Showing papers in "Magazine of Concrete Research in 2014"
TL;DR: In this article, the shape factors that influence the compressive behavior of FRP-confined concrete in square and rectangular sections are investigated and a database of existing test results is assembled.
Abstract: It is well understood that the confinement of concrete with fibre-reinforced polymer (FRP) composites can significantly enhance its strength and deformability. However, the effectiveness of FRP confinement on square and rectangular concrete sections, in which the concrete is non-uniformly confined, is much lower than the effective confinement of circular sections. To investigate the shape factors that influence the compressive behaviour of FRP-confined concrete in square and rectangular sections, current theoretical models are reviewed and a database of existing test results is assembled. The database is then studied, together with a companion database consisting of the test results of FRP-confined concrete in circular sections, in order to capture the change in the effectiveness of confinement due to the change in the sectional shape. The combined database records the compression test results of 1547 specimens with unconfined concrete strengths ranging from 6·2 to 169·7 MPa. It provides a significantly e...
99 citations
TL;DR: In this paper, the experimental results of pull-out tests on short anchorages are presented, where ribbed bars are embedded in cubes of normal-and high-strength concrete with a concrete cover of 4·5 times the bar diameter.
Abstract: Steel-to-concrete bond is a basic aspect of the behaviour of reinforced concrete structures both at serviceability and ultimate states. When bond rules were originally developed, experimental results were mainly obtained on normal-strength concrete and a minimum relative rib area (bond index) was required by building codes to ensure good bond properties. The arrival into the market of high-performance concrete and newer structural needs may require different bond indexes. In the present paper, the experimental results of pull-out tests on short anchorages are presented. Several pull-out tests on ribbed bars, embedded in cubes of normal- and high-strength concrete with a concrete cover of 4·5 times the bar diameter, were carried out in order to better understand the influence of the relative rib area and bar diameter on the local bond behaviour, as well as on the splitting crack width generated by the wedging action of ribs. A total of 96 tests were performed on machined bars of three different diameters (...
95 citations
TL;DR: In this article, an ambient temperature cured ultra-high-performance geopolymer concrete (UHPGPC) was developed by completely eliminating Portland cement and activating industrial byproduct materials such as ground granulated blastfurnace slag and silica fume.
Abstract: This paper presents the development of ambient temperature cured ultra-high-performance geopolymer concrete (UHPGPC). Ultra-high-performance concrete (UHPC) mixtures were developed by completely eliminating Portland cement and activating industrial by-product materials such as ground granulated blastfurnace slag and silica fume. Local standard sand (maximum size 2 mm), quartz sand (600 μm) and 0·16 mm diameter steel fibres of 13 and 6 mm length were used. Fresh properties (density and flowability) and mechanical properties (compressive strength) of the UHPGPC produced under ambient temperature curing conditions were evaluated. Four mixtures with fibres and one mix without fibre addition were studied as the UHPGPC mixtures. The highest average compressive strengths obtained were 175 MPa for UHPGPC with steel fibres (1% 6 mm and 2% 13 mm) and 124 MPa for UHPGPC without fibres. Prismatic specimens (100 × 100 × 500 mm) were cast to determine the flexural strength, which was found to be 10·3–13·5 MPa and 9·1 M...
91 citations
TL;DR: In this paper, the authors proposed an analytical model to predict the CAA capacity of reinforced concrete (RC) sub-assemblages under a column-missing scenario, including partial axial and rotational restraints, and connection gaps at beam ends if any.
Abstract: Compressive arch action (CAA) is a favourable structural mechanism to mitigate progressive collapse of reinforced concrete (RC) frames. To quickly and accurately predict the CAA capacity of RC sub-assemblages under a column-missing scenario, an engineering analytical model is proposed. The model considers all the design parameters in beams and the imperfect boundary conditions of sub-assemblages, including partial axial and rotational restraints, and connection gaps at beam ends if any. The proposed model is then validated with experimental results and extended to calculate progressive collapse resistance due to CAA with dynamic increase factors. Finally, the model is employed in parametric studies. It is found that CAA capacity increases with restraint stiffness only in the regime of weak restraints; in the regime of strong restraints, CAA capacity is not sensitive to variation in restraint stiffness. Furthermore, CAA enhances structural resistance more evidently for sub-assemblages with small span-to-de...
