s s e r P E R B S H I © , y p o C d e l l o r t n o c n U , 2 4 : 9 4 : 5 1 7 0 0 2 / 8 0 / 0 3 , s t e l m a H r e w o T f o h g u o r o B n o d n o L , r e m i t a L K : y p o C d e s n e c i L Building Research EstablishmentR eport (2.3) Ct 5th 1987 The structural adequacy and durability of large panel system dwellings Part 1 of construction Investigations R J Currie, B R Reeves and J F A Moore BUILDING D RESEARCH ESTABLISHMENT s s e r P E R B S H I © , y p o C d e l l o r t n o c n U , 2 4 : 9 4 : 5 1 7 0 0 2 / 8 0 / 0 3 , s t e l m a H r e w o T f o h g u o r o B n o d n o L , r e m i t a L K : y p o C d e s n e c i L The report This report comprises three documents: Part 1 and Part 2, which are not available separately, and a summary in the form of a Building Research Establishment Information Paper, which is available separately. Their full titles are: The structurala dequacya nd durability of large panel system dwellings: Part 1. Investigations of construction by R J Currie, B R Reeves and J F A Moore The structural adequacya nd durability of large panel system dwellings: Part2 . Guidance on appraisal by R J Currie, C S T Armer and 1 F A Moore The structurala dequacy and durability of large panel system dwellings: summary of the report Enquiries In the first instance, general enquiries concerning this report and its findings should be referred to the Building Research Advisory Service at BRE Garston (Tel: 0923 676612). Specific technical questions relating to the contents of the report may be referred to the following contacts at BRE Garston (Tel: 0923 674040): Contact Area of work Dr J F A Moore Overa1l, co-ordination of the BRE programme and its findings and (project leader) implications for the management of LPS dwellings Mr R J Currie Part 1 — BRE investigations into the condition of LPS dwellings Mr B R Reeves Part 1 — BRE site inspections Mr C S T Armer Part 2 — Assessment of the structural implications of the BRE investigations and structural appraisal of LPS dwellings Mr R J Currie Part 2 — Assessment of the risk of corrosion in LPS dwellings Dr R C de Vekey Part 2 — Radar inspection techniques Mr G S T Armer Part 2 — Non-destructive testing techniques other than radar In addition, specialist advice on the performance of materials may be appropriate. The following contacts at BRE Garston are available: Mr K W J Treadaway Corrosion of steel in concrete: mechanisms, diagnosis and repair Mr G W Rothwell Coatings for the protection of reinforced concrete Mr R N Cox Performance of metallic fixings and their protection s s e r P E R B S H I © , y p o C d e l l o r t n o c n U , 2 4 : 9 4 : 5 1 7 0 0 2 / 8 0 / 0 3 , s t e l m a H r e w o T f o h g u o r o B n o d n o L , r e m i t a L K : y p o C d e s n e c i L Building Research Establishment Report The structural adequacy and durability of large panel system dwellings Part 1 of construction Investigations R J Currie, BSc(Eng), CEng, MICE, MlStructE B R Reeves, BSc J F A Moore, MA, BSc(Eng), ARSM, DIC, PhD, CEng, MiStructE Building Research Station Department of the Environment Building Research Establishment Building Research Station Garston Watford WD2 7JR s s e r P E R B S H I © , y p o C d e l l o r t n o c n U , 2 4 : 9 4 : 5 1 7 0 0 2 / 8 0 / 0 3 , s t e l m a H r e w o T f o h g u o r o B n o d n o L , r e m i t a L K : y p o C d e s n e c i L Price lists for all available BRE publications can be obtained from: Publications Sales Building Research Establishment Garston, Watford, WD2 7JR Tel: (Garston) (0923) 674040 This publication is one of a series being prepared as part of the Building Research Establishment's programme of investigation to assist local authorities and their consultants in appraisal, maintenance and repair of large panel system dwellings. OtherB REp ublications on large panel system dwellings are: Building Research Establishment. The structure ofR onan Point and other Taylor Woodrow-Anglianb uildings. BRE Report. Garston, BRE, 1985. Edwards M J. Weatherproof joints in large panel systems: 1 Identification and typical defects. BRE Information Paper 1P8/86. Garston, BRE, 1986. Edwards M J. Weatherproof joints in large panel systems: 2 Remedial measures. BRE Information Paper 1P9/86. Garston, BRE, 1986. Edwards M J. Weatherproof joints in large panel systems: 3 Investigation and diagnosis of failures. BRE Infor- mation Paper IP1O/86. Garston, BRE, 1986. Edwards M J. Weatherproof joints in large panel systems: 4 Flat roofs, balconies and deck accessways. BRE In- formation Paper 1P15/86. Garston, BRE, 1986. Harrison H W, Hunt J H and Thomson J. Overciadding external walls of large panel system dwellings. BRE Report. Garston, BRE, 1986. Morris W A and Read R E H. Appraisal of passive fire precautions in large panel system blocks of flats and maisonettes. BRE Information Paper IP18/86. Garston, BRE, 1986. Reeves B R. Large panel system dwellings. preliminary information on ownership and