The effect of freezing and thawing cycles on mechanical properties of concrete （compressive, splitting tensile strength） was experimentally investigated. According to the pullout test data of three kinds of deformed...The effect of freezing and thawing cycles on mechanical properties of concrete （compressive, splitting tensile strength） was experimentally investigated. According to the pullout test data of three kinds of deformed steel bars, the bond stress-slip curves after freezing and thawing were obtained. The empirical equations of peak bond strength were proposed that the damage accounted for effects of freezing and thawing cycle. Meanwhile, the mechanism of bond deterioration between steel bars and concrete after freezing and thawing cycles was discussed. All these conclusions will be useful to the durability design and reliability calculation of RC structures in cold region.展开更多
In order to investigate the tensile bond anchorage properties of Australian 500N steel bars in concrete, 111 pullout tests were conducted. The precise bond slip values have been gained by using the laser displacement ...In order to investigate the tensile bond anchorage properties of Australian 500N steel bars in concrete, 111 pullout tests were conducted. The precise bond slip values have been gained by using the laser displacement sensor with high resolution, including the complete bond-slip curves. How the main anchorage factors such as concrete strength, bar diameter （8, I0, 12, 16, 20, 24, 28, 32 and 36 mm） the concrete covered, embedded length and transverse reinforcement influencing the bond anchorage properties was studied under tensile condition. The process of the tensile force-slip failure for Australian 500N reinforcing steel can be divided into five stages： elastic stage, local slip stage, slip in ascent stage, slip in descent stage and remnant stage. The formula for calculating the tensile bond strength of Australian 500N reinforcing bar in concrete was proposed according to the test results, including the consistent model for tensile bond-slip relationship.展开更多
The properties of anti-seismic HRB400 steel bars with 25 mm diameter were systematically investigated. The results showed that the properties of the HRB400 reinforced steel bars had been greatly enhanced comparing wit...The properties of anti-seismic HRB400 steel bars with 25 mm diameter were systematically investigated. The results showed that the properties of the HRB400 reinforced steel bars had been greatly enhanced comparing with HRB335 steel bars, i.e. coordination of strength and ductility, strain-aging sensibility, low temperature impact toughness, weld ability and high strain low cycle fatigue. The ductile-brittle transit temperatures of hot-rolled and strain-aged steel bars were evaluated as –17 °C and ?8 °C respectively, and the low temperature impact toughness of HRB400 steel bars remains to be improved. Transmission electron microscopy (TEM) and electron diffraction showed little vanadium existed in ferrite as VN, most of which existed in pearlite as alloy cementite which resulted in the declination of impact toughness. Methods were suggested to improve the anti- seismic properties of steel bars.展开更多
Buildings collapse has now become a recurrent phenomenon in C<span style="white-space:nowrap;">ô</span>te d’Ivoire. Therefore, this study was conducted to find out the reasons for these...Buildings collapse has now become a recurrent phenomenon in C<span style="white-space:nowrap;">ô</span>te d’Ivoire. Therefore, this study was conducted to find out the reasons for these disasters, and check in particular to the extent, and concrete steel bars produced in C<span style="white-space:nowrap;">ô</span>te d’Ivoire and used in buildings’ structures are involved. Samples having 6, 8, 10 and 12 mm in diameter steel taken from the five (5) major manufacturers or suppliers of the Ivorian market were subjected to physical, chemical and mechanical tests to determine their performance. A comparison of these results with the NF EN 10080 and NF A35 080-1 standards made it possible to calculate the probability to have out-of-standard products in a structure. Pieces having 60 cm were cut from three bars of the same thickness and then subjected to tests. These are the chemical test by optical emission spectrometer, physical tests by caliper measurements of diameter, height of bolts and ribs and calculation of linear mass, and tensile tests with the help of hydraulic press. These tests made it possible to determine the characteristics of the steel bars. Then, these characteristics were compared with standards NF EN 10080 and NF A35 080-1, in order to judge their conformity for construction. Finally, the likelihood of having non-standard