2,392 research outputs found
Influence of Gypsum Panels on the Response of Cold-Formed Steel Framed Strap-Braced Walls
In cold-formed steel construction the steel frame is supplemented with either diagonal strap braces or structural sheathing panels (typically steel or wood) to provide overall stability to the structural system and to directly transfer lateral wind and seismic loads through to the foundation as per the design provisions found in AISI S240 (2015) and AISI S400 (2015). Gypsum panels are often specified to provide a fire-resistance rating for the CFS frame, as well as to ensure that adequate sound-proofing exists between adjacent rooms or building units. The engineer may choose to rely on this gypsum to provide additional lateral resistance, as permitted in the AISI Standards. However, in the majority of cases the gypsum panels are considered to be non-structural elements of the building specified by the architect, and as such, are not taken into account in the design of the lateral load carrying system. Whether considered in the design process or not, these gypsum panels do augment the shear resistance of the lateral load carrying system. This study was carried out to evaluate the performance of combined strap-braced / gypsum-sheathed wall systems, with the intent of defining a corresponding design approach. Described herein are the findings of the laboratory phase of the project, comprising 35 wall specimens
Multiple equilibrium states of a curved-sided hexagram:Part I-Stability of states
The stability of the multiple equilibrium states of a hexagram ring with six
curved sides is investigated. Each of the six segments is a rod having the same
length and uniform natural curvature. These rods are bent uniformly in the
plane of the hexagram into equal arcs of 120deg or 240deg and joined at a cusp
where their ends meet to form a 1-loop planar ring. The 1-loop rings formed
from 120deg or 240deg arcs are inversions of one another and they, in turn, can
be folded into a 3-loop straight line configuration or a 3-loop ring with each
loop in an "8" shape. Each of these four equilibrium states has a uniform
bending moment. Two additional intriguing planar shapes, 6-circle hexagrams,
with equilibrium states that are also uniform bending, are identified and
analyzed for stability. Stability is lost when the natural curvature falls
outside the upper and lower limits in the form of a bifurcation mode involving
coupled out-of-plane deflection and torsion of the rod segments. Conditions for
stability, or lack thereof, depend on the geometry of the rod cross-section as
well as its natural curvature. Rods with circular and rectangular
cross-sections will be analyzed using a specialized form of Kirchhoff rod
theory, and properties will be detailed such that all four of the states of
interest are mutually stable. Experimental demonstrations of the various states
and their stability are presented. Part II presents numerical simulations of
transitions between states using both rod theory and a three-dimensional finite
element formulation, includes confirmation of the stability limits established
in Part I, and presents additional experimental demonstrations and
verifications
Multiple equilibrium states of a curved-sided hexagram: Part II-Transitions between states
Curved-sided hexagrams with multiple equilibrium states have great potential
in engineering applications such as foldable architectures, deployable
aerospace structures, and shape-morphing soft robots. In Part I, the classical
stability criterion based on energy variation was used to study the elastic
stability of the curved-sided hexagram and identify the natural curvature range
for stability of each state for circular and rectangular rod cross-sections.
Here, we combine a multi-segment Kirchhoff rod model, finite element
simulations, and experiments to investigate the transitions between four basic
equilibrium states of the curved-sided hexagram. The four equilibrium states,
namely the star hexagram, the daisy hexagram, the 3-loop line, and the 3-loop
"8", carry uniform bending moments in their initial states, and the magnitudes
of these moments depend on the natural curvatures and their initial curvatures.
Transitions between these equilibrium states are triggered by applying bending
loads at their corners or edges. It is found that transitions between the
stable equilibrium states of the curved-sided hexagram are influenced by both
the natural curvature and the loading position. Within a specific natural
curvature range, the star hexagram, the daisy hexagram, and the 3-loop "8" can
transform among one another by bending at different positions. Based on these
findings, we identify the natural curvature range and loading conditions to
achieve transition among these three equilibrium states plus a folded 3-loop
line state for one specific ring having a rectangular cross-section. The
results obtained in this part also validate the elastic stability range of the
four equilibrium states of the curved-sided hexagram in Part I. We envision
that the present work could provide a new perspective for the design of
multi-functional deployable and foldable structures
Adjusting bone mass for differences in projected bone area and other confounding variables: an allometric perspective.
The traditional method of assessing bone mineral density (BMD; given by bone mineral content [BMC] divided by projected bone area [Ap], BMD = BMC/Ap) has come under strong criticism by various authors. Their criticism being that the projected bone "area" (Ap) will systematically underestimate the skeletal bone "volume" of taller subjects. To reduce the confounding effects of bone size, an alternative ratio has been proposed called bone mineral apparent density [BMAD = BMC/(Ap)3/2]. However, bone size is not the only confounding variable associated with BMC. Others include age, sex, body size, and maturation. To assess the dimensional relationship between BMC and projected bone area, independent of other confounding variables, we proposed and fitted a proportional allometric model to the BMC data of the L2-L4 vertebrae from a previously published study. The projected bone area exponents were greater than unity for both boys (1.43) and girls (1.02), but only the boy's fitted exponent was not different from that predicted by geometric similarity (1.5). Based on these exponents, it is not clear whether bone mass acquisition increases in proportion to the projected bone area (Ap) or an estimate of projected bone volume (Ap)3/2. However, by adopting the proposed methods, the analysis will automatically adjust BMC for differences in projected bone size and other confounding variables for the particular population being studied. Hence, the necessity to speculate as to the theoretical value of the exponent of Ap, although interesting, becomes redundant
Einstein billiards and spatially homogeneous cosmological models
In this paper, we analyse the Einstein and Einstein-Maxwell billiards for all
spatially homogeneous cosmological models corresponding to 3 and 4 dimensional
real unimodular Lie algebras and provide the list of those models which are
chaotic in the Belinskii, Khalatnikov and Lifschitz (BKL) limit. Through the
billiard picture, we confirm that, in D=5 spacetime dimensions, chaos is
present if off-diagonal metric elements are kept: the finite volume billiards
can be identified with the fundamental Weyl chambers of hyperbolic Kac-Moody
algebras. The most generic cases bring in the same algebras as in the
inhomogeneous case, but other algebras appear through special initial
conditions.Comment: 27 pages, 10 figures, additional possibility analysed in section 4.3,
references added, typos correcte
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