Murrays Bay Wharf Investigation and Repairs - Options Assessment

Transcription

1 Report Murrays Bay Wharf Investigation and Repairs - Options Assessment Prepared for Auckland Council (Client) By Beca Ltd (Beca) 20 September 2013 Beca 2013 (unless Beca has expressly agreed otherwise with the Client in writing). This report has been prepared by Beca on the specific instructions of our Client. It is solely for our Client s use for the purpose for which it is intended in accordance with the agreed scope of work. Any use or reliance by any person contrary to the above, to which Beca has not given its prior written consent, is at that person's own risk.

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3 Murrays Bay Wharf Investigation and Repairs - Options Assessment Table of Contents 1 Introduction Background Description of the Existing Wharf Structure Condition Assessment Visual Inspection above the Water Line Diving Inspection below the Water Line Timber Stair Case Murrays Bay Wharf Repair Options Option 1 Do the Minimum... 5 Option 2 FRP External Strengthening Option 3 - Steel Beam Strengthening Option 4 Replace Outer Deck Planks Option 5 Replace All Deck Planks Option 6 Replace All Deck Planks and Repair / Strengthen the Existing Piers Option 7 Demolish Existing Wharf and Construct a New Wharf Summary of Options Assumptions and Key Residual Risks Hibiscus and Bays Facilities and Reserves Committee Cost Estimates General Costing Estimate Appendices Appendix A - Site Inspection Photos Appendix B - NZDS Diving Inspection Report Appendix C - Timber Stair Case Inspection Photos Appendix D FRP External Reinforcement Appendix E Repair Cost Estimates Beca // 20 September 2013 // Page // NZ

4 Murrays Bay Wharf Investigation and Repairs - Options Assessment 1 Introduction 1.1 Background On the 15 th and 16 th April 2013, Murrays Bay Wharf was subject to a significant storm event from which, the structure sustained some serious damage. This included significant cracking of the seaward end reinforced concrete deck planks and pier caps and detachment of the recently installed timber stair case located at the end of the wharf. The wharf had recently undergone remedial works which were completed in late 2012 by Quayside Marine and involved installation of a new timber staircase, remedial work to the steel balustrading and some concrete patching of the deck slabs at the seaward end of the wharf. The design of the remedial works was undertaken by Frame Group Ltd (FGL). Following an inspection of the damage sustained to the structure in April 2013 storm event, a recommendation was made by FGL to restrict public access to the outer two spans of the structure. This restriction is still in place. Beca has been requested by Auckland Council to carry out a structural assessment of the wharf and to establish a repair / replacement strategy for the damaged wharf. This report presents a number of repair / replacement options aimed at restoring the wharf to a condition which is deemed safe for public recreational use. Figure 1 Murrays Bay Wharf 1.2 Description of the Existing Wharf Structure The Murrays Bay Wharf is approximately 68m long by 1.2m wide and was originally constructed in its current form in Based on original design drawings provided by Auckland Council, the wharf structure is comprised of: 0.92m (36 ) diameter hollow post-tensioned concrete piers anchored into the sea-bed rock and the reinforced concrete pier caps supporting the deck; 1200mm wide and 180mm deep precast pre-stressed hollow-core concrete deck slabs spanning 7.6m between piers (9 spans in total with 2 deck planks side by side on outermost seaward span (refer Figure 1); Painted steel balustrading connected into the deck (replacement of original timber balustrading). Timber stairs were located at the end of the wharf to provide access between the wharf deck and the water. During the April 2013 storm event, the stairs were detached from the wharf and salvaged intact on the nearby beach. The stairs, designed by Frame Group Ltd, were installed in late 2012 to replace the previous stairs which were also detached from the structure during a storm event in March Beca // 20 September 2013 // Page // NZ

5 Murrays Bay Wharf Investigation and Repairs - Options Assessment 2 Condition Assessment 2.1 Visual Inspection above the Water Line A visual condition inspection of the wharf was completed by Beca on 18 th June The inspection found the following: evidence of longitudinal cracking in all deck spans propagating typically from the pier supports at each end (refer Appendix A Site Photos); evidence of transverse cracking at the outer / seaward support of Span 4 (numbered from land) (refer Appendix A Site Photos 12-15); the outer / seaward two deck spans of the structure where public access was restricted to be in poor condition exhibiting significant longitudinal cracking (refer Appendix A Site Photos 17-19); evidence of rust staining on the underside of the deck indicating active corrosion of the prestressed strands (refer Appendix A Site Photos 3-8); active surface corrosion on the steel balustrading on the outer / seaward 3 spans (refer Appendix A Site Photo 21-22). 2.2 Diving Inspection below the Water Line A diving inspection of the Murrays Bay Wharf piers and pier foundations was carried out on the 28 th August 2013 by New Zealand Diving and Salvage Ltd (NZDS). This inspection was undertaken around mid-tide under good weather conditions allowing good visibility and access to the wharf piles and foundations. A site inspection report was prepared by NZDS following the dive inspection and can be found attached to this report in Appendix B. Under guidance from Beca on site, the divers undertook a detailed inspection and photographic record of each individual pile and footing as well as the reinforced concrete stair footing near the end of the wharf looking for any evidence of scour / undermining of the foundations or apparent damage to the underwater elements of the structure. The findings of the diving report indicate minimal visual evidence of foundation scour (less than 100mm typically) and / or apparent major structural defects (i.e. rust staining, delamination or spalling) on the underwater RC pipe surfaces and foundations. Some minor damage was however observed at the RC pipe joins (refer Appendix B - NZDS Report Photos) on a number of piers which may potentially be a result of movement of the piers and the subsequent bending action due to lateral loading of the structure (i.e. due to waves, wind, etc.) in the past. Whilst the diving report does provide some assurance as to the structural integrity of the wharf foundations, it should be noted that this inspection was of a visual nature only and no physical testing was (nor could easily be) undertaken to confirm the integrity of these elements. The interior of the RC piers and central duct with embedded post-tensioned anchors were not assessed as part of this inspection as it is not possible to gain access to these elements without the need for destructive testing i.e. breaking out / jackhammering of the RC pier caps at the top of each pile. Such testing would also result in the releasing of the stress in the pier tendons subsequently compromising their integrity. 2.3 Timber Stair Case An inspection of the salvaged timber stair case was also undertaken by Beca at the Silverdale Council storage yard on the 28 th August The inspection found the stairs to be largely still Beca // 20 September 2013 // Page // NZ