steel bars in a structure is calculated. These tests indicate that the relative surfaces of the bolts of the various bars HA6, HA8, HA10 and HA12 vary from 0.146 to 0.323 respectively;0.120 to 0.312;0.101 to 0, 297 and 0.142 to 0.482. Likewise, their calculated linear masses of these bars are respectively between 28.3 mm<sup>2</sup> and 222 g/m;50.3 mm<sup>2</sup> and 395 g/m;78.5 mm<sup>2</sup> and 617 g/m;and 113 mm<sup>2</sup> and 888 g/m. In addition, their yield strengths and elongations at break vary from 344 MPa to 582 MPa and from 0.2% to 15% respectively. According to analysis of these results, 100% of steel bars would lead to a steel-concrete adhesion that complies with standard requirements and 100% have a linear mass or density lower than the standard. Similarly, on the mechanical aspect, 70% of steel bars have a yield strength lower than 400 MPa and 95% have an inappropriate ductility. Non-compliance with cross-sections, inadequate performance and non-compliance with the chemical composition of steel bars expose buildings to low durability and even sudden collapse of their structural elements. Concrete steel bars contribute a great deal to failures found in buildings.展开更多
Due to inadequate bearing capacity of the chemically-planted steel bar in low-strength concrete, a new mixed post-installed connection is proposed using small diameter anchoring steel bars and grouting materials toget...Due to inadequate bearing capacity of the chemically-planted steel bar in low-strength concrete, a new mixed post-installed connection is proposed using small diameter anchoring steel bars and grouting materials together to anchor the main steel bar. To investigate the feasibility of the proposed post-installed connections, a series of pull-out tests with different anchors were conducted for comparison,including fully adhesive anchors, partially adhesive anchors,grouting material anchoring connection and the new mixed post-installed connection. The experimental results of the single steel bar pull-out test show that the mixed post-installed connection can effectively enhance the bearing capacity of post-installed steel bars in low-strength concrete. The bearing capacity is increased by nearly two times with no cone-type concrete failure compared with the fully adhesive anchor. The results show that adopting the new mixed post-installed connection can ensure that joint performance meets the requirements if the space dimension is available.展开更多
The performance of concrete beams repaired with epoxy mortar was investigated by constructing twelve beam specimens.All the beam specimens were subjected to a constant current for accelerated corrosion.Six specimens w...The performance of concrete beams repaired with epoxy mortar was investigated by constructing twelve beam specimens.All the beam specimens were subjected to a constant current for accelerated corrosion.Six specimens were corroded without subsequent reparation as a control group,and the other six beam specimens were corroded and repaired utilizing epoxy mortar.All specimens were tested to failure.During test process,we focused on the failure pattern of beam specimens,structural cracks,mid-deflections,bearing capacity,and probed into the influence of corrosion degree and repair of epoxy mortar on the performance of beam specimens.It was observed that corrosion-repaired beams in the loading test were in a bending failure pattern.It is obvious that cracking loads and bending stiffness of repaired beams and corrosion-repaired beams were larger than those of unrepaired beams and secondly-corroded beams.When the mass loss of main steel bars was smaller than 10%,the bearing capacity of the repaired beams was similar to that of the unrepaired beams.When the mass loss of main steel bars was larger than 10%,the bearing capacity of the repaired beams increased significantly compared with that of the unrepaired beams.展开更多
Due to creep characteristics of wood,long-term loading can cause a significant stress loss of steel bars in rein-forced glulam beams and high long-term deflection of the beam midspan.In this study,15 glulam beams were...Due to creep characteristics of wood,long-term loading can cause a significant stress loss of steel bars in rein-forced glulam beams and high long-term deflection of the beam midspan.In this study,15 glulam beams were subjected to a 90-day long-term loading test,and the effects of long-term loading value,reinforcement ratio and prestress level on the stress of steel bars,midspan long-term deflection,and other parameters were compared and analyzed.The main conclusions drawn from this study were that the long-term deflection of the reinforced glulam beams accounted for 22.5%,20.6%,and 18.2%of the total