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2021 Vol. 51, No. 11
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2021, 51(11): 1-6,18.
doi: 10.13204/j.gyjzG21052419
Abstract:
Based on the shear test of two types(Ⅰ and Ⅱ) of shape memory alloy pseudo-rubber(SMAPR) bearings, the effects of loading frequency, loading amplitude, processing technology and pre-compression stress on its shear properties of its non-forming direction were studied. In addition, the self-recovery through temperature-rising and subsequent mechanical properties were investigated for the SMAPR specimen with residual deformation. The results showed that the shear properties of type Ⅰ and Ⅱ SMAPR bearings were stable, and the equivalent damping ratio increased with the increment of shear amplitudes. The shear stiffness and energy dissipation capacity of SMAPR isolators could be greatly improved by applying pre-compression loads. The residual strain of the two types of specimens could both be eliminated through temperature-rising, and the mechanical properties of type Ⅰ specimens were consistent with those before temperature-rising, which had good repeatability.
Based on the shear test of two types(Ⅰ and Ⅱ) of shape memory alloy pseudo-rubber(SMAPR) bearings, the effects of loading frequency, loading amplitude, processing technology and pre-compression stress on its shear properties of its non-forming direction were studied. In addition, the self-recovery through temperature-rising and subsequent mechanical properties were investigated for the SMAPR specimen with residual deformation. The results showed that the shear properties of type Ⅰ and Ⅱ SMAPR bearings were stable, and the equivalent damping ratio increased with the increment of shear amplitudes. The shear stiffness and energy dissipation capacity of SMAPR isolators could be greatly improved by applying pre-compression loads. The residual strain of the two types of specimens could both be eliminated through temperature-rising, and the mechanical properties of type Ⅰ specimens were consistent with those before temperature-rising, which had good repeatability.
2021, 51(11): 7-12.
doi: 10.13204/j.gyjzG21052420
Abstract:
In order to study the influence of wire diameters and nominal densities on the mechanical properties of metallic rubber(MR) cushions in different parameters and preloading conditions, and to verify whether the mechanical properties of metallic rubber cushious stable in preloading conditions, a three-dimensional(3 D) isolation device was proposed based on metallic rubber cushions and springs. Then, vertical isolation shaking table tests were conducted on a scaled isolated transformer model, and the dynamic characteristics of the isolated structure, as well as the vertical acceleration response of the structure under unidirectional or bidirectional input were measured. The results showed that the mechanical properties of metallic rubber under preloading were stable, and the vertical isolation device based on metallic rubber cushions and springs could effectively reduce the natural frequencies of structures and effectively reduce the energy input, and the isolation efficiency increased with the increment of the peak ground acceleration.
In order to study the influence of wire diameters and nominal densities on the mechanical properties of metallic rubber(MR) cushions in different parameters and preloading conditions, and to verify whether the mechanical properties of metallic rubber cushious stable in preloading conditions, a three-dimensional(3 D) isolation device was proposed based on metallic rubber cushions and springs. Then, vertical isolation shaking table tests were conducted on a scaled isolated transformer model, and the dynamic characteristics of the isolated structure, as well as the vertical acceleration response of the structure under unidirectional or bidirectional input were measured. The results showed that the mechanical properties of metallic rubber under preloading were stable, and the vertical isolation device based on metallic rubber cushions and springs could effectively reduce the natural frequencies of structures and effectively reduce the energy input, and the isolation efficiency increased with the increment of the peak ground acceleration.
2021, 51(11): 13-18.
doi: 10.13204/j.gyjzG21052502
Abstract:
Impact of adjacent structures may cause acceleration amplification, stress damage even collapse during strong ground motions. Based on the characteristics of nonlinear strain hardening and friction energy dissipation in shape memory alloy pseudo-rubber(SMAPR), the seismic impact processes in adjacent single-degree-freedom(SDOF) structures with/without SMAPR absorber were compared, and parametric analysis was conducted to study the effects of axial stiffness of SMAPR on structure impact pounding response. The results showed that SMAPR was characterized by high elasticity, high damping and nonlinear strain hardening, which could prolong the impact time, and effectively reduce the impact response over 90%. Axial stiffness was the sensitive parameter to affect the control response, and the response of shock absorption increased with the decrease of axial stiffness.
Impact of adjacent structures may cause acceleration amplification, stress damage even collapse during strong ground motions. Based on the characteristics of nonlinear strain hardening and friction energy dissipation in shape memory alloy pseudo-rubber(SMAPR), the seismic impact processes in adjacent single-degree-freedom(SDOF) structures with/without SMAPR absorber were compared, and parametric analysis was conducted to study the effects of axial stiffness of SMAPR on structure impact pounding response. The results showed that SMAPR was characterized by high elasticity, high damping and nonlinear strain hardening, which could prolong the impact time, and effectively reduce the impact response over 90%. Axial stiffness was the sensitive parameter to affect the control response, and the response of shock absorption increased with the decrease of axial stiffness.
2021, 51(11): 19-24.
doi: 10.13204/j.gyjzG21052708
Abstract:
Based on the theory of nonlinear quasi-zero stiffness, the horizontal and bidirectional directional seismic isolators were desighed and a shaking test on scaled ultra-high-voltage(UHV) transformer models with vibration isolation device was conducted. The peak ground accelevation of 0.4 g, 0.8 g, 1.2 g and 1.6 g in the tests, when the seismic waves were isolated by seismic isolators, the peak ground acceleration of seismic waves acting on the bottom of the UHV transformer model was reduced by 61.53% to 90.00%, and the spectral response curves of seismic waves were reduced, especially in the low frequency range where the ground shaking energy was high. In the contrast tests of the peak acceleration of 0.4 g and 0.8 g, the maximum stress of high-voltage bushings of UHV transformers decreased by 85.77% and 91.75% as the isolation devices were installed. The results of acceleration and strain showed that the isolation devices had significant seismic isolation effect, and the effectiveness of the nonlinear quasi-zero stiffness theory in seismic isolation design was proven.
Based on the theory of nonlinear quasi-zero stiffness, the horizontal and bidirectional directional seismic isolators were desighed and a shaking test on scaled ultra-high-voltage(UHV) transformer models with vibration isolation device was conducted. The peak ground accelevation of 0.4 g, 0.8 g, 1.2 g and 1.6 g in the tests, when the seismic waves were isolated by seismic isolators, the peak ground acceleration of seismic waves acting on the bottom of the UHV transformer model was reduced by 61.53% to 90.00%, and the spectral response curves of seismic waves were reduced, especially in the low frequency range where the ground shaking energy was high. In the contrast tests of the peak acceleration of 0.4 g and 0.8 g, the maximum stress of high-voltage bushings of UHV transformers decreased by 85.77% and 91.75% as the isolation devices were installed. The results of acceleration and strain showed that the isolation devices had significant seismic isolation effect, and the effectiveness of the nonlinear quasi-zero stiffness theory in seismic isolation design was proven.
2021, 51(11): 25-30.
doi: 10.13204/j.gyjzG21052416
Abstract:
According to the internal structure characteristics of the metallic rubber(MR) specimen as well as its mechanical properties, the shear constitutive model was divided into three parts: linear restoring force, coulombs friction force and nonlinear hysteresis force. The metallic rubber was firstly decomposed into several layers, combined with the statistical law of the contact-pair number of inner turn during the shear deformation process, the shear stiffness of the single contact-pair of the metallic rubber was deduced. Then, the expressions of mechanical components were obtained, and the layered shear constitutive model of MR was established. Finally, the accuracy of the constitutive model was verified through the shear experimental test of MR isolators. The results showed that during the shearing process, the metallic rubber contact pair had a contact-separation process, and the number of contact points remained basically unchanged. At the beginning of the unloading stage, the error between the experimental results and the numerical results was small. The layered shear constitutive model agreed well with the results of shear test without pre-compression load. It was shown that the constitutive model had high accuracy and precision, which could be used to assist the lamellar microanalysis of metallic rubber.
