To study the anti-explosion protection effect of polyurea coating on reinforced concrete box girder, two segmental girder specimens were made at a scale of 1:3, numbered as G (without polyurea coating) and PCG (with polyurea coating). The failure characteristics and dynamic responses of the specimens were compared through conducting explosion tests. The reliability of the numerical simulation using LS-DYNA software was verified by the test results. The effects of different scaled distances, reinforcement ratios, concrete strengths, coating thicknesses and ranges of polyurea were studied. The results show that the polyurea coating can effectively enhance the anti-explosion performance of the girder. The top plate of middle chamber in specimen G forms an elliptical penetrating hole, while that in specimen PCG only shows a very slight local dent. The peak vertical displacement and residual displacement of PCG decrease by 74.8% and 73.7%, respectively, compared with those of specimen G. For the TNT explosion with small equivalent, the polyurea coating has a more significant protective effect on reducing the size of fracture. With the increase of TNT equivalent, the protective effect of polyurea on reducing girder displacement becomes more significant. The optimal reinforcement ratio, concrete strength, thickness and range of polyurea coating were also drawn.

This study investigates the blast-resistant performance of a polyurea-coated suspension bridge girder under explosive loads. The Hunan Road Bridge of Shandong was used as a case study through combined test and numerical simulation methods. Two 3 kg TNT charges and one 5 kg TNT charge were used to conduct two single-blast tests and one repeated blast test on a 1:3 scaled segment of a box girder. The tests were labeled as G (box girder without polyurea), PCG (first blast on box girder coated with polyurea), and PCGR (second blast on box girder coated with polyurea). A 1.5 mm polyurea layer was uniformly applied to the top surface. Numerical simulations of the explosion response were performed and validated using LS-DYNA software. The results indicate that under 3 kg of TNT detonation directly above the top plate, sample G exhibited an elliptical perforation, whereas sample PCG only experienced minor local dents without penetration. After a second detonation of 5 kg of TNT above the box chambers, sample PCGR displayed a nearly circular perforation in the top plate, along with cracks near the supports of chambers 1 and 3. For the main girder of the suspension bridge, multiple detonation points caused severe damage, rendering it impassable. However, after polyurea coating, the blast resistance significantly improved, with only minor spalling of concrete on the top plate and no other notable damage, allowing for continued passage. The polyurea layer effectively reduced the vertical displacement of the girder, and this reduction plateaued with increasing coating thickness. Under a 500 kg TNT blast, the optimal polyurea thickness to enhance blast resistance was determined to be 9 mm.

为了研究近场爆炸作用下单箱三室混凝土箱梁的动力响应和破坏特征,开展了缩比试件爆炸试验和数值模拟.以原型桥梁主梁截面按 1∶3 缩比设计和制作了箱梁试件,测量了 3 kg TNT药柱爆炸作用下试件的反射超压、钢筋应变、竖向位移及破洞形态;采用LS-DYNA软件进行了箱梁爆炸响应模拟,结合试验数据验证了数值模拟方法的可靠性;分析了TNT当量、起爆位置、混凝土强度、配筋率对箱梁抗爆性能的影响.结果表明:3 kg TNT药柱于箱梁中间箱室中心正上方 0.4 m处起爆时,在中间箱室顶板中心形成一个椭圆形的贯穿破口,破口沿横、纵桥向长度分别为 41.50、45.50 cm;中间箱室顶板底面的混凝土发生大面积剥落,呈现喇叭状冲切破坏特征;多室箱梁的超宽截面形式使得其爆炸响应沿横桥向分布不均匀;箱梁底板竖向位移峰值和钢筋应变峰值随药量的增大而增大,采用最小二乘法得到了对应的拟合曲线表达式;不同起爆位置下,中间箱室底板中心的竖向位移均大于两侧箱室中心的.

In order to study the dynamic response of self-anchored suspension bridge with extra-wide concrete girder under explosive load, a real bridge was taken as the background, which is the widest on in China at present. Firstly, the refined finite element model (FEM) of the whole bridge was established. The reliability of numerical simulation method was validated by the measured data of the bridge at completion state and explosive test results of scaled girder specimen. The vertical displacement, reinforcement strain, acceleration and failure characteristics of the girder specimen under the explosive load of 3 kg TNT were analyzed. Through parametric simulation, the effects of different scale distance, concrete strength and reinforcement ratio on the explosion response of girder spec-imen were studied. Secondly, the dynamic responses of girder were studied. Finally, the change law of dynamic response at different ages was analyzed. The results show that the elliptical crack is formed on girder top plate. The maximum girder vertical displacement reaches 135.9 mm under 1000 kg, and the maximum increasing ratio of hanger force is 27%. The influence brought by the extra width of girder is significant. The girder vertical displacement changes along transverse direction and the concrete breach sizes are different. In addition, with the increase of service age, the girder displacement increases from 60.50 mm to 106.16 mm under the same explosive load. The research results can provide an important basis for the anti-explosion protection and rein-forcement of similar extra-wide concrete self-anchored suspension bridge.