deflection respectively when the loading value was 20%,30%,and 40%of the estimated ultimate load under the long-term loading.The higher the loading level was,the smaller the proportion of the long-term deflection in the total deflection was.Compared with ordinary glulam beams,the long-term deflection of the reinforced glulam beam was even smaller.Under the condition of the constant loading level,the total stress value of the steel bars decreased by 17.5%,13.6%,and 9.1%,and the proportion of the long-term deflection of the beam midspan in the total deflection was 26.9%,24.2%,and 20.6%respectively when the reinforcement ratio was 2.05%,2.68%,and 3.39%.With the increase of the reinfor-cement ratio,the stress loss of the steel bars decreased,and the proportion of the long-term deflection decreased as well.When other conditions remained constant and the prestress level of the steel bars was 0 MPa,30 MPa,and 60 MPa,the total stress value of the steel bars decreased by 9.1%,9.4%,and 10.2%,respectively,and the propor-tion of the long-term deflection in the total deflection was 20.6%,26.1%,and 64.9%,respectively.With the increase of the prestress value,the stress loss of the steel bars increased,and the proportion of the long-term deflection increased as well.展开更多
A variety of new materials in the field of concrete technology have been developed during the past three decades with the ongoing demand of construction industry to meet the functional, strength, economical and durabi...A variety of new materials in the field of concrete technology have been developed during the past three decades with the ongoing demand of construction industry to meet the functional, strength, economical and durability requirements. Though reinforced concrete has high strength and is most widely used construction material it suffers from disadvantages like corrosion of steel, susceptibility to chemical and environmental attack. In order to overcome the above deficiencies of reinforced concrete new materials （special concrete composites） have been developed over the past three decades. Glass Fibre Reinforced Polymer （GFRP） is one such material with wide range of applications. Based on the preliminary investigations on GFRP bars, an optimum fiber/resin ratio of 7：3 was arrived. The tensile strength of GFRP bars is comparable to that of the mild steel as per the tests carried out, but the modulus of elasticity is about 25-30 percentage of that of steel bars. This paper deals with the experimental investigations carried out on small slab panels supported on all four edges with effective spans of 0.9 m ~ 0.45 m, which is a part of large research problem undertaken with different ratios of 10ng span to short span with different support conditions. The test results are compared with similar slab panels reinforced with conventional mild steel bars.展开更多
Very high concentration of flexural, shear and torsional stresses occurs at the wall-slab junctions in a laterally loaded tall building consisting of planar walls and coupling slabs. Due to this concentration of stres...Very high concentration of flexural, shear and torsional stresses occurs at the wall-slab junctions in a laterally loaded tall building consisting of planar walls and coupling slabs. Due to this concentration of stresses and their interaction, there are great chances of failure to occur at the junction. Also the flexural stresses are not uniformly distributed and have the highest intensity near the periphery of inner walls but are reduced drastically as we move away from the wall-slab junction. Numerous attempts have been made to strengthen the wall-slab junction by using various types of shear reinforcement to ensure that shear failure should not occur. Various methods including fibre reinforcement consisting of twins of twisted steel couplets have already been used. This paper describes a new method of placing 2 inch wide flange I-sections at appropriate locations to improve the shear strength of the wall-slab junctions. Based on systematic research, a new procedure has also been developed to assess the strength of wall-slab junction using the new reinforcement method. Test results showed that a substantial increase, up to 57%, in the shear strength of specimens was obtained by using the new method of shear reinforcement in a laterally loaded tall building.展开更多
