A bald arch is an arch featuring decay on the crucial keystones in stone or masonry buildings. Left unchecked, the progression of the condition will eventually lead to the failure of the arch and any structures supported by it.
A bald arch is an arch featuring decay on the crucial keystones in stone or masonry buildings. Left unchecked, the progression of the condition will eventually lead to the failure of the arch and any structures supported by it.
The structural degradation of arches can occur for a variety of reasons. The stones or masonry components that make up an arch are vulnerable to physical and chemical attack over long periods of time. Sources of damage include atmospheric conditions, human induced mechanical stress, improper design, and natural disturbances like earthquakes or wildlife.
Movement of the ground beneath an arch will eventually destroy it by changing the mechanical relationship between stones in the arch. An arch will evenly distribute forces across the surfaces of each stone when it is properly emplaced. Moving the ground below the arch will negatively affect the distribution of stress. An arch will slump in the center if the two sides move apart. [1] If the sides are moved closer together, a hinge will form in the arch, increasing the stress on that area. [2] Arches can also become angled away from level, inducing forces that are not normal to the faces of the individual stones.
The ground can shift over long periods of time for many reasons: earthquakes, frost, swelling clays, tree roots, animal burrows, and unstable soils all have the potential to move the foundation of a building. [1]
The weather plays an important role in destroying stone structures. Daily or annual freeze/thaw cycles cause water trapped in cracks to expand, breaking up the stones or causing them to shift from their original setting. [1] Frost heaving in the ground may move the structure, making it unstable. [1] Precipitation can also be detrimental for certain materials. Limestone and cement are subject to weathering from rain. [3] Natural rainwater has a pH of 5.6 due to carbon dioxide in the atmosphere. [4] This is low enough to dissolve the calcium carbonate that constitutes limestone and cement. Air pollution can greatly enhance this effect by dropping the pH of the rainwater. [3] In the eastern United States, the pH of rainwater can be as low as 2.0. [4]
Rain can also dissolve salts from the stone or other sources and redeposit the salt into cracks in the stones or between them. The salts will then crystalize as the water evaporates, putting pressure on the edges of the crack and causing the stones to move or chip. [3] This effect is most pronounced in coastal and urban environments. [1] Salt damage is also prevalent in cities that employ salts to deice roads and sidewalks. [1]
If an arch includes mortar between the stones, the mortar becomes a likely point of weathering. As the mortar decays, the stones on either side will become unsupported and lead to failure.
Human activities causing vibration can inadvertently damage stone arches, like other structural elements. [5] The vibrations caused by road traffic can cause stones to grind one another and shift over time. The arch may eventually become unstable and collapse.
Arches that lack adequate support on the sides will slump and fail. All arches convert some of the weight of the structure into a horizontal outwards thrust. The structure may be stable for a time, but the arch will push the walls around it outwards continuously. This is prevented by proper engineering. Arches can be supported by a buttress on the outer wall, thick, heavy wall construction between the arch and the corner, or by using arches in a series so that each arch is opposed by two others on its sides.
The bald arch condition can be prevented by taking precautions during the construction phase and by properly maintaining the stonework over time. Ground movement can be avoided by using a solid foundation. Removing vegetation from near the foundation and preventing animals from burrowing will help to keep the foundation stable.
Frost damage can be reduced by ensuring drainage around the building and by keeping the roof in good condition. This will keep water from saturating the stone and cracking it during cold weather. Keeping water off of the stone will also prevent salt and acid rain damage. Unfortunately, it is not always possible to keep the rainwater off the walls. Paint can be applied to the stones to protect them from rain and pollution, but this is often rejected because it alters the appearance of historic buildings. [3] Cleaning the stone regularly can help to reduce the effects of chemical weathering. [3] Pollutants accumulate on the exterior surfaces of the stone. They react with the stone and degrade the outer portions. This will degrade the appearance of the stone and eventually weaken it to the point of failure. The most popular methods are scrubbing with fresh water or steam cleaning. This is very expensive and time-consuming for a large building. It may be impossible to treat the entire building in one season, and scaffoldings will need to be erected to reach the higher parts.
It is often desirable to preserve an arch because they are common in historic and monumental architecture. Numerous methods are employed for restoring or preserving degraded arches. The first stage in restoring an arch is to evaluate the structure to determine how serious the damage is and what technique is best suited for repair. An architect or engineer will measure the rate of deformation over some period of time, to see how fast the arch is degrading. The deformation could have occurred immediately after construction during the settling period. If that is the case, it is less urgent to repair the damage. [2]
The goal of the restoration is an important consideration. If the goal is only to prevent further deterioration, there will be less work than if the goal is to restore the original condition.
