Secondary Reinforcement Effects Research Articles

FEM Investigation on the Secondary Reinforcement Effect on Shallow Foundation Seated on Geosynthetic Reinforced Soil

FEM Investigation on the Secondary Reinforcement Effect on Shallow Foundation Seated on Geosynthetic Reinforced Soil

Secondary reinforcement effect on the value and location of maximum reinforcement load

This paper numerically evaluates the effect of secondary reinforcement on the value and location of the maximum reinforcement load along the primary reinforcement layers (Tmax) in geosynthetic-reinforced soil (GRS) walls under working stress conditions. Data from three instrumented sections of a well-instrumented GRS wall were used for model validation. A parametric study was carried out considering different controlling factors (i.e. the vertical reinforcement spacing, facing type and secondary reinforcement stiffness and length). The results show that for a constant relative soil-reinforcement stiffness index, the variation of the vertical reinforcement spacing and stiffness may not affect the location and normalised value of Tmax. In general, for the conventionally used type of reinforcement, the secondary reinforcement inclusion reduces Tmax to values lower than those corresponding to the active condition (Ka). For a given facing type, the combined effect of the secondary reinforcement length and stiffness is the main factor that controls the Tmax location. In general, increasing the secondary reinforcement stiffness and length moves the location of Tmax from the back of the facing to a distance corresponding to the length of the secondary reinforcement layers. In addition, for this condition, a flexible face model performs similarly to a block face model.

Effects of re-dispersible latex powder-basalt fibers on the properties and pore structure of lightweight foamed concrete

In order to diminish global energy consumption and environmental pollution, the use of green building materials for construction has been noticeably popularized. In the present study, the use of re-dispersible latex powder-basalt fibers to prepare foamed concrete to improve the performance of foamed concrete has been assessed. The effects of basalt fibers and re-dispersible latex powder on the dry and wet densities, water adsorption rate, compressive strength, and microstructure of the foamed concrete, were then studied. The hydration products and pore structure were analyzed by X-ray diffraction (XRD) spectroscopy and scanning electron microscopy (SEM). The results revealed that basalt fibers slightly affected the density and water adsorption rate. With the increase in the content of re-dispersible latex powder, the wet density of the specimen increased, the dry density decreased, the difference between dry density and wet density increased, and the water adsorption rate decreased. With the addition of a re-dispersible latex powder, the pore size decreased, the pore structure density increased, and the effective pore number was elevated. Furthermore, the compressive strength of double-doped re-dispersible latex powder-basalt fibers was higher than that of single-doped basalt fibers. The XRD analysis of the hydration products and the SEM analysis of the microstructures confirmed that the re-dispersible latex powder formed new hydration products after hydration. These hydration products gathered on the foam surface and became fused to form a film. Also, the polymer membrane interweaves with the hydration products to form a continuous network. The basalt fibers were evenly distributed in the internal structure, penetrated the polymer membrane, and formed a three-dimensional random network system. The random network system could support the bubbles and had the effect of secondary reinforcement. Moreover, the interfacial adhesive force between the fibers and the polymer film dispersed a part of the energy and produced a more continuous and uniform stress field in the structure.

Verification of the secondary reinforcement influence on the strap beams design

The present work aims to expose a methodology for the design of strap beams between pile caps, and to investigate the effect of secondary reinforcement on the behavior of the pile cap located on the property line. For the study, it was selected the deep foundation geometry of a borderline pillar from the infrastructure design of a building. A design methodology was then presented for the foundations' reinforcement. In ABAQUS [1] software, based on the Finite Element Method, a non-linear analysis of four models related to the case study was performed, with the variation of the secondary reinforcement arrangement. It was found that the combined horizontal and vertical secondary reinforcements were efficient to ensure a more ductile failure for the concrete strut. However, the model with the secondary reinforcement inclined at 45º showed the highest resistance.

Seismic Responses of GRS Walls with Secondary Reinforcements Subjected to Earthquake Loading

Secondary reinforcement has been proven to be effective in increasing the performance of geosynthetic-reinforced soil (GRS) walls under working stress conditions, enabling an eco-friendlier environment. However, the seismic responses of GRS walls with secondary reinforcements are still unclear. In this study, in-depth finite element analyses were used to investigate the seismic responses of GRS walls with secondary reinforcement subjected to earthquake motions. The numerical procedure was first validated using measurements obtained from both a field GRS wall with secondary reinforcement and benchmark large-scale shaking table tests. Then, the validated GRS walls procedure was utilized to explore the effects of secondary reinforcement length and stiffness, the vertical spacing of the primary reinforcement, and wall height on the seismic responses. Based on the study, the following findings can be drawn: (i) the secondary reinforcement length and stiffness under various wall heights and peak ground accelerations (PGAs) have a limited influence on the relative lateral facing displacement and acceleration amplification, however, they can significantly decrease the connection load and the maximum reinforcement load; (ii) increasing the length of the secondary reinforcement is more effective for reducing the connection load and the maximum reinforcement load than increasing the stiffness of the secondary reinforcement; (iii) the effect of secondary reinforcement is more evident for greater wall height, the larger vertical spacing of primary reinforcement, and smaller PGA; and (iv) GRS walls with secondary reinforcement could ease the acceleration amplification. The study has highlighted the salient effect of secondary reinforcement on GRS wall performance under seismic conditions.