According to the internal structure characteristics of the metallic rubber(MR) specimen as well as its mechanical properties, the shear constitutive model was divided into three parts: linear restoring force, coulombs friction force and nonlinear hysteresis force. The metallic rubber was firstly decomposed into several layers, combined with the statistical law of the contact-pair number of inner turn during the shear deformation process, the shear stiffness of the single contact-pair of the metallic rubber was deduced. Then, the expressions of mechanical components were obtained, and the layered shear constitutive model of MR was established. Finally, the accuracy of the constitutive model was verified through the shear experimental test of MR isolators. The results showed that during the shearing process, the metallic rubber contact pair had a contact-separation process, and the number of contact points remained basically unchanged. At the beginning of the unloading stage, the error between the experimental results and the numerical results was small. The layered shear constitutive model agreed well with the results of shear test without pre-compression load. It was shown that the constitutive model had high accuracy and precision, which could be used to assist the lamellar microanalysis of metallic rubber.
2021, 51(11): 31-38.
doi: 10.13204/j.gyjzG21042102
Abstract:
The settlement of the Great Wall formed in the Ming dynasty is a typical defensive settlement in northern China, whose distribution essentially is the product of games between farming culture and nomadic culture and forms the foundations of cities and towns in the transition areas. However, the traditional research approaches restrict the deep understanding of dynamic mechanisms. Based on the multi-agent modelling system, the model of location selection for settlements was proposed from the perspective of games between farming culture and nomadic culture. The intrinsic motiration to form settlement patterns was discussed by a bottom-top generation way, taking distribution structure as the verified objecture. The simulation results showed there was a strong correlation between the micro-assistance behavior and macro-settlement distribution, i.e. self-organization of the great wall. Faced to the Great Wall, the settlement pattern in hierarchical radiation was the optimal choice in the effciency principle to balance resources against defensive requirements. The model had better global convergence and computational robustness, which was proved that agent-based simulations had potential applied values in the field of landscape patterns for settlements.
The settlement of the Great Wall formed in the Ming dynasty is a typical defensive settlement in northern China, whose distribution essentially is the product of games between farming culture and nomadic culture and forms the foundations of cities and towns in the transition areas. However, the traditional research approaches restrict the deep understanding of dynamic mechanisms. Based on the multi-agent modelling system, the model of location selection for settlements was proposed from the perspective of games between farming culture and nomadic culture. The intrinsic motiration to form settlement patterns was discussed by a bottom-top generation way, taking distribution structure as the verified objecture. The simulation results showed there was a strong correlation between the micro-assistance behavior and macro-settlement distribution, i.e. self-organization of the great wall. Faced to the Great Wall, the settlement pattern in hierarchical radiation was the optimal choice in the effciency principle to balance resources against defensive requirements. The model had better global convergence and computational robustness, which was proved that agent-based simulations had potential applied values in the field of landscape patterns for settlements.
2021, 51(11): 39-44,210.
doi: 10.13204/j.gyjzG21032615
Abstract:
The design of renewal and reuse for old industrial buildings has always been a focus of high attention by all walks of life in contemporary society. With the rapid development of the national economy, land resources in cities have become increasingly scarce, and a large number of old industrial buildings in the old industrial base cities are facing many problems such as elimination, reconstruction or upgrading. At the same time, with the continuous improvement of the people's material living standards, the citizens' pursuit of culture and art has become more and more intense. The renewal design for transforming abandoned industrial plants into public art spaces is one of the important measures with the background of urban sustainable development and the cultural industry reviving. Starting from the development status of the old industrial base in Liaoning, taking Shenyang Cultural and Creative Cluster Quarter of Hongmei 1939 project as the research object, the rationality of the reform for the block was expounded based on the spatial syntax theory. The paper sorted out and expounded the regeneration strategy of converting abandoned industrial plants into public art spaces from the aspects of historical value, practical functions, interior decoration, design style, etc. The meaning and value of the “industrial image transformation” that transforming abandoned industrial plants into public art spaces were summed up.
The design of renewal and reuse for old industrial buildings has always been a focus of high attention by all walks of life in contemporary society. With the rapid development of the national economy, land resources in cities have become increasingly scarce, and a large number of old industrial buildings in the old industrial base cities are facing many problems such as elimination, reconstruction or upgrading. At the same time, with the continuous improvement of the people's material living standards, the citizens' pursuit of culture and art has become more and more intense. The renewal design for transforming abandoned industrial plants into public art spaces is one of the important measures with the background of urban sustainable development and the cultural industry reviving. Starting from the development status of the old industrial base in Liaoning, taking Shenyang Cultural and Creative Cluster Quarter of Hongmei 1939 project as the research object, the rationality of the reform for the block was expounded based on the spatial syntax theory. The paper sorted out and expounded the regeneration strategy of converting abandoned industrial plants into public art spaces from the aspects of historical value, practical functions, interior decoration, design style, etc. The meaning and value of the “industrial image transformation” that transforming abandoned industrial plants into public art spaces were summed up.
2021, 51(11): 45-53,126.
doi: 10.13204/j.gyjzG20101701
Abstract:
There are rich industrial heritage foundation and distinctive northern modern industrial culture in Shenyang. It is an inseparable topic for urban development to protect the industrial heritage and inherit industrial cultures. Based on national policies of multiple plannings in one and the background that urban renewal affects the protection of the industrial heritage to a certain extent, the problems of damage to the industrial heritage, lack of coordination between protection and renewal plannings, and the low degree of reuse of the industrial heritage were analyzed. The context of multi plannings in one for the industrial heritage protection and reuse mode was constructed, the planning strategy of the industrial heritage was constructed, which included “the overall planning for heritage-protected block connection”, “the detailed planning for connections of the blockes”, and “hierarchical management of protected objects.” In order to construct a practical and effective guiding way for Shenyang's industrial heritage protection and reuse and urban development, it was necessary to improve the management platform of multiple maps in one to resolve the differences, and form the reuse strategy of “repair and display class, use function class, transformation and replacement class”.
There are rich industrial heritage foundation and distinctive northern modern industrial culture in Shenyang. It is an inseparable topic for urban development to protect the industrial heritage and inherit industrial cultures. Based on national policies of multiple plannings in one and the background that urban renewal affects the protection of the industrial heritage to a certain extent, the problems of damage to the industrial heritage, lack of coordination between protection and renewal plannings, and the low degree of reuse of the industrial heritage were analyzed. The context of multi plannings in one for the industrial heritage protection and reuse mode was constructed, the planning strategy of the industrial heritage was constructed, which included “the overall planning for heritage-protected block connection”, “the detailed planning for connections of the blockes”, and “hierarchical management of protected objects.” In order to construct a practical and effective guiding way for Shenyang's industrial heritage protection and reuse and urban development, it was necessary to improve the management platform of multiple maps in one to resolve the differences, and form the reuse strategy of “repair and display class, use function class, transformation and replacement class”.
2021, 51(11): 54-61.
doi: 10.13204/j.gyjzG21032201
Abstract:
In the period of post consumption, the change of consumption spawns new spectacles in urban renewal. Taking Sino-Ocean Taikoo Li as a case, based on the theory of society of spectacles the status in the production of spectacles in historical block renewal was interpreted. The results showed: Taikoo Li was completed the spectacle production by buildings, cultural creation and media, in which every spectacle had different dimensional main bodies and goals. The results proved the production of spectacles was beneficial to rejuvenate urban historical assets and promote of economy, but it might led to over-commercialization.
In the period of post consumption, the change of consumption spawns new spectacles in urban renewal. Taking Sino-Ocean Taikoo Li as a case, based on the theory of society of spectacles the status in the production of spectacles in historical block renewal was interpreted. The results showed: Taikoo Li was completed the spectacle production by buildings, cultural creation and media, in which every spectacle had different dimensional main bodies and goals. The results proved the production of spectacles was beneficial to rejuvenate urban historical assets and promote of economy, but it might led to over-commercialization.
2021, 51(11): 62-66.
doi: 10.13204/j.gyjzG20100604
Abstract:
Based on the development law of fatigue damage of concrete and the section stiffness damage model, the crack propagation of ordinary rebars and prestressed rebars after being subjected to fatigue loads was considered. The damage elastic modulus and nonlinear damage accumulation criteria were used to describe concrete damage, and the effective cross-sectional area was used to reflect the fatigue damage of steel bars. The correction factor of size effect was introduced to further deduce the calculation model of the stiffness degradation of the prestressed concrete beam after being subjected to fatigue damage. The accuracy of the stiffness degradation model was verified by analyzing the experimental research results of prestressed concrete beams in different sizes under cyclically multi-level variable-amplitude loads. The test results showed that the stiffness degradation of prestressed concrete beams and the development of concrete damage under the multi-stage variable-amplitude loading test had similar laws; the calculation results of stiffness by the theoretical deduction formulas had a little deviation from the experimental results.
