Ultimate Strength Model Research Articles

Monotonic and cyclic axial compressive responses of concrete specimens externally confined with different types of FRP composites: experimental and analytical investigations

The main objective of this study was to investigate the monotonic and cyclic axial stress versus strain response of the concrete confined with different types of fiber reinforced polymer (FRP) composites such as cotton fiber rope reinforced polymer (CFRRP), glass fiber reinforced polymer (GFRP) composites and carbon fiber reinforced polymer (CFRP) composites. Another objective was to investigate the applicability of existing ultimate strength models to predict the ultimate strength of concrete confined with CFRRP, GFRP and CFRP composites. For this, a total number of 28 concrete cylinders were cast, strengthened and tested under pure axial compression. The concrete cylinders were strengthened with two and four layers of FRPs. The experimental results indicate that all kinds of FRPs are very useful to alter the ultimate strength and strain of the confined concrete. The highest increase in ultimate strength was recorded for CFRP composite confined specimens and the highest increase in ultimate strain was observed for CFRRP composite confined specimens. Further, both ultimate strength and ultimate strains are found higher in the case of cyclic loads compared with the monotonic load. In general, the stress versus strain curves of cotton fiber rope and glass FRPs are found trilinear. Whereas, stress versus strain curves of CFRP confined specimens are observed to be bilinear. Existing ultimate strength models developed for CFRRP and CFRP composites are found well accurate to predict the ultimate strengths of CFRRP and CFRP confined concrete specimens tested in this study.

Ultimate strength models for spherical shells under external pressure: a comparative study

ABSTRACT The ultimate strength of spherical shells under external pressure has been an attractive topic in the field of marine structures. However, recent studies have revealed that the current theoretical approaches are hardly compatible with the actual hulls, which indicates that the ultimate strength models still need to be reevaluated and unified. To address this challenge, a comparative study has been conducted in this paper. Various analytical approaches and codified rules are compared through screened experiment data that have realistic imperfections and different shape parameters in the range generally applied for marine structures. The model evaluation criteria have been established by implementing statistical model uncertainty factors in terms of bias and coefficient of variation. A comparison of the results has been made from three different aspects including shell shape, R/t and geometrical parameters to evaluate their performance. Based on the calculation outcome, analysis has been made to study the theory behind those models and determine their limitations and recommended application range.

Size effect on compressive behavior of FRP-confined engineered cementitious composites (ECC)

• A first-ever experimental study on the size effect of GFRP- and LRS FRP-confined ECC columns was conducted. • The influences of specimen size, FRP confinement level, and FRP type were examined. • A new size-dependent ultimate stress model of FRP-confined ECC was established. The reliable design of the high-performance column made of fiber reinforced polymer (FRP)-confined engineered cementitious composites (ECC) necessitates a clear understanding of the size effect under axial compression. This paper presents the compressive behaviors of glass FRP (GFRP) and large rupture strain (LRS) polyethylene terephthalate (PET) FRP-confined ECC columns. The specimen size, confinement level, and FRP type were the variables. Five diameters of 100, 200, 300, 400, and 500 mm were designed to cover a wide size range. Results showed that both the compressive strength and ductility of ECC were substantially improved with FRP confinement. Compared with GFRP-confined ECC, PET FRP-confined ECC exhibited higher ductility. The key stresses, namely initial peak stress, post-peak ravine stress, and ultimate stress decreased with increasing specimen size. Nevertheless, the specimen size had a marginal influence on the key strains and dilation behavior. After evaluating the existing size-dependent ultimate strength models of FRP-confined concrete, a new expression for predicting the ultimate strength of FRP-confined ECC was introduced, which was shown to fit well with the test results.

Compressive Behavior of Concrete Containing Glass Fibers and Confined with Glass FRP Composites

In this paper, numerous experimental tests were carried out to study the behavior of concrete containing glass fibers and confined with glass fiber-reinforced polymer (GFRP). Concrete specimens containing different fiber percentages ( 0.3 wt.%, 0.6 wt.%, 0.9 wt.% or 1.2 wt.%) and with different strengths of concrete (8.5 MPa, 16 MPa and 25 MPa) and different confinement levels (two, four and six layers of GFRP) were used as research parameters. The samples were tested to failure under pure axial compression. The results imply that the confinement effect with GFRP is relatively higher for concrete samples containing glass fiber (GFCC) with a percentage equal to 0.6 wt.%. The theoretical of stress ratios (fcc/fco) estimated by using existing ultimate strength models are found to be close to the experimental results for high strength of GFCC, but not close to the experimental results for low strength of GFCC.

