Tests of LiteSteel Beams subject to combined shear and bending actions

This paper presents the details of an experimental study of a cold-formed steel beam known as LiteSteel Beam (LSB) subject to combined shear and bending actions. The LSBs have the beneficial characteristics of torsionally rigid rectangular hollow flanges combined with economical fabrication processes from a single strip of high strength steel. They combine the stability of hot-rolled steel sections with the high strength to weight ratio of conventional cold-formed steel sections. The LSB sections are commonly used as flexural members in residential, industrial and commercial buildings. In order to ensure safe and efficient designs of LSBs, many research studies have been undertaken on the flexural and shear strengths of LSBs. To date, however, no investigation has been conducted into the strength of LSB sections under combined shear and bending actions. Hence a detailed experimental study involving 18 tests was undertaken to investigate the behaviour and strength of LSBs under combined shear and bending actions. Test results showed that AS/NZS 4600 design rules for unstiffened webs grossly underestimated the capacity of LSBs. Therefore improved design equations were proposed for the combined shear and bending capacities of LSBs based on experimental results.

Experimental studies of hollow flange channel beams subject to combined bending and shear actions

This paper presents the details of an experimental study of a cold-formed steel hollow flange channel beam known as LiteSteel Beam (LSB) subject to combined bending and shear actions. The LSB sections are produced by a patented manufacturing process involving simultaneous cold-forming and electric resistance welding. Due to the geometry of the LSB, as well as its unique residual stress characteristics and initial geometric imperfections resultant of manufacturing processes, much of the existing research for common cold-formed steel sections is not directly applicable to LSB. Experimental and numerical studies have been carried out to evaluate the behaviour and design of LSBs subject to pure bending actions and predominant shear actions. To date, however, no investigation has been conducted into the strength of LSB sections under combined bending and shear actions. Combined bending and shear is especially prevalent at the supports of continuous span and cantilever beams, where the interaction of high shear force and bending moment can reduce the capacity of a section to well below that for the same section subject only to pure shear or moment. Hence experimental studies were conducted to assess the combined bending and shear behaviour and strengths of LSBs. Eighteen tests were conducted and the results were compared with current AS/NZS 4600 and AS 4100 design rules. AS/NZS 4600 design rules were shown to grossly underestimate the combined bending and shear capacities of LSBs and hence two lower bound design equations were proposed based on experimental results. Use of these equations will significantly improve the confidence and cost-effectiveness of designing LSBs for combined bending and shear actions.

Seismic Bearing Capacity of Foundations on Cohesionless Slopes

By applying the lower bound theorem of limit analysis in conjunction with finite elements and nonlinear optimization, the bearing capacity factor N has been computed for a rough strip footing by incorporating pseudostatic horizontal seismic body forces. As compared with different existing approaches, the present analysis is more rigorous, because it does not require an assumption of either the failure mechanism or the variation of the ratio of the shear to the normal stress along the footing-soil interface. The magnitude of N decreases considerably with an increase in the horizontal seismic acceleration coefficient (kh). With an increase in kh, a continuous spread in the extent of the plastic zone toward the direction of the horizontal seismic body force is noted. The results obtained from this paper have been found to compare well with the solutions reported in the literature. (C) 2013 American Society of Civil Engineers.