Based on the development law of fatigue damage of concrete and the section stiffness damage model, the crack propagation of ordinary rebars and prestressed rebars after being subjected to fatigue loads was considered. The damage elastic modulus and nonlinear damage accumulation criteria were used to describe concrete damage, and the effective cross-sectional area was used to reflect the fatigue damage of steel bars. The correction factor of size effect was introduced to further deduce the calculation model of the stiffness degradation of the prestressed concrete beam after being subjected to fatigue damage. The accuracy of the stiffness degradation model was verified by analyzing the experimental research results of prestressed concrete beams in different sizes under cyclically multi-level variable-amplitude loads. The test results showed that the stiffness degradation of prestressed concrete beams and the development of concrete damage under the multi-stage variable-amplitude loading test had similar laws; the calculation results of stiffness by the theoretical deduction formulas had a little deviation from the experimental results.
2021, 51(11): 67-74,99.
doi: 10.13204/j.gyjzG21012704
Abstract:
In the calculation of short-term stiffness of filigree slabs in composite slabs with lattice girders, the reasonable consideration of the contribution of lattice girder's stiffness to filigree slabs is directly related to the checking computations in the short-term design conditions. Three full-scale filigree slabs were designed according to Technical Specification for Precast Concsete Structceres(JGJ 1—2014), including two filigree slabs in thickness of 50 mm and one filigree slab in thickness of 60 mm, with length and width dimensions of 3 300 mm and 2 200 mm. The test and the analysis results showed that the bare top bars participated in bearing construction loads, but their role was limited. The reason was that the mechanical properties of the bare part of lattice girders were different from the part of bars embedded in slabs, which led to the larger stiffness of filigree slabs calculated by the method of equal modulus of elasticity. Based on the analysis and comparison of the test results, when the equal elastic modulus was used to calculate the total stiffness of filigree slabs, the section stiffness of the lattice girders by inverse calculations should be reduced. Then, a reduction factor of 0.6 was proposed.
In the calculation of short-term stiffness of filigree slabs in composite slabs with lattice girders, the reasonable consideration of the contribution of lattice girder's stiffness to filigree slabs is directly related to the checking computations in the short-term design conditions. Three full-scale filigree slabs were designed according to Technical Specification for Precast Concsete Structceres(JGJ 1—2014), including two filigree slabs in thickness of 50 mm and one filigree slab in thickness of 60 mm, with length and width dimensions of 3 300 mm and 2 200 mm. The test and the analysis results showed that the bare top bars participated in bearing construction loads, but their role was limited. The reason was that the mechanical properties of the bare part of lattice girders were different from the part of bars embedded in slabs, which led to the larger stiffness of filigree slabs calculated by the method of equal modulus of elasticity. Based on the analysis and comparison of the test results, when the equal elastic modulus was used to calculate the total stiffness of filigree slabs, the section stiffness of the lattice girders by inverse calculations should be reduced. Then, a reduction factor of 0.6 was proposed.
2021, 51(11): 75-80.
doi: 10.13204/j.gyjzG21010413
Abstract:
In order to study the corrosion effect on the inner walls of the grouting sleeves on the mechanical properties of prefabricated concrete structures after long-term service, 10 specimens connected with grouting sleeves were fabricated. The electrochemical method was used to accelerate corrosion on the inner walls of sleeves, and pull-out tests were conducted on specimens. The test results showed that when the corrosion rate was 0% and 3%, the failure modes of the specimens connected with the grouting sleeve were all shown as steel fracture failure. When the corrosion rate reached 6% and above, the failure mode of specimens in connection with grouting sleeves was the pull-out of grouting material, and the ultimate pull-out force and ultimate slip amount decreased with the increase of corrosion rate. Compared with the non-corroded sleeve, when the measured corrosion rate reached 12.74%, the loss of the ultimate pull-out resistance for grouting sleeves connected specimen by rust was by nearly 50%. Aiming at the case that the grouting material was pulled out after the sleeve was corroded, a fracture bond-slip model for the corrosion on the inner wall of the grout sleeve was proposed. It provided theoretical reference to the numerically refined modeling of grouting sleeves connected specimens with corroded inner walls.
In order to study the corrosion effect on the inner walls of the grouting sleeves on the mechanical properties of prefabricated concrete structures after long-term service, 10 specimens connected with grouting sleeves were fabricated. The electrochemical method was used to accelerate corrosion on the inner walls of sleeves, and pull-out tests were conducted on specimens. The test results showed that when the corrosion rate was 0% and 3%, the failure modes of the specimens connected with the grouting sleeve were all shown as steel fracture failure. When the corrosion rate reached 6% and above, the failure mode of specimens in connection with grouting sleeves was the pull-out of grouting material, and the ultimate pull-out force and ultimate slip amount decreased with the increase of corrosion rate. Compared with the non-corroded sleeve, when the measured corrosion rate reached 12.74%, the loss of the ultimate pull-out resistance for grouting sleeves connected specimen by rust was by nearly 50%. Aiming at the case that the grouting material was pulled out after the sleeve was corroded, a fracture bond-slip model for the corrosion on the inner wall of the grout sleeve was proposed. It provided theoretical reference to the numerically refined modeling of grouting sleeves connected specimens with corroded inner walls.
2021, 51(11): 81-89.
doi: 10.13204/j.gyjzG20110403
Abstract:
The connections of anchorage-embedded parts have been widely used in cable-supported curtain walls, which bear large tensile forces. In order to understand the actual mechanical properties of anchorage-embedded parts in connection of cables, 3 specimens of anchorage-embedded parts with a single tensional cable and 2 specimens of anchorage-embedded parts with three tensional cables were fabricated, and the tests of tensile bearing capacity for specimens were performed. The results showed that: when the anchorage length was longer than 30 times the diameter of the steel bar and the end was reinforced, the bond slip failure between the concrete and the anchorage parts would not occur, but only the anchorage parts would break. In the connections, the loads in the side cable would not impact on the bearing capacity of the middle cable. In addition, a single cable connection was simulated by FEM. Comparing the two results, it showed that the load-displacement curve of the anchorage-embedded parts with a single tensional cable obtained by FEM was in good agreement with the curve obtained from tests, and the error of the yield load and the ultimate load all less 6%.
The connections of anchorage-embedded parts have been widely used in cable-supported curtain walls, which bear large tensile forces. In order to understand the actual mechanical properties of anchorage-embedded parts in connection of cables, 3 specimens of anchorage-embedded parts with a single tensional cable and 2 specimens of anchorage-embedded parts with three tensional cables were fabricated, and the tests of tensile bearing capacity for specimens were performed. The results showed that: when the anchorage length was longer than 30 times the diameter of the steel bar and the end was reinforced, the bond slip failure between the concrete and the anchorage parts would not occur, but only the anchorage parts would break. In the connections, the loads in the side cable would not impact on the bearing capacity of the middle cable. In addition, a single cable connection was simulated by FEM. Comparing the two results, it showed that the load-displacement curve of the anchorage-embedded parts with a single tensional cable obtained by FEM was in good agreement with the curve obtained from tests, and the error of the yield load and the ultimate load all less 6%.
2021, 51(11): 90-99.
doi: 10.13204/j.gyjzG21080302
Abstract:
Taking a typical 220 kV transmission tower-line system located in the mining area as the research object, the finite element model of the tower-line system was constructed by ANSYS software. The displacement time history of the control points of the tower and the stress time history of key crossed bracing members and tower legs under the action of boundary layer wind in different directions were studied. The relations between the maximum equivalent stress of legs of the tower and the surface horizontal deformation direction, the deformation degree, and the wind direction angle of boundary layer were analyzed. The results showed that the four leg members were the key members to determine the safety of tower against surface deformation and wind under the action of surface horizontal deformation and boundary layer wind. The displacement of the tower displacement control points were within the allowable range of normal operation. The most unfavorable action direction of surface horizontal deformation was 30°. The most unfavorable directions of boundary layer wind were 30° and 45°. There was a linear relation between the maximum equivalent stress of leg members of the tower and the degree of surface deformation. On this basis, the correlations between the maximum equivalent stress of leg members of the tower and the direction and degree of surface horizontal deformation were obtained, and a safety assessment method of the transmission tower-line system in mining area under the action of surface horizontal deformation and boundary layer wind was proposed.
