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2021 Vol. 51, No. 9
Display Method:
2021, 51(9): 1-8,137.
doi: 10.13204/j.gyjzG20082306
Abstract:
Based on the previous finite element analysis, the experiment took the position of the middle column on the lower shoulder beam as the main variable, and three specimens were designed to study the mechanical properties of double-layer shoulder beams with double-limb side columns. The monotonic loading test was conducted on the specimens. According to the test results, the yield mechanism, failure mode, bearing capacity and the force of the specimen's main parts were analyzed. The results showed that the yield of the specimen was triggered by the shear yield of inner limb side webs of lower shoulder beams, and the failure was caused by the large convex curvature deformation of inner limb side webs of the lower shoulder beams. In accordance with the yield of the measure points at the corners of inner limb webs of lower shoulder beams and load displacement curves, the yield load values of the members were determined. When the position of the middle column was shifted to the outside, the shear force of inner limbs of the lower shoulder beams decreased, and the bearing capacity of specimens improved.
Based on the previous finite element analysis, the experiment took the position of the middle column on the lower shoulder beam as the main variable, and three specimens were designed to study the mechanical properties of double-layer shoulder beams with double-limb side columns. The monotonic loading test was conducted on the specimens. According to the test results, the yield mechanism, failure mode, bearing capacity and the force of the specimen's main parts were analyzed. The results showed that the yield of the specimen was triggered by the shear yield of inner limb side webs of lower shoulder beams, and the failure was caused by the large convex curvature deformation of inner limb side webs of the lower shoulder beams. In accordance with the yield of the measure points at the corners of inner limb webs of lower shoulder beams and load displacement curves, the yield load values of the members were determined. When the position of the middle column was shifted to the outside, the shear force of inner limbs of the lower shoulder beams decreased, and the bearing capacity of specimens improved.
2021, 51(9): 9-15,131.
doi: 10.13204/j.gyjzG20082313
Abstract:
In order to study the design method of double shoulder beams with double-limb side columns, four finite element models of double shoulder beams with double-limb side columns were constructed. The finite element numerical simulation method was adopted. The height of upper shoulder beams, center distance of inner limbs of middle columns, height-span ratio of lower shoulder beams, height of inner limbs of middle columns and section height of inner limbs of middle columns were taken as parameters to determine the bearing capacity, failure mode and internal force distribution in double-layer shoulder beams of side column. The influence of the laws were studied. The results showed that:when the side webs of inner limbs yielded first, the elastic bearing capacity of the members was equaled the bearing capacity of the full section yield of the side webs of the inner limb; when the full section of side webs of outer limbs yielded first, the elastic bearing capacity of the members could be conservatively taken as the corresponding elastic bearing capacity when the internal and external shear forces of the shoulder beam were equal. The shear force calculation of the inner limb of the lower shoulder beam was the same as that of the single-layer shoulder beam; and the shear calculation formula of the main section of the lower shoulder beam in different conditions was given, and the critical value of the shear force on both sides of the lower shoulder beam was deduced, which was used to determine the yield order of the inner and outer sides of the lower shoulder beam. Combined with the characteristics of cross-section stress distribution, the design method of double-layer shoulder beams was proposed.
In order to study the design method of double shoulder beams with double-limb side columns, four finite element models of double shoulder beams with double-limb side columns were constructed. The finite element numerical simulation method was adopted. The height of upper shoulder beams, center distance of inner limbs of middle columns, height-span ratio of lower shoulder beams, height of inner limbs of middle columns and section height of inner limbs of middle columns were taken as parameters to determine the bearing capacity, failure mode and internal force distribution in double-layer shoulder beams of side column. The influence of the laws were studied. The results showed that:when the side webs of inner limbs yielded first, the elastic bearing capacity of the members was equaled the bearing capacity of the full section yield of the side webs of the inner limb; when the full section of side webs of outer limbs yielded first, the elastic bearing capacity of the members could be conservatively taken as the corresponding elastic bearing capacity when the internal and external shear forces of the shoulder beam were equal. The shear force calculation of the inner limb of the lower shoulder beam was the same as that of the single-layer shoulder beam; and the shear calculation formula of the main section of the lower shoulder beam in different conditions was given, and the critical value of the shear force on both sides of the lower shoulder beam was deduced, which was used to determine the yield order of the inner and outer sides of the lower shoulder beam. Combined with the characteristics of cross-section stress distribution, the design method of double-layer shoulder beams was proposed.
2021, 51(9): 16-23,81.
doi: 10.13204/j.gyjzG20082308
Abstract:
Targeted at a new type of double-layer shoulder beams with double-limb middle columns of concrete-filled steel tubes (CFST), the failure process, failure mode and strain distribution of two specimens were studied by in-plane uniaxial loading test. The results showed that under the action of horizontal forces, most of the load was transferred to the lower shoulder beam of specimens, and finally shear failure occured at the grid web in the compression zone of the lower shoulder beam. The ductility of specimens was excellent, and the horizontal bearing capacity of specimens largely depended on the section of the web for the lower shoulder beam; the shear strain was mainly controlled by the upper and lower webs of the shoulder beam for specimens, and the strain distribution near the weld joint was different from that obtained by theory. The strain concentration existed at the flange of the shoulder beam. Based on the analysis results, the calculation model and formula for the horizontal bearing capacity of the double-layer shoulder beam with double-limb middle columns of concrete-filled steel tubes were proposed.
Targeted at a new type of double-layer shoulder beams with double-limb middle columns of concrete-filled steel tubes (CFST), the failure process, failure mode and strain distribution of two specimens were studied by in-plane uniaxial loading test. The results showed that under the action of horizontal forces, most of the load was transferred to the lower shoulder beam of specimens, and finally shear failure occured at the grid web in the compression zone of the lower shoulder beam. The ductility of specimens was excellent, and the horizontal bearing capacity of specimens largely depended on the section of the web for the lower shoulder beam; the shear strain was mainly controlled by the upper and lower webs of the shoulder beam for specimens, and the strain distribution near the weld joint was different from that obtained by theory. The strain concentration existed at the flange of the shoulder beam. Based on the analysis results, the calculation model and formula for the horizontal bearing capacity of the double-layer shoulder beam with double-limb middle columns of concrete-filled steel tubes were proposed.
2021, 51(9): 24-32.
doi: 10.13204/j.gyjzG20082311
Abstract:
In order to study the mechanical property and failure mode of double-layer shoulder beams, so as to provide theoretical support for the design of the double-layer shoulder beam, three specimens of double-layer shoulder beams with triple-limb side columns were designed and tested under monotonic loading. By changing the action position of the inner limb of the middle column on the lower shoulder beam, the effects on the yield load, strain of the main parts, yield mechanism and failure mode of specimens were analyzed. The results showed that the yield of the inner limb web of the lower shoulder beam was the control factor of the yield load for specimens, which could reflect the yield of specimens very well. The yield load of specimens could be determined by the yield of web plates; the bearing capacity of the double shoulder beam was improved in the process of outer shift for inner limbs of middle columns; the failure of specimens was due to the shear type convex deformation of side webs for inner limbs of lower shoulder beams.
In order to study the mechanical property and failure mode of double-layer shoulder beams, so as to provide theoretical support for the design of the double-layer shoulder beam, three specimens of double-layer shoulder beams with triple-limb side columns were designed and tested under monotonic loading. By changing the action position of the inner limb of the middle column on the lower shoulder beam, the effects on the yield load, strain of the main parts, yield mechanism and failure mode of specimens were analyzed. The results showed that the yield of the inner limb web of the lower shoulder beam was the control factor of the yield load for specimens, which could reflect the yield of specimens very well. The yield load of specimens could be determined by the yield of web plates; the bearing capacity of the double shoulder beam was improved in the process of outer shift for inner limbs of middle columns; the failure of specimens was due to the shear type convex deformation of side webs for inner limbs of lower shoulder beams.
