Track 1: DOCUMENTATION AND DIAGNOSTICS – UNDERSTANDING HISTORIC PLACES / Volet 1 : Documentation et diagnostic – Comprendre les lieux historiques

Understanding existing conditions using NDE and targeted probes for a planned rehabilitation of Union Station façade, Toronto

Friday, October 13
10:30 AM - 12:15 PM

This abstract explores the efficient combined application of Non-Destructive Evaluation (NDE) techniques with targeted intrusive probes, to document the construction arrangement and the material condition of the limestone façade at Toronto’s Union Station.
Prior to the planned extensive restoration and revitalization program of 2010-14 there was a requirement to understand the construction and condition of the façade, to be verified by a series of probes and exposures.
In order to ensure that each exposure was targeted to maximize information pertinent to the restoration design, a number of locations across the facade were selected for investigation using the NDE techniques of Ground Penetrating Radar (GPR) and Metal Detection.
153 stone panels were surveyed using these techniques, to identify:
• Limestone panel thicknesses.
• Location and distribution of anchors, fixing stone to back-up masonry.
• Condition of embedded anchors.
GPR is commonly used for the estimation of the thickness of broadly homogenous building materials such as stone, brick and concrete, but this calculation relies on an assumption that the ‘radar velocity’ (the speed at which the radar wave propagates through the material) is in line with published values. Wherever possible, determination of specific material velocity values is prudent, and in this case was facilitated by the localized removal of a number of limestone pieces. In this way, actual stone thicknesses were measured and compared with the GPR data responses for calibration, so that the calculated velocity could then be extrapolated across the rest of the data set collected from the façade.
By combining NDE with targeted probes, the initial observations and analysis from the data could be ‘tested’ through examination of actual building conditions, and analysis parameters could then be modified based on the findings.
The position of each anchor was first identified, then each anchor denoted a ‘corrosion condition’ by measuring the attenuation of the radar signal from around the anchors (where expansive corrosion of the anchors occurs, this causes damage to the surrounding stone and setting compound in the form of micro cracking, which causes the signal attenuation).
However, following the removal of a stone where the GPR data analysis had suggested one ‘sound’ and one ‘corroding’ anchor but two ‘sound’ anchors were instead revealed, the false ‘corroding’ response was shown to correspond with insufficient setting compound having been placed during construction.
The analysis criteria for the remainder of the façade was therefore modified based on these findings, which were shown to be critical to the restoration effort, as 60% of all surveyed anchors connecting the limestone panes to the back-up masonry were shown to have similarly flawed mechanical connections.

Learning Objectives:

Christopher Gray, FRICS

Associate Reality Capture + Preservation
GB Geotechnics USA Inc.

Chris Gray is a fellow of the Royal Institution of Chartered Surveyors – an international expert with over 30 years of experience in the reality capture of complicated buildings in the USA and Internationally. He specializes in the use of innovative survey tools, to include laser scanning and photogrammetry, to generate highly accurate CAD, BIM and more recently augmented and virtual reality. His career includes head of survey procurement at English Heritage, and head of survey at the Getty Conservation Institute. He is co-chair of the APTI Tech Committee for Documentation.


Send Email for Christopher Gray

Stephen J. Kelley, FAIA, SE, FAPT, FUSICOMOS

Stephen J Kelley, Inc.

Stephen J. Kelley is a registered architect and structural engineer in private practice who has devoted these two skills to the preservation of our built cultural heritage. With 35 years of experience, his projects range from small to immense, simple to sophisticated and cover a wide range of building materials and systems. His award-winning projects are located throughout the United States but he has also worked on significant projects in Asia, Europe, Africa, South America and the Caribbean basin. He has published widely on various aspects of preservation and is an educator who has taught at the university level thus sharing his experience with the next generation of preservation professionals. He has served on the Board of Directors of both the US Committee of the International Council on Monuments and Sites (US/ICOMOS) and the Association for Preservation Technology (APT) and was elevated to Fellowship in both organizations. He is a UNESCO Tangible Heritage Expert and is Vice President of the International Scientific Committee on the Analysis and Restoration of Structures of Architectural Heritage (ISCARSAH).


Send Email for Stephen Kelley


Understanding existing conditions using NDE and targeted probes for a planned rehabilitation of Union Station façade, Toronto

Attendees who have favorited this

Please enter your access key

The asset you are trying to access is locked. Please enter your access key to unlock.

Send Email for Understanding existing conditions using NDE and targeted probes for a planned rehabilitation of Union Station façade, Toronto