Ultimate Load Conditions Research Articles

Study on the Bearing Mode and Force Transfer Path of Composite Bucket Foundations

This paper elaborates on a new composite bucket foundation (CBF) structural system for offshore wind turbines. The proposed CBF consists of a special force transition section, a beam system structure upper steel bucket cover and a large-scale steel bucket with honeycomb structure rooms. It can be prefabricated onshore, self-floated on the sea and then towed to the appointed sea area before sinking to the sea soil under negative pressure. This is called the “one-step” installation technology. Arc- and line-type bucket foundations are calculated by both theory and the finite element method to discuss their force transfer paths and bearing modes. Owning to the special structural form, the transition section can effectively convert the huge load and bending moment into controllable tension and compressive stress, as well as adjust the structure balance. The bearing model and percentage of each part of the composite foundation under monotonous and ultimate load conditions are also calculated. Results indicate that the bearing mode of CBF is a typical top cover mode. In addition, the curvature impact of arc-type is studied and the results reveal that the structure type of the transition section is more important than the diameter ratio between the bottom transition section and the bucket.

Full-scale pullout tests and analyses of ground anchors in rocks under ultimate load conditions

This paper, consisting of full-scale pullout tests and theoretical analyses, focuses on the behavior of ground anchors under ultimate load conditions. Three ground anchors with a bonded length of 4m were built in slightly weathered limestone and tested until their ultimate load capacities were passed. The test data indicated that two of the anchors performed well with the ultimate load capacities being nearly 3 times of the design values. The remaining anchor performed below expectation, which was diagnosed of poor grouting. Furthermore, an analytical framework was developed considering the elastoplastic stress-strain relationship at the anchor-rock interface. The developed model revealed that the bond stress was not uniform along the entire bonded length when the ultimate state was reached; instead, the bonded length was composed of plastic and elastic zones. The length of elastic zone was not significantly influenced by the increased load, while the plastic zone extended with the increase of the load. The average ultimate bond stress over the entire bonded length was a function of anchor diameters and bonded length. Thus, current recommended presumptive ultimate bond stresses should be used with caution if the anchor is very short (<4m) or very long (>12m).

Simulation of Time-Varying Spatially Uniform Pressure and Near-Surface Wind Flows on Building Components and Cladding

This paper describes a new full-scale testing apparatus for conducting performance evaluations of full-scale building envelope systems. The simulator can generate spatially uniform, time-varying pressure conditions associated with Saffir-Simpson Hurricane Wind Scale Category 5 winds while compensating for large air leakage through the specimen and also operate a high-speed wind tunnel, both with dynamic control. This paper presents system details, operating characteristics, and an early case study on the performance of large sectional door systems under wind pressure loading. Failure mechanisms are discussed, and finite element modeling is validated for two specimens. It demonstrates successful dynamic load control for large component and cladding systems, as well as simulation of flows near the building surface. These capabilities serve to complement other full-scale wind tunnel facilities by offering tools to generate ultimate load conditions on portions of the building. Further, the paper successfully demonstrates the utility of combining physical testing and computational analysis as a matter of routine, which underscores the potential of evolving full-scale testing to encompass cyber-physical approaches.

Investigation of free vibration and ultimate behavior of composite twin-box girder bridges

Multi spine composite concrete-deck steel-box girder bridges became a very popular choice in highway bridges due to their high torsional and wraping stiffness as well as for economic and aesthetic reasons. This study presents an experimental investigation on both elastic and ultimate behavior of composite box girder bridges in order to study the effect of internal cross bracing between box girders along with the curvature effect at different loading stages. Three composite concrete deck-steel simply-supported twin-box bridge models, two curved and one straight, were fabricated, and tested. First, the response of each model was monitored under free-vibration excitation, then an eccentric loading was applied and the corresponding deflections were recorded in the elastic range. Finally, the bridge models were tested up to collapse. The structural behavior of the three bridge models was compared at the three loading stages. It was noticed that the presence of an external cross bracing system between the steel boxes had an insignificant effect on the developed deflection and the fundamental natural frequency in the elastic range of loading. On the other hand, these external bracings assisted in decreasing the developed deflection approaching failure and in increasing the load carrying capacity by about 8.9%. In addition, the external bracing ensured a better distribution of the stresses under ultimate loading conditions. Moreover, the experimental findings were verified numerically using finite element modeling. A good agreement was noticed to exist between the experimental findings and the numerical results.

