Papers by Keyword: Punching

Abstract: An oxygen-free copper has been utilized as a terminal material in the power transistors and their related electric system in the electric mobiles because of its high electric conductivity and excellent engineering durability in high current usage. The high ductility and its low mechanical strength cause large shear droop and increase of fractured surface. In this report, the shearing of oxygen-free copper was carried out using a punch with a mirror-finished surface roughness. Using the punch tip deflection as a parameter, a comparison of shearing characteristics was made between a punch with a nitrided tool surface and an untreated punch. The influence on the formation of the sheared surface was considered from an investigation of the shearing characteristics. When shearing oxygen-free copper with a thickness of 500 µm, it was shown that by providing a punch tip deflection of approximately one-tenth of the thickness in the punch stroke direction, the shear droop could be kept to 10 % or less of the plate thickness and a burnished surface ratio was approximately kept 90 %.

Abstract: The paper deals with a comparison of the punching shear capacities of the experimental flat slabs without shear reinforcement weakened by openings adjacent columns with the results obtained by the prEC2 model for prediction punching capacity that is introduced in the second generation of Eurocode 2. Within the experiments, 4 slabs with dimensions of 2.5 m x 2.5 m and with a thickness of 200 mm and 8 slabs with a thickness of 250 mm were tested and evaluated. Specimens with a thickness of 200 mm were supported by an elongated column with dimensions of the column’s cross-section 950 x 150 mm and the second set of specimens with a square column with a dimension of 200 mm. The position of openings around the perimeter of the column as well as the distance from a column face were changing. Assessed punching shear capacities and their comparison with laboratory tests show that the prEC2 model significantly underestimates punching capacity when the opening is located at the face of support or near the shorter side of the elongated column if the reduction of the control perimeter length is steering by a radial projection of the opening.

Abstract: The paper deals with the loading test results of an experimental reinforced concrete flat slab fragment, which was supported by an elongated rectangular column. The slab specimen was 200 mm thick and was without shear reinforcement. By experimentally obtained punching capacity, the accuracy of the standard design models for prediction punching resistance will be compared. The results of the experiment were also compared with the results of a numerical nonlinear analysis performed in the Atena program.

Abstract: The paper deals with the results of a loading an isolated fragment of flat slab specimen with two openings located close to the column. Slab specimen was supported by an elongated column and was without shear reinforcement. The accuracy of the relevant design models for prediction punching resistance was tested with obtained test results. All design models provided punching capacity on the safe side. The best accuracy has been achieved by non-linear analysis that was carried out with Atena software.

Abstract: The paper deals with the quality of the current EC2 (2004) model for predicting punching capacity of flat slabs without transverse reinforcement, supported by elongated columns and weakened by two openings placed adjacent to the column. The ratio column’s section height/effective depth of a slab was six. The reference punching capacities were obtained from non-linear analyses carried out on the flat slab fragments. Five different arrangements of the openings were tested with three models that take into account an effect of the openings on the punching resistance. Based on the investigation performed, it was observed that the length 3d of the effective part of a column perimeter along the column height h with the ratio h/d > 3 is very conservative. The whole control perimeter contributed to the punching capacity for all slab fragments tested. Current design model EC2 (2004) is safe in the case of predicting the punching capacity of flat slabs with openings adjacent to the columns if the standard method of reduction of the control perimeter lengths due to openings is used. The most consistent results provided method that is based on the Augustin's proposal for reduction of the control perimeter length.

Abstract: First investigations focus on the usage, processing and material properties of polycarbonate (PC) based materials used in cable duct production. Test coupons were taken from in-situ cable ducts including further additives generally used in industry. Different mechanical and optical analytical methods were performed. Significant differences in tensile properties of polycarbonate/ acrylonitrile butadiene styrene (PC/ABS) compared to mineral reinforced PC were observed. The hardness of mineral reinforced PC is significantly dependent on the geometry of the cable ducts. The fracture behavior and morphology of the PC/ABS fracture surface is directly related to the coupon temperature during Charpy impact testing. The process temperature influences the failure behavior during high impact processing such as high speed punching. Due to the lower impact strength of mineral reinforced PC less film and burr formation compared to PC/ABS are likely. However, the mineral distribution is not homogeneous and therefore subject to further investigation. This study aims at a better understanding of process properties of PC/ABS products, parameter selection, quality improvement and general understanding of underlying microstructural and surface properties.

