Exam 3 Flashcards
A hanging rope, cable, or chain needs supports at its ends that are_____.
fairly stiff
What are cable structures shaped in accordance to?
They have no bending or stiffness so it’s shaped in accordance to the location and magnitude of the loads which it supports.
When will a cable change its profile?
If the loads that are applied to it change location
What quality of the cable has to be dealt with to ensure that the structure does not move excessively?
Lack of rigidity
In which direction is a hanging cable structure fundamentally unstable?
Sideways direction
What do hanging cable structures primarily work in?
Tension (that’s why they are so light)
What do cable stayed structures consist of?
towers or masts from which cables extend to support horizontally spanning members. the supported structural surface must be sufficiently stiff to transfer or resist the lateral and torsional stresses induced by wind, unbalanced live loads, and the normal force created by the upwards pull of the stays
What are the two primary cable configurations in cable stayed structures
radial or fan patterns and parallel or harp systems
What is the difference between radial and parallel systems in cable stayed structures?
Radial systems attach the upper ends of the cable stays to a single point at the tip of the tower, parallel systems secure the upper ends of the cable stays to the mast at different heights
Why is the radial system usually preferred over the parallel system in cable stayed structures?
Because the single point of attachment minimizes the bending moment in the tower. The cable stays are usually attached symmetrically to a single tower or mast with an equal number of stays on both sides
Membrane Structures
Thin, flexible surfaces that carry loads primarily through the development of tensile stresses
Net Structures
membrane structures that have a surface of closely spaced cables instead of a fabric material
three dimensional and double curved and pre-stressed
Pneumatic structures
membrane structures that are placed in tension and stabilized by the pressure of compressed air
What are air-inflated structures?
pneumatic structures supported by pressurized air within inflated building elements which are shaped to carry loads in a traditional manner while the enclosed volume of building air remains at normal atmospheric pressure.
How is the tendency of double membrane structures bulging in the middle restrained?
By using a compression ring or by using internal ties or diaphragms
DEFINITION OF A DOME
Domes are surfaces of revolution, usually generated by rotating an arc of a circle around
a vertical axis.
- A spherical surface structure having a circular plan and constructed of a continuous rigid
material or of short, linear elements.
DOME
Meridional forces are always under full vertical loading
compressive
A dome is similar to a rotated arch except that…
circumferential forces are developed which are
compressive near the crown and tensile in the
lower portion.
Hoop forces, restraining the out-of-plane
movement of the meridional strips in the shell of
a dome, are
compressive in the upper zone and
tensile in the lower zone
What encircles the base if a dome to contain the outward components of the meridional forces
tension ring
Shell
thin, curved surface structure that transfers loads to supports by tension, compression, and shear only.
Developable surfaces
are singly curved, they are straight in one direction curved in the other and can be formed by bending a flat sheet cones and cylinders (or barrels are developable
anticlastic surfaces
doubly curved and have opposite curvature in each direction (saddle shapes including conoids, hyperbolic paraboloids, and hyperboloids) are anticlastic
conoids
generated by sweeping one end of a straight line along a curved path and the other end along a straight line
hyperbolic paraboloids
generated by sweeping a convex parabola along a concave parabola of the same curvature. the same surface can be generated by sweeping a straight line over a straight path at one end and another straight path
Stresses in hypars relate to…
direction of curvature, compression stresses follow the convex curvature (arch) while tension stresses follow the concave curvature (suspension)
Is an arch in compression or tension?
Arches are pure compression forms
How can arches span large areas?
By resolving forces into compressive stresses and eliminating tensile stresses
What is a thrust? (arch)
As forces are carried to the ground the arch will push outward at the base
What happens to thrust as rise (height) decrease?
Rise decrease makes thrust increase.
How are thrusts restrained?
Either with internal ties, or external bracing, such as abutments.
An arch fails due to:
-crushing of the masonry
-sliding o voussoirs
-rotation of some joints about an edge
-uneven settlement of an abutment or pier
How are arches classified?
Type of arch, geometry, materials of construction
How are shells distinguished from traditional vaults?
By their ability to resist tension
Free-form surfaces are____
those which are not mathematically derived.
A dome is similar to a rotated arch except that…
circumferential forces are developed which are
compressive near the crown and tensile in the
lower portion.
