Accuracy of B. N. Zhemochkin's solution for circular slabs on an elastic half-space

Conclusions 1. For absolutely rigid slabs, the solution according to schemes A and B yields an approximation to the exact solution, from above and from below, for all the loadings here considered. Thus it is possible to obtain an upper and a lower evaluation of B. N. Zhemochkin's solution, for any number of unknowns. The solution according to scheme A converges somewhat more rapidly.2. For n=22, the greatest error in the values of the moments in a slab under a uniformly distributed load amounts to 8%. If the number of sections or the rigidity of the slab is increased, the error diminishes.3. For flexible slabs, the solution according to schemes A and B may not yield an approximation from both sides; the determining factors in this case are the flexibility parameters of the slab and the nature of the loading.It must be pointed out that a soil bed is not a linearly-deformable body. Even with small loads, plastic deformations take place in the soil under the edges of beams and slabs; they result in a considerable decrease of the maximum values of the reactions at the edges, and in a modification of the entire diagram of the reactions. For this reason, in many cases involving soil beds, the results of an analysis carried out by using a small number of unknowns show a better agreement with the experimental data than the results obtained by using a greater number of unknowns.Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 1, pp. 5–7, January–February, 1970.     

轴力与双向弯矩作用下方钢管焊接球节点的承载力与实用计算方法研究

国家游泳中心“水立方”结构中采用了连接方钢管、且承受轴力与弯矩共同作用的焊接空心球节点。文献[1]系统研究了方钢管焊接球节点在轴力与单向弯矩作用下的承载能力并建立了实用计算方法。本文进一步对轴力与双向弯矩作用下的这类节点进行深入研究。对轴力与双向等弯矩共同作用的节点,通过有限元分析、试验研究以及简化理论解三条途径,系统研究其受力性能,并提出节点承载力的实用计算方法。而对双向任意弯矩作用的情况,提出了对单向弯矩及双向等弯矩两种情况进行线性插值的简化计算方法。     

A new design method for prestressed concrete continuous flat slabs

This paper presents a simple but relatively accurate procedure for the analysis of unbonded prestressed continuous flat slabs. Bi‐circular curves instead of conventional parabolic ones are introduced to obtain the characteristic parameters of the curved tendon profiles. Based on the proposed tendon profile and theory of thin plates, a series of simple formulae are derived to compute the bending moments of flat slabs. The validity of the proposed method is demonstrated by comparing the results with those obtained from finite element analysis. The results of the analysis presented in this paper indicate that the proposed method turns out to be convenient and reasonably accurate in the analysis of prestressed flat slabs. Copyright © 2004 John Wiley & Sons, Ltd.     

超高性能纤维增强混凝土板的受弯性能试验研究

为研究超高性能纤维增强混凝土(ultra high performance fiber-reinforced concrete, UHPFRC)板的受弯性能,进行了10块UHPFRC板的弯曲试验,研究了板的破坏形态、破坏过程、开裂弯矩、极限弯矩以及混凝土和钢筋的应变。在试验结果基础上,建立了考虑受拉区混凝土抗拉强度和应变硬化效应的UHPFRC板受弯承载力计算式。研究结果表明：UHPFRC板的弯曲破坏形态表现为一条主裂缝并伴有多条微裂缝出现,其破坏过程可分为线性变形、微裂缝发展、主裂缝发展和承载力下降四个阶段;UHPFRC板首次出现裂缝时的弯矩为极限弯矩的50%~55%;在设计板时应以变形作为控制指标,且可以少配或不配钢筋以发挥UHPFRC的材料优势;UHPFRC板在受力过程中表现出显著的应变硬化特性。给出了UHPFRC板的弯曲承载力计算式,可以反映受拉区UHPFRC的应变硬化特性。     

