and reduce site work. Government incentives were also given to encourage the use of industrialised systems for high and low-rise public housing. There was a wide variety of systems and the Bison and Wates systems predominated them. AlI the system buildings used large pre-cast concrete factory-made components to be assembled on site. Ronan Point was the second of nine identical blocks to be completed and comprised 22 floors of flats resting on an insitu concrete podium containing garages and a car deck.

On 16th May 1968, a gaseous explosion in a flat on the eighteenth floor of the block removed the externaI load-bearing flank wa11 of the flat. This triggered a progressive collapse of the corner of the building from the nineteenth floor right down to the leveI of the podium. The incident did not just highlight the deficiency of the pre-cast concrete system buil t buildings but revealed a weakness in design - the risk of col1apse disproportionate to the cause of the accident. The Government immediate1y set up a tribunal of inquiry to investigate the causes of the accident, to consider the implications[~f the findings and to make recommendations. The Report of the Inquiry was published in 1968.

Prior to Ronan Point on 21st July 1963 at Aldershot, one identical buildings of pre-cast concrete frame construction with cladding panels collapsed during erection. The results investigation [~lre published in a report by the Building Establishment in 1963.

of four precast of the

Research

Following the report of the Ronan Point inquiry the Ministry of Housing and Local Government published in November 1968 a Circular 62/68 (Flats constructed with pre-cast concrete panels. APPf~tsa1 and strengthening of existing high blocks. Design of new blocks) dealing with flats constructed of precast concrete panels. The document recommended that alI blocks over six storeys in height built of large pre-cast concrete panels to form loadbearing wal1s or floors or both had to be appraised by a structural engineer who should consider whether they were susceptible to progressive collapse. The Circular was accompanied by an Appendix "Standards to avoid progressive collapse of large panel construction". For new buildings in large pre-cast panel construction two design methods were laid down as follows:-

"Method A:

Method B:

By providing alternative paths of support to carry the load, assuming the removal of a criticaI section of the loadbearing walls. By providing a form of construction of such stiffness and continuity so as to ensure the stability of the building against forces liable to damage the load-supporting members.

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For these purposes, the forces should be assumed as being equivalent to a standard static pressure of 5p.s.i.(O.0345N/mm 2 ). This standard should be used in designing new buildings. Where residual risks are lessened by the control of the incidence of an explosion in magni tude or frequency, a corresponding reduction may be made in the pressure. "

One month after the publication of Institution of Structural Engineers issued documents below:-

the Circular 62/68 in December 1968 the

the two

(a)

(b)

"Structurat4] stability and the prevention collapse" (report numbered RP/68/0l) and

of progressive

Notes on the Ministry of Housing and Local Government Circular 62/68 ("Notes for guidance which may assist in the interpretat'ion of Appefgfx 1 to Ministry of Housing and Local Government Circular 62/68") (report numbered RP/68/02).

The document RP/68/0l stated that the recommendations shown therein were concerned primarily with large residential buildings composed of prefabricated concrete panels. However, for the first time, it extended the scope of the regulations to loadbearing brickwork construction and other tall buildings which have no structural framework. The content of the report and the Appendix (which was an extract from British Standard Code of Practice CP 116 - the structural use of precast concrete) were mainly concerned with precast concrete construction .

The second report RP/68/02 gave guidance notes, comments and explanations which the Institution had drawn up to clarify the intentions of the Ministry in applying Circular 62/68. The document was intended to be used in the design of new residential buildings and in the appraisal of existing buildings of large panel construction.

In December 1968 the Ministry of Housing and Local Government issued a Circular 71/68 to summarise the advice given by the Institution of Structural Engineers regarding the Circular 62/68. Method B was extended to include alternative procedures to be developed by structural engineers to suit particular circumstances supported by tests or other practical experience. For assessing and strengthening existing structures where town gas had been removed, the standard static pressure of 5 p.s.i. was reduced to 2, p.s.i.

