环形截面大偏心受压构件截面延性系数计算

延性是混凝土构件的一项重要特性 ,延性系数是构件延性的度量 ,由于沿周边均匀配筋环形截面偏心受压构件受力计算的特殊性 ,至今没有一个较精确的计算公式。本文根据沿周边均匀配筋环形截面偏心受压构件的工作特点 ,采用常用应力应变关系和基本假设 ,提出了其延性系数的计算方法。     

Bond of GFRP Bars in Concrete: Experimental Study and Analytical Interpretation

The local bond mechanics of glass-fiber reinforced polymer (GFRP) bars in normal strength concrete was investigated through experimental testing and analytical modeling. The experimental program was comprised of 30 direct tension pullout specimens with short anchorages. A novel test setup, specially designed so as to minimize the spurious influence of testing conditions on measured bond properties was adopted in the study. Parameters considered were the bar roughness and diameter, the size effect expressed by the constant cover to bar diameter ratio, and the external confining pressure exerted over the anchorage length by transverse externally bonded FRP sheets. Results of the study were summarized in the form of local bond-slip curves, whereby performance limit states were quantified by the amount of loaded end slip and bond strength. An analytical model of the bond stress-slip response of a GFRP bar was derived from first principles and calibrated against the test data of the present investigation. Using the calibrated model, design values for bond and slip were estimated with reference to the code limit state model for bond.     

Stress concentration and fatigue of profiled reinforcing steels

Stress concentrations arise from profiles of ribbed reinforcing steel bars and in this study the results of calculated stress concentration factors (SCF), by using finite element method, are related to the fatigue test results. It is apparent that the degree of confinement of a ribbed bar embedded in concrete not only affects the magnitude of the ultimate bond stress but also the bond stress-slip relation. Thus the rib geometry or profile pattern is designed for optimum bond characteristics and not for fatigue considerations. However the rib geometry influences the fatigue performance through the SCFs arising from the root radius, width and flank angles of the profiles. It is shown that these latter factors have a significant influence on the fatigue behaviour of reinforcing steel bars.     

推算楔形直杆振动固有频率的上、下限的一种新方法

用积分方程理论中的迭核理论,得到了楔形体振动的固有频率的一个区间估计。本方法不需要假设试函数,也不需要解超越方程,只要计算两个二重积分便可得到基本固有频率的上下限,并且取消了截面变化不大的限制,因此适用范围更广。     

In vitro hydrolytic degradation of poly(para-dioxanone) with high molecular weight

The in vitro hydrolytic degradation of high molecular weight poly (para-dioxanone) was studied by examining the changes of weight retention, water absorption, pH value, tensile strength, break elongation, thermal properties, and morphology of high molecular weight PPDO in phosphate buffered saline (PBS) (pH 7.44) at 37°C for 8 weeks. During the degradation, all samples’ weight retention decreased and water absorption increased significantly, whereas hydrolysis rate of PPDO bars varied with molecular weight. Compared with lower molecular weight samples, higher molecular weight PPDO samples exhibited higher hydrolysis rate. The samples’ glass transition temperature (Tg) decreased notably, while the degrees of crystallinity (Dc) increased. The samples almost totally lost their tensile strengths and breaking elongation after 4 weeks of degradation. The results suggested that the stability of PPDO in vitro hydrolytic degradation increased with the increase of molecular weight.     