Investigation of the behavior of plates supported on linearly deformable layers

Conclusions 1. As the layer thickness decreases (from H/R= to H/R=0.5) the bending moments and deflections decrease by a factor of 2–3 independently of the type of load and the flexibility index.2. As the flexibility index increases (from s=0.5 to s=10), the bending moments decrease by a factor of 2–3 and the plate deflections decrease by a factor of 10–16, independently of the layer thickness.3. The forces in a plate for a layer with H/R=5 agree very closely with the forces calculated for an elastic semiinfinite mass.4. The forces and deflections in a plate for a small layer (H/R=0.5) do not yield a picture corresponding to a Winkler foundation.5. A decrease in the radius of the loading on the central portion of the plate results in a significant increase in the bending moment at the plate center for any values of s and H/R. For any given small radius of the loading, the value of the bending moment at the center depends substantially on s and is practically independent of H/R.6. The values of the forces and plate deflections depend little on the boundary conditions in the lower surface of the compressible layer.7. The approximate method for consideration of the finiteness of the compressible mass proposed by M. I. Gorbunov-Posadov yields results close to those obtained from the analysis of plates on layers with H/R2.Chelyabinsk Polytechnic Institute, Chelyabinsk. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 3, pp. 39–41, May–June, 1976.     

矩形钢管焊接空心球节点承载能力的简化理论解与实用计算方法研究

国家游泳中心“水立方”的新型多面体空间刚架结构采用配合矩形钢管、且承受轴力与弯矩共同作用的焊接空心球节点,目前规范对该类节点的设计方法尚属空白。在有限元分析和试验研究的基础上,进一步研究轴力、弯矩及两者共同作用下矩形钢管焊接空心球节点的承载能力及设计方法。首先推导基于冲切面剪应力破坏模型的节点承载力简化理论解,从而得到节点承载力计算公式的基本形式。在此基础上,利用有限元分析和试验结果,建立了轴力、单向弯矩以及两者共同作用下节点承载力的实用计算公式。对双向任意弯矩作用的情况,提出了基于线性插值的简化计算方法。成果可供实际工程设计采用,也可供相关规程修订时参考。     

Crushing and flexural strength of slab-column joints

In multi-storey buildings, columns are usually not continuous through the slabs to enhance ease of construction. Consequently, in slab-column joints, slabs have to carry column loads in addition to the shear and bending moments due to loads applied to the slab. In most cases, when high strength concrete is used for the columns and normal strength concrete for the slabs, compression stresses at the support areas of the inner columns exceed the uniaxial compressive strength of the concrete of the slab. Due to this reason, most current details for such regions reinforce the concrete of the slab between columns to ensure load transfer. Typically, this is achieved by linking top and bottom columns with reinforcement. Sometimes, it is also needed to incorporate special load transfer devices. This latter solution is however relatively complicated and expensive.In this paper, the crushing and flexural strength of slab-column joints is investigated accounting for an increase of the compressive strength of the failure region (concrete between columns) due to confinement stresses provided by the flexural reinforcement of the slab. The results of an experimental programme on 6 full-scale slabs (250 mm thick) are presented showing that flexural reinforcement of a slab significantly increases the crushing strength of slab-column joints. This allows ensuring load transfer without incorporating special devices or even without linking top and bottom column reinforcement for a wide range of cases leading potentially to more economic designs. An analytical approach, grounded on the theory of plasticity, is also presented allowing one to determine a failure criterion for such regions. This approach, which can also be used for design purposes, leads to an excellent correlation with test results.     

