# Experimental and Numerical Analyses of Timber-Steel Footbridges
## 7 Conclusions  
The results of the experimental and numerical analyses confirmed that the cross-girder stress-strain response is heavily dependent on joint arrangement and stiffness. * The behaviour of a steel-cross-girder-to-timber-block connection manufactured without a corner stiffener seems to be very close to that of a nominally hinged joint. This is confirmed by the compression stresses in the upper flange of the cross-girder (Figure 12a), which were present even at a distance of 50 mm from the wooden block. The compression stresses were caused due to a small positive bending moment;
* Joint stiffness was increased due to the addition of a stiffener with one or two rows of bolts above the upper cross-girder flange, which caused tensile stresses in the upper cross-girder flange (Figure 12a);
* Because of increasing joint stiffness, a decreasing absolute value of stresses in the cross-girder midpoint was observed (Figure 12b), corresponding to the redistribution of the bending moment from the mid-span to the connection with the timber blocks;  
Figure 12: Comparison of measured and computed normal stresses in the upper flange of the cross-girder: (**a**) at the connection and (**b**) in the middle of the span. Figure 13: Comparison of measured and computed deformations of the cross-girder: (**a**) deflection in the middle and (**b**) rotation of the end plate towards the timber block. The higher joint stiffness in samples \"B\" and \"C\" was also proved by the lower values of cross-girder deflection in its mid-span (Figure 13a) and by rotations of the end plate towards the wooden blocks; - The most rigid connection with joint arrangement was observed in the specimens in series \"C\". Normal stresses in the cross-girder mid-span decreased by about 33% in comparison to stresses arising in the same place in specimens of series \"A\"; - In a fully rigid joint, there should be a 65% decrease in stress. This corresponds to the reduction in the bending moment in the mid-span of the cross-girder from \(M=0.35\cdot F/2\), valid for a double-hinged girder, to \(M=0.1225\cdot F/2\) in the case of a double-fixed girder, where \"\(F\)\" is the value of the acting force, according to Figure 9; - The deflection of the cross-girder mid-point decreased by about 55% in specimens in series \"C\" compared to series \"A\", while it should decrease by 79% in the case of full fixation; - Values obtained through experimental analyses naturally show some dispersion due to the large variance in physical and mechanical properties in wood. The end plate rotations calculated from the measured horizontal deformations in particular vary significantly. This can be explained by the significant sensitivity of the calculated rotation value to the accuracy of measurement of horizontal displacements of the end plate against the timber block; - A very important factor influencing joint behaviour is also the way in which they are assembled, especially the level of the prestress in bolts. Bolt prestress increases the friction on the surface between the steel end plate and the timber block, and so the shear resistance of the connection is also enhanced. Naturally, prestress in bolts also increases initial joint rotation stiffness. However, since the level of prestress in bolts was not controlled during the construction of the footbridge analysed in this study, it was not taken into account during numerical analyses. The results of the presented numerical and experimental analyses confirm that the behaviour of the investigated structural detail is semi-rigid. Its bending stiffness especially depends on joint arrangement and on its manner of assembly. An approximation of the structural joint as a perfect hinge may be accepted for preliminary global analysis or in the case of local cross-girder analysis to determine the maximum traffic action effect in the cross-girder mid-point.