Existing Strength Models Research Articles

Strength prediction models for steel, synthetic, and hybrid fiber reinforced concretes

This paper proposes new strength models to predict compressive, splitting tensile and flexural strengths of steel, synthetic and hybrid fiber reinforced concretes. The strength models depending on fiber reinforcing index, concrete compressive strength, and fiber volume fraction have been developed by multiple regression analyses of the experimental results obtained from a comprehensive experimental program. Twenty‐five concrete batches, one control and 24 fiber reinforced concrete with target compressive strength of 40 MPa were produced. Steel and synthetic fibers, namely hooked‐end steel (HF) and polyamide (PA) synthetic fibers of total volume of 0.25, 0.5, and 0.75% were added in single and hybrid forms to concrete mixes. Moreover, the predictions of the proposed strength models have been compared with the existing strength models in the literature. The test results clearly showed that the predictions of the proposed strength models are more accurate than the existing strength models for compressive, splitting tensile and flexural strengths of all the fiber types. Although the existing strength models may be applicable to the prediction of compressive strength of steel, synthetic, hybrid fiber reinforced concrete (FRC), they may not be safely used for splitting tensile and flexural strength of steel, synthetic and hybrid FRC.

Reinforced concrete beams strengthened in flexure with near-surface mounted (NSM) CFRP strips: Current status and research needs

Abstract The near-surface mounted (NSM) FRP strengthening technique has attracted worldwide attention as an effective alternative to the externally bonded (EB) FRP strengthening technique. In the NSM FRP strengthening method, grooves are first cut in the concrete cover of a concrete member for the FRP reinforcement to be inserted and embedded using an adhesive. The NSM FRP method has many advantages over the EB FRP method, including a higher bonding efficiency and a better protection of the FRP reinforcement. Existing experimental studies have shown that FRP strips owned a better bond efficiency compared with other section shapes (e.g. round bars and square bars), due to the fact that they had a larger perimeter-to-cross-sectional area ratio. This paper presents a state-of-the-art review, particularly on the flexural strengthening of RC beams with NSM CFRP strips. The observed failure modes in laboratory experiments of such FRP-strengthened RC beams are classified and the existing strength models are examined along with the failure mechanisms behind. The main knowledge gaps to be bridged in future studies are also identified. This review partially formed the basis of the development of design provisions on the NSM strengthening technique in the relevant Hong Kong design guideline.

Ultimate strengths of FRC rectangular columns subjected to simulated seismic loading: Experimental database and new models

While there are many experimental investigations focusing on seismic behaviour of fibre reinforced concrete (FRC) columns, the studies regarding the accuracies and conservativeness of existing seismic strength models of FRC columns are limited. This paper presents a seismic research database of 322 FRC columns obtained from a comprehensive literature investigation. The characteristic of the database and the effects of main variables on the seismic strengths of FRC columns are analyzed in detail, the accuracies of existing strength models of FRC column are also examined as well. In addition, using the database, considering the effects of fibre and other structural factors on FRC columns, Priestley et al. shear and CFB-FIP moment models are modified respectively. Results show that the two proposed strength models both present better evaluation than other models. On the other hand, a detailed method for assessing the potential failure mode of FRC column subjected to seismic loads is also suggested using the two strength models. The comparative results verify the feasibilities and accuracies of the assessment method in FRC columns.

Strength Models of Axial Capacity of FRP-Confined Circular Concrete Columns

Several numbers of strength models of FRP-confined circular concrete columns have been published by several researchers. In this study, strength models were proposed based on experimental data. Nine existing FRP-confined strength models of column confinement were reviewed in this study and two forms of strength models of FRP-confined circular concrete columns were proposed. The models were proposed based on different number of experimental data collected from literature. Based on the number of experimental data, i.e. 64-, 106-, 156- and 192-, the strength models were developed. The performance of the existing and the proposed strength models were evaluated and compared. The evaluation results showed that the strength models proposed based on 192-data had the best performance among other models proposed with smaller number of data. It was also shown that the proposed strength models had better performance than the existing strength models.