Taking a typical 220 kV transmission tower-line system located in the mining area as the research object, the finite element model of the tower-line system was constructed by ANSYS software. The displacement time history of the control points of the tower and the stress time history of key crossed bracing members and tower legs under the action of boundary layer wind in different directions were studied. The relations between the maximum equivalent stress of legs of the tower and the surface horizontal deformation direction, the deformation degree, and the wind direction angle of boundary layer were analyzed. The results showed that the four leg members were the key members to determine the safety of tower against surface deformation and wind under the action of surface horizontal deformation and boundary layer wind. The displacement of the tower displacement control points were within the allowable range of normal operation. The most unfavorable action direction of surface horizontal deformation was 30°. The most unfavorable directions of boundary layer wind were 30° and 45°. There was a linear relation between the maximum equivalent stress of leg members of the tower and the degree of surface deformation. On this basis, the correlations between the maximum equivalent stress of leg members of the tower and the direction and degree of surface horizontal deformation were obtained, and a safety assessment method of the transmission tower-line system in mining area under the action of surface horizontal deformation and boundary layer wind was proposed.
2021, 51(11): 100-105.
doi: 10.13204/j.gyjzG21031202
Abstract:
In order to research propagation characteristics of fatigue crack for steel bridge decks with open-shaped longitudinal-ribs, the rib-to-deck welded joint and rib-to-diaphragm welded joint were considered as research objects, based on the Yunnan Chuda Expressway Project. The fatigue crack propagation characteristics and optimal design of steel bridge decks with open-shaped longitndinal ribs were systematically studied. The results indicated that the four typical fatigue cracking modes all increased with the increase of crack depth, in the early stage of fatigue crack propagation. When the crack depth reached 4 mm, the fatigue crack growth rates of cracking modes C1, C2 and C3 reached their peaks, and the crack growth rate of the cracking mode C4 increased continuously with the increase of the crack depth throughout the process. The fatigue life of the steel bridge deck with open-shaped longitudinal ribs was controlled by the cracking mode C1 and C4. Increasing the thickness of the deck and laying a concrete cast-in-situ layer could significantly reduce the equivalent stress intensity factor amplitude of the steel bridge deck, but the laying of the cast-in-situ concrete layer had a more significant impact on the fatigue performance of the steel bridge deck. It was recommended to improve the fatigue performance of steel bridge decks by laying cast-in-situ concrete layers.
In order to research propagation characteristics of fatigue crack for steel bridge decks with open-shaped longitudinal-ribs, the rib-to-deck welded joint and rib-to-diaphragm welded joint were considered as research objects, based on the Yunnan Chuda Expressway Project. The fatigue crack propagation characteristics and optimal design of steel bridge decks with open-shaped longitndinal ribs were systematically studied. The results indicated that the four typical fatigue cracking modes all increased with the increase of crack depth, in the early stage of fatigue crack propagation. When the crack depth reached 4 mm, the fatigue crack growth rates of cracking modes C1, C2 and C3 reached their peaks, and the crack growth rate of the cracking mode C4 increased continuously with the increase of the crack depth throughout the process. The fatigue life of the steel bridge deck with open-shaped longitudinal ribs was controlled by the cracking mode C1 and C4. Increasing the thickness of the deck and laying a concrete cast-in-situ layer could significantly reduce the equivalent stress intensity factor amplitude of the steel bridge deck, but the laying of the cast-in-situ concrete layer had a more significant impact on the fatigue performance of the steel bridge deck. It was recommended to improve the fatigue performance of steel bridge decks by laying cast-in-situ concrete layers.
2021, 51(11): 106-111,120.
doi: 10.13204/j.gyjzG21031203
Abstract:
In order to research the fatigue performance of steel bridge deck with open-shaped longitudinal ribs, the rib-to-deck welded joint and rib-to-diaphragm welded joint were considered as research objects, based on the Yunnan Chuda Expressway project, the fatigue performance and key influencing factors of steel bridge decks with open-shaped longitudinal ribs were systematically studied. The results indicated that the length of the longitudinal influence line of rib-to-deck welded joint was mainly between the two adjacent diaphragms of the structural details. The length of the longitudinal influence line of rib-to-diaphragm welded joint was mainly within the two adjacent spans of the structural details. The hot-spot stress amplitude of the deck toe cracking mode(C1) was the largest under the longitudinal moving load, which was 125.8 MPa. After laying an 8 cm thick cast-in-situ concrete layer, the hot-spot stress amplitude of the deck toe cracking mode was reduced to 10.7 MPa, a reduction of 91.5%. The change of the rib height had no significant effect on the stress amplitude of each fatigue cracking mode of the steel bridge decks with open-shaped longitudinal ribs. Increasing the rib spacing would significantly increase the stress amplitude of the diaphragm toe cracking mode(C4). The stress amplitude of each cracking mode of the steel bridge deck with open-shaped longitudinal ribs and cast-in-situ concrete layer was at a low level, the risk of fatigue cracking was small.
In order to research the fatigue performance of steel bridge deck with open-shaped longitudinal ribs, the rib-to-deck welded joint and rib-to-diaphragm welded joint were considered as research objects, based on the Yunnan Chuda Expressway project, the fatigue performance and key influencing factors of steel bridge decks with open-shaped longitudinal ribs were systematically studied. The results indicated that the length of the longitudinal influence line of rib-to-deck welded joint was mainly between the two adjacent diaphragms of the structural details. The length of the longitudinal influence line of rib-to-diaphragm welded joint was mainly within the two adjacent spans of the structural details. The hot-spot stress amplitude of the deck toe cracking mode(C1) was the largest under the longitudinal moving load, which was 125.8 MPa. After laying an 8 cm thick cast-in-situ concrete layer, the hot-spot stress amplitude of the deck toe cracking mode was reduced to 10.7 MPa, a reduction of 91.5%. The change of the rib height had no significant effect on the stress amplitude of each fatigue cracking mode of the steel bridge decks with open-shaped longitudinal ribs. Increasing the rib spacing would significantly increase the stress amplitude of the diaphragm toe cracking mode(C4). The stress amplitude of each cracking mode of the steel bridge deck with open-shaped longitudinal ribs and cast-in-situ concrete layer was at a low level, the risk of fatigue cracking was small.
2021, 51(11): 112-120.
doi: 10.13204/j.gyjzG21062001
Abstract:
The analysis model of four-sided simply-supported thin plates with rectangular holes subjected to linearly varying loads was constructed by using the finite element software ABAQUS. The influence of dimension and spacing of holes on the elastic buckling property, buckling coefficient, and ultimate bearing capacity of perforated thin plates subjected to linearly varying loads was analyzed. The elastic buckling analysis results show that the effect of the spacing of holes was not significant when the spacing of holes could meet a certain limit. With the increase of the dimension of holes, buckling modes of thin plates transformed from the buckling of plates with holes to the buckling of plates adjacent to holes. Finally, buckling coefficients of thin plates with rectangular holes subjected to linearly varing pressure were obtained by finite element analysis. Meanwhile, the calculated formula of buckling coefficients was proposed. The ultimate bearing capacity of thin plates was calculated by using effective width method based on proposed buckling coefficients that the dimensions of rectangular holes had less effect on the ultimate bearing capacity of perforated plates when holes were small. But the effect gradually increased with the increase of dimensions of holes. The proposed effective width method could be used to predict the ultimate bearing capacity of thin plates with rectangular holes subjected to linearly varying loads.
The analysis model of four-sided simply-supported thin plates with rectangular holes subjected to linearly varying loads was constructed by using the finite element software ABAQUS. The influence of dimension and spacing of holes on the elastic buckling property, buckling coefficient, and ultimate bearing capacity of perforated thin plates subjected to linearly varying loads was analyzed. The elastic buckling analysis results show that the effect of the spacing of holes was not significant when the spacing of holes could meet a certain limit. With the increase of the dimension of holes, buckling modes of thin plates transformed from the buckling of plates with holes to the buckling of plates adjacent to holes. Finally, buckling coefficients of thin plates with rectangular holes subjected to linearly varing pressure were obtained by finite element analysis. Meanwhile, the calculated formula of buckling coefficients was proposed. The ultimate bearing capacity of thin plates was calculated by using effective width method based on proposed buckling coefficients that the dimensions of rectangular holes had less effect on the ultimate bearing capacity of perforated plates when holes were small. But the effect gradually increased with the increase of dimensions of holes. The proposed effective width method could be used to predict the ultimate bearing capacity of thin plates with rectangular holes subjected to linearly varying loads.
