Lay, M. G.

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Lehigh University
Lehigh Preserve
Fritz Laboratory Reports Civil and Environmental Engineering
1963
Letter to the editor, International Journal
Mechanical Science, June 1963
M. G. Lay
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Recommended Citation
Lay, M. G., "Letter to the editor, International Journal Mechanical Science, June 1963" (1963). Fritz Laboratory Reports. Paper 1801.
http://preserve.lehigh.edu/engr-civil-environmental-fritz-lab-reports/1801
Welded Continuo':!8 Frames and Their Component~
<"
LETrD." TO TEE miTOR II
INTERNATIONAL JO~ OF "MECEANlCAL SCIENCES
Discus.ion of Paper: '~be Effect of Restraint
upon tht! Collapse Loads of Mild Steel Trusses"
by B. Go Neal and Do So Mansell. "
Into Jour .. Mech o Sc;i. ll 5, po 81-91 11 ' February 19630
lNDEXED
.:
Fritz EngiDeering Laboratory
Lehigh University
Bethlehem II Pennsylvania
" "" \I\l ENG\NEER\NG
YDEPARiNlENi Of C~G"lI\3Qi\l\iOR,(
.June 1963 FRITZ ENL~~~J.}~\~\~~;~ANIA
BElHL£H£I'JI, P£
Fritz Engineering Laboratory Report No .. ~~dL?a~9-·----,
-.-- -----
xzrrm TO THE EDITOR:
Discussion of Paper by Bo Go ~aa1
and Do S. Mansell, Volo 5, Febo 1963
by
The tl1rltar wishes to comm:ent on the 6luthors 8 statement that
the strut curvalS usG!d in thlSir analysis area derivtiQ from BOthe exact
differaotisl equation
:i +. f (y) til 0
This equ4tion 1s not exact ~ the mathematical sense, henca it 1s
of iDtueat to consider whethE it is exact in the senae that its
amsumptlons conform to r.ilty 0 Eq.. (13) SSS'WiJ'iS that the curva-
ture of a strut is expressed by ylt rather than by the IDOre exact
expression .
.,'" [1 + (!)2]~2
This assumption is DOrmsll)' of sufficient accuracy II however II the
authors 0 Fig 0 4. would indic;ate that large X'egionD of the tlWO chartm
show are outside the range of small deflection. theory 0 For iustancG! ,I.
in Fig 0 4&, the line ml2 BI 0 represents a strut wadGr axial load with ..
m mommat m21 applied at one end and a pin at the otber 0 After xeaching
an ~tr~e value Qt m21 a Oo025~ the strut end rotations then reverse
and Di21 ruches another ext&'eme of about -0040.. It would appear that
very large curvatures would. be requii:tad for: a strut under constant
axial load to have 1tQ end momcant change sign sn.d incX"ease to. about
s1zteemtimes its original value ..
A second 4nsswupt1on made by tba authoX"s is that: the moment ...
curvature relationships are siDgle valued 0 Again II tbis 10 a re.\UJon...
able assumption within a range sucb &s co 0 0 025 <1121 <.. + O!' 025 for
218.08 -3-
m12 cOin Fig o 42 0 In the portion of the charts outside of this
range 1I any rceal strut will have been subjected to considerable
elastic unloading of the yielded regioneand the moment-curvat~re
relationship will Qot be single valued.. In ~ddition the strains will
be such as to cause deleterious local effects in msny cr~ssDzectionsDlo
It is apparent, from tha portions of the paper following
Fig 0 1& II that the technique of find~g equilibrium points from curve
intersections (Fig 0 .,) actually does limit the authors a use of the
ch&rts to almost the asma regions as the Writer suggests above ..
This can be seen from the fact tbc\t the steepness of the curve of
Iq .. (9) is limited by considerations of initim1 elastic instability."
It is worth noting that s1milar strut curves to those tU!l~d.
by the authors have bem employed in _recent years to analyze frame~
works iDwh1ch bending mOBamta have bel21\ of & morepredo!Dinarat ..-
natureD2 o Boaever the authorso major point .. that stiffening a .:
joint cmmectioD can recluce the strength of a structure CD is a _
well made and Dovel contribut1oD o
Refertmces:
D1 Galambos t To V 0 and Lay t Mo Go uERd-Moment Endo Rotat1on Character!....
._st1es. of Beam-ColWDQa"p. Fritz Engineering Laboratory Report No~·
2051. 0 35, Lehigh University, 1962 0
D2 Ojalvo ll M" and Levi, Vc liColwma in Planar Continuous Strucbtres la
!Toe II ABCE, 89 (ST1) II Febmary 1963 11 P,; 10
.~. ,"


Letter to the editor, International Journal Mechanical Science, June 1963

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Letter to the editor, International Journal Mechanical Science, June 1963

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