Abstract ：

Form-finding is crucial for the design of typical cable net structures. Based on the original basic force density method, a modified force density method utilizing the concept of relation matrix is proposed in this paper. The modified method realizes the establishment of a clear correspondence between members and nodes of cable net structures. On the basis of the relation matrix, the find function is introduced, and the calculation formula of the modified branch-node matrix is derived. Meanwhile, the corresponding analysis steps and calculation process are given. The modified method is verified by the analysis of representative structural forms. The results show that for the saddle-shaped orthogonal cable net structure, the outcomes obtained from the modified force density method highly agree with the theoretical values, providing preliminary verification of the method's effectiveness. For single-layer spoke cable net structures, the relative error between the results calculated by the modified force density method and the numerical solution is approximately 5 %. The results of both methods are relatively consistent, and the relative error varies in relation to the ratio of inner ring cable force density to radial cable force density. For circular single-layer crossed cable net structure without inner ring, the results of the modified force density method are very close to the numerical solution. The maximum relative error between the two is 6.95 %, and the accuracy is higher than that of the nonlinear finite element method. The outcome of this research demonstrates the accuracy of the modified force density method and its effective application in the form-finding of actual cable net structures.

Keyword ：

Modified force density method Modified force density method Cable net structure Cable net structure Relation matrix Relation matrix Form-finding analysis Form-finding analysis

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Abstract ：

The cable net and membrane of the air-supported membrane structure transmits the load through mutual extrusion, and the contact interaction between the cable net and membrane should be considered in the initial morphological analysis stage. In this paper, a scale model was designed according to a large-span air-supported membrane structure engineering project, and the shape and force of the structure were measured. At the same time, a finite element model of cable-membrane contact was established, and its interaction behavior was regarded as a combined contact state and sliding contact state. The results show that the influence of different contact state analyses on the prestress of the cable net is obvious, and the influence of the sliding contact between the cable and the membrane should be considered in the design of the membrane structure.

Keyword ：

forming test forming test contact analysis contact analysis air-supported membrane structure air-supported membrane structure

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Abstract ：

Annular crossed cable-truss structure (ACCTS) is a novel flexible cable-strut tensile structure. Its stiffness is generated from the prestresses of cables, and the prestresses of cables is mostly controlled by the deformation of cables. So, it is necessary to study the influence of cable length errors on ACCTS and the method of solving control criteria of cable length errors. According to sensitive analysis of cable length errors, the sensitive indexes of all kinds of cables are gained, and the influences of ear-plate and cable on ACCTS are larger and the influences of struts on ACCTS are smaller. Then define ear-plate and cable as sensitivity components, and define strut as non-sensitivity component. Based on sensitive analysis, reliability theory and nonlinear programming theory, the method solving control criteria of cable length errors for ACCTS is proposed. By the method, the control criteria of cable length errors under 4 conditions are studied. The model trial of sensitive analysis of ACCTS with a diameter of 6 m was carried out. The results show that the influences of cable length manufacturing errors on ACCTS are solved by sensitive analysis and the proposed method. The distribution of control criteria of cable length errors is uniform, and can meet the requirements of China and US Codes. The trial values are consistent with the simulation values. The results provide the acceptance criteria for ACCTS, which promotes the application of ACCTS in practical engineering.

Keyword ：

Sensitive analysis Sensitive analysis Annular crossed cable-truss structure (ACCTS) Annular crossed cable-truss structure (ACCTS) Nonlinear programming theory Nonlinear programming theory Reliability theory Reliability theory Control criteria of cable length errors Control criteria of cable length errors

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Abstract ：

To further investigate the dynamic characteristics of the suspend-dome structure, based on a prototype structure of the Lanzhou Olympic Complex Gymnasium, the method of replacing steel with Austenitic 304 stainless steel is proposed. Dynamically scaled model with a geometrical 1:20 was designed. Shaking table dynamic characteristics test was conducted using the white noise excitation method. The response of the scaled model was identified and analyzed by the transfer function method, the frequency domain decomposition method, and the Hilbert-Huang Transformation, respectively, and the measured natural frequency and damping ratio were obtained. The finite element models of the prototype and scaled model were built, and the finite element software ABAQUS completed modal analysis. The simulation results of vibration modes for the prototype structure and scaled model were analyzed. The study shows that the difference between the experimental and simulation results for the natural frequency of the scaled model is within 5%, which indicates that the testing points are reasonably arranged, the test method is correct and finite element modeling method is reasonable. The measured results of the scaled model are essentially consistent with simulation results obtained from the prototype structure by the similitude conversion, indicating that the proposed method of replacing steel with Austenitic 304 stainless steel is reasonable and scaled model is well designed. The correctness of the similarity relation between the scaled model and the prototype structure is verified. The model has closely distributed modes and more vertical modes. The first-order damping ratio identified by the dynamic characteristics test is between 1.85% and 2%.

