Influence of the relative rib area on bond behaviour

Steel-to-concrete bond is a basic aspect of the behaviour of reinforced concrete structures both at serviceability and ultimate states. When bond rules were originally developed, experimental results were mainly obtained on normal- strength concrete and a minimum relative rib area (bond index) was required by building codes to ensure good bond properties. The arrival into the market of high-performance concrete and newer structural needs may require different bond indexes. In the present paper, the experimental results of pull-out tests on short anchorages are presented. Several pull-out tests on ribbed bars, embedded in cubes of normal- and high-strength concrete with a concrete cover of 4.5 times the bar diameter, were carried out in order to better understand the influence of the relative rib area and bar diameter on the local bond behaviour, as well as on the splitting crack width generated by the wedging action of ribs. A total of 96 tests were performed on machined bars of three different diameters (12, 16 and 20 mm) with a bond index ranging from 0.040 to 0.105. The results of 55 pull-out tests on commercial hot-rolled ribbed bars of four different diameters (12, 20, 40 and 50 mm) are also presented to confirm that the bond response also depends on bar diameter (size effect). Experimental results provide information concerning the influence of the relative rib area on bond strength and on the bursting force due to the rib’s wedge action. As the minimum measured bond strength of rebars was always markedly greater than the minimum bond strength required by building codes even when low bond indexes were adopted, the test results point out the possibility of reducing the minimum value of the relative rib area required by Eurocode 2 without limiting the safety coefficient of bond. The reduction also allows a higher structural ductility that can be achieved due to a greater strain penetration of the rebars from concrete cracks

Lapped joints of bars in bundles

The approach of European and North American Design Code rules for design of lapped joints of reinforcing bars within a bundle differ markedly, with the former permitting the same or shorter laps with respect to laps of individual bars, while the other requires longer laps. This paper reports an experimental in- vestigation to evaluate performance of lapped joints in which individual reinforcing bars within a bundle of two or three bars are lapped. The results show that it is not necessary to increase lap lengths of individual bars within a bundle, and that failure is less brittle where lap joints confined by links are staggered longitudinally, whether the lap is between individual bars or is of one bar in a pair or bundle. The outcome does, however, question the validity of the reductions permitted in EC2 for staggering laps, and suggests that it would be prudent to suspend use of the α6 reduction factor for proportion of bars lapped at a section pending more tho- rough investigatio

Experimental Results on Staggered Lapped Bars in FRC

The paper presents experimental results on lap splices in fiber reinforced concrete (FRC). Four point bending tests were carried out on several full-scale beams with all or part of the longitudinal reinforcement lap spliced at mid-span. The beams were reinforced with either 16 mm or 20 mm diameter rebars and included various lap splices configurations varying the percentage of lapped bars. The behaviour of lapped bars in FRC with a volume content of steel hooked fibres equal to 0.5% was investigated. The results show that the post-peak behaviour of FRC can enhance the strength of staggered lapped splices as well as it can reduce their brittleness, thus allowing a reduction of lap length when only a portion of bars at a section are lapped. The results show also the benefits on the durability of concrete members due to the capability of the fibres to markedly reduce the splitting cracks along the splice at service loadings

Experimental and Numerical Analysis on the Core Lateral Thrust in Bolted BRBs

The paper aims at presenting numerical and experimental results on the lateral thrust exerted by the inner core of a buckling restraining brace (BRB) when, after buckling in compression, it arrives into contact with the external restraining case. The BRB consisted of a plate core restrained by bolted U- shaped member, thus allowing an easy assembly of the BRB, as well as the inspection and the substitution of its core after a seismic event [1, 2]. The results of six tests on BRBs having a plate core with a cross section of 5x50 mm2 and a dissipative length of 560 mm are shown. The gap dimension was varied between 0.25 and 0.70 mm. Cyclic displacements of increasing amplitude were applied to the core up to a steel strain of 2%, adopting the loading history prescribed by AISC standards [3]. The instrumented bolts connecting the restraining elements and a thin tactile pressure sensor placed within the gap allowed to steadily monitor both the lateral thrust and the buckling shape of the plate core during the experiment. The results showed that the lateral thrust increased linearly with the gap dimension, thus confirming the trend provided by the analytical formulation proposed by Genna and Gelfi [4]. As reported in Table 1, for a maximum axial force of about 110 kN, the value of the transverse thrust ranged from 36.5 kN in the specimen 1 with a gap of 0.25 mm to 86.6 kN in the specimen 3 with a gap of 0.70 mm. Furthermore, the specimens 6, without stiffening plates in the web of the restraining U- profiles, showed the significant role of the local transverse deformation on the value of the lateral thrust, which was twice the thrust of the specimen 1, characterized by the same gap of 0.25 mm but with a stiffened case. The experimental results allowed to validate a non-linear 3D Finite Element model performed with the code ABAQUS [5]. The numerical analyses accurately predicted the cyclic behaviour of the tested BRBs in term of axial load, buckling shape of the core and lateral thrust action. The difference between the measured thrust and the calculated thrust at the end of the loading history (steel strain c=2%) ranges between -8% to +17%, while the 2D plane stress model proposed in [6] overestimated the lateral thrust of +85%, owing to the inability of the 2D model to describe the local transverse deformations of the case

Effects of new openings on the in/plane behaviour of unreinforced brick masonry walls