In May 1969 the Institution of Structural Engineers issued their report numb~red RP/68/03 "Guidance on the design of dômestic accommodation in loadbearing bri1~ork and blockwork to avoid collapse following an internaI explosion" . The term "domestic accommodation" in that instance included hostel's, hotels and buildings of similar plano The Document was only applicable to new buildings of seven to twelve storeys high. The principIes laid down also applied to buildings of more than twelve storeys but became decreasingly important as the height fell below seven storeys, and they did not apply to buildings of three storeys or less. The document was not intended for application to

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buildings wi th an independent structural frame. The Report concluded that domestic buildings should ideally be designed not only to withstand an appropriate nominal explosion pressure but also to bridge over severe structural damage due to the development of pressures in excess of the nominal pressure.

Building Regulations governing provisions for disproportionate collapse were implemented in 1970 in the fifth amendment to the 1965 Regulations. By then, recommendations in the form of codes of practice were required to unify the various design principIes and guidance already put forward. The outcome was the issue of Addendum No. 1 (1970) to CP l16[7Targe-panel structures and structural connections in pre-cast concrete' which incorporated the cri teria for design against disproportionate collapse in line with those contained in the Building (Fifth Amendment) Regulations 1970.

In September 1971 the Institution of Structura1S1ngineers published a report entitled "Stability of Modern Buildings" which arose from the insti tutions conference on industrialised building which, in turn was linked to the Aldershot collapse. The report dealt with the design of modern high-rise building structures in steel and concrete and the common types of defects and failures in those forms of construction.

A symposium in July 1978 on the stability of low-rise buildings of hybrid construction pro'~l~~ ~urther discussion on principIes for stability. The papers 1 presented at the Symposium covered investigations into gaseous explosions, design principIes and concepts for masonry, timber-framed and steel structures. Wi th regard to the desig7 {ri teria ary141 public accepWJli ty of accidental damage, Moore 12 , Gifford and Bartle expressed concern over the number of human lives at risk in addition to the extent of structural failure. Moore suggested that acceptability of the extent of damage could be measured in relation to the total structure in terms of a proportionate volume, floor area, number of storeys or number of lives affected. Gifford claimed that the maximum number of lives normally at risk should be the principal design cri teria. He suggested the number of lives and extent of floor/roof damage to be 12 lives and 210m 2 • This could correspond to three flats of four persons at a standard of 70m 2

per f1at. The area of damage was considered to be a gross area of 210m 2

to eliminate problems of interpretation in awkward buildings. Bartle brought up the questions of whether higher safety factors should be used for buildings where more people gather together, or whether certain criticaI parts of the buildings required more rigorous design and site supervisiono

Other papers related to the fifth amendment of the Building Regulationhdyc1uded those by Korff "The overall appraisal of brickwork buildings" , Hase1tine ['I:~1 Thomas "Loadbearing brickwork - design for the fifth amendment"[201 and Thomas "Structural brickwork -materiaIs and performance"

The British[211andard Code of Practice CP110: 1972 the Structural Use of Concrete gave recommendations on three dimensional tying and other recommendations on design ag1~~ft disproportionate co1lapse. This code is now superseeded by BS 8110 .

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The cod12~f practice for the Structural Use of Masonry BS 5628: Part 1: 1978 classifies buildings in respect of design against disproportionate collapse in to two categories: Category 1: alI buildings of four storeys and below Category 2: alI buildings of five storeys and above. The details of guidance on design will be discussed in the third section.

In 1985 the Building Research Establishrnent (BRE) published a report on the struf2tffe of Ronan Point and other Taylor Woodrow -Anglian Buildings , giving the details of construction and the defects that commonly occurred.

Since 1985 the BRE has carried out a programme of investigations into f~~rlings constructed from large panel systems (LPS). The report was published in 1987 in two parts. Part 1 describes the investigations by the BRE between April 1985 and August 1986 of the structural adequacy and durability of these dwellings. It also includes a review by the BRE of reports of investigations into these dwellings by owners and their consultants. Part 2 gives general guidance on the appraisal of such dwellings.

REVIEW OF RESEARCH WORK ON THE STABILITY AND BEHAVIOUR OF MASONRY BUILDINGS WHEN SUBJECTED TO GASEOUS EXPLOSIONS OR OTHER ACCIDENTAL

LOADINGS.