76 citations
TL;DR: In this article, the effect of temperature on the microstructure and mechanical properties of reactive powder concrete (RPC) containing polypropylene (PP) fibres was investigated and the experimental results indicated that the compressive and tensile strengths of RPC with PP fibres decreased as temperature increased.
Abstract: This paper illustrates the effect of temperature on the microstructure and mechanical properties of reactive powder concrete (RPC) containing polypropylene (PP) fibres. Thermal conductivity, thermogravimetry, differential scanning calorimetry and mercury intrusion porosity measurements were taken and compressive and tensile strength tests were performed over a temperature range 20–800°C. The PP fibre content, specimen dimensions and explosive spalling were investigated as part of this study, and the various decomposition phases and microstructure were identified using X-ray diffraction and scanning electron microscopy. The experimental results indicated that the compressive and tensile strengths of RPC with PP fibres decreased as temperature increased. RPC containing PP fibres displayed better mechanical properties than normal-strength concrete or high-strength concrete. The addition of PP fibres at a dosage of 2·73 kg/m3 could prevent the explosive spalling of RPC and significantly increase its compressi...
68 citations
TL;DR: In this article, the flexural performance of concrete-encased concrete-filled steel tubes (CFSTs) was investigated and a finite-element analysis (FEA) model was developed to analyse the flexible behavior of the composite member and a set of test data used to verify the FEA modelling.
Abstract: The flexural performance of concrete-encased concrete-filled steel tubes (CFSTs) was investigated. A finite-element analysis (FEA) model is developed to analyse the flexural behaviour of the composite member and a set of test data used to verify the FEA modelling. Full-range analysis of the moment–curvature relation, the stress distributions across the composite section and the interactions between steel and concrete was carried out. It was found that thin-walled steel tubes can be used in concrete-encased CFSTs and develop full plastic strength without local buckling before reaching the ultimate state. A strut-and-tie model is proposed for the load transfer mechanism of a concrete-encased CFST member under bending. Finally, the paper presents a parametric study to derive simplified formulas for predicting the flexural capacity of concrete-encased CFST sections.
49 citations
TL;DR: In this article, the performance of polyvinyl alcohol (PVA) fibres of 6 mm and 12 mm length in concrete was evaluated. And the axial tensile strength of NSFC was the highest at 2.66 MPa, which was 4·29 times higher than NC and 52·9% higher than SFRC.
Abstract: This investigation assessed the performance of polyvinyl alcohol (PVA) fibres of 6 mm and 12 mm length in concrete. Based on total concrete volume, four fibre fractions (0·125, 0·25, 0·375 and 0·5%) were evaluated for their effect on fresh and hardened properties of PVA fibre reinforced concretes (PVA-FRCs). Fly ash was also used as partial replacement of Portland cement in all the mixes. By carrying out a comprehensive set of experiments (compressive strength, splitting tensile strength, modulus of elasticity, modulus of rupture and residual flexural strength), it was observed that PVA fibre significantly enhances the static mechanical properties of concrete as well as improving its post-peak response and ductile behaviour.nerally withstood higher loads than SFRC. At room temperature, the axial tensile strength of NSFC was the highest at 2·66 MPa, which was 4·29 times that of NC and 52·9% higher than that of SFRC. The peak stress of NFSC was approximately 1·8 times that of SFRC. At 400°C, the axial tensi...
46 citations
TL;DR: In this article, reinforcement of the entire cross-section with steel fibres led to a higher load-c... and numerical simulations were carried out to study reinforcement of reinforced concrete with steel and polypropylene fibres in two separate layers.
Abstract: Many studies have been conducted on the behaviour of reinforced concrete (RC) to determine the effects of different fibre types on the mechanical properties of concrete. Tests such as flexural and shear tests are used to evaluate the behaviour of RC. Most previous studies have focused on reinforcement of the entire cross-section with one fibre type, but the use of double-type reinforcement is growing and the lower cost of polypropylene (PP) fibres can be a significant factor in the use of double-type reinforcement. Therefore, in this work, experimental tests and numerical simulations were carried out to study reinforcement of the cross-section with steel fibres, PP fibres or both, in two separate layers. Beams were reinforced using 0·5%, 1% and 2% fibre volume fractions of steel and PP fibres. The beams with a reinforced cross-section with one or two fibre types were evaluated under flexural loading. The results showed that reinforcement of the entire cross-section with steel fibres led to a higher load-c...
45 citations
TL;DR: In this article, the authors present the field observations on the seismic performance of precast concrete structures during the 2011 Van earthquake and another major earthquake with a magnitude of 5·6 occurred on 9 November 2011.
