Incremental Loading Conditions Research Articles

PERFORMANCE OF BAMBOO- AND GLASS-FIBRE-REINFORCED CONCRETE SLAB SUBJECTED TO STATIC AND CYCLIC LOADS

In the construction field, mild steel is using as reinforcement in concrete, which can easily corrode and destroy the environment. So, the construction industries are focusing on alternate materials like natural and synthetic fibres for sustainability. In this study bamboo, glass-fibre bars were used as reinforcement and compared with a normal reinforced concrete slab subject to static and cyclic incremental loading conditions. According to this, the experimental studies were carried out on 9 slab elements of size 600 mm × 450 mm with different forms of reinforcement. The slab elements’ deflection, deformation, load-carrying capacity, stress, strain, crack patterns, stiffness and energy absorption were determined and compared. The ultimate load-carrying capacity of elements like conventional, GFRP and bamboo are 28.90 kN, 29.31 kN and 5.50 kN respectively; similarly, deflection 12.70 mm, 13.50 mm and 8.60 mm were found under static load. In the same way, the ultimate load-carrying capacities of the elements are 24.23 kN, 25.00 kN and 6.80 kN under cyclic loading conditions; deflections of 10.10 mm, 13.50 mm and 3.60 mm, respectively, on conventional, GFRP and bamboo elements. From the test results the stress, strain, energy absorptions were calculated and compared and the energy absorption of bamboo was 9.38% less than conventional and GFRP was 22.49 % higher than conventional elements. The study proved that GFRP material has a significant impact than conventional and bamboo elements and the bamboo reinforcement can be used in light-loading conditions.

Biomechanical Comparison of Uniplanar versus Biplanar Lateral Opening-wedge Distal Femoral Osteotomy Techniques in Terms of Risk for Medial Hinge Fracture.

The effect of osteotomy type on the initial stiffness of the bone-implant construct in lateral opening-wedge distal femoral osteotomy (LOWDFO) using a uniplanar compared with a biplanar technique has been investigated. However, no study has explored the biomechanical risk factors for medial hinge fracture. This study aimed to compare the biomechanical strength of uniplanar versus biplanar LOWDFO regarding the risk for medial hinge fracture during gap opening. Twelve composite femora were divided into two groups (six in each group) based on the distal femoral osteotomy technique: uniplanar versus biplanar LOWDFO. All LOWDFO models were subjected to incremental static loading. The gap distance was expanded by 1 mm, and displacement values were recorded as anterior and posterior gap distances (mm). The average force values of all samples at certain gap distances were recorded, and the head distance was measured. The uniplanar group had higher load values than the biplanar group at all anterior gap distances. These differences were only significant at 2- and 3-mm gap distances (p = 0.025 and 0.037). At all posterior gap distances, the uniplanar group had higher load values than the biplanar group, but these differences only reached statistical significance at 2 mm (p = 0.037). Both groups had similar anterior, posterior, and average gap distances (p = 0.75, 0.522, 0.873). The uniplanar group had a higher head insertion distance (15.3 ± 5.7) than the biplanar group (14.7 ± 2.9), but it was not significant (p = 0.87). The uniplanar group had a lower average load before medial hinge fracture (46.41 ± 13.91 N) than the biplanar group (54.92 ± 31.94, p = 0.81). The biplanar group had an average maximum load value of 64.18 ± 25.6 N, while the uniplanar group had 57.90 ± 12.21 N (p = 0.81). This study revealed that the biplanar osteotomy technique allows a wider opening wedge gap with less risk of a medial hinge fracture than uniplanar LOWDFO.Level of evidence was level 3, case-control series.

Rutting Performance Evaluation of BMD Surface Mixtures with Conventional and High RAP Contents under Full-Scale Accelerated Testing.