6 Murrays Bay Wharf Investigation and Repairs - Options Assessment intact and in generally good condition with the only damage observed at the top and bottom connection locations where the stairs where connected to the wharf and concrete base footing. The observed damage appeared to indicate that the stair fixings failed (rather than the stairs themselves) at both the deck level and at the footing base during the storm event either by one or a combination of the stainless steel fixings directly pulling out from the concrete headstock beam and / or by shear failure / tearing of the timber stringers (refer Appendix C Site Photos). It may be possible to repair and re-use these stairs as part of the overall repairs to the Wharf however this will need be confirmed pending further analysis of the imposed wave action loading on the stairs and wharf structure. This will be undertaken by Beca during the detailed design phase in combination with a peer review of the previous FGL design undertaken in Beca // 20 September 2013 // Page // NZ

7 Murrays Bay Wharf Investigation and Repairs - Options Assessment 3 Murrays Bay Wharf Repair Options 3.1 Option 1 Do the Minimum General Option 1 involves undertaking the bare minimum remedial works as follows: Replace / re-instate stairs to structure (refer Section 3.9.2); Load-test all 9 deck plank spans to a minimum safe rating (i.e. 5kPa to be determined) this involves a form of destructive testing of the structure Discussion Rust staining evident on the soffit of the deck slab indicates that the pre-stressing strands and/or steel reinforcement have started to corrode within the concrete. Cracking in the slab, assumed to be largely caused by the recent storm event damage, provides easy access for chlorides to the strands / steel reinforcement. This will ultimately lead to an increased rate of corrosion of the strands / steel reinforcement leading to expansion of the steel and subsequent de-bonding with the surrounding concrete resulting in an initial reduction in the capacity of the deck and eventual failure if no action is taken. Pre-stressed concrete elements are especially difficult to repair once strand corrosion and concrete spalling begins. The beams are reinforced with high tensile strands which are typically loaded to 50-70% of the Ultimate Tensile Strength of the steel. Each strand consists of individual small diameter wires which are wound or laid to form the strand. The strand contains voids between the wires which allow chlorides and moisture to accumulate, resulting in very localised and severe corrosion from within. The small diameter wires can corrode very rapidly once initiated and can be very severe with little in the way of exterior visible signs of damage. By the time rust staining and cracking can be seen at the outside surface of the concrete, it is likely that the strand has already corroded to the point where it has lost its tensile capacity and cannot be repaired by conventional means. Once enough strands have lost their tensile capacity, the element is at risk of brittle and sudden failure. Experience has shown that once corrosion of pre-stressing strands is initiated, it typically spreads rapidly. The exact timeframe of this deterioration is not possible to determine without destructive testing. The only way to accurately determine the current load capacity of the Murrays Bay Wharf deck slabs is therefore to carry out destructive load testing. Load testing would involve loading the structure, typically at mid-span to a minimum safe load rating multiplied by an appropriate factor of safety (i.e. FOS = 1.5 2). There is however, given the current condition of the wharf deck slabs, a significant risk that the deck slabs may fail under this applied load and need to be replaced anyway. Without accurately assessing the current load capacity of the deck elements, there is a high residual risk with Option 1 of the deck elements being overloaded and failing in the future. Option 2 FRP External Strengthening General Option 2 involves undertaking strengthening work to the existing deck slabs using Fibre Reinforced Polymer (FRP) external reinforcement (refer Figure 2 & Appendix D for further details). This is anticipated to involve the following remedial works: Replace / re-instate stairs to structure (refer Section 3.9.2); Beca // 20 September 2013 // Page // NZ

8 Murrays Bay Wharf Investigation and Repairs - Options Assessment Strengthen the end 2 deck plank spans using Fibre Reinforced Polymer reinforcement; Load-test the remaining deck plank spans to a minimum safe rating (i.e. 5kPa to be determined) this involves a form of destructive testing of the structure Discussion Figure 2 - Installation of External Reinforcement FRP external reinforcement is used to increase the capacity of concrete elements. It is used on concrete structures where structural elements have deteriorated or the structure is experiencing higher loads than the initial design actions. Strips of carbon fibre fabric are attached to the structural element providing additional strength and increasing the load carrying capacity of the structural element. 3.2 Option 3 - Steel Beam Strengthening General Option 3 involves undertaking strengthening work to the existing deck slabs using external steel beam reinforcement. This is anticipated to involve the following remedial works: Replace / re-instate stairs to structure (refer Section 3.9.2); Strengthen the end 2 deck plank spans using steel I-beams or equivalent; Load-test the remaining deck plank spans to a minimum safe rating (i.e. 5kPa to be determined) this involves a form of destructive testing of the structure Discussion Steel beam strengthening repairs involve the use of steel I-beam elements or equivalent to provide extra capacity to the existing concrete slabs. Steel beams would be installed on the underside of the existing concrete slabs between piers to provide support and increase the load carrying capacity of the deck. 3.3 Option 4 Replace Outer Deck Planks General Option 4 involves replacing the outer damaged deck planks with new precast concrete elements. This is anticipated to involve the following remedial works: Replace / re-instate stairs to structure (refer Section 3.9.2); Replace end 2 (damaged) deck plank spans with new precast reinforced concrete deck planks; Beca // 20 September 2013 // Page // NZ

