预应力混凝土叠合梁正常使用极限状态试验研究

基于本试验和目前国内全部预应力混凝土叠合梁正常使用阶段试验结果 ,探讨了预应力混凝土叠合梁在正常使用阶段的受力特征 ,提出了可用于正常使用极限状态控制的计算公式 。

钢-预应力混凝土连续组合箱形梁的整体性能分析

视多室箱梁单位宽度为空腹桁架 ,取桁架的每根杆件为一平面梁单元 ,用三次插值函数描述其位移 ,单元节点位移参数用三次多项式表示为箱梁梁段单元节点位移参数的函数。这样箱梁梁段单元可分为翼板 (顶底板 )、腹板 (斜腹板 )、伸臂和横隔板单元。在进行有限元分析时将其直接迭加至总体刚度矩阵 ,编制相应的程序后可任意分析单箱多室、多箱多室及不规整的多种材料组成的组合箱梁。同时能分析箱梁的畸变、翘曲、局部变形、剪力滞后和荷载横向分布等。用本文编制的程序进行了一座复杂的钢 -预应力混凝土连续组合箱梁桥计算 。

部分预应力混凝土迭合梁设计方法的探讨

本文推导的部分预应力砼迭合梁的设计方法,在使用阶段计算时采用考虑二次受力迭合效应的折算弯矩,在极限状态设计时采用设计弯矩,从而将迭合构件的设计转化为非迭合构件的设计,并且采用控制使用阶段预应力钢筋应力增量或非预应力钢筋应力来满足裂缝宽度控制要求。利用该方法进行部分预应力砼迭合梁的设计,可以较迅速地求出同时满足强度和裂缝宽度限制要求的预应力钢筋和非预应力钢筋的面积。

Finite element failure analysis of continuous prestressed concrete box girders

In order to analyze the load carrying capacity of prestressed concrete box girders, failure behaviors of in-situ deteriorated continuous prestressed concrete box girders under loading are experimentally observed and a finite failure analysis method for predicting behaviors of box girders is developed. A degenerated solid shell element is used to simulate box girders and material nonlinearity is considered. Since pre-stressed concrete box girders usually have a large number of curve prestressed tendons, a type of combined element is presented to simulate the prestressed tendons of box girders, and then the number of elements can be significantly reduced. The analytical results are compared with full-scale failure test results. The comparison shows that the presented method can be effectively applied to the failure analysis of in-situ continuous prestressed concrete box girders, and it also shows that the studied old bridge still has enough load carrying capacity.

Strengthening reinforced concrete beams using prestressed glass fiber-reinforced polymer-Part I: Experimental study

This work is aimed at studying the strengthening of reinforced concrete (R. C.) beams using prestressed glass fi- ber-reinforced polymer (PGFRP). Carbon fiber-reinforced polymer (CFRP) has recently become popular for use as repair or rehabilitation material for deteriorated R. C. structures, but because CFRP material is very stiff, the difference in CFRP sheet and concrete material properties is not favorable for transferring the prestress from CFRP sheets to R. C. members. Glass fi- ber-reinforced polymer (GFRP) sheets with Modulus of Elasticity quite close to that of concrete was chosen in this study. The load-carrying capacities (ultimate loads) and the deflections of strengthened R. C. beams using GFRP and PGFRP sheets were tested and compared. T- and ⊥-shaped beams were used as the under-strengthened and over-strengthened beams. The GFRP sheets were prestressed to one-half their tensile capacities before being bonded to the T- and ⊥-shaped R. C. beams. The prestressed tension in the PGFRP sheets caused cambers in the R. C. beams without cracks on the tensile faces. The PGFRP sheets also enhanced the load-carrying capacity. The test results indicated that T-shaped beams with GFRP sheets increased in load-carrying capacity by 55% while the same beams with PGFRP sheets could increase load-carrying capacity by 100%. The ⊥-shaped beams with GFRP sheets could increase load-carrying capacity by 97% while the same beams with PGFRP sheets could increase the loading-carrying capacity by 117%. Under the same external loads, beams with GFRP sheets underwent larger deflections than beams with PGFRP sheets. While GFRP sheets strengthen R. C. beams, PGFRP sheets decrease the beams’ ductility, especially for the over-strengthened beams (⊥-shaped beams).

Assessment of Long-Time Behavior for Bridge Girders Retrofitted with Fiber Reinforced Polymer

Maintaining both the safety and serviceability of deteriorating highway bridge networks necessitates suitable BMS （bridge maintenance system） tools that can maximize cost effectiveness. Numerous experiments have been conducted to detect the long-term mechanical properties of the epoxy resin materials used in FRP （fiber reinforced polymers） strengthening and maintenance technique. Experiments were used to develop a short-term test and construct a model that can reliably predict the long-term behavior of epoxy resin. Furthermore, FEA （finite element analysis） models were developed, using the ANSYS software, to simulate three unstrengthened and FRP strengthened prestressed concrete girder bridges of different configurations. Models simulate the original and aged properties of construction and retrofitting materials under the application of AASHTO （American Association of State Highway and Transportation Officials） fatigue truck and a site-specific fatigue truck in different scenarios. These models were used to develop the bridge performance chart for the capacity of the bridge, with and without strengthening interventions, as a BMS tool. The results show an immediate significant improvement in the concrete tensile stress with the intervention of FRP strengthening.

Test analysis on prestressed concrete composite beams with steel boxes subjected to torsion and combined flexure and torsion

While modem prestressed techniques have improved the torsion properties of high-strength concrete （HSC） composite beams with prestressed steel （PS） boxes, no research has been reported in either the national or international literature on the an- ti-torque and composite torque properties of this type of beam. With the aim of understanding the torque properties of these beams, this paper presents results of ten comprehensive tests; three of these were based on stirrup spacings and prestressing levels as the main parameters, while the other seven were based on torsional rates. The torsion tests were conducted on the re- sults which established several key parameters, including curves of constant torsion, strain curves of steel torsion, strain distri- bution of steel beams and concrete, curves of bending-moment and mid-span deflection, as well as cross strain distribution.The prestressing impact-factor method was adopted to deduce semiempirical equations for cracking torque in such composite beams. Furthermore, this involves the use of the equation of ultimate torque based on tress-model-theory of the distortion an- gle, the calculated results show good agreement with the measured values. In summary, this paper offers theoretical analysis for future applications of HSC composite beams with PS boxes, and provides both validation of the methods employed and a reference point for on-going research on composite beams and related anti-torque studies.