REG NACA-TM-605-1931 Flat Sheet Metal Girders With Very Thin Metal Web.pdf

1、REPRODUCEDBYNATIONAL TECHNICALINFORMATION $ERVICE IU. S. DEPARTMENT OF COMMERCL :SPRINGFIELD. VA. ZZ161Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-i|Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,

2、-YAT!0i_AL ADVISORY _,_T_-_.O_A str esF,.ps cm -_n _:ze ,zdc_!e of the Tit-der (that is, on axis -) corresoon! +_. the o_,_-._,_t. The stress exerted by the upper spar on the up-richt due to the stressed skin is (See Fi_are 13):- V0 : Z (sin c - cos _ tan _)._ere_Dy, Z = _0 s t (sin a - cos a tan .5

3、),consequently, - VC = _0 s t (sin (_ - cos _ tan _)_.For _0, in itself varia%le over the width t, we use the ap-oroxinate value G0 (according to equation (20a) ) at the pointof aCtach_ent of t:.e -_-_up_isn_ , which inserted, reads as- V0 = om s t sin= _.ForrcetVU we obviously obtain the same value

4、.VC = VU V and vi_ds with (20)Our check is cot-t tan a- V _,:Qs .- (2oc)Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-6 F.A.C.A. Technical _iemorandum !To. 605Introduction of 0_tside Stresses_z.eso distribution in a _.A discussion of _ - _ o_ metal

5、 girder_t the _,oint of introdu.ction of outside stresses is beyond thescope of this paper, o_nd we shall merely coint out sevGral fea-tur es.If a stress (-“_i s. 17) is acplied h _ _ .Here every tension dia:sona! crosses :n_!y one vertical men-_oGr. _*.e ._e . of ,:,.!e._ A of the tension -!irLuon_

6、! becomes 9.p-parent frou_ Fi_a_Z-_ 24. We obtain. _ + _ h , :!_: _ Lsi.n a s-._. _ IJWe write, this value in (26b), resolve tliis equa_ozon* and obtainJ-% -, “ _r-as oleoJ,e_z_ - h cot a) andadjacent uprights have different elastic lines (two i/_0.Here the uprights aze very (infinitely) close toset

7、her.AssunTption a) All uprights have different elastic limes.Axis x is placed parallel to the spar, axis y as be-fore, in the direction of the uprights_ and _ = _(x,y) is thedeflection of the uprights. In this case of infinitely closeuprights _ (x,y) represents at the same time the surface (forit is

8、 connected to the uprichts) into which the web changeswhen buckling.Here it is perhaps more sppropriate to speak of bulging ofthe plate wall (web) instead of bulgin_ of the uprights; thewhole web forms oblique wrinkles (li _-_ a sheet in wrinkling un-der shear).Denoting withtension _, thendz a linea

9、r component in the direction of_ - _ is the angle of the tension diago-8zp.al due to bulging and the original plane of the wall. As seenfrom Figure 26_ angle A, at which the tension is deflectedwhen bulging, is of the order ofA = _/_ t =_2_ tc%z cos _ 8z _ cosWe note thatdx dydz cos _, dz sin c_,Pro

10、vided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-theft, in foot,COS 2- C_3x _y_-“,I dl.ifcrcntiationaccording to the rules of tbc par o_.:_.write this value for A into (24b)cntir.tion), and obtain- Ly4 E JV _ (x tan a)_(including the patti “1 _“ -_-_“-I-

11、S .y_.(x tan_m.n (x,y) 0 But,This equation is_ oi course, fu.lfille:l “- : (n t)ms in every sirmole problem of _:uch_in.T, the ouest$on is to findthose vrlues of -_-y-, _o into the same e_.gle ofslope as the ori_ri_al olane of the sheet. This raises the re-Provided by IHSNot for ResaleNo reproductio

12、n or networking permitted without license from IHS-,-,-LI“.A.C.A. Technical Memor:._ndumL_o. 605 _Isistivity of the i_late wall against bulging.i:oreover, we stre_ _ thin point _ab o_,_othere is an exactbuckling load even for ecc_norzcally arrange uprights, that is,(by equal distortion stiffness of

13、the spars) exactly the s_uuebuckling load as in centrioally arran_._ed uprights . (This ap-plies to very (infinitely) closely spaced uprights. For differ-ant spacing, p_:,romcularly by t l_ cots there is no ptu-ebuckling load in eccentrically sxranged upri_:hts; the conditionsthen are similar to tho

