Abstract:Cold-formed steel structures are natural green and industrialized buildings. Due to the large population, shortage of land resource, as well as serious earthquake disasters, the development of mid-rise cold-formed steel structure becomes very consistent with Chinese national conditions. At present, there are four major technical difficulties existed in the expansion of low-rise cold-formed steel structure systems to mid-rise buildings. Based on the investigation and improvement on the structure system and major components, a new mid-rise cold-formed steel framed composite shear wall structure system was proposed, and two important components of the new structure system were developed, including a composite floor system combining cold-formed steel joists with autoclaved lightweight concrete slabs and cold-formed steel shear wall with sandwich panel units. This paper also reviewed our and other researchers’ latest investigation on some fundamental theory problems, such as the lateral and fire resistances of the new structure system et al. Finally, the author points out some research work need to be conducted for the new structure system from a macroscopic perspective.

Abstract:To accurately determine the vibration reduction effect of single-layer reticulated shells with friction pendulum bearings (FPB), based on the refined finite element models, the isolation mechanism of FPB was given, and single-layer reticulated shells with FPB were analyzed from two aspects of static and dynamic. Structures were analyzed in three aspects including the internal force, deformation and stability under static loading, and were also researched through dynamic time-history analysis under 3-D earthquake waves. The impact of ground motion intensities and parameters of FPB on the seismic performance of single-layer latticed shell was discussed. The analysis results indicate that the static mechanics performance of a single-layer reticulated shell with FPBs can be improved by strengthening the outer ring bars. Under 3-D earthquakes, the bigger the ground motion intensity, the better isolation performance of FPB will be. The optimal friction coefficient of FPB increased with the increase of ground motion intensity. The bigger friction pendulum bearing curvature radius is, the better seismic performance of reticulated shell structure will be.

Abstract:The one-bay and three-story concentrically braced frame built in the zone with a seismic design intensity of 8 degree was constructed with 1：4 scale, and tested using shaking table under 24 different earthquake ground motions to explore the seismic performance of special concentrically braced frame with pinned connections and the failure mode of braced system. The influence of the secondary moments on the columns and the beams was obtained. The results show that, the test model under intensity 8 frequent and rare earthquakes are all less than their limit values pursuant to the GB 50011—2010 code. The structure not only survived after the rare earthquake, even owned a certain security reserve after a series of strong earthquakes. It indicates that the structure system owns good seismic performance in the high seismic region. The secondary moments on the columns and the beams induced by the gusset plate connections become significant especially after the out-of-plane buckling of the braces. Based on the test results under a series of strong earthquakes, the seismic design principle, e.g. strong-connection-weak-member in the braces, is perfectly achieved.

Abstract:Tensairity is a new kind of hybrid structure system using pre-stress to build the initial stiffness. To study the mechanical performance effected by structural deformation under the initial pre-stress, the form finding analysis of a 60 m span spindle Tensairity was conducted by the improved inverse iteration. The effects of form finding were discussed, and the mechanical performance and economics were compared with truss and beam string structure. The results show that: under the initial state the deformation tolerance could be reduced to 0.67% and the inner force distribution differs obviously, and under the load state the vertical bearing capacity decreases 22.24%. Compared with truss and beam string structure, the stiffness is weaker while the steel consumption is 34.80% less. Form finding analysis could effectively control the deformation tolerance under the initial state though having great impact on the mechanical performance, which holds remarkable economic efficiency and application properties.

