Abstract:To investigate whether the indirect steel bar is capable of yielding when the concrete reaches local bearing capacity, the calculation method of tensile stress when the indirect steel bar could not yield, and the possibility of reasonable anchoring of meshed indirect steel bar outside the wedge, 18 specimens reinforced with spiral indirect steel bars and 18 with meshed indirect steel bars were experimentally evaluated, subjected to local compression forces. Results show that when the concrete reached the ultimate load, non-yielding occurred in the indirect steel bars in the area affected by the local pressure. Based on the test results, the volumetric ratios of indirect steel bars corresponding to the yielding of the spiral and meshed indirect steel bars for hot-rolled steel bars with different strength grades (HPB300, HRB400, HRB500, HRB600) were obtained. A calculation method of the tensile stress at the intersection of the meshed indirect steel bar and the outer side of the wedge was established for the situation that the meshed indirect steel bar does not yield under local pressure.

Abstract:Thick concrete slab and concrete transfer beam are important horizontal components in building structures. To explore how to complete the demolition of the two components environmental-friendly and efficiently, static crushing experiments of three thick concrete slab specimens and seven concrete transfer beam specimens were carried out, and reinforcements were cut or removed before crushing. Experimental results showed that when the thick concrete slabs were broken by drilling holes perpendicular to the top surface of the slab, the cracking degree was affected by the horizontal longitudinal reinforcements of the specimens in the static crushing process; the crushing effect could be improved by cutting off along the hole connecting line and its extension line or removing the upper longitudinal reinforcements; the size of the short side of the blocks after crushing was hole spacing or hole edge distance. When the concrete transfer beams were broken by drilling holes inclined downward at the side surface of the beam, the cracking degree was affected by the stirrups and longitudinal reinforcements of the specimens in the static crushing process; the crushing effect could be improved by cutting off the stirrups or longitudinal reinforcements along the orifice connecting line and extension line, and cutting off the stirrups or longitudinal reinforcements along the connecting line and extension line of the intersection of the borehole extension line on the other side surface; the size of the short side of the blocks after crushing was hole spacing or hole row spacing. When the concrete transfer beams were broken by drilling holes perpendicular to the top surface of the beam, after the stirrups at the top of the beam were cut off along the hole connecting line and its extension line, the cracking degree was affected by the tie reinforcements of the specimens in the static crushing process, which could continue to reduce the hole spacing to improve the crushing effect.

Abstract:To investigate the influence of hole forming methods and the thickness of shear wall on the static crushing effect of concrete shear walls, static crushing tests of nine concrete shear wall specimens were carried out. Two crushing methods were adopted: one is drilling holes on the side of the wall obliquely downwards and injecting static crushing agent for crushing, and the other is drilling holes perpendicular to the top surface of the wall and injecting static crushing agent for crushing. In order to improve the crushing effect, the vertically distributed steel bars on the side of the wall were cut off with a saw blade after drilling on the side of the wall, and the horizontally distributed steel bars on both sides of the wall were cut off with the saw blade after drilling on the top of the wall. Test results show that with these two crushing schemes, the short side size of the block produced after crushing was the hole spacing or hole edge spacing. After injecting static crushing agent, with the increment of the wall thickness, the average width of the slits of the specimens drilled obliquely on the side increased, while for the specimens drilled vertically on the top surface, the average width of the slits had no obvious correlation with the wall thickness. The order of the crushing effect was: drilling holes on the top of the wall vertically and cutting off the horizontally distributed steel bars> drilling holes on the top of the wall without cutting the steel bars> drilling holes on the side of the wall obliquely downwards and cutting off the vertically distributed steel bars.