9 Murrays Bay Wharf Investigation and Repairs - Options Assessment Load-test the remaining deck plank spans to a minimum safe rating (i.e. 5kPa to be determined) this involves a form of destructive testing of the structure Discussion The wharf is approximately 40 years old and potentially nearing the end of its intended service life. Given the age of the wharf and rust staining visible on the soffit of the deck, it is probable that the concrete deck is highly contaminated with chlorides and that the rate of further deterioration of these elements is likely to increase quite rapidly. Option 4 proposes to replace rather than repair the existing damaged deck slabs and load test the remaining deck spans to a minimum safe rating. 3.4 Option 5 Replace All Deck Planks General Option 5 involves replacing all wharf deck planks with new precast concrete elements. This is anticipated to involve the following remedial works: Replace / re-instate stairs to structure (refer Section 3.9.2); Replace all 9 deck plank spans with new precast reinforced concrete deck planks Discussion As stated previously, the wharf is approximately 40 years old and potentially nearing the end of its intended service life. Option 5 looks to provide a long-term repair solution aimed at increasing the service life of the structure by reducing the need for future maintenance to the replaced concrete elements (excluding the piers & foundations refer Section 3.9). 3.5 Option 6 Replace All Deck Planks and Repair / Strengthen the Existing Piers General Option 6 involves replacing all wharf deck planks with new precast concrete elements and repairing / strengthening the existing piers. This is anticipated to involve the following remedial works: Replace / re-instate stairs to structure (refer Section 3.9.2); Repair / strengthen the existing 9 piers by installing new passive (i.e. non stressed) anchor bars into the bedrock, a reinforcement cage and marine grade concrete within the existing wharf piers using the RC pipes as formwork (NOTE: preliminary discussions with a leading local Marine Contractor indicate this repair methodology is feasible and most likely preferred over demolition and reconstruction of the piers). Replace all 9 deck plank spans with new precast reinforced concrete deck planks. This option also allows for an increase in the footprint (i.e. width) of the new wharf deck if requested Discussion Option 6 aims to provide Auckland Council with an essentially new reinforced concrete wharf that achieves a number of efficiencies / advantages over a complete re-build of the structure. These include: re-using / retaining the existing pier casings to provide efficiencies in the installation of new vertical wharf piers (i.e. no demolition of existing piers and pier foundations required); retaining the original look of the old wharf; Beca // 20 September 2013 // Page // NZ

10 Murrays Bay Wharf Investigation and Repairs - Options Assessment allowing the option to increase the footprint of the wharf deck whilst retaining the existing (strengthened) piers. 3.6 Option 7 Demolish Existing Wharf and Construct a New Wharf General Option 7 involves full demolition of the existing Murrays Bay Wharf and replacement with a new reinforced concrete wharf. This is anticipated to involve the following remedial works: Full demolition of the existing structure. Construction of a new wharf as designed by Architect / Engineer to either resemble the original structure or be designed as a new wharf (i.e. smaller / larger footprint) - as specified by Auckland Council; Replace / re-instate stairs to structure (refer Section 3.9.2) - if applicable Discussion Option 7 will provide Auckland Council with a long-term low maintenance solution that achieves a number of efficiencies / advantages over Option 6. These include: The new wharf can be designed to accommodate future client / user intentions for the structure and associated budget constraints; Allows the option to increase / decrease the footprint of the wharf deck as required. 3.7 Summary of Options Table 1 below provides a summary of the above repair options detailing the required proposed remedial works, pros and cons as well as the residual risk to Auckland Council of each option. 3.8 Assumptions and Key Residual Risks For Repair Options 1-5, the following assumptions and key residual risks apply: The piers and pier foundations are structurally sound and suitable to be re-used (i.e. require no remediation and / or replacement). As stated previously in Section 2.2, the diving inspection does provide some assurance as to the structural integrity of the wharf foundations, however it is important to note that the interior of the RC piers and central duct with embedded post-tensioned anchors were not assessed as part of this inspection as it is not possible to gain access to these elements without the need for destructive testing i.e. breaking out / jackhammering of the RC pier caps at the top of each pile. Additionally, any such testing is likely to compromise the integrity of these elements. This remains a key residual risk for repair options 1-5. The stairs can be re-instated onto the structure pending endorsement by an analysis of the applied design wave loading onto the stairs and the subsequent loading impacts onto the structure. This risk will not apply to Repair Options 6 & 7, as the replaced / repaired wharf structure (including the piers & foundations) will accommodate and take the design loading actions on the stairs (if applicable) into consideration as part of the detailed design. 3.9 Hibiscus and Bays Facilities and Reserves Committee This section was added to the report following discussion at the Hibiscus and Bays Facilities and Reserves Committee Meeting of 17 September 2013 at Browns Bay. The meeting resolved (in draft) the following: Beca // 20 September 2013 // Page // NZ

