Abstract:Post-earthquake resilience of engineering structures is an important research area of sustainable earthquake engineering in recent years. Restoration and collapse control are realized with the constraint at the base released and the wall panels post-tensioned by unbonded prestressing tendons, which can reduce damage level and even eliminate residual drift owing to the gap-opening mechanism. As an important component of earthquake resilient structural system, self-centering concrete shear wall system is developing continuously. Self-centering shear wall such as controlled rocking wall, hybrid rocking wall, coupled wall with vertical joint, and coupled wall with coupling beam can accomplish restoration, but various dissipating devices result in significantly different levels of energy dissipating. Traditional force-based design is not applicable, so displacement-based performance design should be presented with the improvement of residual drift control, definition of performance level, and section limit state. Fiber model, lumped plasticity model, multi-spring model, and finite element model can accurately simulate the behavior of self-centering shear wall, but there are some differences in parameter sensitivity.Thus, some current research challenges and prospects were presented to provide theoretical and technical support for the development and application of self-centering shear wall structure system: the elastic and inelastic behavior of prestressing tendon which can cause prestress loss and insufficient deformation capacity during rocking, the connection performance between self-centering shear wall and adjacent structural components such as the floor system and its influence on self-centering ability, collapse control with the failure of post-tensioning tendon and dissipating device, and utilization of multiple dissipating rocking interfaces between wall panels to mitigate higher mode effects and estimation of residual drift.

Abstract:To achieve rational design of diaphragms and ramps in precast parking structures, the precast concrete topped and un-topped double-tees with the span of 18 m and 24 m were designed and constructed. A series of full-scale experiments, both of flexural behavior under two point loads and shear capacity with shear-span ratio of 3.0, were carried out. The experimental results verified general feasibility of these double-tees to meet the service requirements of multi-storey parking structures. Because it is hard to obtain static performance of double-tees under various loading patterns from limited magnitude of experimental specimens, nonlinear analysis of double-tees members on basis of discrete models was carried out. The analytical results showed that the analyzing load-deformation curves under simulation of experimental loading condition coincided with the experimental curves. Both the flexural behavior of double-tees under uniform loads and shear performance of the double-tees with shear-span ratios ranging from 1.0 to 9.0 were simulated and analyzed. Moreover, a nonlinear finite element model (FEM) of driving or stopping on the local flange region of double-tees was conducted. Combination of these simulation analysis with static loading experiment reflected advantageous performance of the precast prestressed concrete double-tees, including responses of the crack and deflection control, shear and flexural capacities and local bearing capacity. Assembled effectively, these double tees can be applied to the diaphragm and ramps and provide good performance for precast parking structures.

Abstract:To reduce the crack width of concrete beams reinforced with glass-fiber reinforced polymer(GFRP) bars, this paper proposes a new type construction measure for FRP bars which is fabricated by inserting the GFRP bars into the metal corrugated pipe and filling the interspace with high strength cement-base grouting materials.The internal high-strength cement-based grouting material has good bonding performance with GFRP bars and participates in the pulling, while the external metal bellows can restrain the expansion of internal cohesive cracks and strengthen the bonding effect with concrete. Therefore, the crack width of concrete beams reinforced with GFRP bars is reduced. To verify the feasibility, a monotonic loading flexural test was carried out on six beams reinforced with steel bars,extruded GFRP bars, and the new type GFRP bars, respectively.The effects of longitudinal bars on the crack distribution, average crack spacing, and crack width were investigated. The experimental results show that the new type construction measure can reduce the crack width of beams in the serviceability limit state and delay the appearance of the cracks along the bars compared with general extruded GFRP bars.Besides, the beams treated with the new type construction measure met the code requirement of the maximum crack width of 0.5mm, while the ordinary concrete beams reinforced with GFRP bars did not. The failure modes of beams reinforced with GFRP bars began with concrete crush in compressive zone,and the final destruction were the rupture of longitudinal FRP bars. The flexural capacity of beams reinforced with GFRP bars was higher than that of RC beams and expressed the good deformability before final destruction, in which the average deflection span ratio approximately reached 1/56.

