Ductile Reinforcement Research Articles

General selection of lattice shape in ductile-reinforced brittle structures for increased stiffness

Ductile reinforcements are used in brittle structures to increase the overall stiffness and strength. However, the optimum lattice shape geometry according to which the ductile reinforcements must be laid down, has not been generally established. In this work, a ductile isotropic lattice structure is constructed from a unit cell and the brittle matrix is “filled” in the empty spaces thereafter. In homogeneous stress conditions, the brittle part will experience the same applied remote stress as is felt by the ductile lattice. The statistical theory of brittle failure is invoked to bring home the point that the unit cell area of the lattice is arbitrary (for a given total area) and hence the lattice shape geometry does not influence the probability of survival of the structure. Therefore, a suitable geometry shape (triangle or square) maybe chosen to further enhance the overall stiffness at a given probability of survival. It has been concluded that an (equilateral) triangular lattice is better suited compared to a square lattice if the ductile reinforcement lattice bars have the same stiffness. The technique and conclusion is generally true for any choice of brittle and ductile materials. Also, the conclusion holds true for both compressive and tensile loading.

Fracture behavior of Ti/Al3Ti metal-intermetallic laminate (MIL) composite under dynamic loading

Ti/Al3Ti metal-intermetallic laminate (MIL) composite is fabricated using Ti and Al foils through the vacuum sintering process. The fracture behavior of the MIL laminate composite under dynamic loading is investigated via modified Hopkinson bar loaded three-point bending fracture test. An experimental–numerical hybrid method is used to simulate the fracture behavior of MIL composite. In this method, the brittle damage model and plastic kinematic model are employed to represent the dynamic responses of the brittle intermetallic matrix Al3Ti and ductile reinforcement of Ti, respectively. As the boundary condition, displacement data obtained from dynamic three-point bending fracture test are imported into the finite element software package for simulation. Finite element model is validated through the comparison of the load–displacement curves from numerical simulation and the Hopkinson bar loaded three-point bending test. In addition, the dynamic damage evolution behaviors of the laminate composite, including crack deflection, delamination, plastic deformation, and brittle fracture are investigated using the post-process technique of finite element software package. The current study demonstrates that the MIL composite has excellent damage tolerance due to the multiple energy-absorbing mechanisms.

Influence of confinement reinforcement on the compression stress–strain of grouted reinforced concrete block masonry boundary elements

Reinforced masonry (RM) shear walls are widely used in medium- to high-rise masonry buildings as part of the lateral force resisting system to provide the lateral strength, stiffness and energy dissipation capacity required to resist lateral loads arising from earthquakes or wind. In the past few decades, there has been considerable advancement in the design of RM shear walls for new construction with variable types of confinement of the compressed boundaries of the wall for increasing ductility level. Recent codes and standards for design of masonry structures are introducing the use of Ductile Reinforced Masonry (DRM) Shear Walls with column-like boundary elements for the improvement of the ductility capacity of the walls. A key component in the evaluation of the ductility capacity of shear walls is evaluating the compressive response of their boundary elements. This paper presents an experimental and analytical investigation on the compression stress–strain behavior of fully grouted unconfined and confined reinforced concrete block masonry boundary elements. Full scale boundary elements were constructed and tested under concentric axial compression. An analytical stress–strain model was proposed that can be used in the design and assessment of DRM walls with boundary elements.