Abstract:The existing calculation method for the additional axial force (AAF) in wall piers of coupled walls (CWs) requires complex modeling or computing. To solve this problem and to quantify the effect of AAFs on the strength of CWs, a differential equation with respect to AAF was established using a selected coordinate based on the method of continuous connecting links. New analytical formulas of AAF for three types of lateral loads were developed. A simple and practical calculation method for AAF was proposed, which was compared with existing formulas and numerical simulations. The main factors affecting AAF were analyzed using the proposed method. The effect of AAFs on the strength of CWs was investigated using flexural and shear strength indexes. Results show that AAF could be obtained by the proposed method quickly and accurately if the CW geometry and the types of lateral loads were specified, which is simpler than the existing method. The value of AAF for a CW under different types of lateral loads was more affected by the total overturning moment (OTM) than the base shear. The effect of AAFs reduced the shear strength of CWs and the sum of flexural strength of individual wall piers, but the global flexural strength of CWs was almost linearly increased with the increment of AAFs.

Abstract:The coupling ratio (CR) is an important parameter that measures the mechanical behaviors of coupled walls (CWs). The design method using CR for CWs has been adopted gradually and internationally. To calculate CR in elastic and plastic stages and clarify a reasonable range for its application, a calculation method was proposed based on theoretical derivation and numerical simulation results. The variation of CR during elastic-plastic stage and the responses of CWs with different combinations of elastic and plastic CRs were analyzed. A theoretical formula for calculating top lateral displacement of CWs was put forward, and the suggestion on realizing ideal yielding mechanism for CWs by using CR was given. Results show that the calculation method of elastic and plastic CRs and the formula of top displacement were both effective and reasonable. The elastic CR was mainly controlled by the geometry of CWs, whereas the plastic CR had impacts on the ultimate strength and ductility of CWs, whose upper limit should thereby be set. The difference between plastic CR and elastic CR should be larger than 10% so as to avoid the occurrence of yielding in wall piers prior to most coupling beams. A safer and more reasonable design for CWs can be achieved by calculating and controlling CRs.

Abstract:To study the bond mechanism of steel tube and concrete interface, referring to the method of setting geometric defects in steel structure design code, low-order buckling modes were used to characterize the overall geometric defects and high-order buckling modes were used to characterize local geometric defects. The contact element was set with 100 layers of contact pairs, and the interface bond-slip behavior was defined by the Coulomb friction and sliding criterion. ANSYS restart analysis function was adopted to realize the gradual loss of chemical bonding force, and the finite element model of concrete filled steel tube with geometric defects was established. Simulation results show that the low-and high-order buckling modes of steel tubes were suitable for simulating the overall and local geometric defects of steel tubes, and the superimposed defect size could simulate the geometric defects of ±0.5%D (Dis the outer diameter of the steel tube). The finite element model (FEM) could monitor each load step, describe the time-varying state during the push-out process more accurately, and reproduce the process of the gradual peeling of the steel-concrete bond interface from both ends to the middle of the specimens. The overall geometric defects of the steel tubes corresponding to the two types of bond-slip curves included a downward trend curve after the formation of the inflection point, which corresponds to the low-order buckling mode of the linear meridian, and a slow rise curve after the formation of the inflection point, which corresponds to the low-order buckling mode of the curved meridian. The local geometric defects of steel tubes could be summarized as periodic wave crest-like defects. The empirical relationship between the number of local geometric defect crests and the diameter-thickness ratio of steel tube, bond length, as well as concrete strength was proposed.