Bearing capacity of circular foundations reinforced with geogrid sheets

The ultimate bearing capacity of a circular footing, placed over a soil mass which is reinforced with horizontal layers of circular reinforcement sheets, has been determined by using the upper bound theorem of the limit analysis in conjunction with finite elements and linear optimization. For performing the analysis, three different soil media have been separately considered, namely, (i) fully granular, (ii) cohesive frictional, and (iii) fully cohesive with an additional provision to account for an increase of cohesion with depth. The reinforcement sheets are assumed to be structurally strong to resist axial tension but without having any resistance to bending; such an approximation usually holds good for geogrid sheets. The shear failure between the reinforcement sheet and adjoining soil mass has been considered. The increase in the magnitudes of the bearing capacity factors (N-c and N-gamma) with an inclusion of the reinforcement has been computed in terms of the efficiency factors eta(c) and eta(gamma). The results have been obtained (i) for different values of phi in case of fully granular (c=0) and c-phi soils, and (ii) for different rates (m) at which the cohesion increases with depth for a purely cohesive soil (phi=0 degrees). The critical positions and corresponding optimum diameter of the reinforcement sheets, for achieving the maximum bearing capacity, have also been established. The increase in the bearing capacity with an employment of the reinforcement increases continuously with an increase in phi. The improvement in the bearing capacity becomes quite extensive for two layers of the reinforcements as compared to the single layer of the reinforcement. The results obtained from the study are found to compare well with the available theoretical and experimental data reported in literature. (C) 2014 The Japanese Geotechnical Society. Production and hosting by Elsevier B.V. All rights reserved.

Seismic Bearing Capacity of Shallow Embedded Foundations on a Sloping Ground Surface

By using the lower-bound theorem of the limit analysis in conjunction with finite elements and nonlinear optimization, bearing-capacity factors, N-c and N-gamma q, with an inclusion of pseudostatic horizontal seismic body forces, have been determined for a shallow embedded horizontal strip footing placed on sloping ground surface. The variation of N-c and N-gamma q with changes in slope angle (beta) for different values of seismic acceleration coefficient (k(h)) has been obtained. The analysis reveals that irrespective of ground inclination and the embedment depth of the footing, the factors N-c and N-gamma q decrease quite considerably with an increase in k(h). As compared with N-c, the factor N-gamma q is affected more extensively with changes in k(h) and beta. Unlike most of the results reported in literature for the seismic case, the present computational results take into account the shear resistance of soil mass above the footing level. An increase in the depth of the embedment leads to an increase in the magnitudes of both N-c and N-gamma q. (C) 2014 American Society of Civil Engineers.

Bearing capacity of a circular foundation on layered sand-clay media

The bearing capacity of a circular footing lying over fully cohesive strata, with an overlaying sand layer, is computed using the axisymmetric lower bound limit analysis with finite elements and linear optimization. The effects of the thickness and the internal friction angle of the sand are examined for different combinations of c(u)/(gamma b) and q, where c(u)=the undrained shear strength of the cohesive strata, gamma=the unit weight of either layer, b=the footing radius, and q=the surcharge pressure. The results are given in the form of a ratio (eta) of the bearing capacity with an overlaying sand layer to that for a footing lying directly over clayey strata. An overlaying medium dense to dense sand layer considerably improves the bearing capacity. The improvement continuously increases with decreases in c(u)/(gamma b) and increases in phi and q/(gamma b). A certain optimum thickness of the sand layer exists beyond which no further improvement occurs. This optimum thickness increases with an increase in 0 and q and with a decrease in c(u)/(gamma b). Failure patterns are also drawn to examine the inclusion of the sand layer. (C) 2015 The Japanese Geotechnical Society. Production and hosting by Elsevier B.V. All rights reserved.

Behavior of Brick-Mortar Interfaces in FRP-Strengthened Masonry Assemblages under Normal Loading and Shear Loading