2021, 51(9): 33-40,149.
doi: 10.13204/j.gyjzG20082305
Abstract:
Due to the special structure of double-layer shoulder beams with triple-limb middle columns, the internal force distribution is different from that of double-layer shoulder beams with double-limb or quadruple-limb middle columns. To construct the calculation formula of horizontal bearing capacity of double-layer shoulder beams with triple-limb middle columns, 42 models were designed on the basis of tests and finite element study. The key parameters influencing the horizontal bearing capacity of double-layer shoulder beams with triple-limb middle columns were analyzed by finite element method. The section height ratio of upper layers to lower layers (the height ratio), section height ratio of middle columns to lower layer shoulder beams (the column-beam height ratio) were discussed, the influence of the span-height ratio of the lower shoulder beam (the span-height ratio) on the horizontal bearing capacity of double shoulder beams with three-limb middle columns was studied. The characteristic bearing capacity and displacement of the model were analyzed, and the range of parameters was given. The results showed that the height ratio had little effect on the bearing capacity of the model; the larger the height ratio of the column and beam was, the greater the characteristic bearing capacity was; the larger the span-height ratio was, the greater the bearing capacity of the model was, but the faster the bearing capacity decreased in the later stage. Based on the analysis results, three failure modes and horizontal bearing capacity formulas of the double-layer shoulder beam with triple-limb middle columns were proposed, and the error of the formula was corrected based on the ductile failure of the model.
Due to the special structure of double-layer shoulder beams with triple-limb middle columns, the internal force distribution is different from that of double-layer shoulder beams with double-limb or quadruple-limb middle columns. To construct the calculation formula of horizontal bearing capacity of double-layer shoulder beams with triple-limb middle columns, 42 models were designed on the basis of tests and finite element study. The key parameters influencing the horizontal bearing capacity of double-layer shoulder beams with triple-limb middle columns were analyzed by finite element method. The section height ratio of upper layers to lower layers (the height ratio), section height ratio of middle columns to lower layer shoulder beams (the column-beam height ratio) were discussed, the influence of the span-height ratio of the lower shoulder beam (the span-height ratio) on the horizontal bearing capacity of double shoulder beams with three-limb middle columns was studied. The characteristic bearing capacity and displacement of the model were analyzed, and the range of parameters was given. The results showed that the height ratio had little effect on the bearing capacity of the model; the larger the height ratio of the column and beam was, the greater the characteristic bearing capacity was; the larger the span-height ratio was, the greater the bearing capacity of the model was, but the faster the bearing capacity decreased in the later stage. Based on the analysis results, three failure modes and horizontal bearing capacity formulas of the double-layer shoulder beam with triple-limb middle columns were proposed, and the error of the formula was corrected based on the ductile failure of the model.
2021, 51(9): 41-46,165.
doi: 10.13204/j.gyjzG20082303
Abstract:
In order to study the mechanical properties of double-layer shoulder beams with multi-limbe middle columns of concrete-filled steel tubes (CFST) subjected to braking loads,six specimens of double-layer shoulder beams with multi-limb middle columns of CFST were designed in combination with practical projects.Considering the influence of welding on the mechanical properties of specimens, the intersection of multiple welds was selected for finite element analysis.The results showed that the temperature and stress within 4 cm from the multi-weld junction changed significantly, and the deformation after welding was large, which had a great impact on the mechanical properties of specimens. Therefore, the secondary weld bead should be disconnected in the process of welding of specimens, and the minimum distance between the secondary weld bead and the main weld bead should be no less than 4 cm.At the same time, the fabrication method of shoulder beam specimens was analyzed in detail to minimize the influence of specimen fabrication on its mechanical properties.
In order to study the mechanical properties of double-layer shoulder beams with multi-limbe middle columns of concrete-filled steel tubes (CFST) subjected to braking loads,six specimens of double-layer shoulder beams with multi-limb middle columns of CFST were designed in combination with practical projects.Considering the influence of welding on the mechanical properties of specimens, the intersection of multiple welds was selected for finite element analysis.The results showed that the temperature and stress within 4 cm from the multi-weld junction changed significantly, and the deformation after welding was large, which had a great impact on the mechanical properties of specimens. Therefore, the secondary weld bead should be disconnected in the process of welding of specimens, and the minimum distance between the secondary weld bead and the main weld bead should be no less than 4 cm.At the same time, the fabrication method of shoulder beam specimens was analyzed in detail to minimize the influence of specimen fabrication on its mechanical properties.
2021, 51(9): 47-55,74.
doi: 10.13204/j.gyjzG20082310
Abstract:
In order to construct the calculation formula for the horizontal bearing capacity of double-layer shoulder beams with double-limb or quadruple-limb middle columns of concrete-filled steel tubes (CFST). Based on the results of previous tests and finite element simulations, 43 and 44 models of two kinds of double-layer shoulder beams were designed respectively. From the aspects of characteristic bearing capacity and displacement of the models, the section height ratio (the height ratio) of the upper layer to lower layer shoulder beams, the section height ratio of middle columns to lower layer shoulder beams (the column-beam height ratio), and the ratio of the long span or short span to the height of the lower shoulder beam (the span-height ratio) were analyzed, and the range of the parameters was given. The results showed that the horizontal bearing capacity of the two kinds of double-layer shoulder beams was similar in the change of parameters; with the increase of the height ratio of columns to beams, the model stiffness increased, the yield displacement decreased, and the bearing capacity increased in a parabola; with the increase of the span-height ratio, the bearing capacity of the model increased linearly, but the ductility became worse; with the increase of the ratio of the short span to the height, the flange area of the model for the double-layer shoulder beam with four-limb middle column increased, and the bearing capacity would increased slightly. Based on the results of parameter analysis, the load-shared proportion in each section was determined, and the formula for calculating the horizontal bearing capacity of the model was proposed, and the formula was modified based on the ductile failure.
In order to construct the calculation formula for the horizontal bearing capacity of double-layer shoulder beams with double-limb or quadruple-limb middle columns of concrete-filled steel tubes (CFST). Based on the results of previous tests and finite element simulations, 43 and 44 models of two kinds of double-layer shoulder beams were designed respectively. From the aspects of characteristic bearing capacity and displacement of the models, the section height ratio (the height ratio) of the upper layer to lower layer shoulder beams, the section height ratio of middle columns to lower layer shoulder beams (the column-beam height ratio), and the ratio of the long span or short span to the height of the lower shoulder beam (the span-height ratio) were analyzed, and the range of the parameters was given. The results showed that the horizontal bearing capacity of the two kinds of double-layer shoulder beams was similar in the change of parameters; with the increase of the height ratio of columns to beams, the model stiffness increased, the yield displacement decreased, and the bearing capacity increased in a parabola; with the increase of the span-height ratio, the bearing capacity of the model increased linearly, but the ductility became worse; with the increase of the ratio of the short span to the height, the flange area of the model for the double-layer shoulder beam with four-limb middle column increased, and the bearing capacity would increased slightly. Based on the results of parameter analysis, the load-shared proportion in each section was determined, and the formula for calculating the horizontal bearing capacity of the model was proposed, and the formula was modified based on the ductile failure.
2021, 51(9): 56-64.
doi: 10.13204/j.gyjzG21032705
Abstract:
Some historical settlements with characteristics were found in the Xijiang River basin by an analysis of literatures, maps, fields and aerial photographies. Based on deep analysis of its forms, origins, site selection, defense measures, the similarity of labyrinthine cultural pattern settlements in the Xijiang River basin was obtained. The village construction of the settlements had a similar history and the concepts of sites were similar, and the military defense principles were also used to guide the settlement construction, which ensured the development of settlements complete and sustainable. The labyrinth patterns were divided by three types:vertical and horizontal, radial and disordered labyrinths. By an analysis of the relation between the cultural patterns of settlement labyrinths and settlement defense, it was found that both of them had the characteristics of boundary enclosing, intensive texture and complicated road systems, and the relation of isomorphism and coupling was between settlement patterns and defense forms. The planning and construction of labyrinthine pattern settlements had the typical defensive purposes, and the labyrinth patterns and various defense principles were used to ensure the security of settlements. The surface of the labyrinthine pattern settlements in the Xijiang River basin was the convergence of settlement forms to the labyrinthine culture patterns, and its essence was the exploration of the optimal mode of defense and survival for settlements, and the responses to the optimal survival mode of settlements at the level of settlement patterns.
