As an important connector in cold-formed steel structures,the shear performance and failure modes of self-tapping screws directly affect the mechanical properties and failure modes of the structure.At present,researchers worldwide have focused mainly on the shear capacity of single self-tapping screws,while the studies related to the shear-slip constitutive relationship are scarce.Therefore,this paper summarized and analyzed both previous shear test results of single self-tapping screws and the tests conducted in this study.Using the XTDIC three-dimensional full-field strain measurement and analysis system,an in-depth analysis of the shear failure mechanism of self-tapping screw connections in cold-formed steel was conducted.Considering the effects of screw diameter,plate thickness,and material properties,two shear-slip constitutive models corresponding to the two major shear failure modes of such connections were proposed,which showed good agreement with the experimental results.
The external thermal insulation composite system(ETICS)is crucial for improving building energy efficiency and ensuring building functionality.In recent years,issues such as cracking,hollow-ing,peeling,and high-altitude falling have occurred frequently,posing a significant threat to public safety.A systematic review was conducted on domestic and international research and engineering prac-tice regarding diagnosis and treatment methods for detection,evaluation,and repair of building ETICS.In terms of detection,non-destructive testing techniques were categorized into four types based on their energy forms and physical mechanisms,namely optical,thermal,electromagnetic,and acoustic.The research progress of various non-destructive testing techniques and commonly used destructive testing techniques was systematically reviewed.A comparative analysis was conducted on the technical points,advantages and disadvantages,and applicable scenarios of various detection techniques.In terms of evaluation,the characteristics and progress of existing evaluation methods were summarized from three aspects:qualitative evaluation,quantitative evaluation,and comprehensive evaluation.In terms of repair,the current development status of existing repair methods was introduced from the perspectives of repair technology,repair materials,and repair strategies.Finally,the deficiencies in the research and engineering practice regarding diagnosis and treatment methods for building ETICS were analyzed,and future research directions were discussed.
In recent years,Chinese towns have actively engaged in the international"Slow City Move-ment",seeking development directions and guidance.However,after over a decade of localization,China's slow cities have evolved distinct operational concepts and modes that differ from their Western counterparts,making it necessary to systematically examine and analyze these differences.Taking this as the starting point,this paper clarified the connotation of the"Slow City"concept and reviewed the development of the"Slow City Movement".Through an analysis of Western slow city cases,it summa-rized the renewal approaches and development modes of the Western slow city movement.Subsequently,by comparing the construction methods and development patterns of Chinese slow city cases,it identified the fundamental differences between Chinese and Western slow cities.Finally,it proposed strategies to mitigate these deviations in planning and construction,aiming to provide references and insights for the future development of slow cities in China.
The Nanjing City Wall represents the pinnacle of ancient Chinese city wall construction and holds significant cultural heritage value.However,due to the deterioration of its structural integrity and external environmental factors,it faces substantial safety concerns requiring urgent restoration and rein-forcement.First,this study examined the structural configuration and damage conditions of the section from Jiefang Gate to Xuanwu Gate based on field surveys and literature review.Second,finite element analysis using ANSYS software was conducted on the wall structure.The analysis focused on evaluating the mechanical properties and safety under various combined conditions,including the effects of air-raid shelters and moisture absorption/expansion of internal brick-rubble-soil fill,to identify potential haz-ards.Finally,adaptive restoration and conservation measures were proposed,balancing both the preser-vation of historical appearance and the reinforcement of structural safety.This study implemented tar-geted reinforcement measures for different types and grades of deterioration,including structural strength-ening of wall bodies,rampart top surfaces,and arches.Under the premise of preserving historical appearance,the wall structure was reinforced to achieve minimal intervention conservation for cultural heritage buildings,providing valuable insights and references for the preservation and restoration of ancient city walls.