Abstract:To improve the corrosion resistance of concrete-filled steel tubular column (CFST) and construction inconvenience of FRP-steel tube concrete column (FSCC), a novel composite member is proposed, namely, FRP-interlayer-steel tube concrete column (FIST). In this paper, axial compression tests on FIST, FSCC and CFST were conducted to investigate the failure modes and the loading process. The experimental results indicated that the failure mode of FIST and FSCC was waist drum failure owing to the confinement of FRP, which is different from the shear failure mode of CFST resulting from low steel ratio. Compared with FSCC, whose resin matrix was crushed, FIST avoided this due to the existence of the interlayer. The bearing capacity and ultimate deformation of FIST increased by 35.3% and 22.5% respectively, higher than that of FSCC also owing to the interlayer. The design equation of the bearing capacity of FIST was proposed from the equations of the bearing capacity of CFST and FSCC. Calculations and test results showed good agreement.

Abstract:To investigate the fire performance of circular steel tube confined reinforced concrete (STCRC) columns exposed to natural fire, a finite element model including thermal analysis model and stress analysis model was developed using the software ABAQUS. The main considered parameters were fire heating rate, heating duration time and load ratio. Parametric temperature-time curves recommended by Eurocode 1 were employed as the temperature curves of natural fire, and the ISO-834 standard fire curve was selected as a comparison. The results showed that the faster heating rate and the shorter heating duration time of nature fire resulted in the higher temperature gradient of the composite cross section. Circular STCRC columns exposed to natural fire might fail in the heating phase or the cooling phase. Based on the method of equivalent fire exposure time, the fire resistance under natural fire and standard fire could be converted reciprocally and then compared with each other. It was found that fire safety design with ISO-834 standard fire curve was conservative when the heating rate of natural fire was slower than that of the standard fire. However, fire safety design with ISO-834 standard fire curve was unsafe when the heating rate of natural fire was faster than that of the standard one. Thus, natural fire curve in fire safety design is recommended for this condition.

Abstract:To mitigate disaster caused by the impact of debris flow boulders, a concrete filled steel tubular crib dam was proposed. Solid impact tests were carried out to study the impact dynamic response of the structure, and the response modes of the structure were summarized. The numerical simulation of the test process was performed, and the results were consistent with the test. The parameter analysis of the structure was carried out to study the influence of confinement coefficient of the piles, radius-thickness ratio of the braces, and stiffness ratio of piles and braces on the dynamic response of the structure. Results showed that the typical response modes of the structure included slight damage of member, bending failure of member, and joint failure. The structure performed good overall energy dissipation ability when the pile tube was impacted, while overall energy dissipation was not obvious when the brace tube was impacted. The influence of confinement coefficient of the piles, radius-thickness ratio of the braces, and stiffness ratio of piles and braces on the dynamic response of the structure was constrained by the single-factor variation of the diameter and thickness of piles and braces. These findings suggest that the concrete filled steel tubular crib dam provides good impact resistance.

Abstract:To study the axial compression behavior of concrete-filled steel tube (CFST) at early-age, axial compressive tests of CFST stub columns at different concrete ages were carried out. The bearing capacity and load-strain curve at different ages were obtained. The failure modes, load-strain curves, and the development rules of bearing capacity with age were analyzed. Based on the existing stress-strain relationship of early-age concrete, the constitutive relationship of mature concrete in the GB 50010 was extended to include the case of concrete at early-age. Combined with the above mentioned tests, the finite element model for early-age CFST was established and the axial compression behavior of circular and square CFST at early-age was analyzed. The results show that the confinement effect increases with the growth of age and the confinement effect and load properties of the circular section aresignificantly higher than those of the square section. Based on the bearing capacity of CFST in the mature period, the strength capacity of CFST stub columns at the early age was established by introducing the coefficient of confinement effect due to concrete age. Uniform design method was used to simulate the age-bearing capacity of circular and square CFST stub columns to verify the applicability and high accuracy of the formula. This study provides references for the safe construction of CFST.