Some historical settlements with characteristics were found in the Xijiang River basin by an analysis of literatures, maps, fields and aerial photographies. Based on deep analysis of its forms, origins, site selection, defense measures, the similarity of labyrinthine cultural pattern settlements in the Xijiang River basin was obtained. The village construction of the settlements had a similar history and the concepts of sites were similar, and the military defense principles were also used to guide the settlement construction, which ensured the development of settlements complete and sustainable. The labyrinth patterns were divided by three types:vertical and horizontal, radial and disordered labyrinths. By an analysis of the relation between the cultural patterns of settlement labyrinths and settlement defense, it was found that both of them had the characteristics of boundary enclosing, intensive texture and complicated road systems, and the relation of isomorphism and coupling was between settlement patterns and defense forms. The planning and construction of labyrinthine pattern settlements had the typical defensive purposes, and the labyrinth patterns and various defense principles were used to ensure the security of settlements. The surface of the labyrinthine pattern settlements in the Xijiang River basin was the convergence of settlement forms to the labyrinthine culture patterns, and its essence was the exploration of the optimal mode of defense and survival for settlements, and the responses to the optimal survival mode of settlements at the level of settlement patterns.
2021, 51(9): 65-74.
doi: 10.13204/j.gyjzG20072313
Abstract:
As an important content of public service facilities carrying public resources and social equity, the equity of distribution for the supporting facilities directly influences the equity of residents' access to public resources. Therefore, based on the planning of community life circles and the comprehensive consideration of service levels, accessibility, social equity performances and other measurement indicators, a equity evaluation model was established for the distribution of elderly care facilities in community life circles based on the ArcGIS platform. The equity evaluation and analysis of the distribution of elderly care facilities in Yuhua District showed that:1) the supply level of elderly care facilities in Yuhua District of Changsha City was uneven, and the service level of each unit varied greatly, showing the characteristics of gradual decline along the South Second Ring Road and other roads; 2) the accessible of elderly care facilities varied greatly between different service areas, showing a downward trend from the central urban area to the outskirts; 3) there was a "spatial mismatch" between the distribution of elderly care facilities and the distribution of the elderly population, only a small number of the elderly people could enjoy more resources of elderly care facilities, and at the same time, the level of facility services and the number of per capita resources were not equal. In responses to the above problems, it was recommended to implement a planning strategy of community life circles, that was "evaluation first, partitions between service domains, facility classification".
As an important content of public service facilities carrying public resources and social equity, the equity of distribution for the supporting facilities directly influences the equity of residents' access to public resources. Therefore, based on the planning of community life circles and the comprehensive consideration of service levels, accessibility, social equity performances and other measurement indicators, a equity evaluation model was established for the distribution of elderly care facilities in community life circles based on the ArcGIS platform. The equity evaluation and analysis of the distribution of elderly care facilities in Yuhua District showed that:1) the supply level of elderly care facilities in Yuhua District of Changsha City was uneven, and the service level of each unit varied greatly, showing the characteristics of gradual decline along the South Second Ring Road and other roads; 2) the accessible of elderly care facilities varied greatly between different service areas, showing a downward trend from the central urban area to the outskirts; 3) there was a "spatial mismatch" between the distribution of elderly care facilities and the distribution of the elderly population, only a small number of the elderly people could enjoy more resources of elderly care facilities, and at the same time, the level of facility services and the number of per capita resources were not equal. In responses to the above problems, it was recommended to implement a planning strategy of community life circles, that was "evaluation first, partitions between service domains, facility classification".
2021, 51(9): 75-81.
doi: 10.13204/j.gyjzG21011801
Abstract:
The renovation of industrial relics is the mirror of industrial evolution in physical spaces. The paper divided the renovation of industrial relics in Shanghai into four stages according to the industrial evolution since the reform and opening-up. An evaluation framework on physical authenticity was constructed based on four factors of "Building, Place, Landscape and Other Industrial Elements", so as to analyze the representative cases in different stages, to verify the influence of the urban macro industrial structure as well as the micro industrial functions of research objects on the physical authenticity in the renovation of industrial relics in industrial evolution, and pointed out that physical authenticity revealed the real demand of urban economic development generated by industries, which findings could provide reference to renovation of industrial relics in the coming industrial evolution in Shanghai.
The renovation of industrial relics is the mirror of industrial evolution in physical spaces. The paper divided the renovation of industrial relics in Shanghai into four stages according to the industrial evolution since the reform and opening-up. An evaluation framework on physical authenticity was constructed based on four factors of "Building, Place, Landscape and Other Industrial Elements", so as to analyze the representative cases in different stages, to verify the influence of the urban macro industrial structure as well as the micro industrial functions of research objects on the physical authenticity in the renovation of industrial relics in industrial evolution, and pointed out that physical authenticity revealed the real demand of urban economic development generated by industries, which findings could provide reference to renovation of industrial relics in the coming industrial evolution in Shanghai.
2021, 51(9): 82-89.
doi: 10.13204/j.gyjzG20042601
Abstract:
A new precast shear wall connected by ultra high performance concrete (UHPC) was introduced in the paper. 5 full-scale shear walls were designed to study the aseismic performances of the precast shear wall subjected to quasi-static cyclic loads. The experiment results showed that the prefabricated shear wall with horizontal joints and the cast-in-place wall failed in the same compression-bending mode, the concrete at the bottom of the prefabricated shear wall crushed badly. The shear wall with vertical joints failed in bending-shear mode while a subtle sidesway was observed and the vertical rebars ruptured. For the prefabricated shear wall in the axial compression ratio of 0.35, the thickness of the protective layer of UHPC was small because of the poor quality of the casting, resulting in insufficient anchoring of the rebars in the post-casting area. The new connection form could transfer the stress of rebars effectively, the shear wall with horizontal joints or vertical joints showed slightly higher bearing capacity than the cast-in-place in same axial compression ratio, and the displacement ductility and energy-dissipation capacity were extremely closed. The ultimate shift angles of the 5 shear walls were larger than 1/100, meeting the requirements of GB 50011-2010 Code for Seismic Design of Building.
A new precast shear wall connected by ultra high performance concrete (UHPC) was introduced in the paper. 5 full-scale shear walls were designed to study the aseismic performances of the precast shear wall subjected to quasi-static cyclic loads. The experiment results showed that the prefabricated shear wall with horizontal joints and the cast-in-place wall failed in the same compression-bending mode, the concrete at the bottom of the prefabricated shear wall crushed badly. The shear wall with vertical joints failed in bending-shear mode while a subtle sidesway was observed and the vertical rebars ruptured. For the prefabricated shear wall in the axial compression ratio of 0.35, the thickness of the protective layer of UHPC was small because of the poor quality of the casting, resulting in insufficient anchoring of the rebars in the post-casting area. The new connection form could transfer the stress of rebars effectively, the shear wall with horizontal joints or vertical joints showed slightly higher bearing capacity than the cast-in-place in same axial compression ratio, and the displacement ductility and energy-dissipation capacity were extremely closed. The ultimate shift angles of the 5 shear walls were larger than 1/100, meeting the requirements of GB 50011-2010 Code for Seismic Design of Building.