A considerable amount of research has been carried out especially by the Building Research Establishment and the British Ceramic Research Association into the behaviour of masonry buildings when subjected to gaseous explosions and other accidental loadings.

[26) The B.R.E. survey report showed a graph of average annual

frequency of accidental explosions against estimated peak dynamic pressures. The frequency with which an equivalent static pressure of 34 kN/m' was likely to be reached in an accidental explosion was estimated. The average equivalent static pressure was assumed to be 25 percent less than the estimated dynamic peak pressures. By taking the mean of the maximum and minimum estimates of the dynamic peak pressure, the frequency was found to be about once per year on the basis of the curves. The report recomrded that the 34 kN/m' specified in the Building Regulations 1976 should be retained. The cost of meeting the requirement was considered reasonable for averting the risk of about one serious partia 1 collapse of a building of five or more storeys every 25 years.

Masonry walls may develop considerable resistance to lateral loads by arching either horizontally or vertically. The British Cer~~êT Research Association carried out an extensive programme of research into the behaviour of lightly precompressed brickwalls subject to high lateral loads. It was found that a 215mm wall with a precompression in the order of O.5N/mrn' could by the 3-pin arch mode of failure wir9~tand the pressure of 34 kN/m' referred to in the Building Regulations .

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Research b~3~00d and Simms [29] of the BRE and Riddington and Stafford Smith showed that in the event of the loss of support under a concrete supporting beam, the masonry wall had the ability to arch in-plane by the presence of the composite action between the concrete beam and the brickwork above it. Vertical load above the notional arch would be transmitted beyond the length of the beam which had to resist the horizontal thrust. It was also noted that the arch could still be formed if sufficient restraint existed at both end1 ?f the arch in the damaged structure even in the absence of the beam 9 . This vertical arching could also occur owing to differential changes in vertical support.

The behaviour of masonry structures can be reviewed by a systemar~J study of buildings damaged by gaseous explosions. Mainstone R.J. discussed the available evidence from 14 severe or very severe accidental explosions, alI believed to have been gaseous, in the years 1968-77. These gave indications of the effect of venting, details of connections between structural elements, etc. It was stated that estimates of the probable magnitude of loads had to be largely based on the observable damage after the accidental damage, taking into account the complex dynamic character of the loading and the structural response to it.

Test structures subject to controlled explosions or remova 1 of loadbearing members have provided valuable information on the behaviour of structures during and after an accident .

Sinha and Hendry[31] of Edinburgh University carried out a number of tests showing that a five-storey brickwork crosswall structure could rema in stable following the remova 1 of a major loadbearing wall, although at a substantially reduced factor of safety. The wall layout of the structure was the same on each floor and consisted of three pairs of 114mm crosswalls stabilised by two pairs of shear walls. The slabs were of 50mm pre-cast concrete slabs with 75mm of insitu concrete topping. Subsequent calculation indicated that after the remova 1 of the centre cross-wall there would be a load factor of 1.94 on dead load plus a superimposed load of 1.9 kN/m2. The tests also concluded that a 114mm wall panel in the structure of the type tested could resist a static lateral pressure of 14 to 21 kN/m2.

From the above tests and some subsidiary experiments, it was concluded that i t was possible under rather exceptional circumstances for a pressure in the order of 34kN/m2 to be generated in a domestic gas explosion but in the major:i,ty of cases the maximum pressure attained would be limited to about 24kN/m2 due to the effect of venting.

Morton, Davies and Hendry also carried out some investigations into the behaviour of bric~~9rk ~~luctures panels subjected to accidental loadings. '

experimental and brickwork

The British Ceramic Research Association and the Brickwork ~3~Jlopment Association carried out a series of experimental studies

to investigate the behaviour of full-scale brickwork buildings subject to gaseous explosions and to establish the magnitude of the

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pressures reached. The structure consisted of three loadbearing cross-walls with l27mm reinforced concrete slabs to simulate the top three storeys of a tall cross-wall block. The externaI walls were 280mm cavity walls with various types and sizes of windows and cladding on the non-loadbearing walls. A communicating door was provided between each pair of rooms.

