弹性地基上间断中厚矩形板的非线性振动

研究了弹性地基上带传力杆的间断中厚矩形板结构的非线性振动特性。荷载在传力杆中的传递由竖向弹簧模拟，其弹簧刚度取决于传力杆的特性以及杆与板间的相互作用。根据能量变分原理，考虑地基耦合效应，建立了双参数地基上带传力杆的间断矩形中厚板的非线性运动控制方程。应用伽辽金法和谐波平衡法对该组非线性方程进行了求解。在算例中，讨论了传力杆参数、板的结构参数以及地基参数对中厚矩形板的非线性自由振动特性的影响。     

Evaluation of performance and design of GFRP dowels in jointed plain concrete pavement – part 1: experimental investigation

Dowel bars are provided at the transverse joints of the jointed plain concrete pavement to allow for expansion and contraction of the pavement due to moisture and temperature changes. This paper presents experimental and analytical investigations for the deflection response of glass fibre-reinforced polymer (GFRP) dowels for different joint widths and concrete grades. The results were compared with those obtained from investigations into the conventional epoxy-coated steel dowel bars of similar rigidity. The experimental results showed that the 38 mm (1.5 in.) GFRP dowels perform better in terms of joint face deflection compared with 25 mm (1 in.) epoxy-coated steel dowel bars. In addition, these results showed that the deflection of the GFRP dowel was significantly affected by changing the concrete compressive strength and the joint widths.     

残损古建筑木结构燕尾榫节点抗震性能试验研究

残损是现存古建筑木结构的普遍状况,显著地降低了结构的抗震性能。为研究残损对燕尾榫节点抗震性能的影响,参照宋《营造法式》殿堂三等材的尺寸要求,制作了3个比例为1∶3.2的燕尾榫节点模型,包括1个完好节点、1个模拟榫头真菌腐朽的残损节点和1个模拟榫头虫蛀的残损节点。榫头真菌腐朽和榫头虫蛀分别采用在榫头表面钻一定深度的孔和在榫头钻通孔的方法来模拟。通过低周反复加载试验对残损节点的破坏特征、弯矩-转角滞回曲线、骨架曲线和耗能性能进行了研究,分析了残损燕尾榫节点抗震性能的退化规律。结果表明:残损燕尾榫节点的破坏形态与完好节点的破坏形态类似,主要表现为榫头和卯口有明显的挤压变形、榫头沿枋纵向部分拔出,枋柱整体完好,但残损节点的榫头拔出更早、拔出量更大,模拟虫蛀节点有榫角被挤碎;残损燕尾榫节点的滞回曲线也有明显的"捏缩"效应,但滞回环饱满度较差;残损节点的转动弯矩、转动刚度均明显低于完好节点,但耗能能力基本不变化;当两种不同残损类型的残损程度相近时,人工模拟真菌腐朽节点的转动弯矩更高、转动刚度更大。     

Investigations the effects of fastener, glue, and composite material types on the strength of corner joints in case-type furniture construction

This study was carried out to determine the performance of different construction techniques on the diagonal compression and tension strength of case-type furniture corner joints, and to determine the effects on these joints of some factors including the type of joint, the type of composite board and the glue type. For this purpose, melamine-coated particleboard (MCP) and melamine-coated fiberboard (MCF) panels were bonded with polyvinyl acetate D3 (PVA D3), polyvinyl acetate D4 (PVA D4) and Desmodur VTKA (DVTKA) adhesives on spline joint (Sj), butt joints (Buj), biscuit joints (Bij), plain dowel joints (PDj), grooved dowel joints (GDj). It became evident that the diagonal tension and compression strength of the joints is influenced by panel material, type of adhesive and joints. The diagonal tension strength was greater than the diagonal compression strength of all L-type corner joints. The highest diagonal tension strength was obtained in MCF with DVTKA adhesive and GDj while highest diagonal compression strength was obtained in MCP with PVA D4 and Sj. In both tests, MCF corner joints were stronger than MCP corner joints. Furthermore, diagonal tension and compression strength of the joints glued with PVA D4 adhesive was higher than the similar joints glued with PVA D3 and DVTKA adhesives.     

Evaluation of performance and design of GFRP dowels in jointed plain concrete pavement – part 2: numerical simulation and design considerations

The article presents a numerical investigation using three-dimensional finite element analysis (FEA) to compare the performance of glass fibre reinforced polymer (GFRP) and steel dowel bars as load transfer devices across the transverse joints of jointed plain concrete pavements (JPCP). The FEA model used concrete damaged plasticity formulation to characterise the concrete pavement; elastic, transversely isotropic material characteristics were assumed for the GFRP dowels and classical metal plasticity formulation was used for the steel dowels. The numerical results were validated with the experimental results, and a good agreement was achieved. The results showed less stress concentration in the concrete underneath the GFRP dowels (38 mm diameter) compared with the steel dowels (25 mm diameter) of similar flexural rigidity. Finally, on the basis of a detailed parametric study, design considerations for the GFRP dowels in JPCP are suggested.     