2021, 51(9): 90-97.
doi: 10.13204/j.gyjzG21010604
Abstract:
In order to study the aseismic performance of T-shaped assembled monolithic double-sided composite shear walls with constructional edge members, two full-scale T-shape shear wall specimens were tested. The test results showed that both the composite and cast-in-situ specimens displayed typical bending-shear failure characteristics in the axial compression ratio of 0.2. Compared with cast-in-situ specimens, the ultimate bearing capacity of flanges for composite specimens in the state of tension and compression was reduced by 15.7% and 3.0%; the ductility coefficient of flanges in the state of tension was the same as that of cast-in-situ specimens, while the ductility coefficient of flanges in the state of compression was lower than that of cast-in-situ specimens; the stiffness degradation laws of the two were basically the same. The cumulative energy consumption of composite specimens was significantly lower than that of cast-in-place specimens. The horizontal connection of webs, flanges and T-shaped constructional edges of composite specimens worked well as a whole. According to the test results, it was suggested to improve the stirrup ratio in constructional edge members of the composite specimens.
In order to study the aseismic performance of T-shaped assembled monolithic double-sided composite shear walls with constructional edge members, two full-scale T-shape shear wall specimens were tested. The test results showed that both the composite and cast-in-situ specimens displayed typical bending-shear failure characteristics in the axial compression ratio of 0.2. Compared with cast-in-situ specimens, the ultimate bearing capacity of flanges for composite specimens in the state of tension and compression was reduced by 15.7% and 3.0%; the ductility coefficient of flanges in the state of tension was the same as that of cast-in-situ specimens, while the ductility coefficient of flanges in the state of compression was lower than that of cast-in-situ specimens; the stiffness degradation laws of the two were basically the same. The cumulative energy consumption of composite specimens was significantly lower than that of cast-in-place specimens. The horizontal connection of webs, flanges and T-shaped constructional edges of composite specimens worked well as a whole. According to the test results, it was suggested to improve the stirrup ratio in constructional edge members of the composite specimens.
2021, 51(9): 98-105.
doi: 10.13204/j.gyjzG20081505
Abstract:
The shear performances of concrete deep beams mixed with desert sand were studied, the shear tests for 8 concrete deep beams with desert sand without web reinforcement were conducted subjected to concentrated loads, and the laws of shear-span ratios, reinforcement ratios and the content of desert sand on the mid-space deflection, cracking load, ultimate load, concrete strain and rebar strain of deep beams were analyzed, as well as the damage forms and crack evolution. The test results showed that these specimens didn't conform to the assumption of the plane section when they were damaged. The ultimate load decreased with the increase of shear-span ratios, increased with the increase of reinforcement ratios, increased first and then decreased with the increase of the content of desert sand, and reached its maximum bearing capacity when the content of desert sand was 20%. In the same loads, the mid-span deflection increased first and then decreased with the increase of shear-span ratios, reinforcement ratios and the content of desert sand. The calculation methods of deep beams from Chinese standard GB 50010-2010 and the codes of United States, Canada and Europe were modified, finally the formula for calculating the shear bearing capacity of deep beams mixed with desert sand was proposed.
The shear performances of concrete deep beams mixed with desert sand were studied, the shear tests for 8 concrete deep beams with desert sand without web reinforcement were conducted subjected to concentrated loads, and the laws of shear-span ratios, reinforcement ratios and the content of desert sand on the mid-space deflection, cracking load, ultimate load, concrete strain and rebar strain of deep beams were analyzed, as well as the damage forms and crack evolution. The test results showed that these specimens didn't conform to the assumption of the plane section when they were damaged. The ultimate load decreased with the increase of shear-span ratios, increased with the increase of reinforcement ratios, increased first and then decreased with the increase of the content of desert sand, and reached its maximum bearing capacity when the content of desert sand was 20%. In the same loads, the mid-span deflection increased first and then decreased with the increase of shear-span ratios, reinforcement ratios and the content of desert sand. The calculation methods of deep beams from Chinese standard GB 50010-2010 and the codes of United States, Canada and Europe were modified, finally the formula for calculating the shear bearing capacity of deep beams mixed with desert sand was proposed.
2021, 51(9): 106-112,155.
doi: 10.13204/j.gyjzG20092906
Abstract:
In order to study the influence of pitting corrosion on the stress-strain of concrete confined by stirrups, based on the existing research results, the time-varying damage model of corroded reinforcement with uniform corrosion and pitting corrosion was obtained through analyzing the change rule of pitting depth and probability distribution with corrosion time. Then, the existing confined concrete stress-strain model was modified by analyzing the influence of pitting corrosion on confined concrete with corroded stirrups. Finally, a time-varying stress-strain model of concrete confined by strirrups considering the effect of pitting corrosion was constructed, and the reliability of the model was verified by comparing the calculated results with the experimental results. The results showed that the proposed model could better reflect the change of mechanical properties of concrete with corroded stirrup and provide reference to elaborate numerical analysis of reinforced concrete structure in chloride ion erosion.
In order to study the influence of pitting corrosion on the stress-strain of concrete confined by stirrups, based on the existing research results, the time-varying damage model of corroded reinforcement with uniform corrosion and pitting corrosion was obtained through analyzing the change rule of pitting depth and probability distribution with corrosion time. Then, the existing confined concrete stress-strain model was modified by analyzing the influence of pitting corrosion on confined concrete with corroded stirrups. Finally, a time-varying stress-strain model of concrete confined by strirrups considering the effect of pitting corrosion was constructed, and the reliability of the model was verified by comparing the calculated results with the experimental results. The results showed that the proposed model could better reflect the change of mechanical properties of concrete with corroded stirrup and provide reference to elaborate numerical analysis of reinforced concrete structure in chloride ion erosion.
2021, 51(9): 113-120,201.
doi: 10.13204/j.gyjzG21020604
Abstract:
In the current study of seismic vulnerability of old reinforced concrete-frame structure, the influence of different seismic design criteria and durability on the a seismic performance of structure is not considered together, and the damage indicator which characterizes the structural vulnerability has limitations in the threshold range and dynamic analysis. Hence, considering differences of structural performances caused by concrete carbonization and rebar corrosion, based on different versions of seismic design criteria, the seismic action value according to structures service time was adjusted, three typical five-story steel-concrete frame structures were built. The corresponding finite element models were constructed and the incremental dynamic time-history analysis was conducted. The differential ratio of elastic plastic dissipated energy and the maximum interstory drift were used to characterize the structural damage, then the seismic vulnerability was analyzed and compared. The results showed that the a seismic capacity of the designed structure had been significantly improved and the vulnerability had decreased to a certain extent conducted by the updated seismic criteria. The seismic vulnerability of the same structure first decreased and then increased due to concrete carbonation. The differential ratio of elastic plastic dissipated energy was better than the maximum interstory drift to characterize the seismic vulnerability of existing structures.
In the current study of seismic vulnerability of old reinforced concrete-frame structure, the influence of different seismic design criteria and durability on the a seismic performance of structure is not considered together, and the damage indicator which characterizes the structural vulnerability has limitations in the threshold range and dynamic analysis. Hence, considering differences of structural performances caused by concrete carbonization and rebar corrosion, based on different versions of seismic design criteria, the seismic action value according to structures service time was adjusted, three typical five-story steel-concrete frame structures were built. The corresponding finite element models were constructed and the incremental dynamic time-history analysis was conducted. The differential ratio of elastic plastic dissipated energy and the maximum interstory drift were used to characterize the structural damage, then the seismic vulnerability was analyzed and compared. The results showed that the a seismic capacity of the designed structure had been significantly improved and the vulnerability had decreased to a certain extent conducted by the updated seismic criteria. The seismic vulnerability of the same structure first decreased and then increased due to concrete carbonation. The differential ratio of elastic plastic dissipated energy was better than the maximum interstory drift to characterize the seismic vulnerability of existing structures.
