ATTACHMENT 1 ITEM 5 I&S COMMITTEE MUNNA PT BRIDGE …

of 31

TITLE: EXISTING CONCRETE BRIDGE, MUNNA POINT, NOOSA HEADS STRUCTURAL ENGINEER LEVEL 3 REPORT

DOCUMENT NO: 02600_RP1

DETAILS OF REVISION

REV DATE DETAILS AUTHOR CHECKED

A 15-3-2014 Preliminary issue for discussion CD AB B 21-3-2014 Prelim issue for NSC staff CD DR C 24-3-2014 Issue for general distribution CD CD

The information contained in this document produced by Tod Consulting is solely for the use of Noosa Shire Council, for the purpose for which it has been prepared. Tod Consulting undertakes no duty to nor accepts any responsibility to any third party who may rely upon this document

ATTACHMENT 1 ITEM 5 I&S COMMITTEEMUNNA PT BRIDGE REPAIRS LEVEL 3 BRIDGE REPORT

of 31

Table of contents Table of contents ............................................................................................................................. 2 Glossary of Terms ........................................................................................................................... 2 Executive Summary ........................................................................................................................ 5 1.0 Introduction and Background .................................................................................................. 11 2.0 Review of Existing Reports & Site Observations ..................................................................... 12 3.0 Condition Assessment ............................................................................................................. 21 4.0 Repair Options – Cost Comparison ......................................................................................... 23 5.0 Conclusions ............................................................................................................................. 26 References .................................................................................................................................... 28 Appendix A – Locality plan ............................................................................................................ 29 Appendix B – Original drawings of bridge ..................................................................................... 30 Appendix C – Design loads ........................................................................................................... 30 Appendix D – Risk Assessment methodology ............................................................................... 30 Appendix F – Bridge Condition & Repair staging drawings (not for construction) ......................... 31

Glossary of Terms

• Abutment = a structure at each end of the bridge, that supports the bridge deck. The components of an abutment include ballast wall, wingwalls, pilecap beam, and piles.

• ASR = Alkali Silica Reaction. ASR is sometimes known as AAR (Alkali Aggregate Reaction). Many Queensland aggregates (gravels) that are used for concrete manufacture contain silicates, which react with alkalis in the cement. ASR causes concrete structures to expand and crack. Cracks usually run in the same direction as the main reinforcement. If little or no reinforcement is present, then cracks will run in all directions. ASR only occurs in the presence of water. Unfortunately, seawater contains water and alkalis, which supplement the concrete alkalis and worsen ASR reactions. Modern concretes are often batched with a blend of Portland cement and flyash (and/or other pozzolanics) to prevent ASR problems. TMR tests showed the Munna Point bridge pilecap beams don’t contain flyash.

• Cast-insitu concrete = concrete poured on a construction site

• Carbonation = a process where carbon dioxide from the atmosphere penetrates into concrete and lowers the concrete pH level (more acidic, less alkaline). Once carbonation penetrates in far enough to reach the reinforcement, the reinforcement usually starts corroding.

• Cathodic Protection = electrical cabling and titanium anodes are connected to the reinforcement that needs protection from corrosion. A direct (DC) electrical current is passed through the cabling to put a negative charge into the reinforcement, which stops the corrosion reaction. Cathodic protection Contractor (Freyssinet) advises that the system uses relatively small amounts of electricity –

of 31

an estimated few hundred dollars would protect all 6 pilecap beams of Munna Point Bridge.

• Chlorides = corrosive ions that are part of common salt (from seawater).

• Corrosion = the gradual destruction of materials, (usually metals), by chemical reaction with its environment. Rusting, with the formation of iron oxides, is a well-known example of electrochemical corrosion.

In the past, steel reinforcement in concrete has been believed to be “non-corrodible”, because of the high alkalinity of the concrete and the barrier provided by concrete cover. Unfortunately, thousands of concrete structures have been prematurely damaged by corrosion (of steel reinforcement and high strength steel strands). Usually, corroding reinforcement expands in size as the reaction proceeds, and this breaks off large areas of the surface concrete (known as spalling).

• Corrosion threshold value = chlorides (salts) have penetrated the concrete and built up to a concentration sufficient to cause corrosion of steel reinforcement.

• Deck Unit – See Precast Deck Unit

• Drainage scuppers / scuppers = holes in the bridge deck to let rainwater drain off the deck

• Headstock = reinforced concrete beam that directly supports the bridge deck

• NSC = Noosa Shire Council. NSC was amalgamated into Sunshine Coast Council in 2008, and then de-amalgamated from SCC in 2014.

• Macrocell = corrosion of one area of reinforcement in preference to another within the same component, because of anodic (more positively charged) and cathodic (more negatively charged) processes within the concrete.

For example, wetting-drying cycles of chloride-contaminated water against part of the concrete can result in an anodic area that promotes local corrosion of reinforcement. The anodic reinforcement is sacrificed in preference to electrically connected, more passive reinforcement away from that area. Macrocells can make corroding reo less expansive, and sometime spalling of the concrete doesn’t occur. Thus, there may be no visual warning that reinforcement is corroding.

• Pier = a structure in the water that supports the bridge deck. The components of a pier include a headstock, columns, pilecap beam and piles.

• Piles = long concrete “posts” that extend deep into the creek/canal bed to support the bridge. These contain high strength steel strands (cables) that are tensioned (pulled tight) during construction, to increase each pile’s overall robustness and capacity. Without high strength steel strands, the piles would be unable to carry traffic loads.

• Pilecap beam = reinforced concrete beam poured over the tops of the piles

of 31

• Precast = concrete poured in a remote casting yard and then transported to the bridge site. Precast concrete is usually finished to a better quality than cast-insitu concrete

• Precast Deck Unit = narrow concrete planks that are laid side by side to form the bridge deck. These are made of precast concrete, and contain high strength steel strands (cables) that are tensioned (pulled tight) during construction, to give the deck unit sufficient strength to carry traffic loads. Without high strength steel strands, the deck units would be unable to carry traffic loads.

• Reinforcement / reo = medium strength steel bars that are designed to take the tensions that occur within a concrete structure when it gets loaded (e.g. by traffic on the bridge). Without steel reinforcement, the concrete in the headstocks, columns and pilecap beams would be unable to carry traffic loads.