Application of rheological characteristics of modified bitumen to predict the fatigue life of asphalt mixtures

ABSTRACTFatigue is defined as a fracture phenomenon due to a repetitive load or a variable dynamic load that occurs at a lower load than the ultimate static load. Fatigue stability of an asphalt mixture is its ability of enduring the repetitive flexural loads. In this study, the carbon nanotubes are used as the bitumen modifier in the way that the prepared samples contain 0%, 0.3%, 0.6%, 0.9%, 1.2%, and 1.5% carbon nanotubes. Then, the classic and rheological experiments are conducted on these samples. This additive improves the classical properties of bitumen (softening point, penetration degree, and so on) and also the fatigue parameter of bitumen (i.e., G*Sinδ) in comparison to the standard bitumen. Using the rheological graphs, it can be predicted that adding the carbon nanotubes to bitumen might improve the fatigue life of the asphalt mixtures. To evaluate the accuracy of this prediction, the fatigue experiment are performed on the prepared beam samples using a four-point loading in the case of constant strain (600 microstrain) with a semi-sinusoidal wave at 20°C. The end of the samples’ fatigue life is 50% reduction in their initial rigidity. It is observed that with an increase in the percentage of carbon nanotube in fatigue samples, the fatigue life of asphalt mixtures remarkably increases.

Formation of microcracks near surgical defect in femur: Assessment of ultimate loading conditions

Formation of microcracks near surgical defect in femur: Assessment of ultimate loading conditions

Design and research on the first polish FRP composite road bridge

Abstract The main goal of the research project was to develop and demonstrate the first Polish FRP composite road bridge, starting from concept design and material research, and going thru manufacturing technique selection, detailed FEM analysis and structural testing of elements. The R&amp;D project comprises also the proof test of the completed bridge as well as structural monitoring in exploitation period. The objective of the paper is the description of the bridge and its structural solutions, i.e. FRP box girders and lightweight concrete deck slab acting compositely. Further the FEM analysis of the girder and the bridge span made on design stage has been presented. The VARTM manufacturing technique was used for girders production. Its main steps have been also presented. Finally the research on the new FRP box girder with LRC slab (hybrid girder) has been briefly showed. The full scale prototype girder with the total length of 22 m was tested to evaluate its carrying capacity, modes of failure, basic dynamic parameters as well as overall behaviour under ultimate static load. The FRP girder met the prescribed serviceability and safety criteria. The FEM model of the girder was validated against testing results and was further used for bridge design. Thanks to R&amp;D project the first Polish FRP bridge is likely to be built late autumn 2015. The output of the research project gives a very promising future for the FRP composite bridge application. The research works showed in the paper have been partially financed by the Polish National Centre for Research and Development in the frame of the research project “ComBridge” (www.com-bridge.pl).

3-D cohesive finite element model for application in structural analysis of heavy duty composite pavements

The problem of stiffness degradation in composite pavement systems from localised fracture damage in the quasibrittle cement bound granular mixture are today taken into account only by empirical formulas. These formulas deals with a limited number of materials in a restricted range of design options and would yield unrealistic results in ultimate loading conditions. Cohesive modelling is one of the primary methods to handle localised damage in quasi-brittle materials, e.g., concrete, describing the potential crack in a discrete manner. To increase the versatility of existing methods this paper presents a numerical analysis of the fracture behaviour of cement bound granular mixtures in composite concrete block pavement systems applying a cohesive model. The functionality of the proposed model is compared to experimental investigations of beam bending tests. The pavement is modelled as a slab on grade and parameters influencing the response such as geometry, material parameters and loading position are studied and compared to experimental results. It is found that a cohesive model is suitable for the description of the fracture behaviour of cement bound granular mixtures. Moreover, it can be shown that adequately good prediction of the structural response of composite pavements is obtained for monotonic loading without significant computational cost, making the model applicable for engineering design purpose. It is envisaged that the methodology implemented in this study can be extended and thereby contribute to the ongoing development of rational failure criteria that can replace the empirical formulas currently used in pavement engineering.

