265 research outputs found
Concrete damaged plasticity model for simulation of fibre-reinforced polymer-confined concrete-filled steel tubes
No full text
Cyclic response of FRP-to-concrete adhesive joints: effect of the shape of bond-slip model
No full textAlthough the strengthening of reinforced concrete (RC) structures using externally bonded fiber-reinforced polymers (FRPs) have been widely accepted as an excellent technical solution for structural strengthening, only few studies have been conducted to understand and predict the behaviour of FRP-to-concrete bonded joints under cyclic loadings. This paper summarizes the results of a theoretical study aimed at investigating the effect of the shape of bond-slip models on the behaviour of the FRP-to-concrete bonded interfaces under cyclic loading.
Two bond-slip model shapes, one with a linear descending branch and another with an exponential descending branch were used in this study. Evolution of damage for each bond-slip model was defined using the existing test data on Carbon FRP (CFRP)-to-concrete bonded joints under cyclic loading. These bond-slip models were then used to predict the behaviour of a CFRP-to-concrete bond joint subjected to cyclic loading. The results are then compared with the experimental results from a CFRP-to-concrete single shear pull off test under cyclic loading
Thin-walled timber and FRP-timber veneer composite CEE-sections
Full text linkThis paper compares the structural performance between thin-walled timber and FRP-timber composite Ceesections.
While, thin-walled composite timber structures have been proven to be efficient and ultra-light
structural elements, their manufacturing is difficult and labour intensive. Significant effort and time is required
to prevent the cracking of the transverse timber veneers, bent in the grain direction, when forming the crosssectional
shape. FRP-timber structures overcome this disadvantage by replacing the transverse veneers with
flexible, unidirectional FRP material and only keeping the timber veneers which are bent in their natural rolling
direction. The Cee-sections investigated in this study were 210 mm deep × 90 mm wide × 500 mm high and
manufactured from five plies. For both section types, the three internal plies were thin (1 mm thick) softwood
Hoop pine (Araucaria cunninghamii) veneers, orientated along the section longitudinal axis. The two outer
layers, providing bending stiffness to the walls, were Hoop pine veneers (1 mm thick) for the timber sections
and glass fibre reinforced plastic (0.73 mm thick) for the FRP-timber sections orientated perpendicular to the
inner layers. The manufacturing process is briefly introduced in this paper. The profiles were fitted with strain
gauges and tested in compression. Linear Variable Displacement Transducers also recorded the buckling along
one flange. The test results are presented and discussed in this paper in regards to their structural behaviour and
performance. Results showed that the use of FRP in the sections increases both the elastic local buckling load
and section capacity, the latter being increased by about 24 percent. The results indicate that thin-walled FRPtimber
can ultimately be used as a sustainable alternative to cold-formed steel profiles.Griffith Sciences, Griffith School of EngineeringNo Full Tex
Fire resistance of light gauge steel frame wall systems lined with gypsum plasterboards
Full text linkLight gauge steel frame (LSF) wall systems are increasingly used in residential and commercial buildings as load bearing and non-load bearing elements. Conventionally, the Fire Resistance Levels (FRL) of such building elements are determined using approximate prescriptive methods based on limited standard fire tests. However, recent studies have shown that in some instances real building fire time-temperature curves could be more severe than the standard fire curve, in terms of maximum temperature and rate of temperature rise. This has caused problems for safe evacuation and rescue activities, and in some instances has also lead to the collapse of buildings earlier than the prescribed fire resistance. Therefore a detailed research study into the performance of LSF wall systems under both standard fire and realistic fire conditions was undertaken using full scale fire tests to understand the fire performance of different LSF wall configurations. Both load bearing and non-load bearing full scale fire tests were performed on LSF walls configurations with varying number of plasterboard linings, and stud section sizes. The non-load bearing fire test results were utilized to understand the factors affecting the fire resistance of LSF walls, while load bearing fire test results were used to understand the effects exposure to realistic design fire time-temperature curves. This paper presents the results of full scale experimental study on different wall configurations, highlights the effects of realistic design fire time-temperature curves on wall panels and the factors affecting the fire resistance of LSF walls