The effectiveness of venting was adequately demonstrated. In every case, relief was afforded by windows and cladding. As a consequence the peak pressure in the room of igni tion was always less than 14 kN/m 2 • The effect of cascade explosions proceeding from one room to another was also investigated. No wall was blown out by the explosions and no partia 1 collapse occurred. The following relationship was established:-

where the pressure developed in the room of ignition, in lbf/in 2

the pressure in the second connecting room, in lbf/in2.

It was stated that though the above expression appeared to be a convenient way of estimating the maximum possible pressure attained in the second connecting room in a domestic gaseous explosion, the ratios of the areas and strengths of venting walls and the volumes of the two rooms might also have a significant influence. Further research would thus be required to confirm the above relationship. It was suggested that due to the unavoidable venting in most cases and typical windows and cladding which failed at pressures up to about 1.0 lbf/in 2 (6.90 kN/m2), the pressure built up in the second room would be restricted to less than 2 lbf/in 2 (13.79 kN/m2).

The Institute TNO for Building MateriaIs aY~5fuilding Structures in the Netherlands carried out an investigation in to the structural consequences of gaseous explosions in high-rise blocks of flats. The aim was to determine the magnitude of explosion loadings through a series of explosion tests.

The test structure was constructed wi th reinforced concrete and comprised two compartments roughly comparable to a kitchen and a room in a flat. The walls and floors, of reinforced concrete construction, were designed for a static loading (at failure) of 350 kN/m 2 so as to be amply capable of wi thstanding the explosion pressures. A steel door between the two compartments was closed when tests were carr.ied out only in one of them. The front of both compartments had been left open for the installation of various venting walls. The open side face of the "room" was closed with a one-brick wall to act as a relatively weak loadbearing wall.

In alI thirty four explosions were produced, mostly in the kitchen. Two algebraic expressions were derived for the explosion loading:-

for the first pressure pulse: for the second pressure pulse:

p p

3 + Po 3 + 0.5 Po + 0.04/~2

where p

Po

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explosion loading in kN/m2 to be regarded as a uniforrnly distributed static loading on a structural member; uniforrnly distributed static loading in kN/m2 at which failure of the venting wall(s) occurs; F/V = ratio of the area F in m2 of the venting wall(s) to the volume V in m3 of the room .

Only the larger of the two values of P should be adopted. The above equation could be indicated graphically and for any particular combination of Po and 13, the value of explosion loading P could be found from the diagramo lt was noted that the equations were derived for glass venting walls but could also be used for materiaIs other than glass serving as venting walls, provided the ultima te loading Po of the material is known. The factor of safety for the explosion loading P was suggested as 1 . 0 by Committee B7 of the Building Research Foundation because in a house or flat the likelyhood that a natural gas explosion will occur with a intensity exceeding that envisaged by the explosion loading P achieved in a near ideal laboratory condition was regarded as virtually non-existent.

BUlLOlNG REGULATlONS ANO COOE REQUlREMENTS

The 1976 Building Regulations [27] required alI new buildings of five storeys and above to comply with the following maximum permitted extent of damage : -

Regulation 017(4) stated that:-

lf any portion of any one structural member were to be removed, a) structural failure consequent on that removal would not occur

within any storey other than the storey of which that portion formed part, the storey next above (if any) and the storey next below (if any), and

b) any structural failure would be localised within each storey .

Regulation 018 provided a deemed-to-satisfy definition of the term "localised" . The localisation of structural failure was deemed to be satisfied if the area within which structural failure might occur did not exceed 70m 2 or 15% of the are a of the storey (measured in the horizontal plane) whichever was the lesser.

Regulation 017 (5) considered that where any portion of any one structural member were not removable, that portion should be capable of carrying without structural failure the combination of the following loads:-

a) the combined dead load, imposed load and wind load; b) a load of 34 kN/m2 applied to that member from any direction; and c) the reaction , if any, which would be directly transmitted to that

member by any immediately adjacent part of the building if that part were subjected to a load of 34 kN/m2 applied in the same direction as that specified in b) above.