钢筋混凝土双向板的弯矩调幅方法

参照单向连续板的弯矩调幅方法 ,提出了双向板进行弯矩调幅的原则与方法 ,给出了供进行弯矩调幅用的计算表格 ,并且通过一个设计实例 ,介绍了双向板肋梁楼盖的弯矩调幅步骤与计算结果 ,还将此计算结果与按弹性分析方法和按极限平衡方法计算的结果作了对比     

Effects of scarf joints on bending strength and modulus of elasticity to laminated veneer lumber (LVL)

The role of geometry on the mechanical performance of scarf joints in laminated veneer lumber (LVL) bonded with phenol formaldehyde and melamine formaldehyde (MF) adhesives was investigated. Model joints consists of 3, 4 and 5 mm veneer thicknesses at 30°, 45° and 60° of varying scarf joints for LVL produced from brutia pine (Pinus brutia Ten) and elm (Ulmus compestris l.) woods. However, there is little information available concerning the bending strength and modulus of elasticity for LVL, and in particular, scarf joints in these field. In this study, it was aimed to determine the bending strength and modulus of elasticity for LVL. For this purpose, samples were tested according to TS EN 310 standard. It was observed that the highest bending strength (291.5 N/mm²) and modulus of elasticity (28 101 N/mm²) were obtained in control (solid wood) samples having three layered LVL, jointed with 30° angle and bonded with MF adhesive. As a result of the effects scarf joints on bending strength and modulus elasticity test, if the scarf angle decreases, the properties of LVL increase.     

连续组合板的塑性设计

针对国际上大多数关于连续组合板的规范在设计过程 都都限制使用塑性分析 现状,介绍了对连续板正向,负向受弯的定量研究以及负弯曲条件下实验结果,从这些研究中推导出了在连续设计中使用塑性分析确定弯矩和剪力分布的可能性。     

混凝土楼板对钢框架梁柱节点抗震性能影响的试验研究

为了研究节点区混凝土楼板对钢框架梁柱节点抗震性能的影响,完成了4个不同构造形式的节点试件在低周循环荷载下的破坏试验,分析了节点构造与混凝土楼板配筋率等因素对节点承载力、转动刚度、极限转动能力、耗能能力、延性和极限破坏状态的影响。对节点破坏模式和滞回曲线的分析表明,保证焊接质量是避免节点脆性破坏的重要措施。采用长焊接孔的节点,使钢梁发生了局部屈曲破坏,既可减少局部应力集中,又可提高节点的延性,提高配筋率可以显著增强节点的抗弯承载力。另外,混凝土楼板的存在使节点在构造上存在不对称性,应该在节点设计中给予考虑。     

Fatigue tests and design of thin CHS-plate T-joints under cyclic in-plane bending

A review of existing fatigue design guidelines has been undertaken and shows that there are no fatigue design recommendations for circular hollow section-to-plate T-joints subjected to in-plane bending. This paper therefore reports on the high cycle fatigue behaviour of welded thin-walled circular hollow section (CHS) tubes of thicknesses less than 4 mm that are fillet-welded onto a plate to form a base plate moment connection. The resultant thin CHS-Plate T-joints are subjected to cyclic in-plane bending load to determine their fatigue strength at different stress ranges. The S–N data from the failed thin CHS-Plate T-joints is analysed using the least-squares method of statistical analysis to obtain a design S–N curve. The derived design S–N curve for the thin CHS-Plate T-joints is compared to existing design S–N curves and also that of square hollow section (SHS)-to-plate T-joints under in-plane bending in current fatigue design guidelines. The thin CHS-Plate T-joints are found to have a better fatigue strength compared to the existing S–N curve for SHS-Plate T-joints under in-plane bending. An appropriate design S–N curve from the group of existing design S–N curves is adopted for the design of thin CHS-Plate T-joints.     

Fatigue design of welded very thin-walled SHS-to-plate joints under in-plane bending