Cyclic behavior of exterior beam-column joints strengthened with precast slurry infiltrated fibrous concrete laminates

Beam-column joint is an important component of a reinforced concrete (RC) moment resisting frame and should be designed and detailed properly, especially when the frame is subjected to seismic forces. Many of the existing structures located in the seismic prone zone were designed and built on the basics of earlier codes with inadequate ductile reinforcement detailing. At present, even though these structures are not deteriorated, they are structurally inadequate. Hence, it becomes necessary to upgrade these structures using most economical and reliable strengthening techniques. This paper presents the investigations carried out to study the cyclic behavior of exterior beam-column joints strengthened with precast slurry infiltrated fibrous concrete (SIFCON) laminates. A total of 12 specimens corresponding to four test series were cast and tested under cyclic loading to study the load-deformation behavior, ductility associated parameters, ultimate load carrying capacity and failure characteristics. 20 mm thick precast SIFCON laminates were used to strengthen the conventional RC and fiber RC beam-column joints. For laminates, the fiber volume fraction was 9%. The steel fibers used in the study were round crimpled fibers having 0.5 mm diameter with the aspect ratio 60.

A Parametrical Analysis for the Rotational Ductility of Reinforced Concrete Beams

The assessment of the plastic rotation of reinforced concrete beams is an essential aspect to avoid structural brittle collapses. The value actually available can be generally determined as sum of two different components. The first, due to bending, the second for inclined shear cracks. This paper presents a simplified model which provides the flexural plastic rotation of the rectangular beams with a ``closed-form solution''. The approach is substantially dimensionless and includes main influencing factors the cross -section, as mechanical material properties, ductility, geometrical and mechanical reinforcement ratio, confinement effects. In closing, in order to appreciate the reliability of the procedure, a comparison with models proposed by international technical standards is made.

The FRP Reinforced Shear-Friction Mechanism

The ability of reinforced concrete to resist shear forces across possible sliding planes is a well established area of research and is also recognised as an important aspect of the ability of reinforced concrete members to both resist loads and deformation. This characteristic of reinforced concrete is often referred to as the shear-friction or aggregate interlock mechanism and much of the previous research in this area has dealt with ductile steel reinforcement, which is assumed to yield prior to the shear-friction capacity being attained. In this paper, it is shown that, as FRP is an elastic material, the shear friction behaviour of FRP reinforced concrete is different to that with ductile steel reinforcement. However, and perhaps surprisingly, the shear-friction capacity of FRP reinforced concrete can be just as ductile and strong as steel reinforced concrete.

Study on the Principle of Tunnel Collapse Treatment and its Application

Collapse of crowm broked out with large water gushing at working face during driving tunnel in Ming Ya Zi tunnel’s right tube. According to engineering geology condition and analysis of causes of collapse, double-deck prior ductile grouting reinforcement technique was applied in tunneling surrounding rock consolidation based on the strong pre-support theory.And the result of treatment was successful.Thus,guiding the work of tunnel collapse treatment by strong pre-support theory was proved reasonably and effectively.

Pushover Testing of Circular Adobe Structure

Many unreinforced adobe or mud-brick structures have in the past suffered severe damage from seismic forces and have caused a vast number of deaths. In contrast, some adobe buildings located in seismic regions have performed well under several seismic events. Researchers noticed that most existing circular adobe houses performed well in withstanding earthquakes even though some did not have any additional ductile reinforcement. This paper presents the investigation of seismic performance of unreinforced circular adobe buildings using static pushover testing. A scaled model (1:3 scale) of adobe circular structure were built and tested by static lateral load and pushed to total collapse. The results presented in the form of capacity curves, are compared with the expected lateral loading obtained from the static tilt testing carried out in earlier research. The outcome of this research can be used to evaluate the existing circular adobe houses and can give design recommendations of suitable configurations for new circular adobe buildings.

Mechanical Properties Variation of B500SD High Ductility Reinforcement Regarding its Corrosion Degree

Corrosion effects on reinforcement become evident in the bar section reduction and in the variation of mechanical properties related to ductility. In this research work, 96 B500SD steel bars, previously subjected to different corrosion variables, have been tested. Results show that the elongation of the bars diminishes and the ratio between the maximum tensile stress and the elastic limit increases as the corrosion degree advances. These phenomena can be explained by studying the necking effect and the different steel composition through the manufacture process.

