Assessment of cantilevered concrete balconies by means of practically oriented evaluation tools

. Facing the aging building stock, challenging times can be expected with a sharp increase of reinforced concrete buildings requiring maintenance, repair and/or replacement. For the condition assessment of existing reinforced concrete structures an in-depth and reliable inspection strategy and evaluation is essential to come to a durable and service-life extending repair strategy. A stepwise protocol to evaluate the condition and remaining bearing capacity of cantilevered reinforced concrete (RC) balconies is presented in this paper. Corrosion causing the reduction of the steel section, incorrect positioning of the reinforcement and/or higher loads are the main reasons service life might not be reached or the failure of the balcony can occur. As mentioned in EN 1504-9 and NEN 8700, an adequate diagnosis prior to repair showing the cause and extent of the damage is important (i) to determine the actual bearing capacity, (ii) to make an estimation of the residual lifespan and (iii) to select a durable repair technique and/or define maintenance requirements. In this paper a newly developed protocol for the assessment of the condition and the bearing capacity of the cantilevered RC balconies of a high-rise residential building is demonstrated. A semi-probabilistic method is used by applying partial safety factors based on Eurocode guidelines and fib Bulletin 80. The condition of the structure is determined based on NEN2767 regulations. As corrosion is the main contributor to the degradation of existing concrete structures, a chloride contaminated building with damaged reinforced concrete balconies is selected as case study in order to demonstrate the applicability of the developed protocol and tools.


Introduction
In the late 60s and the mid-70s a significant amount of reinforced concrete structures were build.These structures usually have a service life of approximately 50 years, so we are expecting and facing challenging times with regards to assessment, durable repair and rehabilitation of these reinforced buildings.According to EN 1504-9 the need for an investigation and damage diagnosis prior to a durable repair method is a critical step in the whole process.The repair might fail in early stage when the cause of the problem was not (completely) identified [1].In the past decades numerous incidents of collapsed RC balconies are reported worldwide [2] and it can be expected that the frequency of cases with collapsing concrete elements might increase in time if no actions are undertaken.It has to be determined whether the structural integrity of the cantilevered reinforced concrete elements is endangered or not, in order the avoid sudden collapse.The main cause of deterioration is corrosion of the reinforcement: more than 75% of the damaged reinforced concrete structures are in a way related to corrosion, induced by carbonation of the surrounding cementitious matrix and/or chloride ingress.
Corrosion affects the durability of a concrete structure, resulting in cracks and delamination of concrete parts due to the expansive nature of corroding steel.Furthermore, the structural safety of the structure can be jeopardized as corrosion reduces the cross section of the reinforcement bars in a uniform (due to carbonation) or local way (pitting corrosion initiated by chlorides) and might lead to reduction of the ultimate strain [3].Besides a reduction of the steel area caused by corrosion, lower positioning of the reinforcement and higher applied loadings are reported as the main contributing factors to the failure of cantilevered RC balconies [4].An adequate diagnosis prior to repair showing the cause and extent of the damage is important (i) to determine the actual bearing capacity, (ii) to make an estimation of the residual lifespan and (iii) to select a durable repair technique and/or define maintenance requirements.Codes and regulations mention the importance of a diagnosis, but do not provide a method for obtaining a diagnosis showing the cause and extent of the damage.In this paper a stepwise protocol to evaluate the condition and the actual remaining bearing capacity of cantilevered reinforced concrete (RC) balconies is presented.

Protocol for cantilevered balconies 2.1 Phase 0 -Tender stage: introduction and the need for assessment
The need for an evaluation of the existing structure prior to repair is stated in regulations however a clear method for obtaining a diagnosis is not provided.Based on a critical review of existing standards and guidelines, integrating existing knowledge and on-site experience, a stepwise protocol to evaluate the condition and remaining bearing capacity of cantilevered reinforced concrete (RC) balconies is developed (Figure 1), based on the draft proposal mentioned in [5].The evaluation of (i) the remaining bearing capacity and (ii) the durability (with focus on corrosion damage) are included.The protocol exist of five consecutive phases: 0) tender stage, 1) inspection stage, 2) research stage, 3) assessment stage and 4) report stage.