Abstract:RPC-filled circular steel tube columns can be applied in long-span buildings, high-rise structures, and heavy loading constructions due to its excellent mechanical performance as vertical members. Currently, the formula of load-bearing capacity of RPC-filled circular steel tube column under axial compression is only applicable for the ones with a diameter less than 152 mm. When the diameter is larger than 152 mm, the calculated value is larger than test data. To solve this problem, finite element analysis on RPC-filled circular steel tube columns under axial compression was conducted using ABAQUS. The relationship of RPC confining stress ratio and RPC-filled circular steel tube column displacement curves were investigated. A total of 134 load-displacement curves of RPC-filled circular steel tube columns were calculated. Results show that when the confinement index is less than 0.5, there is no strengthening stage in load-displacement curves of the RPC-filled circular steel tube columns; when the confinement index is larger than 0.5, the strengthening stage in load-displacement curves occurrs; when the confinement index reaches 1, the ultimate load increases as much as 1.3 times that of the loading bearing capacity, and the ductility becomes higher. With same cross section of RPC-filled circular steel tube column, the lateral deformation coefficient and the confinement effect on core RPC increase with the decrease of RPC strength.Based on the results of experimental and numerical analysis, the calculation formula on bearing capacity of RPC-filled circular steel tube column under axial compression with diameter as large as 560 mm were proposed.

Abstract:In order to investigate the mechanical properties and constitutive relation of stress-strain for ULCC (ultra lightweight cement composite), four types of ULCC with different densities ranging from 1 250 kg/m³ to 1 550 kg/m³ and the corresponding compressive strengths ranging from 47.9 MPa to 70.0 MPa were developed in this paper. These ULCC consisted of microlightweight aggregates (cenospheres), cementing materials (cement and silica fume), concrete admixture (shrinkage reducing admixture and superplasticizer) and steel fiber with volume fraction of 1%. An experimental campaign including uniaxial compressive strength tests and uniaxial tensile strength tests was undertaken to investigate the uniaxial compressive and tensile mechanical properties, and the compressive strength, tensile strength, elastic modulus, poisson ratio, uniaxial compression stress-strain curves and uniaxial tension stress-strain curves were obtained. The results show that compressive strength, tensile strength, and elastic modulus all increased with the increasing of densities. The compressive strength and elastic modulus of ULCC were linearly related to densities. The segmented constitutive equations of ULCC under uniaxial compression and uniaxial tension were proposed based on the uniaxial compression stress-strain curves and uniaxial tension stress-strain curves obtained from the tests. The research results can provide theoretical basis for the design and nonlinear finite element calculation of ULCC structure.

Abstract:The influence of different corrosion degree and type on the mechanical properties of steel was studied by tensile test of the standard specimen of the cold-formed thin-walled c-type purline with nine years of service in the industrial environment. By comparing the relationship between the mechanical properties, including the fracture morphology, stress strain curve and mechanical property index, and rust damage degree of damaged steel, the constitutive model of cold bending thin-walled steel was established, and the effect of corrosion on the mechanical properties of different materials was compared with the finite element analysis. The results show that the fracture form of the pitting specimen was a single fracture, and the overall corrosion was diversified: oblique breaking, arc breaking, and staircase break.Pitting specimens all showed the yield platform,the necking segment disappeared, and only when the corrosion rate reached 36.14%, the yield platform disappeared and the brittle fracture occurred. The yield, ultimate strength, elongation, ultimate strain, and modulus of elasticity decreased with the increase of corrosion degree. When the corrosion rate was 36%, the strength decreased about 40%, and the elongation decreased about 70%. The effect of total corrosion on strength was higher than that of pitting corrosion, and the effect of pitting on yield platform length and elongation was greater than that of total corrosion. The effect of rust on the mechanical properties of cold-formed materials was higher than that of hot rolled materials.

Abstract:To investigate the bond between the concrete and the large-diameter strands and reasonably propose design development lengths,pull-out tests of 32 specimens with strands arranged centrically and eccentrically were carried out. The test focused on high-strength and low-relaxation strands of nominal diameters of 15.2 mm, 17.8 mm, and 21.6 mm. Main parameters included the thickness of the concrete cover,the volumetric stirrup ratio, and the anchoring length.The test results show that the pull-out specimens had two failure modes,though testing parameters varied for different specimens.The first mode was concrete splitting failure for a few specimens having both thin cover and small volumetric stirrup ratio, and the other was apparent pull-out of strand for most specimens but no cracking was observed. Based on the failure characteristics and the relationship between the pull-out force and slip, the mechanism of bond failure between strands and concrete was presented. The peak point of the pull-out curve was taken as the sign of failure.A calculation method for the bond strength between strand and concrete was proposed considering the effects of three parameters. The approximate probabilistic method was adopted to analyze the design value of the development length of the strands to meet the requirements of the corresponding reliability index.It can serve for the design and analysis of large-span pre-tensioned concrete members applied in precast structures of public buildings.

