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2020 Vol. 50, No. 6
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2020, 50(6): 1-5,28.
doi: 10.13204/j.gyjz202006001
Abstract:
In order to demonstrate the feasibility of eliminating foundation collapasibility for the two-way soil displacement screw pile (SDS pile) on self-weight collapsible loess, the compaction test of the single and group pile were carried out on the site of high-order deep thickness self-weight collapsible loess on the south coast of the Yellow River in Lanzhou.The deformation of soil around the single pile and the changes of physical and mechanical indexes of soil at different distances from the pile were measured; the changes of the physical and mechanical indexes and the bearing capacity of the soil among piles were measured.The research showed that the variable maximum range of soil properties treated by the SDS pile was in 2 times pile's diameter, the obvious influence range was 1.0 to 1.5 times pile's diameter; when the distance between piles was not more than 2.5 times diameter. The SDS pile could eliminate the collapsibility of the loess.
In order to demonstrate the feasibility of eliminating foundation collapasibility for the two-way soil displacement screw pile (SDS pile) on self-weight collapsible loess, the compaction test of the single and group pile were carried out on the site of high-order deep thickness self-weight collapsible loess on the south coast of the Yellow River in Lanzhou.The deformation of soil around the single pile and the changes of physical and mechanical indexes of soil at different distances from the pile were measured; the changes of the physical and mechanical indexes and the bearing capacity of the soil among piles were measured.The research showed that the variable maximum range of soil properties treated by the SDS pile was in 2 times pile's diameter, the obvious influence range was 1.0 to 1.5 times pile's diameter; when the distance between piles was not more than 2.5 times diameter. The SDS pile could eliminate the collapsibility of the loess.
2020, 50(6): 6-10.
doi: 10.13204/j.gyjz202006002
Abstract:
Based on full scale in-situ immersion tests of SDS piles, the results showed that as the compacting effect of SDS piles, the negative friction resistance of the single pile would be increased, informally called as "factting pile effect". Through research on change laws of collapsible coefficients for soil arround SDS piles, conclusions could obtain that arranging reasonable spacing between plies could eliminate the soil collapsibility between piles and improve bearing capacity of single piles. The SDS pile would be a kind effective improvment method for foundation design of high or superhigh buildings in collapsible loess zones.
Based on full scale in-situ immersion tests of SDS piles, the results showed that as the compacting effect of SDS piles, the negative friction resistance of the single pile would be increased, informally called as "factting pile effect". Through research on change laws of collapsible coefficients for soil arround SDS piles, conclusions could obtain that arranging reasonable spacing between plies could eliminate the soil collapsibility between piles and improve bearing capacity of single piles. The SDS pile would be a kind effective improvment method for foundation design of high or superhigh buildings in collapsible loess zones.
2020, 50(6): 11-15.
doi: 10.13204/j.gyjz202006003
Abstract:
Soil displacement screw(SDS)piles have been widely used in engineering fields, but the theoretical basis of design for SDS piles in collopsible loess zones was still absent. In order to explore the mechanical properties under immersion states, a full-scale immersion test of mechanical properties for SDS piles was carried out. The negative friction characteristics of two-way SDS piles along pile shafts under immersion were obtained.
Soil displacement screw(SDS)piles have been widely used in engineering fields, but the theoretical basis of design for SDS piles in collopsible loess zones was still absent. In order to explore the mechanical properties under immersion states, a full-scale immersion test of mechanical properties for SDS piles was carried out. The negative friction characteristics of two-way SDS piles along pile shafts under immersion were obtained.
2020, 50(6): 16-21.
doi: 10.13204/j.gyjz202006004
Abstract:
Tests have proved that in the collapsible loess, the use of the squeezing effect of soil displacement screw (SDS) piles in the process of pile formation, by adjusting the pile spacing, could not only eliminate the collapsibility of soil around piles, but also improve foundation bearing capacity. Through the fall scale test in site, the relevant design parameters of SDS-pile composite foundation in self-weight collapsible loess zones were preliminarily determined.
Tests have proved that in the collapsible loess, the use of the squeezing effect of soil displacement screw (SDS) piles in the process of pile formation, by adjusting the pile spacing, could not only eliminate the collapsibility of soil around piles, but also improve foundation bearing capacity. Through the fall scale test in site, the relevant design parameters of SDS-pile composite foundation in self-weight collapsible loess zones were preliminarily determined.
2020, 50(6): 29-38.
doi: 10.13204/j.gyjz202006006
Abstract:
The function structure of underground spaces in core zones of urban central railway stations (CAUCRS)is very complicated, and the cognition of its function structure still needs to be deepened. Based on the classification of underground spaces of CAUCRS, the spatial composition characteristics of the underground spaces of CAUCRS, including traffic service functions, commercial functions and integrated pipe corridors were summarized. Then, from the perspective of functional composition, the existing vertical hierarchical modes of underground spaces at home and abroad were analyzed. Finally, the principle of space planning and utilization of underground spaces in CAUCRS was put forward to provide reference for its integrated design.
The function structure of underground spaces in core zones of urban central railway stations (CAUCRS)is very complicated, and the cognition of its function structure still needs to be deepened. Based on the classification of underground spaces of CAUCRS, the spatial composition characteristics of the underground spaces of CAUCRS, including traffic service functions, commercial functions and integrated pipe corridors were summarized. Then, from the perspective of functional composition, the existing vertical hierarchical modes of underground spaces at home and abroad were analyzed. Finally, the principle of space planning and utilization of underground spaces in CAUCRS was put forward to provide reference for its integrated design.
2020, 50(6): 39-44,21.
doi: 10.13204/j.gyjz202006007
Abstract:
In order to study seismic properties of prestressed concrete beams in acid rain corrosion environment, the quasi-static loading tests on 8 prestressed concrete beam specimens were conducted, the failure modes of specimens and the characteristics of the hysteresis curve, skeleton curve, ductility, energy dissipation capacity and stiffness degradation of the beams with different parameters were studied, the effects of concrete strength grades, prestressed levels, and corrosion rates of steel strands on its seismic properties were discussed.The experiment study indicated that prestressed concrete beams during the loading process experienced the stage of elasticity, yield and failure; the hysteresis curves of the prestressed concrete beams were relatively full, the residual deformation was larger and the seismic behaviors were better. The corrosion rate of the steel strand had the greatest impact on the seismic properties. With the increase of the corrosion rate, the ultimate bearing capaicty of the test beams decreased, the hysteretic curve fullness and the cycles of loading decreased constantly.