The technique of glueing precast elements of the Rio-Niteroi bridge

The prestressed concrete superstructure of the 7,884 m long and 26.6 m wide bridge over the Guanabara Bay, connecting the cities of Rio de Janeiro and Niteroi, in Brazil, was constructed by the cantilever method with the help of precast segments which were glued together with epoxy resin. An experimental investigation of the structural behavior of the glued joints was made in a model of the bridge. Important conclusions resulted from the experiment. It has been shown that the glued joints do not affect the safety of the structure. Several investigations were made during the construction for determination of various important features of the glued joints for erection procedures. The behavior of glued joints was studied with the help of a specially developed concrete test piece.     

Failure analysis of timber bolted joints by fracture mechanics

This study concerns the failure of dowel-type joints in glued laminated timber under static loading. Failure of joints with a single bolt or dowel due to cracking parllel to the grain direction is considered. Results presented concern only the first mode of cracking,i.e. splitting under tension perpendicular to the grain. Fracture is analyzed by the use of linear elastic fracture mechanics concepts; the crack propagation condition is assumed to be based upon the critical energy release rate G_Ic. A simplified average stress criterion allows predicting the onset of splitting. An experimental program was carried out on joints for different structural parameters and bolt diameters. The experimental stable crack growth allowed obtaining the load-crack length curves. Another experimental program was carried out in order to compare the fracture energy of a few CIB-type specimens with the critical energy release rate G_Ic being used in the crack propagation simulation. The comparison between experimental and numerical results for the simulation of fracture in joints shows that Linear Elastic Fracture Mechanics provides a good approximation of the load-bearing capacity of bolted joints and may help improve design codes.     

A laboratory investigation on bonding properties of dowels in concrete roads

Inclined dowel bars and unmovable bars may cause pavement cracking in the vicinity to the bar ends. The aim of the investigation is to study if there are any differences in bonding properties due to dowel material, coating or diameter of the dowel. Steel dowels with different coatings and dowels made of composite material are tested. The maximum draw-out force for a draw-out travel of 1.5 mm is measured. The test is repeated four times and ends with a final cycle to establish the constant force needed for a draw-out travel of 5 mm. Steel dowels with bituminous coating show the lowest initial draw-out force. The draw-out force increased 2 to 3 times with a diameter increase of 50% for steel dowels with plastic coatings. For composite dowels the comparing results showed an increase of draw-out force 2 to 5 times with an increase in diameter with one third. The results from the repeating test for several cycles showed that the draw-out and push-back force were almost the same for all dowels. However, for the dowels with bituminous coating a higher push-back force was needed compared to the draw-out force. It should be noted that the testing speed could affect the results, especially for dowels with bitumen.

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Résumé Des goujons d’assemblage inclinés ou inamovibles peuvent engendrer des fissures au voisinage de leur extrémité. L’objectif de cette étude est de déterminer si les propriétés d’adhésion dépendent du matériau utilisé pour le goujon, de son revêtement ou de son diamètre. Des goujons en acier avec différents revêtements ainsi que des goujons en matériau composite sont testés. La force maximale correspondant à une extraction de 1.5 mm est mesurée. Le test est répété quatre fois et est suivi d’un cycle final pour déterminer la force constante nécessaire à une extraction de 5 mm. La plus petite force initiale d’extraction est obtenue pour les goujons en acier avec un revêtement bitumineux. Pour les goujons en acier avec revêtement plastique, la force d’extraction augmente de deux à trois fois lorsque le diamètre augmente de 50%. Pour les goujons en composite, la force d’extraction augmente de deux à cinq fois lorsque le diamètre augmente d’un tiers. Les tests comportant plusieurs cycles ont montré que les forces d’extraction et de rétraction étaient pratiquement similaires pour tous les goujons. Cependant, pour les goujons avec revêtement bitumineux, la force de rétraction était supérieure à celle d’extraction. Il doit être noté que la vitesse avec laquelle les essais étaient réalisés pouvait affecter les résultats, particulièrement pour les goujons avec revêtement bitumineux.

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Editorial note The Swedish Cement and Concrete Research Institute (CBI) is a RILEM Titular Member.     

