To investigate the shear performance of Italian poplar laminated veneer lumber(LVL)beams with opening in the bending-shear region,six standard specimens were designed and tested under four-point bending.The shear failure mechanisms of the LVL beams with opening under various parameters were analyzed.Using the extended finite element method and ABAQUS software,a finite element model of perforated beam with virtual cracks was developed.Parametric analyses were performed considering variations in the diameter-to-height ratio,opening shape,and opening center eccentricity,using the validated model.The results show that the unperforated beam experiences bending failure due to tensile cracking at the mid-span.In contrast,beams with circular opening experience longitudinal shear failure at the ends due to stress concentration around the opening perimeter.The maximum transverse tensile strain around the opening perimeter forms an angle of approximately 45°or 225°relative to the longitudinal axis of beam,consistent with the crack initiation angle.As the diameter-to-height ratio increases to 0.5,both cracking and ultimate load capacities of the beams with circular opening significantly decrease,exhibiting more brittle shear failure.When the diameter-to-height ratio increases from 0.3 to 0.4 and 0.5,the ratio of cracking to ultimate load capacity increases from 0.79 to 0.80 and 0.81,respectively.Using carbon fiber reinforced polymer(CFRP)wrapping around the openings effectively suppresses crack propagation and enhance the structural performance of the perforated beams.For the beam with a diameter-to-height ratio of 0.4,the ultimate load decreases by 17.9％and 5.22％,respectively,for one and two layers of CFRP wrapping,compared to the unperforated beam.When comparing circular-opening beam(diameter-to-height ratio of 0.3)to those with square-opening of the same diameter,the square-opening beam shows a 19.35％and 7.81％reduction in cracking and ultimate load capacity,respectively.Increasing the opening center eccentricity is found to improve both cracking and ultimate load capacities.The prediction formulas for the cracking and ultimate load capacities of LVL beams with opening were proposed.The prediction for cracking load is relatively conservative,and the average error between the predicted and experimental results for the ultimate load is 8％.
Carbon fiber-reinforced polymer-steel composite bars (C-FSCBs) and coral sea-sand aggregate seawater concrete (CSSC) are attractive choices as construction materials for island and atoll engineering construction. Understanding the bond behavior between the C-FSCB and CSSC is crucial for evaluating the mechanical properties of C-FSCB-reinforced CSSC structures. In this study, the bond-slip behavior between the C-FSCB and CSSC was experimentally assessed via pullout tests. The influence of various factors on the bond behavior was discussed, and the bond mechanism between the C-FSCB and CSSC was analyzed. The results indicate that, unlike steel bars, the low rigidity of fiber-reinforced polymer caused surface fiber stripping (i.e., shear damage) of the C-FSCB after interface slip, consequently reducing the squeezing fragmentation of concrete between the ribs. As the diameter and bond length of the C-FSCB increased, the bond strength decreased. Compared to specimens with C-FSCBs, the bond strength of specimens with steel bars of the same diameter increased by 17.9%. The degree of coarse aggregate fracture at the CSSC interface in the splitting failure was much higher than that of normal concrete. Based on existing research data, a formula for calculating the bond strength of C-FSCBs in CSSC has been established to determine the anchorage length of C-FSCBs, and the calculated values accurately predicted the test values.
This paper introduces the development process of building cable structures in China over the past 70 years according to three stages: the initial, slow, and rapid development. It also summarizes the types of cable components and joints of building cable structures. The structural characteristics and representative projects of suspension, cable membrane, beam string (cable-supported), and cable dome structures are reviewed in this paper. Finally, the achievements and prospects of cable structures in China are discussed.
Based on the project of the Guansheng Qujiang Bridge, the flexural mechanical properties of an ultrahigh strength concrete filled steel tube (UHSCFST) were discussed. A total of six UHSCFST beam specimens were tested, and the cube strength (fcu) of the core concrete reached 80.3–115.2 MPa. The effects of concrete strength on flexural bearing capacity, deformation characteristics, and failure modes of UHSCFST specimens were discussed. Test results showed that the bending failure modes of UHSCFST specimens were the same as those of ordinary ones. The failure of UHSCFST specimens was attributed to excessive deflection, and local buckling occurred in the compression zone. Moreover, the bending capacity of the specimens did not decrease, even if they had yielded. Although ultrahigh strength concrete was poured, all of the specimens displayed outstanding bending ductility. The main function of core concrete was to provide radial restraint for the steel tube to avoid premature buckling. When the steel content of the specimen section was constant, the strength increases of core concrete had a slight impact on the bending failure mode, bearing capacity and ductility of UHSCFST specimen. The research results can deepen the understanding of the mechanical behaviors of the UHSCFST composite truss structure.
