Post-tensioned stone is a high-performance composite construction material: stone held in compression with tension elements. The tension elements can be connected to the outside of the stone, but more typically uses tendons threaded internally through a duct formed from aligned drilled holes.
Post-tensioned stone ("PT stone") could consist of a single piece, but drill limitations and other considerations mean it is typically an assembly of multiple components with mortar between pieces. PT stone has been used in both vertical columns (posts), and in horizontal beams (lintels). It has also been used in more unusual stonemasonry engineering applications: arch stabilization, flexible foot bridges, and cantilevered sculptures.
A closely related method is pre-tensioned stone. [1] A duct is drilled into the stone is used to host a steel rod held in tension with jacks while the duct is filled with epoxy grout. After the epoxy has set, the ends of the rod can be released from the jacks, placing the stone under compression. Similar to pre-stressed concrete, the pre- and post-tensioned methods can be used in different contexts.
Post-tensioned stone also has a close affiliation with massive precut stone, which is the central technique of modern load-bearing stonemasonry.
"Post-tensioned stone increases the failure load of stone in bending, but also the stiffness of a structure by reducing joint cracking. This method of construction is widely used for concrete structures, but the advantages of using similar techniques with stone are only just being realised.". [2]
Stone has great compressive strength, so is ideal in compressive structures like stone arches. [3] However, it has relatively weak flexural strength (compared to steel or wood), so in isolation cannot be safely used in wide spans under tension. [3]
For concrete, this problem has been long solved: in addition to conventional tensile reinforcement, engineers developed prestressed concrete methods starting around 1888. Such tension-reinforced concrete applications combine compressive strength with pre-stressed tensile compression for combined strength much greater than either of the individual components, and have been in wide use for decades. One of the early concrete engineers Eugène Freyssinet improved concrete pre-stressing methods, and it is claimed that he also applied post-tensioned concrete methods to stone. [4] As for concrete, post-tensioning maintains stone in compression, thereby increasing its strength.
Post-tensioning is achieved steel tendons either threaded through ducts within the stone elements or along their surface. Once the stone components are in place, the tendons are tensioned using hydraulic jacks, and the force is transferred to the stone through anchorages located at the ends of the tendons. The tensioning process imparts a compressive force to the stone, which improves its capacity to resist tensile stresses that could otherwise cause cracking or failure.
Stone is 'natural precast concrete' so only needs to be cut (and strength tested) and post-tensioned prior to use in construction. Compared to concrete and steel, post-tensioned stone production has dramatically lower energy costs, with concomitant lower carbon emissions. [5]
Post-tensioned stone has potential to replace steel-reinforced concrete in some contexts, as, according to structural engineer Steve Webb "a post-tensioned stone beam is as strong as steel”. [6] "Post-tensioning offers new potential for the revival of masonry as a structural material". [7] Post-tensioned stone has the potential to be used in conjunction with massive precut stone in a range of designs.
In 2020, post-tensioned stone was featured prominently in "The New Stone Age" an exhibition at The Building Centre. [8]
Architect James Simpson writes: "The term 'engineered timber' is already commonly used in construction, so why not a structural 'engineered stone'? ... The most exciting possibility for the stone industry... is the possible creation of a system of engineered stone for framed, or partly framed, structures. This would exploit the compressive strength of stone, which can be greater than that of concrete, combined with post-tensioning by stainless steel rods. Walls, columns, beams and slabs could all be made from small pieces of factory-sawn stone, cut and pre-drilled to a design of standard components." [9]
Compared to reinforced concrete, post-tensioned stone has at least four advantages. [7] [3]
Compared to conventional stonemasonry, post-tensioned stone has substantial structural and weight benefits. [11] In addition, compared to standard stonemasonry, post-tensioned stone preassembly has at least three operational advantages [12]
The wide adoption of post-tensioned stone currently faces a number of challenges, including:
In the early 2020s, the dimension-stone industry in most countries was structured almost entirely for tiles and cladding.
Post-tensioned stone has been used in a range of applications. After experimental use in the 1990s, its application increased in the early 2020s in part due to awareness of the high carbon emissions associated with concrete.
Post-tensioned stone footbridges with spans up to 40 m have been built in Japan, Switzerland, Germany, and Spain, [7] and are sold commercially in spans of up to 20 m by Kusser Granitwerke.
While post-tensioned stone has only been used in construction applications since the 1990s, post-tensioned masonry more generally dates back to at least the early 1800s: "In 1825 a posttensioning method for tunnelling under the River Thames was utilized in England. The project involved the construction of vertical tube caissons of 15m diameter and 21 m height. The 0.75m thick brick walls were reinforced and posttensioned with 25mm diameter wrought iron rods.". [13] In the mid-20th century, the Sydney Opera House shells were constructed from pre-cast concrete masonry beams that were assembled into the roofs using post-tensioning. By 1982, post-tensioned masonry was sufficiently widespread to fill a book published by the Institution of Civil Engineers, though this was brick and precast concrete masonry. [14] In 1985 and 1986, structural engineer Remo Pedreschi and others published studies of post-tensioned brick. [15]
"The advantages of posttensioned stone are much the same as for concrete. It permits the stone to carry larger loads over longer spans than would be possible with conventional units. The stone units can be plant-fabricated in much larger units to span column to column in the building. Window systems can be carried directly on the stone panels, thereby eliminating a separate window support system. … A few structural applications have been built using beams for such building features as porticoes, where the live loads have been limited to roof loads and wind loads.". [17]
"A more than one hundred year old sandstone masonry building, … the GPO Tower will be strengthened with four vertical post-tensioning tendons, 19 diameter 0.5" strands each, and a number of horizontal prestressing bars diameter 35mm at floor levels. ... Special steel chairs will be used to anchor the tendons and spread the anchorage forces of 1,771 kN (400 kips). The anchorages of the unbonded tendons allow for monitoring and adjustment of the tendon forces to compensate volume changes of the sandstone, if necessary." [13]
"Punt da Suransuns is a stress-ribbon bridge with a span of 40 m … constructed with slabs of Andeer granite, which are prestressed over rectangular steel bars … When traversing the bridge the vertical oscillation can be felt, but pedestrians have commented that the bridge is not as flexible as it looks." [24]
Masonry is the craft of building a structure with brick, stone, or similar material, including mortar plastering which are often laid in, bound and pasted together by mortar. The term masonry can also refer to the building units themselves.