2021, 51(9): 121-126.
doi: 10.13204/j.gyjzG21061514
Abstract:
In order to study the mechanical properties of steel-concrete composite beams with high-strength bolt connectors, single-point static loading was conducted on 4 composite beam specimens by changing the pre-tightening forces of high-strength bolts and the spacing of end bolts. The load-deflection curve, the load-slip curve and the strain curve along the height of the section were obtained from the experiment, and then the influence of the two variables on the flexural bearing capacity, initial stiffness and cross-sectional strain of the composite beam was analyzed. The test results showed that the test beam subjected to concentrated loads was typical bending failure, reducing the spacing of the end bolts could improve the bearing capacity and initial stiffness of the composite beam and increasing the pre-tightening force could also increase the initial stiffness of the composite beam, but had little effect on the ultimate bearing capacity.
In order to study the mechanical properties of steel-concrete composite beams with high-strength bolt connectors, single-point static loading was conducted on 4 composite beam specimens by changing the pre-tightening forces of high-strength bolts and the spacing of end bolts. The load-deflection curve, the load-slip curve and the strain curve along the height of the section were obtained from the experiment, and then the influence of the two variables on the flexural bearing capacity, initial stiffness and cross-sectional strain of the composite beam was analyzed. The test results showed that the test beam subjected to concentrated loads was typical bending failure, reducing the spacing of the end bolts could improve the bearing capacity and initial stiffness of the composite beam and increasing the pre-tightening force could also increase the initial stiffness of the composite beam, but had little effect on the ultimate bearing capacity.
2021, 51(9): 127-131.
doi: 10.13204/j.gyjzG19082003
Abstract:
To study influence of construction joints and cast-in-place floors on the "strong column and weak beam" for RC plane frames, horizontal low-cycle repeated tests were conducted on three RC plane frames with one story and two spans, the failure modes and hysteresis curves of each specimen were analyzed. The results showed the plane frame with construction joints at beam ends failed due to plastic hinges at beam ends, and the plane frame with the cast-in-place floors failed due to plastic hinges at column ends; the construction joints at beam ends reduced the integrity of frames, which were more prone to the "strong column weak beam". The aseismic performances of structures were poorer; cast-in-place floors could enhanced the bearing capacity of frame beams, including the yield loads, ultimate loads and corresponding displacement of structures, and increased the structural energy consumption.
To study influence of construction joints and cast-in-place floors on the "strong column and weak beam" for RC plane frames, horizontal low-cycle repeated tests were conducted on three RC plane frames with one story and two spans, the failure modes and hysteresis curves of each specimen were analyzed. The results showed the plane frame with construction joints at beam ends failed due to plastic hinges at beam ends, and the plane frame with the cast-in-place floors failed due to plastic hinges at column ends; the construction joints at beam ends reduced the integrity of frames, which were more prone to the "strong column weak beam". The aseismic performances of structures were poorer; cast-in-place floors could enhanced the bearing capacity of frame beams, including the yield loads, ultimate loads and corresponding displacement of structures, and increased the structural energy consumption.
2021, 51(9): 132-137.
doi: 10.13204/j.gyjzG20061402
Abstract:
In order to improve the aseismic performances of Chinese traditional dwellings constructed with rowlock walls, the high ductility cement-based composite (ECC) was used to strengthen the two sides of the walls, and the reinforcement schemes could be divided into frame plastering reinforcement, framed cross-plastering reinforcement and full plastering reforcement. A total of 4 walls were fabricated and studied by quasi-static tests. The effects of different reinforcement schemes with ECC were studied, and the failure mechanisms and aseismic performances of different reinforcement schemes were analyzed. The test results showed that the bonding properties between ECC and rowlock walls were good, ECC and rowlock walls could resist horizontal load cooperative. The bearing capacity, deformation capacity and energy-dissipation capacity of walls strengthened with ECC were improved. The frame-plastering reinforced wall showed the best ductile deformation capacity and larger initial stiffness. The framed cross-plastering reinforced wall showed the best energy-dissipation capacity and the best hysteretic characteristics. The full plastering-reinforced wall showed the best bearing capacity and higher cracking capacity. The three reinforcement schemes had different advantages and could be selected according to needs in the actual engineering.
In order to improve the aseismic performances of Chinese traditional dwellings constructed with rowlock walls, the high ductility cement-based composite (ECC) was used to strengthen the two sides of the walls, and the reinforcement schemes could be divided into frame plastering reinforcement, framed cross-plastering reinforcement and full plastering reforcement. A total of 4 walls were fabricated and studied by quasi-static tests. The effects of different reinforcement schemes with ECC were studied, and the failure mechanisms and aseismic performances of different reinforcement schemes were analyzed. The test results showed that the bonding properties between ECC and rowlock walls were good, ECC and rowlock walls could resist horizontal load cooperative. The bearing capacity, deformation capacity and energy-dissipation capacity of walls strengthened with ECC were improved. The frame-plastering reinforced wall showed the best ductile deformation capacity and larger initial stiffness. The framed cross-plastering reinforced wall showed the best energy-dissipation capacity and the best hysteretic characteristics. The full plastering-reinforced wall showed the best bearing capacity and higher cracking capacity. The three reinforcement schemes had different advantages and could be selected according to needs in the actual engineering.
2021, 51(9): 138-142,221.
doi: 10.13204/j.gyjzG20080402
Abstract:
An innovative self-centering friction damper was proposed by utilizing the superelastic property of shape-memory alloy (SMA). The damper with a simple structural configuration and clear load-transfer mechanism, consisted of the self-centering device based on large size SMA bars and frictional energy-dissipation devices. To verify the effectiveness and reliability, the experiment of SMA bars with a diameter of 10 mm subjected to cyclic loads was conducted. Then the numerical model of the damper was constructed by finite element analysis software ABAQUS. The change laws of equivalent stiffness, the energy-dissipation per cycle, the equivalent damping ratio and the residual deformation ratio of the damper were discussed in the different displacement amplitudes, friction and prestressing forces of SMA bars. The simulation results showed that the innovative friction damper exhibited a good self-centering and energy-dissipation capability. The residual deformation of the damper was controlled by the friction and the prestressing force of SMA bars.
An innovative self-centering friction damper was proposed by utilizing the superelastic property of shape-memory alloy (SMA). The damper with a simple structural configuration and clear load-transfer mechanism, consisted of the self-centering device based on large size SMA bars and frictional energy-dissipation devices. To verify the effectiveness and reliability, the experiment of SMA bars with a diameter of 10 mm subjected to cyclic loads was conducted. Then the numerical model of the damper was constructed by finite element analysis software ABAQUS. The change laws of equivalent stiffness, the energy-dissipation per cycle, the equivalent damping ratio and the residual deformation ratio of the damper were discussed in the different displacement amplitudes, friction and prestressing forces of SMA bars. The simulation results showed that the innovative friction damper exhibited a good self-centering and energy-dissipation capability. The residual deformation of the damper was controlled by the friction and the prestressing force of SMA bars.
2021, 51(9): 143-149.
doi: 10.13204/j.gyjzG20121417
Abstract:
The dowel-type connection in timber structures with slotted steel plates is a common connection in timber structure engineering, in order to facilitate the design of the timber structure engineering, compression tests of the timber dowel groove and dowel-type connection in glued timber with slotted steel plates were conducted respectively. The results indicated that there were three yield modes of dowel-type connections in timber structures with slotted steel plates under loads, which were consistent with the yield modes in Standard for Design of Timber Structures (GB 50005-2017), and the yield modes could be predicted by calculations. The experimental results showed that the calculation results obtained by the proposed calculation formula for the bearing capacity of the dowel-type connection in timber structures with slotted steel plates were basically in agreement with the test results.