Keyword ：

Dynamic characteristics test Dynamic characteristics test Hilbert-huang transformation Hilbert-huang transformation Frequency domain decomposition Frequency domain decomposition White noise excitation White noise excitation Suspend-dome structure Suspend-dome structure

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Abstract ：

The center-hung scoreboard is a large electronic display device, that usually has a significant weight and is flexibly suspended from the roof of the gymnasium. The suspen-dome structure is one of the common roof structures of gymnasiums. In order to investigate the effect of the center-hung scoreboard on the natural vibration characteristics and seismic response, including acceleration, displacement, and strain, of the suspen-dome structure and considering that the dynamic behavior of the structure under seismic action can be realistically reflected, a shaking table test was carried out based on the suspen-dome structure of the Gymnasium of the Lanzhou Olympic Sports Center. Firstly, according to the size of the shaking table, a dynamic scale model with a geometric similarity ratio of 1:20 was established. After that, the white noise excitation test and numerical modal analysis were conducted on the models with and without the center-hung scoreboard to compare the two modes' natural vibration characteristics. Furthermore, the earthquake simulation test was carried out on the models with and without a center-hung scoreboard, and their various seismic responses, including acceleration, displacement, and strain, were compared and analyzed. Finally, the acceleration response and displacement response of the center-hung scoreboard were investigated. The results show that the higher-order natural frequencies of the suspen-dome structure will increase when the center-hung scoreboard is suspended from the roof, and the swing of the center-hung scoreboard will be excited first in the low-order mode. In addition, the various seismic responses, including acceleration, displacement, and strain, of the model with the center-hung scoreboard are all increased compared to the model without the center-hung scoreboard. Meanwhile, the influence of the center-hung scoreboard on the seismic response of the suspen-dome structure decreases from the inner ring to the outer ring of the structure. Moreover, under the action of an earthquake, the acceleration response and displacement response of the center-hung scoreboard are both extremely high. Considering the center-hung scoreboard in the analysis and design stage of the suspen-dome structure is necessary.

Keyword ：

shaking table test shaking table test seismic response seismic response suspen-dome structure suspen-dome structure natural vibration characteristic natural vibration characteristic center-hung scoreboard center-hung scoreboard

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Abstract ：

To investigate the distribution characteristics of prestressing force and static characteristics of the rib-patterned small rise-span ratio suspend-dome structure, a 1:20 scaled model of the Lanzhou Olympic Gymnasium roof structure was established. During to the small-scale ratio model with dense nodes, according to the principle of constant structural stiffness, a multi-node synchronous loading device was designed. The construction tensile loading test and multi-stage static loading test were carried out. The axial force of rods, vertical displacement of nodes, and radial displacement of supports for the model with initial geometric imperfection under 11 load cases were tested. Test results were used to validate and then refine the numerical simulation using ABAQUS. The study shows that a multi-node synchronous loading device dramatically improved the loading efficiency and satisfied the accuracy requirement of the test. The test results were in good agreement with the simulated results, which verified the correctness of the finite element modelling method, the accuracy of the test method, and the rationality of the measuring point arrangement. The small rise-span ratio suspend-dome structure with a rib -patterned has good elasticity at a low load level. The full-span arrangement of the live load is the most unfa-vorable load case of the structure. The outer loop cable bearing capacity exhibited a higher proportion. The third ring rod was found to sustain the highest load, the outer ring rod is more sensitive to load, and the fourth circle node was found to have the largest vertical displacement in the model. The change of support displacement in practical engineering should not be neglected.

Keyword ：

Suspend-dome structure Suspend-dome structure Model test study Model test study Static performance Static performance Multi-node synchronous loading device Multi-node synchronous loading device

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Abstract ：

In recent years, air-supported membrane structures have been widely used in China's environmental protection of closed coal yards and in sports stadiums. There have been breakthroughs year by year in the numbers constructed, unit area, and span. At present, the largest span of an air-supported membrane structure coal shed has reached 198 m. As the span increases, the force-bearing performance of the structure is more closely related to its shape. In this paper, based on a 225mx198mx66m(Length x width x height) long-span air-supported membrane structure test model, the form-finding and state-finding analysis of the air-supported membrane structure with longitudinal and transverse cable nets were carried out, and the results were compared with the forming test results. The results show that the prestressed state of the structure obtained by the state-finding analysis is closer to the test results. However, there is a specific difference with the target height. At the same time, the form-finding analysis can accurately find the target height, but the structure's cable force and section shape are quite different from the test results.

