Increase In Ultimate Capacity Research Articles

Novel experimental technique to model impression piles in centrifuge testing

A novel experimental technology for small-scale centrifuge tests on piled foundations has been investigated. The technology is suitable for bored piles where the pile shaft has been profiled to improve bearing capacity, such as with the impression pile which has an enhanced shaft capacity owing to the small impressions created along the shaft. In previous centrifuge testing, impression piles have been created by pouring resin into a profiled bore. However, in the technique described, a pile made from three-dimensionally (3D)-printed rigid plastic components with a mandrel mechanism is used to create a nodular shaft surface during model making. Once assembled the pile has the same geometry as the cast-in-situ impression pile. 3D-printed plastic piles allow for fast model making and demonstrate excellent repeatability. Because of the ductile behaviour of the soil–plastic interface the impressions improve the performance of a pile over the entire load settlement curve, not just at ultimate capacity. In addition, a greater increase in ultimate capacity was registered for the 3D-printed plastic impression piles compared to similar resin impression piles. At working load, the 3D-printed plastic impression piles outperformed traditional straight-shafted piles by 90%.

Prediction of compressive strength and evaluation of different theoretical standards and proposed models of brick columns confined with FRP, FRCM, or SRG system

The strength capacity of confined masonry column is one of the topics that need to be studied. In this study, the efficiency of using different types of advanced composite (non-corrosive materials) such as fiber reinforced polymer (FRP), fiber reinforced cementitious matrix (FRCM), or steel reinforced grout (SRG) in confining masonry columns is investigated. A wide range of experimental database of masonry column specimens has been collected from the results that available in scientific literatures. Different theoretical standards and proposed models that used to predict the capacity of masonry columns confined with FRP and FRCM are evaluated based on collected experimental database. Since there is no standard code or specific proposed model for SRG system, the confined capacity of this system is predicted and evaluated using the FRCM proposed models. The justification of using these models is that both FRCM and SRG systems have the same concept of using inorganic material as a paste material. An index named “equivalent fiber reinforcement index (EFRI)” is proposed to capture the key factors that control the behavior of the confined masonry columns with different advanced composite. This index is used as reference parameter for the purpose of the comparison between different strengthening systems. As a result, all types of advanced composite presented a significant increase in ultimate capacity. Also, the behavior of the masonry columns was significantly dependent on the type of fabric used. Different modes of failure were reported, including crushing of masonry block, as well as a deboning of FRP from the masonry substrate and deboning or slippage of fabric within inorganic paste matrix. Compared with other models and standards, the American Concrete Institute Committee 440 (ACI 440) and American Concrete Institute Committee 549 (ACI 549) shows very good predictions for the confined capacity of masonry columns strengthened by FRP and FRCM or SRG respectively.

Centrifuge modelling of monotonic and cyclic lateral responses of a hybrid monopile-bucket foundation for offshore wind turbines

Various hybrid systems combined with several foundation elements have been proposed to improve the lateral performance of monopiles. Among them, the hybrid monopile-bucket foundation which consists of a traditional monopile and a wide-shallow bucket has received more and more attention and has been used in offshore wind pilot projects for supporting OWTs. However, deep insights into its monotonic and cyclic responses are still lacking. This study aims to understand the monotonic load-bearing, the evolution of cumulative displacement, stiffness and bending moment of the hybrid foundation in soft clay. A series of centrifuge model tests were conducted to simulate a hybrid monopile-bucket foundation and a monopile subjected to lateral monotonic and multi-stage cyclic loading. The monopile with the identical pile diameter and embedded length is used as a benchmark. The experimental results show that by the addition of the bucket, the hybrid foundation shows a 30.1% increase in ultimate capacity. Compared to the monopile, the cumulative displacement, unloading stiffness and the growth of bending moment of the hybrid foundation during cyclic can be reduced by up to 25%, 30% and 35.3%, respectively, implying the effectiveness and superiority of the hybrid foundation. Apart from the centrifuge tests, supplementary three-dimensional finite element analyses have also been performed to reveal the bearing mechanism and the sharing ratios of external load and moment carried by the single pile and the bucket of the hybrid foundation. The test and numerical results presented in this study are expected to provide design references for further practical applications of the hybrid foundations.

Ultimate shear response of ultra-high-performance steel fibre-reinforced concrete elements

This paper examines the experimental performance of ultra-high-performance steel fibre-reinforced concrete (UHPSFRC) beams subjected to loads at relatively low shear span-to-depth ratios. The results and observations from six tests provide a detailed insight into the ultimate response including shear strength and failure mode of structural elements incorporating various fibre contents. The test results showed that a higher fibre content results in an increase in ultimate capacity and some enhancement in terms of ductility. Detailed nonlinear numerical validations and sensitivity studies were also undertaken in order to obtain further insights into the response of UHPSFRC beams, with particular focus on the influence of the shear span-to-depth ratio, fibre content and flexural reinforcement ratio. The parametric investigations showed that a reduction in shear span-to-depth ratio results in an increase in the member capacity, whilst a reduction in the flexural reinforcement ratio produces a lower ultimate capacity and a relatively more flexible response. The test results combined with those from numerical simulations enabled the development of a series of design expressions to estimate the shear strength of such members. Validations were performed against the results in this paper, as well as against a collated database from previous experimental studies.