The dowel-type connection in timber structures with slotted steel plates is a common connection in timber structure engineering, in order to facilitate the design of the timber structure engineering, compression tests of the timber dowel groove and dowel-type connection in glued timber with slotted steel plates were conducted respectively. The results indicated that there were three yield modes of dowel-type connections in timber structures with slotted steel plates under loads, which were consistent with the yield modes in Standard for Design of Timber Structures (GB 50005-2017), and the yield modes could be predicted by calculations. The experimental results showed that the calculation results obtained by the proposed calculation formula for the bearing capacity of the dowel-type connection in timber structures with slotted steel plates were basically in agreement with the test results.
2021, 51(9): 150-155.
doi: 10.13204/j.gyjzG20061301
Abstract:
Recognition of bridge dynamic characteristics by vehicle vibration responses has the outstanding advantages of convenience, high efficiency and no impact on traffic. Constraint equations were used to simulate vehicle-bridge contact, the finite element calculation program of coupling vibration of vehicles and bridges was programmed. Based on the fundamental frequency information of bridges contained in vehicle vibration equations, the frequency of continuous girder bridge was identified by Fourier transform, and vehicle speeds, vehicle mass and road surface roughness were analyzed. The results showed that the fundamental frequency identified by vehicle vibration acceleration was in good agreement with the theoretical calculation results in the condition of pavement smoothness; in the case of pavement irregularity, the acceleration difference between two vehicles at the same position of the bridge were transformed by fast Fourier transform, it could greatly reduce the adverse effects of bridge surface roughness;the regularity of influence of speeds on frequency-recognition results was not obvious, and the lower speed was more appropriate; vehicle mass had little effect on the identification results; the grade of bridge deck irregularity had little effect on the identification of bridge frequencies.
Recognition of bridge dynamic characteristics by vehicle vibration responses has the outstanding advantages of convenience, high efficiency and no impact on traffic. Constraint equations were used to simulate vehicle-bridge contact, the finite element calculation program of coupling vibration of vehicles and bridges was programmed. Based on the fundamental frequency information of bridges contained in vehicle vibration equations, the frequency of continuous girder bridge was identified by Fourier transform, and vehicle speeds, vehicle mass and road surface roughness were analyzed. The results showed that the fundamental frequency identified by vehicle vibration acceleration was in good agreement with the theoretical calculation results in the condition of pavement smoothness; in the case of pavement irregularity, the acceleration difference between two vehicles at the same position of the bridge were transformed by fast Fourier transform, it could greatly reduce the adverse effects of bridge surface roughness;the regularity of influence of speeds on frequency-recognition results was not obvious, and the lower speed was more appropriate; vehicle mass had little effect on the identification results; the grade of bridge deck irregularity had little effect on the identification of bridge frequencies.
2021, 51(9): 156-160.
doi: 10.13204/j.gyjzG20041201
Abstract:
The climbing stage is a very unfavorable load case for the temporary supports of internal climbing tower cranes. Due to the short action time of loads, the vertical loads will make obvious dynamic effects. Based on measured data the Tower J of Shenwan Huiyun Center with a construction height of nearly 350 m, the characteristics of bending moment and deformation of the temporary supports subjected to loads were analyzed. The characteristics of the structural members of the temporary support were obtained and the dynamic amplification factors of vertical loads were given. The finite element analysis results showed that the simulation results using the dynamic amplification factors were close to the actual measurement results.
The climbing stage is a very unfavorable load case for the temporary supports of internal climbing tower cranes. Due to the short action time of loads, the vertical loads will make obvious dynamic effects. Based on measured data the Tower J of Shenwan Huiyun Center with a construction height of nearly 350 m, the characteristics of bending moment and deformation of the temporary supports subjected to loads were analyzed. The characteristics of the structural members of the temporary support were obtained and the dynamic amplification factors of vertical loads were given. The finite element analysis results showed that the simulation results using the dynamic amplification factors were close to the actual measurement results.
2021, 51(9): 161-165.
doi: 10.13204/j.gyjzG20041202
Abstract:
Temporary supports transfer loads from tower cranes to permanent structures, which is an important temporary structure in the construction of super high-rise buildings. Two different internal climbing tower cranes and temporary supports used in the construction of two super high-rise buildings were taken as research objects. By finite element calculations, the characteristics of temporary supports subjected to various loads were analyzed. And the position where the most unfavorable loads occured and the corresponding vertical load-distribution coefficient were given. Some measures were proposed to reduced the distribution unevenness of vertical loads on temporary supports of external suspended tower cranes,and the effectiveness was analyzed.
Temporary supports transfer loads from tower cranes to permanent structures, which is an important temporary structure in the construction of super high-rise buildings. Two different internal climbing tower cranes and temporary supports used in the construction of two super high-rise buildings were taken as research objects. By finite element calculations, the characteristics of temporary supports subjected to various loads were analyzed. And the position where the most unfavorable loads occured and the corresponding vertical load-distribution coefficient were given. Some measures were proposed to reduced the distribution unevenness of vertical loads on temporary supports of external suspended tower cranes,and the effectiveness was analyzed.
2021, 51(9): 166-172,126.
doi: 10.13204/j.gyjzG20051003
Abstract:
Various systematic lumped-parameter modes have been developed in recent studies for efficiently representing the dynamic behaviors of unbounded soil. Those systematic lumped-parameter modes are merely constructed by arranging several spring and damper elements, either connected in series or in parallel. Other than their applications in simplifying the analysis and design, those modes have been also analogized to equivalent electric circuits according to their concise mathematical formulation and simple physical correspondence. Based on these new developments in simulating the lumped-parameter modes with equivalent circuits, this research further considered the inclusion of foundation mass and superstructure to extensively explore the possibility of representing the simulation of a complete soil-structure interaction system with a simple circuit experiment. In this study, foundation mass, single-degree-of-freedom superstructure and multi-degree-of-freedom superstructure were added to the original centralized parameter mode to replace soil, so as to gradually establish the equivalent circuit of the complete soil-structure interaction system, carry out simulation tests under three different seismic spectra, and discuss its accuracy and feasibility. Through the comparison of different systems mentioned above, the error of mechanical analysis and equivalent circuit test results was generally less than 10%, which could prove that the equivalent circuit proposed for the complete soil-structure interaction had good test effect and accuracy.
Various systematic lumped-parameter modes have been developed in recent studies for efficiently representing the dynamic behaviors of unbounded soil. Those systematic lumped-parameter modes are merely constructed by arranging several spring and damper elements, either connected in series or in parallel. Other than their applications in simplifying the analysis and design, those modes have been also analogized to equivalent electric circuits according to their concise mathematical formulation and simple physical correspondence. Based on these new developments in simulating the lumped-parameter modes with equivalent circuits, this research further considered the inclusion of foundation mass and superstructure to extensively explore the possibility of representing the simulation of a complete soil-structure interaction system with a simple circuit experiment. In this study, foundation mass, single-degree-of-freedom superstructure and multi-degree-of-freedom superstructure were added to the original centralized parameter mode to replace soil, so as to gradually establish the equivalent circuit of the complete soil-structure interaction system, carry out simulation tests under three different seismic spectra, and discuss its accuracy and feasibility. Through the comparison of different systems mentioned above, the error of mechanical analysis and equivalent circuit test results was generally less than 10%, which could prove that the equivalent circuit proposed for the complete soil-structure interaction had good test effect and accuracy.
2021, 51(9): 173-176,196.
doi: 10.13204/j.gyjzG20091705
Abstract:
To study the influence of different loading points and different loading directions on the load transfer characteristics of a single pile, model tests of the axial compressive piles without or with soil at pile tips and bottom-lifted piles in the same conditions were conducted. Then the laws of axial forces and side friction in different loading modes were obtained. The results showed that the relative limit displacement between piles and soil required for negative frictional resistance was smaller than that of positive frictional resistance. Loading positions significantly influenced on the evoluation of pile side friction, and the maximum of the pile side friction appeared at the one-third length of piles away from the loading point. For axial compressive piles, the middle and upper strata should be fully utilized; and for bottom-lifted piles, the middle and lower strata should be fully utilized. When grouting was inplemented on the sides of piles to improve the vertical bearing capacity, the grouting positions beside the upper and middle parts of pile shafts for axial compressive piles and beside the middle and lower parts of the pile shafts for the bottom-lifted piles should be considered.