Combining the advantages of partially encased composite structure (PEC) and corrugated steel web, a new type of composite PEC beam with corrugated web was proposed in this paper, namely corrugated webbed PEC (CWPEC) beam. In order to investigate the structural performance of the proposed CWPEC beams, four specimens were designed and fabricated. Four-point bending tests were carried out to study their flexural performance and failure modes. The failure process, load-displacement curve and strain distribution of the tested specimens were analyzed. Experimental results showed the high load carrying capacity and superior ductility of the proposed concept. Parametric study indicated that the concrete strength was increased from C30 to C50, the ultimate load slightly increased by 3.38%. The flange strength decreased from Q355 B to Q235, the ultimate load reduced by 9.17%. The flange width decreased from 250 mm to 200 mm, the ultimate load decreased by 22.21%. As comparison, the increase of steel flange width is more efficient to improve section moment capacity. Further analysis verified that the flexural strength of CWPEC beam was mostly provided by flanges with little contribution from the corrugated web. Finally, based on the quasi-plane assumption, prediction formulas for cracking moment and ultimate moment of CWPEC beams were proposed.
A suitable constitutive model for describing the damage behavior of ultra-high performance concrete (UHPC) under various loading histories plays a vital role in analyzing its structural performance. In this work, a consistent elastoplastic damage model is developed for UHPC containing coarse aggregate (UHPC-CA) subjected to static and fatigue loads, in which the driving and alleviating effects induced by the inclusions of coarse aggregate and steel fiber are considered. For damage evolution, based on the acting mechanism of the non-uniformity of stress wave propagation determined by the loading rate on the mechanical responses of UHPC-CA, the loading rate is skillfully integrated into the damage evolution rule to achieve the consistent description of mechanical behaviors of UHPC-CA under static and fatigue loading conditions. Regarding plasticity growth, an empirical plastic deformation model is adopted to improve the computational efficiency of structural nonlinear analysis. To verify the applicability of the proposed model, a user-defined UMAT subroutine is further developed for the subsequent numerical implementation. The comprehensive comparisons between the numerical predictions and independent experimental results at both the material level and structural level solidly demonstrate the capacity of the consistent model to capture the main features concerning the mechanical performance of UHPC-CA subjected to different loading paths.
Irregular buildings that occupy a certain proportion on regional scales are prone to suffer serious damage from earthquakes due to the influence of lateral-torsional coupling effect. However, the current regional seismic damage simulation methods are mainly based on two-dimensional simplified models, which cannot take into account the spatial characteristics of irregular buildings. In addition, the refined finite-element method is unsuitable for the simulation of a host of buildings on a regional scale. This paper proposes a moderately refined seismic damage simulation method for building groups with high efficiency to consider the spatial irregularity characteristics of structures. The moderately refined layer element model is established to simulate the nonlinear behavior of each story of the building with irregular plan configurations. For the elevation-irregular structures, the proposed model can also be used by properly combining the elements representing various stories in series. Additionally, a simplified approach of considering P-∆ effect is incorporated by adding equivalent lateral forces to nodes and the method for determining the hysteretic parameter and backbone curve parameters of the proposed model is illustrated. Then, a two-level accelerated dynamic analysis method is proposed to reduce computation time for seismic damage simulation in region, which involves a perturbation nonlinear dynamic governing equation for a single structure and an OpenMP parallel solution strategy for structure groups. Finally, the two individual numerical examples and the seismic damage simulation for a region are performed to demonstrate the validity and efficiency of the proposed method.
