SCM CASE Study - Opal Tower Case Study PDF

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Opal Tower Case Study...

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SUSTIANABLE CONSTRUCTION MATERIALS - 301339

Contents

Introduction

2

Description

2

Research

3

Initial Observed Damage

3

Causes of Damage

4

Materials

4

Construction and Structural Design

4

Discussion

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Suitability of Materials

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Standards and Regulations

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Conclusions

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References

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Introduction The structural integrity of a building is a key objective of all construction projects. It ensures the safety of the occupants and the quality and longevity of a building. Project managers must ensure that suitable building components are used correctly according to Australian standards and regulations. The objective of a structurally sound building should not be the only characteristic of a successful project, the correct use of building materials to achieve sustainability must also be a key focus of builders. When building standards are not followed and weak building materials are used, buildings can develop problems and defects that are often costly and problematic for builders, residents and stakeholders. There are many case studies that analyse defects in projects that do not follow regulations and do not consist of durable building components. The investigation into structural defects of Sydney’s Opal Tower is an effective case study that focuses on the correct use of building materials and the importance of regulations and certification in construction. The Opal Tower is a well-known apartment complex located at Sydney Olympic Park. The Green tower is a high-rise residential block that consists of 36 storeys and a 3-level basement car park. The construction of the complex was completed in 2018 and residents were allowed to occupy the building in the second half of 2018. It was not until Christmas Eve of 2018 that the 392 residents heard loud noises coming from internal structure of the building. Consequent investigations into the noises identified cracks in load bearing panels Figure 1. The Opal Tower at Sydney Olympic Park (Tabet, on level 10. Due to safety concerns residents 2019) were asked to evacuate the building on Christmas eve 2018. The Opal Tower case study is an effective investigation that supports this report. It will be used to support the argument that suitable building components must be used in construction, and that following Australian standards is important to achieve durable buildings. Description The following report will focus on the effectiveness of building components in construction and the application of Australian standards and regulations. The Opal Tower Investigation will be closely referenced throughout the report. The Opal Tower Investigation report identified numerous causes of damage that align with focus of this report. These causes included (Unisearch Expert Opinion Services, 2019): o Poor quality construction materials o Issues with the foundations, namely differential settlement of the pad footings supporting the building’s columns o Poor quality workmanship or errors during construction o Flaws or errors in the design of the structural systems. o Failure to correctly certify the building against relative Australian Standards 2

The investigation highlights the importance of quality construction materials and effective uses of building systems. Many high-rise developments are similar to the Opal Tower and consist predominately of concrete building materials. Multiple Australian standards were not met during the construction of Opal Tower, these specific standards will be further covered in this report, emphasising the importance of regulations and certification in construction. It should also be noted that Opal Tower’s defects may have been a result of poor design, specifically the thickness of the concrete building system used in load bearing areas of the structure. The report will further discuss the causes of damage and how these causes can be avoided in similar projects within the construction industry. Research The Opal Tower Investigation Report is closely referenced throughout this report. The investigation, research and data that is supplied in the Opal Tower Report was sourced by Unisearch Expert Opinion Services. The contents, personal opinions and recommendations within the report are that of John Carter, Mark Hoffman and Stephen Foster. The Opal Tower case study is an effective source that closely relates to the topics of sustainable building components and the importance of regulation compliance. Initial Observed Damage The areas of the tower that had sustained significant damage were located on Levels 4 and 10. On Level 4 there were cracks on multiple hob beams spanning between columns and the precast panels that they were placed on; these were considered major damage. The damage that was observed on a hob beam above column C34 indicated that the reinforced steal had bowed outwards from the beam. Also noticeable is a lack of cross-tie reinforcement to guard against splitting failure. (Unisearch Expert Opinion Services, 2019). From the numerical analysis, field observations and hand calculations undertaken by Unisearch Expert Opinion Services, it was determined that the damages on level 4 involved: 1. With the design loads assumed, the strength of the Level 4 hob beam spanning columns C16 and C34 does not meet the requirements of AS3600–2009 2. cover concrete above and adjacent to column C34 indicated that the beam is in a state of high stress 3. The strength of the concrete in the hob beam was lower than that assumed in the design 4. Splitting forces are significant and the tie-reinforcement provided was inadequate to resist these forces. 5. The cause of the damage to the hob was by bursting (also known as splitting) of the concrete in the hob beam section. On Level 10 there was also cracks on a hob beam spanning between columns and the panel that the beam was resting on. The hob beam located above column C38 shows splitting along the lines of shear compression, which indicates high levels of stress. There are also indications of bursting and bearing stress on the hob beam which would have been major influences on the formation of the surface failures. From the research and investigation undertaken by Unisearch, it was determined that damages on Level 10 involved: 3