Compressive Behavior of Predamaged Concrete Cylinders Repaired with Jute and Basalt FRP Composites: A Comparative Study

Natural fibers have become a research hotspot in composite materials recently. This study investigated the axial compressive behavior of predamaged concrete repaired by jute fiber–reinforced polymer (JFRP) composites. Basalt FRP (BFRP) was also utilized to repair the predamaged concrete for comparison. Thirty FRP-jacketed concrete cylinders with a diameter of 150 mm and a height of 300 mm were designed and fabricated. Plain concrete cylinders were axially preloaded to three predamage levels, then repaired by JFRP and BFRP composites, and reloaded to evaluate the compressive behavior after repair. The results showed that the predamage of concrete had a noticeable adverse effect on the compressive behavior of JFRP- and BFRP-repaired concrete. Compared with the JFRP-jacketed intact concrete, the compressive strength and initial elastic modulus of the JFRP-repaired predamaged concrete decreased by 6%–18% and 16%–54%, respectively. However, the compressive strength and ultimate strain of the predamaged concrete were still improved by 5%–41% and 82%–291% after JFRP repair, respectively, when compared with those of the plain concrete. On the contrary, the ultimate axial strain and lateral strain capacities of JFRP- and BFRP-repaired concrete were insignificantly affected by the concrete predamage. Under similar confinement ratios, the compressive strengths of JFRP- and BFRP-jacketed intact concrete were close to each other, whereas the axial strain–lateral strain relationship and the variations of the Poisson’s ratios were highly dependent on the FRP types and the number of FRP layers. Based on the test results and data collected from the open literature, an ultimate strength model, an ultimate axial strain model, and a stress–strain relationship model were newly developed for JFRP-repaired predamaged concrete.

Confinement effects of glass FRP on circular concrete columns made with crushed fired clay bricks as coarse aggregates

This paper investigates the confinement effects of low-cost glass fiber reinforced polymer composites on circular concrete columns made with crushed fired clay bricks as coarse aggregates. Two types of locally available fired clay bricks such as solid fired clay bricks and hollow fired clay bricks were used to prepare the crushed fired clay brick aggregated. The crushed fired clay brick aggregates were replaced with natural aggregates by 50 %. In this study, a total number of 32 circular concrete columns were constructed and tested under monotonic axial compression. The other research parameters were strength of concrete (i.e., low strength and high-strength concrete) and number of layers of glass FRP composites such as two, four and six layers. Locally available bi-directional glass fiber and polyester resin were used to develop glass FRP composites. The salient features of glass FRP composites are low-cost, high strength and stiffness. The experimental results indicate that the use of glass FRP composite is very suitable to modify the ultimate load carrying capacity and stiffness of the circular concrete columns made with crushed fire clay bricks as coarse aggregates. In general, the confinement effects of glass FRP on circular concrete columns are found higher for concrete made with crushed fired clay hollow bricks as compared to the concrete made with crushed fired clay solid bricks. Also, increase in ultimate load carrying capacity is found lower for high-strength concrete circular columns as compared with the low-strength concrete circular columns. The analytical investigation reveal that the existing ultimate strength models are suitable to approximately predict the ultimate strength of glass FRP confined circular concrete columns made with crushed fired clay bricks as coarse aggregates. However, the existing ultimate strain models are not suitable to accurately predict the ultimate strain of glass FRP confined circular concrete columns made with crushed fired clay bricks as coarse aggregates.

Axial strength of short concrete-filled plastic tubes

The axial compressive behavior of concrete-filled plastic tube (CFPT) with five different cement–admixture combinations were examined. A commercially available modified polycarboxylate superplasticizer used at five different concentrations. The plastic tube was an un-plasticized polyvinyl chloride (uPVC) made up of three layers: a blue layer sandwiched between two white layers to achieve solid wall construction. Test results showed that the strength of the CFPT specimens influenced by the increase in superplasticizer dosage up to an optimum dosage. Further increase in the admixture-cement ratio had an adverse effect on strength enhancement. To assess the performances of CFPT specimens under monotonic axial compression, an extensive database comprising the test results of the 157 CFPT column established. The database supplemented by the sum of eighteen test results from the current experimental study used to assess the applicability of ten existing FRP-confined concrete, two steel-confined concrete, and one CFPT strength model to predict the strength of CFPT specimens. By considering the light confinement mechanisms of the tube and general regression analysis, four simple ultimate strength models were proposed based on the database assembled in the present study. Three different statistical indices, the coefficient of determination (R2), the Root Mean Square Error (RMSE), and Average Absolute Error (AAE), were used to assess the performance of the strength models. The proposed four strength models yielded the best fitting results compared with the predictions from the existing ten FRP-confined concrete, two steel-confined concrete, and one CFPT strength model.

