Shear Heads Research Articles

KBR selects Clariant[StQuote]s AmoMax catalyst for Acme[StQuote]s green NH3 project in Oman

This investigation examines the performance of hybrid reinforced concrete flat slabs, incorporating fully-integrated shear-heads at connections to steel columns, through a series of numerical evaluations and parametric studies. Validations of the adopted nonlinear finite element procedures, which employ concrete damage plasticity constitutive models, are carried out against experimental results on hybrid members. Complementary verifications on conventional reinforced concrete flat slabs are also undertaken to ensure the reliability of the selected ranges for key modelling parameters. Comparison of the numerical simulations against the test results shows close correlations in terms of ultimate strength, deformations and stress levels in the constituent elements of hybrid members. This is followed by a series of parametric assessments on key structural parameters for hybrid flat slabs with steel shear heads. The results of these investigations enable the identification of three modes of failure as a function of the interaction between the shear-head and surrounding concrete. The findings permit the development of improved analytical models for predicting the response as well as the ultimate strength of such members. In addition, recommendations are given for the determination of shear-head dependent parameters, which are required for practical design purposes, with a particular focus on the embedment length and section size of the shear-head elements. The suggested expressions for assessing the shear-head characteristics offer a more reliable design approach in comparison with existing methods and are suitable for effective practical application and implementation in codified procedures.

Shear Cap Size Selection Method Based on Parametric Analysis of ACI-318 Code and Eurocode 2 Standard.

The scope of the paper is to propose a method for determining the size of shear caps in a slab–column-connections-reinforced concrete structure. Usually, shear heads are used to enhance slab–column connection, especially when the transverse reinforcement does not give the required punching shear load capacity. The dimensions of the shear head should provide the punching shear resistance of the connection inside and outside the enhanced region. The process of selecting the size of the shear head is iterative. The parametric analysis of the ACI 318 code and EC2 standard has the objective of indicating which control perimeter (inside or outside the shear head) has a decisive impact on the punching shear capacity of the connection. Based on the analysis, the authors propose methods for selecting the dimensions of the shear head with practical application examples. The paper is intended to provide scientists, civil engineers, and designers with guidelines to design the process of the slab–column connections with the shear caps.

08.58: Ultimate behaviour and design of hybrid flat slabs with steel shear heads

ABSTRACTThis investigation examines the performance of hybrid reinforced concrete flat slabs, incorporating fully‐integrated shear‐heads at connections to steel columns, through a series of numerical simulations and parametric studies. Validations of the adopted nonlinear finite element procedures, which employ concrete damage plasticity constitutive models, are carried out against experimental results on hybrid members. Comparison of the numerical simulations against the test results shows close correlations in terms of ultimate strength, deformations and stress levels in the constituent elements of hybrid members. This is followed by a series of parametric assessments on key structural parameters for hybrid flat slabs with steel shear heads. The results of these investigations enable the identification of three modes of failure as a function of the interaction between the shear‐head and surrounding concrete. The findings permit the development of improved analytical models for predicting the rotational response as well as ultimate strength of such members. In addition, recommendations are given for the determination of shear‐head dependent parameters, which are required for practical design purposes, with particular focus on the embedment length and section size of the shear‐head elements. The suggested expressions for assessing the shear‐head characteristics offer a more reliable design approach in comparison with existing methods and are suitable for effective practical application and implementation in codified procedures.

Numerical modelling and parametric assessment of hybrid flat slabs with steel shear heads

This investigation examines the performance of hybrid reinforced concrete flat slabs, incorporating fully-integrated shear-heads at connections to steel columns, through a series of numerical evaluations and parametric studies. Validations of the adopted nonlinear finite element procedures, which employ concrete damage plasticity constitutive models, are carried out against experimental results on hybrid members. Complementary verifications on conventional reinforced concrete flat slabs are also undertaken to ensure the reliability of the selected ranges for key modelling parameters. Comparison of the numerical simulations against the test results shows close correlations in terms of ultimate strength, deformations and stress levels in the constituent elements of hybrid members. This is followed by a series of parametric assessments on key structural parameters for hybrid flat slabs with steel shear heads. The results of these investigations enable the identification of three modes of failure as a function of the interaction between the shear-head and surrounding concrete. The findings permit the development of improved analytical models for predicting the response as well as the ultimate strength of such members. In addition, recommendations are given for the determination of shear-head dependent parameters, which are required for practical design purposes, with a particular focus on the embedment length and section size of the shear-head elements. The suggested expressions for assessing the shear-head characteristics offer a more reliable design approach in comparison with existing methods and are suitable for effective practical application and implementation in codified procedures.