Fig. 1. Stepwise protocol for assessment of cantilevered RC balconies
Prior to the investigation, it has to be decided whether an assessment study is needed.Various scenarios exist for which it is urged to investigate the RC balconies: damage can be expected due to the age of the building (end of service life is approaching) or the environment (exterior, sea or saline), damage of the RC elements is already observed, etc.Note that in The Netherlands the assessment of the condition of existing cantilevered RC balconies (more specific: gallery type) is strictly regulated and legally obligated, while this is not the case (yet) in Belgium.However numerous cases of RC buildings and balconies in need of adequate and durable rehabilitation can be expected in the upcoming years.

Phase 1 -Inspection stage: inventory, file investigation and visual inspection
The file investigation includes the collection of information of the original design (plans, reinforcement sketches, as-built reports, etc.).Information about previous repair actions and/or a previous inspection reports are also part of the file investigation.For existing structures, the collection of these documents can be a labour-intensive task.Furthermore, high chances exist on not finding data for aged buildings.In addition, the requirements of the owners also determine the preconditions of the investigation: execution time, available budget and desired lifespan (extension) of the balconies.
A thorough visual inspection of 100% of the balconies (top, bottom and front) with inventory of observed damage (quantification and qualification) is an additional part of phase 1.A schematic visualisation and summary of the considered and most expected defects and damage mechanisms for RC balconies are depicted in Figure 2 and Table 1: -Mechanical damage of concrete: M1 -M3; -Physical damage of concrete: F1 -F6; -Chemical damage of concrete: CH1 and CH2 -Corrosion related damage due to expansive nature of corroding steel reinforcement: CO1-CO3; Corrosion, initiated by carbonation and/or chlorides, is the main deteriorating mechanism in most cases.Corrosion initiated by carbonatation is often visible at the underside or front of the balconies, causing cracks and delamination of large concrete parts (CO2, Figure 2).Corrosion initiated by chlorides leads to local phenomena such as pitting corrosion, which reduces the reinforcement area (CO3, Figure 2) and is mentioned as one of the reasons for the collapse of a gallery in Leeuwarden, the Netherlands in 2011 [4].Therefore the severity of corrosion related damage is high.
Once the visual inspection of the balconies is finalized, the condition of the RC elements can be determined, based on NEN 2767 regulations, and in first stage entirely linked to visual observations.Each element is ranked with a score between 1 (excellent condition) and 6 (extremely poor condition).Once the deterioration mechanisms and damage causes of the RC balconies are determined by means of field testing, sampling and lab testing (Phase 2), the condition score of each balcony can be updated to the actual and proven damage history (Phase 3).

