Nondestructive Evaluation: Structural Performance of Masonry
Masonry is one of the world’s most durable construction materials. Masonry structures can remain in service for hundreds or even thousands of years. Masonry structures often outlive their designers, their original design documents, and their original functions. When historic masonry structures are evaluated for preservation, adaptive use, or additions, there are numerous questions that may arise about the construction and the condition of the brick, stone, concrete block, and mortar. One of the first questions typically asked by the design or investigation team is “How is it performing?” It is important to understand observed distress, such as cracks, corrosion, and surface erosion. Often the cause and/or extent of distress can play a major role in rehabilitation work and in determining what other types of nondestructive evaluation are required. Another common question about masonry is “How strong is it?” In order to conduct a structural evaluation, an engineer must have at least some information about the strength of the masonry. A related question often asked next is “How was it constructed?” Masonry characteristics such as ties, voids, headers, and embedded items are often hidden from view, but these items are critical to understanding how the assembly will perform. Finally, in some cases it is important to ask “What is it doing right now?” It can be vital to understand what types of loads and stresses the masonry is currently experiencing, especially in order predict future performance under new or different loads. Other questions regarding moisture permeability, acoustic properties, or thermal behavior of masonry may also arise. This Practice Point focuses on these fundamental questions by providing a summary of current nondestructive-evaluation tools available for the assessment of historic masonry. While case studies and descriptions of specific nondestructive test methods are fairly common, this article provides an overview of numerous techniques, both listing the technologies available and helping in the selection of an appropriate method. A wide range of evaluation methods are available for use, and many claims are made regarding the accuracy of Practice Points NUMBER 09
Filling in the Blanks: Documenting Concealed Fabric and Deterioration in Existing Structures
The need to develop a highly accurate set of “as-found” condition documents presents a significant challenge in the practice of architecture for any project involving an existing building. For the majority of new buildings, an adequate construction documentation package can be developed simply by applying industry standards along with carefully engineered and well-detailed methods and materials. In contrast, projects involving intervention in existing buildings require an in-depth understanding of the existing building, its methods of construction, and any deterioration that exists. This requirement is particularly critical in the practice of preservation architecture, when renovation, adaptive re-use, and/or restoration projects affect structures with physical fabric of intrinsic historic value. Existing guidelines, such as those of HABS, attempt to ensure that recording is performed in a useful manner that meets certain minimum standards; however, these address only visible conditions, those that can be measured and photographed and those where physical reality is fully observable. Advancements in technology have allowed a marked increase in the ability to understand both the layout of concealed elements, such as wood framing configurations, and the existence of deterioration mechanisms invisible to the naked eye. Unfortunately, these advancements have not necessarily corresponded with the development of standards and guidelines for systematically conducting this type of investigation. Based in part on the author’s experience as a preservation architect, this thesis outlines a methodology and approach for documenting concealed fabric and conditions in historic buildings.
THE APPLICATION OF THE METHOD OF CONVOLUTION TO THE SIMULATION OF THE RESPONSE OF MASONRY ARCH BRIDGES TO GROUND PROBING RADAR
Abstract The development of Ground Probing Radar (GPR) in the investigation of masonry arch bridge systems has been restricted due to the requirement of specialist interpretation of the data. There is therefore a need for a method of simulation which aids the interpretation of GPR surveys. The method of convolution allows rapid simulation of varying geometries and material properties to be investigated. The combination of digital GPR systems along with simulation software will help a better engineering assessment to be made of the many masonry arch bridge systems now under review in the UK at the present time.