The balanced mix design (BMD) constitutes a significant step forward in the pursuit of better-performing asphalt mixtures. This approach/framework offers increased innovative opportunities for the proper design and production of engineered asphalt mixtures without the need to strictly adhere to traditional volumetric requirements. The primary objective of this paper is to conduct a comprehensive investigation of the permanent deformation (rutting) behavior of surface mixtures (SMs) with conventional and high reclaimed asphalt pavement (HRAP) contents through full-scale accelerated testing under incremental loading conditions while accounting for the environmental aging effect. HRAP SMs were designed in this study, marking the initial application of Virginia Department of Transportation (VDOT) BMD special provisions, with attempts to incorporate 45% and even 60% RAP. Results showed that all BMD HRAP mixtures exhibited higher rut depths compared to the control mixture, which can be attributed to the inclusion of high binder contents aimed at enhancing cracking resistance. The asphalt pavement analyzer (APA) rut test and the stress sweep rutting tests were performed on mixtures sampled during production. Correlation analysis revealed significant and strong positive correlations between accelerated pavement testing (APT) and the multilevel laboratory rutting performance tests considered in this study. Finally, while acknowledging the limitations and all the assumptions considered in this study, the correlation analysis recommended refining the VDOT BMD APA rut depth threshold by lowering the current limit of 8 mm to 7 mm to ensure good performing mixtures from a rutting point of view.

Seismic fragility assessment of reinforced concrete moment frames retrofitted with strongback braced system

This study focused on analysing the seismic fragility and retrofitting of reinforced concrete flexural frames using strongback braced system. Using the steel strongback braced system as a means of seismically strengthening and retrofitting reinforced concrete moment frames (RCMFs), this research aims to enhance the effectiveness of RCMFs. In this study, RCMFs of 5-, 10-, and 15-stories are designed according to the first and fourth editions of the Iran Earthquake Standard 2800. The RCMFs designed according to the first edition are strengthened and reinforced using the SB system. The studied structures were analyzed under incremental static loading and time history analysis. The results show that the yield force and maximum base shear for the structures designed with the fourth edition, compared to the structures designed with the first edition, have increased by 1.28–1.42. This demonstrates the necessity of improving structures constructed according to the first edition. Meanwhile, the results of the retrofitted structures with strongback braces show the same or better performance than newly designed structures. The results of the fragility analysis show that the addition of the strong bracing system significantly improves the performance of the structures and brings them closer to the 4th edition standards. The retrofitting system reduces drift ratio between floors and reduces structural damage.

Experimental Investigation of the Performance of Buried Flexible Pipe in Reinforced Sand

Abstract The experimental work of this study deals with the performance of pipe in sand with various responses subjected to incremental static loading where the backfill is reinforced with two types of reinforcement (geogrid and geocell) to investigate the effects of backfill cover. The pipes considered are installed in sand with different densities; i.e., loose, medium and dense sand, and a constant burial depth (2D, where D is the pipe diameter). It was concluded that the maximum deformation occurs at the crown of the pipe. The deformation increases when the sand density decreases. For a burial depth equal to 1.5 D, the maximum strain on the pipe crown increases by about 22.5% when the sand changes from dense to medium and 36.8% when it changes from dense to loose. The vertical stress above a pipe buried in loose sand is reduced by 8.3% when the geogrid width is 2B where B is the footing width, while it is equal to 22% when the geogrid width is B. When a geocell is used, the percent reduction is equal to 62%. The percent reduction in the vertical stress above a pipe buried in medium sand is about 28% when the geogrid width is 2B and 40% when the geogrid width is B and equal to 68% when the geocell is used.

Flexural strength recovery of RC one-way slabs having cut-outs using NSM-SHCC plates

Creating a cut-out in an existing Reinforced Concrete (RC) slab became a common practice to allow passing facility services. This cut-out interrupts the loading trajectories resulting in the existence of weak points. Thus, the ultimate capacity of such slab including cut-out decreases with the increase of the size of the opening. In this paper, a new technique based on near-surface mounted has been employed using precast plates made of Strain-Hardening Cementitious Composites (SHCC). These SHCC plates were designed to compensate the cut reinforcement due to cut-out. The used plates had three different widths; 100, 200 and 300 mm, while their thickness was kept constant at 20 mm. One reference slab without cut-out, in addition to, nine damaged slabs with central cut-outs, were prepared and tested under incremental static loading. The tested slabs have the same dimensions; thickness = 140, effective depth = 120 mm, width = 1200 mm and span = 2200 mm. For the cut-out, a rectangular shape with constant width of 200 mm has been used, while the length parallel to the supporting line was varied considering three values; 200, 400, and 600 mm. All slabs were reinforced with a single bottom steel mesh with a longitudinal reinforcement ratio of 0.65%. The slabs having cut-outs were divided into three groups (I, II and III); each one included three different cut-outs. The slabs of group I were tested without strengthening. On the other hand, group II was strengthened at the tension side only, whereas, group III was strengthened at both tension and compression sides. Based on the experimental findings, the load-carrying capacities of group II raised by 15–57% compared to group I; however, this increase was accompanied by a significant decrease in the developed ductility where the displacement-based ductility index could be dropped by 58% for the slab having cut-out length of 600 mm. For group III, the application of SHCC plates at both tension and compression sides enabled the strengthened slabs to restore nearly the lost capacity resulting from providing the cut-out with a good ductility performance.