Abstract:The static test of steel beam-columns was conducted to investigate the heat effect during process of welding strengthening while under initial load and the influence of different initial load on load-carrying behavior after welding reinforcement. The biaxial-symmetry I section columns were placed under boundary conditions that top of column was movable in plane while displacement constrained out plane and bottom of column was totally constrained. Therein 4 classes of initial loads were separately applied to the top of columns at a fixed in-plane eccentricity. Strengthening scheme was selected by symmetrically welding steel plates to outside surfaces of flanges, and grade of steel was carbon steel type Q345B. The displacement changes of specimen and welding stress and strain distribution of web were discussed during welding strengthening while under load, as well as the buckling mode and stability bearing capacity after strengthening. The results show that welding strengthening procedure decides the development mechanism of welding residual deformation and strain distribution. Initial load affects the magnitude of welding residual deformation while heat input and initial load coeffect the plateau length of load-displacement curve. Lower initial load has little influence on capacity while higher initial load obviously reduces capacity. Besides, the initial geometric imperfections also impact capacity after strengthening.

Abstract:Reynolds numbers have great effects on the pressure distribution of large-span roof structure. To explore these issues, Large Eddy Simulation (LES) numerical method was adopted to calculate mean and fluctuation wind pressure distributions. The pressure values, flow separation and reattachment patterns were examined by corresponding experiment data. Results indicate that the pressure distribution changed dramatically with different Reynolds numbers. Pressure distribution keep srelatively stable in low Reynolds number flow field, while for high Reynolds number flow,pressure varies rapidly at the leading edge area of the roof and gradually decreases to a constant value. The simulation results prove that Reynolds numbers have critical effects on the pressure distribution of the large-span roof structures.

Abstract:A simplified model for seismic analysis of a 1 000 MW tower type lignite boiler steel structure was studied, in which the mass of boiler is added to main steel structure replacing its seismic action. The seismic behavior differences among the simplified model and two models with boiler are studied. One of the two models with boiler used steel bars to inhibit sway of boiler. All of the models remain elastic under small earthquake actions, and the stress responses are the largest in simplified model. Under strong earthquake actions, some concentrically compression steel braces are buckling with plastic deformation and some beams have plastic deformations while eccentrically steel braces in the main steel structures and steel columns remains elastic. Some members near the steel bars develop plastic deformations due to the increased loads applied by the bars, which should be considered in design. Under both small and strong earthquake actions, inter-story deformations of the main structures are much smaller than the design code limits. Both lateral deformations and inter-story deformations of the main structures in the simplified model are the largest.

Abstract:This paper proposed the hybrid simulation test method based on the similar theory for the scale model to reduce the cost and improve the efficiency of the experiment. The proposed method deduces theoretically the similarity conditions of both displacement and force under the identical material between the model and the prototype. The obtained similarity conditions are only used for the physical substructure. The parameters of both the motion equation and the numerical substructure are not changed. So it is easy to use the proposed method for the hybrid simulation testing method. Using the mixed programming method of MATLAB and OpenSEES, this paper realizes both the tradition substructure test method for the scale model, including shear model, bending-shear model and bending model, and the distribution substructure test method for the scale model. Compared with the numerical simulation results of the corresponding full scale model, the proposed method is validated.

Abstract:Two design methods of ETFE cushion were presented which are the three-dimensional patterning based on zero-stress state and the flat-patterning based on nonlinearity of ETFE material. The state definitions and mechanical models were defined for the two methods, respectively. Experiments and numerical simulations were performed to obtain the shapes, stress distributions and the variations. It is found that, for the three-dimensional patterning model, the maximum difference of the shapes between experimental and numerical results is 4 mm and the difference of the stress distribution is 0.4 MPa. For the flat-patterning model, a good agreement between the experimental and numerical results is obtained for the initial shape and it is obtained that the stress distribution decreases while the shape and the ratio of rise to span increase due to the creep properties of ETFE materials. These findings have validated the proposed forming design methods.

Abstract:To explore vibration characteristic of large span floor structure under moving load, based on the large span beam string floor structure of the National Fitness Center in Ejin Horo Banner, Inner Mongolia, the loading measurement and analysis of walking, running, jumping and standing up were conducted by using biomechanical force measuring platform. Considering all kinds of possible load condition, the finite element analysis (FEA) and field measurement were performed for vibration of large span beam string structure floor area. The results show that the dynamic magnification factor of walking, running and jumping is 1.2, 2.4 and 4.9 respectively. The FEA results of large-span floor vertical acceleration induced by pedestrian load excitation are in good agreement with field measurement results and theoretical calculation values.