11 Murrays Bay Wharf Investigation and Repairs - Options Assessment a) Requests that a variant option be developed to remediate the Murrays Bay Wharf in a staged way. b) Requests that the first stage be completed with urgency and this should address the damage to the end two spans and replacement steps. c) Requests that the design of the steps be as close as possible to the original steps with hardwood stringers. d) Requests that the design allows for children to easily jump of the structure. e) Requests that the new design, estimated construction time frame and cost estimate, come to the last business meeting of the Local Board on 23 September f) Notes that further action will be taken to recover costs from the design failure of the steps Variant Option 6a - Staged Construction We understand from the meeting that the remediation of the wharf is intended to deliver an as-new wharf when complete, including remediation of the piles. Thus, to achieve this outcome as part of a staged construction process, a variant option 6a has been developed and is anticipated to involve the following remedial works: a) Stage 1: Repair / strengthen the existing outer 3 piers by installing new passive (i.e. non stressed) anchor bars into the bedrock, a reinforcement cage and marine grade concrete within the existing wharf piers using the RC pipes as formwork (NOTE: preliminary discussions with a leading local Marine Contractor indicate this repair methodology is feasible and most likely preferred over demolition and reconstruction of the piers). Replace outer 3 deck plank spans (spans 7, 8 & 9 (double)) with new precast reinforced concrete deck planks. This option also allows for an increase in the footprint (i.e. width) of the new wharf deck if requested. For the remainder of the structure (i.e. inner 6 spans), undertake one or a combination of the following under the guidance of a qualified structural engineer: i. Load-test the remaining deck plank spans to a minimum safe rating (i.e. 5kPa to be determined) this involves a form of destructive testing of the structure. ii. Alternatively, because this repair option will eventually result in the full reinstatement of the structure over a number of years, in the interim, undertake minimal repairs / strengthening works only to those inner spans deemed necessary to ensure the wharf is safe for public use until the next stage of repair/strengthening works (i.e. spans exhibiting transverse cracking over supports or extensive chloride induced deterioration rust staining, delamination & spalling). Replace / re-instate stairs to structure (refer Section 3.9.2). b) Stage 2: Repair / strengthen the next outer 3 piers by installing new passive (i.e. non stressed) anchor bars into the bedrock, a reinforcement cage and marine grade concrete within the existing wharf piers using the RC pipes as formwork. Beca // 20 September 2013 // Page // NZ

12 Murrays Bay Wharf Investigation and Repairs - Options Assessment Replace the next 3 deck plank spans (spans 4, 5 & 6) with new precast reinforced concrete deck planks. This option also allows for an increase in the footprint (i.e. width) of the new wharf deck if requested. For the remainder of the structure (i.e. inner 3 spans), if deemed necessary by a qualified structural engineer, undertake one or a combination of the following: ii. Load-test the remaining deck plank spans to a minimum safe rating (i.e. 5kPa to be determined) this involves a form of destructive testing of the structure. iii. Undertake minimal repairs / strengthening works only to those inner spans deemed necessary to ensure the wharf is safe for public use until the next stage of repair/strengthening works (i.e. spans exhibiting transverse cracking over supports or extensive chloride induced deterioration rust staining, delamination & spalling). c) Stage 3: Repair / strengthen the final inner 3 piers by installing new passive (i.e. non stressed) anchor bars into the bedrock, a reinforcement cage and marine grade concrete within the existing wharf piers using the RC pipes as formwork. Replace the final inner 3 deck plank spans (spans 1, 2 & 3) with new precast reinforced concrete deck planks. This option also allows for an increase in the footprint (i.e. width) of the new wharf deck if requested. Please note Stages 2 & 3 could be combined into a single repair contract pending availability of funding which would result in significant cost savings to AC (due to the reduction in fixed costs associated with mobilisation of a contractor & plant to site, site establishment, etc.) versus undertaking as separate repair contracts Replacement of Timber Stairs We understand that Resolution c) requests the new / replacement stair design to be as close as possible to the original stair design with hardwood stringers. Noting this, if the decision has been made by AC not to re-use the current existing timber stairs (refer Section 2.3), we recommend consideration be given to the following alternative solutions which impose less load onto the wharf (i.e. allow wave energy to pass through rather than onto the structure) and therefore far less likely to cause damage to the structure in a future extreme storm event. These include: Steel grate stairs as employed in a marine environment refer Figure 3. An egress ladder cheapest solution and imposes minimal load (and risk of future damage) onto the wharf refer Figure 4. Beca // 20 September 2013 // Page // NZ

13 Murrays Bay Wharf Investigation and Repairs - Options Assessment Figure 3 Steel Grate Marine Stairs (North Qld) Figure 4 Egress Ladder Beca // 20 September 2013 // Page // NZ