In order to study seismic properties of prestressed concrete beams in acid rain corrosion environment, the quasi-static loading tests on 8 prestressed concrete beam specimens were conducted, the failure modes of specimens and the characteristics of the hysteresis curve, skeleton curve, ductility, energy dissipation capacity and stiffness degradation of the beams with different parameters were studied, the effects of concrete strength grades, prestressed levels, and corrosion rates of steel strands on its seismic properties were discussed.The experiment study indicated that prestressed concrete beams during the loading process experienced the stage of elasticity, yield and failure; the hysteresis curves of the prestressed concrete beams were relatively full, the residual deformation was larger and the seismic behaviors were better. The corrosion rate of the steel strand had the greatest impact on the seismic properties. With the increase of the corrosion rate, the ultimate bearing capaicty of the test beams decreased, the hysteretic curve fullness and the cycles of loading decreased constantly.
2020, 50(6): 45-50,104.
doi: 10.13204/j.gyjz202006008
Abstract:
In order to simplify the joint construction measures of the two-way truss reinforced concrete composite slab and improve the mechanical properties of the joint, three kinds of reinforced close joint were proposed:strengthened additional reinforcement joint, integral groove joint and interval groove joint. The static loading tests were conducted on three closely jointed composite slabs with different joint construction measures and one composite slab with post-cast strip. The failure modes, crack distribution, stiffness, ultimate bearing capacity and stress development of the joint reinforcement of each composite slab were compared and analyzed. The results showed that strengthening the joint reinforcement could improve the bearing capacity of the composite slabs with close joint; the integral groove and interval groove at the joint could not only control the centralized development of the mid-span cracks of the composite slabs with close joint, improve the crack distribution, but also effectively improve the bearing capacity and stiffness of the composite slabs, and its bearing capacity could reach more than 90% of the post-cast strip composite slabs. Based on the experimental results, the design suggestions and construction requirements of three kinds of strengthened close joint were put forward.
In order to simplify the joint construction measures of the two-way truss reinforced concrete composite slab and improve the mechanical properties of the joint, three kinds of reinforced close joint were proposed:strengthened additional reinforcement joint, integral groove joint and interval groove joint. The static loading tests were conducted on three closely jointed composite slabs with different joint construction measures and one composite slab with post-cast strip. The failure modes, crack distribution, stiffness, ultimate bearing capacity and stress development of the joint reinforcement of each composite slab were compared and analyzed. The results showed that strengthening the joint reinforcement could improve the bearing capacity of the composite slabs with close joint; the integral groove and interval groove at the joint could not only control the centralized development of the mid-span cracks of the composite slabs with close joint, improve the crack distribution, but also effectively improve the bearing capacity and stiffness of the composite slabs, and its bearing capacity could reach more than 90% of the post-cast strip composite slabs. Based on the experimental results, the design suggestions and construction requirements of three kinds of strengthened close joint were put forward.
2020, 50(6): 51-57.
doi: 10.13204/j.gyjz202006009
Abstract:
To study the shear and bending properties of the composite reinforced concrete slabs with reinforcement trusses under concentrated forces of small shear-span ratios, shear and bending tests on one composite reinforced concrete double-layer slab with three reinforcement trusses and one composite reinforced concrete slabs with four reinforcement trusses under two concentrated forces of shear-span ratio of 2.3 were conducted. The shear and bending failure phenomenon and mode, the relationship between bending moments and loading point deflection, the characteristic values of bending moments and mechanics model of cross-sections of composite reinforced concrete slabs under shear and bending moments were obtained. According to the shear strength of interface concrete of composite slabs, the formulas of shear and flexural capacity of composite slabs were deduced. The results showed that the failure mode of composite reinforced concrete slabs under concentrated loads of small shear-span ratio was up to the quantities of steel bar trusses in the interface of composite slabs, setting modes and setting positions. The ultimate shear or flexural capacity and the largest deflection of the composite reinforced concrete slab with four reinforced trusses respectively increased by 20.0% and decreased by 20.7% compared with that with three reinforced trusses, that was, the slab with four trusses was of better shear and flexural performance. The formula of ultimate shear and flexural capacity of composite reinforced concrete slabs were deduced based on the shear failure condition of composite slab interfaces, the calculated values were in good agreement with the test values.
To study the shear and bending properties of the composite reinforced concrete slabs with reinforcement trusses under concentrated forces of small shear-span ratios, shear and bending tests on one composite reinforced concrete double-layer slab with three reinforcement trusses and one composite reinforced concrete slabs with four reinforcement trusses under two concentrated forces of shear-span ratio of 2.3 were conducted. The shear and bending failure phenomenon and mode, the relationship between bending moments and loading point deflection, the characteristic values of bending moments and mechanics model of cross-sections of composite reinforced concrete slabs under shear and bending moments were obtained. According to the shear strength of interface concrete of composite slabs, the formulas of shear and flexural capacity of composite slabs were deduced. The results showed that the failure mode of composite reinforced concrete slabs under concentrated loads of small shear-span ratio was up to the quantities of steel bar trusses in the interface of composite slabs, setting modes and setting positions. The ultimate shear or flexural capacity and the largest deflection of the composite reinforced concrete slab with four reinforced trusses respectively increased by 20.0% and decreased by 20.7% compared with that with three reinforced trusses, that was, the slab with four trusses was of better shear and flexural performance. The formula of ultimate shear and flexural capacity of composite reinforced concrete slabs were deduced based on the shear failure condition of composite slab interfaces, the calculated values were in good agreement with the test values.
2020, 50(6): 58-66.
doi: 10.13204/j.gyjz202006010
Abstract:
Through the static loading test of 8 prestressed-concrete composite slabs with concrete-filled tubular steel trusses connected by close joints, the flexural behavior of the composite slabs in vertical direction of being prestressed was studied under uniformly distributed load, and the plane section assumption was verified. The results showed that the work performance of prestressed concrete composite slab with concrete-filled tubular steel trusses was good. The cracks of double-piece composite plate only appearred at the joint in the middle of the span, while the cracks of triple-piece or quadruple-piece composite plate appear closed. The anti-crack bars of joints had little effect on the improvement of cracking load, but they could share the stress of transverse stress reinforcement, significantly made the crack distribution evenly. The ultimate lood increased with the increase of the lamination thickness. The composite slab far away from the joint was in line with the assumption of plane section. Based on parametric analysis, the main influencing factors of bending stiffness in the vertical prestressing direction of the composite slab were analyzed as follows:the ratio of thickness of the prefabricated plate to that of the composite slab h/H and the width of the prefabricated plate b. Through nonlinear surface fitting, a formula for calculating the influence coefficient of vertical prestress direction stiffness was presented.