Phase 2 -Research stage: (non-)destructive testing and sampling
Several non-destructive (NDT) and (semi-)destructive tests (SDT/DT) can be used to identify the damage mechanisms and causes, to map the (potential) danger zones and to evaluate the remaining bearing capacity.Although proof loading may be a useful method to demonstrate the safety of existing structures this is not included in the protocol.The proposed step-by-step method is intended to avoid overkill of (destructive) testing measurements: the excessive phasing of the examinations can eventually lead to a higher cost and more disturbance.Additional investigations to support the design of repair techniques (e.g.concrete resistivity in case of cathodic protection) are also not included in the described protocol.A brief description of the visual observed deterioration and location of the collected samples is drawn up for each measuring location, illustrated by pictures on site (NDT1).The dimensions (span, thickness) of the concrete slab are measured (NDT2) and finishing layers are identified for which a combination of (non-)destructive techniques (Ground-penetrating radar (GPR), core drilling) are necessary in some cases.
In [4] it is recommended to investigate at least 10% of the balconies by means of non-destructive techniques, however without any further specifications.An accurate covermeter (electromagnetic rebar locator) is used to determine the diameter, the depth and the spacing distance between the rebars.For calculations of the bearing capacity, the characteristics of the reinforcement perpendicular to the facade at the top are determined.A lower position of the main reinforcement (e.g. by errors during construction) is one of the main reasons contributing to an insufficient bearing capacity.It is therefore strongly advised to investigate the entire balcony (or at least 30% in case of continues galleries) in order to come to a reliable conclusion with regards to the bearing capacity.GPR can also be very useful to locate the reinforcement bars in case the thickness of finishing layers exceeds the capacity of the covermeter (approximately 60-80 mm) or different layers of reinforcement are observed.The location of the rebars at the bottom and front are determined for the residual lifetime estimations (durability damage).The attributive properties of the reinforcement (diameter, characteristic steel strength fyk) have to be determined/validated in a destructive way (DT1, Figure 3), as they are an essential property needed for the determination of the actual bearing capacity.(=2400/300) is applied.In case values of 1,0 m% (or higher) are found, there is a considerable risk of pitting corrosion of the steel.Values inferior to 0,4 m% appear to be rather harmless.Chlorides may have been initially admixed (by use of binding accelerator or polluted raw materials) or penetrated (use of de-icing salts, cleaning products, marine environment).However, the number of tests carried out may depend on the suspicion whether or not chlorides will be present.Weakened and delaminated areas can be identified by means of the non-destructive technique.In case of an increased risk of corrosion (e.g.lack of concrete cover, high chloride concentration, etc.) potential mapping (SDT1) is a valuable technique in order to identify possible corroding hot spots (Figure 4).As local connection with the reinforcement is necessary, the technique is semi-destructive.

Condition assessment
Once the inspection of the balconies is finalized, the field and lab testing is finalized and the damage causes is identified, the condition of the RC elements is determined, based on NEN 2767 regulations.Each element is ranked with a score between 1 (excellent condition) and 6 (extremely poor condition), based on severity, extent and intensity of the damage.The severity is directly linked to the identification of the damage mechanism, as mentioned in Table 1.All types concrete damage that can be expected for RC balconies are classified: 1 = minor severity, 2 = average severity, 3 = critical severity.The extent of a defect is considered in relation to its size: incidental (<2%); local (2% to 10%); regularly (10% to 30%); substantially (30% to 70%); general (>70%).The intensity defines the stage of the defect, divided in three classes: initial (damage process is initiated), advanced (damage process is ongoing) and final (damage process is in its end stadium).By combining severity, intensity and extend of the defect, a condition score can be linked to the investigated balcony (Table 2): 1 = excellent condition, 2 = good condition, 3 = average condition, 4 = poor condition, 5 = bad condition, 6 = extremely poor condition.The defect which causes the highest score determines the total condition score of the balcony.A weighted average can be calculated for the balconies on the same floor or façade.

Table 2. Condition score ranking table for critical severity (3) defects
After Phase 1 of the protocol, the condition score is solely based on visual characteristics.However, visual characteristics are no fully reliable indication of the bearing capacity and/or damage cause of the structure.Furthermore certain defects may be hidden by the finishing layers, which supports the fact that additional in depth investigations by means of (non-)destructive techniques is critical in order to increase the reliability of the initial conditions score.Therefore, it is important to re-calculate an updated condition score based on an extended investigation survey or once the assessment stage of durability is finished.The bearing capacity is assessed separately, and is not included in the condition score.Besides the visual characteristics (the condition score), several factors (and combinations) can increase the risk of failure: the absence of an effective waterproofing, structure located in a marine environment [6], the age of the construction, a high span of the cantilever in combination with a heavy-weight railing and the use of de-icing salts are examples of indicators for a higher risk.

