Moment-resisting frame

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Moment-resisting frame is a rectilinear assemblage of beams and columns, with the beams rigidly connected to the columns.

Resistance to lateral forces is provided primarily by rigid frame action – that is, by the development of bending moment and shear force in the frame members and joints. By virtue of the rigid beam–column connections, a moment frame cannot displace laterally without bending the beams or columns depending on the geometry of the connection. The bending rigidity and strength of the frame members is therefore the primary source of lateral stiffness and strength for the entire frame. [1]

A rigid frame in structural engineering is the load-resisting skeleton constructed with straight or curved members interconnected by mostly rigid connections which resist movements induced at the joints of members. Its members can take bending moment, shear, and axial loads.

Bending moment

A bending moment is the reaction induced in a structural element when an external force or moment is applied to the element causing the element to bend. The most common or simplest structural element subjected to bending moments is the beam. The diagram shows a beam which is simply supported at both ends. Simply supported means that each end of the beam can rotate; therefore each end support has no bending moment. The ends can only react to the shear loads. Other beams can have both ends fixed; therefore each end support has both bending moment and shear reaction loads. Beams can also have one end fixed and one end simply supported. The simplest type of beam is the cantilever, which is fixed at one end and is free at the other end. In reality, beam supports are usually neither absolutely fixed nor absolutely rotating freely.

Shear force

Shearing forces are unaligned forces pushing one part of a body in one specific direction, and another part of the body in the opposite direction. When the forces are aligned into each other, they are called compression forces. An example is a deck of cards being pushed one way on the top, and the other at the bottom, causing the cards to slide. Another example is when wind blows at the side of a peaked roof of a house - the side walls experience a force at their top pushing in the direction of the wind, and their bottom in the opposite direction, from the ground or foundation. William A. Nash defines shear force in terms of planes: "If a plane is passed through a body, a force acting along this plane is called a shear force or shearing force."

The 1994 Northridge earthquake revealed a common flaw in steel-frame construction — poorly welded moment connections — and building codes were revised to strengthen them. [2]

1994 Northridge earthquake Earthquake

The 1994 Northridge earthquake was a magnitude of 6.7 (Mw), blind thrust earthquake that occurred on January 17, 1994, at 4:30:55 a.m. PST in the San Fernando Valley region of the County of Los Angeles. Its epicenter was in Reseda, a neighborhood in the north-central area of the San Fernando Valley. The quake had a duration of approximately 10–20 seconds, and its peak ground acceleration of 1.8g (16.7 m/s2) was the highest ever instrumentally recorded in an urban area in North America. Strong ground motion was felt as far away as Las Vegas, Nevada, about 220 miles (360 km) from the epicenter. The peak ground velocity at the Rinaldi Receiving Station was 183 cm/s, the fastest ever recorded.

Early history

Steel moment-resisting frames have been in use for more than one hundred years, dating to the earliest use of structural steel in building construction. Steel building construction with the frame carrying the vertical loads initiated with the Home Insurance Building in Chicago, a 10-story structure constructed in 1884 with a height of 138 ft, often credited with being the first skyscraper. This and other tall buildings in Chicago spawned an entire generation of tall buildings, constructed with load bearing steel frames supporting concrete floors and non-load bearing, unreinforced masonry infill walls at their perimeters. Framing in these early structures typically utilized "H" shapes built up from plates, and "L" and "Z" sections. [3]

Home Insurance Building

The Home Insurance Building was a skyscraper in Chicago, United States, designed by William Le Baron Jenney in 1884, for the Home Insurance Company in New York. Completed a year later, the building is generally noted as the first tall building to be supported both inside and outside by a fireproof structural steel and metal frame, which included reinforced concrete.

The infill wall is the supported wall that closes the perimeter of a building constructed with a three-dimensional framework structure. Therefore, the structural frame ensures the bearing function, whereas the infill wall serves to separate inner and outer space, filling up the boxes of the outer frames. The infill wall has the unique static function to bear its own weight. The infill wall is an external vertical opaque type of closure. With respect to other categories of wall, the infill wall differs from the partition that serves to separate two interior spaces, yet also non-load bearing, and from the load bearing wall. The latter performs the same functions of the infill wall, hygro-thermically and acoustically, but performs static functions too.

