Bend Bars Research Articles

Automatic Estimation System of Building Frames with Integrated Structural Design Information (AutoES)

Construction project participants seek to accurately determine construction costs as soon as a design is completed. However, it may take a minimum of several weeks for cost estimation after the structural design and drawings are completed. Manual quantity surveying is time-consuming and requires significant experience and time. Even if computerized software is used, it is time-consuming to enter structural design information into the estimation software. In addition, the estimated quantity may result in inaccurate cost owing to drawing errors or quantity surveyors’ mistake, and it is not the exact quantity to be put into actual construction, which can cause numerous problems in the construction phase. If the information can be automatically received for estimation, the exact quantity for construction can be estimated without omission or errors. To estimate the exact quantity after structural analysis and design of building projects, this study proposes an automatic estimation system of building frames with integrated structural design information (AutoES). Using the algorithms of AutoES, the task of estimation can be accomplished with an exact bill of quantities including a bar bending schedule within 1 week.

Proposed Methods on Enhancement of Dynamic Response of RC Frames and Soil Structure Interaction

In this paper, proposed methods on enhancement of a nonlinear behavior of reinforced concrete frames subjected to cyclic load. A fully nonlinear dynamic analysis is adapted using three-dimensional finite element analysis by means of ANSYS 16.0 code. All structural elements such as footings, columns and girder are simulated in the numerical model. The concrete is assumed to be nonlinear and isotropic. In addition, some proposed methods are investigated to enhance the performance of RC frames under cyclic loading such as, cross bracing steel at the connections and at girder region as well as additional bent bars at the ends of girder. The results of analyses are presented in terms of envelope capacity, load-displacement relationship, stresses and cracks distribution. The results indicated that the provision of additional reinforcement increased the ultimate lateral capacity, ductility and introduce an additional mechanism for shear stresses for RC frame under cyclic loading. The best performance is observed when the cross-bracing is used at the top and bottom column connections whereas, the lateral capacity and displacement is increased by 12.9 % and 27.63% respectively of that computed for Control Frame. In case of cross-bracing steel at beam column connections and case of cross-bracing at beam region, the lateral capacity of RC frames is about 1.09 and 1.04 times that of control frame respectively. Furthermore, the dynamic analysis is carried out under considering the foundation soil whereas the Drucker-Prager model is used to define the stress strain behavior of soil. Besides, some significant observations on the performance of RC frames with change of the values of parametric study are presented in this paper.

GFRP Bars Anchorage Resistance in a GFRP-Reinforced Concrete Bridge Barrier.

In the present paper, experimental and numerical investigations were conducted on concrete bridge barriers utilizing glass fiber reinforced polymer (GFRP) bars with a hook at their ends. Implementation of these hooked bars instead of the bent bars or headed-end bars in the bridge barriers presented in the Canadian Highway Bridge Design Code (CHBDC) was investigated on American Association for State Highway and Transportation Officials (AASHTO) test level 5 (TL-5) concrete bridge barriers. This research aimed to reach a cost effective and safe anchorage method for GFRP bars at the barrier–deck junction, compared to the conventional bend bars or headed-end bars. Therefore, an experimental program was developed and performed to qualify the use of the recently-developed, small radius hooked bars at the barrier–deck junction. The experimental findings were compared with the design factored applied transverse load specified in CHBDC for the design of the barrier–deck junction as well as factored applied bending moment obtained at the barrier–deck junction using a recently-conducted finite-element modeling. Satisfactory behavior for the developed hooked GFRP bars as well as their anchorage resistance was established and a reasonable factor of safety in design of barrier–deck joint was achieved.

Robocasting of reaction bonded silicon carbide structures

A novel shaping method for the fabrication of reaction bonded silicon carbide structures was investigated in this work. A paste consisting of silicon carbide as inert filler and carbon powder was developed and printed by robocasting technology. Layer by layer deposition of the ceramic paste facilitates the printing of complex shaped structures. Different structures such as lattices, hollow cylinders, bending bars and gyroids were printed using nozzles with diameter of 0.5 mm and 1.5 mm. After pyrolysis at 700 °C and further heat treatment at 1850 °C the samples were infiltrated using the liquid silicon infiltration technique to obtain dense near-net shape RBSC structures. The robocasted structures showed a hardness of approximately 20 GPa, a thermal conductivity of ∼112 W/m*K, Young’s modulus of ∼356 GPa, flexural strength of ∼224 MPa and an amount of residual silicon of approximately 23%. These measured properties are comparable with those of traditionally fabricated RBSC.