14、se in the conventions,l, eccentricallyloaded bucklinT members. )If, for exaz.:p!e, = _l(x,y) is the solution of (24_)for centric uprigfhts _ith torsion-re_Jist_nt spars (_I complieswith 8 _ 0 at upper and lower spar), ._y - tnen _II = _I + ao +a_ y + a y2 + as y3 is likewise a solution of this equat

15、ion.But by appropriate choice of constants a $ O, -Ii now satis-fies_r : constant for upper and lo_er spear. In this mannerthe solution conforms to the case of torsion-resistant spars,which, due to the eccentrical uprights, t_rist at a constantangle over their whole length under loading (Fig. 22). T

16、hecase of perfectly torsion-resistant spars with eccentric uprightsis, of course, identiosl vlith that of rigidly restrained up-rights.Dr. Schmieden, Danzig, made an accurate solution of (2%_)which he intends ,to discuss at some other time. We simplystate his results.Provided by IHSNot for ResaleNo

17、reproduction or networking permitted without license from IHS-,-,-_ _ “ “ ,c_“.2 ,.:. _Vv: :o, 605Tnc )_:c!:?._3 7.o:.:1 of the u_oright isv T = 7.Ol PE (_m)for unrestrained uprights or spars not resistant to distortionvT = II.43 P_ (24n)for perfectly restrained uprights or perfectly distortion-resi

18、stant spars, regardless of whether the vertical members arestressed centrically or eccentrically.A_s_ssu_v_n_tionb) All uprights have the ssme c!astio line. Thebuckling load is:VT = IS (h cot _ PE (2Ao)t /for restrained and unrestrained uprights.As seen from Figure gT, this equation yields the buckl

19、ingload for unrestrained uprights with completely torsion-resistantspars; because the above assumption yields for this case thelowest possible buckling load.The results of all these calculations have been tabulatedin Figure 37, n_nely;AB applies to eccentric or oentric uprights rigidly re-strained o

20、r rigidly attached to distortion resistantspars ;BO applies to oentric, rigidly restrained uprights;BF applies to centric, unrestrained uprights, rigidly at-st_n_ spars;tached to distortion-resi _ _Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-N.A.

21、C.A. Technical ,emorandum i_o. 605 23DF is valid for centric or eccentrically arranged, butunrestrained uprights with spores not resistant todistortion; FG applies to centrioally ,orranged, nonrestrained upri_;hts.The Fig_ures 2_:0 to 2le sheet wall, the bucklingstrength of the latter is naturally a

22、ugmented.The Actual Bucklins Load; Index V.!_lue* J-This section pertains to uprlgho syi_:etrica_lly attachedto the _,_,ebplate.In the Iast see%ion we treated the theoretical bucklingstress of _prig.h_ts vr_tbout consideration of wrink!inc phenomena*It is assumed that t_:_ feeder is familiar _ith my

23、 report “Re-marks on Buc_,l_ug Members; InSex V_,_ue, y,eltscnrlft fur Flug-technik und Liotorluftschiffahrt, 1928, p. 241.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-24 N.A.C.A Technics%! !(emoran- -!3oRo2Sfurtker _./_.,_o = 15“, hence FV - :!50

24、 : L)2,I-O = 1.40; _s -_g1.40 - 0.49 = O.9l cm 2 inc savln_.“ ,o-:ea_._.,_,.os_o $5“:_co,os,re_ _ O.k_dlOO to the -_rcco:din3: _For Kv:-.: 4 -= 1,25, FirTirc 29 y_,_ g = :.,o_0 as tkeYlal!ow_o!c s gross for the u-oright of a trusqc circler; the cross-q o,.,0 4.3 cn_ s-_4socbio.,.a! arcs of tki_ iJ.o

25、iubor is _ OOO$ : 2_(“.ith a, diajonai set at 45 ) co:._.9orc,i !_n 01).) chc;t metal to.! at- 25 7 34 cr: _ T.hc sr,vi._, in weiGht in the uo-t = 85 c;u : 4.0 X _.- _, . _:“rights of t;tc she._t met,_! va.l is 32 o,er a.,:_.tconparad to thatin the trussed Tirder.VS,.on t_.c _:cb ola.bes i_a.vc rel - -e- , _,.,l_:_, o .-L,_, _Ta?.Is (i. e , byProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-