Flexural analysis and design of FRCM-strengthened RC beams

Fabric Reinforced Cementitious Matrix (FRCM) materials are thin, laminated composites consisting of a cementitious matrix that embodies one or multiple layers of continuous synthetic fabrics. FRCM is externally bonded to existing structural members subject to shear, bending, axial, or torsion induced stresses to enhance their performance. In the United States, FRCM material characterization is established by the “Acceptance Criteria AC434,” and the design and analysis of the FRCM-strengthened structural members follows the ACI549.4R-13 design guidelines. This paper investigates the analysis and design of carbon FRCM-strengthened RC beams in flexure. The FRCM-strengthened RC beams were experimentally tested, and the analytical and experimental results are compared in the paper. The ACI 549.4R-13 guidelines and design limitations are also discussed. The analytical and experimental results were in agreement at ultimate capacities. Collective results of studies on flexural strengthening of RC beams with different FRCM systems were used to establish a relationship between FRCM reinforcement ratio and increase in ultimate capacity which will help the designer at design phase to select the optimum FRCM reinforcement ratio for required strengthening demand.

Flexural behavior of composite open web steel joist and concrete slab

Experimental research has been carried out to study the behavior of composite open web steel joists under monotonic loading. Four composite joists were fabricated with two types of web members and span-to-depth ratios were tested. The concrete slab 400 mm wide, and 90 mm overall depth overlaid on a corrugated steel sheet. The composite system was simply supported over 3000 mm span and subjected to a uniformly distributed loading. Test results are presented in terms of slip between composite slab and the top chord of steel joist, load-deflection and load-strain relations. Based on the experimental results, it can be concluded that lowering span/depth ratio has a significant effect on failure pattern with increase in ultimate capacity about 8%. Additionally, the results show that using double angles web type has only a little influence on deflection but increased ultimate capacity about 10% over similar composite joist with rounded bars web.

Applying Various Types of Loading on Continuous Deep Beams Using Strut and Tie Modelling

This work aims at presenting detailed procedures companied by numerical examples for designing reinforced concrete two span continuous deep beams under various types of loading; one concentrated force, two concentrated forces and uniform load for each span. Analysis and design was conducted based on Strut and Tie modeling (STM) of ACI 318M-14 since they contain significant extents of D-regions and they show a marked truss or tied arch action. It was found that changing the loading type has a significant impact on the capacity for the same specimen that has the same dimensions, concrete and steel properties, in addition to the same amount and arrangement of steel reinforcement. In more detail, the increase in the number of concentrated forces causes an obvious increase in ultimate capacity due to the reduction in span to overall height (a/h) ratio and the increase in the value of the strut-tie angle, which causes shortening in the length of the strut. Therefore, the ultimate capacity increased by about (44-70) % when the applied load was changed from 1-concentrated force to 2-concentrated forces or to uniformly distributed load.

Performance of statically indeterminate reinforced glass beams – Experimental comparison with determinate systems and effect of a discontinuous glass section

A well-performing concept is the reinforced glass beam, developed in analogy to reinforced concrete. This concept proved its feasibility both in statically determinate and indeterminate systems, for a variety of parameters. However, the advantages of indeterminacy over determinacy in terms of structural performance and safety are not evaluated for this concept. This paper presents experimental results of similar statically determinate and indeterminate bending tests (i.e. with the same free span length and load point positions) on stainless steel reinforced laminated glass beams, made of annealed float glass (ANG). The interlayer is used to bond the reinforcement. With these results, a comparison is made to quantify the structural efficiency of the latter system, at two test temperatures and for two reinforcement percentages. In addition, statically indeterminate bending test results on ‘discontinuous’ glass beams are presented and compared to those of normal beams to evaluate the effect of local reduced beam stiffness on the system’s load-carrying behaviour. The first investigation led to the conclusion that a 25% increase in ultimate capacity can be reached when applying a statically indeterminate system, provided that the reinforcement-to-glass bond is thoroughly designed for the specific conditions (enabling the beam to form all necessary plastic hinges). Furthermore, when the latter condition is fulfilled, a locally reduced beam stiffness has a limited effect on the overall load-carrying behaviour of the statically indeterminate beam system.