Numerical evaluation of secondary reinforcement effect on geosynthetic-reinforced retaining walls

A finite difference method was employed to evaluate the effect of secondary reinforcement on the performance of Geosynthetic-Reinforced Retaining (GRR) walls. The two-dimensional numerical models used a Cap-Yield soil constitutive model to represent the behavior of backfill. The numerical model was first calibrated and verified by the measured results from a full-scale field test. A parametric study was then performed to investigate the effects of secondary reinforcement length, secondary reinforcement stiffness, secondary reinforcement connection, and secondary reinforcement layout. The numerical results show that an increase in secondary reinforcement length and stiffness can reduce the deflection of the GRR wall and the maximum tensile stress of primary reinforcement. The mechanical connection of secondary reinforcement can also reduce the wall facing deflection and result in relatively small maximum tensile stress and connection stress in the primary reinforcement as compared with no connection to the secondary reinforcement. In addition, a wall with fewer but longer secondary reinforcement layers at certain elevations had relatively smaller wall facing deflections than the baseline case. This comparison demonstrates that more optimal layout of secondary reinforcement exists that could further reduce the maximum wall facing deflections and create a better performing wall while the same or less amount of geosynthetic reinforcement material is used.

Strength of pile caps under eccentric loads: Experimental study and review of code provisions

Pile caps are rigid reinforced concrete structures that transfer column loads, generally consisting of a combination of an axial load and bending moments in one or two directions, to the piles. The design formulations of pile caps for more than two piles were derived from the results of experimental tests under a centered load. The practice of checking both punching and shear failure modes is common as described in the literature review, even though these formulations were developed for more slender elements. Currently, Codes ACI 318-14 and EC2 allow designing pile caps with strut-and-tie models or sectional approaches (shear, punching and flexural designs).In this study, 21 full-scale pile caps with different shear span-depth ratios and reinforcement layouts were studied to investigate the effect of eccentric loading on the strength and accuracy of the code formulations. The results show that in eccentrically loaded pile caps, the ultimate load is reduced but the maximum pile reaction increases and the secondary reinforcement proves effective to enhance the pile cap strength.Although the strut-and-tie models (STM) allow eccentric loads to be taken into consideration, they predict a much lower peak load than that observed at the experimental results and do not adequately reflect either the influence of slenderness or the failure mode.In general the sectional approach provided by Codes ACI-318-14, EC2 and MC-2010 (Level I of Approximation) lead to safe predictions of the peak load but do not always correctly predict the failure mode. The ultimate load predicted by EC-2 formulation comes closest to the experimental peak load, accurately reflects the influence of slenderness and the effect of secondary reinforcement, however, additional assumptions need to be made for its application. The ACI formulation complemented by the CRSI-2008 Special Investigation for deep pile caps is the safest but does not adequately capture the effect of horizontal and vertical secondary reinforcement. The MC2010 LoAI formulation is also conservative but does not detect the influence of slenderness or the contribution of secondary reinforcement.

Carbon fiber/carbon nanotube reinforced hierarchical composites: Effect of CNT distribution on shearing strength

The strength and fracture behavior of carbon fiber reinforced polymer composites with carbon nanotube (CNT) secondary reinforcement are investigated experimentally and numerically. Short Beam Shearing tests have been carried out, with SEM observations of the damage evolution in the composites. 3D multiscale computational (FE) models of the carbon/polymer composite with varied CNT distributions have been developed and employed to study the effect of the secondary CNT reinforcement, its distribution and content on the strength and fracture behavior of the composites. It is shown that adding secondary CNT nanoreinforcement into the matrix and/or the sizing of carbon fiber/reinforced composites ensures strong increase of the composite strength. The effect of secondary CNTs reinforcement is strongest when some small addition of CNTs in the polymer matrix is complemented by the fiber sizing with high content of CNTs.