• Reinforcement cover = the depth that the outside face of reinforcement is embedded below the surface of the concrete. As a basic rule, the greater the reinforcement cover, the better the protection against corrosion

• Safety factor = measures how close a structure or structural component is to failure (partial or total). Sometimes it’s called a factor of safety:

o 1 or less means the structure/component isn’t strong enough to carry its loads. This is often described as having “no safety factor”.

o 2 to 3 is normal for a bridge. o Bridges are designed with larger safety factors than buildings because

trucks are often overloaded beyond their legal load limits, and because newer trucks with heavier configurations come along years after the bridge gets designed. For example, Munna Point Bridge was designed for a loaded semi-trailer (known as a T44) in both lanes. New bridges must be designed for much heavier trucks.

• SCC = Sunshine Coast Council, formed by the 2008 amalgamation of Noosa Shire, Maroochy Shire and Caloundra City Councils

• Substructure is everything below the superstructure such as pilecaps, pilecap beams, abutments, wing walls, headstocks, columns, piles, and other types of foundation systems.

• Superstructure is everything above the supporting structure. Superstructure items include deck units, the bridge barriers, footpaths, etc.

• Transverse stressing bars = high-strength steel bars that are pulled tight during construction, to hold the deck units tightly against each other, so that the deck units effectively act as one slab.

• TMR = Department of Transport & Main Roads Queensland and its previous entities

of 31

Executive Summary In early 2014, the new Noosa Council (NSC) required a Level 3 structural report for the Munna Point road bridge along Noosa Parade. Noosa Parade is a principal connector road between the Noosaville and Hastings St business districts. The road also serves significant residential and holiday-stay areas. NSC engaged Tod Consulting to prepare the report. The bridge is approximately 1.5 kilometres southwest of Hastings St, and crosses a wide saltwater canal connecting Weyba Creek and the Noosa River. Bridge details are as follows: • Developers built the 105 metre long concrete bridge (according to an NSC report

dated 6 Aug 2002). • Estimated construction date is 1979 (according to TMR reports for the bridge). • Some original drawings are available, and these can be seen in Appendix B. • The bridge has showed worsening signs of concrete “cancer” since 1999. In particular:

o The bridge deck has cracks caused by Alkali Silica Reaction (ASR). o Three pilecap beams are in very poor condition, with large cracks and

moderately to seriously corroded reinforcement near the sides and ends (Piers 3, 4 & 5)

o Many piles have cracks caused by ASR. • TMR has numerous bridges in saltwater environments that have experienced similar

problems at a similar age. The reason is that industry knowledge of reinforced concrete corrosion was less advanced before the 1990s, and is still being heavily researched now. This issue has resulted in significant, costly repairs for TMR. For example, the 2.74 kilometre long Houghton Highway bridge at Redcliffe (opened 1979) suffered ASR cracking of the piles, and in 1991, 500 piles were concrete encased below water level, and wrapped with composite fibre wraps above water level.

Tod Consulting reviewed all of the previous Munna Point Bridge reports prepared by TMR, Opus and Arup. A condensed summary of these can be found in Section 2 of this document. In essence, the TMR reports (1999-2004) recommended repairs that were required several years ago. No repairs were carried out. At that time, NSC believed a replacement bridge would be a similar cost: this is certainly not the case in 2014. Later reports also recommended repairs that were not carried out. We carried out site inspections on the 14th, 21st and 28th February 2014, in the presence of NSC’s Mr Adam Britton (Project Coordinator). Noosa Jetty Builders with equipment and personnel. NSC commissioned ALS Industrial to take material tests on the same days as Tod Consulting’s site inspections. Chemical contaminants (chlorides and ASR) in the concrete have reached the level where simple repairs alone will not be effective. Three pilecap beams have dilapidated to

of 31

the point of having little or no safety factor. Without commencing repairs now, the repair bill will exceed the cost of a replacement bridge in a few years and the public are likely to be in danger within 1 year (by mid 2015). Tod Consulting’s bridge condition assessment (2014) can be quickly understood by looking at drawing 02600-SK1 in Appendix F. From our review and investigation, we infer that: 1. Deck Units

• 4 deck units per span are suffering from ASR, and the prestressing strands and reinforcement in these may have corroded. It is conservative to assume these deck units are now structurally ineffective.

• The rest of the deck units are likely to have prestressing strands and reinforcement that are 100% intact.

• Deck units in good condition typically have a large factor of safety for structural capacity, so that the good units will compensate for the lost strength in the ones suffering from ASR.

• The good deck units are likely to suffer ASR cracking and reinforcement corrosion sometime between now and 2016. The repair bill for the deck units will grow exponentially, unless action is taken soon.

2. Headstocks • Headstock reinforcement is likely to be 100% intact

3. Columns

• Column reinforcement is likely to be 100% intact 4. Pilecap Beams

• The top and side reinforcement cover exceeds the 75mm shown on the original drawings, which provides beneficial protection to reinforcement.

• 75-85% of the top reinforcement is likely to still be intact; 50-80% of the bottom reinforcement is likely to still be intact, and 66% of the shear ligatures/stirrups are likely to still be intact

• ASR cracking will continue, and we anticipate that reinforcement will corrode heavily, making the bridge dangerous by 2015.

5. Piles

• All piles have cracks caused by ASR • The majority of the reinforcement in the piles is likely to be intact, based on

the two piles where we removed concrete and observed the reinforcement condition. This is because most of each pile is underwater; with reduced oxygen making the rate of corrosion slower. However, at the pile tops (in the tidal zone), it’s probable that the reinforcement has corroded, but it hadn’t spalled (broken) off the concrete faces at the time of the February 2014 inspections.

of 31

• We expect that significant corrosion of all piles could start in the next 1-3 years (2015-2017), making the bridge dangerous and increasingly costly to repair by 2017.

It is our understanding that there is a limited budget for this project. Tod Consulting’s team has taken this into account in our recommendations. We strongly recommend and urge Council to take actions 1 to 8, so that:

a) Public safety is maintained. b) The repair cost and whole of life costs can be spread over a number of years. c) With impressed-current cathodic protection and protective paint-on coatings, the

bridge life can be extended by an estimated 50 years to year 2064, if these protective measures are properly maintained. The media and the public could find a 24-hour-internet-connected 1979-era bridge interesting (see note i below).