Fragility curves for low-to-mid-rise concrete frame building retrofitted by shear wall-frame system

The need for an earthquake-resistant building must be fulfilled, especially for areas with high levels of earthquake vulnerability, such Indonesia. Installing a shear wall-frame system is one of the strengthening strategies to withstand the lateral forces caused by the earthquake and to achieve satisfactory global seismic behavior of the concrete frame structure. This ongoing research aims to demonstrate the seismic performance of a low to mid -rise concrete frame building equipped with a shear wall-frame system in several configurations. The response of the structure is analyzed through a nonlinear static procedure. Using Seismostruct, FE package, the capacity curve was obtained as structural response subjected to incremental static loading up to collapse load. The output shows that the structure of a shear wall-frame system has a maximum base value of 19.7x103 kN, which is greater than the base sliding value in the non-retrofitted building structure, which is 15.2x103 kN. The obtained fragility curve shows a comparison of the probability of damage to the structures of retrofitted and non-retrofitted shear wall-frame system buildings.

Experimental and finite element modelling of reinforced geopolymer concrete beam

Experimental details procured from the resultant strain and stress of steel and concrete which form the major components of geo-polymer concrete beam. While this method is creates real time behavior, it is enormously time utilizing, and the use of materials can be quite expensive. Computer software simulation would aid in future development of the geo-polymer concrete members. The study is to examine the performance of the geo-polymer concrete (GPC) beam, in the various conditions of crack such as initiation, penetration and pattern, flexural strength, load–deflection and other mode of structure failure which exhibits the realistic behaviour when the actual material is used to create the FE model. This work is express the importance of FE modelling in structural element analysis. It can shows the behaviour of geo-polymer concrete beam until failure. It also gives comprehensive results of the element under critical distribution of stresses and effective strains in member and steel reinforcement in the members. To examine the flexural behaviour of geo-polymer concrete beams using three dimensional FEM analysis. Particularly focused on the failure surfaces of geo-polymer reinforced concrete beam and also the physical properties of flexural cracking behaviour of the beam. Procured results from the analytical calculation using ACI codes are compared with FEM analysis. This investigation is to evaluate the incremental loading conditions with respect to the time until failure. In this paper, we are going to analyze the behaviour under reinforced geo-polymer concrete beam with help of the computer analysis which is fail in flexure. The accessibility of nonlinear models with the help of available computer software. Finite element software simulation for structural members is cost effective.

Impact and static behavior of strain-hardening cementitious composites–strengthened reinforced concrete slabs

Impact loading could impair the entire structure or a part of it, thus making the human life at stake. In this study, to improve the impact resistance of reinforced concrete slabs under drop-weight loading, a thin layer of strain-hardening cementitious composites was added at either tension or compression side of the slab. The main parameter of this study was the three contact surface conditions, namely grinding, grinding plus steel dowels, and grinding plus epoxy adhesive, between the substrate slab and the strain-hardening cementitious composites layer. Therefore, 63 reinforced concrete slabs were prepared and tested under the effect of drop-weight falling from three different heights: 1, 1.5, and 2 m. In addition, for comparison purposes, additional seven slabs were tested under central incremental static loading until failure is presented. It was found that the strain-hardening cementitious composites–strengthening layer enhanced the impact and static response of the strengthened slabs when added at either tension or compression side. Besides, to achieve the outermost impact resistance showing ductile performance, it is better to provide a thin layer of the strain-hardening cementitious composites at the tension side of the slab connected to the substrate slab by epoxy resin applied on pre-prepared grinded surface.