14 Murrays Bay Wharf Investigation and Repairs - Options Assessment Table 1 Murrays Bay Wharf Remedial Options Summary Option 1 Option 2 Option 3 Option 4 Option 5 Option 6 & 6a Option 7 Do the Minimum Fibre Reinforced Polymer External Reinforcement Steel Beam External Reinforcement Replace Deck Slab at End Two Spans Replace Deck Slab at All Spans Replace All Deck Planks and Repair / Strengthen the Existing Piers Demolish Existing Wharf and Construct a New Wharf Description Replace / re-instate stairs only; Load-test all 9 deck plank spans to a minimum safe rating (i.e. 5kPa to be determined) this involves a form of destructive testing of the structure. Replace / re-instate stairs; Strengthen the end 2 deck plank spans using Fibre Reinforced Polymer reinforcement; Load-test the remaining deck plank spans to a minimum safe rating (i.e. 5kPa to be determined) this involves a form of destructive testing of the structure. Replace / re-instate stairs; Strengthen the end 2 deck plank spans using steel I-beams or equivalent; Load-test the remaining deck plank spans to a minimum safe rating (i.e. 5kPa to be determined) this involves a form of destructive testing of the structure. Replace / re-instate stairs; Replace end 2 (damaged) deck plank spans with new precast reinforced concrete deck planks; Load-test the remaining deck plank spans to a minimum safe rating (i.e. 5kPa to be determined) this involves a form of destructive testing of the structure. Replace / re-instate stairs; Replace all 9 deck plank spans with new precast reinforced concrete deck planks. Replace / re-instate stairs; Repair / strengthen the existing 9 piers by installing new passive (i.e. non stressed) anchor bars into the bedrock, a reinforcement cage and marine grade concrete within the existing wharf piers using the RC pipes as formwork. Replace all 9 deck plank spans with new precast reinforced concrete deck planks. Full demolition of the existing structure. Construction of a new wharf as designed by Architect / Engineer to either resemble the original structure or be designed as a new wharf (i.e. smaller / larger footprint) - as specified by Auckland Council; Replace / re-instate stairs (if applicable). Advantages Disadvantages / Residual Risks Lowest capital cost Shortest construction time / shortest closure time for public Wharf will look the same as previous On-going risk of further deterioration / potential failure of original deck planks. No way of when the structure is no longer safe Risk that any of the 9 spans may fail the safe load rating and require replacement anyway Short construction/cure time Minimal change in slab cross section wharf will still look the same Can re-use current deck slab and handrails FRP strengthening could be applied to the rest of the wharf as required in the future Does not require heavy machinery to install Will require a temporary working platform beneath the wharf (typically expensive) On-going risk of further deterioration / potential failure of original non-strengthened deck planks. No way of when the structure is no longer safe Risk that any of the tested spans may fail the safe load rating and require replacement anyway Doesn t require repair of prestressed concrete deck planks Can re-use current deck slab and handrails Could be applied to the rest of the wharf as required in the future Will require heavy machinery to construct/install High corrosion rate due to marine environment, steel will require regular maintenance Steel repairs will be visible on the underside of the structure i.e. change the appearance On-going risk of further deterioration / potential failure of original non-strengthened deck planks. No way of when the structure is no longer safe Risk that any of the tested spans may fail the safe load rating and require replacement anyway Other spans can be replaced as required in the future (delayed costs) Addresses concerns with uncertainty of current and future capacity of the pre-stressed slabs for the end 2 spans only Replaced slabs would be reinforced concrete (i.e. not prestressed) and coated to minimise chloride intrusions meaning future repair requirements will be minimal New deck cross section may need to be thicker than current section (to be confirmed in detailed design), hence deck levels may not be consistent with the remainder of the wharf On-going risk of further deterioration / potential failure of original non-strengthened deck planks. No way of when the structure is no longer safe Risk that any of the tested spans may fail the safe load rating and require replacement anyway Increase service life of the deck planks 50+ years (excl. piers & foundations) Addresses concerns with uncertainty of current and future capacity of prestressed slabs (all slabs) Inconsistent deck level will not be a problem, all sections will be uniform height Residual risk / uncertainty still remains regarding the piers and pier foundations i.e. this option assumes they are structurally sound and suitable to be re-used (refer Sect. 3.9) Increase service life of the entire wharf structure 50+ years (incl. piers & foundations) This option allows for an increase in the footprint (i.e. width) of the new wharf deck if requested. re-using / retaining the existing pier casings to provide efficiencies in the installation of new vertical wharf piers (i.e. no demolition of existing piers and pier foundations required) retains the original look of the old wharf. Longest construction timeframe longer time till public access can be restored Expensive in comparison to the other options Increase service life of the entire wharf structure 50+ years (incl. piers & foundations) The new wharf can be designed to accommodate future client / user intentions for the structure and associated budget constraints Allows the option to increase / decrease the footprint of the wharf deck as required. Longest construction timeframe longer time till public access can be restored Most expensive in comparison to the other options Estimated Construction Time on Site 1 week 2 weeks 2 weeks 1 month 1-2 months Option 6: 2-3 months Option 6a: 3 stages each 1-2 months 3-4 months Cost Estimate *(Refer Sect. 4) $110,000 - $140,000 $160,000 - $200,000 $150,000 - $180,000 $180,000 - $220,000 $280,000 - $350,000 Option 6: $680,000 - $840,000 Option 6a: Stage 1 - $380,000 - $470,000 Stage 2 - $350,000 - $430,000 Stage 3 - $350,000 - $430,000 Total - $1,090,000 - $1,330,000 * $1,000,000 - $1,220,000 Beca // 20 September 2013 // Page // NZ

15 Murrays Bay Wharf Investigation and Repairs - Options Assessment 4 Cost Estimates 4.1 General Table 2 provides indicative order of cost estimates for the various remediation options based on the repair strategies detailed in Section 3 of this report. A detailed breakdown of these cost estimates can be found in Appendix E. Each estimate assumes repair works will be undertaken under a single repair contract and is based on estimated quantities and current market construction rates exclusive of GST. Each option has been compiled assuming estimated construction timeframes as noted in Table 1. Please note that these timeframes are for construction activities on site only and does not include time associated for engineering design, resource consent, tendering of the works nor the tender evaluation and selection process, all of which, will need to be considered in addition when programming the repair works. For Options 6 / 6a & 7, where the structure is likely to undergo significant or complete repair / alteration work, we would expect resource consent to be required from Auckland Council. Please note that option 6a assumes that the construction estimates for each stage (1, 2 & 3) are based on current day construction rates and do not allow for appreciation of costs in the future. Additionally no net present value calculations were undertaken for future expenditures (i.e. Stages 2 & 3) as part of this preliminary costing estimate. 4.2 Costing Estimate Estimates include provision for: Preliminaries including site costs, mobilisation / demobilisation of plant including a work barge, mobile crane and work boat and quality compliance; Construction materials supply and installation, construction equipment and labour costs; Contractor overhead and profit (10%); Engineering design fees (7.5%); Client contract administration costs (5%); Contingency allowance (30%). Beca // 20 September 2013 // Page // NZ