To investigate the damage characteristics of reinforced concrete (RC) buildings during explosive incidents, a large RC slab (4 m × 5 m × 0.15 m) was meticulously designed, fabricated, and subjected to explosion experiments, which were complemented by comprehensive numerical simulations. The dynamic response parameters of the RC slabs under 0.5–1 kg TNT explosions were tested using polyvinylidene fluoride (PVDF) pressure sensors, displacement sensors, and acceleration sensors. The damage morphologies under 5–40 kg TNT explosions were investigated using ANSYS/LS–DYNA 17.0 software. The results show that, with an increase in TNT charge, the RC slab gradually showed minor damage (5 kg), moderate damage (10–20 kg), heavy damage (25 kg), and complete destruction (30–40 kg). For the 20 kg TNT explosion condition, a 1020 mm × 760 mm explosion crater appeared on the top surface, which was in agreement with the 934 mm × 906 mm explosion crater obtained from the simulation. Based on the results, suitable P–I (pressure–impulse) curves for the 4 m × 5 m × 0.15 m RC slab were established. The results can provide a reference for damage assessments of large-sized buildings during explosion accidents.

The finite element (FE) analysis by ANSYS software based on field test was used to study the structural performance of an extra-wide concrete self-anchored suspension bridge under static vehicle loads. The longitudinal, transverse and vertical stresses of the extra-wide girder were analyzed, and the changing criteria of girder stresses induced by vehicle loads were presented. Additionally, the effects of the shear lag on extra-wide box girders were investigated. The results showed that the maximum shear lag coefficient was 1.89 at the junction of bottom plate and outer web at the middle of midspan. Moreover, the non-uniformity of cable force is perceptible under eccentric load. Furthermore, an optimization measure for comparable bridges and essential health monitoring locations were outlined.

Concrete in water environment is easily subjected to the attack of leaching, which causes its mechanical reduction and durability deterioration, and the key to improving the leaching resistance of concrete is to increase the compaction of its microstructure formed by the curing. This paper performs a numerical investigation on the intrinsic relationship between microstructures formed by the hydration of cement and slag and leaching resistance of concrete in water environment. Firstly, a shrinking-core hydration model of blended cement and slag is presented, in which the interaction of hydration process of cement and slag is considered and the microstructure composition is characterized by the hydration products, solution composition and pore structure. Secondly, based on Fick's law and mass conservation law, a leaching model of hardened paste is proposed, in which the multi-species ionic diffusion equation and modified Gerard model are established, and the model is numerically solved by applying the finite difference method. Finally, two models are combined by microstructure composition to form an integrated curing-leaching model, and it is used to investigate the relationship between microstructure composition and leaching resistance of slag-blended cement pastes.

Explosive tests of scaled girder specimens and numerical simulations of prototype girder segments were implemented to study the dynamic response and failure characteristics of extra-wide reinforced concrete box girders subjected to repeated explosions. First, a segmental girder specimen was manufactured at a reduced scale of 1:3 based on the prototype girder of a real bridge. The damage behavior of the specimen was tested by detonating two 3-kg TNT (trinitrotoluene) grains in sequence at a height of 0.40 m above the center of the middle chamber. Second, LS-DYNA software was used to simulate the explosive response of the specimen. The reliability of the numerical simulation method was verified by comparing its results with test data. Finally, the effects of different TNT equivalents, detonation positions, and repeated explosion modes on the anti-explosion performance of the prototype girder segment are simulated. The results showed that the holes in the top plate of the middle chamber of the girder specimen were 41.50 cm x 45.50 cm and 56.80 cm x 63.50 cm along the longitudinal and transverse directions, respectively, under the two explosions. The concrete at the bottom of the top plate peeled off over a wide area, and cracks appeared in the bottom plate close to the supports. In comparing the simulated damage behavior of different girder segment types along the transverse direction, the dynamic response of the T-beam section segment was found to be greater than that of the box section segment under the same explosive charge. The maximum response was located at the road centerline. Moreover, the degree of damage to the girder was more severe under repeated explosions with a certain amount of charge compared with that under a single explosion with twice the amount of charge. The degree of damage to the web, bottom plate, and crossbeam caused by the explosions in sequence from outside to inside the box with two 200-kg TNT grains was more severe than that caused by a single explosion of 400-kg TNT grains. Simultaneous detonations at multiple positions severely degrade the bridge traffic capacity.