1. Design loads provided by WSP indicated the strength of the Level 10 hob beam spanning columns C21 and C38 and the wall panel above it do not meet the requirements of AS3600–2009 2. The observed spalling of the hob beam cover concrete above and adjacent to column C38 implies that the beam is in a state of high stress 3. Splitting of the wall panel and hob beam are evident and the area of tie reinforcement provided was inadequate to control these forces 4. A number of construction issues were observed that may have added to the adverse stress conditions. These include an electrical conduit passing through the cover concrete in a zone of high stress immediately above column C38 and a patch repair of the wall panel, again in a high stress region

Figure 2. Damaged hob beam on Level 10 (Unisearch Expert Opinion Services, 2019)

The observed damage that occurred on the separate levels are thought to be unrelated to each other, as the vertical load lines of the damaged area are different. Causes of Damage From the initial observed damages on levels 4 and 10 of Opal tower there were many multiple hypothesized causes of damage. The observed damages all involved cracking of concrete members in key load bearing areas. The suspected causes included: o Poor quality construction materials, components and systems o Issues with the foundation of the building, settlement, footings o Environmental factors e.g., major storms, winds, extreme changes in temperature o Errors in design of structural systems o Poor quality construction Environmental factors were determined to be very unlikely, as the recorded weather prior to December 2018 showed no extreme weather conditions. Materials 4

Field tests undertaken by Unisearch of the structural integrity of the damaged hob beams indicate that the strength of poured concrete may not have complied with Australian standards. During our investigations, and subsequent to the issue of our interim report, records of strength for the concrete used to construct the hob beam were provided to us. These reveal 28-day strengths of these concrete samples as 50 MPa, where 65 MPa concrete was ordered for supply, indicating that the concrete in the hob may also have been of a lower strength (Unisearch Expert Opinion Services, 2019). Construction and Structural Design There are multiple areas of the built structure that are suspected to not comply with Australian standards. AS3600 is suspected to have not been followed in multiple load bearing columns, specifically the damaged hob beams on levels 4 and 10. Concrete structures that do not comply with AS3600 do not meet the requirements of the National Construction Code Volume 1 (NCC). There are multiple areas of the constructed tower that after inspection, indicated that construction differed from the original design and standards. Grouting: Initial design drawings indicate that full grout coverage is expected between panels and hob beams. During construction approximately only 50-70% of the joint was grouted. Coring of the level 4 hob beam indicated that grouting was incomplete in some areas. The partial grout coverage is suspected to have influenced eccentric load bearing and bursting stress on hob beams. Inadequate Concrete Cover: Concrete cover of the hob beam spanning columns C21 and C38 on level 10 was inadequate which resulted in failed AS compliance and reduced strength. encroachment of column bars, and the placement of an electrical conduit also contributed to the reduced strength of the hob beam and column. Inadequate Tensile Capacity: – After coring and investigation of Panel A, that rests on the hob beam spanning columns C21 and C38 on Level 10. It was discovered that 20 mm diameter reinforcement bars were used instead of 28 mm diameter bars. there was also no evidence that reinforcement cross ties were used to resist bursting forces. Discussion The information and data obtained from the Opal Tower Investigation Report is very informative, detailed and clearly outlines the damages incurred on the tower and the potential causes of these damages. It should be noted that the causes of damage on Opal Tower were directly related to the construction and structural design of the building. Multiple Australian standards were not met which resulted in the finished project not being durable. The concrete components of the building failed to meet regulations which was influenced by the unsuitable materials used in construction. Suitability of Materials Used