Renforcement des ponts par collage de l'armature

Résumé L'application du collage au renforcement des ponts en béton armé et béton précontraint en cas d'insuffisance de l'armature semble être, dans certains cas, très économique et utile. On a appliqué le collage à ce système de renforcement pour la reconstruction de quelques ponts en Pologne. On présente trois cas dans cet article.

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Summary Application of gluing of reinforcing steel to the surfaces of concrete structures seems to be one of the most economic and practical system of strengthening reinforced and prestressed concrete bridges. This method can be applied in many cases of insufficient reinforcing steel in reconstructed bridges. Epoxy resins ensure glued joints with sufficient strength and long term resistance. This system of strengthening has been applied to reconstruct several bridges in Poland. Three examples are described in this paper. In one of these bridges the gluing of reinforcing steel was performed in the upper surfaces of Gerber-plate bridge concrete in negative bending moment areas. The flat steel strips, well cleaned and protected against corrosion, were glued to the specially prepared surface concrete. The other repair work consisted in gluing the flat iron strips on the lower surface of the concrete bridge plate. In this case, high strength bolts were used to fasten the ends of the steel bands to the bridge slab. All the work of strengthening was performed during the winter at low temperatures, from 0 to −20°C. Equally extensive strengthening work with the aid of gluing was performed during adaptation to new loads of the old concrete viaducs in the area of Central Railway Station in Warsaw. Here the steel strips and the additional reinforcing steel were glued to the side surface of the concrete slabs. Anchoring bolts were used in all cases. This method of gluing flat steel strips to strengthen insufficiently reinforced concrete bridges is very simple and economic compared with others.

     

钢-竹组合梁柱边节点拟静力试验研究

钢-竹组合工字形梁和箱形柱的边节点,采用T型钢连接件和螺栓实现组合梁柱之间的连接,并在节点核心区柱子四周焊接钢板形成钢套筒,从而增加节点域的刚度和整体性能。以螺栓数目、强度和有无加劲肋为基本参数,对6个组合梁柱边节点试件进行了拟静力加载试验,观察节点在不同参数条件下的梁端P -Δ 滞回曲线、组合梁柱之间的转角和节点区钢板的剪切变形,得到了梁柱节点的耗能系数、延性系数等抗震性能指标,在此基础上进行了节点区连接件理论转角计算方法分析。试验结果表明,螺栓强度等级和根数对节点核心区的剪切变形和组合梁柱节点的极限承载力影响不大,但节点区钢套筒焊脚尺寸和加劲肋的设置变化对节点转动刚度和抗震性能指标影响显著。根据钢-竹组合节点在弹性阶段的梁端位移和应力、应变关系,提出了组合节点的力学简化模型及连接件转角的计算方法,其计算结果与试验值吻合较好。     

Quasi-static behaviour of composite joints with protruding-head bolts

An experimental study of the quasi-static behaviour of composite bolted joints under tensile and compressive loading has been performed. The joint plates made of quasi-isotropic and 0°-dominated lay-ups were fastened by two, four, or six titanium bolts. Two specimen configurations were tested: single lap and double lap. Strain gauges were applied in order to measure strain between the bolt rows and to calculate the load transfer of the bolt rows. Bolt-movement measurements were performed using extensometers to examine bolt behaviour under static loading. The obtained experimental results showed that bolted joints with four and six bolts perform better resistance to quasi-static loading than joints with two bolts. Strain distribution between two bolts is significantly affected by the bolt presence and their behaviour under loading. The load-transfer calculations showed that different bolt rows transfer slightly different amounts of load.     

Fatigue Strength Evaluation of Resin-Injected Bolted Connections Using Statistical Analysis

Different strategies can be used to perform reparations and reinforcements of ancient bolted and riveted metallic bridges. As the riveting process is not currently a common practice, it requires proper equipment and skilled workers. Another solution is the use of welding. However, the weldability of old steels is poor. Bolts are very attractive alternative solutions, and are most commonly used to repair old metallic bridges. Fitted bolts are expensive solutions; the alternative is the use of resin-injected bolts. The behavior of bolted joints with preloaded resin-injected bolts has been studied using quasi-static and creep tests; however, few studies on the slip and fatigue behavior of these joints can be found in the literature. This paper presents an overview of a few experimental programs that were carried out by several authors aiming at evaluating the fatigue behavior of single and double shear resin-injected bolted connections. A comparison between the experimental data of joints with preloaded standard bolts and preloaded resin-injected bolts shows a fatigue strength reduction in the latter. Since Eurocode 3 (EC3) suggests the same fatigue strength curve for joints made of resin-injected bolts and standard bolts, this may raise some concerns. Furthermore, research on the feasibility of using both bonded and bolted connections is shown. This last study was performed with high-strength low-alloy structural steel plates and an acrylic structural adhesive for metal bonding. For both case studies, a statistical analysis is performed on fatigue experimental data using linearized boundaries and the Castillo and Fernández-Canteli model. Fatigue design curves are proposed and compared with the design suggestions of several European and North American standards.     