Effect of Binder Content on the Slip Rheology and Green Properties of Slip Cast Alumina

The rheology of A96% alumina slips and the physical and mechanical properties of slip cast samples were studied. The slips had a constant solids loading of 40 wt% alumina and a polyvinyl alcohol (PVA) content of 0-3 wt%, as a binder. The rheological behavior and viscosity of the slips were examined to determine the flowability of the slips necessary for the casting process. The slips were prepared by ball milling and the bend bar samples were cast in plaster molds. The green densities and the flexural strength of the bars were measured, and the fracture surfaces were examined by scanning electron microscopy. It was found that the slip viscosity increased with an increase of PVA content. The green flexural strength also increased to a maximum value of 0.52 MPa with increasing PVA up to 2 wt%. The further addition of PVA decreased the flexural strength. The green density did not significantly change with the PVA content, however the samples produced using 3 wt% PVA showed the lowest percentage of theoretical density of 41%. The fracture surface of the 3 wt% PVA sample showed numerous large pores compared with the other samples. Therefore, in this study it was concluded that there is in optimal amount of PVA to produce the highest green density and flexural strength of cast samples. Excess PVA reduced the flowability of the slip and resulted in excess porosity, which decreased the green density and deteriorated the flexural strength.

Quantification of risk and assessment of key safety factors for safe workplace in Indian building construction sites

Construction sites are known to be hazardous as it involves height work, hot work, confined space, etc. Prioritizing and classifying the risk zone may create awareness among the workers and help to prevent them from accidents in high-risk area. To prioritize the risk in building construction sites, Hazard Identification and Risk Assessment (HIRA) technique is adopted. The hazards in the sites are identified through direct observation and previous safety reports, and the risk values are determined using likelihood and severity ratings of each hazard. HIRA study reveals that the building construction site considered in this work has 13.3% of low risk, 37.7% of medium risk, 44.4% of high risk and 4.6% of extreme risk. Total percentage of risk involved in each task is calculated and ranked to know the high-risk task. Through the obtained results, it is noted that crane operation (10.4%), height work (9.1%) and drilling (8.8%) are the three major tasks with high risk. It is observed that in the particular construction site, the percentage of low risk is very less. To know the key safety factors which influence the task to be hazardous, Relative Importance Index is used to rank the factors and it is identified that there is a higher level of disagreement in using Personal Protective Equipment, non-availability of separate gangways and bar bending sheds. If these key factors are addressed, then the hazardous task will become risk free.

Fracture Toughness Analysis of Ceramic and Resin Composite CAD/CAM Material.

To evaluate and compare the fracture toughness of dental CAD/CAM materials of different material classes intended for in-office milling (glass ceramics, hybrid, resin composites) and the influence of aging on this property. The fracture toughness (critical intensity factor, KIc) values of 9 CAD/CAM restorative materials (Ambarino High-Class, Brilliant Crios, Cerasmart, exp. CAD/CAM composite, Katana Avencia, Lava Ultimate, VITA Enamic, IPS Empress CAD, and IPS e.max CAD) were determined using the SEVNB method in a four-point bending setup. Twenty bending bars of each material with a 4 × 3 cross and a minimum length of 12 mm were cut out of CAD/CAM milling blocks. Notching was done starting with a pre-cut and consecutive polishing and v-shaping with a razor blade, resulting in a final depth of v-shaped notches of between 0.8 and 1.2 mm. Half of the specimens were selected for initial fracture toughness measurements. The others were thermocycled in distilled water for 30,000× (5/55°C; 30-second dwell time) before testing. Specimen fracture surfaces were analyzed using confocal laser scanning microscopy. All specimens for each material fractured into two fragments and showed the typical compression curl and brittle failure markings. Comparing initial KIc values, lithium disilicate ceramic IPS e.max CAD showed significantly the highest and leucite-reinforced ceramic IPS Empress CAD significantly the lowest KIc values (p<0.001). All tested CAD/CAM materials with a resin component ranged in the same KIc value group (p>0.999-0.060). After thermal cycling, the highest KIc values were measured for lithium disilicate ceramic IPS e.max CAD, followed by resin composite materials Ambarino High-Class (p<0.001-0.006) and hybrid material VITA Enamic (p<0.001-0.016), while the significantly lowest values were reflected for the resin composite materials Cerasmart, LAVA Ultimate (p<0.001-0.006), and Katana Avencia (p<0.001-0.009). The roughness of the fracture surfaces varied depending on the microstructure of the respective material. The ceramic surfaces showed the smoothest surfaces. The fracture surface of VITA Enamic revealed microstructural inhomogeneities and microcracks. For CAD/CAM resin composite materials, crack paths through the matrix and interfaces of matrix and fillers could be observed at the microstructure level. The materials tested show differences in fracture toughness typical for the class they belong to. With one exception (Ambarino High-Class), thermocycling affected the fracture toughness of materials with a resin component negatively, whereas the leucite and lithium disilicate ceramic showed stability.