Advanced Active Prestressed CFRP in RCC Structures

. The need for rehabilitation of reinforced concrete structures is rapidly increasing. Fibre reinforced polymer (FRP) composite materials for concrete structures have high strength-to-weight ratios that can provide high prestressing forces while adding minimal additional weight to a structure. They also have good fatigue properties and exhibit low relaxation losses, both of which can increase the service lives and the load carrying capacities of reinforced concrete structures. Carbon fiber reinforced polymer (CFRP) composite system is integrated system based on carbon fibres and epoxy resins. By prestressing the CFRP laminates, the material is used more efficiently as a part of its tensile capacity is utilised and it contributes to the load bearing capacity under both service and ultimate load condition. This is an ideal technique as it combines the advantage of using noncorrosive and lightweight advanced composite material in the form of FRP laminates with high efficiency offered by external prestressing. An innovative mechanical anchorage system was developed to prestress the FRP laminates directly by jacking and reacting against the RCC structure.This paper describes the use of Prestressed CFRP laminates for strengthening of RCC structures including practical applications on slabs and bridges. Also it elucidates the post strengthening testing carried out for the validation of this technique.

Optimal material layout – applied on reinforced concrete slabs

This paper introduces a general, finite-element-based optimisation tool for improving the material layout of concrete structures. The application presented is general and exemplified by material optimisation of reinforced concrete slabs. By utilising the optimisation tool, it is possible to determine the optimal material layout of a slab at the ultimate load state based on simple inputs such as outer geometry, boundary conditions, multiple load cases and design domains. The material layout of the optimal design can either be fully orthotropic or isotropic, or a combination with a predefined coupling between design domains and reinforcement directions. The implementation is a lower bound formulation, resulting in a convex optimisation problem that consists of a number of linear constraints from the equilibrium equations and a number of convex non-linear constraints from the yield criteria. By utilising the capabilities of the non-linear interior point method, the non-linear convex yield criteria can be handled directly in the optimal solution process. Further, a graphical user interface is introduced, providing the design engineer with a practical tool for designing optimal structures. Finally, a number of reinforced concrete slab examples validate the method described and show the potential to save large amounts of material in constructions.

Characterizing the combined effects of force, repetition and posture on injury pathways and micro-structural damage in isolated functional spinal units from sub-acute-failure magnitudes of cyclic compressive loading

BackgroundPrevious research suggests that when the magnitude of peak compressive force applied during cyclic loading exceeds 30% of a functional spinal unit's estimated ultimate compressive tolerance, fatigue failure of the cartilaginous endplate or vertebra will occur before intervertebral disc herniation. MethodsThree levels of peak compressive force, three cycle rates and two dynamic postural conditions were examined using a full-factorial design. Cyclic compressive force was applied using a modified material testing apparatus, in accordance with a biofidelic time-varying waveform with synchronous flexion/extension rotation for 5000 cycles. Annulus fibrosus tissue from 36 “survivor” FSUs was excised for histological analysis. Results80% of specimens survived 5000 cycles of cyclic loading. A marked difference of the magnitude of peak compressive force was noted in the Kaplan–Meier survival function of experimental conditions that induced fatigue injury. Overall, in the 40% ultimate compressive tolerance load condition, the probability of survival was less than 67%. The micro-structural damage detected in excised samples of annulus fibrosus tissue consisted of clefts and fissures within the intra-lamellar matrix, as well as delamination within the inter-lamellar matrix. InterpretationConsistent with previous research, our findings support a threshold of peak compressive force of 30% ultimate compressive tolerance, where cyclic loading above this level will likely result in fatigue injury in less than 5000 cycles of in vitro mechanical loading. However, findings from our histological analyses demonstrate that considerable micro-structural damage occurred in specimens that “survived” the cyclic loading exposure.