2021, 51(11): 121-126.
doi: 10.13204/j.gyjzG21061515
Abstract:
The dynamically mechanical performance tests of 47 specimens in three loading rates of 0.6 mm/s, 6.0 mm/s and 60.0 mm/s were performed to study the influence of rebar diameters, loading rates and grouting forms on connection performances compare and analyze the mechanical properties between semi-grouting comection and full-grouted sleeve connection all other factors being equal, and study the influence of sleeve connection methods on comection performances. The formulas of the dynamic bearing capacity and stiffness for the comection of full-grouted sleeve were proposed.The results showed that the failure modes of the specimens at different loading rates were basically the same, all in which were tensile failure of rebars; pull-out failure of rebars and sleeve slip failure only occured in a few specimens. The yield loads and ultimate bearing capacity of the sleeve connection increased with the increase of the diameter of the steel bars; at loading rates of 0.6 mm/s, 6.0 mm/s and 60.0 mm/s, the dynamic loads had little effect on the semi-grouted sleeve connection. With the increase of loading rates, the bearing capacity of the full-grouted sleeve specimens showed an increasing trend as a whole, and the dynamic bearing capacity was higher than the static bearing capacity. The diameter of rebars is an important factor influencing the dynamic stiffness of sleeve grouting connections. As the increcpse the diameter of rebars, the stiffness of specimens increased but the loading rate had a little influence on the stittness when the diameter of rebars was the same.
The dynamically mechanical performance tests of 47 specimens in three loading rates of 0.6 mm/s, 6.0 mm/s and 60.0 mm/s were performed to study the influence of rebar diameters, loading rates and grouting forms on connection performances compare and analyze the mechanical properties between semi-grouting comection and full-grouted sleeve connection all other factors being equal, and study the influence of sleeve connection methods on comection performances. The formulas of the dynamic bearing capacity and stiffness for the comection of full-grouted sleeve were proposed.The results showed that the failure modes of the specimens at different loading rates were basically the same, all in which were tensile failure of rebars; pull-out failure of rebars and sleeve slip failure only occured in a few specimens. The yield loads and ultimate bearing capacity of the sleeve connection increased with the increase of the diameter of the steel bars; at loading rates of 0.6 mm/s, 6.0 mm/s and 60.0 mm/s, the dynamic loads had little effect on the semi-grouted sleeve connection. With the increase of loading rates, the bearing capacity of the full-grouted sleeve specimens showed an increasing trend as a whole, and the dynamic bearing capacity was higher than the static bearing capacity. The diameter of rebars is an important factor influencing the dynamic stiffness of sleeve grouting connections. As the increcpse the diameter of rebars, the stiffness of specimens increased but the loading rate had a little influence on the stittness when the diameter of rebars was the same.
2021, 51(11): 127-131,136.
doi: 10.13204/j.gyjzG210102701
Abstract:
The formwork system used in a super high-rise building project in Xi'an adopted a hydraulic jack-up formwork system, which was mainly composed of primary and secondary trusses, steel columns and outrigger trusses. In order to ensure the structural safety of the jack-up formwork structure in the construction process, based on the overall structure and working principle of the hydraulic jack-up formwork system, the finite element model of the jack-up formwork structure system was constructed, the stress values of the jack-up formwork system in various working conditions were simulated by FEM, the stress monitoring system was used to monitor the key points of the structure in different working conditions. In the same working condition and load combination, the measured stress of the jack-up formwork was compared with the simulation results. The results showed that the measured stress and finite element simulation results effectively verified that the structural stress and deformation of the jack-up formwork could meet the requirements in various working conditions, the structure was safe.
The formwork system used in a super high-rise building project in Xi'an adopted a hydraulic jack-up formwork system, which was mainly composed of primary and secondary trusses, steel columns and outrigger trusses. In order to ensure the structural safety of the jack-up formwork structure in the construction process, based on the overall structure and working principle of the hydraulic jack-up formwork system, the finite element model of the jack-up formwork structure system was constructed, the stress values of the jack-up formwork system in various working conditions were simulated by FEM, the stress monitoring system was used to monitor the key points of the structure in different working conditions. In the same working condition and load combination, the measured stress of the jack-up formwork was compared with the simulation results. The results showed that the measured stress and finite element simulation results effectively verified that the structural stress and deformation of the jack-up formwork could meet the requirements in various working conditions, the structure was safe.
2021, 51(11): 132-136.
doi: 10.13204/j.gyjzG20101008
Abstract:
The seafloor sediments in the South China Sea are mainly composed of cohesionless soil with calcareous sand. It is of great significance to study the compression characteristics of cohesionless soil with calcareous sand for engineering safety. Based on the high-pressure triaxial test system, the effects of the calcareous sand content, initial void ratio and effective stress on the compression characteristics of cohesionless soil were studied. The results showed that the increase of the calcareous sand content could improve the compressibility of cohesionless soil under the same effective stress; when the calcareous sand content exceeded 60%, the compression curves of soil specimens in different initial void ratios would converge in the high effective stress region. Based on the above conclusion, a mathematical model was proposed to describe the compression characteristics of cohesionless soil with calcareous sand. The model showed good prediction effect in different sandy soils. Compared with the existing compression model, the superiority of the model was verified.
The seafloor sediments in the South China Sea are mainly composed of cohesionless soil with calcareous sand. It is of great significance to study the compression characteristics of cohesionless soil with calcareous sand for engineering safety. Based on the high-pressure triaxial test system, the effects of the calcareous sand content, initial void ratio and effective stress on the compression characteristics of cohesionless soil were studied. The results showed that the increase of the calcareous sand content could improve the compressibility of cohesionless soil under the same effective stress; when the calcareous sand content exceeded 60%, the compression curves of soil specimens in different initial void ratios would converge in the high effective stress region. Based on the above conclusion, a mathematical model was proposed to describe the compression characteristics of cohesionless soil with calcareous sand. The model showed good prediction effect in different sandy soils. Compared with the existing compression model, the superiority of the model was verified.
2021, 51(11): 137-142.
doi: 10.13204/j.gyjzG20112307
Abstract:
Rigid pile has obvious effects on bearing properties of composite foundation with reinforced cushions. However, the effect of rigid piles on properties of composite foundation was still in research and the achievements were rarely reported. The changing laws of foundation subsidence, stress of piles and tensile forces of geogrids were analyzed based on some groups of model tests of composite foundation with geogrid-reinforced cushions supported with flexible piles or flexible-rigid piles. The test results showed that subsidence of composite foundation increased with the cycles of cyclic loads. The subsidence of composite foundation could be reduced by addition of rigid piles or of geogrid layers. The effect of adding rigid piles was more obvious than that of adding geogrid layers on reducing subsidence. Axial forces of piles first increased then decreasd along the pile shafts, and the axial forces increased with cycles of cyclic loads. The addition of rigid piles could reduce loads shared by side and corner piles in the same condition of cyclic loads. The tensile forces of geogrids increased with cycles of cyclic loads. The closer to the pile, the greater the tensile forces in geogrids. Tensile forces in geogrids reached the maximum at the junctions of piles and soil. The addition of rigid piles could not only change the distribution of tension forces in geogrids but also increase the tension forces in geogrids.
Rigid pile has obvious effects on bearing properties of composite foundation with reinforced cushions. However, the effect of rigid piles on properties of composite foundation was still in research and the achievements were rarely reported. The changing laws of foundation subsidence, stress of piles and tensile forces of geogrids were analyzed based on some groups of model tests of composite foundation with geogrid-reinforced cushions supported with flexible piles or flexible-rigid piles. The test results showed that subsidence of composite foundation increased with the cycles of cyclic loads. The subsidence of composite foundation could be reduced by addition of rigid piles or of geogrid layers. The effect of adding rigid piles was more obvious than that of adding geogrid layers on reducing subsidence. Axial forces of piles first increased then decreasd along the pile shafts, and the axial forces increased with cycles of cyclic loads. The addition of rigid piles could reduce loads shared by side and corner piles in the same condition of cyclic loads. The tensile forces of geogrids increased with cycles of cyclic loads. The closer to the pile, the greater the tensile forces in geogrids. Tensile forces in geogrids reached the maximum at the junctions of piles and soil. The addition of rigid piles could not only change the distribution of tension forces in geogrids but also increase the tension forces in geogrids.