Abstract: Reinforced concrete flat slabs are frequently used structural members in building construction. One of the most dangerous form of structural failure of these system is punching of the slab by support. The best way how to verify the reliability of standard model for the assessment of punching capacity is comparison of the resistance obtained from the experiments, with the resistances calculated according to the standard. To determine the reliability of the standards a large database of test results is required, but from economical point of view, it is not possible to prepare so many tests in order to fulfill this requirement. The problem can be solved by non-linear analysis which is a tool that allows to substitute actual tests with theoretical ones. The paper deals with non-linear analysis of punching of flat slabs, where the numerical model of flat slab specimens using results taken from the experimental program carried out at the laboratory of Slovak University of Technology. The task was to find the suitable non-linear material model for concrete and reinforcement, choose the proper boundary conditions, the correct load application and choose the appropriate way of modeling. The correct adjustment of the numerical model allows to carry out parametric study of flat slabs.

Abstract: The paper deals with strengthening structures against punching shear with focus on strengthening of existing concrete foundation slabs. These can be slabs of basements of residential, administrative and other buildings. Also, foundations slabs placed on piles can be considered. This is very specific case of strengthening where only one surface of the structure is accessible. Strengthening is often designed using massive new bearing elements, which are space-demanding. Attention is paid to the development of technology that minimizes the resulting constraints on the surrounding area and is sufficiently effective. Inspiration is strengthening of ceiling flat slabs with additional shear reinforcement. Compared to the ceiling slabs, a larger load must be bear to the foundation structures and therefore the shear reinforcements demand larger dimensions. Mechanical expanded anchors are used for anchoring on the inaccessible side. A significant contribution of mechanical anchoring is demonstrated in the tests results which make possible more efficient design of additional punching reinforcement.

Abstract: Two ways how to determine maximum punching resistance of flat slabs with shear reinforcement are currently used. The first way is verification of the concrete strut capacity at the column periphery defined as V_Rd,max. The second limit is defined as k_max multiple of the punching shear resistance without shear reinforcement V_Rd,c. The values of k_max are proposed usually in between 1.4 and 2.0. Results of the experimental tests are presented in the paper that were focused on above mentioned limits, whether failure of the struts can precede any other form of punching failure that is limited by k_max*V_Rd,c. Two experimental slab samples reinforced with high amount of shear reinforcement that increased punching capacity above capacity of the concrete struts were tested together with two slab samples cast without shear reinforcement. Comparison has shown that punching resistance of flat slab with shear reinforcement has been 1.7 times higher than resistance without shear reinforcement. While some standards allow for use k_max value of 1.9 in this case. This indicates that limits based only on the k_max factors may overestimate actual maximum punching shear resistance.

Abstract: Currently, the shaped parts combined with straight, concave, and convex portions are increasingly fabricated. To produce the straight portion, the shearing theory is usually applied. As well as, to produce the concave and convex portions, the punching and blanking theories are usually applied. However, with the same die-cutting process parameters, the comparison of cut surface features of straight, concave, and convex portions has not been investigated yet. Therefore, in the present research, the comparison of the cut surface features in various die-cutting processes, including shearing, blanking, and punching processes are investigated. The finite element method (FEM) was used as a tool to investigate these cut surface features. The cut surface features were investigated and clearly identified via the changes of the stress distribution analyses. The results elucidated that with the same die-cutting process parameters, the different cut surface features were obtained. Specifically, the crack formations were easily generated in the case of blanking process, following by the shearing and punching processes, respectively. Therefore, the smooth cut surface was smallest in the case of blanking process, following by the shearing and punching processes, respectively. The laboratory experiments were carried out to verify the accuracy of the FEM simulation results. Based on the cut surface features, the FEM simulation results showed good agreement with the experimental results in terms of the cut surface features. Therefore, to design the die-cutting process parameters to meet the product requirements of complicated shapes, the understanding on these working process parameters being upon the shaped parts is necessarily.