To study the influence of different loading points and different loading directions on the load transfer characteristics of a single pile, model tests of the axial compressive piles without or with soil at pile tips and bottom-lifted piles in the same conditions were conducted. Then the laws of axial forces and side friction in different loading modes were obtained. The results showed that the relative limit displacement between piles and soil required for negative frictional resistance was smaller than that of positive frictional resistance. Loading positions significantly influenced on the evoluation of pile side friction, and the maximum of the pile side friction appeared at the one-third length of piles away from the loading point. For axial compressive piles, the middle and upper strata should be fully utilized; and for bottom-lifted piles, the middle and lower strata should be fully utilized. When grouting was inplemented on the sides of piles to improve the vertical bearing capacity, the grouting positions beside the upper and middle parts of pile shafts for axial compressive piles and beside the middle and lower parts of the pile shafts for the bottom-lifted piles should be considered.
2021, 51(9): 177-180.
doi: 10.13204/j.gyjzG20070106
Abstract:
Based on the thermal conductivity coefficients of soil skeletons obtained by experiments and the microscopic mechanism of interaction between soil particles and pore water, the influence of the pore water content on thermal conductivity coefficients of frozen soil was analyzed. With the increase of the pore water content, the two characteristic points would appear in the curve of soil thermal conductivity coefficients, they were called "the soil structure control point" and "the soil structure dispersion point" respectively. The curve of thermal conductivity coefficients could be divided into three phases by the two varible characteristics points:1) the combination phase of soil skeletons and strong binding water; 2) the phase of water-filled pores of soil; 3) the phase of soil skeletons damaged by pore water. On the basis, the change laws of soil thermal conductivity in these three stages were studied by using the physical model of heat transfer, and the simple and practical formula of thermal conductivity coefficients was obtained based on the theory of the electric lattice model.
Based on the thermal conductivity coefficients of soil skeletons obtained by experiments and the microscopic mechanism of interaction between soil particles and pore water, the influence of the pore water content on thermal conductivity coefficients of frozen soil was analyzed. With the increase of the pore water content, the two characteristic points would appear in the curve of soil thermal conductivity coefficients, they were called "the soil structure control point" and "the soil structure dispersion point" respectively. The curve of thermal conductivity coefficients could be divided into three phases by the two varible characteristics points:1) the combination phase of soil skeletons and strong binding water; 2) the phase of water-filled pores of soil; 3) the phase of soil skeletons damaged by pore water. On the basis, the change laws of soil thermal conductivity in these three stages were studied by using the physical model of heat transfer, and the simple and practical formula of thermal conductivity coefficients was obtained based on the theory of the electric lattice model.
2021, 51(9): 181-187.
doi: 10.13204/j.gyjzG20090802
Abstract:
Uniaxial compression experiments were conducted for pyroxenite specimens with pre-slotted fissures by the rock mechanics servo-controlled testing system. The laws of initiation, propagation and coalescence of rock specimens with different numbers of fissures were studied. The experiment phenomena were expounded by XFEM simulations. The study showed that the uniaxial compressive strength of pyroxenite specimens decreased linearly with the increase of numbers of cracks; as numbers of pre-slotted fissures increased, the rates of the strain at the pre-slotted fissure tips to that away from the pre-slotted fissures increased. When there were secondary cracks in multiple pre-slotted fissure specimens, stress would rebound after reaching the peak. The process of initiation, propagation and coalescence of specimens with a single, double or three pre-slotted fissures were simulated. The laws of crack initiation, evolution and coalescence processes obtained by numerical simulations were similar to that by tests.
Uniaxial compression experiments were conducted for pyroxenite specimens with pre-slotted fissures by the rock mechanics servo-controlled testing system. The laws of initiation, propagation and coalescence of rock specimens with different numbers of fissures were studied. The experiment phenomena were expounded by XFEM simulations. The study showed that the uniaxial compressive strength of pyroxenite specimens decreased linearly with the increase of numbers of cracks; as numbers of pre-slotted fissures increased, the rates of the strain at the pre-slotted fissure tips to that away from the pre-slotted fissures increased. When there were secondary cracks in multiple pre-slotted fissure specimens, stress would rebound after reaching the peak. The process of initiation, propagation and coalescence of specimens with a single, double or three pre-slotted fissures were simulated. The laws of crack initiation, evolution and coalescence processes obtained by numerical simulations were similar to that by tests.
2021, 51(9): 188-196.
doi: 10.13204/j.gyjzG21022004
Abstract:
The cooperative work of high ductility cement-based composites and hyperelastic shape-memory alloy (SMA) can improve the energy-dissipation capacity and self-repair capacity of structure. The use of shape-memory alloy fiber can effectively solve some problems of shape-memory alloy bars or cables, so it has a broader application prospect. Several groups of test specimens were fabricated by embedding superelastic shape-memory alloy fibers with different diameters and end shapes into high-ductility cement-based materials with up to 3% tensile strain, some of which had different embedded depths. The pull-out tests of specimens were conducted by displacement-controlled loading, the stress-strain curves of pull-out for specimens were obtained, and the effects of various factors on the bonding properties between shape-memory alloy fiber and high-ductility cement-based composites were analyzed. The results showed that the knotted end could greatly improve the bond strength of shape-memory alloy fibers in the high-ductility cement matrix and provide sufficient anchoring forces for shape-memory alloy fibers to exert its superelasticity. The maximum tensile stress of all types of knotted specimens was above 900 MPa, and the maximum could reach 1 142.52 MPa. Among them, the specimen with knotted SMAF with diameter of 1.2 mm and embedded depth of 40 mm had better mechanical properties and fiber utilization ratios.
The cooperative work of high ductility cement-based composites and hyperelastic shape-memory alloy (SMA) can improve the energy-dissipation capacity and self-repair capacity of structure. The use of shape-memory alloy fiber can effectively solve some problems of shape-memory alloy bars or cables, so it has a broader application prospect. Several groups of test specimens were fabricated by embedding superelastic shape-memory alloy fibers with different diameters and end shapes into high-ductility cement-based materials with up to 3% tensile strain, some of which had different embedded depths. The pull-out tests of specimens were conducted by displacement-controlled loading, the stress-strain curves of pull-out for specimens were obtained, and the effects of various factors on the bonding properties between shape-memory alloy fiber and high-ductility cement-based composites were analyzed. The results showed that the knotted end could greatly improve the bond strength of shape-memory alloy fibers in the high-ductility cement matrix and provide sufficient anchoring forces for shape-memory alloy fibers to exert its superelasticity. The maximum tensile stress of all types of knotted specimens was above 900 MPa, and the maximum could reach 1 142.52 MPa. Among them, the specimen with knotted SMAF with diameter of 1.2 mm and embedded depth of 40 mm had better mechanical properties and fiber utilization ratios.
2021, 51(9): 197-201.
doi: 10.13204/j.gyjzG20072117
Abstract:
In order to study the effect of freezing laws for concrete pores on compressive strength in permafrost regions, a self-made low-temperature compressive testing machine was used to gauge the concrete compressive strength. The laws of ice content in different size pores were measured by nuclear magnetic resonance apparatuses. Based on the grey theory, the effect of the ice content in pores on compressive strength was analyzed, and the relation model between ice content and compressive strength was constructed. The results showed that from 0℃ to -10℃, the capillary pores and transition pores freezed rapidly due to the larger pore sizes, so the ice content and compressive strength increased rapidly in the temperature range. Transition pores were the main pores of concrete. At -10℃, 99.7% of the capillary pores and 55.8% of the transition pores had been frozen. At the time, the proportion of gel pore increased and it was hard to be frozen, so the ice content and compressive strength increased slowly. The ice content of the transition pores was the most significant influence on compressive strength, and its correlation degree of grey entropy was 0.985 0. The calculated values of concrete compressive strength based on GM(0,2) Model had an average relative error of 3.33% from the test value.