Numerical studies of gypsum plasterboard and MGO board lined LSF walls exposed to fire
No full textFire resistance of cold-formed light gauge steel frame (LSF) wall systems is enhanced by lining them with\ud
single or multiple layers of wall boards with varying thermal properties. These wall boards are gypsum\ud
plasterboards or Magnesium Oxide (MgO) boards produced by different manufacturers. Thermal properties of\ud
these boards appear to show considerable variations and this can lead to varying fire resistance levels (FRL) for\ud
their wall systems. Currently FRLs of wall systems are determined using full scale fire tests, but they are time\ud
consuming and expensive. Recent research studies on the fire performance of LSF wall systems have used finite\ud
element studies to overcome this problem, but they were developed based on 1-D and 2-D finite element\ud
platform capable of performing either heat transfer or structural analysis separately. Hence in this research a 3-D\ud
finite element model was developed first for LSF walls lined with gypsum plasterboard and cavity insulation\ud
materials. Accurate thermal properties of these boards are essential for finite element modelling, and thus they\ud
were measured at both ambient and elevated temperatures. This experimental study included specific heat,\ud
relative density and thermal conductivity of boards. The developed 3-D finite element model was then validated\ud
using the available fire tests results of LSF walls lined with gypsum plasterboard, and is being used to\ud
investigate the fire performance of different LSF wall configurations. The tested MgO board exhibited\ud
significant variations in their thermal properties in comparison to gypsum plasterboards with about 50% loss of\ud
its initial mass at about 500 ºC compared to 16% for gypsum plasterboards. Hence the FRL of MgO board lined\ud
LSF wall systems is likely to be significantly reduced. This paper presents the details of this research study on\ud
the fire performance of LSF wall systems lined with gypsum plasterboard and MgO board including the\ud
developed 3-D finite element models, thermal property tests and the results
A pathway towards the inverse design of all-composite honeycomb core sandwich panels
Full text linkAll-composite honeycomb cellular core sandwich panels are gaining wide popularity in lightweight structure applications due to their high specific stiffness and strength and multi-functional benefits. The honeycomb cellular core sandwich panels consist of a honeycomb core sandwiched between two face sheets. The performance of such sandwich panel is related to multiple geometric and material parameters of the core and face sheets. Due to a large number of parameters and their complex interactions affecting the performance of the honeycomb cellular core sandwich panels, the optimal design of sandwich panels is difficult and demands a systematic approach by the designer.
This thesis focuses on developing the necessary design tools required for the accurate and efficient inverse design of all-composite honeycomb core sandwich panels considering the key geometric and material parameters of the core and face sheets. First, a strain energy-based homogenisation model is developed to calculate the in-plane and out-of-plane effective stiffnesses of the laminated composite honeycomb core. Unlike the other existing models, the proposed model is applicable for all types of honeycomb cellular core geometries and both single lamella or laminated walls of different materials. Therefore, the proposed model contributes towards significantly enhancing the state of knowledge on the design of honeycomb cellular core sandwich panels. The proposed homogenisation model was validated using the finite element (FE) analysis results of different honeycomb core geometry and material combinations. The results from the proposed model and FE analysis showed a good agreement for all the different honeycomb core configurations considered in the study.
Next, the sandwich panels with honeycomb cores were analysed for the global responses using the equivalent models based on the first-order shear deformation theory (FSDT). The honeycomb cores in the sandwich panels were represented as a homogeneous continuum with the effective stiffness matrix obtained from the proposed homogenisation model. The sandwich panels were analysed for the deflections and in-plane normal stresses of the face sheets under static bending and the global critical buckling load under uniaxial compression using the equivalent models. The predictions were compared against results from the FE models of the sandwich panels with the actual core structure. A good agreement was found between the predictions from the proposed models and the FE results.