Abstract: A destructive earthquake, magnitude of Mw = 7·2 (Richter scale), hit the city of Van, located in eastern Turkey, on 23 October 2011 and another major earthquake with a magnitude of Mw = 5·6 occurred on 9 November 2011. Significant damage was observed in all types of civil engineering structures in the city centre and nearby. This paper presents the field observations on the seismic performance of precast concrete structures during the earthquakes. Possible damaging factors were discussed in detail after a comprehensive site survey. The majority of the investigated structures were industrial precast concrete structures located in the organised industrial zone of Van. In addition to industrial precast concrete structures, a precast multi-storey residential building located in the city centre was also examined. The findings from the site investigations were compared with the seismic behaviour of similar precast concrete structures during the former devastating earthquake in north-western Turkey in 1999. The ...
40 citations
TL;DR: In this article, the splitting tensile strength of geopolymer concrete and mortar under strain rates from 10−7 s−1 to 25 s− 1 was investigated under different strain rates.
Abstract: The splitting tensile strengths of geopolymer concrete and geopolymer mortar under strain rates from 10−7 s−1 to 25 s−1 were investigated. Five mixes – one ordinary Portland cement (OPC) concrete, ...
38 citations
TL;DR: In this article, the effects of expansive agent (EA) and shrinkage-reducing agent (SRA) on the structural properties of ultra-high-performance concrete were investigated.
Abstract: This study investigated the effects of expansive agent (EA) and shrinkage-reducing agent (SRA) on the mechanical and shrinkage properties of ultra-high-performance concrete. Along with a reference specimen, the work considered five different specimens with different ratios of SRA (1% and 2%), EA (5% and 7·5%) and a combination of 1% SRA and 7·5% EA. The test results revealed that compressive strength varied with the inclusion of SRA and EA, while tensile strength decreased according to the admixing of SRA and EA. The free shrinkage strain was obviously reduced by including SRA and EA, and the specimen with 7·5% EA showed the lowest shrinkage strain. The inner steel strain was also decreased by incorporating SRA and EA, and the specimen with a combination of 1% SRA and 7·5% EA exhibited the smallest strain even though it showed a larger free shrinkage strain than the specimen with 7·5% EA. Furthermore, the specimens with EA exhibited a decrease in steel strain after nearly 10 d due to the tensile creep effect.
TL;DR: In this article, the influence of six different mineral admixtures on the long-term properties of concrete within 1080 d is investigated; these admixtures include steel slag, ground granulated blast furnace slag (GGBS), and composite mineral admixture with four different GGBS-to-steel slag ratios.
Abstract: In this paper, the influence of six different mineral admixtures on the long-term properties of concrete within 1080 d is investigated; these admixtures include steel slag, ground granulated blast furnace slag (GGBS) and composite mineral admixtures with four different GGBS-to-steel slag ratios. The results show that steel slag and composite mineral admixtures with a high content of steel slag have many negative effects on the long-term properties of concrete, such as decreasing strength, increasing porosity and chloride penetrability, and decreasing carbonation and sulfate resistance. GGBS tends to improve the long-term properties of concrete. Concrete containing composite mineral admixture with a high content of GGBS can achieve similar long-term strength, porosity, chloride penetrability, and carbonation and sulfate resistance to Portland cement concrete. The influence of the composite mineral admixture composed of 80% GGBS and 20% steel slag on the long-term properties of concrete might be very close ...
TL;DR: In this article, a type of recycled aggregate thermal insulation concrete (RATIC) was proposed, in which thermal insulation particles (TIPs) were used as solid sealed "holes" instead of air holes to allow the thermal conductivity coefficient of the concrete to be reduced.
Abstract: The objective of this study was to prepare a type of recycled aggregate thermal insulation concrete (RATIC), in which thermal insulation particles (TIPs) were used as solid sealed ‘holes' instead of air holes to allow the thermal conductivity coefficient of the concrete to be reduced. This paper presents the results of a laboratory study on the performance of natural and recycled aggregate concrete, which was prepared by the incorporation of TIPs and different mineral admixtures including ultrafine slag (UFS), nanosilica (NS) and nanocalcium carbonate (NCC). The compressive strength, thermal conductivity coefficient and dry density of the concrete mixtures were determined. The experimental results demonstrate that glazed hollow beads, at the optimal level of 130%, significantly reduced the thermal conductivity property of the recycled aggregate concrete. The properties of the concrete were improved by the addition of UFS and NS, while NCC produced a negative impact. As far as compressive strength was conc...
TL;DR: In this paper, the authors investigated the use of ductile connections between precast beams and roof elements for both new structures and as a retrofit measure of existing ones to transfer the horizontal inertial loads and accommodate deformations arising from seismic displacement compatibility.
Abstract: The seismic vulnerability of precast reinforced concrete buildings is often governed by the performance of mechanical connections between precast elements. This aspect was highlighted by recent seismic events in Italy, where several collapses were registered among industrial buildings typical of Italian practice. The building damage was related to failure of connections between beams and columns and between beams and roof elements, which led to the loss of support of the structural elements. Starting from the results of an experimental campaign, the present work investigates the use of ductile connections between precast beams and roof elements suitable for both new structures and as a retrofit measure of existing ones. These connections are able to transfer the horizontal inertial loads and to accommodate deformations arising from seismic displacement compatibility. The relative rotation between the end of the roof elements and the beam, owing to seismic displacement demand, could lead to their contact. ...
TL;DR: In this paper, the use of pre-soaked expanded perlite aggregate (PS-EPA) on the self-healing of cementitious composites by replacing a proportion of normal aggregate with PS-EPA at different replacement rates was assessed.
Abstract: This study assessed the use of pre-soaked expanded perlite aggregate (PS-EPA) on the self-healing of cementitious composites by replacing a proportion of normal aggregate with PS-EPA at different replacement rates. Specimens with and without PS-EPA were stored in water for 28 d and then mechanical loading was applied to produce specimen deterioration. At the age of 28 d, pre-loaded and sound specimens were exposed to continuous air (CA) exposure for 30 d. The degree of deterioration as a result of mechanical pre-loading and the degree of self-healing were determined via characterisation of crack numbers and widths, transport (chloride ion permeability) and mechanical properties (splitting tensile strength), and specimens with and without PS-EPA were compared. The test results revealed that increased PS-EPA content significantly improved the compressive strength and chloride ion permeability of specimens, and that it further enhanced the hydration and healing capability of specimens under CA exposure after...
TL;DR: In this article, the authors exploited the possibility of producing high-volume fly ash (HVFA)-based recycled aggregate (RA) high-strength concrete and found that 50% of desired strength could be achieved even with 50% replacement of cement with fly ash and 50% natural aggregate (NA) with RA.
Abstract: The utilisation of recycled coarse aggregate obtained from demolished concrete has gained momentum in recent years due to its contribution towards sustainability by minimising the use of artificially produced materials and eliminating environmental problems due to dumped waste materials. The present research exploited the possibility of producing high-volume fly ash (HVFA)-based recycled aggregate (RA) high-strength concrete. It was found that 50% of desired strength could be achieved even with 50% replacement of cement with fly ash and 50% of natural aggregate (NA) with RA. An attempt was thus made to study the effects of RA and HVFA on durability characteristics. The parameters considered were resistance to chloride ion penetration, acid attack, sulfate attack and sorption. It was found that replacement of NA with RA and cement with fly ash in higher volumes showed a way of considering economy and environmental effects as criteria, given a little bit of compromise towards strength and durability criteri...
TL;DR: The environment around concrete structures may be influenced by a changing climate, especially in the long run, leading to an acceleration of deterioration Therefore, the safety, serviceability and serviceability of concrete structures can be improved.
Abstract: The environment around concrete structures may be influenced by a changing climate, especially in the long run, leading to an acceleration of deterioration Therefore, the safety, serviceability an
TL;DR: In this paper, the authors investigated the performance of ternary concrete mixtures containing combinations of natural zeolite with silica fume or fly ash and found that the ternaries showed superior transport performance compared with binary mixtures with only one type of supplementary cementitious material (SCM) and a control mixture without any SCM.
Abstract: This paper reports on an experimental investigation into the performance of ternary concrete mixtures containing combinations of natural zeolite with silica fume or fly ash. The performance of the ternary mixtures is compared with the performance of binary mixtures with only one type of supplementary cementitious material (SCM) and a control mixture without any SCM. The experimental programme included strength and transport property evaluations of a control mixture, binary mixtures with 7·5% silica fume or 10% natural zeolite or 20% fly ash as partial replacements of Portland cement, and ternary mixtures containing 5% natural zeolite with 5% silica fume or 10% natural zeolite with 10% fly ash as partial replacements of Portland cement. The results of the study reveal considerable improvements in the transport properties of concrete through replacing a portion of Portland cement with combinations of natural zeolite with silica fume or fly ash. Generally, the ternary mixtures showed superior transport prope...