This part of study represents the applied study;which is a continuation of the experimental study that was carried out in part 1 [1]<span "="">. The experimental study in part 1 focused on ev...This part of study represents the applied study;which is a continuation of the experimental study that was carried out in part 1 [1]<span "="">. The experimental study in part 1 focused on evaluation of the effectiveness of Montmorillonite clay, calcium carbonate, and silicon dioxide nanoparticles for enhancing the performances of epoxy adhesives used in re-assembly of archaeological </span>massive limestones. Based on the obtained results in part 1, the choice fell on epoxy-clay nanocomposites as the best re-assembly adhesive material reinforced with Stainless Steel to conduct the applied study project. The current applied study that <span "="">represents a big project was carried out on 3 archaeological pharaonic massive limestones discovered separately in Ain Shams (Heliopolis) archaeological area in Egypt. The methodology included an accurate archaeological study, followed by analytical, and then the restoration and reassembly process. Firstly;in order to prove whether these artifacts are complementary to each other or not, then with a view to re-assembly and conserving these artifacts in the form of one stone block to be ready for museum display. Referred to the comprehensive archaeological and analytical study of the mentioned archeological stones, the results confirmed that, these stone pieces, in the original were one piece, therefore, it is possible to regrouping again to become one block complementary to each other, and this is what was done in this study.展开更多
Purpose of present work is to develop a reliable and simple method for structural analysis of RC Shear Walls. The shear wall is simulated by a truss model as the bar of a truss is the simplest finite element. An itera...Purpose of present work is to develop a reliable and simple method for structural analysis of RC Shear Walls. The shear wall is simulated by a truss model as the bar of a truss is the simplest finite element. An iterative method is used. Initially, there are only concrete bars. Repeated structural analyses are performed. After each structural analysis, every concrete bar exceeding tensile strength is replaced by a steel bar. For every concrete bar exceeding compressive strength, first its section area is increased. If this is not enough, a steel bar is placed at the side of it. For every steel bar exceeding tensile or compressive strength, its section area is increased. After the end of every structural analysis, if all concrete and steel bars fall within tensile and compressive strengths, the output data are written and the analysis is terminated. Otherwise, the structural analysis is repeated. As all the necessary conditions (static, elastic, linearized geometric) are satisfied and the stresses of ALL concrete and steel bars fall within the tensile and compressive strengths, the results are acceptable. Usually, the proposed method exhibits a fast convergence in 4 - 5 repeats of structural analysis of the RC Shear Wall.展开更多
Following the evolution of currently enforced Performance Based Design standards of reinforced concrete (RC) structures for durability, the designer, rather than complying with given prescriptive limits, may instead s...Following the evolution of currently enforced Performance Based Design standards of reinforced concrete (RC) structures for durability, the designer, rather than complying with given prescriptive limits, may instead specify a cementitious mix design that is proven to exhibit a code prescribed resistance level (class) to a given exposure environment. Such compliance will lead to the protection of the steel reinforcement from corrosion and the cementitious mortar from degradation, during the design lifespan of the structure, under aggressive environmental exposure conditions such as, marine or deicing salts and carbonation. In this context, the enhancement of the physical and durability properties of common cement-based mortars under chloride exposure are experimentally investigated herein. In particular, the experimental program reported herein aims to evaluate the influence of incorporating multi-walled carbon nanotubes on the physical and mechanical properties of reinforced mortars against chloride ions. Furthermore, the anticorrosion protection of cementitious composites prepared with nanomaterials at 0.2% w/w is further investigated, by comparing all test results against reference specimens prepared without any additive. Electrochemical (Half-cell potential, corrosion current) and mass loss of reinforcement steel measurements were performed, while the porosity, capillary absorption and flexural strength were measured to evaluate the mechanical and durability characteristics of the mortars, following a period of exposure of eleven months;SEM images coupled with EDX analysis were further recorded and used for microstructure observation. The test results indicate that the inclusion of the nanomaterials in the mix improved the durability of the mortar specimens, while the nano-modified composites exhibited higher chloride penetration resistance and flexural strength than the corresponding values of the reference mortars. The test results and the comparison between nanomodified and reference mortars showed that the use of CNTs as addition led to protection of steel reinforcing bars against pitting corrosion and a significant improvement in flexural strength and porosity of the mortars.展开更多