16 Murrays Bay Wharf Investigation and Repairs - Options Assessment 1. Do the Minimum Repair Option Replace / re-instate stairs only; Load-test all 9 deck plank spans to a minimum safe rating 2. FRP External Reinforcement Replace / re-instate stairs; Strengthen the end 2 deck plank spans using Fibre Reinforced Polymer reinforcement; Load-test the remaining deck plank spans to a minimum safe rating 3. Steel Beam External Reinforcement Replace / re-instate stairs; Strengthen the end 2 deck plank spans using steel I-beams or equivalent; Load-test the remaining deck plank spans to a minimum safe rating 4. Replace Deck Slab at End Two Spans Replace / re-instate stairs; Replace end 2 (damaged) deck plank spans with new precast reinforced concrete deck planks; Load-test the remaining deck plank spans to a minimum safe rating 5. Replace Deck Slab at all Spans Replace / re-instate stairs; Replace all 9 deck plank spans with new precast reinforced concrete deck planks. 6. Replace All Deck Planks and Repair / Strengthen the Existing Piers Replace / re-instate stairs; Repair / strengthen the existing 9 piers Replace all 9 deck plank spans with new precast reinforced concrete deck planks. 6a. Staged Repair Option Replace / re-instate stairs; Repair / strengthen the existing 9 piers in 3 stages Replace all 9 deck plank spans with new precast reinforced concrete deck planks in 3 stages. 7. Demolish Existing Wharf and Construct a New Wharf Full demolition of the existing structure. Construction of a new wharf Replace / re-instate stairs (if applicable). Table 2 - Cost Estimate Summary Low Cost Estimate ($NZD excl. GST) High Cost Estimate ($NZD excl. GST) $110,000 $140,000 $160,000 $200,000 $150,000 $180,000 $180,000 $220,000 $280,000 $350,000 $680,000 $840,000 Stage 1: $380,000 Stage 2: $350,000 Stage 3: $350,000 Total: $1,090,000* Stage 1: $470,000 Stage 2: $430,000 Stage 3: $430,000 Total: $1,330,000* $1,000,000 $1,220,000 * No net present value calculations were undertaken for future expenditures (i.e. Stages 2 & 3) as part of this preliminary costing estimate. Beca // 20 September 2013 // Page // NZ

17 Appendix A Site Inspection Photos

18 Site Photo 1 Murrays Bay Wharf Site Photo 2 Murrays Bay Wharf

19 Site Photo 3 Deck Slab Rust Staining Site Photo 4 Deck Slab Rust Staining

20 Site Photo 5 Deck Slab Cracking & Rust Staining Site Photo 6 Pier 8 Capping Beam Damage

21 Site Photo 7 Outermost Span Deck Underside (8-9) Site Photo 8 Outermost Span Deck Underside (8-9)

22 Site Photo 9 Outermost Span (8-9) Site Photo 10 Outermost Span Deck Slab Rust Staining

23 Site Photo 11 Outermost Span (8-9) Site Photo 12 Transverse Cracking Over Support (Span 4)

24 Site Photo 13 Transverse Cracking Over Support (Span 4) Site Photo 14 Transverse Cracking Over Support (Span 4)

25 Site Photo 15 Transverse Cracking Over Support (Span 4) Site Photo 16 Deck Slab Cracking & Rust Staining

26 Site Photo 17 Deck Slab Join Cracking (Span 7/8) Site Photo 18 Deck Slab Longitudinal Cracking (Span 9)

27 Site Photo 19 Deck Slab Longitudinal Cracking (Span 9) Site Photo 20 Pier 8 Capping Beam Damage

28 Site Photo 21 Steel Balustrading Corrosion Site Photo 22 Steel Balustrading Corrosion

29 Appendix B NZDS Diving Inspection Report

30 MURRAYS BAY JETTY STRUCTURE REPORT NUMBER: MBJS v AUGUST 2013 BECA ENGINEERING 28TH AUGUST 2013 AUCKLAND, NEW ZEALAND Approved Released... Glenn Hunter Operations Superintendent... Sol Fergus Commercial Manager NEW ZEALAND DIVING & SALVAGE LTD AUCKLAND WELLINGTON DUNEDIN In-water survey approved

31 INTRODUCTION A New Zealand Diving and Salvage Ltd (NZDS) dive team led by Dive Supervisor Mr. G Hunter attended the Murrays Bay jetty structure at request of BECA on the 28 th day of August The attending BECA representative was Mr. M Deane; underwater visibility at the time of the work conducted was good at approximately 2 meters. SCOPE OF WORKS The requested scope was to undertake a visual inspection and provide a written report with supporting photographs. The inspection scope included; Evidence of scour at seabed Condition of the concrete surface of piles Condition of concrete foundations The integrity of the walkway landing sub-tidal footing Stills Photographs of the underside of the upper deck RESULTS CONCRETE WHARF PILES For the purposes of reporting the jetty piles were referenced as 1 through to 9 with No. 1 being the most inshore. PILE No. 1 STRUCTURE CONDITION COMMENTS CONCRETE SURFACES Good No signs of spalling / mechanical damage SEABED SCOUR Minimal Under scour existing on foundation over pour only. JOIN : SUBTIDAL Good JOIN : INTERTIDAL Good FOUNDATION Good Summary Pile No. 1 had a solid concrete foundation pour approximately 300mm proud of the seabed. There appeared to be minimal seabed erosion scouring approximately 100mm down from the original NEW ZEALAND DIVING & SALVAGE LTD MBJS v Page 2 of 13

32 concrete pour and undercutting by no <30mm. There were no signs of failure or damage to the concrete surfaces. PILE 1 TO SEABED INTERFACE SCOUR ZONE PILE No. 2 STRUCTURE CONDITION COMMENTS CONCRETE SURFACES Good No signs of spalling / mechanical damage SEABED SCOUR Moderate Under scour existing on foundation over pour only. JOIN : SUBTIDAL Good JOIN : INTERTIDAL Good FOUNDATION Good Summary Pile No. 2 had a solid concrete foundation pour approximately 400mm proud of the seabed. There appeared to be moderate seabed erosion scouring approximately 200mm down from the original concrete pour and undercutting by no more than 100mm. Scouring was only present in the concrete over pour from the original footing. There were no signs of failure or damage to the concrete surfaces. PILE 2 TO SEABED INTERFACE MODERATE SCOURING AT BASE OF FOOTING NEW ZEALAND DIVING & SALVAGE LTD MBJS v Page 3 of 13

33 CORED HOLE IN SUB-TIDAL PIPE SECTION PILE No. 3 STRUCTURE CONDITION COMMENTS CONCRETE SURFACES Average See sub-tidal join SEABED SCOUR Minimal Under scour existing on foundation over pour only. JOIN : SUBTIDAL Minor Damage seen on lower pipe section join damage JOIN : INTERTIDAL Good FOUNDATION Good Summary Pile No. 3 had a solid concrete foundation pour approximately 400mm proud of the seabed. There appeared to be minimal seabed erosion scouring approximately 100mm down from the original concrete pour and undercutting was minimal. There was minor damage seen to the concrete surfaces where the lower pipe section had an area of damage approximately 150mm x 100mm and 30mm deep. PILE 3 TO SEABED INTERFACE SUB-TIDAL JOIN NEW ZEALAND DIVING & SALVAGE LTD MBJS v Page 4 of 13

34 PILE No. 4 STRUCTURE CONDITION COMMENTS CONCRETE SURFACES Good No signs of spalling / mechanical damage SEABED SCOUR Minimal Under scour seen on foundation. JOIN : SUBTIDAL Minor Damage seen on lower pipe section join damage JOIN : INTERTIDAL Good FOUNDATION Good Summary Pile No. 4 had a solid concrete foundation pour approximately 400mm proud of the seabed. There appeared to be minimal seabed erosion scouring approximately 100mm down from the original concrete pour and undercutting approximately 100mm. There was minor damage seen to the concrete on the lower pipe section which had an area of damage approximately 100mm x 30mm and 20mm deep. PILE 4 TO SEABED INTERFACE SUB-TIDAL JOIN PILE No. 5 STRUCTURE CONDITION COMMENTS CONCRETE SURFACES Good No signs of spalling / mechanical damage SEABED SCOUR Moderate Under scour existing on foundation. JOIN : SUBTIDAL Minor Damage seen to lower pipe section damage JOIN : INTERTIDAL Moderate Damage seen to top of the second pipe section damage FOUNDATION Good Summary Pile No. 5 had a solid concrete foundation pour approximately 400mm proud of the seabed. There appeared to be moderate seabed erosion scouring approximately 100mm down from the original concrete pour and undercutting by 100mm-200mm. There was minor damage seen to the concrete on the lower pipe section which had an area of damage approximately 100mm x 10mm and 20mm deep. NEW ZEALAND DIVING & SALVAGE LTD MBJS v Page 5 of 13

35 The intertidal join had multiple sites of damage around the circumference allowing vision through the centre of the pile. PILE 5 TO SEABED INTERFACE TYPICAL SCOURING AT SEABED SUB-TIDAL PIPE JOIN INTERTIDAL PIPE JOIN PILE No. 6 STRUCTURE CONDITION COMMENTS CONCRETE SURFACES Good No signs of spalling / mechanical damage SEABED SCOUR Moderate Under scour existing on foundation. JOIN : SUBTIDAL Minor Damage seen to lower pipe section damage JOIN : INTERTIDAL Moderate Damage seen to top of the second pipe section damage FOUNDATION Poor Rough pour no foundation block NEW ZEALAND DIVING & SALVAGE LTD MBJS v Page 6 of 13

36 Summary Pile No. 6 had a solid concrete foundation that appeared to be sound although no evidence of form work was apparent as seen on other existing foundations, a messy miss shaped over pour is all that was evident with consistent minor scouring around the footings approximately 100mm high and mm deep. Damage was seen on both the sub and inter-tidal joins PILE 6 FOOTING PILE 6 TO SEABED INTERFACE SUB TIDAL PIPE DAMAGE INTER-TIDAL PIPE DAMAGE PILE No. 7 STRUCTURE CONDITION COMMENTS CONCRETE SURFACES Good No signs of spalling / mechanical damage SEABED SCOUR Moderate Under scour existing on foundation. JOIN : SUBTIDAL Moderate Damage seen to lower pipe section damage JOIN : INTERTIDAL Minor Damage seen to top of the second pipe section damage FOUNDATION Good Pre-formed foundation block w/ landing NEW ZEALAND DIVING & SALVAGE LTD MBJS v Page 7 of 13

37 Summary Pile No. 7 had a solid concrete foundation 500mm proud of the seabed there was a small amount of scouring at the base not exceeding 100 x 100 in depth and height. A second structure for a stair landing had been placed on the side of the footing it consisted of a similar concrete pipe which had been notched out to accommodate the original footing, precast steps / landing have been cast on the top. There were no obvious means of attachment of this landing structure to pile No. 8 and appears only to be sitting on a pre-prepared base. A void in the base of the landing had been filled with grout bags. Both pipe joins on the jetty pile were damaged with the sub tidal join area damaged of by approx. 200 long by 50mm high and all the way through the pipe section. The upper join had only minor chips in the join. PILE 7 TO SEABED INTERFACE STAIRWAY LANDING W/ NOTCHED FOOTING STAIRWAY FOOTING; SEABED INTERFACE TOP OF STAIRWAY PILE No. 8 STRUCTURE CONDITION COMMENTS CONCRETE SURFACES Good No signs of spalling / mechanical damage SEABED SCOUR Moderate Scrap steel placed for scour prevention JOIN : SUBTIDAL Good JOIN : INTERTIDAL Moderate Damage seen to top of the second pipe section NEW ZEALAND DIVING & SALVAGE LTD MBJS v Page 8 of 13