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The Opal Tower is a reinforced concrete building with post-tensioned concrete slabs thought-out the 36-storey structure. Concrete is used throughout the tower, most importantly in the inset slots located on the external face of the building and the hob beams above these columns. Unit learning outcome 4 outlines the importance of suitable materials in building components used in construction. The Opal Tower case study discusses multiple possible causes of damage, with the use of building materials being a strong contributing factor. The strength of the concrete used in the damage hob beams was significantly below the 65Mpa required strength which indicates that the strength of the concrete greatly influenced the damages incurred on the building. Due to the large size and height of the Opal Tower, concrete is the most suitable building material to be used in construction. However, if the concrete is not effectively used and poured correctly, the building will fail to be durable. Using the most suitable material is critical in building, but how the material is used and sourced is just as important. Concrete must be used effectively in construction in accordance with building regulations and additional reinforcement. The strength of concrete must be closely monitored during pouring and after the concrete has set, ensuring that the concrete structure has kept its strength. Standards and Regulations Multiple Australians building regulations were not met during the construction of the Opal Tower which led to the cracking of load bearing hob beams and structural columns. As previously discussed, concrete strengths in the cracked hob beams did not meet the 65MPa strength as per the requirements of AS3600–2009. Minimal grouting coverage in the joints of hob beams failed to meet requirements of design drawings and contributed to the reduced strength of the hob beams. Minimal uses of reinforcement crossties throughout the tower are also thought to have contributed to the reduced strength of the building hob beams. The Opal Tower case study is a great example of the consequences that builders are faced when Australian standards are not met in construction. Unit learning outcome 5 emphasizes the importance of Australian standards and regulations relating to eco-friendly and durable buildings. Regulations are essential and must be met for successful projects to be delivered. The standards that were not met during the construction of Opal Tower did not have any immediate consequences. It was not until after project completion that the damages were discovered and the tower was not considered to be a durable building. There are no short cuts in construction, building regulations must always be followed for builders to deliver successful projects. Conclusion There are many obstacles and challenges involved when delivering large scale projects in the construction industry. It is important that builders assess the suitability of materials used in construction and apply Australian standards and regulations to their construction activities. The Opal Tower Case study is a great example of the negative outcomes that occur when builders are not diligent in their project delivery and fail to use the correct building components in compliance with national standards. Detailed reports of the damages that incurred on Sydney’s Opal Tower, are an effective learning source that other builders can learn from. The flaws that were outlined during the construction and design of the tower emphasize the importance of suitable building materials and close compliance of relative Australian standards. 6

References (Harvard) Calderwood, K. (2020). 500 New Defects Discovered at Opal Tower as Unit Owners Launch Legal Action. [online] www.abc.net.au. Available at: https://www.abc.net.au/news/2020-06-29/opal-tower-owners-launchsupreme-court-case-over-new-defects/12402444. Ding, G.K.C. (2008). Sustainable construction—The Role of Environmental Assessment Tools. Journal of Environmental Management, 86(3), pp.451–464. Tabet, T. (2019). Sydney’s Opal Tower: What We Know so Far. [online] The Urban Developer. Available at: https://www.theurbandeveloper.com/articles/opal-tower-what-we-know-so-far. Unisearch Expert Opinion Services (2019). OPAL TOWER INVESTIGATION FINAL REPORT Independent Advice to NSW Minister for Planning and Housing. [online] . Available at: https://www.planning.nsw.gov.au/-/media/Files/DPE/Reports/opal-tower-investigation-final-report-2018-0222.pdf. Windapo, A.O. (2013). Relationship between Degree of risk, Cost and Level of Compliance to Occupational Health and Safety Regulations in Construction. Construction Economics and Building, 13(2), pp.67–82.

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