Residual Stresses in Elastoplastic Bending of Round Bar

Elastoplastic deformation on the presses and high-temperature heating of the steel sheet cause the large residual stresses in the sheet’s and bar’s wall. The technological operations of the obtaining of metal products, their shape and linear dimensions strongly affect on the distribution within the metal and the maximum values of residual stresses. The uneven cooling of various parts of the sheet and bar, obtained by bending, stamping and forging, also leads to the large residual stresses inside the metal. The greatest residual stresses occur in the weld area, where there is a strong heterogeneity of mechanical and physical properties of the metal due to uneven heating and cooling. Below the new analytical method for calculating of the residual stresses of a round steel bar in the elastoplastic bending is obtained. This method takes into account the diameter of the bar, as well as the modulus of elasticity, the yield strength and the hardening modulus of steel’s bar.

Three-dimensional assessments of crack tip constraint

Crack tip constraint can be used as a means to relate the stresses at the crack tip to a measure of fracture toughness of a material. Current technique to determine crack tip constraint demonstrated in structural integrity standards are based on two-dimensional plane strain approach. This paper explores the possibility of extending the current two-dimensional crack tip constraint solutions to three-dimensional crack problems through an investigation of the asymptotic structure of three-dimensional crack tip stress fields under elastic-plastic non-hardening responses. Analysis was based on three-dimensional boundary layer formulations, combined with full-field solutions of single edge notched bend bars and centre cracked tension panels having a range of thicknesses. The fields along the crack front were examined as a function of load level and thickness. From the results, it is demonstrated that, at the crack tip (r = 0), a family of asymptotic fields develop which feature a constant stress sector directly at the crack tip. Within this sector the fields differ hydrostatically while being similar in respect of the maximum stress deviator. At the intersection with the free surface, an elastic perfectly-plastic corner field which differs from the plane stress field is shown to develop. It is shown that in these fields the level of constraint is parameterised by J/zσo, where z is the distance from the free surface. J/zσo unifies both the change in the maximum principal stress and the mean stress, as a function of thickness and deformation level from all sections of different geometry and thickness specimens. An explicit expression has been developed which demonstrated the constraint loss due to in-plane and out-of plane crack tip constraint effects, allowing a two-parameter fracture mechanics methodologies in a modified form to be extended to fully three-dimensional fields.

SMA bending bars as self-centering and damping devices

This study proposed a new type of the shape memory alloy (SMA) bending bars with a new clamping machine and investigated their bending and cyclic behavior subjected to pushing and pulling actions through experimental works. The aim was to characterize the self-centering and damping capacity of the SMA bending bars to develop self-centering and damping devices and evaluate their efficiency in seismic and dynamic applications. For this aim, two types of SMAs were considered: (1) superelastic SMA (SE SMA) and (2) martensite SMA (MA SMA). First, the bending tests were performed on single SE SMA and MA SMA bars and their corresponding bending behaviors were illustrated in the form of force–displacement curves. Results showed that the MA SMA bar provided higher energy dissipation capacity while the SE SMA could provide a better displacement recovery. Thereafter, the bending behaviors of multiple bars with various combinations of SMA bars, namely, double SE SMA (SS), SE SMA-MA SMA-SE SMA (SMS), and MA-SE-MA (MSM) were investigated. Results showed that MSM provided the highest energy dissipation capacity among all while the SMS showed a better structural performance considering a combination of damping and self-centering capacities. Then, to enhance the displacement recovery and energy dissipation capacity of SMA bars, the single SE SMA bar, and SMS were annealed. Results showed that the annealing enhanced the structural performance, but no perfect displacement recovery was still obtained.