Performance of two shear heads for harvesting biomass in hardwood stands in France

The increasing demand for energy wood in Europe is accompanied by the development of new harvesting tools to mobilize forest biomass, notably hardwood biomass. Two logging operations are targeted more specifically: the first thinnings in regular high forest, and the clear cuttings of traditional coppices and of high productive short rotation coppices. The challenge is to find efficient and sustainable harvesting tools for hardwood trees that are very common in central and southern Europe.Two French manufacturers have recently developed shear heads dedicated to hardwood: Jacquier C360 and Sève S350. Nowadays, many logging companies are investing in these tools, as they are relevant to the whole tree system that has been adopted for harvesting woody biomass.The performance of these shear heads was determined on 3 logging sites in the North East of France. A regression analysis was run in order to evaluate models for cutting productivity of each machine, considering significant factors influencing productivity: tree size and stand type (high forest/coppice).The two shear heads were more productive at high forest than at coppice. The stand type had a significant effect only on the C360’s productivity. At high forest sites with small diameter trees, the C360 was 11.8% more productive than the S350. However, at coppice site, the S350 was 15% more productive than the C360 for harvesting big clumps. Results showed that working in coppice forest requires a head that must be very powerful and have a wide opening.

Structural performance of RC flat slabs connected to steel columns with shear heads

This paper investigates the structural performance of hybrid members consisting of reinforced concrete flat slabs, with and without shear reinforcement, connected to steel columns by means of fully integrated shear-heads. A detailed account of the results from a series of six large scale tests on this form of hybrid structural system is provided. The test results offer a direct evaluation of the full load–deformation behaviour of the specimens as well as the ultimate punching shear strength attained prior to failure at the critical slab perimeter outside the shear-head region. The experimental findings enable the development of analytical models that depict the rotational response and flexural strength as a function of the shear-head embedment length, layout and section size. Additionally, the test results support the definition of a shear-head dependent control perimeter which is used in conjunction with the analytical slab models for full assessment of punching shear strength. The adequacy of strength predictions incorporated in current design methods for conventional reinforced concrete members are also examined in the paper. It is shown that existing design procedures either lack direct guidance for members provided with shear-heads, or lead to overly conservative strength predictions. Finally, in order to provide a reliable evaluation of the ultimate punching shear strength of hybrid elements, analytical design expressions which account for the characteristics of the shear-head system, are proposed. In comparison with conventional reinforced concrete design provisions, the suggested approach captures in a more realistic manner the influence of the embedded length of the shear-heads for such hybrid members with or without shear reinforcement.

Mechanized coppice harvesting with new small-scale feller-bunchers: Results from harvesting trials with newly manufactured felling heads in Italy

The revival of coppice management is being considered as one option to satisfy the increasing market demand for wood biomass. Commonly used harvesting systems in coppice forests (CF) are based on motor manual felling, but further mechanization of CF operations is desirable because of increasing labor costs and the high fatality rates associated with motor manual felling.The goal of this study was to determine the machine performance in terms of productivity, cost-effectiveness and cut quality of new feller-bunchers, when used on different types of CF. The study comprised of five tests on different sites in Italy, four of which represented a specific type of CF.Results showed that harvesting productivity varied from 3.1 to 8.6 dry t per scheduled machine hour (SMH) in multi-stem coppice stands (4.5–16 dry m3 SMH−1). Productivity reached 16.2 dry t SMH−1 in a short rotation forestry (SRF) control stand (39.4 dry m3 SMH−1) and it increased with stump mass. Recorded productivities tested in conventional CF were not as high as achieved in single-stem SRF, or in the mechanized felling of comparable softwood stands, but still matched the requirements of commercial mechanized logging. Costs varied between 3.57 and 20.56 € dry t−1 (1.47–14.17 € dry m3−1). Lowest costs were reached in the SRF stand and highest cost in the Mediterranean CF growing on moderate to steep terrain. Shear heads produced poor cuts and single-action shears performed worst. The disc saw produced very low cuts with low damage levels, which might be acceptable even under current cut quality specifications.

Punching shear strength of steel fibre reinforced concrete slabs

The ultimate strength of reinforced concrete slabs is frequently governed by the punching shear capacity, which may be increased with addition of traditional fitments such as reinforcing steel, headed studs or shear heads. In addition to these traditional methods of strengthening against punching, steel fibre reinforcement has proved to be an effective and viable alternative. The addition of fibres into the concrete improves not only the shear behaviour but also the deformation capacity of reinforced concrete slabs. This paper presents a mechanical model for predicting the punching strength and behaviour of concrete slabs reinforced with steel fibres as well as conventional reinforcement. The proposed model is validated against a wide number of available experimental data and its accuracy is verified. On this basis, a simple design equation for the punching shear capacity of steel fibre reinforced concrete (SFRC) slabs is proposed.