Through the static loading test of 8 prestressed-concrete composite slabs with concrete-filled tubular steel trusses connected by close joints, the flexural behavior of the composite slabs in vertical direction of being prestressed was studied under uniformly distributed load, and the plane section assumption was verified. The results showed that the work performance of prestressed concrete composite slab with concrete-filled tubular steel trusses was good. The cracks of double-piece composite plate only appearred at the joint in the middle of the span, while the cracks of triple-piece or quadruple-piece composite plate appear closed. The anti-crack bars of joints had little effect on the improvement of cracking load, but they could share the stress of transverse stress reinforcement, significantly made the crack distribution evenly. The ultimate lood increased with the increase of the lamination thickness. The composite slab far away from the joint was in line with the assumption of plane section. Based on parametric analysis, the main influencing factors of bending stiffness in the vertical prestressing direction of the composite slab were analyzed as follows:the ratio of thickness of the prefabricated plate to that of the composite slab h/H and the width of the prefabricated plate b. Through nonlinear surface fitting, a formula for calculating the influence coefficient of vertical prestress direction stiffness was presented.
2020, 50(6): 67-70.
doi: 10.13204/j.gyjz202006011
Abstract:
Based on the quasi-static test study of interion beam-column joints for prefabricated concrete frame cast by steel fiber concrete in site and interior beam-column joints cast by ordinary concrete in situ under the same condition, the failure characteristics, hysteretic curve, skeleton curve, stiffness degradation and bearing capacity degradation were analyzed. The results showed that, compared with that of the joints cast ordinary concrete in site, the bearing capacity and deformation capacity of the joints cast by steel fiber concrete in site were improved, the hysteretic performance was significantly improved, and the stiffness degradation of the joints was retarded and the bearing capacity reduction coefficient increased. The addition of steel fiber to the joints could improve the failure mode significantly, which could be conducive to the seismic resistance of the structure.
Based on the quasi-static test study of interion beam-column joints for prefabricated concrete frame cast by steel fiber concrete in site and interior beam-column joints cast by ordinary concrete in situ under the same condition, the failure characteristics, hysteretic curve, skeleton curve, stiffness degradation and bearing capacity degradation were analyzed. The results showed that, compared with that of the joints cast ordinary concrete in site, the bearing capacity and deformation capacity of the joints cast by steel fiber concrete in site were improved, the hysteretic performance was significantly improved, and the stiffness degradation of the joints was retarded and the bearing capacity reduction coefficient increased. The addition of steel fiber to the joints could improve the failure mode significantly, which could be conducive to the seismic resistance of the structure.
2020, 50(6): 71-78,110.
doi: 10.13204/j.gyjz202006012
Abstract:
In order to avoid the resonance damage of the friction pendulum isolation structure and the upper structure, a multi-stage frequency conversion friction pendulum isolation bearing with a variable curvature and friction coefficient arc sliding surface was developed. The mechanical properties and isolation mechanism were expounded. The theoretical analysis of the dynamic equilibrium equation showed that the natural vibration period of the multi-stage frequency conversion friction pendulum isolation bearing was only related to the friction coefficient μ of the frictional pendulum, the radius of the arc surface R and the horizontal displacement of the friction pendulum. The solid model was made, and the mechanical properties such as the restoring force model and friction coefficient were tested by experiments. The ABAQUS finite element software was used to simulate a 6-story frame structure set up by this isolation bearings. The dynamic responses of the structure under earthquake action before and after installing isolator were compared. The research showed that the multi-stage frequency conversion friction pendulum had good stability, frequency conversion capability, self-limiting and self-restoring capacity, and was suitable for multi-stage isolation scheme, which did not need to be equipped with a separate damper. The multi-stage frequency conversion friction pendulum showed the advantages of simple structure, convenient application and good isolation effect.
In order to avoid the resonance damage of the friction pendulum isolation structure and the upper structure, a multi-stage frequency conversion friction pendulum isolation bearing with a variable curvature and friction coefficient arc sliding surface was developed. The mechanical properties and isolation mechanism were expounded. The theoretical analysis of the dynamic equilibrium equation showed that the natural vibration period of the multi-stage frequency conversion friction pendulum isolation bearing was only related to the friction coefficient μ of the frictional pendulum, the radius of the arc surface R and the horizontal displacement of the friction pendulum. The solid model was made, and the mechanical properties such as the restoring force model and friction coefficient were tested by experiments. The ABAQUS finite element software was used to simulate a 6-story frame structure set up by this isolation bearings. The dynamic responses of the structure under earthquake action before and after installing isolator were compared. The research showed that the multi-stage frequency conversion friction pendulum had good stability, frequency conversion capability, self-limiting and self-restoring capacity, and was suitable for multi-stage isolation scheme, which did not need to be equipped with a separate damper. The multi-stage frequency conversion friction pendulum showed the advantages of simple structure, convenient application and good isolation effect.
2020, 50(6): 79-84.
doi: 10.13204/j.gyjz202006013
Abstract:
Concrete filled steel tube frame-core wall-outrigger truss structure system is adopted for buildings with asymmetric vertical setbacks. The seismic performance and damage distribution of the structures were analyzed by using elastic-plastic analysis under rare earthquake action. A three-dimensional numerical model was established, the influence of earthquake amplitude on the damage distribution of irregular high-rise structures was studied. The results indicated that the performance state of the core shear wall was slight damage, and earthquake energy could be dissipated by coupling beams entering to the plastic damage state. The outrigger floor and adjacent upper floors of high-rise structures with asymmetric vertical setbacks had severe damage, the shear wall with obvious damage should be reinforced. The floor slabs where the outriggers were located had a moderate damage caused by horizontal shear action, which should be strengthened. Damage development was more obvious under rare earthquake action than that of fortification earthquake action, but the location and trend of structural damage were more consistent. In conclusion, the seismic weak parts of high-rise structures with symmetric vertical setbacks should be analyzed based on the damage analysis under rare earthquake action.
Concrete filled steel tube frame-core wall-outrigger truss structure system is adopted for buildings with asymmetric vertical setbacks. The seismic performance and damage distribution of the structures were analyzed by using elastic-plastic analysis under rare earthquake action. A three-dimensional numerical model was established, the influence of earthquake amplitude on the damage distribution of irregular high-rise structures was studied. The results indicated that the performance state of the core shear wall was slight damage, and earthquake energy could be dissipated by coupling beams entering to the plastic damage state. The outrigger floor and adjacent upper floors of high-rise structures with asymmetric vertical setbacks had severe damage, the shear wall with obvious damage should be reinforced. The floor slabs where the outriggers were located had a moderate damage caused by horizontal shear action, which should be strengthened. Damage development was more obvious under rare earthquake action than that of fortification earthquake action, but the location and trend of structural damage were more consistent. In conclusion, the seismic weak parts of high-rise structures with symmetric vertical setbacks should be analyzed based on the damage analysis under rare earthquake action.