Notes: i) The cathodic protection system must include a modern internet-connected monitoring system. NSC or their nominated maintenance subcontractor can remotely check that the bridge is protected, and warning messages can be automatically sent to their mobile phones ii) The estimated life is based on the design conditions of today (2014), such as flood levels & velocities, sea levels, air temperatures, vehicle loads and the like. No allowance has been made for increased loads brought on by future climate change or vehicle type changes. ii) Life might be extended further by installing a replacement cathodic protection system, if a bridge engineer deems climate conditions, condition of reinforcement, and condition of high strength steel strand, satisfactory in the future. Special scour protection around piers and abutments, or even lengthening of the bridge might be required by that time.

REPAIRS BETWEEN NOW AND AUGUST 2014: 1. a) Confirm the reinforcement depth on site for the previously tested Pier 4 column, and re-test the (inconclusive) chloride levels from the surface to the reo depth. This will help to confirm if cathodic protection of the columns is required or not in the later stages. b) Install an additional 900mm diameter concrete column between each pilecap beam and headstock (6 columns total). This will effectively reduce stresses in the pilecap beam reinforcement bars to 25-50% of current levels. The concrete and reinforcement should be designed for a 100 year design life using AS5100.5 Bridge Code, and a Portland:Flyash blended cement should be used for the concrete. Real world life is likely to be 50 years, longer if protective coatings (installed in later stages) are maintained. Background to this recommendation The role of the pilecap beams is to transfer the loads amongst the 10 (cracked) piles underneath. Bridges are typically designed with a safety factor of at least 2, so allowing

of 31

for 50% reduction in strength of the pilecap bottom reinforcement, this means the pilecaps could have no safety factor, when two fully loaded semi-trailers pass each other. The current risk to Council is this: if someone drives anything a vehicle(s) across that imposes higher stresses on the bridge:

• A pilecap beam could fail, and • The loads would become concentrated on 4 to 6 of the piles, and • These (cracked) piles are likely to buckle, and then • Partial bridge collapse would occur • Without action, partial collapse is likely to occur sometime within 1-3 years (by

2015-2018). • Using the risk assessment methodology in Appendix D, the overall risk is HIGH,

and it is imperative to reduce the risk. The stresses in the pilecap beams need to be alleviated NOW. Fortunately, for a relatively low cost within the available FY2013/14 budget, these new columns would reduce stresses to safer levels, and give NSC more time to prepare for the main repairs, which need to be staged and completed over the next 3-5 years. The recommended new columns can also be viewed as a low-cost risk management tool. This is because they are likely to prevent catastrophic collapse, if future maintenance/repairs of the pilecap beams and piles were not carried out for some reason. There are constructability and cost benefits too – see item 2 below. OTHER REPAIRS (BETWEEN FY 2014/2015 to 2018/2019): 2. (FY 2014-15): Pilecap beams 3, 4 & 5 (worst condition) - remove cracked concrete

around perimeter of pilecap beams and clean up corroded reinforcement. Arrange for RPEQ engineer to judge if remaining reo is sufficient to carry loads and renew reo if necessary (10-30% chance of being required). Ensure electrical connectivity between bars. Replace removed concrete with use cement based repair grouts or shotcretes that contain 25% flyash or an pre-approved pozzolanic alternative, to prevent introducing more alkalis to the existing concrete (which is ASR prone). Coat full exterior of pilecap beams with silane to exclude water and minimise ASR reaction. Install impressed-current cathodic protection system to pilecap beams to achieve 50-year protection of the pilecap reinforcement. • This operation can be carried out while the bridge is open to road and boat traffic,

if the Stage 1 columns have been installed. Stage 1 columns reduce the risks to the Contractor’s team, the public and Council.

• If the Stage 1 columns have been installed, some of the reinforcement in the pilecap beams can be treated as sacrificial. In our opinion, based on our spot visual checks of reinforcement condition, it is likely that there will be sufficient good reinforcement to safely support the bridge loads, but this will need to be fully checked when the cracked concrete is removed. We anticipate a construction

of 31

cost of $150,000-$200,000 to install the columns, which is offset by a construction saving of $250,000 - $300,000 in pilecap reinforcement repairs.

• The bridge would need to be closed if the Stage 1 columns were not installed, because these pilecap beams already have no factor of safety. Removing concrete from these without Stage 1 columns, whilst allowing traffic on the bridge, would be highly dangerous.

3. (FY 2014-15): Pilecaps 1, 2 & 6 (less damaged) – break out cracked and drummy

concrete. Patch repair with an approved cementitious repair mortar that contains a blend of pozzolanic cement (25% flyash or alternative) to minimise re-introducing alkalis to the existing concrete (which is ASR-prone). Fill small cracks (<0.5mm wide) with injected epoxy. Coat full exterior of pilecap beams to exclude water and minimise ASR reaction. Install cathodic protection system to pilecap beams to achieve 50-year protection of the pilecap reinforcement.

4. (FY 2015-16): Encase all piles with reinforced concrete encasement, to exclude water and chlorides (salt ions), restrain bursting stresses caused by ASR cracking, and strengthen the existing piles. The concrete and reinforcement should be designed for a 100-year design life using AS5100.5 Bridge Code. Portland:Flyash blended cement should be used in the concrete; and the reinforcement should be hot dip galvanised. With these provisions, we anticipate real-world life will be 50 years for the encased piles.

5. (FY 2015-16): Enhance bridge deck waterproofing with sprayed additive over existing

asphalt (type to be advised), and replace all joints with modern alternatives, to exclude water and chlorides from the tops of the deck units. Clean and install plastic lining to each scupper to prevent rainwater and salt permeating into deck concrete.

6. (FY 2016-17): Coat columns, headstocks, underside and sides of deck units with a

protective silane coating to exclude water and chlorides from these elements. 7. (FY 2016-17): Wire brush clean all transverse stressing bars ends, and coat with

protective coating system 8. (FY 2017-18 or earlier): Wire brush clean all traffic barriers and handrails, and coat

with protective coating system. Would be preferable to do in FY 2016/17 because painter will already be there to coat the other components, for items 6) and 7) above.