Determination of shear strength of brick-mortar bed joint is critical to overcome the sliding-shear or joint-shear failure in masonry. In the recent past, researchers have attempted to enhance the shear strength and deformation capacity of brick-mortar bed joints by gluing fiber-reinforced polymer (FRP) composite across the bed joint. FRP composites offer several advantages like high strength-to-weight ratio, and ease of application in terms of labor, time, and reduced curing period. Furthermore, FRP composites are desirable for strengthening old masonry buildings having heritage value because of its minimal interference with the existing architecture. A majority of earlier studies on shear strengthening of masonry available in the literature adopted masonry having the ratio of modulus of elasticity of masonry unit (Emu) to modulus of elasticity of mortar (Em) greater than one. Information related to shear behavior of FRP glued masonry composed of masonry units having Young's modulus lower than mortar is limited. Hence the present study is focused on characterizing the interfacial behavior of brick-mortar bed joint of masonry assemblages composed of solid burnt clay bricks and cement-sand mortar (E-mu/E-m ratio less than one), strengthened with FRP composites. Masonry triplets and prisms with bed joint inclined to loading axis (0 degrees, 30 degrees, 45 degrees, 60 degrees and 90 degrees) are employed in this study. Glass and carbon FRP composites composed of bidirectional FRP fabric with equal density in both directions are used for strengthening masonry. Masonry triplets are glued with glass and carbon FRP composites in two configurations: (1) both faces of the triplet specimens are fully glued with GFRP composites; and (2) both faces of the triplet specimens are glued with GFRP and CFRP composites in strip form. The performance of masonry assemblages strengthened with FRP composites is assessed in terms of gain in shear strength, shear displacement, and postpeak behavior for various configurations and types of FRP composites considered. A semianalytical model is proposed for the prediction of shear strength of masonry bed joints glued with FRP composites. A composite failure envelope consisting of a Coulomb friction model and a compression cap is obtained for unreinforced masonry and GFRP-strengthened masonry based on the test results of masonry triplets and masonry prisms with bed joints having various inclinations to the loading (C) 2015 American Society of Civil Engineers.

Formation, microstructure and development of the localized shear deformation in low-carbon steels

An investigation has been made into the effect of microstructural parameters on the propensity for forming shear localization produced during high speed torsional testing by split Hopkinson bar with different average rates of 610, 650 and 1500 s(-1) in low carbon steels. These steels received the quenched, quenched and tempered as well as normalized treatments that provide wide microstructural parameters and mechanical properties. The results indicate that the occurrence of the shear localization is susceptible to the strength of the steels. In other words, the tendency of the quenched steel to form a shear band is higher than that of the other two steels. It is also found that there is a critical strain at which the shear localization occurs in the steels. The critical strain value is strongly dependent on the strength of the steels. Before arriving at this point, the material undergoes a slow work-hardening. After this point, the material suffers work-softening, corresponding to a process during which the deformation is gradually localized and eventually becomes spatially correlated to form a macroscopic shear band. Examinations by SEM reveal that the shear localization within the band involves a series of sequential crystallographic and non-crystallographic events including the change in crystal orientation, misorientation, generation and even perhaps damage in microstructures such as the initiation, growth and coalescence of the microcracks. It is expected that the sharp drop in the load-carrying capacity is associated with the growth and coalescence of the microcracks rather than the occurrence of the shear localization, but the shear localization is seen to accelerate the growth and coalescence of the microcracks. The thin foil observations by TEM reveal that the density of dislocations in the band is extremely high and the tangled arrangement and cell structure of dislocations tends to align along the shear direction. The multiplication and interaction of dislocations seems to be responsible for work-hardening of the steels. The avalanche of the dislocation cells corresponds to the sharp drop in shear stress at which the deformed specimen is broken. Double shear bands and kink bands are also observed in the present study. The principal band develops first and its width is narrower than that of the secondary band.

Precracked reinforced concrete T-Beams repaired in shear with bonded carbon Fiber-Reinforced Polymer sheets

This study investigates the structural behavior of precracked reinforced concrete (RC) T-beams strengthened in shear with externally bonded carbon fiber-reinforced polymer (CFRP) sheets. It reports on seven tests on unstrengthened and strengthened RC T-beams, identifying the influence of load history, beam depth, and percentage of longitudinal steel reinforcement on the structural behavior. The experimental results indicate that the contributions of the external CFRP sheets to the shear force capacity can be significant and depend on most of the investigated variables. This study also investigates the accuracy of the prediction of the fiber-reinforced polymer (FRP) contribution in ACI 440.2R-08, UK Concrete Society TR55, and fib Bulletin 14 design guidelines for shear strengthening. A comparison of predicted values with experimental results indicates that the guidelines can overestimate the shear contribution of the externally bonded FRP system. © 2012, American Concrete Institute.

