T形板肋对预制带肋底板混凝土叠合板弯曲疲劳性能的影响

为研究T形板肋对预制带肋底板混凝土叠合板弯曲疲劳性能的影响,对3块T形肋底板叠合板和1块整浇板进行弯曲疲劳性能对比试验,主要考察T形板肋与疲劳荷载幅值对试件疲劳破坏形态及疲劳损伤程度的影响,得到了在不同疲劳循环加载次数下的跨中动位移、混凝土应变、预应力筋应变、残余变形等,分析了在不同疲劳循环加载次数下的刚度退化情况、荷载-应变分布规律、裂缝分布规律及剩余承载力等。研究结果表明,经历200万次疲劳循环加载后,T形肋底板叠合板无明显的刚度和强度退化,增设T形板肋的叠合板能达到与整浇板相同的弯曲疲劳性能;T形肋底板叠合板正截面弯曲疲劳强度计算可采用普通预应力混凝土受弯构件正截面疲劳应力验算的4个假定,最终以此建立了其正截面弯曲疲劳强度验算方法。     

Contrast Analysis of the Reinforcement Effect of Pile-Net Composite Foundation

To investigate the effect of consolidation soft soil, three groups of model tests were designed. The first group was PVC pile-net composite foundation, the second was pile-cap-net composite foundation, and the third was PVC and sand pile composite foundation. Butter was coated and plastic membrane was covered on inner side wall of model cast to reduce border effect. The gauges were glued with epoxy on the surface of the model with PVC piles and geogrids to measure the stress of PVC piles and geogrids. Soil pressure cells were installed in the middle of piles and the top of the sand piles, and dial indicators were installed in the middle of road and road shoulder to measure deformations. It is that shown: 1) as for the distribution of the road settlement and the differential settlement, the settlements of the third group are the largest and those of the second group are the least; 2) in terms of the stress ratio of PVC pile and soil, the values of the first group and the third group are similar, while the value of the second group is much larger; 3) the change of geogrid strain is disorderly. There are periodic peaks in the strain of geogrid of pile top and periodic troughs in the soil between the piles. The geogrid strain of the second group measured in the corresponding spot is much larger than those of the other two groups. The results of three groups of tests illustrate that if the condition is permitted, it would be the best to adopt the scheme of pile-cap-net composite foundation, which has better reinforcement effect for soft soil.     

Impact of Temperature in Air-conditioned Room on Blood Rheological Characteristics

Based on the reversed cyclic loading tests of 21 nearly full-size interior joints in completed reinforced concrete frames,the law of bond deterioration of beam bars crossing the joint is tested and analyzed,which is influenced by the axial load ratio,shear-compression ratio,reinforced bar strength,concrete strength and the relative length of beam bars crossing the joint. By the nonlinear fitting method, the formula of the bond stress r between steel crossing interior joints and concrete under different loading step is obtained. According to the loading approach, the propositional formula of the relative length of beam bars crossing the joint hc/d is presented, which is influenced by axial load ratio, shear-compression ratio ,reinforced bar strength and concrete strength.     

Analysis of bearing capability of CFG pile composite foundation

The CFG pile is used to consolidate the foundation in one passenger dedicated line. The field experiments including low strain dynamic testing, bearing capability of single pile and the composite foundation are done, and the bearing capability of composite foundation is calculated, too. The results show that the first and second class piles account for 93.9% and 6.1% respectively, and the bearing capability eigenvalues of single pile and composite foundation are larger than the designed values. The 3D FEM model is established to simulate the stresses of CFG pile top and inter-pile soil changing with load level, and the stress ratio between CFG pile and inter-pile soil is analyzed, too. The following results are got from the calculation results of FEM: 1) the stresses of CFG pile top and inter-pile soil increase with load level, but the increasing rate of the former is larger than the latter; 2) the stress ratio between CFG pile and inter-pile soil increases quickly when the load level is low, and it tends to convergent gradually with load increasing.     

Analysis on Deformation Characteristics of CFG Piles-Gravel Cushion Composite Foundation of the Deep Embedded Secret Passage

In order to investigate the issue in the field of the application of CFG pile application of CFG pile composite foundation technology in deep embedded secret passage of such special structure ground treatment, the settlement deformation of CFG pile composite foundation according to deep are studied and detailed analysis are given in the field test and indoor model test of the gravel cushion with different thickness. Moreover it points out that the cushion compressive deformation must be taken into account, and that the settlement deformation calculation cannot simply consider the amendments of composite foundation. The amendments of cushion deformation must be considered. The effect of the different thickness of cushion on pile-soil stress ratio, total settlement of composite foundation, cushion compression and axial stress of pile body were analysed by using ABAQUS finite element method. Through the analysis of the field test, indoor model test and the numerical simulation of CFG piles-gravel cushion composite foundation of the deep embedded secret passage, a settlement deformation monitoring method has been described and the selection principle of the cushion has determined so as to provide the cushion design basis in the process of composite foundation design.     