Abstract:To investigate the elastic-plastic responses and seismic resistance performance of the long-span spatial exhibition hall under multi-support excitations, the finite element model was established by SAP2000 software, and this model was converted into ABAQUS model by TJU.SAP2ABAQUS interface program. The consistency was verified by modal analysis. Considering unidirectional and three-directional earthquake inputs, the dynamic elastic-plasticity analysis under uniform and multi-support seismic excitations were investigated, respectively. The results indicate that the column-bottom internal forces, shear wall stresses and top displacements under unidirectional multi-support excitations are larger than those under uniform excitation. In contrast to unidirectional multi-support excitations, the column-bottom internal forces and shear wall stresses are larger or less than those under three-directional multi-support excitations, and the top displacements of the structure are amplified. In both sides of structure the effects on column-bottom internal forces are significant under multi-support excitations, and in the middle of structure the effects are small.

Abstract:The mechanical property indexes of 600 MPa and 550 MPa cold-rolled ribbed steel wires were determined through tensile test, and the cracking moment, crack distribution, deflection under different loads and normal section bearing capacity were studied through 32 slabs reinforced with cold-rolled ribbed welded steel fabric to investigate the flexural behavior of slabs reinforced with cold-rolled ribbed welded steel fabric. The results showed that solder joints had no influence on the mechanical properties of 600 MPa and 550 MPa cold-rolled ribbed steel wires. Transverse reinforcements in fabric had little effect on the cracking moment, crack spacing and crack width of this type of slabs. The short-term flexural rigidity equations were established, the flexural rigidity of this type of slabs was 10% greater than ordinary concrete slabs. Based on the failure mode of slabs reinforced with 600 MPa and 550 MPa cold-rolled ribbed steel wires, the calculation method of normal section bearing capacity was proposed.

Abstract:To study the mechanical behavior of precast concrete slab-precast shear wall monolithic joints under the vertical load applied at the cantilever end of the precast slab, static tests of one exterior joint and two interior joints were carried out. The test results indicate that all three specimens failed in a flexural mode with similar crack patterns. The vertical load-deflection curves of the three specimens are about the same before each specimen reached its ultimate limit state. For the three specimens, the fixed end flexural capacities of their precast slabs have no significant difference, and the average ratio of the measured flexural capacity to the calculated capacity following the formula in the current force design code is 1.29. The lapping pressed sleeve splice can transfer the tensile force of the precast concrete slab rebars effectively. The integrity of the total-precast floor can be ensured by adopting the monolithic seam. The monolithic seam in this paper can be used in the precast shear wall structure with total-precast floor.

Abstract:The out-of-plane creep buckling analysis was carried out on quadri-trussed concrete-filled steel tubular (CFST) arches by finite element method to investigate how the pre-buckling deformation induced by the construction process and the time effects influence their out-of-plane stability. All the material properties, which account for time effects and the variation of age at loading during construction, were implemented in ABAQUS with UMAT subroutines. An extensive parametric study was carried out to numerically investigate the out-of-plane creep buckling behavior of quadri-trussed CFST arches. Considered parameters include the slenderness of the arch, the steel ratio, et al. It concludes that the prebuckling deformation induced by construction process and time effects can reduce the out-of-plane buckling loads by up to 22.5% within the range of parameters considered in this paper. Such effects are more pronounced in slender arches with higher sustained loading level or lower α ratio, which need to be accounted for in the design.