An arch may be shored up by adding new materials to the structure. The mode of failure determines how the arch should be reinforced. The most common failure for arches is an outwards movement of stones near the top. An arch will constantly apply pressure sideways, so the outwards pressure must be managed. If the arch is failing sideways, a buttress can be built to contain the lateral thrust. Steel tensioning rods can take the place of an external buttress to maintain the original appearance in some cases. [3]
Removing any stone from an arch without preparing the entire arch will cause it to fail. The arch must be supported before any work can be done. This is done with a falsework of wooden trusses, similar to how the arch is initially built. The entire arch is supported by the wooden falsework. Individual stones can then be removed and repaired or replaced. Repointing or grouting the joints between stones can greatly improve the integrity of the structure. [2] If the arch has slumped it can be shored up using a hydraulic jack, and then the stones can be pushed into place and repointed. This can be a very demanding job, since any structures supported by the arch will need to be supported while the arch is repaired.
The arches also can be reinforced using steel trusses. Some opponents believe that this degrades the appearance of the arches, that it makes them look like dental braces. Without this support, the building would be structurally unsound.
Masonry is the craft of building a structure with brick, stone, or similar material, which are often laid in and bound together by mortar; the term masonry can also refer to the building units themselves. The common materials of masonry construction are bricks and building stone such as marble, granite, and limestone, cast stone, concrete blocks, glass blocks, and adobe. Masonry is generally a highly durable form of construction. However, the materials used, the quality of the mortar and workmanship, and the pattern in which the units are assembled can substantially affect the durability of the overall masonry construction. A person who constructs masonry is called a mason or bricklayer. These are both classified as construction trades.
Weathering is the deterioration of rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs in situ, and so is distinct from erosion, which involves the transport of rocks and minerals by agents such as water, ice, snow, wind, waves and gravity.
The technical meaning of maintenance involves functional checks, servicing, repairing or replacing of necessary devices, equipment, machinery, building infrastructure, and supporting utilities in industrial, business, and residential installations. Over time, this has come to include multiple wordings that describe various cost-effective practices to keep equipment operational; these activities occur either before or after a failure.
An arch bridge is a bridge with abutments at each end shaped as a curved arch. Arch bridges work by transferring the weight of the bridge and its loads partially into a horizontal thrust restrained by the abutments at either side. A viaduct may be made from a series of arches, although other more economical structures are typically used today.
Mortar is a workable paste which hardens to bind building blocks such as stones, bricks, and concrete masonry units, to fill and seal the irregular gaps between them, spread the weight of them evenly, and sometimes to add decorative colors or patterns to masonry walls. In its broadest sense, mortar includes pitch, asphalt, and soft mud or clay, as those used between mud bricks, as well as cement mortar. The word "mortar" comes from Old French mortier, "builder's mortar, plaster; bowl for mixing." (13c.).
The flying buttress is a specific form of buttress composed of an arch that extends from the upper portion of a wall to a pier of great mass, in order to convey to the ground the lateral forces that push a wall outwards, which are forces that arise from vaulted ceilings of stone and from wind-loading on roofs.
Repointing is the process of renewing the pointing, which is the external part of mortar joints, in masonry construction. Over time, weathering and decay cause voids in the joints between masonry units, usually in bricks, allowing the undesirable entrance of water. Water entering through these voids can cause significant damage through frost weathering and from salt dissolution and deposition. Repointing is also called pointing, or pointing up, although these terms more properly refer to the finishing step in new construction.
Earthquake engineering is an interdisciplinary branch of engineering that designs and analyzes structures, such as buildings and bridges, with earthquakes in mind. Its overall goal is to make such structures more resistant to earthquakes. An earthquake engineer aims to construct structures that will not be damaged in minor shaking and will avoid serious damage or collapse in a major earthquake. A properly engineered structure does not necessarily have to be extremely strong or expensive. It has to be properly designed to withstand the seismic effects while sustaining an acceptable level of damage.
Lime mortar or torching is composed of lime and an aggregate such as sand, mixed with water. The ancient Egyptians were the first to use lime mortars, which they used to plaster their temples. In addition, the Egyptians also incorporated various limes into their religious temples as well as their homes. Indian traditional structures built with lime mortar, which are more than 4,000 years old like Mohenjo-daro is still a heritage monument of Indus valley civilization in Pakistan. It is one of the oldest known types of mortar also used in ancient Rome and Greece, when it largely replaced the clay and gypsum mortars common to ancient Egyptian construction.
