Joints in steel rectangular hollow sections filled with concrete present the added difficulty of involving the deformability of the connected faces in bending. This implies that, unless a good estimate of the moment-rotation curve can be obtained, complex and expensive detailing is required to ensure a fairly rigid response of the joint. A first step to achieve the objective of predicting the behavior of such a joint corresponds to an assessment of the initial stiffness of the joint. Starting with a brief review of the current state-of-the-art in the behavior of joints in hollow sections, this paper presents and discusses an analytical model based on an equivalent strip of the loaded face. A simple solution based on this model that has been calibrated with numerical simulations is also derived. The main parameters considered are the thickness of the loaded face and the dimensions of the loading area. Comparisons with some available numerical and experimental results are quite encouraging.

To determine perforation performance, service companies conduct tests to demonstrate the advantages of different technologies of perforating systems. Although studies on jet penetration into rock targets usually focus on the prediction and measurement of penetration depth the repertoire of methods to assemble details of tunnel perforation is very limited. In this paper, the samples that were tested in perforation cell were conducted in an effort to gaining insight into the deformation processes of penetration mechanism. In order to gain intuition about the presence of shear bands the samples were reconstructed in threedimensional images, using microfocus CT Scannig (CT). One of the samples wasn't split before the reconstruction. Remarkably some of the deformation mechanisms are the formation of shear bands surrounding the tunnel and they remain after the fluid flow. This yields the interesting possibility that shear bands are important to the pathway flow. In addition, this fundamental knowledge may also assist understanding the nature of tunnel formation, which take place during the penetration process.