Assessment of damage and actual bearing capacity
Once the tender, inspection and research stage are performed and the condition score is determined, the acquired information can be used in order to come to a funded assessment of the damage (with regards to the durability of the structure) and the bearing capacity of the cantilevered RC balcony.This approach is visualized in Figure 5.Note that the protocol mainly focusses on corrosion damaged RC balconies.

Durability related damage assessment
First the durability related damage is evaluated, in the scope of determining the probability of corrosion of the steel reinforcement to occur within a certain evaluation period teval.As corrosion might influence the bearing capacity of the RC elements, it is important to assess the durability first, prior to the assessment of the bearing capacity.

Fig. 5. Assessment protocol for damage/durability and bearing capacity of RC balconies, with focus on reinforcement corrosion
Therefore it is necessary to determine i) if corrosion can be expected within the evaluation period, and (ii) what mechanism might cause possible depassivation (chloride ingress and/or carbonation).Preventive life extending and curative repair techniques are directly linked to the durability related condition of the element: - Note that by means of probabilistic approaches, e.g.[7] the probability of failure with regards to depassivation of the reinforcement can be determined and evaluated.As input for this analysis, the age of the structure, the concrete cover, the depth of the carbonation front and chloride content profiling is needed and can be determined (non-)destructively in the preceding research stage (Phase 2).

