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Simulation of roof snow loads based on a multi-layer snowmelt model:Impact of building heat transfer

Building Simulation 2024年第6期17卷 907-932页

作者： Xuanyi Zhou Heng Chen Yue Wu Tiange Zhang State Key Laboratory of Disaster Reduction in Civil Engineering Tongji UniversityShanghai200092China

To investigate the impact of building heat transfer on roof snow loads,roof snow loads and snow load thermal coefficients from 61 Chinese sites over a period of 50 years are simulated based on basic meteorological data such as temperature,humidity,wind speed,and precipitation,and a multi-layer snowmelt model considering the building heat ***,the accuracy of the multi-layer snowmelt model is validated using the data of observed ground snow load and roof snow melting *** relationship between meteorological conditions,snow cover characteristics,and thermal coefficients of snow loads in three representative sites is then ***,the characteristics of thermal coefficients in each zone are analyzed by combining them with the statistical results of meteorological data from 1960 to 2010,and the equations of thermal coefficients in different zones on indoor temperatures and roof heat transfer coefficients are fitted ***,the equations in this paper are compared with the thermal coefficients in the main snow load *** results indicate that the snowmelt model using basic meteorological data can effectively provide samples of roof snow *** the cold zone where the snow cover lasts for a long time and does not melt easily,the thermal coefficients of the snow loads on the heating buildings are lower than those in the warm zone due to the long-term influence of the heat from inside the *** coefficients are negatively correlated with indoor temperatures and roof heat transfer *** the indoor temperature is too low or the roof insulation is good,the roof snow load may exceed the ground snow *** thermal coefficients for heated buildings in the main snow load codes are more conservative than those calculated in this paper,and the thermal coefficients for buildings with lower indoor temperatures tend to be smaller.

关键词： snowmelt model roof snow load building heat transfer thermal coefficient load code

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Determination method of mesh size for numerical simulation of blast load in near-ground detonation

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Defence Technology（防务技术） 2024年第8期38卷 111-125页

作者： Doudou Si Zuanfeng Pan Haipeng Zhang College of Civil Engineering Tongji UniversityShanghai 200092China State Key Lab of Disaster Reduction in Civil Engineering Tongji UniversityShanghai 200092China

In order to improve the overall resilience of the urban infrastructures, it is required to conduct blast resistant design for important building structures in the city. For complex terrain in the city, it is recommended to determine the blast load on the structures via numerical simulation. Since the mesh size of the numerical model highly depends on the explosion scenario, there is no generally applicable approach for the mesh size selection. An efficient method to determine the mesh size of the numerical model of near-ground detonation based on explosion scenarios is proposed in this study. The effect of mesh size on the propagation of blast wave under different explosive weights was studied, and the correlations between the mesh size effect and the charge weight or the scaled distance was described. Based on the principle of the finite element method and Hopkinson-Cranz scaling law, a mesh size measurement unit related to the explosive weight was proposed as the criterion for determining the mesh size in the numerical simulation. Finally, the applicability of the method proposed in this paper was verified by comparing the results from numerical simulation and the explosion tests and was verified in AUTODYN.

关键词： Blast load Mesh size effect Numerical simulation Scaled mesh size Verification

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Prediction of lateral wall deflections of excavations in water-rich sands by a modified multivariate-adaptiveregression- splines method

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Frontiers of Structural and civil engineering 2024年第12期18卷 1971-1984页

作者： Dongdong FAN Delujia GONG Yong TAN Yongjing TANG State Key Laboratory of Disaster Reduction in Civil Engineering Department of Geotechnical EngineeringCollege of Civil EngineeringTongji UniversityShanghai 200092China

Machine learning methods have advantages in predicting excavation-induced lateral wall *** to lack of sufficient field data,training data for prediction models were often derived from the results of numerical simulations,leading to poor prediction *** on a specific quantity of data,a multivariate adaptive regression splines method(MARS)was introduced to predict lateral wall deflections caused by deep excavations in thick water-rich *** of lateral wall deflections to affecting factors was *** is disclosed that dewatering mode has the most significant influence on lateral wall deflections,while the soil cohesion has the least *** crossvalidation analysis,weights were introduced to modify the MARS method to optimize the prediction *** of the predicted and measured deflections shows that the prediction based on the modified multivariate adaptive regression splines method(MMARS)is more accurate than that based on the traditional MARS *** prediction model established in this paper can help engineers make predictions for wall displacement,and the proposed methodology can also serve as a reference for researchers to develop prediction models.