The existing fatigue design S–N curve for SHS-to-plate T-joints under in-plane bending is given in the Canadian Standard, CAN/CSA-S16.1-M89, in terms of the classification method. That S–N curve is however based on the class of longitudinally loaded plates with welded non-load carrying attachments, which are different from the SHS-to-plate T-joints. The increased use of welded thin-walled (t<4 mm) tubular joints in the road transport and agricultural industry for applications such as lighting poles, traffic sign supports, truck trailers, swing ploughs, haymakers and linkage graders, means that there is a need to develop fatigue design curves for tubular joints where the tube wall thickness is less than 4 mm. This paper aims to determine fatigue design curves for SHS-to-plate T-joints where the thin-walled tubes have a thickness of less than 4 mm. Tube-to-plate T-joints, made up by welding a square hollow section tube to a plate, are tested under fatigue loading. Constant stress-amplitude cyclic loading is applied to these connections as in-plane bending load. Stress concentration factors (SCFs) have been determined from strain distributions obtained using strain gauge measurements. Analysis of the fatigue test data using least squares method is carried out to determine the design curves of the tube-to-plate T-joints under in-plane bending, for both the classification method and the hot spot stress method. A class of 44 is recommended for the classification method. An S_r._hs–N curve is proposed, with a recommended SCF of 2.0 for the hot spot stress method.     

A numerical model for analysis of riveted splice joints accounting for secondary bending and plates/rivet interaction

The paper presents a numerical procedure for the analysis of riveted splice joints, taking into account the effect of the secondary out-of-plane bending and plates/rivet interaction. The joint is idealized by two separate layers that are linked by beam connectors with variable circular cross-sections, in order to account for the countersunk effect of the rivet heads. Rotational spring elements are used to partially restrain the rivet heads in the x–y plane. Gap elements are used to simulate the in-plane load transfer between the rivets and spliced plates. The efficiency of the method is illustrated by analyzing three models of splice joints. It is shown that the secondary bending largely affects the maximum tensile and compressive stresses within the joint. The difference may reach up to 39%. Finally, experimental comparison is made with photo-elastic test results for a spliced specimen with eighteen rivets. The predicted maximum shear strains along several lines within the splice region, for both cases, are found to be in reasonable agreement. Factors affected the experimental and the finite element results are also discussed.     

Experimental investigations of the reactive strength of soil in the bed of a circular footing subjected to short-term dynamic loads

Conclusions 1. The distribution of contact stresses along the foundation slab of a rigid circular footing in a sandy soil subjected to dynamic loads in a steady-motion regime is saddle-shaped in nature and agrees with corresponding literature data derived from static tests. In this case, an increase in contact stresses from 0.2–0.5 to 1.0–1.5 MPa at the center of the plate will effect a reduction of from 1.60–1.80 to 1.30–1.50 in the concentration factor; this is associated with the enhancement of the role played by plastic deformations in the bed.2. The reactive strength of the soil in the bed of a circular rigid footing subjected to short-term dynamic load can be represented in the form of Eq. (1). In this case, the computed velocity a₁ should be determined with allowance for the actual ₁() curve, which corresponds to the work of the soil beneath the plate under conditions of a certain deformation regime.3. Use of the hypothesis that we have cited will make it possible to predict with an accuracy sufficient for practical calculations the maximum loads on foundation slabs placed on the surface of the ground for structures, and the parameters of their motion under blast-induced loads of rather high intensity.Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 3, pp. 10–12, May–June, 1990.     

Experimental study of a flexible beam on a sand foundation

Summary 1. With the method given for determining the parameters of a sand base, the bending moments of a beam calculated from Winkler's model differ little from the experimental values. In a number of cases the curves of M (Fig. 1, 4), constructed from the theory of a linearly deformed half-space, differ markedly from the experimental curves; this may be explained by the fact that in the author's experiments there was an appreciable difference between the sand base and a linearly deformed half-space.2. The curves of y constructed from both theories coincide fairly closely with the experimental curves, except for the curve constructed from the theory of a linearly deformed half-space (Fig. 1 and 4).3. From an analysis of the experimental and theoretical curves of M and y (Fig. 1–6), we can take it that, in these conditions during loading by a flexible beam, a sand base behaves as though its density varies along the beam, being greater at the center and less at the ends.Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 6, pp. 2–4, November–December, 1964     

Mercury fluxes in a natural forested Amazonian catchment (Serra do Navio, Amapá State, Brazil)