Bond behavior of FRP carbon plates externally bonded over steel and concrete elements: Experimental outcomes and numerical investigations

Abstract The paper is firstly aimed to furnish a review of the current knowledge about the bond behavior of Fiber Reinforced Plastic (FRP)-steel joints with reference to: a) experimental results of bond tests available in the technical literature, and b) existing strength model for estimating the debonding load. In order to assess the influence of geometrical and mechanical properties of the adhesive on the debonding load, parametric analyses have been carried out by means of some selected bond strength models. The effectiveness of these models has been also checked by means of comparisons with experimental debonding loads collected from technical literature. The second objective of the paper is the comparison of the bond behavior of FRP-steel and FRP-concrete joints in order to identify the role of the adhesive on the bond behavior separately from the concrete. The comparison is aimed to assess bond laws for FRP-concrete joints taking into account the only nonlinearities of the adhesive and to model the concrete as a nonlinear material. To this purpose few experimental bond tests were carried out by the Authors on carbon FRP plates bonded over both steel and concrete support according to the same lay-out and set-up. Finally, basing on the experimental bond law assessed for the FRP-steel joints, a Finite Element (FE) plane model with interface elements is developed for validating the experimental results of bond tests.

Strength model for end cover separation failure in RC beams strengthened with near-surface mounted (NSM) FRP strips

As an alternative to externally bonded FRP reinforcement, near-surface mounted (NSM) FRP reinforcement can be used to effectively improve the flexural performance of RC beams. In such FRP-strengthened RC beams, end cover separation failure is one of the common failure modes. This failure mode involves the detachment of the NSM FRP reinforcement together with the concrete cover along the level of the tension steel reinforcement. This paper presents a new strength model for end cover separation failure in RC beams strengthened in flexure with NSM FRP strips (i.e. rectangular FRP bars with a sectional height-to-thickness ratio not less than 5), which was formulated on the basis of extensive numerical results from a parametric study undertaken using an efficient finite element approach. The proposed strength model consists of an approximate equation for the debonding strain of the FRP reinforcement at the critical cracked section and a conventional section analysis to relate this debonding strain to the moment acting on the same section (i.e. the debonding strain). Once the debonding strain is known, the load level at end cover separation of an FRP-strengthened RC beam can be easily determined for a given load distribution. Predictions from the proposed strength model are compared with those of two existing strength models of the same type and available test results, which shows that the proposed strength model is in close agreement with test results and is far more accurate than the existing strength models.

CFRP sheet로 감싼 원형 콘크리트 압축부재의 보강 효과

콘크리트 구조물의 내력성능을 향상시키기 위해 탄소섬유쉬트(Carbon Fiber-Reinforced Plastic Sheet, 이하 CFRP sheet)로 보강된 콘크리트에 대해 많은 연구가 수행되어 왔다. 본 연구는 CFRP sheet로 구속된 콘크리트에 대한 연구 중 미비한 부분을 보완하기 위하여 보강겹수, 시험체의 크기, 형상비, 겹이음길이를 변수로 하여 연구를 수행하였다. 각 시험체별 응력-변형률 곡선을 통해 콘크리트의 거동을 비교하였으며, 최대압축강도를 통하여 CFRP sheet의 보강효과를 확인하였다. 보강겹수의 증가에 따라 콘크리트의 압축성능은 크게 개선되었으며, 시험체의 크기와 형상비의 변화를 통해 이론적인 부분을 검증하였고, 겹이음길이는 둘레의 5%이상으로 해야만 보강효과에 영향이 없는 것으로 확인하였다. 또한 본 연구의 시험결과와 기존 시험결과를 정리하고 이를 기준으로 기존 강도추정모델을 통계 분석함으로 모델의 정확성과 신뢰성을 검증하였다. Many studies have been carried out on carbon fiber-reinforced plastic sheet(hereafter CFRP sheet)-confined concrete specimens for improve structural performance of concrete structures. To complement the existing studies, a parametric study is conducted to examine the effect of various design parameters such as layers of CFRP sheet, size and aspect ratio of specimens, and overlap length. The behavior of CFRP-confined concrete is compared using stress-strain curves of each specimen. And the strengthening effect of CFRP sheet is examined by maximum compressive strength. As the layers of CFRP sheet increases, structural performance of CFRP-confined concrete is significant increased. If the overlap length is more than 5% of circumstance, strengthening effect is not affected. In addition, a test database assembled from test results and existing studies is presented. Using these test database, accuracy and reliability of the existing strength models for CFRP-confined concrete are verified.

Experimental and numerical investigations of beryllium strength models using the Rayleigh-Taylor instability

We present a set of high explosive driven Rayleigh-Taylor strength experiments for beryllium to produce data to distinguish predictions by various strength models. Design simulations using existing strength model parameterizations from Steinberg-Lund and Preston-Tonks-Wallace (PTW) suggested an optimal design that would delineate between not just different strength models, but different parameters sets of the PTW model. Application of the models to the post-shot results, however, suggests growth consistent with little material strength. We focus mostly on efforts to simulate the data using published strength models as well as the more recent RING relaxation model developed at VNIIEF. The results of the strength experiments indicate weak influence of strength in mitigating the growth with the RING model coming closest to predicting the material behavior. Finally, we present shock and ramp-loading recovery experiments.

Axial load behavior of circular and square concrete columns confined with sprayed fiber-reinforced polymer composites

Many experimental and theoretical investigations have been carried out to study the compressive strength of concrete confined externally with unidirectional fiber-reinforced polymer (FRP) composites. These unidirectional FRP(s) include carbon, glass, aramid, polyethylene terephthalate, and polyethylene naphthalates. In this article, the performance of randomly distributed sprayed fiber-reinforced polymer (SFRP) composites on the enhancement of strength and deformability of concrete column through external confinement is investigated. The salient features of SFRP are quick and easy application as well as the uniform tensile properties in all directions. In the present study, 24 small concrete specimens were loaded to failure under the uniaxial compression loading. The study parameters covered SFRP thickness, fiber length, and column sectional shape (circular and square). Test results showed that the external confinement by SFRP is significantly effective to increase the strength and deformability of confined concrete. Based on the experimental results, the performance of existing strength models developed for the unidirectional FRP is assessed to examine its applicability to the SFRP confinement. It is found that none of the existing models is capable of accurately predicting the strength of concrete confined with SFRP. Finally, new strength models based on a linear relationship between confined concrete compressive strength and lateral confining pressure are proposed to predict the compressive strength of circular and square sections. The strengths predicted by the proposed models are found to have a good agreement with experimental results. POLYM. COMPOS., 37:2557–2567, 2016. © 2015 Society of Plastics Engineers

802 薄層平織CFRP積層板の切欠強度のプライスケールおよびサブラミネートスケール依存性(OS8-(1),OS8 オーガナイズドセッション≪複合材料の変形と破壊およびマルチスケール計算技術≫)

Size effect on the static tensile fracture strength of thin-ply woven carbon fiber composite laminates as well as its stacking sequence dependence is studied. Applicability of existing strength models to the notch size and scale dependent tensile fracture strength is also examined. Two kinds of woven fabric composites ([(0/90)_n/(±45)_n]_s and [(0/90)/(±45)]_<ms>) are tested. To observe the effect of specimen size, static tension tests are performed on 1D, 2D and 3D-geometrically similar specimens. Unnotched (UN) and double-edge notched (DEN) were prepared for each size, respectively. To elucidate the size effect on notch sensitivity, furthermore, 1D, 2D and 3D scaled DEN specimens are tested for different notch lengths, respectively. It is observed that the tensile fracture strength of DEN specimens significantly decreases as the size of specimen increases. As the specimen size decreases, the tensile fracture behavior gradually shifts from a LEFM-dominated region to an UN-strength-dominated region.

2D Model of Strength Parameters for Bamboo Scrimber

Experiments were performed to test the compressive strength of bamboo scrimber board at different grain angle directions. Investigation of test samples allows for the identification of the correlation between compression failure stress and various failure mechanisms at different grain angles. The results of the experiments showed that the density of bamboo scrimber influenced compression failure stress linearly. A new approach to describe the failure stresses of bamboo scrimber was proposed. The density was introduced as a model parameter to describe compressive properties at varying angles of grain. In comparison to a one-dimensional model, there was much less relative error between predicted values and measured values by this 2D model. This report aims to improve the precision of existing strength models for various grain angles and to provide a competing method for the practical use of bamboo scrimber.

Effect of column parameters on flax FRP confined coir fibre reinforced concrete

This paper experimentally investigated various column parameters on axial compressive and flexural behaviour of a new type of FRP-confined concrete, i.e. natural flax fibre reinforced polymer (FFRP)-confined coir fibre reinforced concrete (CFRC), which is termed as FFRP–CFRC. This new composite structure was composed of an outer FFRP jacket and a CFRC core. Under axial compression, the column parameters examined include types of FFRP/CFRC interfacial bond (i.e. naturally and mechanically bonded), confinement (i.e. FFRP tube and wrapped), and specimen end condition (i.e. flat and grinded tube ends) and tube thickness (i.e. 2, 4, and 6 layers). Push-out test was further performed to find out the relationship between bond strength and level of confinement. In addition, the experimental results were compared with predictions obtained from 25 existing strength models. In flexure, the effects of bond on load–deflection response, ultimate load, energy absorption, failure mode, load–slip behaviour and load–strain responses of the composite beams were evaluated. Results showed that in compression, with an increase of tube thickness, the strength, energy absorption capacity and ductility increased remarkably. The ultimate stress and strain of FFRP-wrapped specimen were lower than the tube-confined specimen and the influence of tube end condition on confinement performance cannot be ignored. It was also found that there was a strong link between FFRP/CFRC interfacial bond and the confinement performance, i.e. with an increase of bond strength, the level of confinement reduced noticeably. In flexure, both naturally and mechanically bonded FFRP tube-confined CFRC composite beams exhibited high load carrying capacity, energy absorption and ductility. Slip between the tube and the concrete was eliminated in the mechanically bonded beams without compromising the peak load, compared to the naturally bonded beams.

A novel method for assessing rival models of recognition memory

A general comparison is made between the multinomial processing tree (MPT) approach and a strength-based approach for modeling recognition memory measurement. Strength models include the signal-detection model and the dual-process model. Existing MPT models for recognition memory and a new generic MPT model, called the Multistate (MS) model, are contrasted with the strength models. Although the ROC curves for the MS model and strength model are similar, there is a critical difference between existing strength models and MPT models that goes beyond the assessment of the ROC. This difference concerns the question of stochastic mixtures for foil test trials. The hazard function and the reverse hazard function are powerful methods for detecting the presence of a probabilistic mixture. Several new theorems establish a novel method for obtaining information about the hazard function and reverse hazard function for the latent continuous distributions that are assumed in the strength approach to recognition memory. Evidence is provided that foil test trials involve a stochastic mixture. This finding occurred for both short-term memory procedures, such as the Brown–Peterson task, and long-term list-learning procedures, such as the paired-associate task. The effect of mixtures on foil trials is problematic for existing strength models but can be readily handled by MPT models such as the MS model. Other phenomena, such as the mirror effect and the effect of target-foil similarity, are also predicted accurately by the MPT modeling framework.