Abstract:To theoretically analyze the elastic lateral-resistant stiffness of corrugated steel plate shear walls, the relationship between elastic modulus, shear modulus, and unknown Poisson’s ratio of corrugated steel plates with different wave forms was obtained by comparatively analyzing the in-plane deformation of equivalent orthotropic plate under pure shear and pure principal stress in elasticity phase using orthotropic plate theory. The unknown Poisson’s ratio was calculated inversely by shear modulus of steel plate to obtain the unified formula of shear modulus for corrugated steel plates. Applying the unified formula to the elastic lateral stiffness formula of thick steel plates, the elastic lateral stiffness formula of corrugated steel plates was obtained. The elastic lateral-resistant stiffness of corrugated steel plate shear walls was calculated by simple addition of corrugated steel plate stiffness and frame stiffness. The reliability of the proposed formula was verified by existing shear modulus formula of corrugated steel plates. Then, a total of 70 models were simulated based on ABAQUS finite element analysis software for corrugated steel plate shear walls with different wave forms and sizes to verify the uniformity of the proposed formula. Results show that the unified formula was accurate and reliable for calculating the elastic lateral-resistant stiffness of corrugated steel plate shear walls. The wavelength and corrugation expansion length both had significant effects on the elastic lateral-resistant stiffness, while the wave forms of corrugated steel plates had no effect on the variation of elastic lateral-resistant stiffness when the wavelength and corrugation expansion length were constant. Finally, the application scope of the unified formula was determined.

Abstract:Due to the strengths of porous double skin faade (porous DSF) systems in building energy efficiency and architectural aesthetics, they have become increasingly popular in the architectural and engineering fields. Given the fact that porous DSF can soften the flow separation around building corners, it is expected that porous DSF systems should have the potential in controlling wind-induced structural responses. Therefore, a detailed wind tunnel study was conducted to investigate the effects of porous DSF on the wind-induced accelerations and structural wind loads of a typical square tall building, focusing on the influence of the porous DSF coverage area and its location. The performance of the porous DSF under different terrain conditions was also examined during the wind tunnel tests. Research results confirmed the effectiveness of the porous DSF in suppressing the across-wind responses of buildings, especially when the porous DSF located in the upper part of the building and covered at least 1/6 of the total height. It was also found that the effectiveness of the porous DSF varied with reduced wind velocity (a non-dimensional parameter). When the reduced wind velocity was lower than 10.5, the porous DSF system covering the upper 1/3 of the building height could reduce the building acceleration by 20% to 30%. When the reduced wind velocity was higher than 10.5, the building acceleration and structural wind loads could both be reduced by up to 45%. It suggests that porous DSF can not only be utilized to reduce the structural design wind loads in extreme wind events, but also be employed to improve the serviceability performance of the building in normal wind conditions. The wind tunnel tests for different terrain conditions revealed similar effects of porous DSF in reducing across-wind responses. Thus, porous DSF systems can be regarded as an ideal supplement to the existing aerodynamic approaches in building optimization design.

Abstract:To reduce the safety hazards caused by the wind-induced swing of transmission jump lines and to ensure the safety of power transmission, it is necessary to accurately estimate the dynamic response of the wind-induced swing. The current calculation method for wind-induced swing of jump lines in the Electric Power Engineering Design Manual of High Voltage Transmission Lineignores the pulsation amplification effect of the wind load, and the lines designed based on this method may be unsafe. A finite element coupling model of a high-voltage transmission line was established and the non-linear finite element method was used to calculate the wind-induced swing response of direct and circuitous jump lines. Meanwhile, comparison and analysis were carried out to figure out the shortcomings of the manual calculation method. On this basis, the equivalent static wind load was used to replace the horizontal wind load of the jump lines, and the wind load adjustment factor β_c was introduced to give consideration to the pulsation amplification effect of the wind load for revising the calculation method of the manual. Research results show that the manual calculation method ignored the pulsation amplification effect of wind load, which would seriously underestimate the wind-induced swing response of the jump lines.The maximum error between the manual calculation method result and the finite element result was about 37%, while the wind-induced swing response of the jump line calculated by the correction method was very close to the finite element result. The correction method proposed in this paper can be used to finely estimate the wind-induced swing response of jump lines.