Bearing capacity assessment
Once the durability related damage is evaluated, the remaining bearing capacity of the cantilevered RC balconies can be evaluated.To be able to evaluate the remaining bearing capacity several input parameters are necessary and need to be determined by means of the preliminary file survey (Phase 1) and/or on-site testing (Phase 2): the dimensions of the slab, the position of the reinforcement (i.e.concrete cover), the steel section, the material properties (steel and concrete strength) and the durability related condition of the element (concrete and/or steel damage).Calculations are performed in Ultimate Limit State (ULS).Insufficient load-bearing capacity due to reduction of steel section or by execution errors such as incorrect positioning of the reinforcement can cause suddenly failure of the cantilevered structure.
The comparison of the assessment value of the applied and the resistant bending moment (MEa vs. MRa respectively) is the critical failure mechanism for cantilevered slabs.
At first, the remaining bearing capacity of the design is checked.This calculation can only be made possible if the file survey was successful and the necessary input parameters are known.If not, this check-up is not executable.Consecutively, depending on the outcome of the damage assessment, different scenarios are possible (Figure 5).For case A, if initiation of depassivation is not yet reached (I) and not expected within teval, no reduction of the steel section due to corrosion is expected and concrete quality is intact.A safe estimation is made for the concrete strength and steel quality without performing any on-site destructive sampling and lab testing.If there is no presumption of corrosion damage (no visible corrosion damage, carbonation front is lower the concrete cover, chloride content is lower than the critical value) and the remaining bearing capacity is sufficient (i.e.MEa < MRa), no additional inspection is needed and the bearing capacity is acceptable.However, if MEa exceeds MRa it might be useful to determine steel quality and concrete compressive strength on site rather than using estimated conservative values.In case depassivation is expected or already occurred within teval (case B, I-II-III), the bearing capacity is checked for a reference period tref of 1 year, taking into account a reduced steel cross section As,corr of which it might be expected that corrosion reduced the amount of steel, hence reducing the resisting bending moment.Therefore additional investigation is needed to evaluate the actual condition of the steel reinforcement (e.g.potential mapping, destructive visualization of the steel) in the final year of teval.If the bearing capacity is not sufficient in that case, due to the low position of the reinforcement, repair and/or strengthening measures should be prescribed.Protection and monitoring is advised in the other case where the bearing capacity is sufficient, as the propagation of the corrosion process might worsen the condition rapidly.
For the evaluation of the bearing capacity, the comparison of the applied and the resistant bending moment (MEa vs. MRa respectively) is the critical failure mechanism for cantilevered slabs.The remaining distributed variable load qk,rem which the cantilevered RC balcony has to withstand aside from the permanent loadings (weight, finishing layers, etc.), is therefore determined by means of Equation 1.It should meet the required values prescribed in EN 1991-1: 2.5 -4.0 kN/m².
where fyk is the characteristic yield strength of reinforcing steel, fck is the characteristic value of cylinder compressive concrete strength, ω1 is the mechanical reinforcement ratio, μd is the relative bending moment, As1 is the area of longitudinal tension reinforcement, d is the effective depth, b is the (unit) width of the element, l is the span length, gk is the characteristic value of the distributed permanent load, pk is the characteristic value of the distributed permanent load of the finishing layers and Pk is the characteristic value of the permanent load due to the railing.
The reliability of a new concrete structure is mostly verified based on a semi-probabilistic method by applying partial factors according to the Eurocodes (EC).The partial safety factors for material properties γs-γc and for applied loading γp-γq are mentioned in EN 1990-1992.However, updating existing buildings to current standards requires a greater investment than implementing these requirements into a design.In addition, the remaining working life is often smaller than the assumed 50 years for new buildings and the actual structural condition can be obtained by on-site measurements.Therefore, the often conservative requirements for new building might underestimate the behaviour of existing structures.Alternative partial factors for existing structures are presented in fib Bulletin 80.The Additional Partial Factor Method (APFM) as mentioned in [8] will be considered for evaluating the bearing capacity.The partial factors for existing structures according to APFM are determined by multiplying an adjustment factor with the partial factors given in the Eurocode.This adjustment factor for a variable is calculated considering alternative values for the reliability index β", coefficient of variation V" and reference period tref".When β", V" and tref" are equal to the values implemented for new structures, the adjustment factor is set to 1, and therefore this methodology is compatible to the framework of the Eurocode [8].It should however be emphasized that fib Bulletin 80 has been developed for non-deteriorating structures.Hence, the partial factors suggested in fib Bulletin 80 should be applied only in case (i) no deterioration is currently present and corrosion initiation is not expected to occur within the evaluation period (i.e. the desired remaining working life), or (ii) it is used to only assess whether at the point in time of the investigation there is already an insufficient safety level (i.e.already without considering the structure is envisaged to further deteriorate), enabling to detect already a required intervention on that basis.In case one needs to assess the safety level considering deterioration, the verification should take basis in an annual verification and partial factors can be obtained from references [12,13].
The geometrical and material properties obtained during Phase 2 are used in this assessment stage.The dimensions of the RC balcony (width, length, thickness) can be easily obtained on site (NDT2).If the material properties fyk and fck are unknow a rather conservative estimation is made.However, if additional testing is performed (DT4-DT5), the in situ characteristic value in situ fck,is and/or fyk,is can be integrated in the calculations.One of the key parameters is the effective depth has a decisive effect on the bearing capacity of the cantilevered slab as mentioned in [5].Generally, an average value of the effective depth is obtained from the reinforcement detection measurements (NDT3) at the upside of the balcony according to Equation 5: dm = hrc -μc -φ/2 (5) where dm is the average value of the effective depth, hrc is the thickness of the concrete element, μc is the average concrete cover and φ the diameter of reinforcement bar.However, for existing structures, a wide range of individual results of the concrete cover can be found at the investigated location used for calculating a mean value of the effective depth.Therefore, an updated value for d, indicated as d", is considered by taken into account the coefficient of variation of the measurements in situ Vd,is and the number of measurements (Equation 6).According to EN 1992-1-1, the nominal concrete cover is defined as the minimal cover cmin plus an allowance in design for deviation cdev.The value of cdev is often set to 10 mm.The coefficient of variation of the effective depth assumed in the design phase is represented as Vd1 and is considering the standard deviation of a uniform distribution with range [-10mm;10mm].