关键词： lateral wall deflection machine learning multivariate adaptive regression splines method excavation database water-rich sand

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Responses of a short column-supported highrise tower to adjacent deep excavations in water-rich sandy strata and dynamic optimization of protection plans

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Frontiers of Structural and civil engineering 2024年第11期18卷 1775-1793页

作者： Jun-Cheng LIU Yong TAN State Key Laboratory of Disaster Reduction in Civil Engineering Department of Geotechnical EngineeringCollege of Civil EngineeringTongji UniversityShanghai 200092China

A highrise tower atop short columns in Nantong,China was threatened by excavation of a subway station *** an elaborate protection plan composed of isolation piles,artificial recharge and underpinning was executed throughout the excavations,the tower underwent unacceptable settlements and notable *** combination of field measurements and numerical simulations,this paper investigates the tower’s responses to the adjacent excavations,examines the effects of adopted protection plans and explores potential effective protection ***,the responses of the tower and the effectiveness of the three implemented measures were examined,and the contributory factors triggering intolerable tower deformations were identified;then,the effects of primary protection parameters were quantified,including the length,stiffness and layout of isolation piles,the water level surrounding recharge wells after recharging and the depth and location of wells,and the length of underpinning *** reveals that the underpinning plan had the best protection effect,followed by isolation piles and recharging *** timing of protection measures and termination manners of recharging are two critical factors in restraining tower ***,underpinning the tower with 36-m long steel pipe piles solely before implementation of adjacent excavations could be another optimal protection scheme.

关键词： highrise tower excavation piled-raft footing protection field performance numerical simulation

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A unified stochastic damage model for concrete based on multi-scale energy dissipation analysis

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Science China(Technological Sciences) 2024年第3期67卷 863-877页

作者： GUO ChengGong LI Jie College of Civil Engineering Tongji UniversityShanghai 200092China State Key Laboratory of Disaster Reduction in Civil Engineering Shanghai 200092China

This work proposes a unified damage model for concrete within the framework of stochastic damage mechanics. Based on the micro-meso stochastic fracture model(MMSF), the nonlinear energy dissipation process of the microspring from nanoscale to microscale is investigated. In nanoscale, the rate process theory is adopted to describe the crack growth rate;therefore, the corresponding energy dissipation caused by a representative crack propagation can be obtained. The scale gap from nanoscale to microscale is bridged by a crack hierarchy model. Thus, the total energy dissipated by all cracks from the nanoscale to the microscale is gained. It is found that the fracture strain of the microspring can be derived from the above multi-scale energy dissipation analysis. When energy dissipation is regarded as some microdamage to the microspring, the constitutive law of the microspring is no longer linearly elastic, as previously assumed. By changing the expression of the damage evolution law from fracture strain to energy dissipation threshold, the new damage evolution model is derived. The proposed model can not only replicate the original static model but also extend to cases of rate dependence. By deriving the fracture strain under different strain rates, the rate sensitivity of concrete materials can be reflected. The model parameters can be conveniently obtained by identifying them with experimental data. Finally, several numerical examples are presented to verify the proposed model.

关键词： concrete damage model stochastic damage rate dependent energy dissipation

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Seismic design and analysis of a high-rise self-centering wallbuilding:Case study

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Frontiers of Structural and civil engineering 2023年第11期17卷 1690-1706页

作者： Ying ZHOU Rui WANG Yiqiu LU State Key Laboratory of Disaster Reduction in Civil Engineering College of Civil EngineeringTongji UniversityShanghai 200092China

Post-tensioning self-centering walls are a well-developed and resilient ***,despite extensive research,the application of this technology has previously been limited to low-rise buildings.A ten-story selfcentering wall building has now been designed and constructed using the state-of-art design methodologies and construction detailing,as described in this *** building is designed in accordance with direct displacement-based design methodology,with modification of seismic demand due to relevant issues including higher-mode effects,second order effects,torsional effects,and flexural deformation of wall *** sections are designed with external energydissipating devices of steel dampers,and seismic performance of such designed self-centering walls is evaluated through numerical *** is the first engineering project that uses self-centering walls in a high-rise *** seismic design procedure of such a high-rise building,using self-centering wall structures,is comprehensively reviewed in this work,and additional proposals are put *** of construction detailing,including slotted beams,flexible wall-to-floor connections,embedded beams,and damper installation,is *** demonstration project promotes the concept of seismic resilient structures and contributes to the most appealing city planning strategy of resilient cities at *** paper could be a reference for industry engineers to promote the self-centering wall systems worldwide.

关键词： self-centering wall post-tensioned precast concrete wall seismic resilient structure high-rise building seismic design engineering practice

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A modern survey method for determining live loads based on multi-source and open-access data on the Internet

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Frontiers of Structural and civil engineering 2024年第8期18卷 1135-1147页

作者： Chi XU Jun CHEN Jie LI School of Civil Engineering Tongji UniversityShanghai 200092China The State Key Laboratory on Disaster Reduction in Civil Engineering Tongji UniversityShanghai 200092China

Sufficient survey data are required to describe the stochastic behaviors of live ***,due to manual and on-site operation required by traditional survey methods,traditional surveys face challenges like occupant resistance,high costs,and long implementation *** study proposes a new survey method to access live load data online and *** samples are acquired from multi-source,open-access and dynamically updated data on the *** change intervals,geometrical dimensions and object quantities are obtained from transaction information,building attributes and virtual reality models on real estate websites,*** object weights are collected from commodity information on e-commerce *** integration of the aforementioned data allows for the extraction of necessary statistics to describe a live load *** proposed method is applied to a live load survey in China,covering 20040 m^(2),with around 90000 samples acquired for object weights and load *** survey results reveal that about 70%−80%of the amplitude statistics are attributable to 1/6 of the total object types.