The distributed mortise-tenon joint is a novel type of joint used in large-diameter shield tun-neling to resist longitudinal shear dislocation deformation between adjacent rings.Using the Wuhu Chengnan Extra-Large Diameter River-Crossing Tunnel as a prototype,this study established a numeri-cal model for the joint and segment shear behavior,incorporating the effects of local plastic damage.The research investigated the shear-resistance evolution of distributed mortise-tenon joints and their influence on longitudinal load transfer in the tunnel.A comparison was made with continuous mortise-tenon seg-ments.Finally,the reliability of the numerical results was verified against a theoretical calculation model.The results showed that:1)Under applied displacement,the shear force variation in distributed mortise-tenon joints exhibited three distinct stages(Ⅰ-Ⅲ).In Stage Ⅰ,the joint contributed negligibly to shear resistance.In Stage Ⅱ,the shear resistance increased sharply,reaching 64.4％of the total by the end of this stage.In Stage Ⅲ,the shear force began to stabilize.2)During shearing,the mortise-tenon joints above the waist experienced relatively rapid growth in shear resistance and contributed signifi-cantly,accounting for 76％of the total at the end of the engagement stage.3)The longitudinal stress relaxation coefficient λ of the distributed mortise-tenon segment reached 17.1％at the ultimate shear limit,whereas that of the continuous ring-type mortise-tenon segment reached 29.6％.The relatively smaller relaxation area of the former is beneficial for controlling the longitudinal stability and preventing leakage of the overall tunnel structure.
To address the problem of missing multi-source monitoring data of offshore wind turbines caused by sensor failures or communication interruptions under harsh operating conditions,this paper proposes a novel imputation model based on a multi-head gated residual network.This method achieves collaborative fusion of supervisory control and data acquisition(SCADA)data and structural vibration monitoring data through feature concatenation,employs a gated residual network to extract deep nonlin-ear coupling features,and uses a multi-head parallel output architecture for the independent reconstruc-tion of these two heterogeneous data types.During the training stage,a dynamic masking mechanism combined with a hybrid loss function is adopted to enhance the model's adaptability to complex aerody-namic operating conditions.Validated with field data from a 10 MW offshore wind turbine,the proposed model achieved a high coefficient of determination under training conditions,enabling accurate recon-struction of missing multi-source data.In generalization tests for non-training periods,although the coef-ficient of determination of the model's predictions fluctuated slightly,the model still effectively captured the overall trends of monitoring signals.Notably,the degradation in generalization performance for vibra-tion data was less pronounced than that for SCADA data,demonstrating its greater stability.The pro-posed method can significantly improve the completeness and reliability of multi-source monitoring data for wind turbines and holds considerable potential for engineering applications.
The stadium roof of Xiamen New Sports Center is mainly composed of giant arches,connect-ing grid frames,roof trusses,and facade curtain wall supporting structures,etc.Two giant arches are arranged from south to north,and a connecting grid is arranged between them.The main truss is arranged from east to west,supported by the giant arches and the slanted columns of the stands;the east and west facades are equipped with curtain wall supporting structures.The main installation idea of the roof is"first the main structure,then the secondary structure,and finally the curtain wall structure".Compared with the final formed structure,the structure's geometry,load-transfer system,stiffness,boundary constraints,and load actions have been changing during the construction and forming pro-cesses,and the corresponding structure's displacement and stress have also been changing continu-ously.The stress on some oblique struts at the temporary support points of the connecting grid is too large,and reinforcement measures need to be taken.After the installation is completed,small additional stresses and additional deformations are locally produced in the structure,which have little impact on the bearing capacity and normal use of the structure.This analysis can be used to judge the mechanical ratio-nality of the roof installation scheme,provide a theoretical basis for the preparation of the construction scheme,and serve as a reference for the construction mechanics design of similar projects in the future.