Note that the above timeframes are estimates. The actual timeframes could vary: the bridge should be monitored regularly for any unexpected dilapidation or damage, and recommended actions should be carried out earlier if necessary to maintain safe operation. Actions 1 to 8 are detailed in Drawings S01-S04, Appendix F. Refer to Section 4.0 (Table 1, Option 2) of this document for estimated costs.

of 31

Detailed engineering design of the work will be required, before commencing construction. An RPEQ Engineer experienced in bridge design can design/specify the columns, new deck joints, deck waterproofing and even protective coatings. The impressed-current cathodic-protection system will need to be designed by a specialist engineer: it is common for these to be designed and constructed by specialist contractors with their own engineers, such as Freyssinet and Savcor. Construction work should be carried out by a specialist contractor, or by an experienced bridge contractor with a specialist subcontractor. Conventional building or civil contractors are not suitable for this type of work.

of 31

1.0 Introduction and Background In early 2014, the new Noosa Council (NSC) required a Level 3 structural report for the Munna Point road bridge along Noosa Parade. Noosa Parade is a principal connector road between the Noosaville and Hastings St business districts. The road also serves significant residential and holiday-stay areas. NSC engaged Tod Consulting to prepare the report. The bridge is approximately 1.5 kilometres southwest of Hastings St, and crosses a wide saltwater canal connecting Weyba Creek and the Noosa River. Bridge details are as follows: • Developers built the 105 metre long concrete bridge (according to an NSC report

dated 6 Aug 2002). • Estimated construction date is 1979 (according to TMR reports for the bridge). • Some original drawings are available, and these can be seen in Appendix B. • The bridge deck is composed of precast deck units. These are tied together with

tensioned stressing bars. • The 7 spans of the bridge deck are supported on cast-insitu headstocks (except at

each bridge end, where each abutment provides the support). Each headstock is supported by two columns, which rest on pilecap beams. There are 10 precast piles underneath each pilecap beam. These piles were driven into canal’s bed during construction. See figure 1.

• The bridge was originally designed for T44 semi-trailer trucks (see Appendix C), based on the thickness of the precast deck units.

• A posted speed limit of 50 km/hour was observed in the vicinity of the bridge. • Traffic volumes in 2011 were 5300-7100 vehicles per day in each direction, per study

prepared by Hayes traffic engineering in 2011. • TMR have a number of bridges in similar saltwater environments of similar age, with

similar problems. These environmental conditions have contributed significantly to many of the bridge structures requiring significant repairs within the first 50 years with 1% or less reaching a 100 year design life (Humphreys et al, 2007). The reason is that industry knowledge of reinforced concrete corrosion was less advanced before the 1990s, and is still being heavily researched now. This issue has resulted in significant, costly repairs for TMR. For example, the 2.74 kilometre long Houghton Highway bridge at Redcliffe (opened 1979) suffered ASR cracking of the piles, and in 1991, 500 piles were concrete encased below water level, and wrapped with composite fibre wraps above water level.

of 31

Figure 1: Bridge components

2.0 Review of Existing Reports & Site Observations The bridge condition in 2014 can be quickly understood by looking at drawing 02600-SK1 in Appendix F. A condensation of the various bridge condition reports & assessments that have been prepared since 1999 follows:

1999 – 2002: TMR prepared bridge condition reports and recommendations for NSC o Deck units

§ Some dilapidation of deck units in Spans 3 and 4 was observed § Fine longitudinal cracks were found along the bottom of some deck units.

TMR suggests that alkali silica reaction (ASR) may be present.

o Pilecap Beams § Large cracks had appeared in the sides, about 150mm to 400mm from the top

of pilecap beams at Piers 3, 4 and 5. § Chlorides (salts) exceeded corrosion threshold value at TMR’s assumed

reinforcement depth of 70 to 77mm. Notes: TMR probably obtained these depths from the original drawings. TMR concluded that reinforcement had started corroding and this would accelerate at time went on. (Tod Consulting found that reo was significantly deeper than this in 2014. Extrapolation of TMR results suggests chlorides in the pilecaps may have been below the corrosion threshold value in 2002 for the real depths).

of 31

§ Carbonation had not penetrated far into the pilecap concrete, except at TMR Core 7 on Pier 5, where the concrete had cracked.

§ Alkali Silica reaction (ASR) was found in the pilecap concrete, by petrographic analysis. Notes: The TMR analyst noted the potential for ASR was “very mild” and described the actual ASR reaction as “mild”. The concrete was made with unblended [Portland] cement. Modern concrete in Queensland is batched with a blend of Portland cement and flyash (pozzolanic cement) to prevent ASR problems.

§ Concrete compressive strength can be taken as 39 MPa, from testing of TMR Core 13.

o Piles

§ 5 of the 6 piles that were inspected by divers had vertical cracks on all faces. Notes: Pile 1 (Pier 1), Pile 10 (Pier 2), Pile 2 (Pier 3), Pile 2 (Pier 4) and Pile 5 (Pier 5) were cracked. Pile 10 (Pier 6) was not.

§ TMR advised that alkali silica reaction (ASR) must be present in the piles. Notes: TMR comments were based on the crack width, orientation and consistent appearance with TMR piles with similar ASR problems. No lab testing of piles for ASR was carried out.

o Repair actions § None taken

2004: NSC arranged for a visual inspection and diving inspection o Pilecap Beams

§ Cracks in the pilecap beams had worsened

o Piles § Pile 1 (Pier 2) and Pile 3 (Pier 2) had cracks that a ruler could be pushed into.

o TMR recommendations

§ Repair cracks/delaminations in pilecaps [beams] § Control corrosion of steel in pilecaps [beams] by cathodic protection § Confine piles with encasement

o Repair actions

§ None taken 2009-2010: OPUS prepared bridge condition reports for the SCC o Deck units

§ Chlorides were just below the corrosion threshold value for the tested deck units (Deck unit 2 and 4 were tested, adjacent to Pier 3)

§ Carbonation had not penetrated far (5-15mm) into the deck units

of 31

§ ASR was confirmed to be present in the deck units. Predominate damage was limited to the kerb units and deck units with drainage scuppers.

o Headstocks

§ Chlorides were below the corrosion threshold value for the tested headstocks § Carbonation had not penetrated far (10-20mm) into the headstocks § ASR potential is present in the headstocks, but has not commenced yet.