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Regu1ation D19, provided deemed-to-satisfy requirements in respect of D17 for bui1dings of reinforced, prestressed or p1ain concrete (whether cast in-situ or pre-ast). Reference was made to comp1iance with the re1evant recornrnendations in (a) CP110: Part 1: 1972 and (b) CP1l4: 1969, CPl15: 1969 or CP1l6: 1969 as read with CP1l6: Addendurn No.1: 1970.

The current Bui1ding Regu1ations 1985[36] Schedu1e 1 Disproportionate Co11apse states:-

Requirement A3 of

Requirement Disproportionate Co11apse Structure A3. The bui1ding sha11 be so constructed that in the event of an accident the structure wi11 not be damaged to an extent disproportionate to the cause of the damage.

Limits on app1ication This a)

b)

requirement app1ies on1y to:-a bui1ding having five on more storeys (each basement leveI being counted as one storey); and a pub1ic bui1ding the structure of which incorporates a c1ear span exceeding nine metres between supports."

The Bui1ding Regu1ations 1ist under "Provisions meeting the Requirement" the fo110wing Codes and Standards which may be used in designing to meet the above requirement:-

BS 8110: Parts 1 and 2: 1985 BS 5950: Part 1: 1985 and BS 5628: Part 1: 1978

The Regu1ations Inforrnation":-

a1so state under the heading "Addi tiona1

"Structura1 fai1ure of any member not designed as a protected key e1ement or member, in any one storey, shou1d not resu1t in fai1ure of the structure beyond the irnrnediate1y adjacent storeys or beyond an area within those storeys of:-a) 70m z or b) 15 per cent of the area of the storey whichever is 1ess."

The current Regu1ations state the requirements in a more straight forward manner than the 1976 Regu1ations. The perrnitted horiionta1 extent of structura1 fai1ure is 70m 2 or 15% of the area of the storey and the perrnitted vertical extent inc1udes the storey where the accident takes p1ace, the next one above and the next one be10w.

For the first time, the Bui1ding Regu1ations recognise the concern over the number of human 1ives possib1y at risk and therefore inc1ude pub1ic bui1dings with wide spans within the 1imits of app1ication irrespective of the number of storeys.

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h d · f [23] 1 . f' T e Co e of Practl.ce for Structural Use o Nasonry c assl. l.es buildings in respect of design against accidental damage into two categories:-

Category 1 buildings: Category 2 buildings:

alI buildings of four storeys and below alI buildings of five storeys and above

AlI buildings must have plan form and construction to provide robustness, interaction of components and containment of spread of damage and should also comply with clause 20.2. No additional detailed recommendations are made in respect of Category 1 buildings (4 storeys and below) .

Category 2 buildings (five storeys and above) should have adequate residual stability after accidental damage such that collapse of any significant portion of the structure is unlikely to occur.

Table 12 of the Code gives the designer 3 options for design:­Option 1 - Full Analysis The notional remova 1 of members analysis should be applied to alI vertical and horizontal members of the structure (except protected members) such that they are removable, one at a time, without causing a collapse of the structure. Option 2 Full Horizonatal Ties and Removal of Vertical Element Analysis. Full peripheral, internaI and column or wall ties should be provided at each floor leveI and at roof leveI but where the roof is of light-weight construction, no such ties are required at that leveI. The notional remova 1 of member analysis should only be applied to alI vertical members (except protected members). Option 3 - Full Horizontal and Vertical Ties Full peripheral, internaI and column or wall ties as option 2 plus full vertical ties.

Clause 20.2 requires the design of masonry structure to be robust and stable enough to support loads arising from normal use. And, in addition to this, the Code requires that there should be a reasonable probability that the structure will not collapse catastrophically under the effect of misuse or accident.

Unlike the Building Regulations the Code does not mention the permitted extent of damage. Clause 37.1 recommends that the damaged structure should have adequate residual stability and that collapse of any significant portion of the structure is unlikely to occur.