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Skyscraper tall building

A skyscraper is a continuously habitable high-rise building that has over 40 floors and is taller than approximately 150 m (492 ft). Historically, the term first referred to buildings with 10 to 20 floors in the 1880s. The definition shifted with advancing construction technology during the 20th century. Skyscrapers may host offices, residential spaces, and retail spaces. For buildings above a height of 300 m (984 ft), the term supertall skyscrapers can be used, while skyscrapers reaching beyond 600 m (1,969 ft) are classified as megatall skyscrapers.

Truss structure that consists of two-force members only

A truss is an assembly of beams or other elements that creates a rigid structure. In engineering, a truss is a structure that "consists of two-force members only, where the members are organized so that the assemblage as a whole behaves as a single object". A "two-force member" is a structural component where force is applied to only two points. Although this rigorous definition allows the members to have any shape connected in any stable configuration, trusses typically comprise five or more triangular units constructed with straight members whose ends are connected at joints referred to as nodes.

Beam (structure) structural element capable of withstanding load by resisting bending

A beam is a structural element that primarily resists loads applied laterally to the beam's axis. Its mode of deflection is primarily by bending. The loads applied to the beam result in reaction forces at the beam's support points. The total effect of all the forces acting on the beam is to produce shear forces and bending moments within the beam, that in turn induce internal stresses, strains and deflections of the beam. Beams are characterized by their manner of support, profile, length, and their material.

Seismic retrofit Modification of existing structures to make them more resistant to seismic activity

Seismic retrofitting is the modification of existing structures to make them more resistant to seismic activity, ground motion, or soil failure due to earthquakes. With better understanding of seismic demand on structures and with our recent experiences with large earthquakes near urban centers, the need of seismic retrofitting is well acknowledged. Prior to the introduction of modern seismic codes in the late 1960s for developed countries and late 1970s for many other parts of the world, many structures were designed without adequate detailing and reinforcement for seismic protection. In view of the imminent problem, various research work has been carried out. State-of-the-art technical guidelines for seismic assessment, retrofit and rehabilitation have been published around the world – such as the ASCE-SEI 41 and the New Zealand Society for Earthquake Engineering (NZSEE)'s guidelines. These codes must be regularly updated; the 1994 Northridge earthquake brought to light the brittleness of welded steel frames, for example.

Earthquake engineering interdisciplinary branch of engineering

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. Earthquake engineering is the scientific field concerned with protecting society, the natural environment, and the man-made environment from earthquakes by limiting the seismic risk to socio-economically acceptable levels. Traditionally, it has been narrowly defined as the study of the behavior of structures and geo-structures subject to seismic loading; it is considered as a subset of structural engineering, geotechnical engineering, mechanical engineering, chemical engineering, applied physics, etc. However, the tremendous costs experienced in recent earthquakes have led to an expansion of its scope to encompass disciplines from the wider field of civil engineering, mechanical engineering, nuclear engineering, and from the social sciences, especially sociology, political science, economics, and finance.

Steel frame building technique in which a skeleton frame of vertical steel columns is constructed in a rectangular grid; made the skyscraper possible

Steel frame is a building technique with a "skeleton frame" of vertical steel columns and horizontal I-beams, constructed in a rectangular grid to support the floors, roof and walls of a building which are all attached to the frame. The development of this technique made the construction of the skyscraper possible.

Skyscraper design and construction

The design and construction of skyscrapers involves creating safe, habitable spaces in very high buildings. The buildings must support their weight, resist wind and earthquakes, and protect occupants from fire. Yet they must also be conveniently accessible, even on the upper floors, and provide utilities and a comfortable climate for the occupants. The problems posed in skyscraper design are considered among the most complex encountered given the balances required between economics, engineering, and construction management.

The term structural system or structural frame in structural engineering refers to the load-resisting sub-system of a building or object. The structural system transfers loads through interconnected elements or members.