In order to investigate the hysteretic behaviour of concrete-filled double tubular(CFDT)columns,the quasi-static tests on 12 square CFDT members with inner circular steel tubes were completed.The influence of the axial load ratio(0.2,0.4 and 0.6)and the diameter-thickness ratio(30,44.5 and 57)of inner circular steel tubes on the failure modes of specimens,horizontal load-displacement curves and seismic performance were examined.Based on the fiber beam element subroutine iFiberLUT and ABAQUS software,a numerical model was developed to predict the test results and analyze the effects of various parameters on the horizontal load-displacement skeleton curves.The test results show that the circumferential local buckling of outer steel tube in the lower zone of columns gradually become obvious with the increase of the axial load ratio,while the diameter-thickness ratio of inner steel tube exhibit slight effect on the deformation capacity of columns.Within the parameters of this study,all horizontal load-displacement hysteretic loops are relatively full,and the average value of displacement ductility coefficient and viscous damping coefficient of all specimens are 0.326 and 0.6 respectively,showing a superior deformation and energy dissipation capacity.With an increase in the axial load ratio,the bearing capacity,the ductility and horizontal stiffness of specimens decrease,but the strength degradation is slight.When the axial load ratio increases from 0.2 to 0.6,the cwerage peak load decreases by 53.4％.The parameter analysis indicate that with an increase in the width-thickness ratio,the improvement of the diameter-thickness ratio of outer steel tube can lead to a more obvious increase in the peak loak of members,but increasing the axial load ratio can mitigate the influence of the diameter-thickness ratio of inner steel tube on the bearing capacity.
The interface bonding effect can determine the overall mechanical properties of the reinforced components to a large extent. This paper proposed an improved interface treatment method between FRP grid-ECC composite layer and concrete that could quantify the interface roughness, and the effect of this method on the interface bonding behavior was investigated through the double-shear test. Four groups of twelve specimens, including one group without interface treatment and three groups with different interface treatment rates, were tested to reveal their bond-slip relationship. The test results demonstrated that the improved method was effective, with the ability to inhibit interface peeling; moreover, as the interface treatment rate increased, the bonding effect enhanced, and the failure mode gradually transitioned from critical fracture to composite layer fracture. Furthermore, the bond-slip model and the bearing capacity formula for the improved method were established, and the predicted values were well matched to their corresponding test results.
Based on the in-depth analysis of the current design status of the underground system of the project,the disadvantages such as wasting of temporary support resources,environmental pollution and carbon emission increase caused by the separation of geotechnical and structural specialties in the foundation pit was pointed out,and the theory and design method of the geotechnical structural permanent support system of deep foundation pit was put forward.The composition and construction process of the permanent support system were explained,and the design principle of the limit state of the permanent support system's bearing capacity and normal use limit state was given.The load combination and calculation contents of three stages of excavation,construction and normal use of foundation pit were clearly defined,and the finite element method and elastic fulcrum method applicable to the division limits of deep and deep foundation pits and their permanent supporting structures were suggested respectively.It is emphasized that durability analysis of support components should be carried out,and it is proved that the basement exterior wall of permanent support structure of geotechnical structural deep foundation pit is basically free from earth pressure,which changes the current situation that the support structure in the excavation stage and the basement exterior wall in the use stage bear soil pressure respectively,that is,twice the building materials resist soil pressure,and shows the engineering value of the permanent support structure in deep foundation pit and its popularization significance.
Based on the construction practice of more than 30 years in China,the advantages and disadvantages of the existing temporary concept of deep foundation pit support and the concept of combining with the main structure were analyzed,and the permanent concept of promoting the development of foundation pit support engineering was proposed.Combined with a foundation pit project in Jinan,the successive elevations of the three concepts and the calculation contents of the corresponding supporting structure were explained,and the structural geotechnical and geotechnical structural design methods that adapt to the concept of combining with the main structure and the concept of permanence were defined.The design of composite soil nailing wall combined with anti-floating anchor,as well as the mechanical properties and durability of anti-floating anchor in the structure of anti-floating anchor with overhanging support and horizontal floor permanent support were analyzed,the influence of permanent support on the mechanical mechanism of basement exterior wall was analyzed,and the evolution direction of deep foundation pit support concept and the design improvement content adapted to it were explained.It is of guiding value to reflect on the management system of geotechnical and structural design in China,promote the progress of foundation pit and foundation design theory and method,and promote the practice of ＂new development concept＂ in foundation pit engineering.