Experimental and numerical investigations on the impact resistance of SHCC-strengthened RC slabs subjected to drop weight loading

In this paper, a thin layer of Strain-Hardening Cementitious Composites (SHCC) is provided in either tension or compression side of RC slabs aiming to improve their impact resistance under the effect of drop weight loading. The main parameter of the current study is the condition of the contact surface between the substrate slab and the SHCC overlay that was prepared by grinding, grinding plus steel dowels or grinding plus epoxy adhesive. Accordingly, 63 RC slabs were prepared and tested under the effect of drop weight falling from three different heights; 1, 1.5 and 2 m. It was found that the SHCC strengthening layer enhanced the impact resistance of the strengthened slab when added at either tension or compression side. However, in order to attain the outermost impact resistance showing ductile performance, it is better to provide a thin layer of the SHCC at the tension side of the slab connected to the substrate slab by epoxy resin applied on pre-prepared grinded surface. Furthermore, numerical simulations based on ABAQUS software package were performed on the strengthened slabs. Their results showed good agreement with the experimental findings from the viewpoint of the kinetic energy. Besides, the impact failure loads were determined numerically for the studied slabs and compared with those obtained from incremental static loading tests.

Thermally-induced mechanical behaviour of a single proppant under compression: Insights into the long-term integrity of hydraulic fracturing in geothermal reservoirs

With the increasing demand persisting for energy extraction from geothermal resources, many scientific research studies have been carried out on the performance of proppants to improve the energy extraction process. Knowledge of the after-effects of proppants exposed to realistic geothermal reservoir conditions is crucial. Therefore, the aim of the experimental study reported here was to investigate the mechanical behaviour of a single proppant under incremental loading conditions, and the mineralogical and microstructural alterations due to exposure to elevated temperatures (100 °C, 200 °C, 300 °C and 400 °C) and different cooling conditions (slow cooling and quenching). Significant mechanical weakening, overall strength reduction of 52.19% and 69.74% and Young’s modulus reduction of 43.64% and 55.45% for the slow cooling and quenching cooling techniques were observed in a single proppant when the temperature increased from room temperature (25 °C) to elevated temperatures. Scanning electron microscopy revealed the occurrence of thermal cracks inside the proppant microstructure, together with the alteration of the mineral structure, and significant changes in zeolite, Na-feldspar and K-feldspar were observed upon exposure to elevated temperatures. The post-failure behaviour of a single proppant was studied conducting 3-D X-ray computed tomography (CT) scanning. Under normal loading conditions, proppants cleave and generate large fragments like a flower, and this happens suddenly and quite violently through the material. Interestingly, post-failure analysis revealed that the failure mechanism of a single proppant consists of three major stress levels, where initially proppant fails at a high stress level and gains some crushing-associated strength at later stages.

A study on rotational behaviour of a new industrialised building system connection

The performance of an Industrialised Building System (IBS) consists of prefabricated reinforced concrete components, is greatly affected by the behaviour of the connection between beam and columns. The structural characteristics parameters of a beam-to-column connection like rotational stiffness, strength and ductility can be explained by load-rotation relationship of a full scale H-subframe under gravitational load. Furthermore, the connection’s degree of rigidity directly influences the behaviour of the whole frame. In this research, rotational behaviour of a patented innovative beam-to-column connection with unique benefits like easy installation, no wet work, no welding work at assembly site, using a hybrid behaviour of steel and concrete, easy replacement ability, and compatibility with architecture was investigated. The proposed IBS beam-to-column connection includes precast concrete components with embedded steel end connectors. Two full-scale H-subframes constructed with a new IBS and conventional cast in-situ reinforced concrete system beam-to-column connections were tested under incremental static loading. In this paper, load-rotation relationship and ratio of the rigidity of IBS beam-to-column connection are studied and compared with conventional monolithic reinforced concrete connection. It is concluded that this new IBS beam-to-column connection benefits from more rotational ductility than the conventional reinforced concrete connection. Furthermore, the semi-rigid IBS connection rigidity ratio is about 44% of a full rigid connection.