An Experimental Investigation on the Load Settlement and the Bulging Behaviour of Stone Columns Placed on Highly Palstic Clays

Background: Stone columns are used to increase bearing capacity, improve the drainage conditions, reduce foundation settlements, improve slope stability, reduce seismic subsidence, and reduce lateral spreading and liquefaction potential, control the deformation and accelerate consolidation, permit construction on loose/weak soil fills. Statistical Analysis: When a stone column is placed on high plastic clays, the load carrying capacity of the stone column would vary depending upon various parameters. This experimental investigation was performed to check the ultimate load carrying capacity and the bulging failure of stone columns with varying Length to Diameter (L/D) ratio of the stone column, Consistency Index (IC) and the Liquid Limit (LL) of the soil on which the stone column is resting by conducting various tests like CBR test. Findings: After conducting the tests it is found that the ultimate load carrying capacity of the stone column increases up to a certain L/D ratio, beyond that value there would be no further increase in ultimate capacity. The Vertical extent of Bulging (BV) is mainly influenced by L/D ratio and the lateral extent of Bulging (BL) is predominantly influenced by IC. The results thus obtained from the present investigation will be helpful in finding the failures in stone columns by varying the load acting on it and also to check the load carrying capacity of stone columns with other parameters with respect to the L/D ratio. Improvements: As bulging failure is considered to be the predominant type of failure for stone columns especially in clayey soils, an attempt can be made to see that the length of stone column doesn't exceed 2-3 times of its diameter beyond which the bulging would surely happen.

Mechanically fastened hybrid composite strips for flexural strengthening of concrete beams

While externally bonded fiber-reinforced polymer reinforcing has become an accepted technology for the flexural strengthening of reinforced concrete members, less information is available on flexural strengthening using mechanically fastened FRP (MF-FRP). This study presents the development of a vacuum-infused, hybrid glass–carbon MF-FRP system for the flexural strengthening of reinforced concrete beams. Two different FRP fabric architectures were considered to assess the impact of fiber orientation on behavior. The resistance of the MF-FRP composite strips to freeze–thaw cycling and saltwater submersion was assessed with single-fastener tension–bearing testing. Test results indicate that the MF-FRP system should display adequate residual capacity in typical cold-climate bridge applications. The flexural strengthening capabilities of MF-FRP composite strips were evaluated using four-point bending tests of MF-FRP-strengthened, steel-reinforced concrete beams and non-strengthened beams. The flexural test results for two glass–carbon MF-FRP reinforcing systems show an average increase in ultimate capacity of nearly 50% with good ductility. Flexural fatigue testing was conducted on four MF-FRP reinforced specimens. The cyclic flexural test results indicate that the strength gains that can be realized with the MF-FRP systems used here may be limited by fatigue performance, and that fatigue is an area that warrants further study.

Destructive Testing and Finite Element Analysis to Determine Ultimate Capacity of Skewed Steel I-Girder Bridges

Current bridge design and rating techniques are based at the component level and thus cannot account for the increase in ultimate capacity that bridges experience because of system-level interactions. Compared with that of a normal bridge, the ultimate capacity of a bridge increases to an even greater extent as bridge supports are skewed because of changes in load paths. Although advances in computer technology have made it possible to conduct accurate system-level analyses, which would allow for more efficient bridge design and rating, the knowledge base surrounding system-level bridge behavior is still too small to make it a highly accurate or intuitive tool. To advance system-level design and rating, two studies were undertaken. First, to evaluate the ultimate capacity of a skewed simple-span steel bridge, a ⅕-scale, slab-on-steel girder bridge was tested to ultimate capacity and then modeled by using finite element analysis. This test provided both insight into the system behavior and validation of an ABAQUS Explicit analysis algorithm and associated modeling techniques. Second, to investigate the effects of skew on the ultimate capacity of simple-span bridges, a parametric study was conducted with finite element analysis. A four-girder, simple-span bridge was modeled with skews varying from 0 to 75 degrees. The results showed that the ultimate capacity of the bridge increased with skew; these results were compared with simple analytical equations to provide insight into the fundamental behavior and load distribution characteristics of skewed bridges.

Flexural Reinforcement of Glulam Timber Beams and Joints with Carbon Fiber-Reinforced Polymer Rods

Fiber-reinforced polymer (FRP) composites have largely been used in combination with masonry and concrete structural elements in the last decade. Recent applications showed that new advantages may also be achieved in the field of timber structures, even if currently steel fasteners are used mainly in connecting systems. This study investigated the possibility of using carbon FRP (CFRP) rods as glued-in reinforcement of glulam beams and as glued-in connectors for glulam timber head joints that should transfer flexural moment between two adjacent beams. Half-scale beams were tested both with and without the presence of FRP reinforcement. Flexural behavior of CFRP-reinforced beams was compared with unreinforced beams that were used as control specimens. Two different amounts of CFRP reinforcement were used in the beam section. Experimental results showed a significant influence of the CFRP rods, because the reinforced beams demonstrated an increase in ultimate capacity and stiffness. Experimental results were also compared with numerical analysis, which showed good accordance with regard to the load and deflection values. Full-size head joints were prepared and tested. Flexural behavior of the joints was compared with the mechanical properties of monopiece beams that were used as reference specimens. Three different force transfer lengths were used for the construction of CFRP-timber joints. Experimental results showed that the use of CFRP rods in timber joints was successful, because the capacity of the CFRP-jointed beams was almost the same as that of the monolithic beams for the longest bond length that was adopted. This result is important in order to find an adequate alternative to traditional joints made with steel bolts and plates, which are unable to create rigid connections, increase dramatically the weight of timber structures, and may be subjected to corrosion in an aggressive environment. A numerical modeling based on the virtual work principle was also conducted and theoretical results were found in good accordance with the experimental results for the tested joint.