Existing brick masonry buildings are frequently modified to satisfy nowadays living demands. Such modifications may include new windows or doors that connect two rooms and require openings to be cut from load bearing walls. In current design practice, these interventions are generally designed and verified for vertical load, but the structural behavior of these altered walls when submitted to in-plane loads (due to seismic actions) is not yet fully understood. Thus, design practice may be inaccurately estimated. The objective of this work is to evaluate, numerically and experimentally, the effects of introducing openings in masonry solidbrick walls subjected to in-plane loading. Three main parameters are considered for the numerical studies: i) walls dimensions, ii) opening type, iii) opening size. As expected, results show that walls with medium-large openings are the most vulnerable case-scenario. These numerical results have addressed the design of a representative wall tested at the University of Brescia. The preliminary results of this experimental program are included in this pape

Experimental and numerical assessment of masonry walls with new openings strengthened with steel frame

The creation of new openings in masonry walls is a frequent intervention executed in existing buildings of unreinforced masonry composed of clay bricks. These openings are widely seen at the street-level, where spaces are modified to create new windows or doors for new stores, garages or offices. Depending on their size and position, these interventions may cause significant decrease of the wall’s original in-plane strength and stiffness, thus, compromising the building seismic resistance. For example, when several garages are created, one after another, the risk of inducing the soft-story mechanism, when earthquake forces arrive, increases. Another example is when a door of significant size is introduced in an originally solid masonry wall, which was a key object to guarantee the box-like behavior of the structure. The opening would reduce the cross section of the remaining piers and spandrel, and thus, weaken the wall’s seismic strength. These changes in the original wall have consequences in the box-like behavior, as during earthquake events, the load demands on the remaining shear walls might be larger than their shear capacity. Therefore, strengthening techniques must restore as much as possible the loss of stiffness and strength. Besides, for masonry structures, the technique must be reversible and respect the compatibility between materials, particularly in the case of protected assets. In an attempt to complying with these requirements, engineering practitioner often introduce steel profiles forming a frame inside the opening. Steel is usually preferred because of its high level of reversibility and the stiffness and strength it can provide to masonry without substantially increasing the building self-weight. The design of this steel frame and the stiffness of the masonry wall with opening is based in the available analytical tools, i.e., the Timoshenko Beam Theory. From these calculations, the loss of stiffness when passing from a solid wall to a perforated wall is about 75% for cantilever boundary conditions and 55% for double-fixed. Thus, very stiff profiles for the steel frame are required. In theory, these profiles are capable of fully restoring the stiffness and resistance. The present work is dedicated to evaluate the effectiveness of this steel frame technique by means of experimental and numerical methods. The experimental program was designed to provide full assessment of the effects of introducing a new door opening in brick masonry walls, from the perforation process to the application of in-plane cyclic loads . A flexible steel frame was designed using numerical tools and consisted in four profiles welded together and tied to the surrounding masonry wall by means of dry-driven dowels. The numerical model was validated against the experimental results, and show that neither a very stiff steel frame nor a more flexible one is capable of restoring the original solid wall’s stiffness. However, both are capable of restoring the in-plane strength and ductility. This paper, also shows that using a very stiff profile might lead to a rather brittle response of the reinforced wall, as the masonry starts cracking before activating the frame. This would not happen with a more flexible profileItalian Ministry of Education, University, and Research (MIUR) for her Doctoral Scholarship is gratefully acknowledged. The Authors also thank the technicians A. del Barba, A. Botturi from laboratory Pietro Pis

Von Bezold assimilation effect reverses in stereoscopic conditions

Lightness contrast and lightness assimilation are opposite phenomena: in contrast, grey targets appear darker when bordering bright surfaces (inducers) rather than dark ones; in assimilation, the opposite occurs. The question is: which visual process favours the occurrence of one phenomenon over the other? Researchers provided three answers to this question. The first asserts that both phenomena are caused by peripheral processes; the second attributes their occurrence to central processes; and the third claims that contrast involves central processes, whilst assimilation involves peripheral ones. To test these hypotheses, an experiment on an IT system equipped with goggles for stereo vision was run. Observers were asked to evaluate the lightness of a grey target, and two variables were systematically manipulated: (i) the apparent distance of the inducers; and (ii) brightness of the inducers. The retinal stimulation was kept constant throughout, so that the peripheral processes remained the same. The results show that the lightness of the target depends on both variables. As the retinal stimulation was kept constant, we conclude that central mechanisms are involved in both lightness contrast and lightness assimilation

Hepatosplenic T-Cell Lymphoma Mimicking Acute Onset of Cholestatic Hepatitis in a Young Immunocompetent Man: A Case Report

We herein report a case of hepatosplenic T-cell lymphoma (HSTCL) incidentally found in a 30-year-old man who came to the emergency department after an ankle trauma. At admission, laboratory tests revealed abnormal liver enzymes and pancytopenia, and imaging showed mild hepatosplenomegaly. During hospitalization, the patient's clinical condition worsened rapidly, with a concomitant increase in cholestatic enzymes, severe jaundice, and the worsening of pancytopenia. Causes of liver injury, including many infectious diseases, were explored until the diagnosis of HSTCL was made by liver and bone marrow biopsies. Subsequently, the patient underwent six cycles of chemotherapy with a CHOP (cyclophosphamide, hydroxydaunorubicin, oncovin and prednisone or prednisolone) regimen and one with Hyper-CVAD (fractionated cyclophosphamide, vincristine, doxorubicin, dexamethasone) but, despite this aggressive treatment, died due to disease progression 2 months after diagnosis. This rare disease should be considered in the diagnostic workup of acute cholestatic hepatitis presenting with concomitant hepatosplenomegaly and cytopenia