Analysis of the First Cracks Generating Between Two Holes Under Incremental Static Loading with an Innovation Method by Numerical Modelling

The application of Non-Explosive Expansion Materials (NEEM) has recently been increased in hard rock quarry mining, especially in granitic rocks. The most important mention in the quarry mining methods is determination of hole pattern, because it relates to cost of exploitation of the rock blocks, directly. It needs to predict the rock fracture process which it depends on the length of the first cracks and the growing to join together. A new algorithm has been suggested to evaluate of the first crack length by the linear elastic fracture mechanics (LEFM) theory. It requires determining a stress concentration factor which an experimental model has been utilized. A case study has been selected to verify of the numerical results which it is a granite mine in Iran. Numerical modeling has been applied to illustrate of rock fracture process and crack path and the results showed if the size of elements near the crack tip equal to grain size of the rock material or the ratio of the element length per diameter of the hole is selected about one per fifty, accuracy of the crack path prediction can be acceptable. On the other hand selection of an adequate rock slip criterion for crack planes is important, because of friction between two planes of a crack, plays an important role to predict of the crack growth. Also this research showed that Mohr-Coulomb criterion without cohesion is a suitable model for crack’s elements and Hoek-Brown failure criterion is an adequate model for rock substance.

α-Al2O3 nanoslab fracture and fatigue behavior

Strain rate effects and cyclic loading behavior, relevant for fatigue initiation processes, of single crystalline α-Al2O3 nanoslab structures in vacuum have been characterized and compared under finite temperature dynamic loading and incremental static loading conditions by reactive molecular dynamics and ionic relaxation simulations, respectively. Different failure mechanisms for each loading case are observed and compared in view of known applicable material failure mechanisms. In particular, structure size effects along with unit cell and bulk defect distribution based mechanisms are considered. The effects of lateral pre-strain are assessed. Conclusions are drawn regarding conditions which could lead to low cycle failure of the material.The results indicate that finite temperature and strain rate result in lower failure strains, as compared to static relaxation calculations, however low strength enhancement of ductility with kinematic strain hardening upon repeated loading may occur. We suggest that the latter facilitates a shakedown mechanism. Positive pre-straining results in increased stress triaxiality (hydrostatic vs. equivalent stress), which significantly reduces crack healing probability, due to single sharp crack propagation. Instead, volume pre-relaxation results in multiple crack branching and/or amorphous band formation, which facilitates crack healing and deformation induced transition to purely elastic response (shakedown) possibility. Amorphization, which manifests as small strain plasticity enhancement, is found to occur ahead of propagating cracks due to multiple dislocation mechanism as a low energy barrier partially reversible low density phase transition, both at static and finite temperature/strain rate conditions. The observed property changes and phase change related defect healing mechanisms have been investigated further by bulk unit cell simulations and validated against DFT calculations.

Detailed FE and DE Modelling of Stone Masonry Arch Bridges for the Assessment of Load-carrying Capacity

This paper reports on numerical modelling strategies for assessment of the load capacity of stone arch bridges based on realistic knowledge of the constituent material properties. Detailed micro-models based on FEM and DEM with suitable nonlinear behaviour of the bridge materials are used to evaluate the bridge structural behaviour under incremental static loading. Simplified modelling strategies based on rigid blocks analysis is also used for comparative purposes. Results of laboratory testing performed to characterize the deformability and strength parameters of the bridge materials (masonry and infill) are used to support the structural analysis. The study comprised four existing road bridges located in the North of Portugal. Experimental modal identification of the bridge cases has also been included in the study with the aim of updating and validating the bridge models.

Development of a crack growth predictor for geomaterials using detrended fluctuation analysis and optical flow method

Several conventional methods like seismic, micro-seismic, acoustic, electromagnetic etc. have been proposed to investigate the crack initiation and growth in rocks during static and dynamic loading conditions. These conventional sensors are prone to acquire noise and moreover these methods do not provide comprehensive knowledge about failure process since data are collected at a few points attached to a rock sample. This paper presents the application of detrended fluctuation analysis method and optical flow method of image analysis for analyzing failure mechanism of rock specimen under uniaxial loading condition. Two predictors, normalized cumulative fluctuation coefficient (NCFC) and normalized cumulative standard deviation of strain (NCSS) have been developed for forecasting the same. Both the predictors are developed by analyzing consecutive image frames under incremental loading conditions and are found to be powerful markers for categorizing the crack initiation period, stable crack growth period and collapse period in the rock failure process. It is also obtained that NCFC and NCSS produce almost similar results even if they are derived using different image analysis concepts. Numerous laboratory experiments have been conducted to check the applicability of the both the predictors. Based on the experimental data, it is envisaged that both the predictors can be used as precursors for monitoring rock failure mechanism.