The effects of geometric parameters on the failure strength for pin-loaded multi-directional fiber-glass reinforced epoxy laminate

A numerical and experimental study was carried out to determine the failure of mechanically fastened fiber-reinforced laminated composite joints. E/glass–epoxy composites were manufactured to fabricate the specimens. Mechanical properties and strengths of the composite were obtained experimentally. Tests have been carried out on single pinned joints in [0/90/0]_s and [90/0/90]_s laminated composites. A parametric study considering geometries was performed to identify the failure characteristics of the pin-loaded laminated composite. Data obtained from pin-loaded laminate tests were compared with the ones calculated from a finite element model (PDNLPIN computer code). Damage accumulations in the laminates were evaluated by using Hashin's failure criteria combined with the proposed property degradation model. Based on the results, ply orientation and geometries of composites could be crucial for pinned laminated composite joints.     

多钉连接钉载分配特性研究方法

利用金属-复合材料层合板紧固件多钉连接件开展拉伸载荷下钉载分配特性的试验和有限元分析研究。试验件为一列三钉单搭接和双搭接连接件。通过应变电测技术获得连接件典型截面应变分布, 再间接估算钉载分配比例。建立了试验件二维、三维有限元模型, 并计算获得应变和钉载分配结果。对比发现, 应变的计算值与实测值吻合, 但钉载分配的计算结果与实测结果存在较大偏差。分析表明: 基于表面应变测量估计钉载分配的方法不能反映连接件的附加弯矩对多钉钉载分配比例的影响; 采用经过应变测量结果验证的有限元模型, 通过数值计算确定钉载分配是一种可行的技术途径; 而应用简化的板-梁二维有限元模型计算钉载分配可以满足工程精度要求。     

碳纤维/树脂复合材料多钉连接钉载系数测试方法

为解决由于碳纤维/树脂复合材料多钉连接结构中钉载分配状态和测试方法不同导致的钉载系数测试分散性不明确的问题,针对应变片和钉载矢量传感器两种测试方法,提出基于不确定度理论的钉载系数相对测量不确定度的计算模型,并计算两种测试方法对碳纤维X850/树脂复合材料单剪、双剪连接结构钉载系数的相对测量不确定度。结果表明,应变片测试方法中,单剪结构钉载系数无法准确测量,双剪结构钉载系数相对测量不确定度通常超过2.8%,且随结构中螺栓数目和应变片贴片角度偏差的增加而增大;钉载矢量传感器测试方法中,单剪、双剪结构钉载系数均可测试,且针对任意螺栓数目结构,其钉载系数相对测量不确定度最大不超过1.5%。      

Failure analysis of submersible pump system collapse caused by assembly bolt crack propagation by stress corrosion cracking

Mechanically fastened joints using bolts are critical components in submersible pump systems. These bolts are subjected to aggressive environments in oil wells. Tightening torque preload and motor's weight are the principal loads that bolts support mechanically plus an occasional pipe flexure. Additionally, a corrosive sulfide-rich water environment presents an extremely demanding chemical condition. A better understanding of those failure mechanisms affecting such components could provide more safety, as well as costs and time saving during the operation of pump systems in wells.An assembly bolt from a submersible pump was fractured during service. Failure was the result of stress corrosion cracking (SCC) originated by pit corrosion. Mechanical and optical tests were performed to identify property changes. SEM with EDS, XRF and OES analyses were used to characterize the material and crack propagation. The fractured bolt material specification was medium carbon steel, while the material specified by the manufacturer was Ni–Cu alloy. The origin of the crack was located on a stress concentration region, but its nucleation was a result of high corrosive conditions.     

Contact-free measurement and numerical and analytical evaluation of the strain distribution in a wood-FRP lap-joint

Wood specimens to each of which a laminate of carbon fibre reinforcement polymers (FRP) was glued (creating a lap joint in each case) were loaded to failure. A total of 15 specimens of three types differing in the glued length (anchorage length) of the FRP laminate (50, 150 and 250 mm respectively) were tested, their strength, stiffness and strain distribution being evaluated. Synchronized digital cameras (charge-coupled devices) used in testing enabled strain fields on surfaces they were directed at during the loading procedure to be measured. These results were also evaluated both analytically on the basis of generalized Volkersen theory and numerically by use of the finite element method. The lap joints showed a high level of stiffness as compared with mechanical joints. A high degree of accuracy in the evaluation of stiffness was achieved through the use of the contact-free evaluation system. The load-bearing capacity of joints of this type was found to be dependent upon the anchorage length in a non-linear fashion. The experimental, analytical and numerical results were shown to be in close agreement with respect to the strength and the strain distribution obtained.     