Experimental and numerical investigation into the methods of determination of mode I static fracture toughness of rocks

Fracture toughness, as a measure of resistance against crack instability and propagation, is one of the most important parameters in fracture mechanics of rocks and other solid materials. Different methods have so far been proposed in order to determine mode I fracture toughness. In practice, however, considerable differences between their results have been reported. In this study, six conventional tests, including the Single Edge Round Bar Bending test, the Chevron Bend test, the Semi-Circular Bend test, the Straight Notch Disk Bend test, the Brazilian disk test, and the Flattened Brazilian Disk test have been performed on a uniform specimen of gabbro rock for determination of mode I fracture toughness. A notable maximum difference of 42% is observed between the results.The tests are categorized into three groups in terms of their similarities. Several factors which affect the prediction of fracture toughness are investigated by both the numerical and experimental evidences. Distribution of the fracture process zone around the crack tip, is numerically computed using the 3D finite element analysis and based on both the “normal tensile stress” and the “von-Mises” criteria. According to the investigated features, the Chevron Bend test is the most reliable test for determination of the fracture toughness. Furthermore, the distribution of fracture process zone around the crack tip in this test is non-uniform which leads to over estimation of fracture toughness predicted by the effective crack theory.

Cutting speed and feed-rate influence on fatigue behavior of dry machined UNS A97075 alloy

Fatigue behavior takes a special relevance in manufacturing aeronautical parts due to safety reasons. Considering friendly environmental techniques, dry machining results in higher severe cutting conditions, which may negatively affect the part surface integrity, depending on cutting parameters values applied. In this sense, surface finish can be related to fatigue behavior. Notwithstanding, there is a lack of research that evaluates how cutting parameters affect fatigue life of aeronautical aluminum alloys, and their relationship with geometrical deviations. This work aims to analyze cutting speed and feed-rate influence on fatigue behavior of aeronautical aluminum alloy UNS A97075-T6 dry turned specimens. In order to do this, several rotating bar bending fatigue test have been carried out. Surface roughness have been also analyzed through the arithmetical mean roughness value (Ra) and the mean roughness depth (Rz). Results obtained seem to indicate that an increase of feed-rate and cutting speed negatively affects the fatigue life of the tested specimens, taking surface conditions a special influence in this behavior.

On the Remarkable Fracture Toughness of 90 to 97W-NiFe Alloys Revealing Powerful New Ductile Phase Toughening Mechanisms

Tungsten is generally too brittle to serve a robust structural function. Here, we explore the fracture toughness of 90 to 97%W (by wt.) liquid phase sintered tungsten heavy alloys (WHAs). The room temperature (RT) maximum load fracture toughness (KIc or KJm ≈ 38 to 107 MPa√m) of WHA, containing only 3 to 10 wt.% of a NiFe-based ductile phase (DP), is ≈ 5 to 13 times higher than KIc typical of monolithic W (≈ 8 MPa√m). RT tests for a range of precracked bend bar sizes generally show extensive stable ductile tearing (DT), except in the case of the 97 wt.%W alloy, where elastic fracture occurs in all but the smallest specimen tests. Nevertheless, even in this case the KIc = 38 ± 4 MPa√m, which is still almost 5 times higher than that for monolithic W. Tests with the smallest specimens down to -196°C, to partially emulate irradiation hardening, show decreasing toughness and a transition to elastic fracture at a temperature of -150°C for 90W to -25oC for 97W. However, even at -196°C, the 97W KIc is ≈ 3 times that of monolithic W at RT. In contrast to classical ductile phase toughening by macrocrack bridging, WHA toughening mainly involves new mechanisms associated with arrest, blunting and bridging of numerous dilatationally shielding process zone microcracks.

