Planar Grillages Made of Short Steel Reciprocal Beams

The paper presents the concept of planar grillages made of the beams of only one length, assembled according to the principle specific for reciprocal frames. The joints of beams are located along their lengths, in the distance freely adopted from the end of the beam, what enables constructing from identical beams the grillages of different dimensions and density of beams, so also the carrying capacity. The analysis is inspired by research of Jose Sanchez and his collaborators (Sanchez, Escrig, Rodriguez 2010, Sanchez, Escrig 2011), especially in terms of selection of beams, which have been assumed same in the form of steel rectangular pipes. The eight grillages made of identical beams, but differing in pattern of layout and of density of beams and thus dimensions of the whole grillage, have been taken into consideration. It has been assumed that each the grillage is subjected to influence of identical external load. The joints have been considered alternatively, both as stiff or articulated ones. The aim of the analysis was to compare the maximum bending moments and deflections in grillages. The calculations have been made with the use of Robot Structural Analysis Professional software. The results show that along with the increase of the distance between the joints of the beams, the difference between the parameter values measured for grillages of the same beams arrangement, but differing in the use of rigid or articulated joints, decreases. It is possible to obtain the same carrying capacity in the grillage spatially arranged in the way specific for reciprocal frame, but with the application of articulated joints, as in the grillage classically arranged, with the use of stiff joints. The relative ease of making articulated joints in relation to rigid joints is the essential advantage. The grillages of bigger sizes can be constructed from identical beams as the smaller ones, and their carrying capacity is limited only to a small extent. The paper presents direct comparison of the values of analysed parameters, as well as the comparison of relative load and beam efficiency coefficients, given in the form of graphs. Static analysis is supplemented with the description of the possibility of constructing grillages made of steel beams in a manner ensuring simple assembly and cooperation with the floor slab, in particular through the use of slim floor technology.