According to Clauses 37.1.1 and 22(d), the protected member (referred to as the protected key element in the Building Regulations) during an accident should be designed to resist the worst combination of the following loads applied to it:-

a) 0.95 Gk or 1.05Gk, b) 0.35 Qk (use 1.05 Qk for storage or permanent imposed loads). c) 0.35Wk, d) accidental design load of 34 kN/m' and reactions from attached

building components also subjected to 34 kN/m'

where

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Gk is characteristic dead load Qk is characteristic imposed load Wk is characteristic wind load

The current Building Regulations do not include in the requirements the details of loads to be considered in design but refer to the structural codes of practice.

CONCLUSIONS

It can be seen from the reported investigations of structural damage to buildings caused by gaseous explosions and from experimental studies that masonry structures can develop considerable resistance to accidental loads by arching and their inherent robustness. The effectiveness of venting walls or cladding to reduce explosion loading has been recognised. The pressure of 34 kN/m 2 is considered as conserva tive but acceptable for design to allow for domestic gaseous explosions.

The mode l tests should be viewed as qualitative rather than quantitative in nature. The equivalent static explosion loading on the structural elements will be influenced by factors like the are a and strength of venting walls; the shapes and volumes of the room where the explosion may take place and those of the interconnected rooms; the quantity, type, mixture and position of the explosive; the relationship between the pre ssure fluctuation frequency and the natural frequency of the structural elements, and the method of measurement of the pressures attained.

Since the Ronan Point incident there has been no significant advance in the basic design concepts for the elimination of hazards, robustness, three dimensional tying, notional removal of loadbearing members and protected key elements. It is currently a common practice in the design of new buildings to consider possible causes of accidents related to the individual circumstances of the buildings concerned . In this context air crash, deliberate bombing and atomic fallout are excluded as they are highly unlikely for normal buildings. Buildings that are subject to particular hazards, for example, chemical plants, ammuni tion dumps, tall buildings near the paths of aircrafts, etc. should be considered individually.

There is no absolute safety against all forms of hazards or different magnitudes of accidental loadings. The level of safety in terms of the number of human lives that could be lost i n an accident and the extent of structural failure can only be judged by the perceived public opinion and the economics of repair or replacement.

REFERENCES

1. Griffiths H., Pugsley Sir A. and Saunders Sir O. Report of the inquiry into the collapse of flats at Ronan Point, Canning Town. London, HMSO, 1968.

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2. The collapse of a precast concrete building under construction.

3.

Technical statement by the Building Research Station, London, HMSO, 1963.

Ministry of constructed strengthening London, 1968.

Housing and Local Government. Circular 62/68: Flats with pre-cast concrete panels. Appraisal and of existing high blocks. Design of new blocks.

4. Structural Stability and the prevention of progressive collapse, RP/60/01, London, lnstitution of Structural Engineers.

5. Notes for Guidance which may assist in the interpretation of Appendix 1 to Ministry of Housing and Local Government Circular 62/68, RP/68/02, London, lnstitution of Structural Engineers.

6. Guidance on the design of domestic accommodation in loadbearing brickwork and blockwork to avoid collapse following an internaI explosion, RP/68/03, London, lnstitution of Structural Engineers, 1969.

7. British Standards lnstitution. Addendum No. 1 (1970) to CPl16: 1965 and CPl16: Part 2: 1969, London, BSl, 1970.

8. Stability of modern buildings, London, lnstitution of Structural Engineers, 1971.

9. Mainstone R.J. Accidental explosions and impact: some lessons from recent incidents, Proceedings of the symposium on stabili ty of low-rise buildings of hybrid construction, London, lnstitution of Structural Engineers, 1978, pp. 13-23.

10. Creasy L.R. PrincipIes and concepts, Proceedings of the symposium on stability of low-rise buildings of hybrid construction, London, lnstitution of Structural Engineers, 1978, pp. 5-11.

11. Sutherland R.J.M. PrincipIes of ensuring stability, 1978.

12. Moore J.F.A. The stability of low-rise masonry construction, Proceedings of the symposium on stability of low-rise buildings of hybrid construction, London, I. Struct. E., 1978, pp. 38-46.