Shear stress distribution of flat-plate using Finite Element Analysis

ABSTRACT The development of a linear numerical model of flat-plate to predict shear stress distribution around slab column connection is presented in this paper. An attempt is made to model the slab, flexural reinforcement and shear reinforcement using three dimensional solid elements. The proposed finite element model has been proved to be capable of simulating the shear behavior of slab-column connection and to be suitable for analysis of structural performance of flat plate structures. Numerical results obtained from this model have good agreement with the available results of other researcher’s numerical model with one dimensional rebar element. Keywords: Flat plate, ABAQUS, shear reinforcement, slab-column connection. 1. Introduction Flat-plate slab system is widely adopted by engineers as it provides many advantages such as reduction of floor height, more spatial planning due to no beams present. These advantages further results in reduction in material cost. In the flat plate slab-column connection is always subjected to combination of high bending moments and shear stresses, which develop a punching, shear failure. This failure is undesirable as it occurs without warning and may lead to progressive collapse of slab. Due to large tensile stresses, the potential diagonal crack in the form of truncated cone or pyramid is formed around the column. The failure surface extends from bottom of the slab at the support, diagonally upward up to the top surface. The angle of inclination with the horizontal depends on slab reinforcement. Hence, designing of flat-plate requires a special attention for both strength and ductility when punching shear being consider. The punching shear capacity of the slab-column connection is affected by the size of the column, the depth of slab, flexural reinforcement and compressive strength of slab etc. The punching shear capacity can be increased by using a larger column diameter, larger effective depth, more flexural reinforcement, higher concrete compressive strength or by shear reinforcement. Among these methods, the most effective way to enhance the slab-column connection is to use shear reinforcement at the punching shear zone (ACI 421 R-99), which is permitted by most of the building codes. The provision of punching shear reinforcement in various forms help in increasing the shear and ductility of the concrete. The various forms of shear reinforcements include stirrups, shear studs, bend up bars, shear heads (placed above the column), etc. According to ACI 318-05, the shear strength is a function of compressive strength of concrete and geometrical condition. The provision given in EC2 also includes the size effect and the effect of the flexural reinforcement ratio. Allowable shear strength of concrete with shear reinforcement is calculated as 0.125 √f

Analytical and Numerical Methods for the Design of Maddock Mixers in Single Screw Plasticizing Technology

AbstractSummary: In single screw plasticizing technology dispersive mixing elements, i.e., axial and spiral Maddock shear heads, are often used to improve the melt quality. Mathematical models are necessary to efficiently design the mixing section. An analytical model for the design of Maddock mixers is presented in this work. In addition, a CFD‐software package is employed to determine the flow and pressure field for different geometries and processing conditions. For the design and process analysis of fluted dispersive mixers the validity and potential of simplified analytical solutions are compared to more versatile and detailed CFD‐simulations.

Evaluation of a probe for predicting beef tenderness

A series of three experiments were conducted to evaluate the performance of the MIRINZ (Meat Industry Research Institute of New Zealand) tenderness probe. In the first experiment, assessments on raw samples from two different muscles ( longissimus lumborum and semimembranosus) were obtained using the tension head. Results indicated D50 values (torque at 50° of rotation) were the most highly related to both sensory (taste, olfactory, and feeling factors measured by a trained sensory panel) and consumer (hedonic ratings provided by untrained consumers) properties and were the values of choice, since all probe values were essentially measuring the same characteristics. In the second experiment, assessments were made using both the tension and shear heads on raw and cooked striploin ( longissimus lumborum) steaks. Results confirmed probe values were essentially measuring the same characteristics, but indicated raw tension head, area 2 values (area before 50° of rotation) were more highly related to both sensory and consumer properties than were D50 values. However, probe values from raw samples did not account for a sufficient amount of variation in either sensory or consumer properties to be useful predictors of these traits, and stepwise, linear regression did not improve the predictive value of raw probe values, since all probe values were interrelated. Probe values on cooked samples indicated the shear head and area 3 values (area under the entire trace) were the most related to both sensory and consumer properties and were the values of choice. Based upon the amount of variation accounted for in sensory and consumer traits, probe area 3 values using the shear head on cooked samples provided greater predictive value for both sensory and consumer traits than Warner–Bratzler shear values obtained from steaks cooked either fresh or after being frozen and thawed. In experiment 3, correlations with individual, parametric character notes from the texture profiles of two different muscles provided no clear indication as to the textural properties being assessed by the probe. However, the MIRINZ probe appears to be a quick viable alternative to the Warner–Bratzler shear for providing an objective measure of cooked meat tenderness.

Eccentrically loaded interior slab-column connections with shearhead reinforcement

The paper deals with the problem of the load- carrying capacity of interior slab-column connections when the axial load and unbalanced moment are transferred simultaneously. In order to obtain the data for analysis, tests were undertaken on full-scale models with shearheads, whose arm lengths were varied. From these test results, the authors propose a method to determine the shear stresses corresponding to the load-carrying capacity of slab-column connections with shear heads.