2021, 51(11): 143-148,194.
doi: 10.13204/j.gyjzG20111802
Abstract:
Most of tested piles in domestic construction sites are not loaded to the ultimate loads, and the estimation on the bearing capacity of piles is often underestimated, so that the potential of pile foundations cannot be reasonably brought into play. To correctly calculate the bearing capacity of rock-socketed piles, the classical theory of the limit equilibrium for pile tips was used to calculate the ultimate resistance of pile tips, the friction force on sliding surfaces above the plane of pile tips was taken as the increment of the bearing capacity. By the verification of static load tests for 11 test piles, the ultimate bearing capacity of pile tips embedded in moderately weathered granite was 30% higher than that one calculated by Code for Design of Building Foundation(GB 50007-2011). Further, 10 engineering piles were screened out to be tested. The results showed that: on the same maximum load level, the rock foundation under 5 pile tips damaged to column-block shapes but the bearing capacity of pile tips did not reach the ultimate, and still had greater bearing potential. The rock foundation under 2 pile tips damaged to crushed stones, the bearing capacity of pile tips was close to the ultimate but 22.8% higher than that one calculated by GB 50007-2011. By comparing and analysis of test data from 11 test piles and 10 engineering piles, it showed that If the pile length was more than 25 times of pile diameters, the friction resistance of stratum around piles including the rock-socketed length and the resistance of pile tips all didn't fully bring into play. The optimum rock-socketed depth was 1.0 to 2.0 times the pile diameter. The influence of the sediment thickness under the pile tips on the bearing capacity was not obvious when the thickness of the sediment was more than 50 mm, the influence of structure difference for the rock stratum on the bearing capacity was more than 30%.
Most of tested piles in domestic construction sites are not loaded to the ultimate loads, and the estimation on the bearing capacity of piles is often underestimated, so that the potential of pile foundations cannot be reasonably brought into play. To correctly calculate the bearing capacity of rock-socketed piles, the classical theory of the limit equilibrium for pile tips was used to calculate the ultimate resistance of pile tips, the friction force on sliding surfaces above the plane of pile tips was taken as the increment of the bearing capacity. By the verification of static load tests for 11 test piles, the ultimate bearing capacity of pile tips embedded in moderately weathered granite was 30% higher than that one calculated by Code for Design of Building Foundation(GB 50007-2011). Further, 10 engineering piles were screened out to be tested. The results showed that: on the same maximum load level, the rock foundation under 5 pile tips damaged to column-block shapes but the bearing capacity of pile tips did not reach the ultimate, and still had greater bearing potential. The rock foundation under 2 pile tips damaged to crushed stones, the bearing capacity of pile tips was close to the ultimate but 22.8% higher than that one calculated by GB 50007-2011. By comparing and analysis of test data from 11 test piles and 10 engineering piles, it showed that If the pile length was more than 25 times of pile diameters, the friction resistance of stratum around piles including the rock-socketed length and the resistance of pile tips all didn't fully bring into play. The optimum rock-socketed depth was 1.0 to 2.0 times the pile diameter. The influence of the sediment thickness under the pile tips on the bearing capacity was not obvious when the thickness of the sediment was more than 50 mm, the influence of structure difference for the rock stratum on the bearing capacity was more than 30%.
2021, 51(11): 149-153,185.
doi: 10.13204/j.gyjzG21060210
Abstract:
Taking river sludge polluted by heavy metal as research objects, using cement as cementitious material, industrial waste fly ash and mineral powder as auxiliary cementitious materials, AlCl3, gypsum as the admixture, the polluted sludge was cemented and the leaching tests were conducted on cemented specimens. The optimum proportion for cemented specimens of the minimum leached concentration of heavy metals was selected by the single mixing experiment and orthogonal experiment. The specimens cemented prepared by the optimal proportion were performed long-age curing tests and freeze-thaw tests. The results showed that when the AlCl3 content was 4% and curing age was 1 d, the water content of specimens decreased obviously. When the content of cement, mineral powder, fly ash and gypsum in specimens was respectively 12%, 14%, 6% and 0.4%, the leached concentration of Ni, Cd, Pb and Hg from spcimens decreased by 78.04%, 85.78%, 67.79% and 90.00%. The leached concentrations of Ni, Cd, Pb and Hg from specimens respectively decreased by 74.26%, 83.75%, 62.27% and 88.62% after 200 freeze-thaw cycles. The leached concentrations of Ni, Cd, Pb and Hg from specimens decreased by 85.42%, 90.29%, 78.84% and 92.83% respectively, when specimens were cured for 300 d. The results showed that the leached concentrations of heavy metals from specimens met the requirements of Specifications Planting Soil for Greening(CJ/T 340-2016) and the cemented soil had a good performance of stabilizing heavy metals.
Taking river sludge polluted by heavy metal as research objects, using cement as cementitious material, industrial waste fly ash and mineral powder as auxiliary cementitious materials, AlCl3, gypsum as the admixture, the polluted sludge was cemented and the leaching tests were conducted on cemented specimens. The optimum proportion for cemented specimens of the minimum leached concentration of heavy metals was selected by the single mixing experiment and orthogonal experiment. The specimens cemented prepared by the optimal proportion were performed long-age curing tests and freeze-thaw tests. The results showed that when the AlCl3 content was 4% and curing age was 1 d, the water content of specimens decreased obviously. When the content of cement, mineral powder, fly ash and gypsum in specimens was respectively 12%, 14%, 6% and 0.4%, the leached concentration of Ni, Cd, Pb and Hg from spcimens decreased by 78.04%, 85.78%, 67.79% and 90.00%. The leached concentrations of Ni, Cd, Pb and Hg from specimens respectively decreased by 74.26%, 83.75%, 62.27% and 88.62% after 200 freeze-thaw cycles. The leached concentrations of Ni, Cd, Pb and Hg from specimens decreased by 85.42%, 90.29%, 78.84% and 92.83% respectively, when specimens were cured for 300 d. The results showed that the leached concentrations of heavy metals from specimens met the requirements of Specifications Planting Soil for Greening(CJ/T 340-2016) and the cemented soil had a good performance of stabilizing heavy metals.
2021, 51(11): 154-158.
doi: 10.13204/j.gyjzG20110202
Abstract:
Cement-stabilized soil has the characteristics of poor durability generally. By a series of unconfined compression tests, compactness tests, dry wet cycle tests and CBR tests on cement-stabilized soil mixed with the super absorbent ploymers, the strength, compactness and durability of the cement-stabilized soil reinforced by SAP were analyzed and studied. The experimental results proved that: adding SAP could improve the unconfined compressive strength of cemented soil, up to 185% and improve the compaction characteristics of cement-stabilized soil, the optimal moisture content could be increased by 2%. With the increase of drying and wetting cycles, the mass loss of SAP-cement-stabilized soil could be reduced, while the unconfined compressive strength could be improved by 121%, which indicated that SAP could improve the durability of cement-stabilized soil; the CBR of specimens cemented with cement and SAP were slightly lower than that cemented with cement. Adding SAP could obviously improve many indexes of pavement performances for cement-stabilized soil and meet the requirements of subgrade fillings of high-grade highways.
Cement-stabilized soil has the characteristics of poor durability generally. By a series of unconfined compression tests, compactness tests, dry wet cycle tests and CBR tests on cement-stabilized soil mixed with the super absorbent ploymers, the strength, compactness and durability of the cement-stabilized soil reinforced by SAP were analyzed and studied. The experimental results proved that: adding SAP could improve the unconfined compressive strength of cemented soil, up to 185% and improve the compaction characteristics of cement-stabilized soil, the optimal moisture content could be increased by 2%. With the increase of drying and wetting cycles, the mass loss of SAP-cement-stabilized soil could be reduced, while the unconfined compressive strength could be improved by 121%, which indicated that SAP could improve the durability of cement-stabilized soil; the CBR of specimens cemented with cement and SAP were slightly lower than that cemented with cement. Adding SAP could obviously improve many indexes of pavement performances for cement-stabilized soil and meet the requirements of subgrade fillings of high-grade highways.