In situ ultrahigh vacuum transmission electron microscopy studies of palladium silicide island formation on silicon (111) 7×7 surface

Pd was deposited onto Si (111) 7×7 surface at approximately 700 K inside an ultrahigh vacuum transmission electron microscope. Plan-viewed transmission electron microscopy (TEM) observation indicated that the islands have two kinds of shapes, round and rectangular (one-dimensional) ones. In a diffraction pattern for the rectangular islands, extra spots along the 〈110〉 direction of the Si surface, spacing of which is 1/8 times as long as that of Si (220) spots, were seen. A high resolution TEM image showed the corresponding superstructure in the rectangular islands. In situ observation of the growing process of the rectangular islands showed repeat of introduction and relief of strains during the growth, suggesting that such superstructure would be constructed by stacking compositionally different phases or introducing defects so that the periodically maximized strain is relieved.     

Flexural strength characteristics of non-load bearing masonry walls in Kuwait

The controlling factor in designing non-load bearing masonry walls, such as those used in Kuwait, is the lateral resistance to wind loads. To ensure safety of the walls, data is needed on the flexural strength characteristics of walls constructed with locally-available materials. The flexural strength of masonry walls constructed with autoclaved aerated-concrete blocks, sand-cement concrete blocks or calcium silicate bricks was evaluated in a test program that involved testing small-scale walls or wallettes. The tests were performed in accordance with the British Standard for unreinforced masonry. The autoclaved aerated-concrete block wallettes were constructed with epoxy glue mortar, whereas the concrete block and calcium silicate brick walletters were constructed with sand-cement mortar. Two stages of testing were undertaken to evaluate bending parallel to bed joints and bending perpendicular to bed joints. The flexural strengths required by British and American codes exceed the strengths of the concrete block and calcium silicate brick walls used in Kuwait, implying that the allowable tensile stress requirements of these codes are not safe for assessing the lateral resistance of the walls. The format used for the autoclaved aerated-concrete block wallters, which is identical to the standardized format for concrete block wallettes in the British standard, is suitable for determining the flexural strength of full-size autoclaved aerated-concrete block walls.     

Variation in flexural properties of photo-pultruded composite archwires: analyses of round and rectangular profiles

Prototype continuous, unidirectional, fiber-reinforced composite archwires were manufactured into round and rectangular profiles utilizing a photo-pultrusion process. Both 0.022 inch (0.56 mm) diameter and 0.021 × 0.028 inch (0.53 × 0.71 mm) rectangular composites were formed utilizing commercially available S2-glass® reinforcement within a polymeric matrix. Reinforcement was varied according to the number, denier and twists per inch (TPI) of four S2-glass® yarns to volume levels of 32–74% for round and 41–61% for rectangular profiles. Cross-sectional geometry was evaluated via light microscopy to determine loading characteristics; whereas two flexural properties (the elastic moduli and flexural strengths) were determined by 3-point bending tests. Morphological evaluation of samples revealed that as the TPI increased from 1 to 8, the yarns were more separated from one another and distributed more peripherally within a profile. For round and rectangular profiles utilizing 1 TPI fibers, moduli increased with fiber content approaching theoretical values. For round profiles utilizing 1 TPI and 4 TPI fibers, flexural strengths increased until the loading geometry was optimized. In contrast, the flexural strengths of composites that were pultruded with 8 TPI fibers were not improved at any loading level. Doubling the denier of the yarn, without altering the loading, increased both the moduli and flexural strengths in rectangular samples; whereas, the increases observed in round samples were not statistically significant. At optimal loading the maximum mean moduli and strengths equaled 53.6 ± 2.0 and 1.36 ± 0.17 (GPa) for round wire and equaled 45.7 ± 0.8 and 1.40 ± 0.05 (GPa) for rectangular wires, respectively. These moduli were midway between that of martensitic NiTi (33.4 GPa) and beta-titanium (72.4 GPa), and produced about one-quarter the force of a stainless steel wire per unit of activation. Values of strengths placed this composite material in the range of published values for beta-titanium wires (1.3–1.5 GPa). © 2000 Kluwer Academic Publishers