Abstract:To study the influence of the variation of key parameters of the head of monopole (two-wheel type) on the wind load and its change law, wind-tunnel tests were carried out on large-scale models of the head of monopole in uniform flow field, based on the high-frequency force balance technology. The influence of monopole diameter, antenna size, overhang distance, and other parameters on the drag coefficient was analyzed, the variation of the drag coefficient in the range of high Reynolds number was studied, and the contribution of the external antenna to the overall resistance of the head of monopole was discussed. Results show that the drag coefficient of the integrated models was not sensitive to the variation of the Reynolds number, and it decreased as the monopole diameter increased. The drag coefficient was greatly affected by the wind direction angle, and the descending slope of the drag coefficient increased as the monopole diameter increased, while the downward trend gradually tended to be gentle. In this study, the ratio of the resistance of the external antenna to that of the integrated models was defined as the antenna shape influence coefficient. Test results show that the influence coefficient increased with the increase in the Reynolds number and tended to be stable in the range of high Reynolds number. As the monopole diameter increased, the influence coefficient decreased, and the contribution of the antenna to the integrated models was weakened. The antenna size had little effect on the drag coefficient and its variation trend. The drag coefficient increased as the overhang distance increased, and its variation with Reynolds number was less affected by the overhang distance.

Abstract:To alleviate the problems of the aerodynamic shape optimization (ASO) method of bridge section based on wind tunnel test, such as manpower and material cost as well as limited search range, the ASO method of main girder based on numerical calculation and mathematical strategy was proposed. Taking the streamlined box girder of Sutong Changjiang Bridge as an example, the lower web inclination angle and beam height were selected as design variables, the computational fluid dynamics (CFD) simulation and flutter time domain method were adopted as numerical calculation methods to replace the wind tunnel test, the experimental design, hybrid ant colony genetic algorithm, and Kriging model were used as the collaborative mathematics strategy to replace the trial-and-error method, and the optimal parameter matching scheme of the flutter performance of the beam section was explored. The optimization results show that the critical flutter wind speed of the optimal section in the design domain was 8% higher than that of the original section. The lower web inclination angle had a greater influence on the flutter performance than the beam height, and there was interaction between the two variables. The numerical ASO method of main beam section could better replace the wind tunnel test for shape optimization, and the research could be used as reference for the selection of long-span bridge sections.

Abstract:To study the seismic performance of embedded column base with low embedment ratio, eight column bases with a scale ratio of 1∶2 were designed to carry out experiments. The effects of parameters such as stud, embedment ratio, axial load, and flange thickness on the failure mode, hysteretic curve, skeleton curve, ductility, stiffness degradation, and energy dissipation capacity of the column bases were analyzed. Results show that the embedded column base with low embedment ratio had two failure modes, i.e., the secondary pouring surface failure of the concrete and the buckling failure of the bottom of the steel column. The failure modes of the embedded column base could be effectively improved by arranging studs or applying axial pressure, which could transform the secondary pouring surface failure into the buckling failure of the steel bottom and improve the energy dissipation capacity of the column base. When the embedded column base was under no stud and no axial load, the increase of the embedment ratio from 1.0 to 1.5 reduced the damage degree of the secondary pouring surface and ensured its continued bearing capacity, but could not change the failure mode. In engineering design, studs should be set when the embedment ratio of the embedded column base is equal to 1.0.

Abstract:In order to improve the calculation efficiency for seismic reliability of cast iron pipelines with bell-and-spigot joints, a Monte Carlo simulation method based on active learning Kriging model (AK-MCS) was proposed to calculate the seismic reliability of buried pipelines. A seismic response analysis model for buried pipeline system was established, in which the beam element was adopted to simulate the pipeline structure, and soil spring and joint spring were used to simulate the pipe-soil interaction and the constraint of adjacent pipe segments respectively. Considering the randomness of critical parameters such as the allowable displacement of pipeline joints, the depth of the pipeline, the unit weight, and the friction angle of the surrounding soil, based on the safety criteria of the allowable relative joint displacement, the active learning Kriging method was used to establish a surrogate model between the relative displacement of the pipeline joint and the random parameters. The safety margin of the pipeline joint was subsequently obtained through the validated surrogate model. Numerical results show that the relative difference of the pipeline failure probability between AK-MCS method and standard MCS method was less than 5%, and the computational time of the AK-MCS method was only about 2% of the standard MCS method. Therefore, the proposed AK-MCS method is an efficient alternative to evaluate the seismic reliability of buried pipelines.