Computer-Aided Design and Manufacturing Technology for Identification of Optimal Nuss Procedure and Fabrication of Patient-Specific Nuss Bar for Minimally Invasive Surgery of Pectus Excavatum

The Nuss procedure is one of the most widely used operation techniques for pectus excavatum (PE) patients. It attains the normal shape of the chest wall by lifting the patient’s chest wall with the Nuss bar. However, the Nuss bar is for the most part bent by a hand bender according to the patient’s chest wall, and this procedure causes various problems such as the failure of the operation and a decreased satisfaction of the surgeon and patient about the operation. To solve this problem, we proposed a method for deriving the optimal operation result by designing patient-specific Nuss bars through computer-aided design (CAD) and computer-aided manufacturing (CAM), and by performing auto bending based on the design. In other words, a three-dimensional chest wall model was generated using the computed tomography (CT) image of a pectus excavatum patient, and an operation scenario was selected considering the Nuss bar insertion point and the post-operative chest wall shape. Then, a design drawing of the Nuss bar that could produce the optimal operation result was derived from the operation scenario. Furthermore, after a computerized numerical control (CNC) bending machine for the Nuss bar bending was constructed, the Nuss bar prototype was manufactured based on the derived design drawing of the Nuss bar. The Nuss bar designed and manufactured with the proposed method has been found to improve the Haller index (HI) of the pectus excavatum patient by approximately 37% (3.14 before to 1.98 after operation). Moreover, the machining error in the manufacturing was within ±5% compared to the design drawing. The method proposed and verified in this study is expected to reduce the failure rate of the Nuss procedure and significantly improve the satisfaction of the surgeon and patient about the operation.

Strength limits in mesoscaled 3Y-TZP ceramics for micro-surgical instruments

Micro-surgical instruments are a new application for mesoscale ceramics formed using the lost mold-rapid infiltration forming (LM-RIF) process. Instrument strength and reliability are the foremost concerns for this sensitive application. It is hypothesized that increasing grain size can improve the damage tolerance of the parts associated with the transformation toughening in the 3Y-TZP material, while retaining high strength. In this work, mesoscale bend bars (314 × 22 × 18 µm) of 3Y-TZP fabricated using the LM-RIF process were heat treated at 1400 °C for 1 h, 8 h, or 16 h, respectively, to obtain samples with different grain sizes. Strength tests were performed under three-point bending and results were evaluated using Weibull statistics. Fractographic and confocal Raman spectroscopic analyses were carried out to interpret the data.Experimental findings showed that the characteristic strength decreased with increasing grain size contrary to the damage tolerance hypothesis. An Orowan-Petch model was recalled to correlate the strength with the flaw size to grain size ratio. At fine grain sizes the strength was controlled by the flaws introduced by the LM-RIF process, whereas at large grain sizes the strength become more grain size controlled. Although larger-grained samples did have a higher propensity to transform, and thus increase toughening, exaggerated grain growth in some of the specimens tested caused an additional flaw population which led to an overall lower strength. Finally, based on the experimental observations and fracture mechanics considerations, we believe that an upper bound of ∼2.5 GPa exists for the strength of mesoscale as-fabricated 3Y-TZP ceramic parts.

EXPERIMENTAL DETERMINATION OF CHARACTERISTICS OF CRACK-RESISTANCE OF DISPERSE-STRENGTHENED COMPOSITES BASED ON NON-SATUTATED POLYESTERS

Based on the series of tests for three-point bending of rectangular bars with central cuts on a universal test machine, using the compliance and K-methods, experimental values of the fracture toughness characteristics of the material under investigation were obtained. In this work, the characteristics of the fracture resistance of casting artificial stone (CAS) were determined. The obtained values of the mechanical characteristics of the material are comparable to those of the natural stone. As a result of the experiments, tension-compression diagrams for CAS and also the dependence of compliance from the relative length were obtained. Considering the substantial technological advantages of this composite, it is concluded that it is practical to use this material.