Since the proposed equivalent model for the sandwich panels cannot capture the possible local failures which are essential part of the sandwich panel design, new simplified semi-analytical models were developed to explicitly consider the local failures. A semi-analytical approach was developed for predicting the critical shear buckling load of the laminated composite honeycomb cores of different shapes. In the proposed model, two different boundary conditions were considered for the edges of the core walls. While using simply-supported boundaries for all the edges of the core wall gave conservative predictions of the critical shear buckling load, boundary conditions of rotationally restrained longer edges of the wall gave very close predictions of the critical shear buckling strain to the results from the FE analysis. The effect of different fibre lay-ups and shear loading conditions on the shear buckling strength were investigated for honeycomb cores with different shapes. A semi-analytical model was also proposed to predict the intracellular buckling of laminated composite face sheets with non-rectangular cells. The proposed approach was formulated to be as general as possible to take into account different geometric shapes of the cell, rotational restraints at the boundaries of the cell, and different loading conditions which had not been considered in the existing analytical solutions. Using the proposed approach, first, intracellular buckling of laminated composite face sheets with hexagonal cell was studied under various compressive loadings. While the proposed approach with simply-supported boundaries for the cell gave conservative results, predictions with rotationally restrained boundaries for cell gave very close predictions to the FE results considering various conditions such as different cell sizes, core density, face sheet’s fibre lay-up and loadings. The effect of all these different parameters on the intracellular cellular buckling load of the laminated composite face sheets were also studied
An innovative hybrid concrete-FRP composite bridge girder for pedestrian bridges
Full text linkIn the past two decades, fibre-reinforced polymer (FRP) materials have gained wide acceptance within the civil engineering community due to many excellent properties of FRPs such as high strength-to-weight ratio, ease of handling and excellent corrosion resistance. Amongst the applications of FRPs in civil infrastructure, FRP bridge systems have gained great attention. FRPs are used in new bridge construction as bridge decks and bridge girders, as well as all FRP or hybrid systems. FRP bridge systems offer many advantages over traditional concrete or steel solutions. These advantages include lightweight, faster installation, better durability, higher fatigue resistance, easy installation and lesser traffic interruption.
While FRP bridge systems can provide many advantages, FRPs are relatively more expensive, therefore efficient usage of FRP materials is necessary to reduce costs. Often hybrid systems, such as concrete-FRP bridge composite bridge systems where concrete is used as the main compression element tend to provide more economical solutions than all FRP bridge systems. Significant research has been carried out in developing concrete-FRP hybrid bridge deck systems. Several issues related to concrete-FRP bridge systems have been identified, namely: (a) premature failures such as punching failure, web-flange separation, and buckling of the webs limiting the capacity of the system; (b) lack of ductility and sudden brittle failures at ultimate loads conditions; and (c) conservative designs resulting in lower utilization of material strength. The above issues must be addressed to ensure best benefits of concrete-FRP hybrid bridge systems can be fully utilized.
This thesis presents a study towards the development of a lightweight, durable, economical, and easy-to-install Hybrid Concrete-FRP Composite (HCFC) bridge girder system. To ensure better utilization of the materials, and to minimize the risks of brittle failures, the proposed design is based on the hypothesis that through control of a bridge failure initiation to be in an element with significant nonlinear behaviour, nonlinear load-displacement behaviour of a hybrid concrete-FRP bridge system can be achieved leading to sufficient warnings before final failure, therefore lower capacity reduction factors can be used with a higher material utilization.
In the conceptual design of the HCFC girder, concrete was selected as the main compression element, Carbon FRP (CFRP) was selected as the main tensile reinforcement, glass FRP (GFRP) reinforced web stiffener was selected as the main shear element, and steel shear keys were selected as the element transferring the force between concrete and the webs. Failure was controlled to be in the steel shear keys, which is the main nonlinear element in the HCFC girder systems.
A preliminary design methodology was developed, and a 2 m span small-scale HCFC girder was designed to match the capacity of a reinforced concrete (RC) beam. Three small-scale HCFC girders were manufactured and tested under 4-point bending. Test results showed failure in the shear keys, and resulted in nonlinear load-displacement behaviour. Therefore, small-scale test results verified the research hypothesis of this thesis. HCFC girder also showed significantly higher weight-specific load capacity than the RC beam.