2020, 50(6): 85-92.
doi: 10.13204/j.gyjz202006014
Abstract:
Based on finite element method with concrete damaged plasticity model, a comprehensive study was carried out to investigate the effects of steel pipe diameter d, wall thickness of pipe t, diameter of pile D, length of pile H, and water cement ratio of grouting on the mechanical properties. The reliability of numerical simulation results was verified by test results. The results showed that with the increase of ratio of the diameter of steel pipe to pile d/D, the ultimate bearing capacity of the micro-steel-pipe piles increased correspondingly, and the critical values of d/D, which caused to the ultimate bearing capacity changed remarkably, were 0.28 and 0.72. Furthermore, the three dominant failure modes were indicated, they were steel pipe yield failure, steel pipe with outer grouting failure and grouting outside pipe failure. And then, the theoretical calculation formula for calculating the ultimate bearing capacity of micro-steel-pipe piles in three stages was obtained, and the theoretical calculation results were in good agreement with the experimental results and numerical simulation results. When the steel pipe diameter was the same and the thickness of the steel pipe wall increased, the axial load of the pile and the axial strain curve of the steel pipe tended to be softened for thinner wall of pipe, and then shifted to be ideal plasticity and hardening characteristics, and the ultimate bearing capacity of micro-steel-pipe pile increased linearly with the increase of the wall thickness. When the pipe diameter and the diameter ratio of the steel pipe to pile were the same, the grouting compressive strength was reduced by about 45%, the ultimate bearing capacity of the pile was only reduced by about 7.1%, it indicated that the grouting strength had no significant effect on the bearing capacity of the micro-steel-pipe piles.
Based on finite element method with concrete damaged plasticity model, a comprehensive study was carried out to investigate the effects of steel pipe diameter d, wall thickness of pipe t, diameter of pile D, length of pile H, and water cement ratio of grouting on the mechanical properties. The reliability of numerical simulation results was verified by test results. The results showed that with the increase of ratio of the diameter of steel pipe to pile d/D, the ultimate bearing capacity of the micro-steel-pipe piles increased correspondingly, and the critical values of d/D, which caused to the ultimate bearing capacity changed remarkably, were 0.28 and 0.72. Furthermore, the three dominant failure modes were indicated, they were steel pipe yield failure, steel pipe with outer grouting failure and grouting outside pipe failure. And then, the theoretical calculation formula for calculating the ultimate bearing capacity of micro-steel-pipe piles in three stages was obtained, and the theoretical calculation results were in good agreement with the experimental results and numerical simulation results. When the steel pipe diameter was the same and the thickness of the steel pipe wall increased, the axial load of the pile and the axial strain curve of the steel pipe tended to be softened for thinner wall of pipe, and then shifted to be ideal plasticity and hardening characteristics, and the ultimate bearing capacity of micro-steel-pipe pile increased linearly with the increase of the wall thickness. When the pipe diameter and the diameter ratio of the steel pipe to pile were the same, the grouting compressive strength was reduced by about 45%, the ultimate bearing capacity of the pile was only reduced by about 7.1%, it indicated that the grouting strength had no significant effect on the bearing capacity of the micro-steel-pipe piles.
2020, 50(6): 93-97,174.
doi: 10.13204/j.gyjz202006015
Abstract:
Considering the actual excavation conditions of the water-level fluctuation zone in the Three Gorges reservoir area, the effects of different pore water pressure cycles and unloading rates of confining pressure on the mechanical properties of sandstone were studied by the indoor triaxial unloading experiment. The results were as follows:1) the effect of the pore water pressure cycles and unloading rates of confining pressure on peak intensity of deviator stress and deformation modulus of sandstone was significant. The more the cycles, the smaller the peak intensity and deformation modulus; the faster the unloading rates, the larger the peak intensity and deformation modulus; 2) when destroyed, axial and circumferential rates of strain variations or peak confining pressure all increased with the increase of pore water pressure cycles and decreased with the increase of unloading rates of confining pressure, however, the impact on the circumferential was more obvious than the axial; 3)the rupture angles of the sandstone under 0.3 MPa pore water pressure were not relevant to the unloading rates of pore water pressure.
Considering the actual excavation conditions of the water-level fluctuation zone in the Three Gorges reservoir area, the effects of different pore water pressure cycles and unloading rates of confining pressure on the mechanical properties of sandstone were studied by the indoor triaxial unloading experiment. The results were as follows:1) the effect of the pore water pressure cycles and unloading rates of confining pressure on peak intensity of deviator stress and deformation modulus of sandstone was significant. The more the cycles, the smaller the peak intensity and deformation modulus; the faster the unloading rates, the larger the peak intensity and deformation modulus; 2) when destroyed, axial and circumferential rates of strain variations or peak confining pressure all increased with the increase of pore water pressure cycles and decreased with the increase of unloading rates of confining pressure, however, the impact on the circumferential was more obvious than the axial; 3)the rupture angles of the sandstone under 0.3 MPa pore water pressure were not relevant to the unloading rates of pore water pressure.
2020, 50(6): 98-104.
doi: 10.13204/j.gyjz202006016
Abstract:
Stratum subsidence due to dewatering will cause damage to buried beams such as municipal pipelines, underground pipe galleries and subway tunnels. With the increase of time and dewatering, the damage of being gradually aggravated will affect the safety. Based on the formula of logarithmic stratum settlement curve and the theory of elastic foundation beam, the analytical solutions for deformation and internal forces of buried beams were deduced, and a numerical solution was the obtained by the finite difference method. The results of examples showed that the analytical solution was much in accord with the numerical solution. These two solutions were verified by the calculating results of PLAXIS 3D FEM. The analytical solution was used to analyze the effect of parameters on deformation and internal forces of buried beams. The slope of the stratum subsidence funnel had the greatest effect on buried beams. Reducing the stratum subsidence funnel grade could reduce the damage to buried beams.
Stratum subsidence due to dewatering will cause damage to buried beams such as municipal pipelines, underground pipe galleries and subway tunnels. With the increase of time and dewatering, the damage of being gradually aggravated will affect the safety. Based on the formula of logarithmic stratum settlement curve and the theory of elastic foundation beam, the analytical solutions for deformation and internal forces of buried beams were deduced, and a numerical solution was the obtained by the finite difference method. The results of examples showed that the analytical solution was much in accord with the numerical solution. These two solutions were verified by the calculating results of PLAXIS 3D FEM. The analytical solution was used to analyze the effect of parameters on deformation and internal forces of buried beams. The slope of the stratum subsidence funnel had the greatest effect on buried beams. Reducing the stratum subsidence funnel grade could reduce the damage to buried beams.