2021, 51(11): 159-164,24.
doi: 10.13204/j.gyjzG21030802
Abstract:
In order to study the deformation performance and damage development of pebble concrete under triaxial compression, based on the parameters of confining pressure, 27 Φ100×200 cylinder specimens were designed and tested under triaxial compression.The results showed that the failure patterns of the specimens under triaxial compression were divided into vertical splitting failure, oblique shear failure and transverse rupture failure according to different confined pressures. As the confining pressure increased, the peak of the stress-strain curve of specimens increased, the descending section of the stress-strain curve gradually flattened, and the energy dissipation increased. The confining pressure could significantly improve the ductility of pebble concrete and restrain the damage development of pebble concrete. Finally, the functional relations between the lateral confining pressure and the actual energy dissipation was presented by fitting the experimental data.
In order to study the deformation performance and damage development of pebble concrete under triaxial compression, based on the parameters of confining pressure, 27 Φ100×200 cylinder specimens were designed and tested under triaxial compression.The results showed that the failure patterns of the specimens under triaxial compression were divided into vertical splitting failure, oblique shear failure and transverse rupture failure according to different confined pressures. As the confining pressure increased, the peak of the stress-strain curve of specimens increased, the descending section of the stress-strain curve gradually flattened, and the energy dissipation increased. The confining pressure could significantly improve the ductility of pebble concrete and restrain the damage development of pebble concrete. Finally, the functional relations between the lateral confining pressure and the actual energy dissipation was presented by fitting the experimental data.
2021, 51(11): 165-170,38.
doi: 10.13204/j.gyjzG21022608
Abstract:
The Chinese National Standard High Strength Low Alloy Structural Steels(GB/T 1591-2018) requires that Q345 steel must be replaced by Q355 steel from February 1, 2019. Its residual mechanical properties after a fire are the key indicators for post-fire safety evaluation. As a widely-used fire extinguishing method in fire, water cooling is the fastest and most efficient firefighting method. Therefore, a uniaxial tensile test was conducted on the domestic Q355 steel specimens after water cooling from high temperature. The stress-strain curves and related mechanical properties of Q355 steel after water cooling from high temperature were obtained, and the variations of the residual mechanical properties of Q355 steel after water cooling high temperature were analyzed. The differences in mechanical properties of Q355 steel and Q235, Q460 and Q690 steels after cooling from high temperatures were also compared and analyzed. The results showed that when the heating temperature was lower than 600 ℃, the mechanical properties of Q355 steel had relatively small changes, and the maximum changes in yield strength and elastic modulus did not exceed 10%. When the temperature exceeded 600 ℃, the yield strength of Q355 steel after being immersed in water was cooled. And the ultimate strength increased with the increase of temperature, but the elongation decreased with the increase of temperature. After cooling from high temperatures, the Q355 steel had similar changes with Q235, Q460 and Q690 steels in mechanical properties, but the specific change range had differences. Finally, based on the test results, a mathematical model of the change in mechanical parameters of Q355 steel cooled by water was established. This model could be used to effectively evaluate the mechanical properties of Q355 steel after fire.
The Chinese National Standard High Strength Low Alloy Structural Steels(GB/T 1591-2018) requires that Q345 steel must be replaced by Q355 steel from February 1, 2019. Its residual mechanical properties after a fire are the key indicators for post-fire safety evaluation. As a widely-used fire extinguishing method in fire, water cooling is the fastest and most efficient firefighting method. Therefore, a uniaxial tensile test was conducted on the domestic Q355 steel specimens after water cooling from high temperature. The stress-strain curves and related mechanical properties of Q355 steel after water cooling from high temperature were obtained, and the variations of the residual mechanical properties of Q355 steel after water cooling high temperature were analyzed. The differences in mechanical properties of Q355 steel and Q235, Q460 and Q690 steels after cooling from high temperatures were also compared and analyzed. The results showed that when the heating temperature was lower than 600 ℃, the mechanical properties of Q355 steel had relatively small changes, and the maximum changes in yield strength and elastic modulus did not exceed 10%. When the temperature exceeded 600 ℃, the yield strength of Q355 steel after being immersed in water was cooled. And the ultimate strength increased with the increase of temperature, but the elongation decreased with the increase of temperature. After cooling from high temperatures, the Q355 steel had similar changes with Q235, Q460 and Q690 steels in mechanical properties, but the specific change range had differences. Finally, based on the test results, a mathematical model of the change in mechanical parameters of Q355 steel cooled by water was established. This model could be used to effectively evaluate the mechanical properties of Q355 steel after fire.
2021, 51(11): 178-185.
doi: 10.13204/j.gyjzG21032205
Abstract:
Axial compression tests for 9 joints of PVC tube columns with core steel tubes wrapped with CFRP strips and reinforced conncrete beams were conducted, so as to study their failure modes and stress-strain relations, the effects of joint height, the length of core steel tubes, the steel proportions of core steel tubes, and the stirrup ratios of joints were studied. The experimental results showed that the concrete of joint zones was crushed and destroyed, and the PVC-CFRP tubular confined concrete column was not damaged. When the tensile strain of the joint concrete reached the ultimate tensile strain, the stress-strain curves of the joints deviated from linear growth. The gradients of the stress-strain curves increased with the increase of the stirrup ratios in joints and the steel proportion of core steel tubes increased or with the decrease of the joint height. Based on Mander's model, an accurate model for estimating the stress-strain relations of the joints was constructed, and it agreed well with test data.
Axial compression tests for 9 joints of PVC tube columns with core steel tubes wrapped with CFRP strips and reinforced conncrete beams were conducted, so as to study their failure modes and stress-strain relations, the effects of joint height, the length of core steel tubes, the steel proportions of core steel tubes, and the stirrup ratios of joints were studied. The experimental results showed that the concrete of joint zones was crushed and destroyed, and the PVC-CFRP tubular confined concrete column was not damaged. When the tensile strain of the joint concrete reached the ultimate tensile strain, the stress-strain curves of the joints deviated from linear growth. The gradients of the stress-strain curves increased with the increase of the stirrup ratios in joints and the steel proportion of core steel tubes increased or with the decrease of the joint height. Based on Mander's model, an accurate model for estimating the stress-strain relations of the joints was constructed, and it agreed well with test data.
2021, 51(11): 186-194.
doi: 10.13204/j.gyjzG21021802
Abstract:
With the increase of photovoltaic power generation projects, more and more industrial plants have been equipped with photovoltaic panels on the roofs. With the increase of service loads on roof, purlins can not meet the requirements of bearing capacity, so it is often necessary to be reinforced. Combined with the background of a 5 MW self-consumption distributed photovoltaic power generation project, a new method for purlin reinforcement was proposed based on the reinforcement method of enlargement sections, that was, L-shaped angle steel was added at the lower flange of the original C-section purlins for reinforcement, and the two were connected by core-pulling rivets. On that basis, the bearing capacity tests of three reinforced steel purlin specimens were conducted to study the mechanical properties and failure modes of purlins, and the load-displacement curve, load-strain curve, bearing capacity, and stiffness of specimens were obtained. Through the finite element software ABAQUS, the accurate finite element models of specimens were constructed, and the numerical simulation analysis was conducted. The finite element results and test results were compared and analyzed to verify the accuracy of test results and the effectiveness of the new reinforcement method. The results showed that: the new reinforcement method of C-section steel purlins proposed in the paper was feasible. The bearing capacity and stiffness of the reinforced steel purlins could satisfy the requirements of relevant specifications, and the ultimate bearing capacity was about 1.49 times of the design value of bearing capacity of original purlins.