In view of the excellent mechanical property of Ultra-High Performance Concrete (UHPC), a new method of using steel plate and UHPC (SP-UHPC) composite to strengthen damaged reinforced concrete (RC) beams was proposed. Four-point bending tests were conducted to investigate the failure modes, deformation characteristics, crack resistance, and bearing capacity of five SP-UHPC strengthened beams (SPUB), one reinforced UHPC strengthened beam (RUB), and one reinforced concrete beam (RCB). Additionally, the impacts of different strengthening techniques, the thickness of steel plate and UHPC on the flexural performance of the strengthened beams were investigated and discussed. The effects of the shear strength of UHPC-RC interface on the bearing capacity of the strengthened beams were analyzed. The test results show that the failure mode of strengthened beams is interface peeling failure. Compared with RCB, the cracking moments of SPUBs and RUB increased by about 214.5%-271.5% and 43.7%, respectively. The bearing capacity of SPUBs and RUB increased by 53.1%-73.7% and 53.4%, respectively. The flexural stiffness of strengthened beams increased by nearly one time on average. Compared with RUB, the SPUBs showed a superior crack resistance and interface slip resistance. The increase in the thickness of the steel plate and UHPC can improve the flexural stiffness and the strain behavior of strengthened beams significantly. Based on the test results, the calculation formulae of UHPC cracking moments and bearing capacity of SP-UHPC strengthened beams were proposed considering the effective anchorage length of interface, the strain hardening behavior of UHPC, and the residual strain in RC beam. The calculation results of UHPC cracking moments and bearing capacity coincide with the test results, demonstrating the accuracy of proposed calculation formulae.
Stainless steel tube-confined steel-reinforced recycled concrete columns (SSTCSRRC) have the potential to be widely used in engineering structures due to their advantages of aesthetic appearance and reutilization of waste materials. However, there is currently little research work on this new type of thin-walled stainless steel composite columns. This paper investigates the behaviour of SSTCSRRC stub columns under axial compression. Tests on seven circular and seven square stub columns were carried out, and the main variables include the thickness of the stainless steel tube, the recycled brick aggregate (RBA) replacement ratio and the specimen type. The results indicate that the confinement effect of the stainless steel tube improves the ultimate strength and ductility of the columns, and the ultimate strength decreases with an increase in RBA placement ratio. A high RBA placement ratio or using cross-shaped section steel can significantly improve the ductility of the columns. A finite element (FE) model was developed to simulate the axial compressive behaviour of SSTCSRRC stub columns. Based on the numerical data of 130 FE models, the design formulas for axial compressive strength and stiffness of SSTCSRRC stub columns were proposed.
Based on the design concepts of damage control and concentrated energy consumption of key energy-consuming components, this paper puts forward an earthquake-resilient prefabricated column foot joint. Expounds the structural composition, advantages and seismic design requirements of this new type column foot joint in detail. After comprehensively considering the mechanical mechanism of the column foot joint, the load-bearing capacity correction coefficient and the height ratio of lateral force-resisting shear member (LRSM) inflection point are introduced, and the design theory is established accordingly, including the dimension of LRSMs, the number of connecting bolts and the stiffness of connecting beams. The rationality and applicability of the proposed design theory are verified by 18 groups of 90 finite element models, and several test specimens. The research shows that the design theory proposed in this paper can accurately predict the yield load and initial stiffness of the new type column foot joint, and effectively control the bolt slip time and the connecting beam failure time. The new column foot joint designed according to this design theory has excellent bearing capacity and ductility. The plastic damage of this joint can be basically controlled on the lateral force-resisting energy-consuming device (LRECD), which has the premise of earthquake-resilient.
A type of recycled aggregate concrete shear wall was proposed in this work, which used the painted ultra-high-strength steel (UHSS) reinforcements with low bond strength and high yield strength in the boundary elements. For investigating the seismic resistance and resilient performance of this shear wall, six shear walls with the shear-to-span ratio of 1.5 were fabricated and tested under the cyclic loads. The variables studied in this paper were the types of the longitudinal reinforcement in the boundary elements, the existence of steel fibers, the presence of the concealed bracings (X-shaped) and the different axial compression ratios. The test results indi-cated that specimens with the UHSS reinforcement in the boundary elements decreased the residual deformation substantially and improved the resilient properties. The higher axial compression ratio enhanced lateral force resistance of shear wall but aggravated concrete damage which was adverse to the resilience. In addition, the utilization of steel fibers in concrete significantly reduced the crack width. The shear wall including concealed bracing not only showed much higher lateral force resistance, but also had desirable resilient performance under the large deformation. Finally, a simplified calculation model for such shear walls was proposed on the basis of experiment. And the good accuracy of the calculation model was verified by comparing the calculation results and the measured results.
