New Technique Could Preserve Historic Buildings
Researchers from the University of Sheffield have reportedly developed a new method to assess the safety of stone and brick constructions, which could help preserve historic stone buildings and bridges.
According to the release, the team hopes that this approach will allow for more masonry structures to be restored and used long into the future, rather than demolished and replaced. The thrust layout optimization method, carried out by the university’s Department of Civil and Structural Engineering, was recently published in the journal Proceedings of the Royal Society A.
About the Research
The university says that, since the late 1600s, engineers have used scientist Robert Hooke’s “thrust line method” to evaluate the safety of masonry buildings and bridges. However, the traditional method has limitations, such as exercising careful judgement, neglecting the possibility of failure due to sliding and providing unclear assessments of certain areas’ tensile capacity.
“Stone and brick masonry has been used for millennia to form buildings and bridges ranging in scale from humble dwelling houses to cathedrals and railway viaducts. Many of these structures have considerable historic value, and, to ensure they remain safe and fit for purpose, effective assessment methods are required,” said research team leader Matthew Gilbert, professor of Civil Engineering.
“A long-running problem is that the ways in which applied forces are successfully transmitted down to the ground in masonry structures are often not intuitively obvious, so digital tools that help explain this to engineers are potentially invaluable.
Our researchers have developed a new engineering technique which could help to preserve historic structures such as medieval cathedrals. (1/2) pic.twitter.com/IuU2n2Np7Q— The University of Sheffield (@sheffielduni) May 22, 2023
“The current climate crisis also makes it particularly important that engineers have access to efficient and reliable tools to assess the safety of existing masonry constructions—helping to ensure that these can be used long into the future, rather than being needlessly demolished and replaced.”
To overcome these limitations, Sheffield researchers developed a new approach that can reportedly be applied to masonry constructions of any geometry, with or without openings. The method also identifies regions in structures where some tensile capacity is needed.
The new thrust layout optimization technique is an extension of Hooke’s model, the team explained. Additionally, the researchers report they have open source software that, with further development, will allow practicing engineers and architects to assess the safety of stone and brick masonry constructions.
“There has been a resurgence in interest in using stone in construction, as it’s a low embodied carbon material—however, suitable digital analysis and design tools are needed to translate this interest into more widespread use,” said lead author Isuru Nanayakkara, a research student at the university.
“Currently, engineers have been turning to analysis and design tools that are better suited for steel and concrete structures, which means that steel reinforcement is sometimes being used in new masonry designs when it’s not needed. We hope that our new thrust layout optimization technique can help here—we’re making available open-source software for interested structural engineers and architects and we welcome their feedback on this.”
Recent Historic Structure Research
Earlier this year, in January, a team of researchers from the Massachusetts Institute of Technology, Harvard University and laboratories in Italy and Switzerland were studying ancient Roman concrete to crack the code of what makes the material ultradurable.
For their study, the team looked at how concrete structures like the Pantheon and ancient Roman aqueducts, as well as structures that have undergone harsh conditions such as docks, sewers, and seawalls or those constructed in seismically active locations, managed to stay intact after all this time.
The team of researchers had recently discovered ancient concrete-manufacturing strategies that incorporated several key self-healing functionalities. Previously, other researchers observing the same ancient concrete were often noted to attribute the material’s durability on a mixture of pozzolanic material, such as volcanic ash, and millimeter-scale bright white mineral known as “lime clasts.”
In October 2021, researchers from MIT and the University of Utah conducted research on a 2,050-year-old Roman tomb for insight into concrete resilience. For their study, researchers looked at the tomb of first-century noblewoman Caecilia Metella.
A landmark on the Via Appia Antica, the tomb of Caecilia Metella consists of a rotunda-shaped tower on a square base, measuring roughly 70 feet tall and 100 feet in diameter. The tomb was constructed in about 30 BCE, when the Roman Republic was transforming into the Roman Empire, using a mixture of coarse brick or volcanic rock aggregate bound with mortar made with lime and volcanic tephra (porous fragments of glass and crystals from explosive eruptions).
The crystals, formed from the potassium-rich mineral leucite, dissolved over time, causing the structure to remodel and reorganize the interface between volcanic aggregates and the cementitious binding matrix, improving the cohesion of the concrete.
Looking at the microstructure of the concrete, researchers discovered that the concrete mixture used for the tomb was similar to the mortar used in the Markets of Trajan 120 years later. The glue of the Markets of Trajan mortar consists of a building block called the C-A-S-H binding phase (calcium-aluminum-silicate-hydrate), along with crystals of a mineral called strätlingite.
What made the tomb’s concrete stronger, however, was the leucite that managed to strengthen the structure over centuries of rainwater and groundwater percolating through the tomb’s walls, reconfiguring the C-A-S-H binding phase.