Mercury (Hg total) fluxes were calculated for rainwater, throughfall and stream water in a small catchment located in the northeastern region of the Brazilian Amazon (Serra do Navio, Amapá State), whose upper part is covered by a natural rainforest and lower part was altered due to deforestation and activities related to manganese mining. The catchment area is 200 km from the nearest gold mining (garimpo). Minimum and maximum Hg concentrations were measured monthly from October 1996 to September 1997 and were 3.5–23.4 ng l⁻¹ for rainwater, 16.5–82.7 ng l⁻¹ for throughfall (March–August 1997) and 1.2–6.1 and 4.2–18.8 ng l⁻¹ for stream water, in natural and disturbed areas, respectively. In the natural area, the inputs were 18.2 μg m⁻² year⁻¹ in rainwater and 72 μg m⁻² year⁻¹ in throughfall. This enrichment was attributed to dry deposition. The stream output of 2.9 μg m⁻² year⁻¹ indicates that Hg is being recycled within the forest as other chemical species or is being retained by the soil system, as confirmed by the cumulative Hg burden in the 0–10 cm surface layer, which was 36 480 μg m⁻². When the disturbed area of the catchment was included, the stream output was 9.3 μg m⁻², clearly indicating the impact of the deforestation of the lower part of the basin on the release of mercury. The Hg burden in the disturbed area was 7560 μg m⁻² for the 0–10 cm surface layer.     

深埋圆形隧洞板裂化弧形岩板凹曲变形的论证

以锦屏二级水电站TBM开挖的圆形断面施工排水洞为例,首先根据围岩实际破坏特性明确指出围岩劈裂后产生弧形岩板的客观存在性,然后提出其存在发生凹曲变形（指其发生弯曲方向指向隧洞外部、半径减小即曲率增大的弯曲变形）的可能性,最后从力学分析与数值试验两个方面对弧形岩板发生凹曲变形的可能性进行了论证。论证显示：对处于垂直地应力与水平地应力不相等条件下的深埋圆形隧洞,弧形岩板可以发生凹曲变形,发生的控制因素是两向应力差对圆形隧洞产生的垂直方向压缩、水平方向拉伸的压扁作用。弧形岩板凹曲变形的论证对今后深入认识深埋圆形隧洞完整或较完整硬岩动力破坏的发生机制提供了一条新思路。     

Stresses in a bed beneath rigid and flexible foundations under initial and repeated loadings

Conclusion The experiments indicated that repeated loading of flexible foundations (in contrast to rigid foundations) may result in significant variation in the stresses beneath them, which will lead to an appreciable increase in bending moments, elongations in reinforcement, and even to failure of the flexible foundation under a loading that did not give rise to dangerous deformations during the initial loading.Scientific-Research Institute of Bases and Underground Structures. Giproniiaviaprom. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 1, pp. 29–31, January–February, 1987.     

Effect of inelastic soil deformations on forces in crossed-strip foundations

Conclusions 1. Strip foundations on soils having slump-type settlements and on undermined territories should be designed with an increased pressure on the soil, which leads to a more intense redistribution of the contact pressures and to a decrease of bending moments in the case of slumping. In all cases, it is necessary to take into account residual deformations of the soil, otherwise the effect of reducing the bending moments is exaggerated and, accordingly, the reliability of the structure decreases. 2. Replacement of the p-s diagram having two explicitly expressed segments by a bilinear diagram can be used for developing engineering methods of calculation. The programs developed can also be used for calculating slabs on a nonlinear inelastic bed, with replacement of the slab by a crossed system of beams. In this case, the flexural and torsional rigidities of the replacing beams should be taken equal to Db, where D is the cylindrical rigidity of the slab and b is the width of the band being replaced. 3. Consideration of nonlinear deformation of soils leads to a substantial decrease of forces in foundations. In the calculations performed, the decrease of the maximum values of the bending moments was 30%. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 5, pp. 23–26, September–October, 1982.