Durability and Compression Properties of High-Strength Concrete Reinforced with Steel Fibre and Multi-walled Carbon Nanotube

High-strength concrete (HSC) reinforced with steel fibre (SF) and carbon nanotube (HSCRSC) is a new type of high-strength composite concrete with good fluidity, high strength, toughness, durability and other remarkable advantages. HSCRSC can be widely used in underground structures, such as wellbores. In this study, HSCs ranging from 70 to 100 MPa were designed, and the effects of fibre on the performance of the HSCs were compared and analysed through single-doped and double-mixed SF and multi-walled carbon nanotubes. Results showed that the fibre effectively improved the uniaxial and multiaxial compressive strengths and durability of HSCs and changed the failure mode from brittle to ductile, especially in the case of multiaxial compression failure. HSCs remained intact, but the plain concrete specimens had fractured forms, such as flakes, columns and layers. Moreover, the ultimate strength of the biaxial compression was between 1.10 and 1.39 times higher than that of the uniaxial compression, satisfying the Kufer–Gerstle criterion. The ultimate strength of the triaxial compression was between 1.24 and 2.55 times higher than that of the uniaxial compression, adhering to the Willam–Warnke meridian criterion. The modified B3 model met the prediction accuracy of shrinkage and creep for HSC and surpassed the biaxial and triaxial compression ultimate strength models provided in this study. The absolute value of the relative error was less than 6%, indicating that the model and test data were reliable. All test results showed that HSCRSC exhibited satisfactory comprehensive performance.

Fibre beam element models for nonlinear analysis of concentrically loaded circular CFT columns considering the size effect

The fibre beam element (FBE) method has been widely used to investigate the behaviors of concrete-filled steel tube (CFT) columns for its high efficiency and accuracy. The existing models were generally developed or calibrated by using specimens with relatively small size, in which the size effects were ignored or poorly incorporated. Additionally, most existing FBE models focused on CFT stub columns. In this paper, a new FBE model for nonlinear analysis of concentrically loaded stub and slender columns was proposed, in which the size effects on the effective stress-strain relationships of steel tube and core concrete were well incorporated. The proposed FBE models were then used to develop an ultimate strength model for the design of both stub and slender columns. A total of 1029 specimens assembled from 72 previous studies were used to verify the proposed models. The results suggested that the proposed FBE model performs quite well for both small- and large- size CFT stub columns and predicts the behaviors of slender columns with reasonable accuracy. Moreover, the ultimate strength model developed based on the proposed FBE models was found to make satisfying prediction of test results.

Numerical study of the behaviors of axially loaded large-diameter CFT stub columns

Experimental researches on the behaviors of large-diameter concrete-filled steel tube (CFT) columns are quite limited because of expenses and capacity of testing equipment. Finite element (FE) technique is an alternative and efficient method if suitable models of materials are available. Many FE models have been proposed to simulate the behaviors of CFT columns. Results predicted by the existing models are generally found to agree well with the experimental results of CFT columns, the diameters of which, however, are generally <300 mm. It is uncertain whether these models are still suitable for the columns with diameters larger than 300 mm. In this paper, a unified FE model applicable to both small- and large-diameter CFT stub columns is proposed. The proposed FE model is then used to study the influence of column parameters and size on the behaviors of steel tube and confined concrete in CFT columns, based on which an ultimate strength considering size effect is proposed. It was found that the existing FE model predicts conservative results for large-diameter columns, whereas the proposed model performs well for both small- and large-diameter columns. Parametric studies suggest size effect on the behavior of confined concrete in a CFT column is more significant than that of steel tube, which, however, is mitigated due to the confinement effect resulting from steel tube when compared with that of plain concrete. Finally, the proposed ultimate strength model is found to perform well and more accurate than the existing model.