Abstract:To investigate the cracking resistance and avoid the vertical and local circumferential cracks at the bottom of the concrete outer tank during the construction period due to hydration heat, concrete shrinkage and temperature changes for 160 000 m³ liquefied natural gas (LNG) tanks, using the finite element numerical simulation technology, the influence of shuttering material, construction quality, construction season and pouring temperature on cracks was figured out with an incremental method. The results show that concrete shrinkage leads to a sustaind growth of concrete tensile stress, the thermal stress fluctuates according to the changing of construction temperature and construction quality and construction season have a strong inference on cracks. Based on this basis, the thermal tress is dismantled according to the effect of each influencing factor, and the whole thermal stress is the superposition of the thermal stress under single influence of hydration heat, concrete shrinkage, construction season and pouring temperature. Some suggestions on anti-cracking measures are proposed, mainly by regulating the construction season, complementally by improving the quality of construction.

Abstract:The assembled bucking-restrained braces (BRB) wrapped with carbon fiber were proposed to improve the repairability and corrosion resistance. The damaged inner core element can be replaced by cutting the fiber material to make the outer restrained components separated, which makes the inner core to be replaced easily after earthquake, and the proposed assembled BRB can also improve the corrosion resistance of outer steel tube. Four assembled BRB specimens were tested by quasi-static tests, and different loading schedules and constraint ratios were considered. The results show that new assembled BRBs could undergo fully-reversed axial yielding cycles nearly without loss of stiffness and strength, and the ductility and energy absorption capacity are large enough. The carbon fiber cloth successfully connects outer confined elements and effectively resists the lateral thrust exerted by inner core. Multi-wave buckling phenomenon occured in the inner core element, and deformation appeared in wrapped material under compression load. The hysteretic curves of BRBs “jump” in the compression stage. The hysteretic behavior and energy dissipation capacity of BRBs get worse with more obvious multi-wave buckling. The new assembled BRB has good hysteretic behavior and provides a new way to realize assembling of BRBs.

Abstract:To study the seismic response of isolated structure under different reserved slippage, mild steel cone rod was taken as limit and energy dissipation device, Stateflow logic diagram was applied to simulate the motion state of isolation layer, and Bouc-Wen model was used to describe the hysteretic characteristic of elastic-plastic bar limit. MATLAB/Simulink simulation model of friction sliding isolation frame structure was established, the dynamic and energy response was analyzed, and the dynamic response of pure friction structure was compared with the shaking table test. Results show that the simulation results are consistent with experimental results. With the increase of reserved slippage, the acceleration response of the upper structure is not significantly increased. But isolation layer slippage is increased and limit device deformation is decreased. Damping energy dissipation has little to do with reserved slippage. The slippage change mainly changes earthquake input energy, which has less influence to other energy index.

Abstract:The freeze-thaw cycling tests for 6 pieces of RC shear wall specimens with span ratio 2.14 were conducted by artificial climate laboratory, and quasi-static experiments were implemented. The hysteresis loops with different concrete strength grade and freeze-thaw cycles were obtained, and the skeleton curves were achieved. The effects on seismic performance indicators including the ultimate capacity, rigidity, ductility and energy dissipation capacity were analyzed. Results show that with freeze-thaw cycles increasing the bearing capacity of the RC shear wall, the displacement ductility coefficient and the plastic corner decrease significantly, while the strength attenuation and stiffness degradation rate increase, and the energy dissipation capacity decreases. Along with the enhancement of concrete strength grade by same freeze-thaw cycles, the bearing capacity and accumulated energy are improved, then the strength attenuation and stiffness degradation rate are reduced, but the ductility decreases after increasing at first. It indicates that with the concrete strength increasing the RC shear wall has better seismic performance after freezing and thawing.

Abstract:Three kinds of foam concretes with different density were used and three different embedment lengths of wires were selected to study the pull-out behavior of steel wire from foam concrete. After 7 days of curing, steel wire was pull-out from the foam concrete. Test data including pull-out force and wire-end displacement were obtained. Experimental results show that pull-out peak load and corresponding wire end slippage increase with the embedment length and density of foam concrete. Based on the test results, a pull-out model of wire from foam concrete is developed with assumption of three stage bond strength assumptions. The model results are well agreed with the test results. The developed model can simulate pull-out behavior of steel wire with different embedment length. Base on this model, relationships of steel wire pull-out strength versus embedment length and pull-strength versus number of steel wires in foam concretes can be obtained.