Abstract:To investigate the influence of specimen size on bond performance between corroded reinforcing steel bars and concrete, three cube specimens of different dimensions were cast with 10D length per side, where D is the diameter of longitudinal rebars (D=14 mm,20 mm,25 mm). Pull-out specimens with reinforcement mass loss percentage of 0%, 0.5%, 1.0%, 2.0%, 5.0%, 8.0%, and 10.0% were obtained using current accelerated method. The variation laws of bond characteristics were analyzed considering the influence of reinforcement corrosion ratio and specimen size. The experimental results show that the expansive cracks appeared earlier and the maximum crack width was larger as the dimensions of specimens increased. The bond strength and the initial bond stiffness first increased and then gradually decreased as the concrete deterioration and reinforcement corrosion levels increased for specimens of different dimensions, and the bond energy dissipation decreased as the mass loss of reinforcement increased, whereas the specimen with larger diameter (D=25 mm) was more sensitive to the corrosion than that of the specimen with smaller diameter (D=14 mm, 20 mm). Moreover, the free-end slip and the bond energy dissipation for specimens of different dimensions decreased slowly before the corrosion-induced cracks appeared, and then decreased rapidly when the corrosion-induced cracks appeared, which had no significant effects on corrosion level after the corrosion-induced cracks appeared. Based on the experimental results, the empirical model of the residual bond stress between corroded rebar and concrete was proposed, which can evaluate the residual bond strength with different diameter of reinforcement.

Abstract:To study the bond behavior between the ribbed steel bars and sleeve constrained grouting material, pull-out tests were conducted on 45 specimens. The failure modes, ultimate bearing capacity and ultimate average bond strength were studied. The influences of bar diameter, anchorage length and sleeve dimension on the ultimate average bond strength were discussed. Bond-slip constitutive relations between the ribbed steel bars and grout constrained by sleeve were fitted. Equations were proposed for calculating the characteristic bond strengths and their corresponding slip value. Critical anchorage lengths, at which length bar broke or yielded and bar-grout slippage occurred at the same time, were calculated. The test results showed that with the increase of the bar diameter, the ultimate bearing capacity increased, and the ultimate average bond strength increased as a whole. With the increase of anchorage length, the ultimate bearing capacity increased, but the ultimate average bond strength decreased. In the range from 13.78% to 18.51%, the increase of steel content had little positive effect on the average bond strength. Because no coarse aggregate is contained in the grout, the slip value corresponding to the ultimate average bonding strength when the steel bar was anchored in grout was greater than that when the steel bar was anchored in concrete. Based on the energy analysis of the bond slip curve, it concluded that as the diameter and anchorage length of the bar increased, the brittleness coefficient of the specimen decreased generally, indicating the increase of the specimen’s ductility. Due to the confinement of the sleeve, the critical anchorage length decreased greatly.

Abstract:To study different wind demand exceeding probability assessment of the membrane roof, Chongqing was taken as an example. Taking PEER performance-based seismic design method as reference and considering the randomness of wind field, the probability distribution characteristics of monthly maximum wind speed samples in recent ten years were calculated, and the designed maximum wind speed risk curve was obtained by polynomial fitting. The horizontal wind speed spectrum was represented by Davenport spectrum. The nonlinear characteristics of membrane roof structure were considered, and the relationship between resistance requirements (vertical displacement limit) and the average wind speed spectrum values was approximately represented by a power function. The expression of the mean annual frequency of exceedance for displacement demand was derived. A flat membrane roof was taken as an example, 30 pulsating wind speed time intervals were generated with the AR method, and structural response analysis was carried out. Through calculation, the transcendental probability and recurrence interval corresponding to different performance levels of the roof were obtained. The results show that polynomial fitting has a better effect on the derivation of the expression of annual average exceeding probability. Performance-based wind resistance probabilistic evaluation method for membrane roofs can obtain the transcendental probabilistic evaluation values of different displacement requirements of structures through a small number of structural analyses.