By conducting wind tunnel pressure measurement test based on a rigid model of a long-span cantilevered roof,the estimation of non-Gaussian extreme wind pressure on the roof surface and the pre-diction of peak factors were studied.The time series of wind pressure on the roof surface was obtained through experiments,and the distribution characteristics of the mean wind pressure coefficient,fluctuat-ing wind pressure coefficient,skewness,and kurtosis on the roof surface were analyzed under typical wind directions of 0 °,45 °,and 90 °.The Gaussian peak factor method and the revised Hermite series method were used to calculate the peak factor at typical measuring points,respectively.The non-Gaussian characteristics and wind pressure fitting at typical measuring points were evaluated based on five probability density functions,and the minimum wind pressure estimation was obtained using the revised Hermite series method and the existing extreme wind pressure evaluation method,respectively.Finally,the peak factor was predicted using a general regression neural network.The results showed that the minimum wind pressure on the roof surface was significant under typical wind directions of 0 °,45 °,and 90 °,and the long tail of the wind pressure distribution was measured in the negative direction;the Gaussian peak factor method was found to frequently underestimate the peak factor of non-Gaussian wind pressure;the revised Hermite series method estimated the peak factor more accurately and performed best in wind pressure fitting,especially in the negative pressure long tail section;the revised Hermite series method obtained better minimum estimates;the general regression neural network based on the fourth-order statistics of wind pressure time history exhibited good prediction performance.
In previously reported experimental studies on T-head square-neck one-sided bolted(TSOB)beam-to-square hollow section(SHS)column joints,bolt pull-out failure caused by the bulge deformation of the column wall has been identified as a typical failure mode.To prevent SHS wall defor-mation under the bending moment at the beam ends and to improve the deformation capacity of the joint,this paper proposes assembled H-steel strengthening measures for beam-column joints.Monotonic static load tests were conducted on four joints with H-steel components to explore the influence of the length and plate thickness of the strengthening components on the structural response of the joints.The test results showed that the H-steel components prevented bolt pull-out failure and increased the yield and peak bending moments of the joints by 69.3％-72.6％and 22.5％-39.4％,respectively.It is recom-mended that TSOB beam-to-SHS column joints use extended H-steel components,the cross-section of which should be designed according to the internal force of the joint.
Hyperbolic cooling tower shells are mostly cast-in-place reinforced concrete thin-walled structures.Their high-altitude construction poses significant challenges,and geometric imperfections often occur due to issues in construction layout accuracy.Focusing on a specific engineering case,this study employed terrestrial laser scanning(TLS)technology to capture precise geometric imperfection data of the tower shell.Based on the scanned data,finite element models of the hyperbolic cooling tower,both with and without geometric imperfec-tions,were developed using ABAQUS.The effects of geometric imperfections on the mechanical properties of the cooling tower,as well as the sensitivity of different load effects to these imperfections,were systematically investigated.The results indicated that when the actual imperfection magnitude was introduced based on the measured distribution pattern,the bearing capacity and crack resistance of the tower shell decreased signifi-cantly.Moreover,no deterioration in mechanical properties was observed when the imperfection magnitude remained below 150 mm.The effects of dead load and external wind pressure were highly sensitive to geometric imperfections,whereas temperature effects remained almost unaffected.Furthermore,the locations along the meridian lines of the tower shell where the maximum external wind suction occurs were identified as critical regions for safety assessment.
When a concentrically braced steel frame structure is subjected to seismic fortification-level or rare earthquake action,the central brace often loses its bearing capacity due to the buckling instability of diagonal brace members under compression.To prevent brace instability,an energy-dissipating brace composed of a rectangular steel tube and perforated web plates is proposed.This brace not only retains the advantages of the central brace,but also incorporates the benefits of metal dampers.Under fortification-level earthquakes,the metal dampers installed at both ends of the square steel tube of the brace yield first and dissi-pate seismic energy,thus ensuring that the square steel tube of the brace remains in an elastic state at all times.A quasi-static loading test was conducted on an energy-dissipating brace.The effects of different arrangements of perforated energy-dissipation plates on the brace's hys-teretic performance,bearing capacity,stiffness degradation,and energy dissipation capacity were studied.The experimental results indicated that the brace was mainly dissipated by the yielding of the inter-perforation plate components of the energy-dissipating plate.The hyster-esis curve of the specimen was full,demonstrating good energy dissipation capacity.During the loading process,the force-transmitting square steel tube of the energy dissipation brace always maintained elastic,but the brace failed due to the failure of the perforated web plate.Before the specimen lost its load-bearing capacity,there was no sudden decrease in strength or stiffness,and the brace did not become unstable during the loading process.Under cycles of the same magnitude,the brace's strength did not degrade significantly.