Lateral and Axial Capacity of Monopiles for Offshore Wind Turbines

Offshore wind has enormous worldwide potential to generate increasing amounts of clean, renewable energy. Monopile foundations are considered to be viable in supporting larger offshore wind turbines in shallow to medium depth waters. In this paper, the lateral and axial response of monopiles installed in undrained clays of varying shear strength and stiffness is investigated using three-dimensional finite element analysis. A combination of axial and lateral loads expected at an offshore wind farm located in a water depth of 30 m has been used in the analysis. Numerically derived monopile axial capacities will be compared to those calculated using an established method in the literature. In addition, the lateral monopile capacity will be determined at ultimate limit state and compared to that at the serviceability limit state. Through a parametric study, it will be shown that with the exception of extremely high axial loads that border on monopile axial capacities, variation in axial loads does not have a significant effect on the ultimate lateral capacity and lateral displacement of monopiles. © 2013 Indian Geotechnical Society.

Precracked reinforced concrete t-beams repaired in shear with prestressed carbon fiber-reinforced polymer straps

The results of an experimental and numerical investigation involving unstrengthened reinforced concrete (RC) T-beams and precracked RC T-beams strengthened in shear with prestressed carbon fiber-reinforced polymer (CFRP) straps are presented and discussed. The results provide insights into the influence of load history and beam depth on the structural behavior of both unstrengthened and strengthened beams. The strengthened beams exhibited capacity enhancements of 21.6 to 46% compared to the equivalent unstrengthened beams, demonstrating the potential effectiveness of the prestressed CFRP strap system. Nonlinear finite element (FE) predictions, which incorporated the load history, reproduced the observed experimental behavior but either underestimated or overestimated the post-cracking stiffness of the beams and strap strain at higher load levels. These limitations were attributed to the concrete shear models used in the FE analyses.

Shear behaviour of steel-fibre-reinforced concrete simply supported beams

The structural behaviour of steel-fibre-reinforced concrete beams was studied using non-linear finite-element analysis and existing experimental data. The work aim was to examine the potential of using steel fibres to reduce the amount of conventional transverse steel reinforcement without compromising ductility and strength requirements set out in design codes. To achieve this, the spacing between shear links was increased while steel fibres were added as a substitute. Parametric studies were subsequently carried out and comparisons were also made with BS EN 1992-1-1 predictions. It was concluded that the addition of steel fibres enhanced the load-carrying capacity and also altered the failure mode from a brittle shear mode to a flexural ductile one. The provision of fibres also improved ductility. However, interestingly it was found that adding excessive amounts of fibres led to a less-ductile response. Overall, the study confirmed the potential for fibres to compensate for a reduction in conventional shear reinforcement.

Seismic behavior of capacity designed masonry walls in low seismicity regions

Eurocode 8 representing a new generation of structural design codes in Europe defines ‎requirements for the design of buildings against earthquake action. In Central and ‎Western Europe, the newly defined earthquake zones and corresponding design ground ‎acceleration values, will lead in many cases to earthquake actions which are remarkably ‎higher than those defined so far by the design codes used until now in Central Europe. ‎ In many cases, the weak points of masonry structures during an earthquake are the corner ‎regions of the walls. Loading of masonry walls by earthquake action leads in most cases ‎to high shear forces. The corresponding bending moment in such a wall typically causes a ‎significant increase of the eccentricity of the normal force in the critical wall cross ‎section. This in turn leads ultimately to a reduction of the size of the compression zone in ‎unreinforced walls and a high concentration of normal stresses and shear stresses in the ‎corner regions. ‎ Corner-Gap-Elements, consisting of a bearing beam located underneath the wall and ‎made of a sufficiently strong material (such as reinforced concrete), reduce the effect of ‎the eccentricity of the normal force and thus restricts the pinching effect of the ‎compression zone. In fact, the deformation can be concentrated in the joint below the ‎bearing beam. According to the principles of the Capacity Design philosophy, the ‎masonry itself is protected from high stresses as a potential cause of brittle failure. ‎ Shaking table tests at the NTU Athens Earthquake Engineering Laboratory have proven ‎the effectiveness of the Corner-Gap-Element. The following presentation will cover the ‎evaluation of various experimental results as well as a numerical modeling of the ‎observed phenomena.‎