With the increase of photovoltaic power generation projects, more and more industrial plants have been equipped with photovoltaic panels on the roofs. With the increase of service loads on roof, purlins can not meet the requirements of bearing capacity, so it is often necessary to be reinforced. Combined with the background of a 5 MW self-consumption distributed photovoltaic power generation project, a new method for purlin reinforcement was proposed based on the reinforcement method of enlargement sections, that was, L-shaped angle steel was added at the lower flange of the original C-section purlins for reinforcement, and the two were connected by core-pulling rivets. On that basis, the bearing capacity tests of three reinforced steel purlin specimens were conducted to study the mechanical properties and failure modes of purlins, and the load-displacement curve, load-strain curve, bearing capacity, and stiffness of specimens were obtained. Through the finite element software ABAQUS, the accurate finite element models of specimens were constructed, and the numerical simulation analysis was conducted. The finite element results and test results were compared and analyzed to verify the accuracy of test results and the effectiveness of the new reinforcement method. The results showed that: the new reinforcement method of C-section steel purlins proposed in the paper was feasible. The bearing capacity and stiffness of the reinforced steel purlins could satisfy the requirements of relevant specifications, and the ultimate bearing capacity was about 1.49 times of the design value of bearing capacity of original purlins.
2021, 51(11): 195-199.
doi: 10.13204/j.gyjzG20101901
Abstract:
Based on the test results of brick masonry walls strengthened with pre-stressed steel belts under horizonal monotonic and quasi-static loading, the failure criterion of anisotropic brick masonry walls under biaxial compression proposed by Ganz was used to analyze the test data, and the results from the theoretical calculation were closer to that from the test, which proved the feasibility of the calculation method. In addition, combined with the stress characteristics of brick masonry walls strengthened with pre-stressed steel belts, some suggestions were given for the ratio of horizontal compressive stress to horizontal compressive strength of brick masonry walls.
Based on the test results of brick masonry walls strengthened with pre-stressed steel belts under horizonal monotonic and quasi-static loading, the failure criterion of anisotropic brick masonry walls under biaxial compression proposed by Ganz was used to analyze the test data, and the results from the theoretical calculation were closer to that from the test, which proved the feasibility of the calculation method. In addition, combined with the stress characteristics of brick masonry walls strengthened with pre-stressed steel belts, some suggestions were given for the ratio of horizontal compressive stress to horizontal compressive strength of brick masonry walls.
2021, 51(11): 200-204.
doi: 10.13204/j.gyjzG20031011
Abstract:
Super high-rise buildings are characterized with high height, complex structure, and tough construction safety management. Aiming at the safety issue, a reliability-based method to evaluate accident risks of super high-rise buildings under construction was proposed. Through investigation of literature and interview with experts, a index system of risk loads and risk resistance construction accidents for super high-rise buildings was constructed and the measurement metrics were determined. Then an approach to adjusting the probability of risk loads by risk resistance was presented, and the quantitative risk evaluation method was built as well by combining risk consequence assessment. The proposed method could effectively reduce the risks of super high-rise buildings under construction and thus improve the levels of safety management for super high-rise building under construction.
Super high-rise buildings are characterized with high height, complex structure, and tough construction safety management. Aiming at the safety issue, a reliability-based method to evaluate accident risks of super high-rise buildings under construction was proposed. Through investigation of literature and interview with experts, a index system of risk loads and risk resistance construction accidents for super high-rise buildings was constructed and the measurement metrics were determined. Then an approach to adjusting the probability of risk loads by risk resistance was presented, and the quantitative risk evaluation method was built as well by combining risk consequence assessment. The proposed method could effectively reduce the risks of super high-rise buildings under construction and thus improve the levels of safety management for super high-rise building under construction.
2021, 51(11): 205-210.
doi: 10.13204/j.gyjzG21061602
Abstract:
A long-span steel plant was adopted a steel frame structure system. Under the construction, the deflection of steel beams on the first floor exceeded the limit of Standard for Classification of Steel Structures(GB 50017—2017). In order to meet the requirements of construction and subsequent use, it was necessary to strengthen the steel beams on the first floor of the structure. Through the calculation of the jacked steel beams and the monitoring of the on-site jacking process before and after reinforcement, the comparison and analysis of the structural stress and deformation before and after reinforcement showed that the excessive deformation of the steel beams was due to many reasons such as design and construction. The designed jacking devices could well realize the jacking of steel beams, and the reinforcement scheme for the jaking of steel beams was reasonable. After the steel beams were strengthened and jacked, the traffic demand of the existing crane beam was met, the structure became safe and reliable, which proved that the reinforcement scheme for lifting was safe and economical.
A long-span steel plant was adopted a steel frame structure system. Under the construction, the deflection of steel beams on the first floor exceeded the limit of Standard for Classification of Steel Structures(GB 50017—2017). In order to meet the requirements of construction and subsequent use, it was necessary to strengthen the steel beams on the first floor of the structure. Through the calculation of the jacked steel beams and the monitoring of the on-site jacking process before and after reinforcement, the comparison and analysis of the structural stress and deformation before and after reinforcement showed that the excessive deformation of the steel beams was due to many reasons such as design and construction. The designed jacking devices could well realize the jacking of steel beams, and the reinforcement scheme for the jaking of steel beams was reasonable. After the steel beams were strengthened and jacked, the traffic demand of the existing crane beam was met, the structure became safe and reliable, which proved that the reinforcement scheme for lifting was safe and economical.
2021, 51(11): 211-217.
doi: 10.13204/j.gyjzG21062216
Abstract:
Taking the “Wooden Pavilion” of Jiangsu Green Building Expo Park as an example, “passive design” was the preferred strategy in every stage of architectural design and the applicable green technique was determined according to local conditions. Incorporating passive energy-saving design into architectural creation, the performance simulation of building energy saving design was carried out by applying relevant software. The integration of green building design and modern timber structure techniques was discussed from the three aspects of green building design that responds to regional climate, energy-saving design of envelope structure and prefabricated timber structure techniques. The wind field outside the building, the building orientation, the indoor space environment and the external envelope enclosure of the timber structure were simulated and analyzed by using the relevant software. Meanwhile, the thickness of exterior wall and roof insulation materials was optimized from the perspective of economy. The results showed that reasonable building orientation and functional space organization, high-performance envelope enclosure of timber structure, planting roof, adjustable exterior shading as well as photovoltaic integrated design could effectively reduce building energy consumption and achieve the energy-saving goal of ultra-low energy consumption buildings.
Taking the “Wooden Pavilion” of Jiangsu Green Building Expo Park as an example, “passive design” was the preferred strategy in every stage of architectural design and the applicable green technique was determined according to local conditions. Incorporating passive energy-saving design into architectural creation, the performance simulation of building energy saving design was carried out by applying relevant software. The integration of green building design and modern timber structure techniques was discussed from the three aspects of green building design that responds to regional climate, energy-saving design of envelope structure and prefabricated timber structure techniques. The wind field outside the building, the building orientation, the indoor space environment and the external envelope enclosure of the timber structure were simulated and analyzed by using the relevant software. Meanwhile, the thickness of exterior wall and roof insulation materials was optimized from the perspective of economy. The results showed that reasonable building orientation and functional space organization, high-performance envelope enclosure of timber structure, planting roof, adjustable exterior shading as well as photovoltaic integrated design could effectively reduce building energy consumption and achieve the energy-saving goal of ultra-low energy consumption buildings.
2021, 51(11): 218-224.
doi: 10.13204/j.gyjzG21022001
Abstract:
Focusing on the development clues of manufacturing industry and construction industry, the paper explored the historical origin, contemporary spekulation and integration features between them. This was followed by a discussion of the application mode and its reference value of systematic integration techniques for prefabricated light-weight buildings based on product thinking. The paper presented how systematic integration techniques were adopted in a small public prefabricated building in Australia through design and construction processes tracking, investigations of construction organizations, and practitioners' interviews based on the Meyer Timber Sydney Office in Sydney. The application mode and its reference value in the off-site construction industry in Australia were analyzed and summarized, in order to provide a reference and enlightenment for the research and practices of lightweight buildings towards new type building industrialization China.
Focusing on the development clues of manufacturing industry and construction industry, the paper explored the historical origin, contemporary spekulation and integration features between them. This was followed by a discussion of the application mode and its reference value of systematic integration techniques for prefabricated light-weight buildings based on product thinking. The paper presented how systematic integration techniques were adopted in a small public prefabricated building in Australia through design and construction processes tracking, investigations of construction organizations, and practitioners' interviews based on the Meyer Timber Sydney Office in Sydney. The application mode and its reference value in the off-site construction industry in Australia were analyzed and summarized, in order to provide a reference and enlightenment for the research and practices of lightweight buildings towards new type building industrialization China.
2021, 51(11): 225-226.
Abstract:
