Engineer Bernard Musarurwa
It is a requirement that every structure, be it a building, a bridge, a dam, a powerline, any form of infrastructure, be inspected periodically for structural integrity, and fitness for purpose. Sadly, It is a requirement that every structure, be it a building, a bridge, a dam, a powerline, any form of these inspections are not being conducted regularly, if at all, due to lack of resources, expertise, or in most cases, ignorance, or quite often, plain “ignoring”.
So, it is more disconcerting where inspections have been conducted, and defects noted, and yet no remedial action is taken for over a decade; then it becomes a matter of waiting for a disaster to happen, which perhaps may be the only way to jolt the relevant authorities to take action.
This is the case of the flyovers on Simon Mazorodze (Beatrice Road) interchange with Rotten Row, which bridges were inspected in 2006, and serious structural defects were noted, and reported upon, and yet no action has been taken to date.
Unfortunately, this is not the only case of “ignoring” to take remedial action on defective structures, with several other bridges on the national highways having been inspected and reported upon that remedial action was required.
One prays and hopes that there will be no fatalities or casualties when the inevitable collapse of one of the bridges, a building, an escalator/lift, or any other infrastructure that requires attention, due to “ignoring” to conduct inspections, and to take remedial action.
The City of Harare (CoH) in 2006 invited a consulting engineering firm to conduct inspections and to report on the defects noted at the Simon Mazorodze Road (Beatrice Road) flyover at the interchange with Rotten Row.
The investigations also included the other two adjacent flyovers on Rotten Row and Lytton Road.
The CoH’s engineers, together with the consultant’s engineers, inspected the 3 flyovers on Thursday 21 September 2006, and again the engineers conducted another more detailed inspection on Friday 29 September 2006.
From the two inspections, the consultant was able to ascertain firsthand the extent of defects to be able to propose the requisite intervention strategies required for the repair of the structures, and to outline the scope of the work required to conduct a detailed assessment of the manifesting defects, and the structural analysis required to be able to make detailed recommendations of the appropriate remedial works.
The CoH engineers indicated that the original design drawings for the structures were available and would be availed to the consultant.
The CoH would also provide logistical support (traffic control as well as materially: inspection cranes, labour, etc.) for the fieldwork.
The three structures are described briefly below, based on the cursory inspections conducted then in 2006.
Simon Mazorodze Road
This is a grade-separation structure with Rotten Row over Simon Mazorodze Road.
It is a five span bridge and the form of structure comprises two table spans with a drop-in central span. The table spans are in beam and slab construction with two sets of six beams that appear to be independent. The drop-in span is in solid slab construction.
The bridge piers comprise six hexagonal columns with individual bearings at the top of each column. The detail of the half joints and the abutment support was not visible and needs to be checked.
The defects observed include spalling of concrete exposing rusted reinforcement steel bars in the beams at several locations. This defect was prevalent to beams in the middle of the structure where laitance and efflorescence from ingress of moisture was severe. This coincided with the gravel median island of the dual carriageway, suggesting that the island and deck slab were pervious along the centre.
There were also signs of moisture ingress along the joints at the abutments and at the central table span.
The principal observed defects occur in the outer beams and the adjacent inner beams, which would suggest that if the rusted reinforcement steel bars are no longer contributing to the load bearing capacity, that would then leave only the central four sound beams carrying the full loading on the two traffic lanes of Rotten Row.
This is a grade-separation structure with Rotten Row over Lytton Road and several railway lines.
The bridge has three spans in contiguous precast concrete beam and slab construction. The drawings will show if this slab is voided which will impact on the interpretation of the defects.
The main defect manifesting is the ingress of moisture at joints between the precast beams and the cast in-situ edge beams. A bee-hive was observed over one of the western piers!
This is a grade-separation structure with Charter Road over Lytton Road and several railway lines.
The structural form is similar to the Lytton Road Bridge.
As with the similar adjacent Rotten Row road-over-rail flyover, the prevalent defect is ingress of moisture at the joints, especially at the outer edge beams.
There was also a damaged parapet panel, apparently caused by a wayward motor vehicle.
The consultant proposed back then in 2006 the need to conduct more thorough and detailed investigations to establish the exact nature and extent of the defects noted.
This would entail probing and scanning (ideally with an X-ray camera) the areas of spalling concrete and rusted reinforcement bars. This applies to all three structures, although this defect was only noted at the Simon Mazorodze Road flyover.
The ingress of moisture is prevalent at all three structures. It will be necessary to expose the joints and all locations where there are signs of moisture ingress. This may entail excavation and removal of surfacing, kerbing and median islands to expose construction joints and any cracks in the deck everywhere there are signs of moisture ingress.
During the detailed inspections any other latent defects will be noted and investigated.
noted at all 3 structures may suggest damage to both the concrete and
reinforcement steel, thus the integrity of both must be thoroughly investigated
by exposure where possible or by other means such as rebound hammer (Schmidt)
and metal detection (bar meter) where suspect.
Based on the findings of the investigations, the extent and scope of the defects will be analysed in as far as they may affect the structural integrity and serviceability of the structures. It is noted that there are main reinforcement bars rusted through at several locations at the Simon Mazorodze flyover and these are most likely compromising the load bearing capacity of the structure.
The design drawings of the structures that were said to be available will be vital in the structural analysis and design of temporary support for repairs to damaged beams.
RECOMMENDATION OF REPAIR STRATEGIES
Recommendations for remedial works will be based on findings from the detailed defects investigations and structural analysis.
It is envisaged, as a minimum, that all joints, and any cracks, that are allowing the ingress of moisture will require to be exposed so that they may be sealed. This will entail removal of the bituminous surfacing and other materials. Contraction and construction joints will need to be reinstated and waterproofed. Drainage features, such as scupper pipes, will need to be reinstated or installed where possible and necessary.
Where reinforcement bars have rusted and concrete has spalled or has been damaged, these will require reinstating, replacing and reconstituting. This will entail sand blasting, drilling and chipping away concrete around damaged bars to expose sound steel bars to an extent to provide sufficient lap lengths of the replacements bars with the sound old bars, to ensure adequate bonding and load transfer. There will be need to design and provide structural grillage support to carry the design load while any structural members are being rehabilitated.
Shotcrete may be required to reinstate the damaged concrete.
There will be inevitable disruption to traffic during both the investigations and the remedial works.
Due to the high volumes of traffic at the sites of all 3 structures, it is imperative to minimise the duration of any road or lane closures. Therefore it will be necessary and prudent to co-ordinate the investigations and the repairs to be done in the shortest possible time and as simultaneously as practical. For example, the exposure of joints should be followed as quickly as possible with the reinstatement thereof; the exposure of reinforcement should be followed by the replacement of damaged bars and concrete while the structural support is still in place.
Of essence will be the CoH’s ability to secure funding for both the technical services and remedial works to ensure continuity of the two. The Road Fund administered by the Zimbabwe National Road Administration (ZiNaRA), which Fund has a provisionary budget for emergency works, is ideally positioned to provide the requisite funds.
Given the time constraints and the need for expedience, the CoH may need to approach the Procurement Regulatory Authority of Zimbabwe (PRAZ) to authorise the procurement procedures for the direct appointment of the requisite specialist services for both the technical (inspections, investigations and design) and construction services for the remedial works.