Deflection Prediction of Steel and FRP-Reinforced Concrete-Filled FRP Tube Beams

This paper presents the results of experimental and theoretical investigations that study the flexural behavior of reinforced concrete-filled fiber-reinforced polymer (FRP) tubes (RCFFTs) beams. The experimental program consists of 10 circular beams [6 RCFFT and 4 control reinforced concrete (RC) beams] with a total length of 2,000?mm, tested under four-point bending load. The experimental results were used to review and verify the applicability of various North American code provisions and some available equations in the literature to predict deflection of RCFFT beams. The measured deflections and the experimental values of the effective moment of inertia were analyzed and compared with those predicted using available models. The results of the analysis indicated that the behavior of steel and FRP-RCFFT beams under the flexural load was significantly different than that of steel and FRP-RC members. This is attributed to the confining effect of the FRP tubes and their axial contribution. This confining behavior in turn enhanced the overall flexural behavior and improved the tension stiffening of RCFFT beams. For that, the predicted tension stiffening of steel and FRP-RCFFT beams using the conventional equations (steel or FRP-RC member) underestimates the flexural response; therefore, the predicted deflections are overestimated. Based on the analysis of the test results, the Branson’s equation for the effective moment of inertia of RC structures is modified, and new equations are developed to accurately predict the deflection of concrete-filled FRP tube (CFFT) beams reinforced with steel or FRP bars.     

Behavior of Beams Strengthened with Novel Self-Anchored Near-Surface-Mounted CFRP Bars

A commonly observed failure mode in laboratory tests involving surface bonded fiber-reinforced polymer (FRP) laminates or near-surface-mounted (NSM) bars is premature delamination, that is, the separation of the FRP from the substrate well before the FRP reaches its ultimate strain capacity. To delay the onset of delamination and to ensure that the NSM FRP reinforcement continues to contribute to member strength after partial delamination, a new self-anchored carbon fiber-reinforced polymer (CFRP) bar was developed and tested for this investigation. This bar is made with a series of monolithic spikes that can be anchored deep inside the concrete. In addition to cutting grooves into the concrete cover for the placement of the primary reinforcing bar, holes are drilled deep into the concrete to insert the spikes. To test the performance of this bar, six large, simply supported, reinforced, concrete beams were retrofitted with NSM bars and tested in four-point bending. Two beams were strengthened with NSM bars without anchors or spikes but were otherwise similar to the self-anchored bar and served as control specimens (Series?B1). Two beams were strengthened in flexure with the new self-anchored NSM bars (Series?B2), and the remaining two beams (Series?B3) were strengthened in flexure and shear by using the self-anchored NSM bars as partial shear reinforcement. The effect of the proposed strengthening system on the beams’ strength, failure mode, deformability, and ductility are discussed on the basis of the experimental results. The anchors delayed delamination and enabled the NSM bar to experience at least a 77% higher strain at failure than the companion bar without anchors. The anchors also increased beam displacement ductility and energy ductility at a 20% strength degradation by at least 34% and 42%, respectively.     

Evaluation of Flexural Behavior and Serviceability Performance of Concrete Beams Reinforced with FRP Bars

Flexural behavior and serviceability performance of 24 full-scale concrete beams reinforced with carbon-, glass-, and aramid-fiber-reinforced-polymer (FRP) bars are investigated. The beams were 3,300?mm long with a rectangular cross section of 200?mm in width and 300?mm in depth. Sixteen beams were reinforced with carbon-FRP bars, four beams were reinforced with glass-FRP bars, two beams were reinforced with aramid-FRP bars, and two were reinforced with steel, serving as control specimens. Two types of FRP bars with different surface textures were considered: sand-coated bars and ribbed-deformed bars. The beams were tested to failure in four-point bending over a clear span of 2,750?mm. The test results are reported in terms of deflection, crack-width, strains in concrete and reinforcement, flexural capacity, and mode of failure. The experimental results were compared to the available design codes.     

筋板布置型式对机床动态性能的影响

以M2120A内圆磨床为对象,比较了采用不同筋板型式后各主要零件及整机的动态性能。分析结果表明,依据零件的振型特点选用相宜的筋板型式可明显提高其动刚度,而且由改进后的各零件组合而成的整机磨床比原磨床具有更好的动态特性。     

三维布筋系统钢筋显示技术研究

三维布筋系统采用“三维钢筋设计、二维剖切出图”的方案,通过建立与实际工程一致的结构——钢筋三维混合模型,来实现结构设计．并可自动生成工程图。但与一般结构体及面不同,钢筋通常是线,它在传统三维系统中渲染显示有一定困难。介绍了一种新的显示方法,它可以提供直观、快捷的钢筋线显示,方便指导结构设计。