Modelling of load–deflection of concrete beams internally prestressed with unbonded CFRP tendons

A theoretical model was developed for predicting the flexural load–deflection of simply supported concrete beams internally prestressed with unbonded carbon fibre reinforced polymer (CFRP) tendons under four-point loading. At each state in the load–deflection curve (initial cracking state, initial yielding state (if any) and ultimate load state), three equivalent rectangular curvature blocks, which can closely simulate the beam rotations at the supports and the midspan beam deflection, were determined by iteratively correcting the strain value of the unbonded tendon. The validity of the model was demonstrated by comparing its predictions with the test results of four rectangular beams and two T-beams with different prestressing reinforcement ratios, initial prestressing and type of auxiliary bar. The developed model was used to examine the effects of different parameters on the first cracking and ultimate strengths of the beam and the additional strain of the unbonded tendon to the effective strain.

Slim‐floor construction – design for ultimate limit state

AbstractThis paper presents the design method for slim‐floor construction that comprises a steel beam and a concrete or composite floor slab in which the beam is integrated within the depth of the slab. The slabs are either supported on a plate attached to the bottom flange or the bottom flange of the beam itself. The main design parameters and load transfer mechanisms are discussed. Plastic analysis has been adopted for the design of the bending capacity at the ultimate load condition and the design procedures described are in accordance with the principles given in Eurocode 4. Attention is paid to the type of shear connection between steel and concrete.

Effects of Seawater Corrosion and Freeze-Thaw Cycles on Mechanical Properties of Fatigue Damaged Reinforced Concrete Beams

The effects of seawater corrosion and freeze-thaw cycles on the structural behavior of fatigue damaged reinforced concrete (FDRC) beams were experimentally studied. Results show that the residual strength of FDRC beams reduces as the fatigue load level (the ratio of maximum fatigue load to the ultimate static load) increases. The reduction in the loading capacity of FDRC beams in atmosphere environment was about 6.5% and 17.8% for given fatigue load levels of 0.2 and 0.3, respectively. However, if FDRC beams are exposed to the environment of seawater wet-dry cycles or to the environment of alternating actions of freeze-thaw and seawater immersion, as expected during the service life of RC bridge structures in coastal regions or in cold coastal regions, a more rapid reduction in the strength and stiffness of the beams is observed. The significance of an accurate simulation of working load and service condition RC bridge structures in coastal regions and cold coastal regions is highlighted.

A testing platform for durability studies of polymers and fiber-reinforced polymer composites under concurrent hygrothermo-mechanical stimuli.

The durability of polymers and fiber-reinforced polymer composites under service condition is a critical aspect to be addressed for their robust designs and condition-based maintenance. These materials are adopted in a wide range of engineering applications, from aircraft and ship structures, to bridges, wind turbine blades, biomaterials and biomedical implants. Polymers are viscoelastic materials, and their response may be highly nonlinear and thus make it challenging to predict and monitor their in-service performance. The laboratory-scale testing platform presented herein assists the investigation of the influence of concurrent mechanical loadings and environmental conditions on these materials. The platform was designed to be low-cost and user-friendly. Its chemically resistant materials make the platform adaptable to studies of chemical degradation due to in-service exposure to fluids. An example of experiment was conducted at RT on closed-cell polyurethane foam samples loaded with a weight corresponding to ~50% of their ultimate static and dry load. Results show that the testing apparatus is appropriate for these studies. Results also highlight the larger vulnerability of the polymer under concurrent loading, based on the higher mid-point displacements and lower residual failure loads. Recommendations are made for additional improvements to the testing apparatus.

