Üç kenarı mafsallı diğer kenarı boşta dikdörtgen çelik levhalarda narinlik taşıma yükü ilişkisi

Abstract

Çelik yapının bir çok mühendislik uygulamalarında, berkitilmemiş" bir kenarı boşta ve diğer üç kenarından maf- sallı mesnetlenmiş dikdörtgen levhalar, taşıyıcı konstrük- siyonun önemli elemanları olarak çalışmaktadır. Genelde narin olan bu levhalar, basınç kuvveti ile zorlanmaları durumunda beklenenden önce buruşabilmektedirler. Bu ne denle yukarıda tanımları yapılan söz konusu levhaların, gerçek taşıma davranışlarının bilinmesi gerekmektedir. Bu amaçla, levhaların buruşma yükleri, taşıma yükleri ve yük-şekil değiştirme davranışları deneysel olarak incelen miştir. Bahis konusu levhalarla ilgili bu hususları tespit edebilmek için, haç şeklinde enkesitli 10 adedi narin ve 8 adedi kısa toplam 18 deney epruveti hazırlanmıştır. Bu epruvetler, maf sallı mesnetlenmiş karşılıklı iki enine kenarından düzgün yayılı basınç türü yük ile yüklenmekte dir. 10 adet narin epruvetin her biri 4 levhayı içerdi ğinden 40 adet levha denenmiş. olmaktadır. Deney verileri üzerinde irdeleme ve değerlendirme yapılmıştır. Ayrıca bu deneysel sonuçlar Türkiye'de zaman zaman kullanılan.yabancı standardlara göre kuramsal olarak hesaplanan sonuçlarla da karşılaştırılmıştır. Sonuç olarak, yapılan deneyler sonucu elde edilen verilerden hareketle levhaların taşıma yükleri ve yük-şekil değiştirme davranışları elde edilmiştir. Levhaların deneyler sonucu elde edilen taşıma yüklerinin çeşitli ülke normları ile karşılaştırılmaları sonucu narin levhala rın taşıma yükleri normlar tarafından önerilen değerler den fazla çıkmıştır. Üç tarafından maf sallı mesnetli dördüncü kenarı boşta olan levhaların taşıma yükleri ile ilgili matematiksel bağıntılar bulunup öneri olarak veril miştir.

Rectangular steel plates loaded in their plane with hinged supports on three edges and one edge free are employed as important components of steel structures. If these plates are subjected to compressive stresses, they exhibit premature local buckling due to their slenderness. It is therefore necessary to determine the actual load bearing behaviour of plates supported by hinges on one end and free at the other. For this purpose, the local buckling loads, bearing capacity and stress-strain behaviour of such plates has been investigated. Ten cross-shaped plates where manufactured to study their properties. This shape provided 4.10 = 40 plates with three hinged supports and one free end. These specimens were loaded with a uniformly distributed pressure from two respective hinged ends. The compresive strains on the surfaces, the axial shortening, and deflexions perpendicular to the plane of loading have been measured. Conclusions detailed below have been derived from the measurements. In addition, the conclusions have been compared, with the results, obtained bv the use of standards from other countries. A- BEARING LOADS OF PLATES WITH HINGED SUPPORTS ON THREE SIDES AND ONE FREE The bearing loads of this kind of plates are closely related to their slenderness ratio. As seen from Figure 4.68, Chapter 4 the bearing loads have come out to be below the ideal local buckling curve as foreseen by DIN 4114, for plates with slenderness.up to b/t = 20,50. In other words, the experimental bearing load is less than the ideal, theoretical value. The bearing load however is found to be more than the ideal local buckling load after the limit value b/t=20,50 For the purpose of comparison, it can be quoted that the experimental value u/aF reaches 0,56 for b/t = 26,9 2 but o/aF becomes 0,3 68 on the ideal local buckling curve for the same slenderness ratio. This means that the bearing load increases by 36,28 % relative to the ideal local buckling value. IX It is clear that the ratio of ideal local buckling load as given by DIN 4114, to that of experimental bearing load increases with increasing slenderness. The following relationship has been derived through the analysis of experimental results. 7,7083 °F. (bj 0,809 B- THE BEARING- LOAD - DEFLEXION (DEFORMATION) RELATIONSHIP OF PLATES Special bearing plates are placed at the top and bottom of the olates at support points. It is assumed that the plate is supported by hinges at its transverse ends by the application of these brackets. Accordingly, deflexion of the plate is appdoximately sinusoidal. It is found that the final deformation of the plates is not at all influenced by the initial deflexion values. C- THE DEFORMATION (AXIAL SHORTENING) - BEARING LOAD RELATIONSHIP As mentioned in Chapter 4, the deformations (shortening) in short plates tends to increase while the force tend to drop by a certain amount if the test was continued after reaching the bearing load. This drop has been observed to be roughly in the order of 20 %, after which a constant level is attained. In plates of medium slenderness,. the force reaches the bearing load at a considerably early stage, but the magnitude of decrease of force is much less, once this l'bad is reached. In the slender region, the force diminishes much slower after the bearing load is reached. x D- SUGGESTIONS The most appropriate theoretical relationships to represent the experimental results have been determined to be a b for - = f ( - ) °F t a 7,7083 op {b}0f809 for - = f ( X ) °F * /> + 0,265 ka the above relationship transforms info cp Xv + 0,265 if the value -JT X - V is assumed. XI Similar to the European Steel Convention (ECCS) curves, the formula 1 + 0,01 (X - 0,735) + X2 °F 1,1 X2 2 1,1 \ AT + 0,01 (X - 0,735) + X2]2 - 2,9 X2 V V V has been developed to express the relationship studied. Initial deflexions that will appear during manufacture of plates should not exceed predetermined values (Figure 1.18). Experiments show that large initial deflexion values appear to influence the bearing load capacity of the plates. The bearing loads obtained for specimens with higher initial deflexions in the medium slenderness zone are slightly lower than the loads for specimens with lower deflexions. The bearing loads obtained by testing of plates have exhibited safe behaviour, especially in the slender zone, when evaluated in the light of standards from different countries. E- COMPARISON OF EXPERIMENTALLY OBTAINED BEARING LOADS WITH DIFFERENT STANDARDS 1. Comparison of Test Result with Federal Germany DASt Ri.012 Specification. The relationship of experimentally obtained bearing load to idealised plate slenderness Xv has been plotted in Figure 4.69. The loads are compared with Xv as foreseen in DASt Ri.012 in Figüre 4.70. Xll It can be observed in Fig. 4.70 that the bearing': load measured in models tested (E-7, E-8, E-9, E-10)-" ar'ei. greater than those predicted by the West Germany' ?.-'.?..''.. DASt Ri.012. Bearing loads for the remaining models.. however were lower. It can be concluded that, in general, the bearing loads for slender plates have been obtained to be higher than predicted by the standard mentioned w 2. Comparison of Test Results with the East Germany. TGL 13503/02 Standard. The relationship between the experimental bearing load- A with the idealised plate slenderness is given in. Figure 4.69. The experimental results are compared with the East German Standard in Figure 4.7İ. The bearing loads measured for samples E-9 and E-10 are higher than those predicted by the East German Standard. The loads for the rest of the plates were, however below those predicted by this standard.