The Sensitivity of Vibration Characteristics of Reinforced Concrete Beams under Incremental Static and Cyclic Loading

The use of changes in vibration properties for global damage detection and monitoring of existing concrete structures has received great research attention in the last three decades. To track changes in vibration properties experimentally, structures have been artificially damaged by a variety of scenarios. However, this procedure does not represent realistically the whole design-life degradation of concrete structures. This paper presents experimental work on a set of damaged reinforced concrete beams due to different loading regimes to assess the sensitivity of linear and non-linear vibration characteristics. Of the total set, three beams were subject to incremental static loading up to failure to simulate overloading, and two beams subject to 15 million loading cycles with varying amplitudes to produce an accelerated whole-life degradation scenario. To assess the vibration behaviour in both cases, swept sine and harmonic excitations were conducted at every damage level. The results show that resonant frequencies are not sensitive enough to damage due to cyclic loading, whereas cosh spectral and root mean square distances are more sensitive, yet more scattered. In addition, changes in non-linearity follow a softening trend for beams under incremental static loading and are significantly inconsistent for beams under cyclic loading. Amongst all examined characteristics, changes in modal stiffness are found to be most sensitive to damage and least scattered, but modal stiffness is tedious to compute due mainly to the difficulty of constructing restoring force surfaces from field measurements.

Fracture characteristics of notched investment cast TiAl alloy through in situ SEM observation

TiAl alloys were produced by investment casting method combined with induction skull melting (ISM) technique. In situ scanning electron microscopy (SEM) was utilized to study the fracture characteristics and crack propagation of a notched investment cast TiAl specimens in tension under incremental loading conditions. The whole process of crack initiation, propagation and failure during tensile deformation was observed and characterized. The results show that the fracture mechanism was sensitive to not only the microcracks near the notched area but also lamellar orientation to loading axis. The high tensile stress leads to the new microcracks nucleate along lamellar interfaces of grains with favorable orientation when local stress intensity reaches the toughness threshold of the material. Thus, both plasticity and high tensile stress are required to cause notched TiAl failure.

Nonlinear Analysis of CFRP- Prestressed Concrete Beams Subjected to Incremental Static Loading by Finite Elements

In this work a program is developed to carry out the nonlinear analysis (material nonlinearity) of prestressed concrete beams using tendons of carbon fiber reinforced polymer (CFRP) instead of steel. The properties of this material include high strength, light weight, and insusceptibility to corrosion and magnetism. This material is still under investigation, therefore it needs continuous work to make it beneficial in concrete design. Four beams which are tested experimentally by Yan et al. are examined by the developed computer program to reach a certain analytical approach of the design and analysis of such beams because there is no available restrictions or recommendations covering this material in the codes. The program uses the finite element analysis by dividing the beams into isoparametric 20-noded brick elements. The results obtained are good in comparison with experimental results.

Finite element prediction of debonding onset in short fiber reinforced polymers incorporating a hybrid interphase region

A robust finite element procedure for investigating damage evolution in short fiber reinforced polymeric composites under external loads is developed. This procedure is based on an axisymmetric unit cell composed of a fiber, surrounding interphase and bulk matrix. The hybrid interphase concept involves a degraded material phase, the extent of which is material and property dependent. One of the most significant features of the model relies on establishment of variable adhesion conditions between the primary material phases. The unit cell is discretized into linearly elastic elements for the fiber and the matrix and interface elements which allow debonding in the fiber–matrix interface. The interface elements fail according to critical stress and critical energy release rate criteria. The tension and shear aspects of failure are uncoupled, although the resulting nonlinear problem is solved implicitly utilizing quasi-static incremental loading conditions. Final failure resulting from saturation and breakage is modeled by the vanishing interface element technique. Details of the propagation of interface cracks and the initiation of debonds are also observed and discussed for various shapes of fiber end. Numerical results reveal an intense effect of the fiber-end geometry on the initial fiber–matrix de-cohesion. The present finite element procedures can generate meaningful results in the analysis of fiber-reinforced composites.