There has been extensive discussion as to whether the scope of site classification II is too broad in current Chinese seismic code. To address this issue, this study aims to optimize the site classification scheme for Chinese seismic code using clustering analysis of site amplification. Firstly, we estimate the empirical site amplification factors of KiK-net stations by the residual analysis method, and classify them by the site classification scheme of Chinese seismic code. Next, we perform k-means clustering analysis on the stations of site class II, considering site amplification factors, equivalent shear wave velocities and thicknesses of sedimentary layers as explanatory variables, and obtain two clusters with distinct site amplification effects. Finally, we use correlation analysis and Receiver Operating Characteristic (ROC) curve to guide the optimization of site classification scheme, and suggest dividing site class II into two subclasses, IIa and IIb, by a threshold of 15m for the thickness of sedimentary layer. The proposed optimized classification scheme would be beneficial for improving the seismic design code and could be further applied to the development of ground motion models and seismic hazard analysis.
Bobbin friction stir welding (BFSW) is a variant of the conventional friction stir welding (CFSW); it can weld the upper and lower surface of the work-piece in the same pass. This technique involves the bonding of materials without melting. In this work, the influence of tool design on the mechanical properties of welding joints of 6061-T6 aluminum alloy with 6.25 mm thickness produced by FSW bobbin tools was investigated and the best bobbin tool design was determined. Five different probe shapes (threaded straight cylindrical, straight cylindrical with 3 flat surfaces, straight cylindrical with 4 flat surfaces, threaded straight cylindrical with 3 flat surface and threaded straight cylindrical with 4 flat surfaces) with various dimensions of the tool (shoulders and pin) were used to create the welding joints. The direction of the welding process was perpendicular to the rolling direction for aluminum plates. Tensile and bending tests were performed to select the right design of the bobbin tools, which gave superior mechanical properties of the welded zone. The tool of straight cylindrical with four flats, 8 mm probe and 24 mm shoulders diameter gave better tensile strength (193 MPa), elongation (6.1%), bending force (5.7 KN), and welding efficiency (65.4%) according to tensile strength.
A new type of fully prefabricated slab-beam joint was proposed.The fully prefabricated is fully prefabricated in the factory and transported to the construction site,and the beam and slab are assembled uniformly by post reinforcements and cast-in-place concrete joint.In order to study the mechanical performance of prefabricated concrete slab-beam joints under vertical loads and simulate the stress state of the slab-beam joint with intermediate support in actual engineering,static tests were carried out on the fully prefabricated slab-beam joint,fully cast-in-place slab-beam joint,and semi-precast slab-beam joint.Also,numerical modeling was conducted by software ABAQUS.According to Code for design of concrete structures(GB 50010-2010),the flexural bearing capacity was checked.The crack development,steel strain,and characteristic bearing capacity of three specimens were compared.The experimental results was compared to the results from the finite element simulation and code calculation results.The results show that compared to cast-in-place members,the structural joint section of prefabricated members fails before the maximum section under bending,and the crack develops slowly.The arrangement of the post reinforcements can effectively delay the development of the crack and improve the flexural bearing capacity of members.The results between the finite element simulation results and experimental results were close.When the load direction is perpendicular to the superimposed surface,the prefabricated member with rough treatment of superimposed surface can be calculated as a whole without considering the relative slip of superimposed surface in finite element simulation.
China is the country with the largest number of steel structure construction and ownership.The traditional engineering defect diagnosis method of steel structure can not meet the current demand.With the rapid development of computer technology,the introduction of artificial intelligence into the field of engineering diagnosis has gradually become a research hotspot.According to the summary of the research status at home and abroad,a review of the research on intelligent recognition of common steel structure surface defects based on computer vision was provided,and a set of general technical framework combined with the actual situation in China was summarized.Firstly,the general process of surface defect intelligent detection and recognition were summarized,namely:image acquisition,target extraction and defect recognition,and then uses this as a framework to introduce the content and principles of various computer vision methods.Next,three kinds of common surface defects of steel structure were introduced:lack and loose-ness of high-strength bolts,surface corrosion,and the latest research progress of intelligent identification technology of surface cracks and the shortcomings of current methods.Finally,the future research direction of surface defect intelligent recognition based on computer vision was discussed and prospected.
Based on the detection,identification and reinforcement design of a school catering building located in the large thickness collapsible loess site,the detection identification and reinforcement design of existing buildings in the large thickness collapsible loess site after uneven settlement were studied and summarized.Through detection identification,reinforcement design and design services for an existing building that has uneven settlement due to flooding in a collapsible loess site,the procedures and treatment methods for the hidden trouble caused by uneven settlement of the foundation of the existing building in a collapsible loess site by using pit static pile were summarized.The calculation method of static pressure pile reinforcement and local jacking correction design were also summarized,and some conclusions were concluded,which can provide reference for subsequent similar projects.