2020, 50(6): 105-110.
doi: 10.13204/j.gyjz202006017
Abstract:
In order to study the anchorage mechanism of pressure cables more accurately, considering the anchor cable tunnel to be bent, based on the basic solution of Mindlin and the stress analysis of the plane stress state, the theoretical solution of shear stress at any point in the internal and external curves of the pressure anchor cable bending anchorage section were derived. A case was analyzed based on the existing research results, the results showed that the peak shear stress on the internal curve was larger than that on the external curve, the peak shear stress on the straight line was larger than that on the internal curve, and the prestressed loads and the radius of curvature were positively correlated with the shear stress distribution curve and the peak shear stress.
In order to study the anchorage mechanism of pressure cables more accurately, considering the anchor cable tunnel to be bent, based on the basic solution of Mindlin and the stress analysis of the plane stress state, the theoretical solution of shear stress at any point in the internal and external curves of the pressure anchor cable bending anchorage section were derived. A case was analyzed based on the existing research results, the results showed that the peak shear stress on the internal curve was larger than that on the external curve, the peak shear stress on the straight line was larger than that on the internal curve, and the prestressed loads and the radius of curvature were positively correlated with the shear stress distribution curve and the peak shear stress.
2020, 50(6): 111-116,38.
doi: 10.13204/j.gyjz202006018
Abstract:
The early-age mechanical properties of ultra-high pumping self-compacting concrete (SCC) have an extremely important impact on the formulation of construction scheme of ultra-high buildings, and are the basic key problems of construction mechanics of ultra-high buildings. Thirty standard cylindrical specimens of 150 mm×300 mm were produced in the same batch for ultra-high pumping SCC used in a 400-meter high-rise building. The mechanical properties of the specimens at early age were tested, the failure process and failure modes of the specimens were observed, and the axial load-displacement curve, compressive strength and elastic modulus were obtained. The variation of various performance indexes with age was analyzed. The formulas for calculating the strength and elastic modulus of ultra-high pumping SCC at early age and the stress-strain constitutive equation were presented. The results showed that the ultra-high pumping SCC had good integrity. With the increase of age, the falling section of the axial load-displacement curve became more and more steep, indicating that the brittleness of concrete increased. The change trends of the axial compressive strength and elastic modulus with age were similar, when the age was not longer than 21 d, the growth rate of elastic modulus was greater than that of compressive strength, when the age was at 21 d to 56 d, the growth rate of elastic modulus was less than that of compressive strength, and the calculated value was close to the measured value according to the formula of mechanical properties at early age proposed in the paper. When the age was not longer than 14 d, the deformation capacity of the concrete attenvated faster, and when the age was longer than 14 d, the deformation capacity changed little. The curves of the variable constitutive equation agreed well with the measured ones.
The early-age mechanical properties of ultra-high pumping self-compacting concrete (SCC) have an extremely important impact on the formulation of construction scheme of ultra-high buildings, and are the basic key problems of construction mechanics of ultra-high buildings. Thirty standard cylindrical specimens of 150 mm×300 mm were produced in the same batch for ultra-high pumping SCC used in a 400-meter high-rise building. The mechanical properties of the specimens at early age were tested, the failure process and failure modes of the specimens were observed, and the axial load-displacement curve, compressive strength and elastic modulus were obtained. The variation of various performance indexes with age was analyzed. The formulas for calculating the strength and elastic modulus of ultra-high pumping SCC at early age and the stress-strain constitutive equation were presented. The results showed that the ultra-high pumping SCC had good integrity. With the increase of age, the falling section of the axial load-displacement curve became more and more steep, indicating that the brittleness of concrete increased. The change trends of the axial compressive strength and elastic modulus with age were similar, when the age was not longer than 21 d, the growth rate of elastic modulus was greater than that of compressive strength, when the age was at 21 d to 56 d, the growth rate of elastic modulus was less than that of compressive strength, and the calculated value was close to the measured value according to the formula of mechanical properties at early age proposed in the paper. When the age was not longer than 14 d, the deformation capacity of the concrete attenvated faster, and when the age was longer than 14 d, the deformation capacity changed little. The curves of the variable constitutive equation agreed well with the measured ones.
2020, 50(6): 117-122.
doi: 10.13204/j.gyjz202006019
Abstract:
The variations of the temperature, humidity, salt frog and acid rain in Shenzhen area and their effects on durability of concrete structures were described. According to the survey and field test data of building durability in Shenzhen in the past 20 years, the classification weighted assessment method was adopted to evaluate the effect factors of durability. Then the durability damage grade of concrete structures was evaluated and the durability status of concrete structures in Shenzhen was obtained. The factors affecting durability of concrete structures in Shenzhen area, including corrosion rates of reinforcement bars, concentrations of Cl-, relative carbonation depths of concrete, area damage ratios, strength grades and crack widths, were fuzzily evaluated by the analytic hierarchy process, and the key factors were got.
The variations of the temperature, humidity, salt frog and acid rain in Shenzhen area and their effects on durability of concrete structures were described. According to the survey and field test data of building durability in Shenzhen in the past 20 years, the classification weighted assessment method was adopted to evaluate the effect factors of durability. Then the durability damage grade of concrete structures was evaluated and the durability status of concrete structures in Shenzhen was obtained. The factors affecting durability of concrete structures in Shenzhen area, including corrosion rates of reinforcement bars, concentrations of Cl-, relative carbonation depths of concrete, area damage ratios, strength grades and crack widths, were fuzzily evaluated by the analytic hierarchy process, and the key factors were got.
2020, 50(6): 123-127,134.
doi: 10.13204/j.gyjz202006020
Abstract:
Precast U-griders can effectively reduce the height of the line and traffic noise, and can be convenient to maintain. But for U-griders and other open thin-walled members, the beam will occur torsional deformation, which has the effect of bending and twisting except for bending deformation when the loading plane is not a longitudinal symmetry plane, including the centroid principal inertia plane. As the torsional stiffness and shear stiffness of U-griders are much smaller than those of closed thin-walled components or solid section members, it's easy for U-griders to occur torsion instability, resulting in unexpected engineering accidents. Therefore, it is necessary to further study the torsional shear stress and strain of the cross section. In transit of U-griders, there may be only three points of being supported (one point suspended in midair) due to the road irregularity, which will cause torsion deformation of beam concrete. The mechanical properties of U-griders under eccentric loads were studied, and the influence of the torsional shear stress on the structure of U-griders was analyzed, which could provide experimental and theoretical basis for the design of similar bridges.