As the architectural form of the highest grade and most complex construction found in the Lan-zhou region,the gable-and-hip roof features gable framing and craftsmanship that represent the most prominent characteristics of local construction techniques.Its gable framework,in particular,reflects a distinctive status that sets it apart from other architectural forms.Focusing on the gable construction of gable-and-hip roof in the Lanzhou area,this study employs architectural surveying and interviews with master carpenters to systematically analyze both the typology of"typical practices"in the structural framework and the construction logic of"typical components".The research aims to uncover the prin-ciples underlying the gable construction of gable-and-hip roof,with the goal of supplementing and refin-ing the inheritance of wooden construction techniques in the Lanzhou region,and further contributing to the establishment of a construction atlas of gable-and-hip roof across different areas.
This study applied machine learning to predict and optimize the hygrothermal performance of bamboo-woven mud walls,highlighting their potential in addressing environmental challenges.Genera-tive adversarial networks(GANs)were first used to augment limited experimental data,addressing small-sample constraints.A back propagation(BP)neural network was employed to analyze and predict the performance of the wall materials.After optimization via a genetic algorithm(GA),the model's R2 improved to 0.77,indicating significantly enhanced predictive performance.These findings confirm the feasibility of using machine learning in the reuse of traditional building materials and provide a digital theoretical basis and technical support for the preservation and renewal of bamboo-woven mud walls.
In order to study the hysteretic behavior of aluminum alloy T-shaped beam-column joints after exposure to high temperatures,the stress and deformation mechanisms of T-shaped beam-column joints were analyzed by comparing quasi-static loading tests with ABAQUS finite element simulations,and a parametric finite element parameter analysis was carried out.The results showed that the finite element model accurately simulated the test process.When the joint was subjected to high temperatures of 450℃,300 ℃,150 ℃,and room temperature,the failure mode was brittle fracture.Hysteresis curves were pinched due to bolt slip.Increasing the thickness of the T-stub gusset plate reduced the stress con-centration at the corner of the gusset plate,and the failure mode of the joint shifted to the deformation failure of the hole at the beam end.Increasing the number of gusset plate bolts mitigated the decrease in the bearing capacity of the joint caused by sliding and improved the bearing capacity of the joint during the middle and late stages of loading.At normal temperature,increasing the thickness of gusset plate prevented brittle fracture of the joint.The joint that experienced a maximum temperature of up to 150 ℃exhibited seismic performance similar to that at room temperature.With the increase of temperature,the allowable axial compression ratio range of the joint gradually decreased,and the failure mode of the joint shifted to early buckling failure of the column.After the maximum temperature exceeded 150 ℃,the ductility of the beam-column joint increased while the bearing capacity decreased,necessitating addi-tional reinforcement.
This paper introduces the U.S.standard system for existing buildings,analyzes the seismic evaluation techniques,and focuses on the FEMA P-154-2015 rapid visual screening method and the ASCE/SEI 41-23 three-level evaluation process.The United States adopts a grading mode characterized by"graded screening,differentiated evaluation,and targeted reinforcement"for the governance of exist-ing buildings.This mode offers the advantages of flexibility and high efficiency,while also having certain limitations.By comparing the standards of the two countries and considering China's actual conditions,this paper proposes recommendations,such as defining benchmark buildings to simplify the evaluation process and improving performance-based assessment methods to complement traditional appraisals.It aims to provide technical references for construction projects under"the Belt and Road"initiative,thereby offering insights for the scientific and standardized management of existing buildings as well as for urban renewal.