Abstract:To study the differences of various ground motion parameters in the selection of horizontal bidirectional ground motion records, by taking the “Code for Seismic Design of Buildings” (GB 50011—2010) as an example, the differences of ground motion characteristics and structural responses of selected records were compared. The records were selected in order of error by linear amplitude and full period spectrum matching method under two working conditions, which were then input to 4-story and 12-story concrete frame structures to analyze the story displacement angle and story shear force. Meanwhile, the characteristics and sensitivity of the selected ground motion records were compared. Results show that the structural response, scaling coefficient, and ground motion characteristics of the records selected by the maximum direction spectrum have less discreteness in comparison with those of sum of mean square spectrum and geometric average spectrum. Compared with the target spectrum, the records selected by the maximum direction spectrum are more conservative in medium and short periods, and those selected by sum of mean square spectrum and geometric average spectrum are more conservative in medium and long periods. When using maximum direction spectrum for ground motion selection, the sensitivity of effective peak acceleration (EPA) and effective peak velocity (EPV) of the selection results are higher, while those of sum of mean square spectrum and geometric average spectrum are lower. In practical engineering application, it is suggested that different ground motion parameters should be selected according to different engineering requirements under the premise of ensuring economy and practicability.

Abstract:The construction of masonry structures with removed walls can realize the reutilization of the removed walls and promote the further development of industrialized demolition and construction of masonry structures. To study the seismic resistance of masonry structures built with removed walls, the similarities and differences between masonry structures built with removed walls and ordinary masonry structures were analyzed. Twenty ground motion records were selected for incremental dynamic analysis of brick masonry structure model with structural column spacing, number of stories, and masonry strength as basic parameters, peak ground acceleration as ground shaking strength index, and maximum inter-story displacement angle as structural damage index. Based on the established seismic vulnerability curves and seismic damage matrix of brick masonry structures, it was found that the seismic performance of brick masonry structures built with removed walls was significantly improved compared with conventional brick masonry structures under the same conditions, which was mainly due to the relatively dense structural columns used for the splicing of the removed walls. The number of stories and masonry strength directly affected the seismic capacity of the structure. It is recommended that the total number of stories and total height of the structure should not exceed the requirements of GB 50011 when reusing removed walls, and reasonably assessment of the mechanical properties and integrity of the removed walls should be conducted. It is also necessary to ensure that the seismic measures for masonry structures built with removed walls are not lower than those for new masonry structures under corresponding seismic intensity requirements.

Abstract:Nearly saturated natural ground is widely distributed in nature, and the study of the consolidation characteristics of nearly saturated composite ground with impervious piles has theoretical significance and engineering application value. Based on the assumption of the equal strain condition between soil and pile and considering the compressibility of pore fluid, a consolidation governing equation was derived for nearly saturated composite ground with impervious piles. The initial condition of pore pressure was determined according to the property that the specific flow is equal to zero at the moment of loading. Using separate variable method and superposition method, the analytical solutions of pore pressure were obtained under instant loading and single ramp loading and under the loading which remained constant with depth and changed arbitrarily with time. The calculation formulae of consolidation degree and immediate settlement were derived. When the compressibility of pore fluid was taken into account, the composite ground produced not only immediate pore pressure but also immediate settlement. The higher the air content was, the smaller the initial pore pressure and the consolidation degree defined by consolidation settlement were. The higher the air content and the compressive modulus of pile were, the larger the immediate settlement was. Even when the air content was only 0.2%, the ratio of immediate settlement to total settlement exceeded 97.3% in the pre-stressed pipe pile improved ground. Since the equivalent compressive modulus of soil ground significantly increased with the installation of piles and the bulk modulus of pore-water significantly decreased with air contents, the research reveals that it is necessary to take into account the compressibility of pore-water in the consolidation behavior analysis of nearly saturated composite ground with impervious piles, otherwise it will cause large theoretical errors.