Abstract:Under the stormy weather, rainfall directly changes the aerodynamic force of the structural surface and further affects the turbulence action of wind, but current wind resistance designs for cooling towers all ignore the additive effects of rainfall. To explore the effects of wind-rain on mechanical properties of cooling tower structures, a domestic large cooling tower which is the world’s tallest (210 m) was taken as an example, and based on wind-rain bidirectional coupling algorithm, the flow fields of cooling tower under three typical wind speeds were simulated based on computational fluid dynamics (CFD) technology. The discrete phase model (DPM) were added and the iterative computations of rain-wind coupling of 9 different combinations of wind speed-rain intensity were carried out. On this basis, the influence laws of different combinations of wind speed-rain intensity on rain drops moving trajectory and rainfall on tower drum surface were studied. Then the fitting formulas of equivalent pressure coefficients were proposed. The coupling models of the large cooling tower under different working conditions were established by the finite element method, and the structural responses of tower drum, pillars, and ring foundation under different wind speed-rain intensity combinations were compared. The research provides references for load forecast of such large cooling towers under extreme climates and complex working conditions.

Abstract:The strong ground-motion records selection in structural collapse fragility analysis was studied. To consider the seismic hazard difference within target sites, the conditional mean spectrum (CMS) was used as the target spectrum for ground-motion records selection in the increment dynamic analysis (IDA) method. The CMS was constructed through the China seismic deaggregation and probability seismic hazard analysis. Taking three different 2D structures as examples and based on the seismic safety evaluation of two cities in China, the CMS was constructed to analyze the collapse fragility curves with IDA method, and the results were compared with the results obtained from the uniform hazard spectrum, the code spectrum, and recommended recordings in ATC63. The results indicate that the collapse fragility curve using code spectrum is the steepest, the results of the uniform hazard spectrum and ATC63 are the next, and the suggested method is the flattest. Meanwhile, for the long period 1.5 s structure, the envelope CMS is implemented to consider the influence of the multiple model period effect instead of the single period CMS which underestimates the collapse fragility calculation result significantly for the long period structures.

Abstract:To obtain the floor response spectrums and design spectrums of museum before and after isolation and perform seismic protection design for accessory structure, two finite element models of seismic non-isolated and isolated museums were established and verified through environment vibration tests. Seven seismic motions were selected, and the difference between floor waves and seismic waves was analyzed through peak acceleration and frequency spectrum. Taking the floor waves as the input, the floor acceleration response spectrums before and after isolation were calculated through MATLAB. The design spectrums were fitted according to the theory of seismic design spectrum. The results show that the dynamic characteristics of finite element model(FEM) are in a good agreement with test values.The peak acceleration of isolated structure is about 75% lower than that of the non-isolated structure. The predominant frequency of floor waves is the natural frequency of structure, which is mainly controlled by the main structure.The floor acceleration response spectrums are the results of earthquake working together with structure,which reflects the characteristics of both.The floor acceleration design response spectrums and mathematical formulas are obtained and divided into different sections before and after isolation. The non-isolated design response spectrum has 1 flat and the isolated design response spectrum has 2 flats. The research results of the design spectrum can be used in the seismic protection design of the accessory structures in different structures.

Abstract:To study the structural damage characteristics of marine soft clay under lateral unloading path,stress path tests under lateral unloading condition on the clay obtained from Ruian, Wenzhou were carried out to study the influence of lateral unloading path and structure on stress-strain relationship, shear strength, initial tangent modulus, and other typical mechanical properties. The influences of stress path and soil depth on initial structure and characteristics of structural damage were analyzed. The experimental results show that the structure of Wenzhou soft clay is strong and its stress-strain relation is obviously strain-softening. Under lateral unloading condition, the initial tangent modulus is linearly related to the average consolidation pressure, and the slope is 1.4 times that of the loading condition. The corresponding strain at peak strength of shear stress is smaller than that under loading conditions. The stress ratio structural parameters of soft clay under lateral unloading condition were presented.The results show initial stress ratio structural parameters under lateral unloading condition is obviously larger than those under loading condition. The structural damage curves can be divided into three sections: smooth damage, accelerated damage and deceleration damage.The structural damage rate under loading condition in accelerated damage section is faster than that under lateral unloading condition. The difference of structural damage rate which needs more attentionis related to the anisotropy of soft clay.