关键词： live load online survey method data acquisition data integration

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Longitudinal shaking of culvert-frame combined underground structure

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Frontiers of Structural and civil engineering 2025年第1期19卷 123-142页

作者： Yong YUAN Xuzhao LAN Department of Geotechnical Engineering Tongji UniversityShanghai 200092China State Key Laboratory for Disaster Reduction in Civil Engineering Tongji UniversityShanghai 200092China

The underground structure with stiffness mutation at the culvert-frame connection suffers from discrepant dynamic responses when earthquakes *** paper studies the seismic responses of an underground structure consisting of two portions of box frames and twin jacked culverts in soft *** two portions of box frames(Part A and Part C)have the same 2-storey and 3-span cross sections,rigidly connected to the two parallel jacked culverts(Part B)with F-type sockets between joints.A series of 1g shaking table tests is conducted on the modeled soil−structure *** are installed within the model soil,upon culverts,and on the top of mid slabs of box *** extensions and closures of culverts are *** white noise case is carried out to assess dynamic characteristics of the model *** synthetic earthquake cases are conducted to investigate the model system’s seismic responses under earthquakes with varying *** acceleration responses of the model soil at different distances from Part A are *** extent of discrepancy in acceleration of culverts and box frames is quantified by the correlation *** characteristics of the joint extension and closure are summarized.

关键词： shaking table test underground structure culvert-frame metro station soft soil

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Development of component stiffness equations for thread-fixed one-side bolt connections to an enclosed rectangular hollow section column under tension

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Frontiers of Structural and civil engineering 2024年第4期18卷 568-586页

作者： Fu-Wei WU Yuan-Qi LI Department of Structural Engineering Tongji UniversityShanghai 200092China State Key Laboratory of Disaster Reduction in Civil Engineering Tongji UniversityShanghai 200092China

The derivation and validation of analytical equations for predicting the tensile initial stiffness of threadfixed one-side bolts(TOBs),connected to enclosed rectangular hollow section(RHS)columns,is presented in this *** unknown stiffness components are considered:the TOBs connection and the enclosed RHS ***,the trapezoidal thread of TOB,as an equivalent cantilevered beam subjected to uniformly distributed loads,is analyzed to determine the associated *** on the findings,the thread-shank serial-parallel stiffness model of TOB connection is *** analysis of the tensile stiffness of the enclosed RHS face due to two bolt forces,the four sidewalls are treated as rotation constraints,thus reducing the problem to a two-dimensional plate *** to the load superposition method,the deflection of the face plate is resolved into three components under various boundary and load *** to the plate deflection theory of Timoshenko,the analytical solutions for the three deflections are derived in terms of the variables of bolt spacing,RHS thickness,height to width ratio,***,the validity of the above stiffness equations is verified by a series of finite element(FE)models of T-stub *** proposed component stiffness equations are an effective supplement to the component-based method.

关键词： initial stiffness component based method thread-fixed one-side bolt rectangular hollow sections analytical equation

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Investigation on lateral seismic isolation system of a typical long-span single-tower cable-stayed bridge for mountainous areas

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Frontiers of Structural and civil engineering 2025年第3期19卷 341-357页

作者： Shichun ZHANG Junjun GUO Wei LIU Jibo LI Zhongguo GUAN State Key Laboratory of Disaster Reduction in Civil Engineering Tongji UniversityShanghai 200092China China Highway Engineering Consulting Co. Ltd.Beijing 100089China

This study focuses on a reasonable lateral isolation system for a typical long-span single-tower cable-stayed bridge with a significantly asymmetric span arrangement that is particularly suitable for mountainous areas. Based on the Jinsha River Bridge, the significant structural asymmetry and its effects on structural seismic responses were analyzed. The significantly asymmetric characteristics could result in complex dynamic behavior in seismic conditions and the lateral seismic responses of the structure are governed by multiple modes. A multilinear model composed of an ideal elastoplastic element and a multilinear elastic element was used to simulate different hysteresis, and a parametric analysis was conducted to investigate the appropriate damping hysteresis for the lateral seismic isolation of such a bridge. It shows that the inverted S-shaped hysteresis has relatively smaller secant stiffness and could help to balance the great difference in the lateral stiffness of the tower/piers. Thus, the inverted S-shaped hysteresis could lead to more efficient damping effects and less base shear forces of the tower/piers. A correlation between the reasonable yield forces of the dampers in the lateral isolation system, determined through an influence matrix-based method, and the shear forces of the corresponding bearings in the lateral fixed system was also observed. Moreover, the influence of geological conditions including different terrain and site conditions on the reasonable lateral isolation system was further investigated. It suggests to use dampers at all tower/pier locations when the side span crosses a steep valley slope, while a lateral isolation system without using dampers at the auxiliary piers could be employed when the side span crosses a gentle valley slope. Soft sites require larger damper yield forces and cause greater seismic responses compared to hard sites.

关键词： single-tower cable-stayed bridge lateral isolation system multilinear model influence matrix geological conditions

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