condition. BRE Report. Garston, BRE, 1986. ISBN for complete set of 2 parts plus Information Paper 0 85125 250 8 ISBN 0 85125 251 6 ©C rown copyright 1987 First published 1987 Second impression 1987 Applications to reproduce extracts from the text of this publication should be made to the Publications Officer at the Building Research Establishment s s e r P E R B S H I © , y p o C d e l l o r t n o c n U , 2 4 : 9 4 : 5 1 7 0 0 2 / 8 0 / 0 3 , s t e l m a H r e w o T f o h g u o r o B n o d n o L , r e m i t a L K : y p o C d e s n e c i L Contents Page Preface iv 1 Introduction 1 2 of Scope investigations 1 3 Main findings of BRE investigations 3 4 Discussion 6 5 Conclusions 7 Acknowledgements 9 References 9 Appendix A Summary of investigations of LPS dwellings by BRE 11 Appendix B Review by BRE of reports of investigations of LPS dwellings by owners and their consultants 63 111 s s e r P E R B S H I © , y p o C d e l l o r t n o c n U , 2 4 : 9 4 : 5 1 7 0 0 2 / 8 0 / 0 3 , s t e l m a H r e w o T f o h g u o r o B n o d n o L , r e m i t a L K : y p o C d e s n e c i L Preface a In October 1984 the Minister for Housing and Construction announced programme of investigations by the Building Research Establishment (BRE) of dwellings constructed from large panel systems. This report arises from the programme and is in two parts. Part 1, the present part, describes the investigations of structurala dequacy and durability of large panel system (LPS) dwellings, and Part 2 gives general guidance on the appraisal of such dwellings. Research related to these investigations is continuing, particularly in relation to accidental loads such as those which may arise from explosions or fire. Fur- ther guidance, therefore, may be developed for assessing the sensitivity of LPS dwellings to accidental loads. There are other aspects of the BRE programme of investigation of LPS dwellings which may impinge on the main theme of this report. Lack of weathertightness of joints be- tween components or in flat roofs, for example, may in some circumstances promote the corrosion of reinforcement, quite apart from causing environmental problems of rain penetration. Recent guidance on inspection, diagnosis and remedy of such problems is available"23'4. The possibility of spread of fire and smoke through gaps or voids may require considera- tion5 and in general there will be needs for periodic appraisal of the passive fire precau- tions in buildings6. It may be appropriatet o integrate inspections or any subsequent remedial measures in relation to weathertightness or passive fire precautions with the other issues addressed in this report. The remaining major issue of LPS dwellings which is still under investigation in the BRE programme is that of the environment within the flat or house. Ventilation rates, insula- tion standards and heating systems are being examined in order to identify ways in which an appropriate balance between them may be achieved to improve comfort and to limit condensation and mould growth at a reasonable cost. The BRE programme also aims to ensure that any remedial measures will not cause side- effects, such as interstitial condensation or cold bridging, which may have adverse effects on the durability of the structure. Equally, any remedial measures to the structure or the weather envelope, or passive fire precautions, should not have undesirable side-effects on each other or on the internal environment. iv s s e r P E R B S H I © , y p o C d e l l o r t n o c n U , 2 4 : 9 4 : 5 1 7 0 0 2 / 8 0 / 0 3 , s t e l m a H r e w o T f o h g u o r o B n o d n o L , r e m i t a L K : y p o C d e s n e c i L 1 Introduction 1.1 This first part of the report describes the investi- ings and conclusions have been based on detailed in- gations of the construction of large panel system formation contained in Appendix A, which describes (LPS) dwellings carried out by the Building Research the field investigations carried out by BRE, and on Establishment (BRE) between April 1985 and August more general information, not verified independently 1986. It provides the basis for the guidance on ap- by BRE, given in Appendix B, which comprises a praisal of structural adequacy and durability of LPS review by BRE of reports of investigationso f LPS dwellings given in Part 2 of this report. dwellings carried out by owners and their consultants. The broad implications of these findings are con- 1.2 Sections 2 and 3 of this part describe, respective- sidered in Section 4, and conclusions are drawn in ly, the scope of the investigations and the findings in Section 5. relation to large panel systems as a whole. The find- . . . . . . . 