Façade inspection for falling objects from tall buildings in Singapore

Purpose – This paper highlights a crucial public safety issue due to falling objects from tall residential buildings in Singapore. A systematic façade inspection regime and a system of evaluation of severity for the detection and assessment of potential falling objects from tall buildings are presented. Design/methodology/approach – The research uses qualitative case study approach with 450 tall residential buildings sampled for the study. The common materials, elements, components with high risk of falling objects, the nature and type of the falling, the critical factors affecting the falling, the respective level of severity, and the effectiveness of various diagnostic techniques and protocols, are summarised. Findings – Façade for tall residential buildings in Singapore comprises mainly cementitious materials cast in situ or precast, with fixtures and architectural features, all of which have potential of falling. The common anomalies arising from each material and fixture/features are identified, the causes evaluated and their implications to future design, construction and maintenance analysed. Originality/value – This study provides original and significant information to a crucial public safety issue, settingdesignandconstructioncriteriathatwillserveasabenchmarkfornewandexistingfacades,applicabletoallcitiesdominatedbytallbuildings.Thepaperpresentsoriginalfigures,checklistsandguidesasabasisfor readers ’ consideration to use according to their respective unique conditions.


Introduction
In the year 2018, the percentage of public residential building in Singapore exceeding the age of 20 and 30 years were 74 and 56%, respectively (Figures 1 and 2).It is not surprising that more and more incidents of falling objects from height have occurred.The city has reported more than 90 incidents in the past three years where parts of facades fell off (Plate 1).Not only have these cases appeared on media headlines, they have gone all the way into the parliament as a serious public safety issue.
A new legislation on periodic façade inspection (PFI) was passed in Singapore on 6 March 2020, subjecting facades of older tall buildings for a mandatory inspection every seven years by a qualified person for potential falling objects.This new inspection regime is applicable to all buildings taller than 13 m and older than 20 years.
This paper discusses a study designed to evaluate the causes of common falling cases and the roles of relevant professionals in preventing or mitigating such occurrences on the outset of the planning/design stage.A systematic façade inspection regime and a system of evaluation of severity, for the detection and assessment of potential falling objects from tall buildings are presented.

Methodology
The state-of-the-art of regional and global counterparts in terms of standards and best practices for façade inspection and maintainability to prevent falling objects from tall buildings were reviewed.Relevant global standards relating to maintainability factors (e.g.SS, BS, ISO, EN, AS and ASTM) were incorporated in the databank as the foundation phase for the creation of a viable and evidenced based appraisal system.
Case and field study of commonly occurring problems that may lead to falling objects from 450 tall residential buildings were conducted with consideration of factors shown in Table 1.
Face-to-face interviews and workshops with the respective professionals involved in the design, construction and operation of the buildings were conducted for detailed investigation on each problem for their (1) problem types; (2) extent of problem; (3) failure mechanism; (4) good practices in design/construction/FM and (5) environmental issues.

Periodic façade inspection
Legislations worldwide similar in principles to that of Singapore's PFI include: (1) US (ASTM, 2019a, b  Determination of whether such defects, deterioration are of any concern; and Recommendation of remedial measures to be carried out.

Façade inspection for falling objects
For building with wide spread defects observed, the Competent Person may recommend a full facade investigation of localised areas or the whole building for BCA's consideration and approval prior to the fall.

Types of façade
A building facade essentially falls into one of the following four types: with their characteristics summarised in Figure 3.
As most residential buildings in Singapore fall under Type 1 and Type 2, this paper focuses on mass and barrier walls.

Potential falling objects
Common anomalies of different "materials" and "features" which would lead to falling objects are summarised in Figures 4 and 5 (Chew, 2016, Chew et al., 2018).
One other potentially high fatal falling object is falling windows.Figure 6 shows the statistics of window falling off from tall buildings in Singapore.Investigations show that about 80% of the fallen windows were casement windows.The majority of them had fallen due to corrosion of the aluminium rivets holding the friction stays, as well as improper design; installation; maintenance; and wear and tear of the friction stays.Façade inspection for falling objects (Chew et al., 1997, Chew, 1998) are some of the methods used (Plate 2).Areas with dilapidation and displacement of façade elements are identified, together with areas with potential falling objects (latent defects), for detailed investigation in Stage 2.

Façade inspection
Stage 2 -close-up hands-on inspection of each elevation.This is the stage to conduct close-up hands-on inspection of at least 10% of each elevation, as identified from Stage 1.This stage requires the deployment of façade access systems.A variety of instrumentation from tapping to non-destructive and destructive tests may be utilised to examine the extent and severity of the anomalies (Chew, 1992, 1999a, b, c, 2000a, b, c, Chew et al., 2001).Recommendations for remedial measures are made based on risk evaluation of the results (Table 3).For building with wide spread defects observed, a full facade investigation of Stage 2 may be recommended.

Summary of results
Tables 4-6 summarise: (1) Lessons learnt from past and present mistakes, showing the causations of the anomaly, who is responsible for what and how to prevent the occurrence of the anomaly and (2) Recommendations for new buildings in the future, to consider issues related to design, construction and maintenance at the outset of the planning stage, to prevent the occurrence of falling objects from facades, with relevant international standards specified.
Table 4 shows the concerns for design, construction and maintenance on the outset of the planning/design stage, for structural components, e.g.column, beams, slabs, walls and other load bearing and non-loading components.Table 5 shows the concerns for design, construction and maintenance on the outset of the planning/design stage, for architectural components, e.g.finishes, furnishings and other elements that contribute to the aesthetic value and liveability.
Table 6 shows the concerns for design, construction and maintenance on the outset of the planning/design stage, for service components which include vertical and horizontal circulation systems, electro-mechanical and sanitary connections.(continued ) imperative that all façades must be designed, constructed and maintained adequately with public safety in mind, preventing falling objects from height.The new legislation Singapore recently implemented on PFI is discussed and guides and checklists are recommended.In addition to existing buildings, the paper sets quality benchmarks for future new buildings, spearheading the integration of designers, constructors and facility managers on the outset of the planning/design stage, by providing easy to read tables summarising (1) knowledge learnt from past mistakes and (2) quality benchmarks.Based on predictive/preventive approach, the tables serve to define acceptable standards in design, construction and operation practices to prevent falling objects from facades.
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IJBPA 41,6 Figure 1.Percentage of public residential building in Singapore exceeding the age of 20 years

Table 4 .
Façadestructural ConclusionsFalling objects from tall building façades including materials, components and features/ fixtures are life threatening public safety issue that have been reported globally.It

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Admixtures for concrete, mortar and grout -Part 2 : Definitions, requirements -Concrete admixtures -Definitions, requirements, conformity, marking and labelling BS 6037-1Eurocode 2: Design of concrete structures, Part 1-1 General rules and rules for buildings BS 6093