In order to study the effect of freezing laws for concrete pores on compressive strength in permafrost regions, a self-made low-temperature compressive testing machine was used to gauge the concrete compressive strength. The laws of ice content in different size pores were measured by nuclear magnetic resonance apparatuses. Based on the grey theory, the effect of the ice content in pores on compressive strength was analyzed, and the relation model between ice content and compressive strength was constructed. The results showed that from 0℃ to -10℃, the capillary pores and transition pores freezed rapidly due to the larger pore sizes, so the ice content and compressive strength increased rapidly in the temperature range. Transition pores were the main pores of concrete. At -10℃, 99.7% of the capillary pores and 55.8% of the transition pores had been frozen. At the time, the proportion of gel pore increased and it was hard to be frozen, so the ice content and compressive strength increased slowly. The ice content of the transition pores was the most significant influence on compressive strength, and its correlation degree of grey entropy was 0.985 0. The calculated values of concrete compressive strength based on GM(0,2) Model had an average relative error of 3.33% from the test value.
2021, 51(9): 202-206,229.
doi: 10.13204/j.gyjzG20051212
Abstract:
Based on the idea of the equivalent parameters method and energy method, the theoretical formula of composite variable cross-section struts was deduced. Firstly, the wall of the composite compression strut was equivalent to an orthotropic shell whose main axis direction was consistent with the axial direction of the strut based on the idea of the equivalent parameters method, then, the composite strut could be approximated as an orthotropic strut. Thirdly, aiming at the orthotropic compression strut, the buckling deflection equation of compression structs was assumed, and the formula for the theoretical stability load was deduced based on the energy method. Finally, the accuracy of the formula was verified and discussed by comparison with ones by the finite element method, the results showed that:the theory formula in could accurately predict the critical load of the composite variable cross-section compression strut.
Based on the idea of the equivalent parameters method and energy method, the theoretical formula of composite variable cross-section struts was deduced. Firstly, the wall of the composite compression strut was equivalent to an orthotropic shell whose main axis direction was consistent with the axial direction of the strut based on the idea of the equivalent parameters method, then, the composite strut could be approximated as an orthotropic strut. Thirdly, aiming at the orthotropic compression strut, the buckling deflection equation of compression structs was assumed, and the formula for the theoretical stability load was deduced based on the energy method. Finally, the accuracy of the formula was verified and discussed by comparison with ones by the finite element method, the results showed that:the theory formula in could accurately predict the critical load of the composite variable cross-section compression strut.
2021, 51(9): 207-215.
doi: 10.13204/j.gyjzG21020316
Abstract:
For grouting sleeve members, the cement-based grouting material in the grouting sleeve is regarded as the concrete in a broad sense. In order to study the effectiveness of ultrasonic tomography in nondestructive testing of the compactness of grouting sleeve members, the compactness of the grouting material in the sleeve was analyzed from three aspects of theoretical research, finite element simulations and experimental testing. The results showed that:the ultrasonic wave could not propagate directly through the sleeve where the grouting material was completely empty, but diffracted according to the shortest path. The difference of the distribution diagram for sound velocity was not obvious due to the sleeve void, the lower acoustic velocity region corresponding to dense or empty states could not be effectively identified from the acoustic velocity. For the inspection method of inclined ducts with inclined ports, the compactness of the distribution diagram of grouting material in the sleeve could be inferred by observing the loss of the grouting material in the inclined duct.
For grouting sleeve members, the cement-based grouting material in the grouting sleeve is regarded as the concrete in a broad sense. In order to study the effectiveness of ultrasonic tomography in nondestructive testing of the compactness of grouting sleeve members, the compactness of the grouting material in the sleeve was analyzed from three aspects of theoretical research, finite element simulations and experimental testing. The results showed that:the ultrasonic wave could not propagate directly through the sleeve where the grouting material was completely empty, but diffracted according to the shortest path. The difference of the distribution diagram for sound velocity was not obvious due to the sleeve void, the lower acoustic velocity region corresponding to dense or empty states could not be effectively identified from the acoustic velocity. For the inspection method of inclined ducts with inclined ports, the compactness of the distribution diagram of grouting material in the sleeve could be inferred by observing the loss of the grouting material in the inclined duct.
2021, 51(9): 216-221.
doi: 10.13204/j.gyjzG21012703
Abstract:
The Jinan convent, built in 1983, is a historical building of two-story masonry-timber structure with a loft.It was monolithiclly moved in June 2020 by Self-Propelled Modular Trailers. and which was the largest masonry structure building moved by trailers in China at that time. The determination of the movement scheme for the project, the maintance reinforcement design before the movement, the trailers layout, the underpinning structure design, and the foundation and basement design were introduced. Analysis on the force calculation of underpinning structure was conducted according to joint or separated force of the trailers and the structure. The force on the trailer beams could be calculated according to the inverted beam method. The underpinning structure within the building outline could be designed according to the masonry structure with bottom frames of supports or trailers. The underpinning structure overhanging outside the building outline needed to be strengthened as cantilever beams. According to the requirements of the reverse construction method for underground buildings, the underground structure was designed to integrate the piles and columns.
The Jinan convent, built in 1983, is a historical building of two-story masonry-timber structure with a loft.It was monolithiclly moved in June 2020 by Self-Propelled Modular Trailers. and which was the largest masonry structure building moved by trailers in China at that time. The determination of the movement scheme for the project, the maintance reinforcement design before the movement, the trailers layout, the underpinning structure design, and the foundation and basement design were introduced. Analysis on the force calculation of underpinning structure was conducted according to joint or separated force of the trailers and the structure. The force on the trailer beams could be calculated according to the inverted beam method. The underpinning structure within the building outline could be designed according to the masonry structure with bottom frames of supports or trailers. The underpinning structure overhanging outside the building outline needed to be strengthened as cantilever beams. According to the requirements of the reverse construction method for underground buildings, the underground structure was designed to integrate the piles and columns.
2021, 51(9): 222-229.
doi: 10.13204/j.gyjzG20070708
Abstract:
Baned on in-depth analysis of the concept and connotations of the railroad heritage in UK, the early history of railroad development in UK, the generation of the railroad heritage and its conservation history were sorted out; the promoting roles and synergistic mechanisms of different social forces such as government agencies, social organizations and railroad enthusiasts in the conservation of the railroad heritage were revealed; the conservation and utilization strategies of the heritage landscape of railroads in UK were summarized in terms of conservation and utilization for the architectural heritage, collection experiences in museums, tourism development, route sightseeing, guidance of urban renewal, etc. Finally, based on the situations of China's heritage landscape of railroads, the reference suggestion from two aspects of government management function and social organization power were proposed, and the development directions of exploration in the future for Chinese heritage landscape of railroads were recoramended from the following four aspsetc:highlighting humanistic values, driving rural development, linking tourist area construction, and guiding urban renewal and reuse.
Baned on in-depth analysis of the concept and connotations of the railroad heritage in UK, the early history of railroad development in UK, the generation of the railroad heritage and its conservation history were sorted out; the promoting roles and synergistic mechanisms of different social forces such as government agencies, social organizations and railroad enthusiasts in the conservation of the railroad heritage were revealed; the conservation and utilization strategies of the heritage landscape of railroads in UK were summarized in terms of conservation and utilization for the architectural heritage, collection experiences in museums, tourism development, route sightseeing, guidance of urban renewal, etc. Finally, based on the situations of China's heritage landscape of railroads, the reference suggestion from two aspects of government management function and social organization power were proposed, and the development directions of exploration in the future for Chinese heritage landscape of railroads were recoramended from the following four aspsetc:highlighting humanistic values, driving rural development, linking tourist area construction, and guiding urban renewal and reuse.