Abstract:To investigate the influence of moisture absorption/desorption on the flexural property degradation of glass fiber reinforced polymer (GFRP) laminates under hot/wet aging environments, three-point bending tests were carried out. The flexural properties of specimens were compared under dry, unsaturated, and saturated water absorption conditions at test temperatures 20 ℃ and 40 ℃. A moisture absorption-desorption process was considered as a cycle to investigate the mechanical degradation and permanent damage of GFRP laminates induced by moisture diffusion. Experimental results show that the combination effects of moisture and temperature reduced the flexural strength and elastic modulus of GFRP laminates, and the reduction rate of flexural strength was much larger than that of elastic modulus. At the test temperature of 40 ℃, unrecoverable losses of elastic modulus (15.0%) and flexural strength (16.4%) occurred for GFRP laminates experiencing one cycle of moisture absorption-desorption process, which was not evident at the test temperature of 20 ℃.Moreover,a coupled hygro-mechanical finite element (FE) model was developed to characterize the mechanical behaviors of GFRP laminates at different moisture absorption/desorption stages, and was subsequently validated with flexural test results.

Abstract:In order to achieve pull-through of transverse rebar of one-way precast slab to form two-way slab without wet operation or welding, considering the operability and efficiency of construction, steel plate composite blind bolts as rebar mechanical connectors were proposed. To study the tensile properties of the connectors, a monotonic tensile test was performed on 22 specimens. The research parameters were steel plate strength, number of bolts, pre-tightening force, and anchorage length, and the failure form, ultimate bearing capacity, load-displacement curve, and deformation capacity were investigated. Research results show that there were two failure modes of the specimens including fracture and pull-out of rebar. For the quenched and tempered 45＃ steel cover plate, the critical anchorage length of the reinforcing bar of the connector was between 2d and 3d. When it was less than the critical anchorage length, the rebar experienced scraping plough type pull-out; when it was larger than the critical anchorage length, the rebar would fracture. When the number of the connecting bolts was four, the specimens realized equal-strength connection of rebars. With the decrease in the width of the connecting cover, the critical anchorage length increased. Under the same anchorage length, the tensile strength of the joints increased with the increase in the pre-tightening force of the bolts. For the Q460C high-strength steel cover plate, the failure modes were deformation of the tooth nails and pull-out of the rebar. Under the same experimental conditions, the failure modes of the specimens with ribbed bars and rounded steel bars were the same. The formula for calculating the tensile bearing capacity of the proposed connector was proposed, and the analytical values agreed well with the experimental results, which could provide references for relevant design and research.

Abstract:To solve the problems of repair and reinforcement of existing old rural houses, taking a single-layer masonry structure with two bays in Beijing as the prototype, according to the idea of inner frame reinforcement, a reinforcement method based on embedded light steel frame reinforcement and supplemented by steel plate reinforcement was proposed, and a 1/4-scale masonry structure shaking table model was designed for shaking table test. Test results show that the model structure had obvious damage under the action of small earthquake, and the transverse wall of the structure had obvious extraversion under the action of moderate earthquake and large earthquake. However, due to the reinforcement and restraint effect of steel frame and steel strip, the structure did not collapse, the degree of the external flashover was controlled within the safe range, and the strengthened structure achieved the goal of “no collapse in large earthquakes”. With the successive loading of seismic loads, the natural frequency of the structure decreased gradually. With the increase in seismic intensity, the acceleration amplification coefficient of the test model decreased on the whole. When the inner steel frame and steel strip were used for reinforcement, the acceleration amplification coefficient of the structure had a slight increase. The displacement of the structure increased with the increase in the earthquake magnitude, and the displacement of the front cornice was greater than that of the rear cornice, leading to the torsion effect. The inner steel frame remained undamaged after the earthquake, which avoids the overall collapse of the structure and ensures the safety of the structure.