In
structural engineering
Structural engineering is a sub-discipline of civil engineering in which structural engineers are trained to design the 'bones and muscles' that create the form and shape of man-made structures. Structural engineers also must understand and cal ...
, a diaphragm is a structural element that transmits lateral loads to the vertical resisting elements of a structure (such as
shear wall
In structural engineering, a shear wall is a vertical element of a system that is designed to resist in-plane lateral forces, typically wind and seismic loads. In many jurisdictions, the International Building Code and International Residential Co ...
s or
frames). Diaphragms are typically horizontal, but can be sloped such as in a gable roof on a wood structure or concrete ramp in a parking garage. The diaphragm forces tend to be transferred to the vertical resisting elements primarily through in-
plane shear stress
Shear stress, often denoted by ( Greek: tau), is the component of stress coplanar with a material cross section. It arises from the shear force, the component of force vector parallel to the material cross section. '' Normal stress'', on ...
. The most common lateral loads to be resisted are those resulting from
wind
Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few ...
and
earthquake
An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, fr ...
actions, but other lateral loads such as
lateral earth pressure
Lateral earth pressure is the pressure that soil exerts in the horizontal direction. The lateral earth pressure is important because it affects the consolidation behavior and strength of the soil and because it is considered in the design of geotec ...
or
hydrostatic pressure
Fluid statics or hydrostatics is the branch of fluid mechanics that studies the condition of the equilibrium of a floating body and submerged body " fluids at hydrostatic equilibrium and the pressure in a fluid, or exerted by a fluid, on an i ...
can also be resisted by diaphragm action.
The diaphragm of a structure often does double duty as the
floor
A floor is the bottom surface of a room or vehicle. Floors vary from simple dirt in a cave to many layered surfaces made with modern technology. Floors may be stone, wood, bamboo, metal or any other material that can support the expected load ...
system or
roof
A roof ( : roofs or rooves) is the top covering of a building, including all materials and constructions necessary to support it on the walls of the building or on uprights, providing protection against rain, snow, sunlight, extremes of t ...
system in a
building
A building, or edifice, is an enclosed structure with a roof and walls standing more or less permanently in one place, such as a house or factory (although there's also portable buildings). Buildings come in a variety of sizes, shapes, and func ...
, or the
deck of a
bridge
A bridge is a structure built to span a physical obstacle (such as a body of water, valley, road, or rail) without blocking the way underneath. It is constructed for the purpose of providing passage over the obstacle, which is usually someth ...
, which simultaneously supports gravity loads.
Diaphragms are usually constructed of
plywood
Plywood is a material manufactured from thin layers or "plies" of wood veneer that are glued together with adjacent layers having their wood grain rotated up to 90 degrees to one another. It is an engineered wood from the family of manufactured ...
or
oriented strand board in
timber
Lumber is wood that has been processed into dimensional lumber, including beams and planks or boards, a stage in the process of wood production. Lumber is mainly used for construction framing, as well as finishing (floors, wall panels, w ...
construction;
metal
A metal (from ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electrical resistivity and conductivity, e ...
deck or composite metal deck in
steel
Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistan ...
construction; or a
concrete slab
A concrete slab is a common structural element of modern buildings, consisting of a flat, horizontal surface made of cast concrete. Steel- reinforced slabs, typically between 100 and 500 mm thick, are most often used to construct floors and ...
in
concrete
Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most wid ...
construction.
The two primary types of diaphragm are flexible and rigid. Flexible diaphragms resist lateral forces depending on the tributary area, irrespective of the flexibility of the members that they are transferring force to. On the other hand, rigid diaphragms transfer load to frames or shear walls depending on their flexibility and their location in the structure. The flexibility of a diaphragm affects the distribution of lateral forces to the vertical components of the lateral force resisting elements in a structure
An Investigation of the Influence of Diaphragm Flexibility on Building Design through a Comparison of Forced Vibration Testing and Computational Analysis
Parts of a diaphragm include:
*the membrane, used as a shear panel to carry in-plane shear
*the drag strut member, used to transfer the load to the shear walls or frames
*the chord, used to resist the tension and compression forces that develop in the diaphragm, since the membrane is usually incapable of handling these loads alone.
Structural system
Floors
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