Dynamic Behavior of Geogrid Reinforced Pile Supported Embankments under Moving Load

In order to investigate the dynamic behavior of geogrid reinforced pile supported embankments (GRPS) under moving load, a three dimensional coupled mechanical and hydraulic model was built by FLAC 3D. The results from two cases including unreinforced and no pile embankments, and geogrid reinforced pile supported embankments were presented. The behaviors of vertical displacement, pile soil stress ratio, excess pore water pressure, and vertical acceleration under two cases were compared and discussed. Additionally, studies on the effect of speed and weight of the moving load were performed. It is indicated that the value of vertical displacement, pile soil stress ratio, excess pore water pressure, and vertical acceleration of GRPS decrease evidently compared with those of unreinforced and no pile embankment, which is caused by the soil arching effect and the reinforcement effect. It is also shown that the greater the axle load value is, the less the beneficial effect of GRPS on the vertical displacement. With the increase of the moving speed of the load, the vertical displacement increases.     

简谐SH波作用下管桩的振动特性

在一维波动模型的基础上得到了简谐SH波作用下桩周土和桩芯土的位移。在三维轴对称的情况下,运用势函数和分离变量法求解了简谐水平集中荷载和SH波引起的管桩桩周土和桩芯土的振动问题,得到了桩周土和桩芯土的径向位移和环向位移。考虑管桩土动力相互作用和管桩土的连续性边界条件对简谐水平集中荷载和SH波作用下管桩的振动进行了研究,得到了管桩桩顶的动力放大因子。通过数值算例分析可知,简谐SH波作用下管桩存在共振现象;管桩管壁过薄宜导致桩基失稳;相同外径情况下采用管桩要比实芯桩的抗震性能更好。     

Spatial Calculation Methods of Three Main Trusses Continuous Plate truss Composite Bridge

According to the structural features of three main trusses continuous plate truss composite bridge, two composite beam methods are presented by constructing the displacement mode of composite beam elements and deriving the stiffness matrix of composite beam elements. The characteristic of composite beam method one is that the bridge slab is taken as the top flange of the chord of main truss and combined with the chord of main truss to form a steel concrete composite beam; the characteristic of composite beam method two is that the bridge slab is taken as the top flange of longitudinal and traverse beam and form a steel concrete composite beam with longitudinal and traverse beams. And as for the conventional plate beam composite method, the slab is characterized by forming bridge slab system with continuous isotropic sheets and longitudinal and traverse beams to bear load. Also, the comparison between theoretical results and experimental ones verifies the effectiveness of the above three methods.     

新型组合梁板连接中板的抗弯性能

在高层建筑结构设计中，由于上部荷载较大或梁的跨度较大，使得梁的截面高度较高，通常会影响建筑的有效层高和建筑的总体高度。为了减小各层梁板结构高度，有效增大各层净高，提出了一种钢箱梁嵌入现浇板的新型组合梁板连接方式。针对这种新型连接方式，对6个钢箱梁混凝土板组合连接区域进行了板承受支座负弯矩的单调加载试验，对比分析了采用钢箱梁嵌入混凝土板组合楼盖与传统栓钉连接组合楼盖中板抵抗支座负弯矩的性能差异；并利用ABAQUS对试件进行了有限元分析。试验与有限元分析结果表明：采用钢箱梁嵌入板连接组合方式，其混凝土板抵抗支座负弯矩的能力与传统连接方式板抵抗支座负弯矩能力没有明显差异。     

Field Comparative Experimental Study on Bearing Capacity of Both Bored Pile with Branches and Plates and Column Bored Pile at the Same Site

Compared with column bored pile,the bored pile with branches and plates is a new type of piles with higher bearing capacity and lower settlement.Field comparative tests related to ultimate bearing capacity of both the bored piles with branches and plates and column bored piles at the same site in Huzhou city of province Zhejiang in China were studied through self-balanced method under static pressure.The results testify that,compared with column bored pile under the same geological conditions,the bored pile with branches and plates can obtain better economic benefit such as: increasing ultimate compressive bearing capacity and ultimate extraction bearing capacity used per cubic meter concrete over 75.3%and 118.9%respectively,while dropping consumption of reinforced concrete upwards of 41.9%and 44.1% respectively,reducing settlement and pile length under the same loading.The tests will present an objective reference to the new type of piles in both theoretic study and application to analogous engineering.     