In order to study the influence of concrete shrinkage and creep effect and temperature change on the extra-wide concrete self-anchored suspension bridge under vehicle load, the Hunan Road Bridge, which is the widest concrete self-anchored suspension bridge in China, was chosen as background. Firstly, the refined finite element model (FEM) was established, which was validated by the measured data of field load test. Secondly, the structural states at different ages were predicted. Finally, the evolution laws of component responses were analyzed. The research results show that the bearing type of girder has significant influence on the response change trends. The shear lag effect of girder and local effect of wheel are significant. Under the temperature rise of 20 °C and standard vehicle load, the maximum tower displacement is 0.033 m after 30 years. In addition, the longitudinal tensile stress in most area of bottom plate at middle section exceeds 5 MPa. Moreover, the difference of girder deflection between road centerline and edge reaches 0.07 m under eccentric load after 10 years. The research results can provide an important basis for the health monitoring and safety evaluation of similar extra-wide concrete self-anchored suspension bridges.

针对混凝土结构基本原理课程传统教学模式中存在的主要问题,结合南京理工大学的教学实践,对微课教学模式在该课程建设中的应用展开研究.通过重塑既有教学内容,选择合适知识点,合理设计教学内容,为学生准备"短、平、快"的"碎片化"的微课(程)资源,供其灵活自主地按需选择学习,增加学生的课程参与度并提高教学效率,使学生在有限的学时内获得更多的专业知识,取得了良好的教学效果,为其他土木工程专业课程建设提供了参考与借鉴.

针对高校土木工程专业实践教学环节存在的诸多问题,以南京理工大学土木工程专业为例开展研究.首先,分析了高等教育所面临的变局,提出本科人才培养方案是改革的破局点,实践教学是本科人才培养链条上至关重要的一环;其次,分析了高校土木工程专业实践教学环节存在的问题;最后,介绍了南京理工大学土木工程专业基于"321"人才培养模式的四层次递进式实践教学体系,并详细阐述了课程思政融入点、毕业要求支撑关系、考核方式改革、教学内容更新、线上线下混合式实习平台、青年教师工程实践保障机制等改革措施.

针对混凝土的多相多尺度材料组成特征及其复杂力学响应问题,首先,根据混凝土中各组成材料的几何特征,将C-S-H凝胶、硬化水泥浆体、砂浆及混凝土细观组成分别视为纳观、微观、亚细观和细观尺度上的复合材料,并利用颗粒空间堆积方法,重构了混凝土各尺度复合材料的简化几何模型;其次,基于重构的几何模型和等效夹杂理论,通过等效刚度的升阶计算和应力响应的降阶计算,建立各尺度复合材料应力响应之间的过渡关系,推导混凝土多尺度应力响应方程,并编制相应的计算程序;最后,以单轴压缩载荷作用为例,数值计算载荷作用下混凝土各尺度复合材料中的应力响应,分析骨料空间位置和相互作用以及水化产物刚度、几何形状和空间取向对其应力响应的影响规律.结果表明,单轴压缩载荷作用下,混凝土细观组成中的应力分布并不均匀;骨料颗粒之间的距离影响到混凝土中的应力分布,其有效影响范围约为骨料粒径的6倍;水泥水化产物的刚度、几何形状和空间取向是影响其应力分布的重要因素,刚度越大,所受应力越大,与载荷作用方向的夹角越小,长椭球形水化产物沿载荷作用方向的应力越大,扁椭球形水化产物与之相反.

针对高校课程思政教育存在的诸多问题,文章以混凝土结构基本原理课程为例开展研究.在学情分析的基础上,通过教学方法的创新、教学与科研相结合、思政教学点的优化设计等手段,抓准抓实课程思政,积极推进一流本科课程建设;构建了以学生为中心的课程教学模式,实现了知识、能力、素质、情怀有机融合的教学理念.

为适应当前国家新基建形势对土木工程专业人才的新要求,南京理工大学土木工程专业对本科人才培养模式进行针对性的改革.在学校"321"本科人才培养新方案的总体框架下,研究本专业人才培养模式改革的四大主要措施,构建"基础+进阶"课程体系、设置学科交叉融合课程、构建递进式实践教学体系、设置专业选修课程模块.在此基础上,详细阐述南京理工大学土木工程专业在"321"本科人才培养模式下具体培养目标,预期实现本专业人才培养适应于国家基础设施建设发展需要,为相关院校专业修订人才培养方案提供参考借鉴.