To overcome the problem that steel bars are put too close at a flame joint with special-shaped beam and column,mechanical performance of three groups of six RC flame joints with special-shaped(L,T and+)column and disp...To overcome the problem that steel bars are put too close at a flame joint with special-shaped beam and column,mechanical performance of three groups of six RC flame joints with special-shaped(L,T and+)column and dispersed-steel bars-beam on the top floor under cyclic loads were studied.Experimental comparison was conducted between special-shaped(L,T and+)column and normal beams.The cracking load,yielding load,ultimate bearing capacity,failure patterns,and hysteretic properties at joint core area were investigated.The seismic behaviors of the joints with different proportions of dispersed-steelbar beams were analyzed.The results of experimental analysis indicate that the mechanical and seismic behaviors of frame joints with T-shaped and+-shaped column are nearly not changed when suitable proportion steel bars are dispersed to flange plane.Stiffness degeneration of flame joint with L-shaped column is rather serious due to concrete damage stiffness.Theoretical result indicates that distributing area of the dispersed steel-bar beams in the flange plate should be strictly controlled to avoid anchor destroy.展开更多
基金the National Natural Science Foundation of China(No.50479059)
文摘The effect of freezing and thawing cycles on mechanical properties of concrete （compressive, splitting tensile strength） was experimentally investigated. According to the pullout test data of three kinds of deformed steel bars, the bond stress-slip curves after freezing and thawing were obtained. The empirical equations of peak bond strength were proposed that the damage accounted for effects of freezing and thawing cycle. Meanwhile, the mechanism of bond deterioration between steel bars and concrete after freezing and thawing cycles was discussed. All these conclusions will be useful to the durability design and reliability calculation of RC structures in cold region.
基金Project(DP0988940) supported by Australian Research Council Discovery Grant Program Project(2011M500930) supported by Postdoctoral Science Foundation of China+1 种基金Project(11KJB560003) supported by College Natural Science Foundation of Jiangsu Province,ChinaProject(163050072) supported by the Talent Introduction Foundation of Nanjing Forestry University,China
文摘In order to investigate the tensile bond anchorage properties of Australian 500N steel bars in concrete, 111 pullout tests were conducted. The precise bond slip values have been gained by using the laser displacement sensor with high resolution, including the complete bond-slip curves. How the main anchorage factors such as concrete strength, bar diameter （8, I0, 12, 16, 20, 24, 28, 32 and 36 mm） the concrete covered, embedded length and transverse reinforcement influencing the bond anchorage properties was studied under tensile condition. The process of the tensile force-slip failure for Australian 500N reinforcing steel can be divided into five stages： elastic stage, local slip stage, slip in ascent stage, slip in descent stage and remnant stage. The formula for calculating the tensile bond strength of Australian 500N reinforcing bar in concrete was proposed according to the test results, including the consistent model for tensile bond-slip relationship.
文摘The properties of anti-seismic HRB400 steel bars with 25 mm diameter were systematically investigated. The results showed that the properties of the HRB400 reinforced steel bars had been greatly enhanced comparing with HRB335 steel bars, i.e. coordination of strength and ductility, strain-aging sensibility, low temperature impact toughness, weld ability and high strain low cycle fatigue. The ductile-brittle transit temperatures of hot-rolled and strain-aged steel bars were evaluated as –17 °C and ?8 °C respectively, and the low temperature impact toughness of HRB400 steel bars remains to be improved. Transmission electron microscopy (TEM) and electron diffraction showed little vanadium existed in ferrite as VN, most of which existed in pearlite as alloy cementite which resulted in the declination of impact toughness. Methods were suggested to improve the anti- seismic properties of steel bars.