TL;DR: In this paper, the bond properties of naturally corroded reinforced concrete members were experimentally investigated and the results indicated that the bond strength decreased with increasing maximum splitting crack widths, however, the bond capacity was higher for the naturally corrosionded specimens.
Abstract: The bond properties of naturally corroded reinforced concrete members were experimentally investigated. Thirteen specimens were taken from the northern edge beam of Stallbacka Bridge, a girder bridge in Sweden. The specimens exhibited different levels of corrosion-induced damage, including concrete cracking and cover spalling. The damage was carefully documented and the specimens were tested in suspended four-point bending tests. Their general behaviour was monitored through measurements of applied loads and vertical deflections. At the same time, the local anchorage behaviour was recorded at the end regions. The test results showed around 5% lower anchorage capacity for damaged specimens compared with the reference ones. The residual bond strength was studied with respect to the observed damage. These tests, and artificial corrosion results from the literature, indicate that the bond strength decreased with increasing maximum splitting crack widths. However, the bond capacity was higher for the naturally corroded specimens. The results thus show an obvious difference between artificial and natural corrosion, and furthermore indicate that the provisions given in fib Model Code 2010 are on the safe side. These test results contribute to further knowledge regarding the structural behaviour of corroded reinforced concrete structures.
TL;DR: In this paper, the effects of varying size and location of openings on the punching shear behavior of two-way reinforced concrete slabs were investigated by examining the slabs' bearing capacities, stiffnesses and energy consumption capacities obtained from test results.
Abstract: The effects of opening size and location on the punching shear behaviour of two-way reinforced concrete (RC) slabs were investigated. The experimental study was carried out on eight experimental specimens with openings at different variable locations and a reference specimen with no opening. Two-way square slabs (2000 × 2000 × 120 mm) were tested by applying an axial load from the top of a square column (200 × 200 mm) located at the centre of the slab specimen. The test specimens studied had different opening sizes (300 × 300 mm and 500 × 500 mm) and locations: each size of opening was positioned in parallel and diagonal locations adjacent to the column and 300 mm from the column. The effects of varying size and location of openings on the punching shear behaviour of two-way RC slabs were interpreted by examining the slabs' bearing capacities, stiffnesses and energy consumption capacities obtained from test results. The load-carrying capacities of the test specimens were calculated using the equations of ...
TL;DR: In this article, a new empirical model to estimate the joint shear strength of both exterior and interior beam-column connections is proposed in order to calibrate the model, a large database of 98 reinforced concrete (RC) exterior and 73 RC interior beamcolumn connections displaying joint failure mode was compiled from the literature.
Abstract: A new empirical model to estimate the joint shear strength of both exterior and interior beam–column connections is proposed In the model, four parameters that have the most influence on joint shear strength are considered Among these four, a new parameter is introduced to consider the bond condition and the possibility of beam bars transferring joint shear force into the columns Consideration of this parameter in the model significantly improves the accuracy of the predicted joint shear strength To calibrate the model, a large database of 98 reinforced concrete (RC) exterior and 73 RC interior beam–column connections displaying joint failure mode was compiled from the literature A parametric study was also carried out to evaluate the dependence of the predicted to tested joint shear strength ratio on the four influence parameters using the database The proposed model showed superior performance over existing models Moreover, comparisons of the predicted joint shear strength with experimental resul
TL;DR: In this article, the effects of curing on the mechanical properties, chemical composition, microstructure and shrinkage of optimised alkali-activated concretes (AACs) based on ternary mixtures of fly ash (FA), blast-furnace slag (BFS) and Portland cement (PC) were compared.
Abstract: The effects of curing on the mechanical properties, chemical composition, microstructure and shrinkage of optimised alkali-activated concretes (AACs) based on ternary mixtures of fly ash (FA), blast-furnace slag (BFS) and Portland cement (PC) were compared. Heat treatment was found to accelerate the early-age strength development of both the PC concrete and the AAC. The long-term strength of AAC was not adversely affected by the heat treatment after 90 d of dry curing. Water curing slightly enhanced the ultimate long-term strength of non-heat-treated AAC specimens but had barely any effect on the heat-treated specimens. Conversely, the dry-cured PC specimens showed a significant decrease in long-term compressive strength. The ultimate drying shrinkage of the PC concrete was lower compared with the AAC, independent of the type of applied curing. In the case of AAC, the drying shrinkage was significantly decreased by the application of heat treatment while water curing did not have any measurable effect. Co...