Abstract:Numerical simulations were performed to further investigate the effects of beam-to-column connections, reinforced ways, etc. on the hysteretic behavior of three tested steel frames with unbonded steel plate brace encased in panel (referred to as panel BRB), which is termed as steel frame with panel BRB (panel BRBF) hereafter. The values of the parameters used to reflect the hardening behavior of panel BRBs were determined based on cyclic tests of panel BRBs. In general, hysteretic curves of panel BRBFs and mechanism on yielding or buckling of steel members acquired from simulations agreed with those from tests. Yielding of panel BRBs occurred at inter-story drifts of 1/463~1/350 in tests and 1/416~1/305 in simulations, and plastic deformations of steel frames were not obvious prior to the drift of 1/50. Ductility and energy dissipation capacity of panel BRBFs were good and the design aim that yielding of panel BRBFs is mainly concentrated on panel BRBs was realized. Within the drift of 1/30 and prior to deterioration of load carrying capacity of steel frames, the panel BRBFs with moment-resisting beam-to-column connections and the panel BRBF with non-moment-resisting beam-to-column connections, in which steel frames nearly remained elastic, showed trilinear and bilinear skeleton curves, respectively. The trilinear curve of each panel BRBF can be acquired by putting the bilinear skeleton curves of both panel BRB and steel frame together. The reinforced ways of adding steel plates at the ends of steel beams near moment-resisting beam-to-column connections let yielding of beams occur far away from the beam-to-column connections and ensured both enough strength of the connections and stable energy dissipation capacity of steel frames. The beam in the panel BRBF with non-moment-resisting beam-to-column connections had large flexural yielding when one brace in a chevron panel BRB failed locally, and the overall lateral resistance of structure was not deteriorated. Besides, simplified methods by employing beam and truss elements to simulate hysteretic behavior of panel BRBFs were proposed.

Abstract:To generate regular and fluent structured grids over free-form surfaces, especially complex multiple surfaces for architectural design, an adaptive grid generation method was proposed. First, the surface region to be meshed was determined by four boundary curves. Second, a pair of disconnected boundary curves was divided into n+1 segments respectively and n lines were acquired by connecting pairs of segment points on the same relative positions. Third, these n curves and the other pair of boundary curves were divided into m+1 segments respectively, and m polylines on the other direction were attained by connecting these segment points on the same relative locations. These two sets of curves were divided and reconnected in turn iteratively until the locations of segment points did not change obviously. Finally, the (m+2)×(n+2) segment points were connected into a grid in a desired pattern. During the generation, the grid size was adaptive to boundary conditions or surface shapes by adjusting the rules of curve dividing, and various girds was generated by defining different rules of point connections. The case study indicates that this method is easy to operate, fast to generate, and widely applicable, and the resulting grids have fluent lines, regular shapes, and various patterns, which can meet architectural demands.

Abstract:To establish a mechanical model and shear bearing capacity calculation method for reinforced concrete masonry walls, a prediction method based on the analysis of the shear failure test characteristics of reinforced concrete masonry walls was proposed,in which the softened strut-and-tie model was adopted and the softening effect of concrete block masonry under compression was considered. The rationality of softened strut-and-tie model was verified by the 54 existing tested reinforced concrete block masonry walls failed in shear, and the prediction results were compared with those of relevant formulas at home and abroad. The research results show that good agreement is achieved between the prediction results and tested results, and the prediction results are closer to the tested results than those of relevant formula with a lower coefficient of variation value.Furthermore, this model has a clear and definite mechanical model and it can reasonably reveal the shear failure mechanism of reinforced concrete block masonry walls with span-to-depth ratios no greater than 2.0.

Abstract:To investigate the shear performance of alkali-activated slag ceramsite concrete hollow block masonry,tests on 108 masonry prisms with Mb25~Mb130 of alkali-activated slag paste and Mb25~Mb80 of alkali-activated slag mortar with pottery sand were carried out. The results show that the shear strength of masonry with alkali-activated slag paste was less than that with alkali-activated slag mortar, and the shear strength of masonry with alkali-activated slag mortar was lower than that with ordinary cement and composite mortars, respectively. The shear strength of masonry increased as the compressive strength of alkali-activated slag paste and mortar increased. The effects of Na₂O contents and sand to cementitious materials ratios on the shear strength of masonry should not be ignored. Based on the results, the formulae for the shear strength of alkali-activated slag ceramsite concrete hollow block masonry with alkali-activated slag pastes and mortars were developed, respectively.