909 一方向CFRPの非主軸強度の試験片寸法依存性(OS9-(3)オーガナイズドセッション《複合材料の変形と破壊およびマルチスケール計算技術》)

A systematic examination of the effect of specimen size on the off-axis static tensile strength of a unidirectional carbon/epoxy laminate has been attempted for different fiber orientations. For this purpose, static tension tests are first performed on one-, two- and three-dimensional geometrically similar unnotched specimens of the unidirectional CFRP laminate, respectively. The comparison of the results on 2D-geometrically similar specimens indicates that the off-axis tensile strength tends to decrease as the width of specimen increases. In contrast, the off-axis tensile strength of 1D-geometrically similar specimen tends to increase as the thickness of specimen increases. The opposite features of the 1D and 2D scale effects reduce the scale effect on 3D-geometrically similar specimens in quantitative terms. The present study also suggests a difference between the scale dependences of the on-axis and off-axis strengths of the unidirectional CFRP laminate not only in quantitative terms but also in qualitative terms. Existing strength models are also tested for accuracy of prediction of the multidimensional scale effects on the off-axis tensile strength of the unidirectional CFRP laminate.

Unified Strength Model Based on Hoek-Brown Failure Criterion for Circular and Square Concrete Columns Confined by FRP

Most existing models for evaluating the strength of fiber-reinforced polymer (FRP)-confined concrete columns are based in an early work. In this paper, a new model based on the Hoek-Brown failure criterion is proposed. The existing strength models for FRP-confined circular and square concrete columns are reviewed, evaluated, and compared with the proposed model. An updated database that includes a large number of test data are then used to evaluate the models. Comparisons between the models and the test results demonstrate the accuracy of the proposed model. Apart from this improved accuracy, the proposed model also has a unified form for both circular and square columns, and can be used to predict the strength of columns that have existing damage or cracks. Test data for FRP-repaired concrete columns are collected from the literature and used to evaluate and demonstrate the performance of the proposed model in predicting the strength of FRP-confined deficient columns.

Effect of cross-sectional aspect ratio on the strength of CFRP-confined rectangular concrete columns

This paper presents the results of an experimental study on the behavior of axially loaded short rectangular columns that have been strengthened with carbon fiber-reinforced polymer (CFRP) wrap. Three series of uniaxial compression tests were conducted on 45 specimens. The parameters considered were the aspect ratio, defined as the depth (longer side)/width (shorter side) of the cross-section, and the number of CFRP layers. The behavior of the specimens in the axial and transverse directions was investigated. The test results clearly demonstrate that the strength gain in the confined concrete columns relative to the original unconfined columns, f c c / f c o decreases as the aspect ratio increases, until it becomes insignificant when the aspect ratio reaches 2. The test results are compared with the theoretical predictions of existing strength models and significant differences are found, indicating the need for further model development. A new model for the strength of FRP confined rectangular concrete columns is proposed, based on the test results from this work and results collected from the literature.

Behavior of Large-Scale Rectangular Columns Confined with FRP Composites

This paper focuses on axially loaded, large-scale rectangular RC columns confined with fiber-reinforced polymer (FRP) wrapping. Experimental tests are conducted to obtain the stress-strain response and ultimate load for three field-size columns having different aspect ratios and/or corner radii. Effective transverse FRP failure strain and the effect of increasing confining action on the stress-strain behavior are examined. Existing strength models, the majority of which were developed for small-scale specimens, are applied to predict the structural response. Since some of them fail to adequately characterize the test data and others are complex and require significant calculation, a simple design-oriented model is developed. The new model is based on the confinement effectiveness coefficient, an aspect ratio coefficient, and a corner radius coefficient. It accurately predicts the axial ultimate strength of the large-scale columns at hand and, when applied to the small-scale columns studied by other investigators, produces reasonable results.

플랫플레이트-기둥 접합부의 뚫림전단강도

초록·키워드 목차 오류제보하기 등록된 정보가 없습니다. ABSTRACT1. 서론2. 변수연구3. 접합부의 뚫림전단강도4. 뚫림전단강도 설계식6. 결론참고문헌요약