Science for Humanitarian Emergencies and Resilience (SHEAR) scoping study: Annex 3 - Early warning system and risk assessment case studies

This report provides case studies of Early Warning Systems (EWSs) and risk assessments encompassing three main hazard types: drought; flood and cyclone. The case studies are taken from ten countries across three continents (focusing on Africa, South Asia and the Caribbean). The case studies have been developed to assist the UK Department for International Development (DFID) to prioritise areas for Early Warning System (EWS) related research under their ‘Science for Humanitarian Emergencies and Resilience’ (SHEAR) programme. The aim of these case studies is to ensure that DFID SHEAR research is informed by the views of Non-Governmental Organisations (NGOs) and communities engaged with Early Warning Systems and risk assessments (including community-based Early Warning Systems). The case studies highlight a number of challenges facing Early Warning Systems (EWSs). These challenges relate to financing; integration; responsibilities; community interpretation; politics; dissemination; accuracy; capacity and focus. The case studies summarise a number of priority areas for EWS related research: • Priority 1: Contextualising and localising early warning information • Priority 2: Climate proofing current EWSs • Priority 3: How best to sustain effective EWSs between hazard events? • Priority 4: Optimising the dissemination of risk and warning information • Priority 5: Governance and financing of EWSs • Priority 6: How to support EWSs under challenging circumstances • Priority 7: Improving EWSs through monitoring and evaluating the impact and effectiveness of those systems

Shear bond strength of resin cements to human dentin

OBJECTIVES: The objectives of this in vitro study were (1) to assess the bond strength of the universal cement RelyX Unicem to dentin and to compare it with three conventional resin cements, (2) to test the influence of aging on their bonding capacity and (3) to test the influence of the operator on bonding quality by performing the same test in two different centers. METHODS: 160 third molars, divided into 80 for tests at the University of Zurich (Z) and 80 for tests at the University of Berne (B), were assigned to 2 x 8 subgroups of 10 teeth each. The specimens were prepared with the corresponding bonding agents and acrylic rods were luted either with RelyX Unicem (U), RelyX ARC (A), Multilink (M) or Panavia 21 (P). All specimens were stored in water for 24h (W) and half of the specimens were subjected to 1500 cycles of thermocycling (5 degrees C and 55 degrees C) (T). Bond strength was measured by means of a shear test. RESULTS: After water storage RelyX Unicem exhibited lowest bond strength (UWZ: 9.2+/-1.6 MPa, UWB: 9.9+/-1.2 MPa, AWZ: 15.3+/-6.0 MPa, AWB: 12.2+/-4.3 MPa, MWZ: 15.6+/-3.3 MPa, MWB: 12.4 MPa+/-2.4, PWZ: 13.4+/-2.9 MPa, PWB: 14.9+/-2.6 MPa). Thermocycling affected the bonding performance of all four cements. However, bond strength of RelyX Unicem was least influenced by thermocycling (UTZ: 9.4+/-2.9 MPa, UTB: 8.6+/-1.3 MPa, ATZ: 11.4+/-6.3 MPa, ATB: 13.3+/-3.7 MPa, MTZ: 15.4+/-3.1 MPa, MTB: 10.3+/-2.4 MPa, PTZ: 11.1+/-2.8 MPa, PTB: 11.3+/-2.8 MPa). SIGNIFICANCE: Although the bond strength of RelyX Unicem to dentin was lower in comparison to RelyX ARC, Multilink and Panavia 21, its bond strength was less sensitive to variations in handling and aging.