13. Rhodes P.S. Weak points tn hybrid construction, Proceedings of the symposim on stability of low-rise buildings of hybrid construction, London, I. Struct. E., 1978, pp. 23-27.

14. Gifford F.W. Precast concrete construction, Proceedings of the symposium on stability ' of low-rise buildings of hybrid construction, London, I. Struct. E., 1978, pp. 34-37.

15. Wah D.F. Timber-framed dwellings, Proceedings of the symposium on stability of low-rise buildings of hybrid construction, London, I. Struct. E., 1978, pp. 46-47.

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16. Needham F. H. symposium on construction, pp. 48-50.

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Stabili ty of Stee 1 Structures, Proceedings of the stability of low-rise buildings of hybrid

London, Institution of Structural Engineers, 1978,

17. Bartle R.R. Building Regulations - some problems of application, Proceedings of the symposium on stability of low-rise buildings of hybrid construction, London, I. Struct. E., 1978. pp. 51-53.

18. Korff J.O.A. The overall appraisal of brickwork buildings. 1978.

19. Haseltine B.A. and Thomas K. Loadbearing brickwork - design for the fifth amendment.

20. Thomas K Structural brickwork - materiaIs and performance, B.D.A.

21. British Standards Institution. The structural use of concrete. BS Code of Practice CP 110: 1972. London, BSI, 1972.

22. British Standards Institution. Structural use of concrete. BS Code of Practice BS 8110: 1985. London, BSI, 1985.

23. British Standards Institution. Code of practice for structural use of masonry Part 1. Unreinforced masonry. BS 5628: Part 1: 1978. London, BSI, 1978.

24. The structure of Ronan point and other Taylor Woodrow-Anglian Buildings, BRE Report, Garston, BRE, 1985.

25. Currie RJ, Reeves BR and Moore JFA the structural adequacy and durability of large panel system dwellings. Part 1 Investigations of Construction . Currie RJ, Armer GST and Moore JFA. Part 2 Guidance on appraisal. BRE, 1987.

26. Mainstone R.J., Nicholson H.G. and Alexander S.J. Structural damage in buildings caused by gaseous explosions and other accidental loadings, 1971 - 1977, London HMSO, 1978.

27. The Building Regulations 1976. Statutory Instrument 1976 No. 1676 Building and Buildings . London, HMSO, 1976.

28. West, H.W.H., Hodgkinson, R.H., and Webb, W.F.: The resistance of clay brick walls to lateral loading, TN 176, British Ceramic Research Association, 1971.

29. Wood, R.H., and Simms, L.G.: Alternative design method for the composite action of heavily loaded brick panel walls supported on reinforced concrete beams, BRE Current Paper CP 26/69, Garston, 1969.

30. Riddington, J .R., and Stafford Smith, B.: A composite method of design for heavily loaded wall-beam structures, Proceedings ICE Pt. 1, 1978.

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31. Hendry A.W. and Sinha B.P. The stabi1ity of a five storey brickwork cross-wa11 structure fo11owing the remova 1 of a section of a main load-bearing wall.

32 Morton J., Daries S.R. and Hendry A.W. The stability of loadbearing brickwork structures following accidental damage to a major bearing wall or pier, Proceedings of the second international brickwork masonry conference (Stoke-on-trent) 1971, ed. West H.W.H. and Speed K.H., British Ceramic Research Association, 1971,pp. 276-81.

33. Morton J. and Hendry A.W. An experimental investigation of the lateral strength of brickwork panels with precompression under dynamic and static loading, Proceedings of the third international brick masonry conference (Essen) 1973, ed. Foertig L. and Gobel K. (Bundesverband der Deutschen Ziegelindustrie, Bonn, 1975) pp. 362-9.

34. Astbury N.F., West H.W.H., Hodgkinson HR., Cubbage P.A. and Clare R. Gas explosions in load-bearing brick structures, B. Ceram. R.A. Spec. Pub. No. 68, 1970.

35. Dragosavic M. Structural measures against natural -gas explosions in high-rise blocks of flats. Heron, 1973, 19 (4) 1-51.

36. The Building Regulations 1985, HMSO, 1985.