2 of Scope investigations Objectives the likely long-term durability of these dwellings in 2.1 The BRE investigations aimed to: relation to corrosion of reinforcement. This would give a basis for suggestingt est regimes to enable Assess overall the 'as built' form of construction the long-term performance of individual buildings 1 to be assessed by their owners, with suitable 2 Assess the quality of workmanship and materials reliability and cost-effectiveness used in large panel structures to provide informa- tsitorunc otino nth e nature and extent of variability of con- 2w.h2i cThh mesaey t absek nse ccoemsspaarrye f obrr oaa dfulyll t aop tphreai msaal ion fs ate pstsr uc- ture and its durability. 3 Review the data obtained from inspections of large panel structures in order to provide an overview of Systems inspected the present and long-term structural soundness of these dwellings. This would give a basis (a) for sug- 2.3 Records of construction indicate that about gesting procedures for assessing the ability of in- 160 000 dwellings have been constructed in the United dividual buildings to carry normal and accidental Kingdom using large panel systems. Recently pub- loads, and (b) for designing any remedial measures lished information7 relates only to about 70% of this total. The number of flats in blocks over 4 storeys 4 Review the data obtained from inspections of large high in England is given in the form of a histogram in panel structures in order to provide an overview of Figure 1. It shows the variety of systems and the preponderance of some of them. 30 000 20 000 0 0 n0) E zS 10 5 (I) O IS 0) 0 -o0J) (1) -CJo 00 1 5 10 15 20 23 Ranking of systems in descending numerical order Figure 1 Numbers of flats in buildings over 4 storeys high constructed from different large panel systems, in England s s e r P E R B S H I © , y p o C d e l l o r t n o c n U , 2 4 : 9 4 : 5 1 7 0 0 2 / 8 0 / 0 3 , s t e l m a H r e w o T f o h g u o r o B n o d n o L , r e m i t a L K : y p o C d e s n e c i L Table 1 Systems examined by BRE and by consultants Approximate Number of blocks examined percentage of total LPS housing System By BRE By consultants stock in the UK+ + Balency 2 34 2.5 Bison 2 198** 23.3 Bryant 2 Not examined 8.3 Camus 2 11* 4.6 HSSB 3 — 3 6** 59 Selleck Nicholls Williams 5 Not examined 2.9 Shepherd Spacemaker + Not examined 1.8 Skarne 4 4 5.3 TWA 1 1 5.8 Wates 3 2** 14.2 Cebus 6 0.5 PAC Not 0.2 Tracoba examined 14 0.5 YDG 33** 2.7° 85.4% *+* + BNausmede roonu sD oOthEe rf igbulorcekss f eoxra dmwienlleindg —s, n1o98 f4ig ures available * 98 dwellings examined at one site — no figures on number of blocks available No figures given in consultants' reports + Visual inspection of complete estate at one site A high proportiono f these blocks have now been demolished Previously reported BRE investigation5 2.4 The condition of dwellings of the Taylor ly 18¾ of the stock, were not specifically investigated Woodrow-Anglian (TWA) system, which account for by BRE. (They are: Anglia, Basingstoke Development 5.8% of the total population of LPS dwellings, has Group, Beale, Belfry, BRS, Carlton, Cebus, Dudley been reported previously by BRE5. The present in- BC, Fram, Fram/BRS, Gerrard, GLE, Gregory, vestigation aimed to carry out inspections to form an Housing Development Consortium, Laing/BRS, overview of the conditions obtaining in the remaining Lecaplan, Metracon, MFC, Modus, NCB, PAC, LPS system, and examples of buildings in 11 LPS Ridgeway, SB2, Southend 3M, Stubbings, Sundh, systems were examined. These 11 systems account for Tracoba, Trentrox, and YDG.) Nevertheless it is con- approximately 80% of the remaining LPS dwellings. sidered that the findings reported here and the conclu- Table 1 gives the numbers of blocks and systems in- sions derived from them are likely to apply in princi- spected by BRE, and also the coverage provided by ple to most large panel systems. the consultants' reports, and compares them with the corresponding total stock (UK figures). Method of working 2.5 Despite the ready co-operation of building owners 2.7 The method of working adopted by BRE com- in making buildings available for inspection, the sam- prised four activities: ple examined was limited necessarily by the availabili- ty of individual dwellings. As a result the sample was 1 Historical reviews of performance with the building not random but nevertheless contained dwellings owners which had been vacated primarily for non-structural reasons. The observations cannot be regarded there- 2 Visual inspection of the structures and opening up fore as forming a statistically valid sample but should joints physically (some 70, of various types) by be regarded as a factual account of a number of case removal of concrete to inspect and examine re- histories. inforcement details and quality of concrete in the connections between precast panels. This was 2.6 In the large panel systems investigated, the forms followed by comparing these observations as far as of panels and methods of connecting them were essen- possible with the specification and drawings for the tially the same. The only more obvious variations structure, with the general details of