Sustainable reinforced masonry walls under lateral in-plane load: Experimental behavior and code-based predictions

Reducing the quantities of materials is an effective means of increasing environmental sustainability. To improve the environmental sustainability of hollow unit reinforced masonry low-rise structures in hurricane or earthquake-prone regions, it is reasonable to use squat walls with horizontal reinforcement in the form of steel mesh. Eight near full-scale walls were tested with control variables as the type and amount of horizontal reinforcement—masonry mesh; fabric reinforcement, and hexagonal wire mesh. Also, the type of masonry unit was 150mm concrete, 150mm clay, and 100mm clay. The walls were tested under in-plane lateral monotonic load to failure and the load–displacement behavior and crack patterns were recorded. The investigation focused on the ultimate load conditions and code-based equations were used to determine theoretical failure loads for comparison with the test failure loads. Given the significance of shear to the response of squat walls, 7 shear strength equations from various codes and other studies were investigated, as well as a failure criterion that considers bending–shear interaction. The performance of the walls was favorable in terms of structural requirements hence can be used for sustainable construction in the manner proposed. Code-based strength equations can be used to design the walls but it is necessary to account for bending–shear interaction.

Discussion of “Behavior of Coupling Band Joints in Buried Corrugated Steel Pipelines” by David Becerril García and Ian D. Moore

Discussion of “Behavior of Coupling Band Joints in Buried Corrugated Steel Pipelines” by David Becerril García and Ian D. Moore

Shear behavior of post-tensioned FRP-reinforced concrete slabs under static and fatigue loading

A reinforcement system for short span concrete slab bridges combining post-tensioned carbon FRP (CFRP) tendons with non-prestressed glass FRP (GFRP) reinforcement can limit the stresses in the GFRP bars to significantly improve fatigue performance. Despite this, the failure mode may be governed by shear and conventional stirrups are, in general, not practical for the construction of slab bridges; therefore the use of innovative shear reinforcement methods is required. Twenty-five FRP-post-tensioned slabs with various types of FRP shear reinforcement were tested under static or fatigue loading. The main variables included the size, shape and type of FRP shear reinforcement used. Fatigue shear strengths at one million cycles were typically in the range of 50–60% of the ultimate static load capacity. Double-headed shear bars were found to be an excellent solution for the shear reinforcement of shallow concrete members which were easy to install and provided high load capacities and good fatigue performance. The fatigue shear strengths of members with anchored shear reinforcement were conservatively predicted using the simplified modified compression field theory, accounting for the change in concrete tensile strength under fatigue loading.

Test Study on Size Effect Characteristics of Mechanical Performanceof Pure Bending Plastic Hinge in RC Members

Studies on size effect of plastic hinge of RC members are still rare at the present stage. This paper explores the development and failure characteristics of plastic hinge of pure bending section and analysis relevant mechanical parameters of size effect. Measured tests data show that plastic hinge equivalent length is close to the depth of beam which has no obvious size effect. However, plastic rotation capacity of plastic hinge has a significant size effect. Plastic rotation capacity decreases with section size increases if evaluate it based on ultimate load state, and increases with section size increases if evaluate it based on measured max load state.

Research on the FRP bridge girder under static load

The CFRP composite materials due to their excellent mechanical properties are more and more often used in civil engineering. In recent more than ten years one could have observed f.e. much more wider application of FRP in bridge construction. The main goal of the ongoing research project was to develop and demonstrate FRP composite bridge girder, including their technical design, material research, manufacturing technique selection and structural testing on full scale model. The objective of the paper is the development and research on a new FRP bridge girder fabricated by VARTM manufacturing technique. The reduced scale prototype girder with the total length of 13,5 m was tested to evaluate its carrying capacity, overall behavior under ultimate static load, as well as modes of failure. The girder met the prescribed serviceability and safety criteria and is likely to be implemented on-site soon for bridge construction. The output of the research project gives a very promising future for the FRP application in bridge engineering.