Keyword ：

Air-supported membrane structure Air-supported membrane structure Cable net Cable net Forming test Forming test State-finding State-finding Form-finding Form-finding

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Abstract ：

The LED display, i.e., the center-hung scoreboard, nowadays has become an indispensable display device in large stadiums, and some of which with weight is more than 30t. To investigate the influence of center-hung scoreboard load on the dynamic characteristics of the suspend-dome structure, a 1:20 dynamically scaled model of the Lanzhou Olympic Sports Complex was designed, considering different lifting-lowering heights of the center-hung scoreboard by changing the sling length. Shaking table dynamic characteristics experiment was conducted by using the white noise excitation method for the suspend-dome structure with the sling lengths of 200 mm, 400 mm, and 600 mm individually. The change rule of dynamic characteristic pa-rameters such as natural frequencies and damping ratios was concluded by the Hilbert-Huang Transformation method for modal identification and the transfer function method for checking. With the increase of sling length, the natural frequencies of the center-hung scoreboard become smaller, and the damping ratios become more extensive. Compared with the results of the scaled model without a center-hung scoreboard, the high-order natural frequencies and damping ratios of the overall structure with the center-hung scoreboard are significantly increased, and the coupling effect between the center-hung scoreboard and the structure should not be ignored in the dynamic analysis. The test values were compared with the simulation results of Abaqus as well. It is shown that the test values of the scaled model are essentially consistent with the simulation results, which indicates that the test points are reasonably arranged, the test method is correct, and the finite element modeling method is accurate. The effects of sling stiffness and sling length on the dynamic characteristics of the suspend-dome structure were studied by Abaqus software. The results show that the sling stiffness hardly affect the dynamic characteristics of the overall model. When the sling length is less than 300 mm, the lifting-lowering of the center-hung scoreboard influences the distribution of the natural frequency and the vibration mode of the overall structure. In this range, the lifting-lowering of the center-hung scoreboard should be focused on actual engineering.

Keyword ：

Center-hung scoreboard Center-hung scoreboard Sling stiffness Sling stiffness Suspend-dome structure Suspend-dome structure Dynamic characteristics experiment Dynamic characteristics experiment Sling length Sling length

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Abstract ：

A new type of cable-strut tension structure named Annular Crossed Cable-truss Structure(ACCTS) comprises a series of planar cable-truss frames crossed each other. To investigate the force mechanism of ACCTS, a cable-truss frame model with 2-bar and 6-cable has been developed, and its initial stiffness formula has been derived as well. The model is further simplified to make it is upper and lower vector heights equal, a nd then the initial stiffness formula and the critical slack load formula are further deduced. Based on ANSYS software and cable-truss frame with a span of 60m, the influences of the number of struts and position of jumped layout on the cable-truss frame are studied. According to the former 60m span cabletruss frame's research results, the jumped layout of ACCTS with a span of 100m is studied. The static and dynamic performances of two schemes, the optimal jumped layout scheme and the original scheme, are systematically studied. It is shown that the number of struts would be about 6 similar to 8 for the planar cable-truss frame and the optimal order of jumped layout is strut 6-7 -> strut 4-5 -> strut 2-3. The optimal order of jumped layout of ACCTS agrees with that of the cable-truss frame, verifying the feasibility of conclusions. In the condition of no variati on in the original structure's static and dynamic performance, the optimal scheme of the jumped layout will lower the steel consumption and enhance the buckling loads. Moreover, it also simplifies structure for easy construction. Copyright (C) 2021 by The Hong Kong Institute of Steel Construction. All rights reserved.

Keyword ：

Static and dynamic performance Static and dynamic performance Force mechanism Force mechanism Jumped layout Jumped layout Planar cable-truss frame Planar cable-truss frame Annular Crossed Cable-truss structure (ACCTS) Annular Crossed Cable-truss structure (ACCTS)

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Abstract ：

Early-age heat-induced cracking is a potentially fatal problem for critical concrete structures such as liquefied natural gas storage tanks. This paper reports on a novel automatic air-cooling system designed to solve the problem. The system was designed following a series of air-cooling experiments in China on concrete walls during the first 72 h after casting. An air velocity of approximately 12 m/s appears to provide effective cracking control for ambient air temperatures up to 30 degrees C, while the optimal cooling segment length was found to be approximately 14 m. The paper aims to provide a reference for the application of air cooling for any large-scale concrete structures at risk of early-age cracking.

Keyword ：

thermal effects thermal effects field testing & monitoring field testing & monitoring concrete technology & manufacture concrete technology & manufacture

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