Design similar scale model of a 10,000 TEU container ship through combined ultimate longitudinal bending and torsion analysis

This paper firstly figures out a similar scale model regarding ultimate strength experiment of a typical ultra large container ship (ULCS) through combined ultimate longitudinal bending and torsion analysis, in which the similarity theory is proposed to design the scale model for reflecting the progressive collapse behaviors of true ships in ultimate strength model test. The present study presents the similarity between scale model and true ship in cross-section considering the height of neutral axis, the section modulus, the inertia moment about neutral axis and the polar inertia moment should fit the geometrical similarity theory, and in strength considering buckling strength and shear ultimate strength of plates and stiffened panels should fit the strength similarity theory. Numerical investigations are conducted on the ultimate strength of a 10,000 TEU container ship and the similar scale model under pure hogging bending, pure torsion and combined bending and torsion, respectively. The nonlinear finite element method (NFEM) is adopted considering the effects of initial deformations and both material and geometric nonlinearities. Finally, the numerical results are compared with each other and discussed showing a good agreement in both elastic and inelastic range during the progressive collapse behaviors, which means the similar scale model can represent the true ship regarding ultimate strength test. And the similarity theory is verified quite stable after the uncertainty analysis.

Probabilistic Design Models for Ultimate Strength and Strain of FRP-Confined Concrete

AbstractThis paper presents a probabilistic procedure for deriving design models for the ultimate strength and strain of fiber–reinforced-polymer (FRP)-confined concrete. First, a large database of axial compression tests performed on circular FRP-confined concrete specimens is collected for calibrating an ultimate strength model, based on the Drucker-Prager criterion, and an ultimate strain model, based on the ultimate dilation rate. The database is also employed for deriving a probabilistic model for the FRP strain efficiency factor. The calibrated models, though simple, show superior performance over some of the models in the literature. Then, using the Central Limit Theorem and considering uncertainty in the mechanical properties of the concrete and FRP material as well as their correlation, analytical probabilistic design models for the ultimate strength and strain of FRP-confined concrete are derived. These models can be used in the design and reliability analysis of FRP-confined columns.

Design Method of Hull Structure Model for Ultimate Strength Test

Based on the several practical research on real ship hull ultimate strength model test, a design method of hull structure model for ultimate strength test, which combine the numerical simulation analysis with a similar model design are proposed.

Optimal design for concrete pavement situated above box culvert: experimental and numerical study

This study examined the pavement distress data obtained from the field as well as the effects of the soil cover depth, joint position and reinforced slab length on the behaviour of concrete pavement using the finite element method. An ultimate strength model with a similarity of 1/2 was designed and constructed. Finite element analysis incorporating an implicit direct numerical integration scheme was conducted to obtain an optimal design for the pavement structure above a box culvert. An accelerated pavement test was conducted for validation, in which a realistic traffic load was imposed on the pavement model constructed in the laboratory. The strain histories were measured at each section and compared with those of numerical analysis. The optimal joint position and reinforced slab length that can minimise the damage to the pavement structure above a box culvert were also determined.

보강된 이음부가 적용된 조립식 프리캐스트 콘크리트 아치의 단면 강도 평가

선행연구에서 제안된 조립식 프리캐스트 콘크리트 아치의 구조성능이 실험적으로 평가되었다. 본 연구에서는 이에 대하여 재료 및 접촉 비선형을 고려한 유한요소해석을 수행하였으며, 실험결과와 비교하여 콘크리트 블록 간의 마찰계수를 결정하였다. 아치부재 단면의 강도를 평가하기 위해 탄성해석으로 단면력을 산정하여 이를 단면의 공칭강도와 비교하였다. 모든 실험체에서 평가된 최대 하중은 부재단면의 공칭강도를 상회하였으며, 실험과 유사한 결과를 보였다. 따라서 탄성해석과 단면의 극한강도모델에 의한 방법은 설계시 콘크리트 블록과 보강된 이음부로 구성된 조립식 프리캐스트 콘크리트 아치의 단면 강도를 효과적으로 평가할 수 있을 것으로 판단된다. In the previous study, the structural performance of proposed precast concrete arch with reinforced joint was evaluated by structural experiment. In this paper, finite element analysis considering both material and contact nonlinearity was carried out on the specimens of the previous study. Based on the result of analysis and experiment, friction coefficient between concrete blocks was determined. To evaluate the strength of sectional member, elastic analysis was carried out on the arch using linear elastic analysis program. The section force was compared with the nominal strength of arch section. It was concluded that the maximum load of all the specimens exceed the nominal strength of arch section. Those results of the strength evaluation were similar to the results of structural experiments. Therefore, it is concluded that the elastic analysis and ultimate strength model can effectively evaluate the strength for the proposed precast concrete arch composed of concrete blocks and reinforced joint in design.