文摘Buildings collapse has now become a recurrent phenomenon in C<span style="white-space:nowrap;">ô</span>te d’Ivoire. Therefore, this study was conducted to find out the reasons for these disasters, and check in particular to the extent, and concrete steel bars produced in C<span style="white-space:nowrap;">ô</span>te d’Ivoire and used in buildings’ structures are involved. Samples having 6, 8, 10 and 12 mm in diameter steel taken from the five (5) major manufacturers or suppliers of the Ivorian market were subjected to physical, chemical and mechanical tests to determine their performance. A comparison of these results with the NF EN 10080 and NF A35 080-1 standards made it possible to calculate the probability to have out-of-standard products in a structure. Pieces having 60 cm were cut from three bars of the same thickness and then subjected to tests. These are the chemical test by optical emission spectrometer, physical tests by caliper measurements of diameter, height of bolts and ribs and calculation of linear mass, and tensile tests with the help of hydraulic press. These tests made it possible to determine the characteristics of the steel bars. Then, these characteristics were compared with standards NF EN 10080 and NF A35 080-1, in order to judge their conformity for construction. Finally, the likelihood of having non-standard steel bars in a structure is calculated. These tests indicate that the relative surfaces of the bolts of the various bars HA6, HA8, HA10 and HA12 vary from 0.146 to 0.323 respectively;0.120 to 0.312;0.101 to 0, 297 and 0.142 to 0.482. Likewise, their calculated linear masses of these bars are respectively between 28.3 mm<sup>2</sup> and 222 g/m;50.3 mm<sup>2</sup> and 395 g/m;78.5 mm<sup>2</sup> and 617 g/m;and 113 mm<sup>2</sup> and 888 g/m. In addition, their yield strengths and elongations at break vary from 344 MPa to 582 MPa and from 0.2% to 15% respectively. According to analysis of these results, 100% of steel bars would lead to a steel-concrete adhesion that complies with standard requirements and 100% have a linear mass or density lower than the standard. Similarly, on the mechanical aspect, 70% of steel bars have a yield strength lower than 400 MPa and 95% have an inappropriate ductility. Non-compliance with cross-sections, inadequate performance and non-compliance with the chemical composition of steel bars expose buildings to low durability and even sudden collapse of their structural elements. Concrete steel bars contribute a great deal to failures found in buildings.
基金The National Natural Science Foundation of China(No.51409084)the Natural Science Foundation of Jiangsu Province(No.BK20130836)
文摘Due to inadequate bearing capacity of the chemically-planted steel bar in low-strength concrete, a new mixed post-installed connection is proposed using small diameter anchoring steel bars and grouting materials together to anchor the main steel bar. To investigate the feasibility of the proposed post-installed connections, a series of pull-out tests with different anchors were conducted for comparison,including fully adhesive anchors, partially adhesive anchors,grouting material anchoring connection and the new mixed post-installed connection. The experimental results of the single steel bar pull-out test show that the mixed post-installed connection can effectively enhance the bearing capacity of post-installed steel bars in low-strength concrete. The bearing capacity is increased by nearly two times with no cone-type concrete failure compared with the fully adhesive anchor. The results show that adopting the new mixed post-installed connection can ensure that joint performance meets the requirements if the space dimension is available.
基金supported by the National Natural Science Foundation of China(No.51279074)the Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘The performance of concrete beams repaired with epoxy mortar was investigated by constructing twelve beam specimens.All the beam specimens were subjected to a constant current for accelerated corrosion.Six specimens were corroded without subsequent reparation as a control group,and the other six beam specimens were corroded and repaired utilizing epoxy mortar.All specimens were tested to failure.During test process,we focused on the failure pattern of beam specimens,structural cracks,mid-deflections,bearing capacity,and probed into the influence of corrosion degree and repair of epoxy mortar on the performance of beam specimens.It was observed that corrosion-repaired beams in the loading test were in a bending failure pattern.It is obvious that cracking loads and bending stiffness of repaired beams and corrosion-repaired beams were larger than those of unrepaired beams and secondly-corroded beams.When the mass loss of main steel bars was smaller than 10%,the bearing capacity of the repaired beams was similar to that of the unrepaired beams.When the mass loss of main steel bars was larger than 10%,the bearing capacity of the repaired beams increased significantly compared with that of the unrepaired beams.
基金This research work was supported by the Fundamental Research Funds for the Central Universities(2572017DB02)the natural science foundation of Heilongjiang Province(LH2019E005)the natural science of Heilongjiang Province(LH2020E009).