Likely to be a problem in the future if action isn’t taken

o Pilecap Beams § New cracks had appeared in the sides near the bottom of the pilecap beams

at Piers 3, 4 and 5. Cracks had also appeared across the tops and ends of the same pilecap beams. There were rust stains evident at various points along side and end cracks, which indicated that reinforcement had corroded.

§ Chlorides (salts) exceeded corrosion threshold value at Opus’ assumed reinforcement depth of 75mm, on the sides of Pier 3’s pilecap beam. Chlorides were below the corrosion threshold value on the top of the same pilecap beam. The bottom was not tested. Notes: Opus probably obtained these depths from the original drawings. (Tod Consulting later found that reo was deeper than this in 2014. Extrapolation of Opus’ results suggests chlorides in the uncracked sections of the sides may have been just below the corrosion threshold value in 2010 for the real side cover of 89 to 93mm).

§ Carbonation had not penetrated far (1-2mm) into the pilecap beams § ASR was found to be present in the pilecap beams. (Pier 3 concrete was lab

tested)

o Piles § 10 piles were inspected by diver: the majority of these had vertical cracks

which were 1-5mm wide at the surface. 2 of the piles had cracks that were 5-10mm wide at the surface – these were Pile 1 (Pier 2) and Pile 2 (Pier 5).

o Opus recommendations § Remove existing asphalt, apply waterproofing to top and protective coating to

underside of deck; and resurface deck with new asphalt § Coat abutments, headstocks, columns and pilecap [beams] with surface

protective coating § Cathodic protection system, concrete encasement of the piles or underpinning

of the pilecaps were also major remedial work items

o Repair actions § None taken

2011: Arup prepared a design for bridge substructure replacement per SCC brief SCC directed Arup to design a complete replacement of the substructure (with driven piles and long-spanning headstocks) with a 100-year design life. The headstocks were

of 31

designed to be wider than the existing bridge, so that shared use off-road pathways and anti-jump provisions could be added in the future. The cost estimate did not include repairs or coatings for the existing deck. In our opinion, these repairs are necessary, and we have added cost allowances to the below estimate, for deck coatings, repair of deck joints, cathodic protection of new pilecaps, coating of stressing bars ends, NSC project management costs and a contingency. The estimated cost:

• New substructure (piles, columns, headstocks & removal of existing piles, pilecaps & columns) = $6,031,588 (per Arup 2011 report) + waterproofing & coating underside of existing bridge deck (allow $200,000) + replace deck joints ($75,000) + cathodic protection of pilecaps and piles to ensure 100 year life (allow $380,000) + clean up and coat all stressing bar ends (allow $20,000) design & project management costs (allow $650,000) + contingency (allow 10%) + GST = estimated $8,092,247 + GST.

• Optional: The deck for a 3.5 metre wide shared use pathway (cycles & pedestrians) would be an estimated additional cost of $2,500,000 to 3,000,000 + GST.

2012-2013: SCC plans to introduce the design into a future construction budget February 2014: Tod Consulting carried out investigation of bridge The new Noosa Council (NSC) engaged Tod Consulting to carry out site inspections and report on the bridge condition. We attended site on the 14th, 21st and 28th February 2014, and our observations were as follows: o Deck units

• Visual inspection, review of previous investigations and acceptance of previous investigation conclusions

o Headstocks • Visual inspection, review of previous investigations and acceptance of previous

investigation conclusions • The headstocks were not cracked

o Columns

• The columns were not cracked o Pilecap Beams

• Core drilling down to reinforcement level on top of the pilecap beams revealed that top reinforcement has not corroded. Reinforcement cover was measured at 100mm.

of 31

• Core drilling into mid-sides of pilecap beams revealed that side reinforcement (ligatures/stirrups, side bars and main steel at corners) has significantly corroded, to the point of being ineffective. Side reinforcement was measured at 89-93mm.

• Core drilling into side near bottom of pilecap beam (Pier 4) revealed that the main bar in the bottom corner has corroded moderately but would still be 60-80% effective. Side reinforcement cover to main bar was measured at 105mm.

• Pilecap beams for Piers 3, 4 and 5 had wide longitudinal cracks in the sides, which appear to have worsened since the 2009 Opus report.

• Pilecap beams for Piers 1, 2 and 6 were in better condition with smaller cracks, but these appeared to have worsened since Opus’ 2009 report.

o Piles

• Pile 3 (Pier 1) and Pile 8 (Pier 1) had no signs of corrosion in the prestressed strands, spiral wire and head bar reinforcement, where a small area of concrete was removed in each pile. Notes: This was despite being directly where cracks were in the concrete from the surface to the reinforcement level. The holes were filled with underwater repair plastic-filler.

• ASR cracking of the piles appeared to have slowed since TMR and Opus reported the problem. A inspection using pole mounted underwater camera of Piles 3 & 8 (Pier 1); Piles 2, 3, 8 & 9 (Pier 4); and Piles 2, 8 & 9 (Pier 5); did not reveal any cracks exceeding 1-3mm on the sides that could be viewed.

• Piles 2 & 3 (Pier 4) had a steel band around them near the top, indicating earlier repairs.

2.1 Laboratory Test results NSC commissioned ALS Industrial to take material tests on the same days as Tod Consulting’s site inspections. Their report can be seen in Appendix E. A summary of ALS Industrial’s results follows: o Columns

• Carbonation was at safe levels (0 to 6mm penetration, so nowhere near reinforcement).

• Chlorides were well below corrosion threshold in one tested column (Pier 2), • Chloride levels were higher but inconclusive in the other tested column (Pier 4).

The test (50mm depth) did not extend to the likely reinforcement depth (assumed to be 75-80mm). By extrapolation of the results, it appears that the chloride levels would be at, or just below, the corrosion threshold at the likely reinforcement depth. Note that the original drawings do not include the notes about reinforcement depth (cover), and no jackhammering of the columns was carried out to confirm the reo depth (cover) on site. Tod Consulting recommends that the reo depth be confirmed on site (for the Pier 4 column), and the chloride level be retested from surface to measured reo depth. This will help to confirm if cathodic protection of the columns is required or not.

of 31

o Pilecap Beams • Carbonation was at safe levels (0 to 14mm penetration, so nowhere near

reinforcement). • Chlorides in the supposedly better pilecaps (Piers 1, 2 & 6) varied: in pilecaps of

Piers 1 & 6, the chlorides were below corrosion threshold at the reinforcement depth, which is consistent with the smaller amount of cracks observed. In the pilecap of Pier 2, chlorides exceed the corrosion threshold at the reinforcement depth of 89mm to 100mm.