近爆作用下压型钢板组合楼板动力响应及影响因素数值分析

利用有限元软件ANSYS/LS-DYNA,采用流固耦合的计算方法,对压型钢板组合楼板在近爆炸荷载作用下进行了不同工况的数值模拟,得出其受力形态,分析其动力响应及破坏过程,找出影响楼板动力响应的主要因素。数值分析结果表明：适当增加混凝土厚度和提高压型钢板强度,可以显著降低组合楼板的跨中最大位移,提高组合楼板的延性和抗爆性能;组合楼板中钢筋间距的变化,对组合楼板抗爆性能影响较小。     

水压力环境中混凝土经历循环荷载后的抗压强度

研究了水压力环境中混凝土在经历循环荷载后的动态压缩强度，分析了水压力和循环次数对混凝土强度的影响。试验应变速率为10^-5/s、10^-4/s、10^-3/s和10^-2/s，水压为0~10 MPa。试验结果表明，在不同水压力下饱和混凝土的强度都随应变速率提高而增加，也随水压力提高呈增加地趋势。在相同水压力下，应变速率越高，混凝土强度提高越显著。饱和混凝土经过循环荷载后，其强度随荷载循环次数的增加呈现出先提高后降低的现象。应变速率越高，混凝土强度最大时所对应的荷载循环次数也相应增加。还构建了饱和混凝土强度与应变速率、水压力的关系，其与试验数据吻合较好。进一步引入了管道孔隙模型，并基于汞压法的原理和孔隙分布特点，考虑混凝土孔隙的微观结构解释了孔隙水对混凝土强度的作用机理。     

Deflection and Stress Analysis of a Pavement Slab under Temperature Gradient and Axial Loading Coupling

It has been established that a pavement slab will curl up if a temperature gradient exists across the depth of a slab. A negative temperature gradient causes the slab edge to curl up while a positive temperature gradient curls up the slab center. Temperature stress in slabs is induced by self-weight and other slab constraints. At present in P. R. China, the total stress considered in cement concrete pavement design includes the load stress plus the temperature stress, and only transverse cracking from bottom to top is considered for concrete pavement. Slab responses under axial loads and temperature gradient coupling are not included. We modeled a single slab with a frictionless interface between the slab and foundation using the finite element method. Slab deflection and stress were calculated under axial loads at different slab positions and negative or positive temperature gradient coupling. The calculated results show that the different conditions of axial loads and temperature gradient coupling will change the maximum tension and cause various types of cracks in a slab.     

An Equivalent Shear Displacement Method of Single Capped Pile in Layered Soil

Based on the interaction of single pile, cap and soil, the load transfer matrixes of single pile and soil were proposed to establish an equivalent shear displacement method of single capped pile in layered soil. With the compatibility of displacement at the interface between the pile and the soil, equilibrium equations of pile and soil could be derived. With the increase of the total load on the pile cap, the lateral friction at the interface of the pile and the soil becomes so large that the occurrence of the sliding takes place. While there is little sliding at the interface between the soil under cap and the soil outside of the cap because of the less lateral friction, which gives rives to less settlement of the soil outside of the cap. Eventually, the results of the finite element method, existing theoretical method and the model tests were compared with those from the analytical method and were found to be in good agreement. The increase of the ratio of length to diameter does not infinitely enlarge the overall stiffness of the single capped pile, because the pile cap would afford part of the loading all the time.     

Evaluation on the Damage Evolution of the CRCP+AC Composite Pavement by the Concrete Dameged Plasticity Material Model

In the study on the CRCP+AC composite pavement, the form and distribution pattern of cracks are two important factors influencing the performance and the lifetime of the pavement. The concrete damaged plasticity material model incorporated in the general purpose finite element software named ABAUQS was adopted to describe the mechanical characteristics of the CRC slab. Combining with the temperature field database drawn from the three-dimensional transient heat transfer analysis, the structural damage under the condition of temperature changing is analyzed. The structural damage evolution and the crack behavior of the CRC slab subjected to the thermal-mechanical coupling condition are further analyzed, which suggests that the role of the asphalt concrete surface is not confined only to the scope of improving the performance of the road, its capacity for improving the stress state of CRCP slab is worthwhile to be affirmed. And the reasonable thickness of AC layer should be designed in consideration of the thermal contraction and damage properties of the CRC slab comprehensively.     