Portal frame construction method

Portal frame structures are designed to span between supports and rely on fixed joints with moment resisting capacity where vertical supports connect to horizontal beams or trusses. Portal frame structures can be constructed using a variety of materials and methods. These include steel, reinforced concrete and laminated timber such as glulam. The connections between the columns and the rafters are designed to be moment-resistant, i.e. they can carry bending forces. "They were first developed in the 1960s, and have now become the most common form of enclosure for spans of 20 to 60 m"

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.

Steel building Part of civil engineering

A steel building is a metal structure fabricated with steel for the internal support and for exterior cladding, as opposed to steel framed buildings which generally use other materials for floors, walls, and external envelope. Steel buildings are used for a variety of purposes including storage, work spaces and living accommodation. They are classified into specific types depending on how they are used.

Steel design, or more specifically, structural steel design, is an area of structural engineering used to design steel structures. These structures include schools, houses, bridges, commercial centers, tall buildings, warehouses, aircraft, ships and stadiums. The design and use of steel frames are commonly employed in the design of steel structures. More advanced structures include steel plates and shells.

Vehicle frame main supporting structure of a motor vehicle

A vehicle frame, also known as its chassis, is the main supporting structure of a motor vehicle, to which all other components are attached, comparable to the skeleton of an organism.

Tube (structure) system to resist lateral loads in structural engineering

In structural engineering, the tube is a system where, to resist lateral loads, a building is designed to act like a hollow cylinder, cantilevered perpendicular to the ground. This system was introduced by Fazlur Rahman Khan while at the architectural firm Skidmore, Owings & Merrill (SOM), in their Chicago office. The first example of the tube’s use is the 43-story Khan-designed DeWitt-Chestnut Apartment Building, since renamed Plaza on DeWitt, in Chicago, Illinois, finished in 1966.

Steel plate shear wall

A steel plate shear wall (SPSW) consists of steel infill plates bounded by boundary elements.

A buckling-restrained brace (BRB) is a structural brace in a building, designed to allow the building to withstand cyclical lateral loadings, typically earthquake-induced loading. It consists of a slender steel core, a concrete casing designed to continuously support the core and prevent buckling under axial compression, and an interface region that prevents undesired interactions between the two. Braced frames that use BRBs – known as buckling-restrained braced frames, or BRBFs – have significant advantages over typical braced frames.

Hybrid masonry

Hybrid masonry is a new type of building system that uses engineered, reinforced masonry to brace frame structures. Typically, hybrid masonry is implemented with concrete masonry panels used to brace steel frame structures. The basic concept is to attach a reinforced concrete masonry panel to a structural steel frame such that some combination of gravity forces, story shears and overturning moments can be transferred to the masonry. The structural engineer can choose from three different types of hybrid masonry and two different reinforcement anchorage types. In conventional steel frame building systems, the vertical force resisting steel frame system is supported in the lateral direction by steel bracing or an equivalent system. When the architectural plans call for concrete masonry walls to be placed within the frame, extra labor is required to ensure the masonry fits around the steel frame. Usually, this placement does not take advantage of the structural properties of the masonry panels. In hybrid masonry, the masonry panels take the place of conventional steel bracing, utilizing the structural properties of reinforced concrete masonry walls.

Rigid-frame bridge type of bridge

A Rigid-frame bridge is a bridge in which the superstructure and substructure are rigidly connected to act as a continuous unit. Typically, the structure is cast monolithically, making the structure continuous from deck to foundation. The connections between members are rigid connections which transfer bending moment, axial forces, and shear forces. A bridge design consisting of a rigid frame can provide significant structural benefits, but can also be difficult to design and/or construct.

Structural support is a part of a building or structure providing the necessary stiffness and strength in order to resist the internal forces and guide them safely to the ground. External loads that act on buildings cause internal forces in building support structures. Supports can be either at the end or at any intermediate point along a structural member or a constituent part of a building and they are referred to as connections, joints or restraints.

References

  1. Bruneau, Michel. et al., (2011). Ductile Design of Steel Structures. McGraw-Hill Companies, Inc. ISBN   978-0-07-162395-7.page 347
  2. "20 Years After Northridge Quake, Buildings Remain Vulnerable."
  3. Hamburger, Ron. et al., (2009). Seismic Design of Steel Structures. National Institute of Standards and Technology . NIST GCR 09-917-3.page 3