Vd,is=
where σc is the standard deviation of concrete cover and n the number of measurements.If the measured coefficient of variation Vd,is exceeds the assumed Vd1 then Vd2 is considered for d".If Vd,is ≤ Vd1, then d" equals d.
where α is a sensitivity factor and set to 0.8, as the effective depth is a dominant variable, and β" is the reliability index for the existing structure taking into account economic and human safety considerations [13].
The factor for multiplying d to obtain d" depending on Vd2 and β" is given in Figure 6.

Phase 4 -Report stage: intervention decision
Once Phase 3 is finalized the conclusions of the investigation are summarized in an inspection report.This report includes the final condition score and complete durability related damage diagnosis, evaluation of the remaining bearing capacity and residual life estimation.Based on the results, recommendations to continuous monitoring, preventive maintenance and/or curative repair (possible techniques, materials, urgent intervention,...) based on the principles described in EN 1504-9 should be created, preferably in a life cycle perspective with respect to both costs and environmental impact [11].

Case study
A high rise building situated in Brussels with cantilevered RC balconies (NW oriented) is selected to demonstrate the applicability of the developed protocol.This building, constructed in 1961, has 16 floor: each floor has a length of 33 meters and the span of the cantilever is 1.5 meters.The RC plate has a thickness of 100 mm and is covered with a cementitious screed of 30 mm, representing an exposed area of approximately 100 m² per floor.Additional info can be found in [5].Three floors (F1, F8 and F16) were selected to evaluate the durability and the  In Phase 2 an in depth field survey and investigation was performed on 9/17 floors of which F1, F8 and F16 are selected for the assessment demonstration of this paper.First of all high chloride contents (exceeding Ccrit) were found at the level of the rebars for floor F8 and F16 (2.38 m% cement and 5.94 m% cement), most likely caused by the use of CaCl2 as binding accelerator.According to the protocol it therefore can be assumed that depassivation and corrosion is most likely to be present in teval.Assessment with regards to durability related damage leads to the conclusion that repair and protection will be needed (I and II).Furthermore, the previously obtained condition score can be upgraded.As corrosion is initiated by mixed-in chlorides all floors are ranked with condition score 5, as corrosion damage has a critical severity, the process is believed to occur generally (>70%) due to the presence of mixed-in chlorides and the corrosion process is already in an advanced stage as rust stains are noticeable .
Finally the bearing capacity of the RC balconies is checked.As original plans were available, the design of the RC balconies can be evaluated.A recalculation based on the partial factors method according to Eurocode regulations results in a remaining capacity of 3.97 kN/m², which is acceptable.
For the three selected floors, the upper reinforcement was detected by a covermeter, the non-destructively obtained values were checked by core drilling and the diameter of the rebars was validated destructively and actually equals 10 mm [15].For F1 lower values for the mean effective depth were found (57,6 mm), F16 revealed higher values (87,2 mm) , where 77,1 mm was found for F8.According to the results of the field survey, F1 is determined to 'Case A' and F8 and F16 to 'Case B' (Figure 5).The partial factors according fib Bulletin 80 for existing balconies are determined using the Additional Partial Factor Method (APFM) with β" = 3.0 and tref" = 50 years for case A and 1 year for case B, the coefficient of variation is equal to the value considered for new structures.As high chloride contents (>2m%cement) were found at F8 and F16 it can be expected that corrosion already started.Additional testing was executed: potential mapping (SDT1) in combination with destructive core drilling for visualization of the steel rebars.A clear difference between the two floors is noticeable (Figure 4): the observed crack on F16 accelerates the corrosion which was also observed visually: Qcorr approximately 20% for F16 (Figure 3), negligible for F8.Results for F1, F8 and F16 according to APFM are given in Figure 8.The insufficient bearing capacity of F1 is a result of the low position of the rebars, while for F16 it is a consequence of the reduction of As1 due to the corrosion process.This case clearly demonstrates the feasibility of the protocol for assessment of cantilevered concrete balconies.It revealed that floor F1 and floor F16 need adequate repair and strengthening due to lower positioning of the rebars (F1) and severe corrosion due to crack parallel to the building (F16) respectively.Although high chloride concentrations were found in floor F8, the bearing capacity is sufficient.Additional testing by means of potential mapping (SDT1) and destructive validation (DT1) did not reveal any corrosion related damage.Nevertheless, condition monitoring is recommended.