Abstract:To absorb blast energy and reduce blast load on buildings during explosion, a novel energy absorption connector filled with aluminum foam was proposed. Lateral impact loading tests on the proposed energy absorption connectors were conducted to study their energy absorption performance. In the tests, effects of filled aluminum foam and plate thickness on the energy absorption performance of the connectors were investigated. Force-displacement curves of the connectors with aluminum foam showed three stages, including elastic deformation, plastic deformation and aluminum foam densification stage. The plastic deformation of pleated plate and compression of aluminum foam contributed to energy absorption, while the connectors without aluminum foam only relied on plastic deformation to absorb energy. The FE models of the connectors were established utilizing LS-DYNA and then validated with the tests results. It was proved that the proposed connectors showed considerable energy absorption performance which could be largely improved by filling the connector with aluminum foam.

Abstract:To obtain the anti-vibration performance and anti-vibration design method of the spring bearing for vertical vibration isolation of large facilities, taking the horizontal displacement limitation situation of the cover and the vertical force as the basic parameter, the pseudo-static test of the horizontal repeated load and horizontal displacement of the spring isolation bearing of 10 specimens of 100 kN and 300 kN was completed, and hysteresis curve considering the influence of vertical load was obtained. The hysteresis relationship was linear elastic relationship under the initial small displacement, and the influence of vertical compression on the single-circle limit lateral displacement was negligible.After a large displacement, the hysteresis curve showedcertain energy consumption due to the limitation of the cover plate.When the cover plate hadno displacement limitation, the cumulative effect of vertical compression and horizontal deformation can cause irreversible plastic deformation of the local spring, and its energy consumption capacity and limit lateral displacement ability were large. Based on the test results, the methods for determining the elastic stiffness and elastic deformation limit of two types of spring isolation bearings were proposed. The suggestion was madethat the elastic deformation of the spring vibration isolating support should be combined with vertical deformation under the influence of rare earthquakes. The research results can provide references for seismic performance evaluation and seismic design of large-scale facilities such as large anechoic chambers or semi-anechoic chambers with vertical vibration isolators.

Abstract:An evaluation method for the component importance of pin-jointed structures based on the redundancy theory was proposed. On the basis of the uniformity of the element-redundancy, the quotient of the standard deviation and the mean value of the element-redundancy was defined as the redundancy distribution index. The component importance of pin-jointed structures was evaluated by the redundancy distribution indexes of the remaining structures in the cases with different component removals. The redundancy distribution indexes of the remaining structures were defined as the component importance indexes. Three practical examples were given for illustration. The results showed that the redundancy distribution index can reflect the uniformity of the element-redundancy, and the proposed method is able to effectively evaluate the component importance of pin-jointed structures. The smaller the redundancy distribution index is, the more uniform the structural redundancy distribution is, which indicates better structural robustness. The higher the component importance index is, the greater the impact of corresponding member on the structural robustness is.

Abstract:The natural frequency is the key factor that determines the dynamic deformation and stress of structure.The natural frequencies of the existing cooling towers are mainly obtained by finite element analysis, and there is no simple and effective formula for estimating the natural frequencies of the cooling towers.To resolve this problem,a large cooling tower was takenas the reference tower. Firstly, 38 models were obtained by changing the typical parameters of the reference tower, and the dynamic characteristics were analyzed.The law of fundamental frequency changing with the structure parameters was also extracted.Then, the sensitivity of the structural natural frequency parameters was analyzed by Latin hypercube sampling method, and the sensitive factors of various structural parameters under different orders were obtained.On this basis, the practical estimation formula of multi-parameter fundamental frequency considering sensitivity factor weight was innovatively fitted. Finally, eight cooling towersof typical height and typein China were selected for the field measurements, and the first 10-order self-oscillation frequencies of cooling tower were obtained by different mode identification methods.Further, the goodness of fit was analyzed using eight seat structure parameters of cooling tower. The results show thatthe natural frequencies are most sensitive to the height of cooling towers, and the sensitive factors are significantly higher than those of other parameters.By using 8 measured towers, the formula for estimating fundamental frequency isverified. The maximum value of self-vibration frequency fitting is 0.996, in which the mean value and mean variance of each target tower are 0.948 and 0.047, respectively. The estimation formula ofthe natural frequencies is of high accuracy and stability.