• Crack depths were 12 to 198mm deep on the top of pilecap beam (Pier 4), according to survey using ultrasonic pulse velocity device.

o Piles

• Chlorides were (unsurprisingly) found to be well over the corrosion threshold in Pile 1 (Pier 1). However, it should be noted that it was very difficult to take a test sample on site because even at extreme low tide, the top of the pile was still getting wet from waves, and its likely that saltwater intrusion made the results artificially high. ALS Industrial notes although the piles are primarily in a submerged condition and this restrictive of oxygen ingress, they are in a substantively compromised position with regard to corrosive stability.

2.2 Tod Site Investigation Photos

Photo A – Pier 1, small cracks at bottom of pilecap beam

Photo B – Pier 2, small cracks at top of pilecap beam

of 31

Photo C – Pier 3, large cracks in top, smaller cracks at bottom of pilecap beam

Photo D – Pier 4, large cracks in top and bottom of pilecap beam

Photo E – Pier 5, large cracks along top of pilecap beam, none visible at bottom

Photo F – Pier 6, small cracks along top of pilecap beam, none visible at bottom

Photo G – Pier 3, Cores B, taken in top of pilecap beam, near middle.

Photo H – Pier 3, Cores A taken in top of pilecap beam, near middle. Ligatures in good condition. 100mm cover.

of 31

Photo J – Pier 3, Core B, taken in top of pilecap beam, near side. ASR crack from surface to reo level.

Photo K – Pier 3, Core B taken in top of pilecap beam, near side. Ligatures x 2 corroded to depth of 3mm approximately, say 20-30% of strength left. Main bar has surface rust only. 100mm cover to ligatures.

Photo L – Pier 3, Core C, taken in side of pilecap beam. ASR crack from surface to reo level

Photo M – Pier 3, Core C, taken in side of pilecap beam. Ligature almost completely rusted away. 89mm cover to ligature.

Photo N – Pier 4, coring down to visually see condition of reinforcement

Photo P – Pier 4, cores taken from concrete

of 31

Photo Q – Pier 4, Cores 1 & 2 taken in top of pilecap beam, 380mm and 600mm away from side respectively. Ligatures in good condition. 100mm cover.

Photo R – Pier 4, Core 3 taken in top of pilecap beam, 135mm from side. Main bar in good condition. Ligature top in good condition, some corrosion visible at corner. 100mm cover.

Photo S – Pier 4, Core 4A taken in side of pilecap beam, near bottom. Rust stains and ASR crack at surface

Photo T – Pier 4, Core 4A. ASR crack extends from side face in to reo bar. Significant corrosion of main bar. 105mm cover

Photo U – Pier 5, Core A taken in top of pilecap beam, near side. ASR crack extends from surface to reo level

Photo V – Pier 5, Core A taken in top of pilecap beam, near side. Main bar in perfect condition. 139mm cover to main bar.

of 31

Photo W – Pier 5, Core B taken in top of pilecap, near middle. ASR crack extends from surface to reo level

Photo X – Pier 5, Core A taken in top of pilecap, near middle. 2 x ligatures in fair condition with surface rusting. 103mm cover.

Photo Y – Pier 1, Pile 3 – Temporary hole opened in side of pile. ASR crack extends from surface to reo level. High strength steel strand (tensioned) in good condition. Wire spiral cage in good condition. 67mm cover to high strength steel strand. 60mm cover to wire spiral cage.

Photo Z – Pier 1, Pile 8 – Temporary hole opened in side of pile. ASR crack extends from surface to reo level. High strength steel strand and wire spiral cage in good condition. Reinforcement headbar in fair to good condition. 68mm cover to high strength steel strand. 61mm cover to wire spiral cage.

3.0 Condition Assessment Tod Consulting’s bridge condition assessment (2014) can be quickly understood by looking at drawing 02600-SK1 in Appendix F. We infer the following conclusions from the previous testing, inspections and our own testing in 2014: o Deck units

• 4 deck units per span are suffering from ASR, and the prestressing strands and reinforcement in these may have corroded. It is conservative to assume these deck units are now structurally ineffective.

• The rest of the deck units are likely to have prestressing strands and reinforcement that are 100% intact.

of 31

• Deck units in good condition typically have a large factor of safety for structural capacity, so that the good units will compensate for the lost strength in the ones suffering from ASR.

• The good deck units are likely to suffer ASR cracking and reinforcement corrosion sometime between now and 2016. The repair bill for the deck units will grow exponentially, unless action is taken soon.

o Headstocks • The headstocks have not cracked • Headstock reinforcement is likely to be 100% intact

o Columns

• Column reinforcement is likely to be 100% intact. A few more tests will be required to confirm this.

o Pilecap Beams

• The top and side reinforcement cover exceeds the 75mm shown on the original drawings, and adopted in the TMR and Opus reports. Tod Consulting measured top cover was 100mm, and measured side cover was 89 to 93mm.

• Reinforcement near the top centre of the pilecap beams has not corroded. • Reinforcement near the sides of pilecap beams has significantly corroded, to the

point of being ineffective. • Reinforcement near the bottom of pilecap beams is probably starting to corrode

now. • On this basis, 75-85% of the top reinforcement is likely to still be intact; 50-80% of

the bottom reinforcement is likely to still be intact, and 66% of the shear ligatures/stirrups are likely to still be intact.

• It is likely that the corroding reinforcement on the sides (and potentially bottom) of the pilecap beams has protected the rest of the reinforcement due to Macrocells (wetting-drying cycles of saltwater against part of the concrete can result in an anodic area that promotes local corrosion of reinforcement. The anodic reinforcement is sacrificed to temporarily protect the electrically connected, more passive reinforcement away from that area).