Precast U-griders can effectively reduce the height of the line and traffic noise, and can be convenient to maintain. But for U-griders and other open thin-walled members, the beam will occur torsional deformation, which has the effect of bending and twisting except for bending deformation when the loading plane is not a longitudinal symmetry plane, including the centroid principal inertia plane. As the torsional stiffness and shear stiffness of U-griders are much smaller than those of closed thin-walled components or solid section members, it's easy for U-griders to occur torsion instability, resulting in unexpected engineering accidents. Therefore, it is necessary to further study the torsional shear stress and strain of the cross section. In transit of U-griders, there may be only three points of being supported (one point suspended in midair) due to the road irregularity, which will cause torsion deformation of beam concrete. The mechanical properties of U-griders under eccentric loads were studied, and the influence of the torsional shear stress on the structure of U-griders was analyzed, which could provide experimental and theoretical basis for the design of similar bridges.
2020, 50(6): 128-134.
doi: 10.13204/j.gyjz202006021
Abstract:
In order to investigate the mechanical properties of steel plates with round holes under repeated tensile and compressive loads, the numerical analysis for steel plates with round holes under four patterns of repeated tensile and compressive loads were carried out. The deformation patterns, stress-strain hysteretic curves and strength coefficients under the ultimate state were compared and analyzed. Then the influence laws of loading patterns, opening forms and diameters of holes on hysteretic performances of specimens were obtained. The results showed that the phenomena of stress concentration were occured surrounding round holes of steel plates under repeated tensile and compressive loads, and the phenomena of stress concentration under the tensile state was more obvious than that of the compressive state. The maximal strain values under the repeated loading were the dominated effect on degeneration of hysteretic properties of specimens, while the number of repeated loading cycles had less influence on degeneration of hysteretic performances. When the quantity and diameter of round holes were small, the effects of the openings on hysteretic properties of specimens were not obvious. While the quantity or diameter of round holes was bigger, the effects of the openings on hysteretic properties of specimens would become obvious.
In order to investigate the mechanical properties of steel plates with round holes under repeated tensile and compressive loads, the numerical analysis for steel plates with round holes under four patterns of repeated tensile and compressive loads were carried out. The deformation patterns, stress-strain hysteretic curves and strength coefficients under the ultimate state were compared and analyzed. Then the influence laws of loading patterns, opening forms and diameters of holes on hysteretic performances of specimens were obtained. The results showed that the phenomena of stress concentration were occured surrounding round holes of steel plates under repeated tensile and compressive loads, and the phenomena of stress concentration under the tensile state was more obvious than that of the compressive state. The maximal strain values under the repeated loading were the dominated effect on degeneration of hysteretic properties of specimens, while the number of repeated loading cycles had less influence on degeneration of hysteretic performances. When the quantity and diameter of round holes were small, the effects of the openings on hysteretic properties of specimens were not obvious. While the quantity or diameter of round holes was bigger, the effects of the openings on hysteretic properties of specimens would become obvious.
2020, 50(6): 135-143.
doi: 10.13204/j.gyjz202006022
Abstract:
Five high-strength steel T-stub connection specimens were designed, and the effect of welding seams of weld access hole liners on the fracture behaviors of beam-column joints was studied by loading and unloading cycle loading tests and finite element numerical analysis. Based on the research on T-stub connections, three specimens of steel frame beam-column joints were designed, and the fracture behaviors of beam-column joints was studied by the quasi-static loading test.The results indicated that welding seams of weld access hole liners of the high-strength steel T-stub connection had a significant effect on the fracture behaviors of the specimens. When weld access hole liners with double-sided weld or four-sided weld were adopted, the peak stresses in the welding seams could be moved to webs under ultimate loads. Compared with the specimens of the weld access hole liner with single-sided welding, the plastic deformation capacity of the specimens was improved significantly. The ductility and ultimate bearing capacity of steel frame beam-column joints were improved by changing the traditional weld of the weld access hole liner to double-sided or four-sided welding. Compared with the specimens of the weld access hole liner with single-sided weld, the ductility coefficients and ultimate bearing capacity of the specimens with double-sided weld increased about 29% and 23%, respectively; the ductility coefficients and ultimate bearing capacity of the specimens with four-sided welding increased about 70% and 33%, respectively.
Five high-strength steel T-stub connection specimens were designed, and the effect of welding seams of weld access hole liners on the fracture behaviors of beam-column joints was studied by loading and unloading cycle loading tests and finite element numerical analysis. Based on the research on T-stub connections, three specimens of steel frame beam-column joints were designed, and the fracture behaviors of beam-column joints was studied by the quasi-static loading test.The results indicated that welding seams of weld access hole liners of the high-strength steel T-stub connection had a significant effect on the fracture behaviors of the specimens. When weld access hole liners with double-sided weld or four-sided weld were adopted, the peak stresses in the welding seams could be moved to webs under ultimate loads. Compared with the specimens of the weld access hole liner with single-sided welding, the plastic deformation capacity of the specimens was improved significantly. The ductility and ultimate bearing capacity of steel frame beam-column joints were improved by changing the traditional weld of the weld access hole liner to double-sided or four-sided welding. Compared with the specimens of the weld access hole liner with single-sided weld, the ductility coefficients and ultimate bearing capacity of the specimens with double-sided weld increased about 29% and 23%, respectively; the ductility coefficients and ultimate bearing capacity of the specimens with four-sided welding increased about 70% and 33%, respectively.
2020, 50(6): 144-149.
doi: 10.13204/j.gyjz202006023
Abstract:
To exploring axial bearing capacity of circular hollow section steel K-joints strengthened by collar plates, the axial loading tests of two groups, totally four circular hollow section steel K-joints were conducted, the deformation and failure modes of the joints were studied. The effects of the brace to the chord diameter ratio β and collar plate reinforcement methods on the ultimate strength and load-displacement curves were analyzed. The research showed that the deformation and failure modes of the joints were characterized by plastic deformation of braces, local dents of chords, and brace fractures and weld cracking. The load increased rapidly at the initial stage of loading. As the actuator displacement increased, the load growth rate became slower and then the peak appeared, after that the load began to decrease. The increase of the β and the collar plate reinforcement had an obvious improvement on the ultimate strength of the K-joint, and the ultimate bearing capacity were respectively increased by at least 35% and 27%.
To exploring axial bearing capacity of circular hollow section steel K-joints strengthened by collar plates, the axial loading tests of two groups, totally four circular hollow section steel K-joints were conducted, the deformation and failure modes of the joints were studied. The effects of the brace to the chord diameter ratio β and collar plate reinforcement methods on the ultimate strength and load-displacement curves were analyzed. The research showed that the deformation and failure modes of the joints were characterized by plastic deformation of braces, local dents of chords, and brace fractures and weld cracking. The load increased rapidly at the initial stage of loading. As the actuator displacement increased, the load growth rate became slower and then the peak appeared, after that the load began to decrease. The increase of the β and the collar plate reinforcement had an obvious improvement on the ultimate strength of the K-joint, and the ultimate bearing capacity were respectively increased by at least 35% and 27%.
