Civil Engineering Reference
In-Depth Information
Figure A.7
Extreme examples of setbacks: traditional pyramid in Egypt (
left
), modern US pyramids in Indianapolis
(
middle
) and an inverted pyramid in Dallas (
right
)
Figure A.8
Unfavourable discontinuities and axes with offsets in elevation
Key
: Circles indicate areas of concern
(as discussed in Section 2.3.2.2) and cause large stress concentrations in connected structural elements.
This problem frequently occurs in RC frames when large fl at beams frame into columns along their
weak axes. In this case, the difference between the widths of beams and columns may endanger the
uniform transfer of fl exural, shear and axial actions between the connected members. This type of detail
also generates high stress concentrations at beam- to - column joints.
Beams or columns supported on beams should be avoided since the imposed local demand, especially
in torsion and shear, is very diffi cult to accommodate. In V- , inverted V - and K- braced frames, braces
do not intersect beam-to-column joints at both ends. Brace- to - beam and brace - to - column connections
are located along the spans and heights, respectively, as shown in Figure A.9. Short columns generated
in K-braced frames give rise to unfavourable failure modes.
Under horizontal seismic forces, the compression brace buckles and its load-bearing capacity is
reduced dramatically. Tests carried out by Hassan and Goel (1991) on steel structures showed that the