• ASR cracking will continue, and we anticipate that reinforcement will corrode heavily, making the bridge dangerous by 2015.

o Piles

• The majority of the reinforcement in the piles is likely to be intact, based on the two piles where we removed concrete and observed the reinforcement condition. This is because most of each pile is underwater; with reduced oxygen making the rate of corrosion slower. However, at the pile tops (in the tidal zone), it’s probable that the reinforcement has corroded, but it hadn’t spalled (broken) off the concrete faces at the time of the February 2014 inspections. We expect that significant corrosion of all piles could start in the next 1-3 years (2015-2017), making the bridge dangerous and increasingly costly to repair by 2017.

of 31

4.0 Repair Options – Cost Comparison Doing nothing is not an option. TMR identified the main issues in 1999, and unfortunately no repair action has been taken since then. It is extremely fortunate that the bridge has dilapidated slower than expected. This gives Council enough time to respond in a planned fashion, and spread the repair/maintenance cost over the next 3-5 years. There are effectively two options to compare: 1) Construct the new substructure designed by Arup, which would provide wider headstocks that could be used to widen the bridge in the future; or 2) repair the existing bridge, which could also be widened in the future when money becomes available. Construction of a new bridge is not a realistic option, because construction would require the bridge crossing to be shut down for 18 months or more. Repairs need to commence NOW. We compare the two options in the following table. Table 1: Cost Comparison of New substructure versus repairing the existing bridge Option 1) – Construct new substructure under bridge, as designed by Arup. 50 year deck life & 100 year substructure life (if maintenance schedule is properly followed). From our review of the design report for this option, it appears that there is no special allowance for sea level rises or associated canal erosion.

Option 2) – Repair the existing bridge. 50-year life if maintenance schedule is properly followed. This option makes no special allowance for sea level rises or associated canal erosion

Works to be carried out: Install new piles and pilecaps just outside existing bridge footprint. Construct new columns. Construct longer, larger headstocks that envelop existing headstocks. Demolish existing columns, pilecap beams and existing piles down the bed level.

Works to be carried out: Install extra 6 columns; break out cracked and drummy concrete in pilecap beams and repair; install cathodic protection to pilecap beams (50yr life); coat pilecap beams with silane; strengthen and encase all piles using galvanised reo and Portland: flyash blended concrete; spray waterproofing compound over deck; install plastic lining in scuppers; replace deck joints; coat headstocks, columns, abutments and underside + sides of deck with protective silane. Clean up and coat all stressing bar ends.

of 31

Option 1) – Construct new substructure under bridge, as designed by Arup. 50 year deck life & 100 year substructure life (if maintenance schedule is properly followed). From our review of the design report for this option, it appears that there is no special allowance for sea level rises or associated canal erosion.


Project delivery cost = estimated $8,092,247 + GST. This cost would be incurred over 1-2 financial years. Important note: These costs DON’T deliver any extra bridge width. An additional $2.5 to $3 million would be required to supply and install a 3.5 metre wide shared path on one side of the bridge Cost breakdown: New substructure (piles, columns, headstocks & removal of existing piles, pilecaps & columns) = $6,031,588 (per Arup 2011 report) + waterproofing & coating underside of existing bridge deck (allow $200,000) + replace deck joints ($75,000) + cathodic protection of pilecaps and piles to ensure 100 year life (allow $380,000) + clean up and coat all stressing bar ends (allow $20,000) + design & project management costs (allow $650,000) + contingency (allow 10%) + GST.

Project delivery cost = estimated $2,783,000 + GST. This cost will be spread over 3-5 financial years. Cost breakdown: Access craft & scaffolding ($175,000) + traffic control (allow $20,000) + 6 new columns ($180,000) + pilecap beam repairs ($600,000) + cathodic protection to pilecap beams ($310,000) + 60 pile encasements ($720,000) + deck waterproofing & scupper linings (allow $100,000) + replace deck joints ($75,000) + silane coatings to pilecap beams, columns, headstocks, abutments and deck underside + sides ($130,000) + clean up and coat all stressing bar ends (allow $20,000) + design & project management costs (allow $ 200,000) + contingency (allow 10%) + GST.

2017 Maintenance: Recoat bridge traffic barriers and handrailing = allow $50,000 + GST

2017 Maintenance: Recoat bridge traffic barriers and handrailing = allow $50,000 + GST

of 31



2030 Maintenance: $ 960,000 + GST Cost breakdown: Recoat pilecap beams, columns, headstocks, abutments, underside + sides deck (allow $130,000). Recoat barrier rails and handrails (allow $50,000). Replace deck wearing surface and waterproofing (allow $230,000). Install cathodic protection to deck ($400,000). Transformer-rectifier & cabling maintenance (allow $150,000)

2030 Maintenance: $ 1,260,000 + GST Cost breakdown: Recoat pilecap beams, columns, headstocks, abutments, underside + sides deck (allow $130,000). Recoat barrier rails and handrails (allow $50,000). Replace deck wearing surface and waterproofing (allow $230,000). Install cathodic protection to deck ($400,000). Contingency for pilecap repairs of ASR cracks (allow $300,000). Transformer-rectifier & cabling maintenance (allow $150,000)

2050 Maintenance: $660,000 + GST Cost breakdown: Recoat pilecap beams, columns, headstocks, abutments, underside + sides deck (allow $130,000). Recoat barrier rails and handrails (allow $50,000). Replace deck wearing surface, deck joints and waterproofing (allow $330,000). Transformer-rectifier & cabling maintenance (allow $150,000)

2050 Maintenance: $960,000 + GST Cost breakdown: Recoat pilecap beams, columns, headstocks, abutments, underside + sides deck (allow $130,000). Recoat barrier rails and handrails (allow $50,000). Replace deck wearing surface, deck joints and waterproofing (allow $330,000). Contingency for pilecap repairs of ASR cracks (allow $300,000). Transformer-rectifier & cabling maintenance (allow $150,000)

Electricity costs for cathodic protection over 50 year life: $42,500 + GST $500/yr x 15 years (pilecap beams only) + $1000/yr x 35 years (deck + pilecap beams)

Electricity costs for cathodic protection over 50 year life: $42,500 + GST $500/yr x 15 years (pilecap beams only) + $1000/yr x 35 years (deck + pilecap beams)

of 31



Comparison life costs (between 2014 and year 2064) = estimated $9,804,747 + GST Notes:

1. All costs are shown in today’s dollars. No allowance for inflation or interest has been made.

2. Costs estimates are for comparison purposes only. For detailed costs, it would be necessary to develop detailed Engineering solutions and arrange for estimates or tenders from an Estimator or Civil Contractor

3. Extra bridge deck width is not included in this estimate. Only the existing width is included.

4. The existing deck will be at the end of its life at this time. Installing a new cathodic protection system, if bridge engineer deems condition of reinforcement and high strength steel strand adequate at that time, could extend life.