Experimental Study of In-Plane Shear Behavior of Fiber-Reinforced Concrete Composite Slabs

AbstractThis study investigates the in-plane shear behavior of composite slabs reinforced with different types of secondary reinforcements. Experimental results of 20 large-scale composite slabs constructed with two different deck profiles (reentrant and trapezoidal) are presented. The slabs were instrumented and tested in a cantilever diaphragm configuration under monotonic in-plane shear to assess and compare the effect of secondary reinforcement on their in-plane shear capacity. Five types of secondary reinforcements were considered: Conventional WWM of sizes A142 and A98, synthetic macrofibers at dosage rates of 3.0 and 5.3 kg/m3, and hooked-end steel fibers at a dosage rate of 15.0 kg/m3. Tests were carried out for both strong and weak orientation of decking. The load-deflection and load-strain responses were measured, and the cracking pattern and sequence were observed. The results showed that fibers notably improved the in-plane shear behavior (strength and ductility) of the composite slabs. Stee...

Effect of Secondary Processing and Nanoscale Reinforcement on the Mechanical Properties of Al-TiC Composites

Aluminium based composites containing 1, 1.5 and 2wt. % of nano-sized Titanium Carbide particulates (TiC), with an average of 45nm, reinforcement were synthesized using low energy planetary ball mill followed by hot extrusion. Microstructural characterization of the materials revealed uniform distribution of reinforcement, grain refinement and the presence of minimal porosity. Properties characterization revealed that the presence of nano-TiC particulates led to an increase in hardness, elastic modulus, 0.2% yield strength (0.2% offset on a stress-strain curve), and the stress at which a material exhibits a specified permanent deformation, Ultimate Tensile Strength (UTS) and ductility of pure aluminum. Fractography studies revealed that the fracture of pure aluminum occurred in ductile mode due to the incorporation and uniform distribution of nano-TiC particulates. An attempt is made in the present study to correlate the effect of nano-sized TiC particulates as reinforcement and processing type with the micro structural and tensile properties of aluminum composites. The mechanical properties, namely, the UTS, hardness, grain size and distribution of the reinforcement in the base metal were studied in as sintered and extruded conditions. Orowan strengthening criteria was used to predict the yield strength of Al-TiC composites in the present work and experimental results were compared with the theoretical results.

Undrained Fragility of Clean Sands, Silty Sands, and Sandy Silts

In this paper, intergranular (\Ie\dc\N) and interfine (\Ie\df\N) void ratios and confining stress are used as indices to characterize the stress-strain response of gap-graded granular mixes. It was found that at the same global void ratio (\ie) and confining stress, the collapse potential (fragility) of silty sand increases with an increase in fines content (FC) due to a reduction in intergranular contact between the coarse grains. Beyond a certain threshold fines content (FC\Dth\N), with further addition of fines, the interfine contact friction becomes significant. The fragility decreases and the soil becomes stronger. The value of FC\Dth\N depends on \ie and the characteristics of fines and coarse grains. At FC FC\Dth\N), fine grain friction plays a primary role and dispersed coarse grains provide a beneficial, secondary reinforcement effect. At the same \Ie\df\N, the collapse potential decreases with an increase in sand content. Beyond a certain limiting fines content, the soil behavior is controlled by \Ie\df\N, the collapse potential decreases with an increase in sand content. Beyond a certain limiting fines content, the soil behavior is controlled by \Ie\df\N only. An intergranular matrix diagram is presented that delineates zones of different behaviors of granular mixes as a guideline to determine the anticipated behavior of gap-graded granular mixes. New equivalent intergranular contact void ratios, (\Ie\dc\N)\Deq\N and (\Ie\df\N)\Deq\N, are introduced to characterize the behavior of such soils at FC FC\Dth\N, respectively.

Conditioning of affect-induced breath-holding spells

Breath holding spells often arise in the context of affectively dramatic conflict situations between mother and child. Assessment by psychopathological screening instruments, however, has not given empirical evidence of an increased psychiatric morbidity in these children. Therefore, in our study we did not concentrate on basic psychopathology but on behavioral variables that might be effective during the ongoing attack episode and, hereby, exert an influence on the risk of chronification (relapse rate). The main goal of this approach is to examine secondary reinforcement effects on the attack behavior according to the learning principle of operant conditioning. Our sample consisted of 28 children and ten siblings as control group. To control for effects of behavioral disorders in the sample, we applied the Marburger Verhaltensliste (MVL) on the level of the child, and the Familienfragebogen (FFBO-III) on the level of family adaptation. The main assessment instrument, however, was the Functional Behavior Analysis (FBA) in order to measure the trigger, reaction and consequence conditions in the course of given attack episodes. MVL and FFBO-III results confirm the lack of basic psychopathology in the patients and their families. The individualized FBA's can be transformed in a taxonomy of five distinct types. All the first three types are triggered by intensive conflict situations and show a high relapse rate (type 1) if the mother reacts in a rewarding manner with positive consequences for the child (reinforcement condition), a dramatically reduced rate (type 2) if the mother reacts neutral (extinction condition), or a heterogeneous pattern (type 3) if the mother reacts punishing (punishment condition). In type 4 (pallid type) and type 5 (triggered spontaneously), respectively, no responsiveness to conditioning effects can be recognized. With respect to parent counselling, a recommendation for a quiet and consequent reaction can be concluded, especially in the case of a preceding conflict situation. The empirical results are integrated into a hypothetical model on pathogenesis that delineates the interaction of neurophysiological and behavioral factors in the maintenance of breath-holding spells.

