DD2378 City Hall Structural Integrity Investigation and Diagrid Survey

A leak on the remembrance gallery was observed mid May 2019, investigated July/August 2019 and identified as coming from the diagrid heating system pipe located behind the ‘Christmas Tree’ façade on the north side of City Hall.

On the 13 May 2019, Arup attended to inspect and carry out Non-Destructive Testing (NDT) around the area of the leak in the horizontal diagrid pipe adjacent to Level 4. Some reduction of wall thickness around the area of the leak was observed. Arup carried out a series of spot checks along the underside of the pipe to attempt to detect other areas of reduced wall thickness. Within the limitations of this inspection technique, five other areas of reduced wall thickness were identified.

Given these findings, Arup recommended further, more detailed investigative works. These further works are the subject of this proposal. Due to concerns regarding the structural integrity of the façade, this emergency work was commissioned with support from TfL Procurement, as a single source tender, from Arup. The justification for the single source tender was the urgency of the situation and Arup’s expertise in this matter.

The expenditure was required for a technical survey and report to be carried out by Arup and the provision of access equipment by All Clean Services Ltd. to allow access to the high-level areas of the Diagrid structure. All Clean Services Ltd were appointed via an existing contract for services that was procured in accordance with the GLA Contracts and Funding Code to provide window cleaning, abseiling and high-level access works, until 2022.

The survey works by Arup and All Clean Services Ltd is complete and a detailed survey and structural analysis report outlining the finding has been compiled by Arup. The works were started as soon as it was identified that there was a leak, as time was of the essence to establish what the risks are and what condition the pipes are in. The works were started prior to the DD approval as it was critical to establish the condition of the pipes as soon as possible. As such the costs have already been incurred and this report is therefore also seeking confirmation of the verbal approval to the incurred costs provided by the GLA’s Chief of Staff and Chief Officer.

Confirmation of approval is therefore sought for expenditure of £95,000 to Arup for Technical advice, survey work, a detailed structural analysis report and a single source exemption for Arup, in addition to expenditure of £25,000 to All Clean Services Ltd for access equipment and abseilers’ to facilitate the survey.

The survey of the diagrid used a combination of magnetic flux leakage (MFL) and ultrasonic testing (UT). These are both non-destructive inspection techniques and were undertaken by Arup’s specialist sub-contractor Advanced Engineering Solutions Ltd. (AES).

The current condition of the isolated horizontal piping at Level 4 has been assessed by Arup and appropriate advice given due to concern around its structural stability.

Arup have provided a detailed assessment of the general condition of the internal pipe surface and identify locations of pitting/localised corrosion.

A detailed report on the condition of the diagrid, its suitability for heating, a review of LTHW water quality management has been provided by Arup. They have provided commentary on the feasibility of repairing and maintaining the existing system and made recommendations for future maintenance and monitoring.

Arup recommend decommissioning of the diagrid perimeter heating system, undertaking a cosmetic repair and installing an alternative diagrid heating system.

Further recommendations are to treat the whole low temperature hot water (LTHW) system with a suitable biocide, cleaning and disinfection of the make-up water pressurisation unit and pipework and ongoing monitoring of the system.

Under section 149 of the Equality Act 2010 (the “Equality Act”), as a public authority, the GLA must have ‘due regard’ to the need to eliminate unlawful discrimination, harassment and victimisation, and to advance equality of opportunity and foster good relations between people who share a protected characteristic and those who do not. Protected characteristics under the Equality Act comprise age, disability, gender re-assignment, pregnancy and maternity, race, religion or belief, sex, sexual orientation and marriage or civil partnership status. Facilities Management have determined there will be no impacts on those with protected characteristics under the Public Sector Equality Duty arising from delivery of these services.

Key Risks & Issues

The diagrid structurally supports the façade and hangers for the spiral ramp, and forms part of the low temperature hot water (LTHW) perimeter heating system. Any structural defects would make the building structurally unsafe thereby render City Hall uninhabitable, hence why survey works were required urgently.

The risks associated with the recommended remedial words will be assessed prior to works being carried out.

Links to Mayoral strategies

Facilities Management support the operation of the Greater London Authority’s estate and therefore indirectly support all Mayoral strategies and operations.

Consultations and impact assessments

The investigation will be used to consider the impact on users of the building and used in consultation with the landlords in relation to the fully repairing lease agreement.

Approval is sought for confirmation of expenditure of £120,000 to fund an onsite survey and inspection as a result of leaks from the diagrid heating system at City Hall. The cost will be funded from Resources 2019-20 Estates Reserves.

Sections 1 to 5 of this report indicate that the decisions requested of the Director (in accordance with the GLA’s Contracts and Funding Code) concern the exercise of the GLA’s general powers, falling within the GLA’s statutory powers to do such things considered to further or which are facilitative of, conducive or incidental to the promotion of economic development and wealth creation, social development or the promotion of the improvement of the environment in Greater London; and in formulating the proposals in respect of which a decision is sought officers have complied with the Authority’s related statutory duties to:

• pay due regard to the principle that there should be equality of opportunity for all people;
• consider how the proposals will promote the improvement of health of persons, health inequalities between persons and to contribute towards the achievement of sustainable development in the United Kingdom; and
• consult with appropriate bodies.

In taking the decisions requested, the Director must have due regard to the Public Sector Equality Duty; namely the need to eliminate discrimination, harassment, victimisation and any other conduct prohibited by the Equality Act 2010 and to advance equality of opportunity and foster good relations between persons who share a relevant protected characteristic (race, disability, sex, age, sexual orientation, religion or belief, pregnancy and maternity and gender reassignment) and persons who do not share it (section 149 of the Equality Act 2010). To this end, the Director should have regard to section 3 (above) of this report.

The approval to incur the expenditure is sought as confirmation of verbal agreement, the reasons for which are set out at paragraph 1.5 of this report. Accordingly, the Director should take account of those reasons in considering whether to approve the recommendations of this report.

Section 9.1 of the Contracts and Funding Code (the ‘Code’) requires the GLA to seek a call-off from a suitable framework, where possible, or if not, undertake a formal tender process which will be managed by TfL in respect of the services. However, the director may approve an exemption from this requirement under section 10 of the Code upon certain specified grounds. Officers have indicated at paragraph 1.3 of this report why an exemption was sought to appoint Arup and the Director may approve the proposed exemption if satisfied with the content of this report.

Officers have indicated in paragraph 1.4 of this report that the services/supplies that were provided by All Clean Services Ltd were procured in accordance with the Public Contracts Regulations 2016 in accordance with the GLA’s Contracts and Funding Code.