Fig. 2 .
Fig. 2. Observed damage on top, bottom and side of cantilevered RC balconies.
Based on the prior visual investigation of Phase 1 different area are selected on which Phase 2 is performed.The basic field testing and sampling procedure includes a combination of non-destructive (NDT) and destructive (DT) measurements: -Description of visual damage characteristics of the selected location (NDT1) -Measuring dimensions of the balcony and identifying layers (NDT2) -Rebar detection (NDT3) and determination of the attributive properties of the reinforcement (DT1) -Chloride content determination (DT2) -Determination of carbonation depth (DT3) -Rebound hammer (NDT4) -Additional testing: potential mapping (SDT1), in-situ strength determination of steel (DT4) and/or concrete (DT5).

Fig. 3 .
Fig. 3. Destructive validation for determination of attributive steel properties and layer thickness of the balcony Corrosion damage initiated by carbonation in the case of balconies is (often) less severe: the longitudinal reinforcement is often situated outside the moisture exchange area and corrosion by carbonation does not significantly reduce the diameter of the bars.The bearing capacity is therefore not affected significantly, in comparison to corrosion initiated by chlorides (where pitting corrosion might occur).However, carbonatation damage is often visible at the front or bottom of the balcony which of course can result to dangerous situations of falling concrete parts and delamination.The most commonly used technique to determine the carbonation front (DT3) is by spraying acid-base indicator (e.g.phenolphthaleine) on a fresh created fracture surface as described in EN 14630.Additional on-site testing can be performed: determination of the hardness and uniformity of the concrete cover by means of a rebound hammer (NDT4, test procedure according to EN 12504-2).

Fig. 4 . 2 . 4 Phase 3 -
Fig. 4. Identification of corrosion hot spots by means of semidestructive potential mappingFurthermore, with regards to the assessment of the bearing capacity of the RC balconies (Phase 3) insight on the material characteristics can increase the reliability of the analysis.Therefore tensile strength test on an extracted piece of steel reinforcement (DT4, according to EN 15630-1) and/or compressive strength test on drilled cores to determine the strength of the existing concrete element (DT5, according to EN 13791) can be necessary

Fig. 6 .
Fig. 6.Value of d"/d considering Vd2The steel section As1 can determined by means of the file survey or by means of on-site testing (NDT3).If corrosion of the steel reinforcement is likely to occur or to be present (scenario B) the condition of the steel needs to be taken into account, e.g. by means of expressing steel section as As,corr, of which its value is determined by means of additional testing (SDT1, DT1) and calculations.The corrosion process reduces the diameter and also might lead to a reduction in yield strength and ultimate strain according to[9][10].
remaining bearing capacity.According to the original design documents the elements are reinforced with longitudinal tension rebars with diameter 10 mm and spacing distance 100 mm, totalizing an area of 864 mm²/m tension reinforcement, with a cover of 20 mm.Therefore the design value of the effective depth equals 75 mm.These rebars are anchored in the RC beams/plates of the building.No details were found on the concrete strength class or the steel quality.During the visual inspection in Phase 1, the condition score is determined on exclusively visual characteristics.(Figure 7): floor 1 has condition score 2 (good condition, mainly due to failing coating), floor 8 has condition score 4 (poor condition, mainly due to failing joints and local rust stains, floor 16 has condition score 5 (bad condition, due to the presence of a crack parallel to the building).

Fig. 7 .
Fig. 7. Visual inspection: failing coating and joint, local rust stains and cracks parallel to the building.

Table 1 .
Observed damage of RC balconies