Diagram Tegangan dan dimensi Balok
FIGURE 3-4
HORIZONTAL LOADS MUST BE TRANSFERRED FROM ONE SUBSYSTEM SLICE
TO THE NEXT BY SHEAR RESISTANCE BETWEEN SLICES.
(a
)
LOAD
CONCENTRAT
ED
AT TOP
SHEa/-s1cc’ SHEAR (VS) rRorl IS
CONSTANT “SLICE” ABOVE
SHEAR
RESISrANGE
FROtI
‘SLICE~BELQw
•~_~~2~
SHEAR
(V)FRON1
~SUCE ABOVE
AVERAGE
SHEAR
STRESS:
AVERAGE
SHEAR
STRESS
t~ .tLJh./
—
SHEAR RESISrANCE
FROM “SLICE? BELOW
-AVERPeZ
SHEAR
STRESS; + ~7
-
A
-CE
LOA.
D
SHEAR RESISTANCE
FROM “SLICE~ BELOW
other hand, Figure 3-4b illustrates that if the total horizontal load (H) were to
be distributed evenly along the height of a building (w = H/h), the shear at any point
(hi) would accumulate from zero at the top to (V1 = wh~). The shear diagram would
be triangular with the maximum (V= H) at the foundation and (~) will vary with slice
location.
Distributed loads can arise from the surface of a building because it offers
resistance to wind. Thus, for symmetric elevations, a wind load is often
On the
Overall Integrity and Major Subsystem Interaction
assumed to be fairly evenly distributed over a building’s height and, in design,
would be assumed to yield a triangular shear diagram.
Unevenly distributed horizontal loads may result from foundation movement due to
earthquake or nonsymmetric elevations under wind load. Figure 3-4c illustrates a
common type of earthquake load distribution, wherein the shear force is assumed
to vary over the height of a rectangular building. TIw load per slice varies
according to its mass and its distance from the foundation. Thus, for even mass
distribution, the load diagram is assumed to be an inverted triangle, the shear
diagram parabolic.
Thus far we have illustrated that horizontal slices represent basic subsystems that
must interact to resist and transfer not only axial compression under vertical
loading, but also horizontal shearing forces under horizontal loading. In a
continuously solid form, such a structural capability between imaginary slices is
inherent. However, if a solid form were actually to be constructed by stacking
blocks, it would not necessarily tend lo satisfy the requirement for shear
resistance- Figure 3-5 illustrates what would happen if sufficient shear resistance
were not achieved between the blocks. In primitive buildings this was
accomplished by either relying on friction between heavy stone blocks or by
physically keying the joint
FIGURE 3-5
FAILURE TO TRANSFER SI-tEAR RESISTANCE BETWEEN SUBSYSTEM BLOCKS
WILL
RESULT IN COLLAPSE OF FORM.
14
N
-H
FIGURE 3-6
PRIMITIVE MEANS Of TRANSFERRING SHEAR
RESISTANCE BETWEEN SUBSYSTEM BLOCKS.
FRICTION
H —H
KEYING
H —H
—~
4-
Overall Integrity and Malor Subsystem Interaction
FIGURE 3-8
-
HORIZONTAL LOAD DISTRIBUTION DETERMINES SHEAR (I’)
SHEAR
(H ~
LOAD
MOMENT
(Nb.)
SECTIONAL SHAPE
AND DEPTH
DETERMINES THE
REQUIRED
DISTRIBUTION OVER {h)
OF:
(a)
AND MOMENT (M);
C-T FORCES.
DEIERMIMAJICtJ Of
OVERTURN RESISTING
FORCES roR”sucC
AT h~:
-, o.tT” —
_I
(b)
-M
_________
c
‘. VRTSISTJSG
ARM
I
that, for equal (V),
cases (a) and (c)
produce moments
larger than case
(b).
Also note that the
magnitude of the
C-T couple Is
determined by the
magnitude of the
moment and the
distance between
C and T.
It is a natural
property of a
continuously solid
form to resist both
shear and bending
to some degree,
-M
although most materials will exhibit different