38 FOUNDATION damage Good Summary Pile No. 8 had a solid concrete foundation approx. 500mm high there were no signs of under scour evident although there were heavy pieces of scrap metal placed around the base of the pile obscuring the original seabed level suggesting there had been an earlier scouring problem dealt with using scrap metal. A small amount of damage was seen to the intertidal join consisting of pieces of the lower pipe broken away. PILE 8 FOUNDATION SCRAP STEEL AT BASE OF PILE 8 PILE 8 SUBTIDAL JOIN PILE 8 INTERTIDAL JOIN PILE No. 9 STRUCTURE CONDITION COMMENTS CONCRETE SURFACES Good No signs of spalling / mechanical damage SEABED SCOUR Minor Under scour existing on foundation. JOIN : SUBTIDAL Good JOIN : INTERTIDAL Good FOUNDATION Good NEW ZEALAND DIVING & SALVAGE LTD MBJS v Page 9 of 13

39 Summary Pile No. 9 had a solid concrete foundation 500mm proud of the seabed there was a small amount of scouring at the base not exceeding 100 x 100 in depth and height. PILE 9 FOOTING REF: 1 PILE 9 FOOTING REF: 2 PILE 9 SUB TIDAL JOIN PILE 9 INTER-TIDAL JOIN UPPER DECK PHOTOGRAPHS The following images are a representation of key joining components of the structure. NEW ZEALAND DIVING & SALVAGE LTD MBJS v Page 10 of 13

40 UPPER DECK AT PILE 9 UPPER DECK OFFSHORE FROM PILE 8 UPPER DECK INSHORE FROM PILE 8 UPPER DECK OFFSHORE FROM PILE 7 UPPER DECK INSHORE FROM PILE 7 UPPER DECK OFFSHORE FROM PILE 6 NEW ZEALAND DIVING & SALVAGE LTD MBJS v Page 11 of 13

41 UPPER DECK INSHORE FROM PILE 6 UPPER DECK OFFSHORE FROM PILE 5 UPPER DECK INSHORE FROM PILE 5 UPPER DECK OFFSHORE FROM PILE 4 UPPER DECK INSHORE FROM PILE 4 UPPER DECK OFFSHORE FROM PILE 3 NEW ZEALAND DIVING & SALVAGE LTD MBJS v Page 12 of 13

42 UPPER DECK INSHORE FROM PILE 3 UPPER DECK OFFSHORE FROM PILE 2 UPPER DECK INSHORE FROM PILE 2 UPPER DECK OFFSHORE FROM PILE 1 UPPER DECK SHORE TO PILE 1 NEW ZEALAND DIVING & SALVAGE LIMITED 134 GRACEFIELD ROAD, SEAVIEW, LOWER HUTT PO BOX , LOWER HUTT, 5040, NEW ZEALAND P: E: nzds@nzds.co.nz W: NEW ZEALAND DIVING & SALVAGE LTD MBJS v Page 13 of 13

43 Appendix C Timber Stair Case Inspection Photos

44 Silverdale Site Photo 1 Timber Stair Case Silverdale Site Photo 2 Timber Stringer Connection / Plate (Top)

45 Silverdale Site Photo 3 Timber Stringer Failed Connection (Bottom) Silverdale Site Photo 4 Timber Stringer Failed Connection (Bottom)

46 Silverdale Site Photo 5 Failed Timber Handrail (Top) Silverdale Site Photo 6 Timber Stringer Failed Connection (Top)

47 Appendix D FRP External Reinforcement

48 frp Leading technology April 2011 Grafton Bridge» Welcome to this edition of FRP Leading Technology, which highlights some interesting recent applicattions of Fibre Reinforced Polymer (FRP) structural strengthening materials in New Zealand. FRP Leading Technology is produced by BBR Contech and Sika (NZ) Ltd. Contech and Sika have been associated with FRP in New Zealand since 1994 and have developed a great deal of expertise in the various FRP techniques. The design and installation of FRP solutions requires a high level of engineering understanding. The combination of Contech s specialist engineering capability and Sika s strong sales network, together with the sound engineering know-how held by both companies, creates a strong alliance that provides well engineered, well constructed and cost competitive FRP solutions to the marketplace. A century of progressive technology Auckland s iconic Grafton Bridge, the world s largest single span reinforced concrete arch bridge when constructed in 1910, has continued its history of innovation, utilising Sika CarboShear technology in its 2010 strengthening. When it was completed in 1910, Grafton Bridge was at the forefront of construction technology, boasting the world s largest single span of reinforced concrete. The 296-metre-long bridge, which soars 43 metres above Grafton Gully, has attracted international acclaim as an engineering structure of unique value. Its impressive resume includes: Recognition by the American Concrete Institute as one of the 100 most significant concrete structures in the world. Receiving the inaugural NZ Concrete Society Enduring Concrete Award in Registration as a Category I structure by the New Zealand Historic Places Trust owing to its outstanding technological merit and magnificence as a townscape element. Almost 100 years after it was built, the bridge was recently strengthened as part of the Auckland Central Connector project. This has provided it with essential seismic resistance (enabling it to withstand a one-in-1000-year earthquake) as well as the capacity to carry increased bus traffic and cope with future transport innovations such as light rail all without altering the bridge s appearance or changing its heritage status. The work included: strengthening the bridge columns using steel bar reinforcements strengthening the bridge beams by applying Sika CarboDur carbon fibre plates and Sika CarboShear L Plates installing new, reinforced-concrete shear keys and deck linkage to resist horizontal earthquake forces repairing cracks in the existing concrete and removing algal growth replacing deck joints and bridge bearings. Main contractor Brian Perry Civil engaged BBR Contech, as the specialist subcontractor, to supply and apply nearly 600 metres of Sika CarboDur FRP strips and 830 CarboShear L plates to the bridge structure. The CarboDur strips were applied to the underside of the beams to provide additional mid-span moment resistance. The CarboShear L plates were A joint venture in FRP technology Continue over page 1