construction were surface finish, panel arrangement (which may given in the original National Building Agency cer- have structural implications) or layout on site or tificates, or with information gained from similar estate. Some 29 systems, accounting for approximate- buildings of a similar age s s e r P E R B S H I © , y p o C d e l l o r t n o c n U , 2 4 : 9 4 : 5 1 7 0 0 2 / 8 0 / 0 3 , s t e l m a H r e w o T f o h g u o r o B n o d n o L , r e m i t a L K : y p o C d e s n e c i L 3 Testing concrete in the panels and joints for depth 2.8 These activities were undertaken with the co- of carbonation and chloride content*. Some 400 operation of the building owners and in many cases in samples were taken, 30% being from the outer conjunction with their engineers or consultants. In the envelope of which a third were from external sur- latter case the availability of structural drawings and faces the greater number of locations examined provided a greater insight into the condition of the structures and 4 Review of relevant consultants' reports made possible a more efficient survey. •i.• • • S 3 Main findings of BRE investigations Introduction 3.1 The results of inspections carried out by BRE are that specified in the original design. In some cases reported in Appendix A. Appendix B provides sum- these variations consisted of detailed changes such as maries prepared by BRE of reports of investigations smaller diameter bars or changes to the type of end made by building owners and their consultants. The treatment given to the reinforcement. These minor two appendices together give a consistent view of the variations were probably carried out to facilitate con- range and variety of conditions which may be en- struction of the in-situ joints on site. countered in large panel construction. 3.7 In many instances other changes appear to have 3.2 The standard of workmanship and compliance been introduced in successive buildings as construction with the design were found to differ considerably be- proceeded. Those commonly found were the omission tween buildings of the same system and between of site-installed dowel bars between intersecting loop buildings on the same site. However, the standard of bars projecting from the precast components, or the workmanship and construction practice was found to misplacement of loop bars so that no interconnection be reasonably consistent throughout individual was possible. buildings. 3.8 A few examples were found of reinforcement be- 3.3 It is possible to draw only generalised observa- ing cut off or bent back where it projected from the tions and conclusions which apply to the population precast components. In some cases this resulted in of LPS buildings as a whole because of the differ- joints without shear keys and in a lack of physical ences found between buildings. The findings and connection between the precast components other observations do not apply equally to all LPS build- than the bond between the precast concrete and the ings; some buildings were found to be virtually as in-situ concrete. Most cases identified were in vertical designed and to have suffered only minimal deteriora- joints between panels and, in particular, at corner tion. locations. 3.4 The findings are considered below under the four 3.9 Where reinforcement was exposed it was generally headings of reinforcement in joints, reinforcement in found to be in good condition (condition 0 or 1, il- panels, precast concrete, and in-situ concrete, fol- lustrated in Plate 32 in Appendix A). In a few cases in lowed by some points specific to parapets and the outer envelope where joints had been poorly con- balconies. structed the reinforcement condition corresponded to condition 2 (Plate 32). No cases were found where a substantial loss of cross-section had occurred. Reinforcement in jointst 3.5 This reinforcement includes steel positioned on 3.10 Buildings with tying deficienciesw ere found in site, steel cast projecting from precast panels to form all ages of construction inspected, although buildings part of the connection, steel used as a levelling system constructed about 1969 to 1972, immediately after the during erection, connections to non-loadbearing partial collapse of Ronan Point, tended to have fewer panels, and steel added subsequently as part of deviations from the design intentions and, as a result strengthening measures. of redesign, had more substantial connection details specified. There is some evidence which suggests that 3.6 In a substantial number of buildings the arrange- increased vigilance in supervision of construction ment of reinforcement in the joints between the waned in later years. precast components was found to be different from 3.11 Where strengthening to wall/floorj oints had been specified following the partial collapse of Ronan tThroughout this report chloride contents are referred to as a percentage, eg I .0o. These figures are the percentage of total chloride ion by weight of cement. Three categories of chloride tin this report the term 'joints' is used to describe zones in which content are used, ie low, medium and high, which correspond to precast components come together, and the term 'connections' is less than 0.4o, 0.4 to 10¾, and over l.OWo respectively. reserved for the physical devices or mechanisms within the joints. 