5. The substructure (piles, pilecap, columns, headstock) should have a further 50 years of life, provided that maintenance schedule is followed

Comparison life costs (between 2014 and year 2064) = estimated $5,095,500 + GST

Notes:

1. All costs are shown in today’s dollars. No allowance for inflation or interest has been made.

2. Costs estimates are for comparison purposes only. For detailed costs, it would be necessary to develop detailed Engineering solutions and arrange for estimates or tenders from an Estimator or Civil Contractor

3. Extra bridge deck width is not included in this estimate. Only the existing width is included.

6. The existing deck will be at the end of its life at this time. Installing a new cathodic protection system, if bridge engineer deems condition of reinforcement and high strength steel strand adequate at that time, could extend life.

4. The substructure (piles, pilecap, columns, headstock) will be at the end of its life at this time. Life could be extended by installing a new cathodic protection system, if condition of reinforcement and high strength steel strand is deemed adequate by bridge engineer at that time

We can see that Option 2 (repair the bridge) is clearly a lower cost to Council and the community, now and over the next 50 years. Option 1 would have a project delivery cost of 2.9 times higher than recommended Option 2 (repair the bridge); and Option 1 comparison-life costs would be 1.9 times higher than Option 2.

5.0 Conclusions In summary, the cracked pilecap beams, cracked piles and high chloride test results, initially indicated the reinforcement would be in very poor condition. The observed reinforcement in the pilecap beams of Piers 3, 4 & 5 and piles (No. 3 & 8, Pier 1) suggest that reinforcement is in better condition than we first expected. It appears that macrocells

of 31

have formed in the pilecap beams so that corroding reinforcement is (temporarily) protecting the remaining good reinforcement. In the piles, it appears that the reduced oxygen below tide level has resulted in slower than expected corrosion rates. This has given more time than expected to complete repairs (commence now, complete by FY2017/2018). Essentially, there are two options: Option 1 is to rebuild the substructure and keep the existing deck; Option 2 is to repair the existing bridge. Either needs to commence now. Complete replacement of the bridge is not a realistic option, as the bridge crossing would need to be shut down for 18 months or more; or alternatively a costly staged method of construction would be required. Tod Consulting strongly recommends and urges Council to adopt Option 2 (repair the existing bridge), so that:

a) Public safety is maintained. (Right NOW, the pilecap beams of Piers 3, 4 & 5 are likely to be suffering very high stresses when two loaded semi-trailers pass each other)

b) The repair cost and comparison-life costs are kept at reasonable levels, and able to be spread over a number of years, rather than being largely incurred in FY2013/14 & FY2014/15. A relatively small cost incurred in FY2013/14 for 6 new columns will give increased safety and time to take planned action over the next 3-5 years. Delaying any longer will only result in spiralling increases to repair/rebuild costs and risk.

c) With impressed-current cathodic protection and protective paint-on coatings, the bridge life can be extended by an estimated 50 years to year 2064, if these protective measures are properly maintained.

Notes: i) The cathodic protection system must include a modern internet-connected monitoring system. NSC or their nominated maintenance subcontractor can remotely check that the bridge is protected, and warning messages can be automatically sent to their mobile phones. The media and the public could find a 24-hour-internet-connected 1979-era bridge interesting. ii) The estimated life is based on the design conditions of today (2014), such as flood levels & velocities, sea levels, air temperatures, vehicle loads and the like. No allowance has been made for increased loads brought on by future climate change or vehicle type changes. iii) Life might be extended further by installing a replacement cathodic protection system, if a bridge engineer deems climate conditions, condition of reinforcement, and condition of high strength steel strand, satisfactory in the future. Special scour protection around piers and abutments, or even lengthening of the bridge might be required by that time.

Refer to the drawings S01-S04 in Appendix F for timing of each repair. Note these timeframes are estimates. The actual timeframes could vary: the bridge should be monitored regularly for any unexpected dilapidation or damage, and recommended actions should be carried out earlier if necessary to maintain safe operation.

of 31

Detailed engineering design of Option 2 will be required, before commencing construction. An RPEQ Engineer experienced in bridge design can design the columns. The impressed-current cathodic-protection system will need to be designed by a specialist engineer: it is common for these to be designed and constructed by specialist contractors with their own engineers. Construction work should be carried out by a specialist contractor, or by an experienced bridge contractor with a specialist subcontractor. Conventional building or civil contractors are not suitable for this type of work.

References AS5100.5 Australian Standard – Bridge design—Concrete, 2004, Standards Australia AS5100.7 Australian Standard – Bridge design—Rating of existing bridges, 2004, Standards Australia Bertolini, Elsener, Pedeferri, Polder, Corrosion of Steel in Concrete – Prevention, Diagnosis, Repair, 2004, Wiley-VCH Humphreys, Setunge, Fenwick, Alwi, Strategies for Minimising the Whole of Life Cycle Cost of Reinforced Concrete Bridges Exposed to Aggressive Environments, 2007, QUT Islam, Akhtar, A Critical Assessment to the Performance of Alkali-Silca Reaction (ASR) in Concrete, 2013, Canadian Chemical Transactions

of 31

Appendix A – Locality plan

of 31

Appendix B – Original drawings of bridge See attached file: AppendixB MunnaPointBridgedrawings.pdf

Appendix C – Design loads Original design vehicle: T44 vehicle (nominally equivalent to semi-trailer tipper, 44 tonnes)

Appendix D – Risk Assessment methodology

of 31

The Risk Matrix (excerpt from Jacobs Sverdrup – “Working with the Risk Assessment Matrix”)

Appendix E – ALS Industrial field & lab testing report See attached file: AppendixE_ALSIndustrialLabReport.pdf

Appendix F – Bridge Condition & Repair staging drawings (not for construction) See attached file: AppendixF_MunnaPointBridgerepairs.pdf

Appendix G – Previous reports by TMR, Opus & Arup See attached file: AppendixG_MunnaPointBridge_PreviousReports.pdf

ATTACHMENT 1 ITEM 5 I&S COMMITTEE MUNNA PT BRIDGE …

Documents

Transcript of ATTACHMENT 1 ITEM 5 I&S COMMITTEE MUNNA PT BRIDGE …