Abstract:Three kinds of foam concretes with different density were used and three different embedment lengths of wires were selected to study the pull-out behavior of steel wire from foam concrete. After 7 days of curing, steel wire was pull-out from the foam concrete. Test data including pull-out force and wire-end displacement were obtained. Experimental results show that pull-out peak load and corresponding wire end slippage increase with the embedment length and density of foam concrete. Based on the test results, a pull-out model of wire from foam concrete is developed with assumption of three stage bond strength assumptions. The model results are well agreed with the test results. The developed model can simulate pull-out behavior of steel wire with different embedment length. Base on this model, relationships of steel wire pull-out strength versus embedment length and pull-strength versus number of steel wires in foam concretes can be obtained.

Abstract:Experimental study on the behavior of circular Q460 high strength steel reinforced concrete (SRC) columns under small eccentric compression was conducted, to investigate the failure mode and failure process. The SRC column presents typical flexural failure and shows good ductility. The development of the diagonal crack is effectively confined by the encased steel. The stress distribution and development of the steel reinforcement were studied using finite element method. It indicates that stress redistribution occurs due to the crushing of concrete, which results in the increase of the axial force and moment applied to the steel. The parameter effects were investigated. The compression-bending capacity of the SRC column increases approximately linearly with the increase in the steel reinforcement strength and steel ratio. The design theory of SRC column is enriched based on the comparison analysis on the flexural strengths of the SRC column calculated by the universal superposition method and the N-M correlation curve.

Abstract:A simulated hot wall condition was provided by a thermostat oven in lab and the exothermic and endothermic process of organic phase change material macro encapsulation box was measured when different quantity of conductive fins was installed or the box was filled with copper foam. The results show that the increasing quantity of fins leads to the reduction of complete phase transformation time, while the installation of excessive fins can decrease the effective heat release time for the package box with small thickness. The usage of copper foam results in the more uniform temperature distribution, and further reduces the complete phase transformation time in thick encapsulation box. The complete phase transformation time in a 45 mm thick encapsulation box is decreased by 64.8% when both the installation of 15 conductive fins and the copper foam filling are applied. The application of these two methods provides a good solution for the slow endothermic process of macro encapsulation box containing huge volume of organic phase change material under hot wall environment.

Abstract:To investigate the thermodynamic property of rock, the impact compression tests of granite within different temperatures were performed under different strain rates (50-250 s^-1). Results show that the strain-rate sensitivities subjected to different temperatures are quite different. When the temperature rises to 700 ℃, the effect of strain rate on compressive strength is the weakest, while that on peak strain is obvious. The effect of strain rate on elastic modulus tends to have no regularity. The elastic modulus increases with the increase of strain rate at 20 ℃ and 700 ℃, but it takes on a downward trend at 300 ℃ and 500 ℃. There is little change in the dynamic compressive strength at 300 ℃ compared to the room temperature. When the temperature reaches 500 ℃, the thermal damage becomes obvious, the dynamic compressive strength and elastic modulus significantly reduce, but the peak strain increases. At 700 ℃, the thermal damage phenomenon is serious, and the compression strength and elastic modulus sharply decrease. In addition, with increasing the actual temperature, the color of the tested rock changes and its breakage degree also deepens.

Abstract:To improve the recycled concrete aggregates (RA) quality for using in self-compacting concrete (SCC), the effect of four alternative treatment methods of RA with two sources on the fresh and hardened properties of RA-SCC were evaluated. The result shows that the RA sources and parent concrete strength has great influence on the quality and properties of RA. While after the pretreatment of RA, the RA qualities from different sources are improved and the performance difference of RA-SCC becomes small. The presoaking in the water glass dispersion and cement-fly ash slurry can significantly improve self-consolidating characteristics of fresh RA-SCC. The thermal expansion method, low-concentration acid dissolution method and water glass dispersion method provide denser and connected microstructures leading to the significant improvement in tensile strength, dry shrinkage resistance and frost resistance of RA-SCC. Most enhancement methods have a limited effect on compressive strength and modulus of elasticity.