TL;DR: In this paper, the influence of a number of factors on surface chloride content and diffusion coefficient was investigated for modeling chloride ingress in concrete cubes made from 100% CEM I, 70% cEM I + 30% pfa (pulverised fuel ash) and 50% cem I + 50% GGBS (ground granulated blastfurnace slag) cements were subjected to either one-week (1 d wetting with 3, 10% or 50% sodium chloride solutions and 6 d drying at 20°C).
Abstract: Corrosion of steel in concrete structures remains a major problem worldwide, and surfaces periodically wetted with chloride solution are particularly vulnerable. BS 8500-1 cover requirements have been calculated using the error function solution to Fick's second law of diffusion. However, the values of surface chloride content (Cs) assessed via the diffusion coefficient are rather low, suggesting the cover thicknesses may have been underestimated, which could account for the high incidence of reinforcement corrosion. This paper investigates the influence of a number of factors on Cs and the diffusion coefficient and considers the implications for modelling chloride ingress. Concrete cubes made from 100% CEM I, 70% CEM I + 30% pfa (pulverised fuel ash) and 50% CEM I + 50% GGBS (ground granulated blastfurnace slag) cements were subjected to either one-week (1 d wetting with 3%, 10% or 50% sodium chloride solutions and 6 d drying at 20°C) or two-week (2 d wetting with 50% sodium chloride solution and 12 d dr...
TL;DR: In this article, a series of water absorption experiments were conducted on concrete samples after being subjected to uniaxial compressive or tensile loading, and three load levels were considered.
Abstract: Microcracks, which are always present in concrete, play a critical role in the durability of concrete because they provide additional pathways for aggressive agents such as chlorides to penetrate into the material. A thorough understanding of the transport properties of cracked/damaged concrete is thus essential for predicting its long-term durability. In addition, for concrete in an unsaturated state, water acts as the main medium for the ingress of chloride ions into concrete. This paper presents an experimental investigation into the capillary absorption of concrete after being subjected to compressive or tensile loading. Sorptivity is chosen as a parameter to describe the rate of water penetrating into concrete since it can characterise the tendency of cementitious materials to absorb and transmit water by the capillary mechanism. A series of water absorption experiments were conducted on concrete samples after being subjected to uniaxial compressive or tensile loading. Three load levels were consider...
TL;DR: In this paper, the properties of self-consolidating concrete (SCC) containing different percentages of metakaolin (MK) by varying the mixture components and mixture proportions were investigated for the effects on compressive strength, flowability, passing ability and high-range water-reducer admixture (HRWRA) demand.
Abstract: This paper studies and evaluates the properties of self-consolidating concrete (SCC) containing different percentages of metakaolin (MK) by varying the mixture components and mixture proportions. In total, 32 mixtures with varied percentages of MK and mixture compositions are investigated for the effects on compressive strength, flowability, passing ability and high-range water-reducer admixture (HRWRA) demand. The percentage of MK, coarse-to-fine aggregate (C/F) ratio, coarse aggregate size, binder content and percentage of air entrained in the mixture are varied to study the influence of these variables on the fresh properties of SCC containing MK. SCC mixtures containing silica fume and SCC containing slag are also tested for comparison. The results show that increasing the percentage of MK up to 20% in SCC increases the compressive strength, viscosity, passing ability and HRWRA demand, but decreases the flowability of the mixture. In addition, the flowability of SCC mixtures improves with larger aggre...
TL;DR: In this paper, a component-based joint model is introduced into macromodel-based finite-element analysis (macro-FEA), in which beams are modelled as fibre elements.
Abstract: The behaviour of structures subjected to progressive collapse is typically investigated by introducing column-removing scenarios. Previous experimental results show that large-deformation performances of reinforced concrete (RC) assemblages under a middle column removal scenario (MCRS) involve discontinuity due to bar slip and fracture near the joint interfaces. To consider the effects of the discontinuity on structural behaviour, a component-based joint model is introduced into macromodel-based finite-element analysis (macro-FEA), in which beams are modelled as fibre elements. The joint model consists of a series of non-linear springs, each of which represents a load transfer path from adjoining members to a joint. The calibration procedures of spring properties are illustrated systematically. In particular, a macro-bar stress–slip model is developed to consider the effects of large post-yield tensile strains and finite embedment lengths on the bar stress–slip relationship. Comparisons of simulated and o...