Effects of ductile phase volume fraction on the mechanical properties of Ti–Al 3Ti metal-intermetallic laminate (MIL) composites

Metal-intermetallic laminate (MIL) composites consisting of alternating layers of Ti, Al, and the intermetallic Al 3Ti have been fabricated by reactive foil sintering in open air. Six initially identical stacks of alternating Ti–3Al–2.5 V and 1100-Al foils were processed for different lengths of time, yielding specimens with different metal and intermetallic volume fractions. Their mechanical properties have been investigated with an emphasis on the effect of residual Al at the intermetallic centerline on composite strength and fracture toughness, as well as fracture and failure modes. Samples were cut from each composite plate (in layer orientations parallel and perpendicular to the intended load direction) for mechanical testing in compression and four-point bending under quasi-static and high-rate loading conditions. Examination of the damaged specimens and their fracture surfaces by optical and scanning electron microscopy was performed to establish a correlation between the failure mechanisms present, composite strength, and microstructure. Results indicated that regardless of loading direction, cracks always initiated in the intermetallic region, rarely at the centerline, and crack propagation and failure were heavily influenced by the thickness of the residual aluminum layers. There is an ideal residual aluminum volume fraction that represents the amount of ductile reinforcement that maximizes the combined properties of strength, toughness and stiffness.

Strength and ductility of reinforced concrete slabs containing welded wire fabric and subjected to support settlement

This paper describes a numerical investigation of the impact of steel ductility and support settlement on the strength and ductility of continuous one-way reinforced concrete slabs containing low ductility welded wire fabric (WWF). A finite element model is developed for the investigation using the software ATENA and the results of a series of concurrent laboratory experiments are used to validate the numerical solution. A parametric investigation is conducted using the numerical model to investigate the various factors that influence structural behaviour at the strength limit state. The ductility of the main flexural reinforcement has a profound impact on the ultimate load behaviour of continuous one-way slabs subjected to support settlement, particularly when the reinforcement consists of cold drawn welded wire fabric. Both the strain at peak stress ( ε s u ) and the tensile strength to yield stress ratio ( f s u / f s y ) of the tensile reinforcement have a significant effect on the strength and ductility of reinforced concrete slabs, both with and without support settlement. When ε s u ≥ 5 % and f s u / f s y ≥ 1.08 (i.e. for normal ductility reinforcement), the reduction of strength caused by support settlements of up to span/100 is small and, for design purposes, can be ignored, even when significant redistribution of actions has been assumed. However, for low ductility reinforcement (i.e. when ε s u < 3.5 % and f s u / f s y < 1.05 ), support settlement may result in a significant loss of load carrying capacity. The load-deflection curves are brittle, even for the slabs with zero support settlement, and the slabs have little ability to undergo plastic deformation at or close to the peak load. In all cases with low ductility steel, fracture of the steel occurs at one of the critical sections at deformations not much larger than that at the formation of the first plastic hinge and failure is catastrophic, with little warning.

Effect of Ductile and Brittle Phases on Deformation and Fracture Behaviour of Molybdenum and Niobium Silicide Based Composites

A comparative study on the microstructure-mechanical property relationships in the molybdenum and niobium silicide based composites has been carried out with emphasis on the role of the ductile and brittle phase constituents at ambient and elevated temperatures. The MoSi2, MoSi2-20 vol.% SiC and -Mo-Mo3Si-Mo5SiB2 composites have been prepared by powder metallurgy processing. Furthermore, the niobium silicide based composites, having a eutectic of Nb solid solution (Nbss) and (Nb,Mo)5Si3, and either Nbss or (Nb,Mo)5Si3 as the primary phase in the hypoeutectic or hypereutectic compositions, respectively, have been processed by arc melting. The increase in fracture toughness with respect to that of MoSi2 is modest in the MoSi2-SiC composites, and more significant in the multiphase Mo-Mo3Si-Mo5SiB2 and Nbss-(Nb,Mo)5Si3 based in-situ composites with ductile reinforcements. The ductile phase, either Mo or Nbss aids in toughening chiefly through crack arrest and bridging, and undergoes plastic yielding under constraint during deformation, leading to a higher energy of fracture. In the MoSi2 and MoSi2-SiC composites, the matrix grain size has a significant role in high temperature strength retention and strain hardening behaviour. In the ductile phase reinforced composites, the hard silicide-based intermetallic phases contribute to elevated temperature strength, while the constrained plastic deformation of the -Mo or Nbss is responsible for much higher rate of strain hardening than in the MoSi2 and MoSi2-SiC composites.