Based on the learnings from the small-scale HCFC girder tests, further improved design methodology based on a detailed finite element (FE) modelling approach was developed. In the detailed FE model, the behaviour of the concrete-to-web interface through shear keys was modelled using cohesive elements. The behaviour of the cohesive elements in shear was obtained through experimental testing of concrete-web shear pull-off test specimens. Using the developed FE modelling approach, a 2 m span medium-scale HCFC pedestrian bridge girder was designed. HCFC girder consists of concrete as the compression element, bi-directional GFRP in-filled with chopped glass fibre (GF) strand-epoxy mix as the webs, CFRP laminate at the bottom of the girder as the main tensile element, and steel shear keys as the key element transferring forces between the concrete and the web. The designed medium-scale HCFC girder was manufactured and tested under 3-point bending. Load-displacement behaviour was found to be significantly nonlinear. Experimental behaviour showed an excellent agreement with the FE model predictions. Failure was found to initiate as interface shear failure, and the final failure was due to the failure of concrete near the mid-span. High utilization of the CFRP laminate was achieved.
Based on the learnings from the medium-scale girder tests, further improvements for the HCFC girder design were carried out. Using the FE modelling approach, a large-scale 5.1 m span pedestrian HCFC bridge girder was designed. Different to the medium-scale bridge girder, GF-reinforced timber elements were used as the webs of the girder. In total four large-scale HCFC girders were manufactured. For two of the girders, CFRP and GFRP were used as shear elements, while for the other two only GFRP was used as the main shear elements. All four girders were tested using a four-point bending test setup.
Load-displacement behaviour of all four girders showed nonlinear behaviour. The failure mode of all the girders was due to the cracking of concrete parallel to the girder axis along the webs. Careful investigation of the failed specimens showed no signs of failure in webs, box, or Cee sections, therefore, proving that the design approach was adequate.
All four girders well exceeded the requirements for serviceability limit state loads as well as the ultimate limit state loads for pedestrian bridges. The ultimate load of the girders was found to be related to manufacturing quality. Loss of bonding between the web components (i.e. reinforcement and the web stiffeners) resulted in lower ultimate load capacity.
Using the FE modelling approach, a sensitivity study was carried out to investigate the effect of concrete strength, shear key stiffness and strength, and web reinforcement stiffness on the behaviour of the HCFC girders. It was found that an increase in concrete strength with higher initial stiffness and strength of the shear key behaviour resulted in concrete failure without much nonlinearity in the concrete-web interface while an increase in FRP stiffness, with higher concrete strength and high interface strength, also resulted in concrete crushing failure without much nonlinearity in the concrete-web interface, but increased the initial stiffness of the girder. Higher concrete strength, but low shear key stiffness and strength resulted in lowering the initial stiffness and the load capacity of the girder but provided good nonlinearity while higher concrete strength and higher shear key stiffness but with low shear key strength resulted in increasing the initial stiffness of the girder while lowering the load capacity but provided good nonlinearity. The sensitivity study showed the importance of selecting the right concrete strength, FRP stiffness, and shear key behaviour to obtain the best HCFC girder performance.
While the FE modelling approach was found to provide excellent predictive capabilities, the FE modelling approach is computationally demanding and thus difficult to use as a design tool. Therefore, a simplified analytical model was developed to assist in the design of the HCFC girders. The model was developed using a novel composite element from existing literature which consist of two beam elements to model the tension and compression elements, and spring elements to model the interface elements. In the current study, this element was modified to consider concrete as one of the beam elements, FRP elements (including the shear webs and the tensile reinforcement) as the second beam element, and steel shear keys as the spring elements. Similar to FE models, traction-separation models used to define cohesive element behaviour were used to define the behaviour of the interface springs. The analytical model was verified against the experimental results. A good agreement was found. This analytical model can be used effectively in estimating the dimensions of the different components of the HCFC girders including the design of the concrete to web interface shear mechanism with the steel shear keys
MPs Showing Up to Work
No full textThis infographic is available in English and Sinhala.This infographic shows MP attendance between August 2020 and December 2022, whereby Parliament has met for 231 days during this period. On 121 days, 47 MPs or more were absent whereas on 45 days, 74 MPs or more were absent. Further, this infographic highlights following 10 MPs who were absent for more than 50% of the sittings: R. Sampanthan (ITAK), Harin Fernando (SJB), Palani Thigambaram (SJB), Dilum Amunugama (SLPP), Tiran Alles (SLPP), S. Noharathalingam (ITAK), Wimal Weerawansa (SLPP), C. V. Wigneswaran (TMTK), Wijeyadasa Rajapaksa (SLPP) and Arundika Fernando (SLPP)
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