文摘Due to creep characteristics of wood,long-term loading can cause a significant stress loss of steel bars in rein-forced glulam beams and high long-term deflection of the beam midspan.In this study,15 glulam beams were subjected to a 90-day long-term loading test,and the effects of long-term loading value,reinforcement ratio and prestress level on the stress of steel bars,midspan long-term deflection,and other parameters were compared and analyzed.The main conclusions drawn from this study were that the long-term deflection of the reinforced glulam beams accounted for 22.5%,20.6%,and 18.2%of the total deflection respectively when the loading value was 20%,30%,and 40%of the estimated ultimate load under the long-term loading.The higher the loading level was,the smaller the proportion of the long-term deflection in the total deflection was.Compared with ordinary glulam beams,the long-term deflection of the reinforced glulam beam was even smaller.Under the condition of the constant loading level,the total stress value of the steel bars decreased by 17.5%,13.6%,and 9.1%,and the proportion of the long-term deflection of the beam midspan in the total deflection was 26.9%,24.2%,and 20.6%respectively when the reinforcement ratio was 2.05%,2.68%,and 3.39%.With the increase of the reinfor-cement ratio,the stress loss of the steel bars decreased,and the proportion of the long-term deflection decreased as well.When other conditions remained constant and the prestress level of the steel bars was 0 MPa,30 MPa,and 60 MPa,the total stress value of the steel bars decreased by 9.1%,9.4%,and 10.2%,respectively,and the propor-tion of the long-term deflection in the total deflection was 20.6%,26.1%,and 64.9%,respectively.With the increase of the prestress value,the stress loss of the steel bars increased,and the proportion of the long-term deflection increased as well.
文摘A variety of new materials in the field of concrete technology have been developed during the past three decades with the ongoing demand of construction industry to meet the functional, strength, economical and durability requirements. Though reinforced concrete has high strength and is most widely used construction material it suffers from disadvantages like corrosion of steel, susceptibility to chemical and environmental attack. In order to overcome the above deficiencies of reinforced concrete new materials （special concrete composites） have been developed over the past three decades. Glass Fibre Reinforced Polymer （GFRP） is one such material with wide range of applications. Based on the preliminary investigations on GFRP bars, an optimum fiber/resin ratio of 7：3 was arrived. The tensile strength of GFRP bars is comparable to that of the mild steel as per the tests carried out, but the modulus of elasticity is about 25-30 percentage of that of steel bars. This paper deals with the experimental investigations carried out on small slab panels supported on all four edges with effective spans of 0.9 m ~ 0.45 m, which is a part of large research problem undertaken with different ratios of 10ng span to short span with different support conditions. The test results are compared with similar slab panels reinforced with conventional mild steel bars.
文摘Very high concentration of flexural, shear and torsional stresses occurs at the wall-slab junctions in a laterally loaded tall building consisting of planar walls and coupling slabs. Due to this concentration of stresses and their interaction, there are great chances of failure to occur at the junction. Also the flexural stresses are not uniformly distributed and have the highest intensity near the periphery of inner walls but are reduced drastically as we move away from the wall-slab junction. Numerous attempts have been made to strengthen the wall-slab junction by using various types of shear reinforcement to ensure that shear failure should not occur. Various methods including fibre reinforcement consisting of twins of twisted steel couplets have already been used. This paper describes a new method of placing 2 inch wide flange I-sections at appropriate locations to improve the shear strength of the wall-slab junctions. Based on systematic research, a new procedure has also been developed to assess the strength of wall-slab junction using the new reinforcement method. Test results showed that a substantial increase, up to 57%, in the shear strength of specimens was obtained by using the new method of shear reinforcement in a laterally loaded tall building.
文摘This part of study represents the applied study;which is a continuation of the experimental study that was carried out in part 1 [1]<span "="">. The experimental study in part 1 focused on evaluation of the effectiveness of Montmorillonite clay, calcium carbonate, and silicon dioxide nanoparticles for enhancing the performances of epoxy adhesives used in re-assembly of archaeological </span>massive limestones. Based on the obtained results in part 1, the choice fell on epoxy-clay nanocomposites as the best re-assembly adhesive material reinforced with Stainless Steel to conduct the applied study project. The current applied study that <span "="">represents a big project was carried out on 3 archaeological pharaonic massive limestones discovered separately in Ain Shams (Heliopolis) archaeological area in Egypt. The methodology included an accurate archaeological study, followed by analytical, and then the restoration and reassembly process. Firstly;in order to prove whether these artifacts are complementary to each other or not, then with a view to re-assembly and conserving these artifacts in the form of one stone block to be ready for museum display. Referred to the comprehensive archaeological and analytical study of the mentioned archeological stones, the results confirmed that, these stone pieces, in the original were one piece, therefore, it is possible to regrouping again to become one block complementary to each other, and this is what was done in this study.