2020, 50(6): 150-155.
doi: 10.13204/j.gyjz202006024
Abstract:
Taking a substation framework with lightning rods in a 500 kV substation as an example, the full-scale static load test of the intersecting joint based on the original was designed and performed. The bearing capacity and strain distribution characteristics of the joint were analyzed. On this basis, a full-scale static load test of the reinforced intersecting joint was also conducted and compared with the former test. The results showed that the original designed intersecting joint of the lightning rod had poor flexural capacity and unreasonable details, which could be easily torn along the weld under the action of out-of-plane bending moment. When adding stiffeners to the joint, the problem of stress concentration on the joint could be effectively alleviated, resulting in a significant improvement of the bearing capacity and flexural stiffness of the strengthened joint.
Taking a substation framework with lightning rods in a 500 kV substation as an example, the full-scale static load test of the intersecting joint based on the original was designed and performed. The bearing capacity and strain distribution characteristics of the joint were analyzed. On this basis, a full-scale static load test of the reinforced intersecting joint was also conducted and compared with the former test. The results showed that the original designed intersecting joint of the lightning rod had poor flexural capacity and unreasonable details, which could be easily torn along the weld under the action of out-of-plane bending moment. When adding stiffeners to the joint, the problem of stress concentration on the joint could be effectively alleviated, resulting in a significant improvement of the bearing capacity and flexural stiffness of the strengthened joint.
2020, 50(6): 156-160,188.
doi: 10.13204/j.gyjz202006025
Abstract:
Four full-scale special-shaped composite steel concrete columns were tested under quasi-static loading, and the hysteretic curve, bearing capacity, displacement and ductility, stiffness degeneration and energy dissipation were analyzed. The results showed that compared with the full-scale special-shaped reinforced concrete column specimens, the addition of steel inside the specimens could slow down the development of cracks and reduce the damage degree of the specimens. Bending failure occurred when the special-shaped column specimen had a large shear-span to depth ratio. When the shear span to depth ratio was small, the shear failure occurred to the specimen. Compared with the full-scale special-shaped reinforced concrete column specimen, on a premise of ensuring the internal reinforcement ratio of the specimen, the addition of steel inside specimens could improve the seismic performance of specimens, including bearing capacity, hysteresis performance, deformation capacity, energy consumption capacity and stiffness degradation rate. When the longitudinal reinforcement ratio of the special-shaped reinforced concrete column was reduced and the steel was added inside specimens, the bearing capacity was improved.
Four full-scale special-shaped composite steel concrete columns were tested under quasi-static loading, and the hysteretic curve, bearing capacity, displacement and ductility, stiffness degeneration and energy dissipation were analyzed. The results showed that compared with the full-scale special-shaped reinforced concrete column specimens, the addition of steel inside the specimens could slow down the development of cracks and reduce the damage degree of the specimens. Bending failure occurred when the special-shaped column specimen had a large shear-span to depth ratio. When the shear span to depth ratio was small, the shear failure occurred to the specimen. Compared with the full-scale special-shaped reinforced concrete column specimen, on a premise of ensuring the internal reinforcement ratio of the specimen, the addition of steel inside specimens could improve the seismic performance of specimens, including bearing capacity, hysteresis performance, deformation capacity, energy consumption capacity and stiffness degradation rate. When the longitudinal reinforcement ratio of the special-shaped reinforced concrete column was reduced and the steel was added inside specimens, the bearing capacity was improved.
2020, 50(6): 161-166,149.
doi: 10.13204/j.gyjz202006026
Abstract:
In order to obtain the practical calculation formula of resistance to lateral stiffness of a new type lightweight composite steel frame wall filled with foam concrete, the monotonic loading test was conducted on DD-1, DD-1 (D-300) and DD-2 (D-400) respectively and the quasi-static loading test was carried out on DZ-1 (D-300) and DZ-2 (D-400) repeatedly. The equivalent tension and compression bars were simplified for the steel mesh skin plate and the equivalent compression bar was simplified for the foam concrete. Using the displacement method to deduce the lateral stiffness calculation formula, and then the DD-1's test results were used to validate the lateral stiffness calculation formula of lightweight composite steel frame wall covered with steel grid skin plate, using the test results of DD-1 (D-300), DD-2 (D-400), DZ-1(D-300), DZ-2 (D-400) to obtain the stiffness correction factor of the equivalent compression bar of foam concrete, and then obtain the lateral stiffness calculation formula for the new composite wall. The results showed that the calculation results obtained by the displacement method were in good agreement with the test results.
In order to obtain the practical calculation formula of resistance to lateral stiffness of a new type lightweight composite steel frame wall filled with foam concrete, the monotonic loading test was conducted on DD-1, DD-1 (D-300) and DD-2 (D-400) respectively and the quasi-static loading test was carried out on DZ-1 (D-300) and DZ-2 (D-400) repeatedly. The equivalent tension and compression bars were simplified for the steel mesh skin plate and the equivalent compression bar was simplified for the foam concrete. Using the displacement method to deduce the lateral stiffness calculation formula, and then the DD-1's test results were used to validate the lateral stiffness calculation formula of lightweight composite steel frame wall covered with steel grid skin plate, using the test results of DD-1 (D-300), DD-2 (D-400), DZ-1(D-300), DZ-2 (D-400) to obtain the stiffness correction factor of the equivalent compression bar of foam concrete, and then obtain the lateral stiffness calculation formula for the new composite wall. The results showed that the calculation results obtained by the displacement method were in good agreement with the test results.
2020, 50(6): 167-174.
doi: 10.13204/j.gyjz202006027
Abstract:
In order to investigated the influence of volume content of steel fibers and longitudinal reinforcement ratio on the bending behaviour of recycled aggregate concrete beams mixed with steel Fibers reinforced with BFRP bars, the bending performance tests of seven beams were carried out. The results showed that the volume content of steel fibers and reinforcement rate both had a certain influence on the flexural capacity of recycled aggregate concrete beams mixed with steel fibers reinfored with BFRP bars. Compared with the recycled aggregate concrete beams reinforced with BFRP bars without steel fibers, the initial crack load and ultimate load of the test beams with 1.0% steel fibers volume content were increased by 32.8% and 18.2% respectively. With the increase of the contents of BFRP bars, the flexural capacity of recycled aggregate concrete beams reinforced with BFRP bars increased significantly. In addition, based on the experiments, the paper also combined with the relevant current norms and theories to verify the flexural capacity, deflection and crack width of the recycled aggregate concrete beams reinforced with BFRP bars, and compared the experimental values with the theoretical calculation results.