In this paper, the three-dimensional finite element model (FEM) of reinforced concrete slab was established by ANSYS/LS-DYNA software. The numerical simulations of the explosion responses of slab were carried out by LOAD_BLAST_ENHANCED (LBE) method. The dynamic responses and damage laws of slab under different conditions were analyzed, including different modeling method, charge, rebar diameter and constraint condition. Finally, the space-time conservation-element and solution-element (CESE) method was used to simulate the propagation processes of pressure and temperature of shock wave. The results show that the CESE method can be used to analyze the damage effect of target structure under complex explosion loads considering pressure shock and thermal shock.

This study presents the structural health monitoring system of an I-shaped steel-concrete composite girder bridge during construction and vehicle load tests. Strains and deflections were monitored. A finite element model was built and calibrated. Vehicle load tests were carried out for various load conditions. Measured results show that the strains in the concrete slab and steel beams changed rapidly in the first 15 days and stabilized. The composite girder was in an elastic working state under the vehicle load tests. This research provides guidance for the construction control and safety evaluation of similar I-shaped steel-concrete composite bridges in the future.

The progressive collapse resistance of the terminal building of Zhongchuan Airport in Lanzhou, China was studied, which is a long-span curved spatial grid structure with main trusses. Firstly, the finite element model was built using MSC. Marc software adopting the fiber model based on material. Secondly, an improved method of zoned concept judgment and sensitivity analysis was proposed to determine the key components. Thirdly, the initial failure components were removed individually based on the alternate load path method (AP method). The responses of remaining structure were calculated using nonlinear dynamic analysis method. Lastly, the influences brought by the cross-sectional sizes of grid members were investigated through conducting parametric analysis. According to the results, the proposed selection method can avoid omitting the key components. The structural responses are significant when removing the concrete filled steel tubular (CFST) column SC14 directly supporting the front middle part of the roof, with a maximum vertical displacement of 10 m at cantilever end, which should be focused on for this kind of large-span spatial structure. In addition, the tensile strength and cross-sectional area of the upper and lower chords should be increased by 20% to enhance the progressive collapse resistance of the structure, and the changes of axial compression ratios of the columns supporting the roof have little effects.

Mathematical modelling method (MMM) is widely applied in engineering issues. But the performance of MMMs is rarely compared, especially with high dimensional variables. This research focused on the comparison among three mostly used MMMs, i.e., quadratic polynomial (QPMM), kriging (KMM) and neural network (NNMM), based on model updating of a bridge with 13 variables and in-situ data. Firstly, 200 indetermined samples by Latin Hypercube sampling were generated and the relevant responses were computed by finite element model (FEM). Secondly, explicit expressions of responses by MMMs were established. Finally, with the optimization program and explicit expressions, updated variable groups were optimized. From the process and results of FEM updating, it shows that all the MMMs lead to an acceptable result as the discrepancies were reduced sharply. In terms of accuracy, KMM and NNMM are better than QPMM, but in terms of efficiency, KMM is time-consuming.

针对混凝土结构基本原理课程传统教学中的"痛点"问题,结合教学实践,确定了"力"为主线、"实"为过程、"能"为目标,实现知识、能力、素质、情怀有机融合的教学创新思路.教学团队在实践中引入IDEA StatiCa软件,学生通过模拟仿真分析,建立结构受力过程的直观形象,突出了课程的创新性;采取教师讲授、生讲生评、边讲边练、案例分析、课堂翻转等综合教学方法,增强了课程的高阶性;构建了全方位全过程考核评价体系,提升了课程的挑战度,达到了学生概念能理解、知识能掌握、方法会应用、设计能完成、学习有收获的教学效果.

Model updating for bridge engineering structures to obtain precise finite element model is an efficient tool at present. But with the dimension of the potential parameters during optimization increasing, it brings a challenge to present optimization methods. To improve the performance of convergence process and the probability of detecting global extremum, a combination model updating method of modified particle swarm optimization (MPSO) and response surface method was proposed herein. MPSO has less modification to PSO as only modifying the particle position with Gaussian white noise at a probability and the performance was significantly superior than PSO illustrated by testing functions. A beam model updating example based on the proposed method was tested, the convergence ability and accuracy were compared with genetic algorithm which is widely applied in bridge model updating. Finally, the proposed method was successfully applied to model updating of an existing bridge engineering structures with thirteen variables. (C) 2020 Elsevier Ltd. All rights reserved.