3 s s e r P E R B S H I © , y p o C d e l l o r t n o c n U , 2 4 : 9 4 : 5 1 7 0 0 2 / 8 0 / 0 3 , s t e l m a H r e w o T f o h g u o r o B n o d n o L , r e m i t a L K : y p o C d e s n e c i L Point, the strengthening measures proposed had Precast concrete usually been implemented on site. There were a few 3.19 The precast wall panels were generally found to cases, however, where the proposed strengthening be well made apart from the lack of care taken in the schemes had not been implemented, had only been positioning of reinforcement (see above). The strength partially implemented or had been poorly installed. of the precast concrete proved to be adequate. 3.12 Levelling bolts were occasionally found displaced 3.20 Recorded carbonation depths in panels are from the vertical, and in a few panels there was minor shown in Figure 2. The results show that the mean cracking around bolt locations. It is not possible to carbonation depth in the panels tested was 11 mm say whether the deformation of the bolts or the with some panels carbonated to a depth of 25 mm or presence of cracks were the result of damage, either more. during manufacture of the panels or during the original construction period, or of load transfer. 3.21 The measurements of chloride contents obtained by BRE for all precast panels are given in Figure 3. 3.13 In many cases storey-height non-loadbearing This shows that chloride was definitely added to 5.2% panels and spandrel panels were supported by the of samples and was probably added to a further main structural walls using metal brackets or angle 12.3%. The BRE results indicate that calcium chloride connections. Little corrosion was found in this form had been added during manufacture to some com- of connection, the main faults identified being the oc- ponents in the Skarne, Bison and HSSB systems and casional omission of bolts (as shown in Plate 18 in that this useS of calcium chloride was intermittent. One Appendix A) and the failure to tighten some of the of the other systems inspected by BRE had chloride bolts provided. contents in the range 0.4 to 1.0% which is insufficient to conclude positively that calcium chloride had been 3.14 Connections of non-loadbearing panels were added but indicates a strong likelihood that it was loose in some places and outwards movement was in- used, although possibly not to the maximum doses dicated by cracking visible at internal vertical joints. allowed at the time. This cracking was observed only in some low-rise buildings and in the upper storeys of a few high-rise 3.22 The most common use of calcium chloride was buildings. found in minor repairs to panels carried out at the factory or after delivery on site. The corners and 3.15 The connection of non-loadbearing spandrel edges of panels were the parts which had been panels to the structural cross walls was the only repaired most commonly using concrete containing substantial provision found for ensuring the longitu- dinal stability in some low-riset erraced dwellings. 120 Reinforcement in panels 110 3.16 The precast panels themselves had generally been 100 manufactured as specified, but in some cases the posi- tion of the reinforcement and occasionally the thick- 90 ness of the skins of sandwich panels were found to be 0a 80 C incorrect. The consistency and accuracy of spacing of n 70 Mean, 11.6mm the reinforcement in the panels was often poor. In 0 Mean without Shepherd Spacemaker, 10.2 mm 60 particular, low concrete cover to the reinforcement at .0 edges of components and around window openings z was found which had given rise to local cracking and spalling due to the corrosion of the reinforcement as a result of carbonationo f the concrete. 3.17 In a few sandwich panels, lateral displacement of the insulating layer during panel manufactureh ad 5 produced uneven thicknesses of concrete 'skins' which Depth of carbonation mm) affected adversely both the concrete cover to the panel reinforcement and the length of embedment of the ties between the skins. r 20 In-situ concrete 3.18 The most widely reported defect in the construc- 8. 10 I_______ ______M_e an, 12.4mm tion of sandwich panels concerned the ties between the two skins of sandwich panels8. Both the number 0 0 25 >25 of ties per panel and the material of manufacture Depth of carbonation mm) were found to be at variance with the original specifications and on occasions differed from one Figure 2 Depths of carbonation in precast and in-situ components building to another on the same site. measured by BRE