Structural dampness is the presence of unwanted moisture in the structure of a building, either the result of intrusion from outside or condensation from within the structure. A high proportion of damp problems in buildings are caused by ambient climate dependent factors of condensation and rain penetration. Capillary penetration of fluid from the ground up through concrete or masonry is known as "rising damp" and is governed by the shape and porosity of the construction materials through which this evaporation-limited capillary penetration takes place. Structural damp, regardless of the mechanisms through which it takes place, is exacerbated by higher levels of humidity.
Damp proofing in construction is a type of moisture control applied to building walls and floors to prevent moisture from passing into the interior spaces. Dampness problems are among the most frequent problems encountered in residences.
The 1975 Kinnaur earthquake occurred in the early afternoon of 19 January. It had a magnitude of 6.8 on the surface wave magnitude scale and a maximum perceived intensity of IX (Violent) on the Mercalli intensity scale, causing extensive damage in Himachal Pradesh, in northern India. Its epicentre was in Kinnaur district in the southeastern part of Himachal Pradesh and caused 47 casualties. Landslides, rock falls and avalanches caused major damage to the Hindustan-Tibet Road. The earthquake affected many monasteries and buildings in the state and led to an extensive restoration work in the late 1970s and early 1980s in Himachal Pradesh. The Spiti and Parachu valleys in particular suffered the greatest damage being on the north–south Kaurik-Chango fault, causing damage to landmarks such as Key Monastery and Tabo Monastery.
Concrete degradation may have many different causes. Concrete is mostly damaged by the corrosion of reinforcement bars due to the carbonatation of hardened cement paste or chloride attack under wet conditions. Chemical damages are caused by the formation of expansive products produced by various chemical reactions, by aggressive chemical species present in groundwater and seawater, or by microorganisms. Other damaging processes can also involve calcium leaching by water infiltration and different physical phenomena initiating cracks formation and propagation. All these detrimental processes and damaging agents adversely affects the concrete mechanical strength and its durability.
The expansive force of rusting, which may be called oxide jacking or rust burst, is a phenomenon that can cause damage to structures made of stone, masonry, concrete or ceramics, and reinforced with metal components. A definition is "the displacement of building elements due to the expansion of iron and steel products as the metal rusts and becomes iron oxide". Corrosion of other metals such as aluminum can also cause oxide jacking.
Conservation and restoration of ceramic objects is a process dedicated to the preservation and protection of objects of historical and personal value made from ceramic. Typically, this activity of conservation-restoration is undertaken by a conservator-restorer, especially when dealing with an object of cultural heritage. Ceramics are created from a production of coatings of inorganic, nonmetallic materials using heating and cooling to create a glaze. These coatings are often permanent and sustainable for utilitarian and decorative purposes. The cleaning, handling, storage, and in general treatment of ceramics is consistent with that of glass because they are made of similar oxygen-rich components, such as silicates. In conservation ceramics are broken down into three groups: unfired clay, earthenware or terracotta, and stoneware and porcelain.
Structural integrity and failure is an aspect of engineering that deals with the ability of a structure to support a designed structural load without breaking and includes the study of past structural failures in order to prevent failures in future designs.
The conservation and restoration of frescoes is the process of caring for and maintaining frescos, and includes documentation, examination, research, and treatment to insure their long-term viability, when desired.
The conservation and restoration of lighthouses is when lighthouse structures are preserved through detailed examination, cleaning, and in-kind replacement of materials. Given the wide variety of materials used to construct lighthouses, a variety of techniques and considerations are required. Lighthouses alert seagoers of rocky shores nearby and provide landmark navigation. They also act as a physical representation to maritime history and advancement. These historic buildings are prone to deterioration due to their location on rocky outcrops of land near the water, as well as severe weather events, and the continued rise of sea levels. Given these conditions preservation and conservation efforts have increased.
Daytona Beach Coquina Clock Tower is a clock tower located in Daytona Beach, Florida. It is a contributing property within the Daytona Beach Bandshell and Oceanfront Park Complex historic district which was entered into the United States National Register of Historic Places (VO7135) on February 25, 1999 from a multiple property submission under the following areas of significance: Entertainment, Recreation, Community Planning and Development, and Architecture.