Mechanical behavior of Mo and Ta wire-reinforced bulk metallic glass composites

In this study, 80% volume fraction ( v f ) composites were fabricated with 0.25 mm Mo or Ta wire combined with Zr 57 Nb 5 Al 10 Cu 15.4 Ni 12.6 bulk metallic glass. Quasistatic compression and tension tests were performed. Neutron diffraction was used to measure in situ internal reinforcement strains inside the composites during compressive loading. The composites demonstrate enhanced toughness, mainly due to ductile reinforcements, as well as excellent damage tolerance associated with relatively strong interface. Mo wire composites show higher strength and toughness than Ta composites.

The Bridged Crack Model for the Analysis of Brittle Matrix Fibrous Composites Under Repeated Bending Loading

In this paper, we present a fracture-mechanics based model, the so-called bridged crack model (Carpinteri, A., 1981, “A Fracture Mechanics Model for Reinforced Concrete Collapse,” Proc. of IABSE Colloquium on Advanced Mechanics of Reinforced Concrete, Delft, I.A.B.S.E., Zürich, pp. 17–30; Carpinteri, A., 1984, “Stability of Fracturing Process in R.C. Beams,” J. Struct. Engng. (A.S.C.E.), 110, pp. 544–558) for the analysis of brittle matrix composites with discontinuous ductile reinforcements under the condition of repeated bending loading. In particular, we address the case of composites with very high number of reinforcements (i.e., fiber-reinforced composites, rather than conventionally reinforced concrete). With this aim, we propose a new iterative procedure and compare it to the algorithm recently proposed by Carpinteri, Spagnoli, and Vantadori (2004, “A Fracture Mechanics Model for a Composite Beam with Multiple Reinforcements Under Cyclic Bending,” Int. J. Solids Struct., 41, pp. 5499–5515), showing the advantages in terms of computational efficiency. Furthermore, we analyze the combined effects of crack length, brittleness number, and fiber number on the cyclic behavior of the composite beam, showing the conditions enhancing the energy dissipation in the composite system. Eventually, we analyze crack propagation and propose, consistently with the model premises, a fracture-mechanics-based crack propagation criterion that allows one to simulate cyclic bending tests under the fixed grip condition.

Ductility of Flat Plates: Comparison of Shear Reinforcement Systems

Most building codes allow shear reinforcement to increase the punching capacity of flat plates. This study tests 2 shear reinforcement systems to evaluate their ability to provide not only increased punching capacity, but also ductile behavior to flat plates to prevent a brittle failure mode. The findings indicate that specimens with shear studs failed in premature punching before reaching their flexural capacity event if the nominal punching capacity according to two codes exceeds the column reaction corresponding to all flexural reinforcement reaching its actual yield stress. This was found to be more serious for flat plate structures than for test specimens due to the provisions of ACI 318-05 for design and lateral distribution of the flexural reinforcement in flat plates. Proposed modification of the code provisions is provided. The specimens with ductility reinforcement could resist considerable additional deflection with continuously increasing loading after overall yield of the flexural reinforcement. This indicates that the system has the ability to sustain moment redistribution and accidental loads and to reliably prevent progressive collapse.