Structural engineering is a sub-discipline of civil engineering in which structural engineers are trained to design the 'bones and joints' that create the form and shape of human-made structures. Structural engineers also must understand and calculate the stability, strength, rigidity and earthquake-susceptibility of built structures for buildings and nonbuilding structures. The structural designs are integrated with those of other designers such as architects and building services engineer and often supervise the construction of projects by contractors on site. They can also be involved in the design of machinery, medical equipment, and vehicles where structural integrity affects functioning and safety. See glossary of structural engineering.
Reinforced concrete, also called ferroconcrete, is a composite material in which concrete's relatively low tensile strength and ductility are compensated for by the inclusion of reinforcement having higher tensile strength or ductility. The reinforcement is usually, though not necessarily, steel bars (rebar) and is usually embedded passively in the concrete before the concrete sets. However, post-tensioning is also employed as a technique to reinforce the concrete. In terms of volume used annually, it is one of the most common engineering materials. In corrosion engineering terms, when designed correctly, the alkalinity of the concrete protects the steel rebar from corrosion.
Stonemasonry or stonecraft is the creation of buildings, structures, and sculpture using stone as the primary material. Stonemasonry is the craft of shaping and arranging stones, often together with mortar and even the ancient lime mortar, to wall or cover formed structures.
A beam is a structural element that primarily resists loads applied laterally across the beam's axis. Its mode of deflection is primarily by bending, as loads produce reaction forces at the beam's support points and internal bending moments, shear, stresses, strains, and deflections. Beams are characterized by their manner of support, profile, equilibrium conditions, length, and material.
Prestressed concrete is a form of concrete used in construction. It is substantially "prestressed" (compressed) during production, in a manner that strengthens it against tensile forces which will exist when in service.
This page is a list of construction topics.
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.
Structural steel is a category of steel used for making construction materials in a variety of shapes. Many structural steel shapes take the form of an elongated beam having a profile of a specific cross section. Structural steel shapes, sizes, chemical composition, mechanical properties such as strengths, storage practices, etc., are regulated by standards in most industrialized countries.
Precast concrete is a construction product produced by casting concrete in a reusable mold or "form" which is then cured in a controlled environment, transported to the construction site and maneuvered into place; examples include precast beams, and wall panels for tilt up construction. In contrast, cast-in-place concrete is poured into site-specific forms and cured on site.
This is an alphabetical list of articles pertaining specifically to structural engineering. For a broad overview of engineering, please see List of engineering topics. For biographies please see List of engineers.
The history of structural engineering dates back to at least 2700 BC when the step pyramid for Pharaoh Djoser was built by Imhotep, the first architect in history known by name. Pyramids were the most common major structures built by ancient civilizations because it is a structural form which is inherently stable and can be almost infinitely scaled.
In structural engineering, a prestressed structure is a load-bearing structure whose overall integrity, stability and security depend, primarily, on prestressing: the intentional creation of permanent stresses in the structure for the purpose of improving its performance under various service conditions.
In structural engineering, a pre-engineered building (PEB) is designed by a PEB supplier or PEB manufacturer with a single design to be fabricated using various materials and methods to satisfy a wide range of structural and aesthetic design requirements. This is contrasted with a building built to a design that was created specifically for that building. Within some geographic industry sectors pre-engineered buildings are also called pre-engineered metal buildings (PEMB) or, as is becoming increasingly common due to the reduced amount of pre-engineering involved in custom computer-aided designs, simply engineered metal buildings (EMB).
Structural engineering depends on the knowledge of materials and their properties, in order to understand how different materials resist and support loads.
In the Eurocode series of European standards (EN) related to construction, Eurocode 2: Design of concrete structures specifies technical rules for the design of concrete, reinforced concrete and prestressed concrete structures, using the limit state design philosophy. It was approved by the European Committee for Standardization (CEN) on 16 April 2004 to enable designers across Europe to practice in any country that adopts the code.
Kolbjørn Saether P.E., M.ASCE was an American structural engineer in the City of Chicago for 47 years. Saether dedicated his life to engineering and was known as a leader in his field. He was a past director of the Structural Engineers Association of Illinois and was the organization's president from 1980 to 1981. During his career he developed innovative engineering solutions for skyrise building construction that are now part of the Chicago skyline, published theoretical insights to enhance the state of the art in structural engineering, and patented novel techniques to advance the art of building construction.
This glossary of structural engineering terms pertains specifically to structural engineering and its sub-disciplines. Please see glossary of engineering for a broad overview of the major concepts of engineering.
This page is a glossary of Prestressed concrete terms.
Massive-precut stone is a modern stonemasonry method of building with load-bearing stone. Precut stone is a DFMA construction method that uses large machine-cut dimension stone blocks with precisely defined dimensions to rapidly assemble buildings in which stone is used as a major or the sole load-bearing material.