文摘Purpose of present work is to develop a reliable and simple method for structural analysis of RC Shear Walls. The shear wall is simulated by a truss model as the bar of a truss is the simplest finite element. An iterative method is used. Initially, there are only concrete bars. Repeated structural analyses are performed. After each structural analysis, every concrete bar exceeding tensile strength is replaced by a steel bar. For every concrete bar exceeding compressive strength, first its section area is increased. If this is not enough, a steel bar is placed at the side of it. For every steel bar exceeding tensile or compressive strength, its section area is increased. After the end of every structural analysis, if all concrete and steel bars fall within tensile and compressive strengths, the output data are written and the analysis is terminated. Otherwise, the structural analysis is repeated. As all the necessary conditions (static, elastic, linearized geometric) are satisfied and the stresses of ALL concrete and steel bars fall within the tensile and compressive strengths, the results are acceptable. Usually, the proposed method exhibits a fast convergence in 4 - 5 repeats of structural analysis of the RC Shear Wall.
文摘Following the evolution of currently enforced Performance Based Design standards of reinforced concrete (RC) structures for durability, the designer, rather than complying with given prescriptive limits, may instead specify a cementitious mix design that is proven to exhibit a code prescribed resistance level (class) to a given exposure environment. Such compliance will lead to the protection of the steel reinforcement from corrosion and the cementitious mortar from degradation, during the design lifespan of the structure, under aggressive environmental exposure conditions such as, marine or deicing salts and carbonation. In this context, the enhancement of the physical and durability properties of common cement-based mortars under chloride exposure are experimentally investigated herein. In particular, the experimental program reported herein aims to evaluate the influence of incorporating multi-walled carbon nanotubes on the physical and mechanical properties of reinforced mortars against chloride ions. Furthermore, the anticorrosion protection of cementitious composites prepared with nanomaterials at 0.2% w/w is further investigated, by comparing all test results against reference specimens prepared without any additive. Electrochemical (Half-cell potential, corrosion current) and mass loss of reinforcement steel measurements were performed, while the porosity, capillary absorption and flexural strength were measured to evaluate the mechanical and durability characteristics of the mortars, following a period of exposure of eleven months;SEM images coupled with EDX analysis were further recorded and used for microstructure observation. The test results indicate that the inclusion of the nanomaterials in the mix improved the durability of the mortar specimens, while the nano-modified composites exhibited higher chloride penetration resistance and flexural strength than the corresponding values of the reference mortars. The test results and the comparison between nanomodified and reference mortars showed that the use of CNTs as addition led to protection of steel reinforcing bars against pitting corrosion and a significant improvement in flexural strength and porosity of the mortars.
基金This work was partly financial supported by the National Natural Science Foundation of China(Grant No.50678016).
文摘To overcome the problem that steel bars are put too close at a flame joint with special-shaped beam and column,mechanical performance of three groups of six RC flame joints with special-shaped(L,T and+)column and dispersed-steel bars-beam on the top floor under cyclic loads were studied.Experimental comparison was conducted between special-shaped(L,T and+)column and normal beams.The cracking load,yielding load,ultimate bearing capacity,failure patterns,and hysteretic properties at joint core area were investigated.The seismic behaviors of the joints with different proportions of dispersed-steelbar beams were analyzed.The results of experimental analysis indicate that the mechanical and seismic behaviors of frame joints with T-shaped and+-shaped column are nearly not changed when suitable proportion steel bars are dispersed to flange plane.Stiffness degeneration of flame joint with L-shaped column is rather serious due to concrete damage stiffness.Theoretical result indicates that distributing area of the dispersed steel-bar beams in the flange plate should be strictly controlled to avoid anchor destroy.