Analysis and design of RC structures strengthened with mechanically fastened FRP laminates: A review

The use of Mechanically Fastened Fiber Reinforced Polymer (MF-FRP) laminates is emerging as a viable alternative to adhesively bonded FRP laminates for the rehabilitation of reinforced concrete (RC) members such as beams and slabs. A recently published state-of-the-art review of the experimental research has demonstrated the viability and effectiveness of MF-FRP systems. This paper provides a state-of-the-art review of the analytical and numerical studies performed over the last decade with the aim of: (a) predicting the strength, the load-deformation response and the failure mode of rehabilitated RC members, and (b) accounting for the interfacial behavior between the concrete and the MF-FRP laminate. Ultimate strength models and constitutive models are critically reviewed based on their key assumptions and formulations and compares the analytical predictions with previously reported experimental results.

SIFCON strengthening of concrete cylinders in comparison with conventional GFRP confinement method

This paper presents SIFCON strengthening as a new method of confinement in comparison with GFRP confinement. The experimental part of the work is focused on the investigation of confinement in concrete specimens with unconfined strength ranging from 15 to 40MPa, enclosed with GFRP sheets or SIFCON jacket. Several parameters such as number of layers and ply configuration for GFRP method and jacket strength, fiber length and jacket thickness for SIFCON method have been investigated. Furthermore, the ultimate strength models of FRP-confined concrete have been classified and evaluated with test results and the first step in modeling the ultimate strength of SIFCON-confined concrete has been taken. The results show that SIFCON confinement method can be regarded as a competitive method with respect to the well-known FRP confinement method and some of the available models of FRP confinement can also give good estimation of the ultimate strength of concrete confined by SIFCON method.

Ultimate strength model experiment regarding a container ship’s hull structures

The results of an experimental investigation into the ultimate hogging strength of a container ship’s hull structures are presented. On the basis of derived similar conversion relationships, a test model is designed to reflect the possible failure modes under hogging moment. Comparisons between the container ship and test model are carried out by linear analysis, non-linear finite element analysis and idealised structural unit method. The collapse modes and stress distributions for plating and longitudinals are discussed. Welding residual stresses and initial distortions are simulated approximately in ABAQUS code, and the results of ultimate strength obtained by the arc-length method are consistent with the experimental results.

A New Ultimate Strength Model of Notched Composite Laminates — Including the Effects of Matrix Failure

A new ultimate strength model is developed to predict the final failure, with the influence of matrix failure, of notched cross-ply laminates. The present model is based on the estimation of the local stresses and the redistribution of the local stresses in the critical damage zones around the notches. The new ultimate strength model can be stated as: when the local stresses in the critical-load-carrying elements reach their failure strength, the critical-load-carrying element will fail and the ultimate failure will occur. In order to estimate the local stress concentration in the critical damage zones, a method is developed and applied to decompose the local stress concentration into several parts, e.g., the geometrical contribution, the stacking-ratio contribution, and the damage contribution. Combined with a single numerical simulation for a notched laminate, the damage-dependent stress concentration of the laminate can be established for different notches and it is then utilized to predict the ultimate strength of notched laminates with different notches. The applications of this method show that the model prediction agrees with the experimental observations satisfactorily.

Ultimate Strength of Resistance Spot Welds Subjected to Combined Tension and Shear

Abstract A new test setup and data concerning the ultimate strength behavior of resistance spot welds in a mild strength steel subjected to combined tension and shear loads are presented. A test plan based on a design of experiments (DOE) with three design factors (coupon width, coupon length, and nugget diameter) was conducted to investigate the influence of the factors on the ultimate strength of the resistance spot welds under different loading angles. In this program, test loads were monotonically applied to the resistance spot weld at a specific angle until the load carrying capacity of the resistance spot weld was exceeded. It was found that the nugget diameter contributes the most (more than 70%) to the total variation of the recorded ultimate strength and that the coupon length has little effect. A deterministic ultimate strength model was proposed to take into account the interaction of in-plane shear and 90° out-of-plane tensile loading in the resistance spot weld. A reliability model was also demonstrated to evaluate the ultimate strength of a single resistance spot weld.