Effects of Matrix Ductility on Damage Tolerance of Diagonally Reinforced Coupling Beams

This paper investigates the effect of the ductile deformation behavior of high performance hybrid fiber-reinforced cement-based composites (HPHFRCCs) on the shear behavior and damage of diagonally reinforced coupling beams under reversed cyclic loading. The effects of matrix ductility on deflections, crack widths, crack patterns, failure modes, and ultimate shear load of the coupling beams have been examined. The combination of a ductile cement-based matrix and steel reinforcement is found to result in improved energy dissipation capacity and damage-tolerant inelastic deformation behavior. Test results showed that the coupling beam constructed with an HPHFRCC material exhibited excellent strength, deformation capacity, and damage tolerance capacity, in comparison with the regular reinforced concrete beam.

Ductility reinforcement for flat slabs in seismic areas

The reinforcement concept ‘ductility reinforcement’ has previously been shown to give flat slabs such extremely ductile behaviour that the punching failure mode for gravity loading can be considered safely eliminated. That concept is now tested for imposed cyclic storey drift during earthquakes and found to be capable of resisting even severe earthquakes without any additional precautions than those already taken for normal gravity loading. The specimens were loaded with gravity load up to about 75% of their flexural yield capacity in order to simulate the ultimate limit load case involving seismic loads. Design recommendations are given based on these findings, where assessment of transferred moment between slab and column as currently dictated by North American practice is not required.

Strain Localization and its Impact on the Ductility of Reinforced Concrete Slabs Containing Welded Wire Reinforcement

Welded wire fabric (WWF) is commonly used in reinforced concrete (r.c.) slabs. WWF is classified in Australia as Class L or low ductility reinforcement and, as such, the characteristic strain at peak stress (termed the uniform elongation) is not less than 0.015 and the ratio of tensile strength to yield stress (0.2% proof stress) is not less than 1.03. A r.c. slab containing low ductility steel usually fails in bending by fracture of the tensile reinforcement at the critical section, well before the concrete in the compression zone becomes overstressed, and the conventional understanding of ductile under-reinforced flexural failure is not valid. The failure is brittle and results in complete collapse of the span, often with little or no warning. This paper explores the collapse load behaviour of slabs containing WWF, highlighting the great significance of strain localization in lightly reinforced slabs and its adverse impact on ductility. The results of tests on several simply-supported and continuous one-way slabs reinforced with WWF are used to illustrate the discussion.

Ductility of bulk metallic glasses and their composites with ductile reinforcements: A numerical study

Yield behavior of bulk metallic glasses containing voids is elucidated by using unit-cell analyses and the relevant material parameters; and the results are compared with the available constitutive models. These analyses clearly show that caution is needed when transferring the constitutive models associated with void growth and ductile damage in usual metallic materials to bulk metallic glasses, largely because of the different deformation modes in bulk metallic glasses resulting from the pressure dependency of the yield surface and intrinsic softening behavior. With the constitutive model calibrated from the unit-cell analysis, the influences of a wide range of parameters (mechanical properties, volume fraction and morphology of ductile reinforcements) on the ductility of metallic glass composites are explored. The results indicate that, even though the ductile reinforcements may alter the evolution and morphology of the shear bands, the overall failure behavior is still controlled by the metallic glass matrix, leading to very little or no improvement in the composite ductility in comparison to the ductility of metallic glass matrix. The results are compared with experimental studies available in the literature.

Enhanced Plasticity of Zr-based Bulk Metallic Glass Matrix Composite with Ductile Reinforcement

A composite material containing uniformly distributed micrometer-sized Nb particles in a Zr-based amorphous matrix was prepared by suction cast. The resulting material exhibits high fractured strength over 1550 MPa and enhanced plastic strain of about 29.7% before failure in uniaxial compression test at room temperature. Studies of the serrations on the stress–strain curves and the shear bands on the fractured samples reveal that the amplitude of the stress drop of each serration step corresponds to the extent of the propagation of a single shear band through the materials. The composite exhibits more serration steps and smaller amplitude of stress drop due to the pinning of shear band propagation by ductile Nb particles.