Abstract:This paper studied the effect of corrosion damage on bearing properties of eccentric steel columns. Outdoor exposure salt spray accelerated corrosion tests of 7 H-type steel members were performed for 3 years at most, and then the material tests, of which the specimens were extracted from end region of the members, were conducted to investigate the relationship between the corrosion rate and the mechanical properties. Through the experiments of 2 non-corroded H-type columns and 7 corroded H-type columns, the experimental results show that the bearing capacity, stiffness and ductility ratio decrease with increasing corrosion degree, and the corresponding deflection increases. The stiffness and strain hardening effect are weakened by corrosion damage, which influences the plastic property and decreases the plastic adaption coefficient. The corroded compression-bending column models with the various sectional dimensions and lengths were calculated by using the validated fem simulation method, hereby, the deterioration law formulas of the bucking strength and the plastic adaption coefficient were established based on the corrosion mass loss ratio.

Abstract:To dynamically predict reliability of bridge members with real-time monitored information, with the long-term mass monitored data of health monitoring system, the data-based dynamic model including monitoring equation and state equation was built, and then the mixed Gaussian particle filter(MGPF) was introduced. With particle filter method, Bayesian method and dynamic model, the posteriori distribution parameters of state variable and one-step forward prediction distribution parameters of monitored data were predicted. Through resampling technique, with MGPF, the prediction precision of dynamic model can be increased. Based on the real-time monitoring data, the weights of resampled particles can be constantly updated. Therefore, the problem of particle degradation is solved. Finally based on the real-time predicted distribution parameters, with the first order second moment (FOSM) method, the on-line and dynamic reliability of bridge members is predicted.

Abstract:The three-story frame models with different damage conditions were established to study the application of wavelet analysis in damage identification. The time history analysis was applied, and the response data were used to identify the damage location through wavelet analysis. The different damage identification indexes are discussed, and the results show that the wavelet packet energy curvature is better than the other to identify local damage. Then the sensitivities of input signals are discussed, and the results show that the acceleration is more sensitive to local damage than velocity and displacement. In the end, the meshing size, the acceleration sensor location and the sampling frequency are discussed, and the results show that all of them affect the damage location identification result. The accuracy of the damage localization increases when the meshing size decreases, the distance between the acceleration sensor location and the damage location decreases, and the sampling frequency increases.

Abstract:The current acceleration seismic design spectra has the disvatages including that its precision and the statistics features in different period stage have obvious differences, and the spectrum characteristics of the low-order spectrum based on the artificial signals mismatch the real statistics characteristics. The unified smooth spectrum which adopts unique function was presented based on the linear modle of displacement spectrum, and a new ground motion simulation method considering lower-order spectrum was proposed. The analysis results indicate that the smooth spectrum has the advantages such as simple form, high accuracy for all the period stages. The simulated earthquake signal fulfills the spectrum characteristic requirement for acceleration spectrum, velocity spectrum and displacement spectrum. The smooth spectrum has uniform characteristics including function form, the spectrum characteristics on multiple orders, elasto plasticity and multiple dimensions, and it is suitable for dynamic analysis and ground motion simulation.

Abstract:To design and analyze the incomplete structure during construction and ensure construction safety, it is necessary to clarify all kinds of external actions (loads) and their effects during construction. This paper presented the load types, design values of the loads and load combinations in the Design Loads on Structures During Construction in the construction stage, and emphatically focused on the determining procedure of construction loads and load factor, the combination method of construction load and dead load, live load, environmental load and lateral earth pressure, then compared them with Chinese current standards. It is proposed to compile the codes for construction loads in China systematically using the concept of ASCE construction specification, investigating the uncertainty of load in the construction stage, and introducing the proposed values of construction load and load factors.