Failure to replicate visual discrimination learning with a 1-min delay of reward

Two experiments were carried out in an attempt to replicate Lett's (1974) demonstration of visual discrimination learning with a 1-min delay of reward. In Experiment 1, controls for olfactory cues were introduced by testing animals in different orders from day to day and by reversing the positions of the discrimination chambers within days; also, secondary reinforcement effects were precluded by the use of opaque rather than transparent doors to the discrimination chambers. No evidence of learning was found either in a group of rats returned to the home cage during the delay or in a group left in the apparatus during the delay. It was hypothesized that the failure to find improvement in Experiment 1 might have resulted from either the controls for odor cues or from a lack of memory retrieval cues provided by the apparatus. In Experiment 2, both of these hypotheses were tested and neither was supported. The Lett group in Experiment 2 was run according to the exact procedures used by Lett and still no learning was demonstrated. It was concluded that further demonstrations of visual discrimination learning with a 1-min delay of reward will be necessary for the acceptance of the validity of this phenomenon.

An evaluation of secondary reinforcement effects in a comparison of partial reinforcement and partial delay of reinforcement.

An evaluation of secondary reinforcement effects in a comparison of partial reinforcement and partial delay of reinforcement.

Secondary reinforcement: Signal or substitute reward? A further study

Rats were trained to press a bar in a Skinner box and were then given food pellets independently of the bar presses. In one group of rats, a tone followed each bar press, and another occurrence of the same tone preceded the delivery of the food pellet. A second group had the tone following bar press but no tone preceding food pellets. The third group had tone before pellet but no tone following bar press. The fourth group had no tones at all. The bar pressing response was largely extinguished, but the rates of extinction did not differ among the groups. In reconditioning the third group showed more secondary reinforcing effects than groups 1, 2 and 4. The failure to demonstrate secondary reinforcement effects in group 1 is interpreted to mean that prediction of response outcome is a more potent factor than association with reward in a situation where there is a conflict between the two.

Secondary reinforcement in infants

A spatial discrimination was successfully formed by 10-month-old infants during a single experimental session on the basis of secondary reinforcement. In the first task, Ss received paired presentations of a tone and cereal for touching a target. After each reinforcement, 23 sec elapsed before another could be received and S heard a second tone during this period. In the second task, Ss heard the food-paired tone ( T +) each time they touched one of 2 new targets and heard the second tone ( T n ) each time they touched the other target. The number of responses producing T + was reliably greater than the number producing T n , thus demonstrating a genuine secondary reinforcement effect.

Secondary reinforcement effects of placement procedures in a runway situation

In Experiment 1 rats were given (a) differentially, (b) nondifferentially, or (c) nonrewarded placements interpolated among nonrewarded runs. Differential placements produced significant increments affecting only start speeds. In Experiment 2 prior continuously- or partially-rewarded placements each produced significant increments in goal speeds, but not in start speeds, and did not differ in their secondary reinforcing effects.

Reinforcement control of “autistic” verbalization in the mynah bird

In an attempt to provide suggestive support for Mowrer’s “autistic” theory of imitative speech, food reward was differentially paired with taped presentations of verbal phrases (response-correlated stimuli) from the vocabularies of two talking mynah birds. Monitoring of free speech subsequent to daily experimental sessions indicated that verbal response hierarchies were changed from baseline in the predicted direction of a secondary reinforcement effect for both Ss in the first training phase, and for one bird in an attempted replication.

Delay of reward as a secondary reinforcer

Thirty rats were trained and extinguished in an alley of a Grice apparatus to determine whether or not delay of reward had secondary reward value. Half of Ss had delay associated with reward (DR) and nondelay associated with nonreward; half(DNR) had the opposite. In extinction half of each group had delay box confinement, half did not. An alternating reward and nonreward pattern was used in training and Ss in both groups showed clear evidence of patterned running. Group DNR ran significantly faster in training and extinction, but the expected secondary reinforcement effects were not found.

The effect of secondary reinforcement on differential instrumental conditioning in rats

A food cup placed in S− maintained response strength to that stimulus, confirming the hypothesis that secondary reinforcement retards discrimination learning because of its effect on the incorrect response. No effects were noted on S+ or on speeds to the old S− in a subsequent reinforcement stage.