Finite Element Analysis of the Influence of Steel Strength on Beam-to-column Composite Connections

Because high material strength and composite load-bearing are emphasized in constructing members for high-rise steel frame structures, in a composite connection, steel strength has a dramatic influence on both the bearing performance and the composite action of the concrete slab. Based on a finite element analysis, we discuss the composite effect and the connection breaking mode, focusing on the performance change of the composite effect in adopting high strength steel. It can be found from the results that, along with the improvement of the steel strength, the elastic and plastic ultimate strength of the composite connection will increase, the ductility will decrease to a certain extent, and the composite effect of the concrete slab will diminish. The collapse of the concrete in a positive moment side contacting the column flange is viewed as the limiting state of the connection.     

门架式抗滑桩结构模型试验研究

为了对门架式抗滑桩的结构特性有进一步的认识和提升，进行了门架式抗滑桩三维地质力学模型试验与门架式抗滑桩结构模型试验。通过在桩身内部贴置应变片以及桩身的关键位置处放置千分表，来测量在推力荷载施加过程中，门架式抗滑桩的桩身应力变化特点及关键位置点的位移变化特征。试验结果表明：门架式抗滑桩桩前、后排桩桩顶位移大于滑动面处位移，后排桩桩身位移大于前排桩桩身位移；前、后排桩桩身内力均呈现明显的“s”型分布，桩顶应力不为零，其数值随着推力荷载的增大的而增大。     

Probability Analysis of Failure Cause for Light Weight Steel Structure under Snow Disaster

In the current unified standard for reliability design, it lacks full considerations of the range of load effect ratio for reliability analysis of light weight steel structures. Firstly, a computational method based on stress was proposed to calculate load effect ratio, which solves the problem that which kind of load effects can be chosen to calculate load effect ratio when the member fails with actions of several kinds of internal forces. Then, the range of load effect ratio was studied for light weight steel structures after some analyses of several members with this method. It is found that the load effect ratio of light weight steel structures can adopt large values under the disadvantage distributions of snow load. The reliability was also calculated for light weight steel structures designed with current partial factors. Its result shows that the reliability of light weight steel structure is low. Finally, the reliability was analyzed for light weight steel structures with different load effect ratios when snow load exceeded the design standard level. It indicates that the reliability is low for light weight steel structures with large load effect ratio. This provides some complementary explanations for the phenomena that the light steel structures are more likely to fail under snow disaster.     

FEA of the Loading Capacity of Monolithic Composite Slim Floors with Deep Decks

Steel concrete composite slim floors with the steel beam encased in concrete floor slabs have many advantages, including low structural height, high fire resistance and rapid construction times. These features make such floors a promising for use in multi storey steel buildings. We established a 3D finite element model of a monolithic composite slim floor using the ANSYS software package. We analyzed the loading capacity, deformation behavior, natural vibration frequency, the influence of reinforcement, and the concrete in the floor rib under a uniformly distributed vertical load. We calculated the effective width of mid girder and secondary beams. The following conclusions can be drawn from the analysis results: First, monolithic composite slim floors possess high loading capacity for common buildings. Second, the concrete rib and reinforcement ratio in the rib have significant effects on floor loading capacity. Third, calculation of effective primary beam width should be based on analysis of monolithic floors rather than single beams.     

Experimental Analysis of Time-dependent Shear Behavior on Stud Connectors

With regard to the long span continuous composite beams, the early composite shear stud strength at the joint surface between the steel girder and concrete slab at different concrete ages should be considered while the concrete slabs are casted by phases in construction stage. In this study, the push-out test of stud shear connectors were conduced at different concrete ages. Meanwhile, the change law of the ultimate shear strength, ultimate slip deformation, design shear strength, and shear stiffness of the stud shear connectors with concrete ages were analyzed, and the corresponding time-dependent calculation equations were presented. The results include that the main failure modes of stud shear connectors are the concrete slab splitting failure before 3-days concrete age. The load-slip laws of stud shear connectors at different concrete ages are basically the same, however, the shear strength and stiffness all increase with the concrete ages prolonging, and the increase degree is faster at early ages, but slower at later ages, which indicates that the early composite shear stud strength at the joint surface of composite beams should not be neglected.