Elasticity Theory Solution of the Problem on Bending of a Narrow Multilayer Cantilever with a Circular Axis by Loads at its End

An exact solution of the problem on plane bending of a narrow multilayer cantilever bar with a curved circular axis by tangential and normal loads distributed on its free end face is presented. The natural (for a bar structure) cylindrical circular coordinate system is used to describe the structure and geometry of the bar. The solution is obtained by directly integrating the equations of a plane elasticity theory problem using an analytical description of the mechanical characteristics of the discrete-inhomogeneous multilayer bar. Physical relations that take into account the cylindrical orthotropy of the material of bar layers and the conditions of absolutely rigid contact of layers are used in constructing the solution. The theoretical relations are realized for the test problem on determining the strain-stress state of a four-layer cantilever with a semiring axis. The solution obtained allows one to predict the strength and rigidity, to develop optimum design techniques, and to construct analytical solutions of different problems on bending of multilayer curved bars.

Anchorage Performance of GFRP Headed and Bent Bars in Beam-Column Joints Subjected to Seismic Loading

Concrete slabs, beams, and columns reinforced with glass fiber-reinforced polymer (GFRP) reinforcement have shown considerable deformability under monotonic loading; however, they have not been fully investigated under seismic loading. In efforts to understand the seismic behavior of GFRP-reinforced concrete (RC) moment-resisting frames subjected to seismic loading, this paper presents an investigation of the anchorage of GFRP bars in exterior beam-column joints. Four full-scale exterior beam-column joints were tested under cyclic reversed load simulating seismic loading conditions. Parameters tested in this study included end anchorage details of beam bars in the joint (90-degree hooks or anchor heads) and their surface texture (sand coated or mechanically deformed). Experimental results showed that all specimens successfully sustained 4.0% loading drifts and that surface texture showed an insignificant influence on the overall behavior.

Mechanical and hydrolytic degradation of an Ormocer®-based Bis-GMA-free resin composite

The aim of the study was to evaluate the mechanical stability of bisphenol A-glycidyl methacrylate (Bis-GMA) and Ormocer-based resin composites before and after water absorption and to examine water saturation. Disc-shaped specimens of the Bis-GMA (Grandio SO, Voco) and the Ormocer-based (Admira Fusion, Voco) dental resin composites were produced, stored in water, and weighed after pre-determinedtimes to measure the absorbed water. Bend bars were produced and stored for 24h in dry conditions as well as in distilled water for 14days or 60days at 37°C. The initial flexural strength (FS) under quasi-static loading and flexural fatigue strength (FFS) under cyclic loading were determined under 4-point bending.Fracture toughness (KIc) of both composites was measured using the single-edge-V-notch-beam (SEVNB) technique after the same storage conditions under 3-point bending. Within the first 14days, storage conditions did not affect the initial FS of Grandio SO, while a significant drop in initial FS was observed for Admira Fusion after 2weeks in water and most of the water was absorbed within this time. FFS for the Bis-GMA composite was not reduced before 2months in water, whereas for the Ormocer®-based composite, there has been a significant decrease in strength after cyclic fatigue already at 2weeks of water storage. KIcof Admira Fusion decreased significantly after both storage periods, while KIcof Grandio SO decreased only significantly after 2weeks of water storage. All mechanical properties of the Bis-GMA composite were superior to those of the Ormocer®-based material, except water sorption. Water storage seems to have a much more pronounced effect on the mechanical properties of Ormocer®-based dental composites in comparison to Bis-GMA-based composites.

Performance of Rayleigh-Based Distributed Optical Fiber Sensors Bonded to Reinforcing Bars in Bending.

Distributed Optical Fiber Sensors (DOFSs), thanks to their multiple sensing points, are ideal tools for the detection of deformations and cracking in reinforced concrete (RC) structures, crucial as a means to ensure the safety of infrastructures. Yet, beyond a certain point of most DOFS-monitored experimental tests, researchers have come across unrealistic readings of strain which prevent the extraction of further reliable data. The present paper outlines the results obtained through an experimental test aimed at inducing such anomalies to isolate and identify the physical cause of their origin. The understanding of such a phenomenon would enable DOFS to become a truly performant strain sensing technique. The test consists of gradually bending seven steel reinforcement bars with a bonded DOFS under different conditions such as different load types, bonding adhesives, bar sections and more. The results show the bonding adhesives having an influence on the DOFS performance but not on the rise of anomalies while the reasons triggering the latter are narrowed down from six to two, reaching a strain threshold and a change in structure’s deformative behavior. Further planned research will allow identification of the cause behind the rise of strain-reading anomalies.