In order to investigated the influence of volume content of steel fibers and longitudinal reinforcement ratio on the bending behaviour of recycled aggregate concrete beams mixed with steel Fibers reinforced with BFRP bars, the bending performance tests of seven beams were carried out. The results showed that the volume content of steel fibers and reinforcement rate both had a certain influence on the flexural capacity of recycled aggregate concrete beams mixed with steel fibers reinfored with BFRP bars. Compared with the recycled aggregate concrete beams reinforced with BFRP bars without steel fibers, the initial crack load and ultimate load of the test beams with 1.0% steel fibers volume content were increased by 32.8% and 18.2% respectively. With the increase of the contents of BFRP bars, the flexural capacity of recycled aggregate concrete beams reinforced with BFRP bars increased significantly. In addition, based on the experiments, the paper also combined with the relevant current norms and theories to verify the flexural capacity, deflection and crack width of the recycled aggregate concrete beams reinforced with BFRP bars, and compared the experimental values with the theoretical calculation results.
2020, 50(6): 175-182.
doi: 10.13204/j.gyjz202006028
Abstract:
The prestress loss of concrete structure reinforced with prestressed carbon fiber reinforced plastics (CFRP) is an important factor affecting the reinforcing effect. In order to study the prestress loss law of large-sized concrete column strengthened with prestressed carbon fiber reinforced plastics (CFRP). According to the law, the CFRP was strengthened annularly by self-locking anchorage. The test results showed that friction loss was the main loss in tension process. The larger the prestress, the rougher the surface of the column and the larger the size of the section of the column, the greater the friction loss. The prestressing loss was caused by the deformation of anchorage, the shrinkage of CFRP sheets and the relaxation of CFRP sheets. The friction loss in tension process accounted for 70.9% to 80.8% of the total loss of CFRP sheets, while the loss after loading accounted for 19.2% to 29.1% of the total loss. Under the same conditions, the total CFRP loss of 1 m diameter column was 17.1% to 17.5% higher than that of 0.305 m diameter column. On the basis of experiments, the formulas for calculating the prestress loss during tension and loading were presented, which could provide a reference for calculating prestress loss.
The prestress loss of concrete structure reinforced with prestressed carbon fiber reinforced plastics (CFRP) is an important factor affecting the reinforcing effect. In order to study the prestress loss law of large-sized concrete column strengthened with prestressed carbon fiber reinforced plastics (CFRP). According to the law, the CFRP was strengthened annularly by self-locking anchorage. The test results showed that friction loss was the main loss in tension process. The larger the prestress, the rougher the surface of the column and the larger the size of the section of the column, the greater the friction loss. The prestressing loss was caused by the deformation of anchorage, the shrinkage of CFRP sheets and the relaxation of CFRP sheets. The friction loss in tension process accounted for 70.9% to 80.8% of the total loss of CFRP sheets, while the loss after loading accounted for 19.2% to 29.1% of the total loss. Under the same conditions, the total CFRP loss of 1 m diameter column was 17.1% to 17.5% higher than that of 0.305 m diameter column. On the basis of experiments, the formulas for calculating the prestress loss during tension and loading were presented, which could provide a reference for calculating prestress loss.
2020, 50(6): 183-188.
doi: 10.13204/j.gyjz202006029
Abstract:
In order to study the influence of carbon fiber reinforced ploymer (CFRP) sheets on the mechanical properties of concrete-filled glass fiber reinforced ploymer (GFRP) short columns strengthened with CFRP sheets, the experimental research on the design parameters of CFRP sheets layers and concrete strength grades was carried out. The failure modes, ultimate bearing capacity, load-displacement curves and load-strain curves of the specimens were obtained. The ultimate bearing capacity, ductility and stiffness of the pultruded GFRP tubes concrete short columns were analyzed. The results showed that the ultimate bearing capacity of the pultruded GFRP tubes concrete short column was obviously improved after CFRP sheets reinforcement. When the layers of the reinforced CFRP sheet were 3, the average ultimate bearing capacity of the specimens increased by 116.93%, and the failure modes of the specimens were changed from brittle failure to ductile failure with the increase of CFRP layer. When the specimen failed, the side wall cracking damage gradually turned to the end damage, and the ductility was improved. Keeping the wall-thickness (t) of the pultruded GFRP tube at 5 mm, when the aspect ratio (H/B) of the pultruded GFRP tube was 2.25 and the aspect ratio (B/t) was 20, the overall deformation capacity of the specimens with the concrete strength grade C30 had better deformation capacity and the ultimate bearing capacity which was significantly higher than the concrete strength grades C20 and C40.
In order to study the influence of carbon fiber reinforced ploymer (CFRP) sheets on the mechanical properties of concrete-filled glass fiber reinforced ploymer (GFRP) short columns strengthened with CFRP sheets, the experimental research on the design parameters of CFRP sheets layers and concrete strength grades was carried out. The failure modes, ultimate bearing capacity, load-displacement curves and load-strain curves of the specimens were obtained. The ultimate bearing capacity, ductility and stiffness of the pultruded GFRP tubes concrete short columns were analyzed. The results showed that the ultimate bearing capacity of the pultruded GFRP tubes concrete short column was obviously improved after CFRP sheets reinforcement. When the layers of the reinforced CFRP sheet were 3, the average ultimate bearing capacity of the specimens increased by 116.93%, and the failure modes of the specimens were changed from brittle failure to ductile failure with the increase of CFRP layer. When the specimen failed, the side wall cracking damage gradually turned to the end damage, and the ductility was improved. Keeping the wall-thickness (t) of the pultruded GFRP tube at 5 mm, when the aspect ratio (H/B) of the pultruded GFRP tube was 2.25 and the aspect ratio (B/t) was 20, the overall deformation capacity of the specimens with the concrete strength grade C30 had better deformation capacity and the ultimate bearing capacity which was significantly higher than the concrete strength grades C20 and C40.
2020, 50(6): 189-195.
doi: 10.13204/j.gyjz202006030
Abstract:
As a country with numerous heritages, Italy has a well-established management system for protected heritage areas. Based on the analysis of the value of Ivrea's industrial heritage and the unscrambling of adaptive protection strategies, the paper expounded the significance of public cognitive platform, sound conservation management plan and continuation of industrial spirit for the development of industrial heritage. For the purpose of studying the protection mode of industrial heritage, the paper adopted the methods of literature research and case study to explore its contribution to the protection of industrial heritage in China into provide reference and reflection.
As a country with numerous heritages, Italy has a well-established management system for protected heritage areas. Based on the analysis of the value of Ivrea's industrial heritage and the unscrambling of adaptive protection strategies, the paper expounded the significance of public cognitive platform, sound conservation management plan and continuation of industrial spirit for the development of industrial heritage. For the purpose of studying the protection mode of industrial heritage, the paper adopted the methods of literature research and case study to explore its contribution to the protection of industrial heritage in China into provide reference and reflection.