TL;DR: In this paper, an analytical method is developed for determining the crack extension resistance curve of concrete, where the difference in stress intensity factor caused by external forces and by cohesive stress within the fracture process zone is equal to the initial cracking toughness, crack propagation is initiated.
Abstract: Owing to its importance in evaluating the fracture behaviour of concrete, crack extension resistance has been studied based mainly on experimental results. In this paper, an analytical method is developed for determining the crack extension resistance curve of concrete. It is assumed that, when the difference in stress intensity factor caused by external forces and by the cohesive stress within the fracture process zone is equal to the initial cracking toughness, crack propagation is initiated. According to this assumption, the crack extension resistance curve of concrete is expressed analytically as either the stress intensity factor caused by external forces, or the sum of the initial cracking toughness and the stress intensity factor by the cohesive stress within the fracture process zone. One advantage of this method is that, unlike other methods, the experimentally measured load–crack mouth opening displacement curve is not required in calculating the crack extension resistance curve. Based on numeri...
TL;DR: In this article, an experimental investigation into the strength of normal air-entrained concrete (NAEC) under biaxial and triaxial compression loading conditions was carried out.
Abstract: The strength of concrete under biaxial compression and triaxial compression is higher than the strength under uniaxial compression, but the level of increase is affected by factors such as the type of concrete, differences in testing machines, loading rate, etc. Based on this, an experimental investigation into the strength of normal air-entrained concrete (NAEC) under biaxial and triaxial compression loading conditions was carried out. The experimental results on NAEC were compared with the multiaxial compression strengths of other types of concrete obtained using the same testing machine. According to the test data, failure criteria and multiaxial ultimate strength envelopes in principal stress space were proposed. The test results indicated that biaxial compressive strength is higher than uniaxial compressive strength and the maximum increase of ultimate strength occurred at a biaxial compression stress ratio of 0·5 for all types of concrete. A relationship between biaxial compressive strength, triaxia...
TL;DR: In this article, an experimental investigation was conducted to study the influence of steel fibres on the tension stiffening effect and cracking behavior of geopolymer concrete (GPC) prisms cast and tested under uniaxial tension.
Abstract: An experimental investigation was conducted to study the influence of steel fibres on the tension stiffening effect and cracking behaviour of geopolymer concrete (GPC). A total of ten concentrically reinforced concrete prisms (60 × 60 × 600 mm) were cast and tested under uniaxial tension. Out of these, two were made of GPC and the remainder were of steel-fibre-reinforced GPC. The grade of concrete was M40. Different volume fractions of 0·25% (16·62 kg/m3), 0·50% (39·25 kg/m3), 0·75% (58·87 kg/m3) and 1% (78·50 kg/m3) of crimped steel fibres of aspect ratio 66 were used. The test results indicate that the incorporation of steel fibres improves the tension stiffening effect and reduces the spacing and width of cracks. A method was also proposed to predict the width of cracks.
TL;DR: In this article, the effect of sodium tripolyphosphate (STPP) on the fluidity of cement paste with lignin sulfonate (LS), sulfonated naphthalene formaldehyde condensate (FDN) and polycarboxylate ether (PCE) superplasticiser (SP) was studied.
Abstract: The effect of sodium tripolyphosphate (STPP) on the fluidity of cement paste with lignin sulfonate (LS), sulfonated naphthalene formaldehyde condensate (FDN) and polycarboxylate ether (PCE) superplasticiser (SP) was studied. The adsorption amounts of LS, FDN and PCE were assessed using UV spectrophotometry and total organic carbon analysis; the concentration of Ca2+ ions in solution and the adsorption amounts of STPP were tested with plasma emission spectrometry and the electrokinetic properties of the cement particles were confirmed using ζ-potential measurements. Based on analysis of the adsorption amounts, the Ca2+ concentration, ζ-potential and fluidity of cement paste, the competitive adsorption between SPs and STPP was investigated. The result shows that SP and STPP can all adsorb onto the surface of cement particles and there is competitive adsorption between STPP and SP. STPP prevents Ca2+ releasing and pre-empts the adsorption sites of SP; it causes a reduction in the adsorption amount of SP and ...