【作者】 赵军卫；

【导师】 郑文忠；

【作者基本信息】 哈尔滨工业大学 ， 结构工程， 2008， 博士

【摘要】 局部受压承载力计算是预应力混凝土结构设计中的关键问题之一。我国在上个世纪八十年代对局部受压问题进行了一系列的研究,其研究成果已写入我国相关设计规范。近些年来的工程实践和科学研究表明,我国现行的《混凝土结构设计规范》(GB50010-2002)(以下简称现行规范)中局部受压承载力计算方法存在一些问题有待完善。围绕这些问题,论文开展了五个方面的研究工作。(1)针对现行规范公式中没有考虑预留孔道及孔道直径大小对混凝土局部受压强度提高系数的影响这一问题,完成了12个带预留孔道的素混凝土棱柱体试件的局部受压试验。研究了预留孔道直径和局部受压的计算底面积与混凝土局部受压面积的比值Ab/Al(以下简称局压面积比)的变化对素混凝土试件局部受压性能的影响,获得了试件破坏形态、楔形体特征、荷载位移曲线及裂缝开展特点等第一手试验资料。研究表明,预留孔道的存在将使混凝土局部受压强度提高系数降低,其降低幅度随孔道直径的增大而增大,不同局压面积比下的降低规律大体相同。提出了考虑预留孔道大小影响的局部受压承载力计算公式,即在现行规范局部受压承载力计算公式中引入了预留孔道影响系数λ_d。λ_d随预留孔道直径与承压板边长的比值和预留孔道直径与试件边长的比值的增大而线性降低,其中后一个比值的变化对λ_d影响显著。(2)针对现行规范公式中没有反映出间接钢筋内表面范围内混凝土核心面积对局部受压承载力的影响这一问题,完成了29个配置间接钢筋的混凝土棱柱体试件轴心局部受压试验。研究了间接钢筋型式、混凝土核心面积、局压面积比等参数变化对混凝土局部受压性能的影响,获得了试件破坏形态、楔形体特征、荷载位移曲线、裂缝开展特点及间接钢筋应变分布等第一手试验资料。研究表明,混凝土核心面积对局部受压承载力影响显著,当网片式间接钢筋的种类、直径、根数、网片间距不变或螺旋式间接钢筋的种类、直径及螺旋间距不变时,混凝土核心面积越大,间接钢筋对局部受压承载力的贡献越大。提出了混凝土核心面积与局部受压面积的比值Acor/Al不小于1.35时的考虑混凝土核心面积影响的局部受压承载力计算方法。这个方法的思路是将现行规范局部受压承载力计算公式中配置间接钢筋的局部受压承载力提高系数βcor以多项式5.91βcor-4.52代替。提出了Acor/Al小于1.35时的混凝土局部受压承载力计算方法。这个方法的思路是将现行规范局部受压承载力计算公式中间接钢筋贡献项乘以间接钢筋强度折减系数λ_s,而且当Acor/Al<1时将公式中βcor取为1,将间接钢筋对局部受压承载力贡献项中的局部受压净面积Aln以Acor,n代替,Acor,n为Acor扣除孔道、凹槽部分的面积。λ_s与局压面积比Ab/Al和Acor/Al两个比值有关,且随着两比值乘积的增大而增大。(3)针对预应力梁在与其垂直的边梁侧面锚固的情况,完成了12个模拟这一锚固情况的混凝土试件局部受压试验。研究了承压板宽度不变情况下长度变化及边梁宽度变化时,边梁对预应力梁锚固区局部受压性能的影响,获得了试件破坏形态、荷载位移曲线、间接钢筋应变分布等第一手试验资料。研究表明,边梁对预应力梁端部局部受压锚固区有较强的约束作用。当局部受压计算底面积在预应力梁侧以外的尺寸不大于2倍的边梁宽度、边梁宽度不小于局部受压面积的短边尺寸时,局部受压计算底面积可以按照与局部受压面积同心、对称的原则扩展到边梁侧表面中。(4)针对我国现行标准中混凝土局部受压承载力计算公式对活性粉末混凝土(RPC)的适用性问题,完成48个活性粉末混凝土棱柱体试件局部受压试验。研究了活性粉末混凝土强度等级和局压面积比变化对其局部受压性能的影响,获得了试件破坏形态、裂缝开展特点、楔形体特征和荷载位移曲线等第一手试验资料。研究表明,RPC局部受压性能与普通混凝土局部受压性能基本相似,其局部受压承载力也随局压面积比的增大而增大,同面积比条件下,RPC局部受压强度提高系数较普通混凝土局部受压强度提高系数低。掺加钢纤维能明显改善RPC的局部受压性能,但钢纤维的掺量对其局部受压性能影响较小。基于试验结果分别提出了素RPC和掺加钢纤维RPC局部受压承载力的两类计算模式。素RPC局部受压承载力计算模式Ⅰ中RPC强度影响系数随局压面积比增大而线性降低;模式Ⅱ利用单一的RPC局部受压强度影响系数综合考虑RPC强度及局部受压两因素对试件局部受压承载力的影响。掺加钢纤维RPC局部受压承载力计算模式Ⅰ取RPC强度影响系数为常数;模式Ⅱ利用单一的RPC局部受压强度影响系数综合考虑钢纤维特征及掺量、RPC强度及局部受压等因素对试件局部受压承载力的影响。(5)给出了局部受压承载力计算及端部间接钢筋配置的建议方法。更多还原

【Abstract】 Calculation of local compression bearing capacity is one of pivotal problems in design of prestressed concrete structure. A series of problems on local compression have been investigated in the eighties of the twentieth century. The research achievement has been involved in relevant national design criterions. Engineering practice and science research in latest years show that there are some problems in the calculation method of local compression bearing capacity in the current Code for Design of Concrete Structure (“the Current Code”for abbreviation) and they need to be improved. To solve these problems, five parts of research work are accomplished in this dissertation.(1) The influence of ducts and its diameter on the enhancement coefficient of concrete strength for local compression has not been taken into account in the calculation formula in the Current Code. Considering this problem, local compression experiments on 12 plain concrete prism specimens with ducts are completed. The influence of ducts’diameter and the ratio of calculated bottom area for local compression (Ab) to local compression area of concrete (Al) on local compression performance of plain concrete specimens have been researched. The first-hand experimental data are got, such as failure modes of specimens, features of the wedges, load-displacement curves and characteristics of crack distribution. Researches show that the enhancement coefficient of concrete strength for local compression decreases due to ducts, and the decrease degree increases with the increase of diameter of ducts. The law for decrease of concrete strength is the same in general for different Ab/ Al. The calculation formula for local compression bearing capacity of concrete considering the influence of diameter of ducts is brought forward, in which an influence coefficientλ_d is introduced. Theλ_d decreases linearly with the increase of the ratio of diameter of ducts to length of bearing plate and the ratio of diameter of ducts to length of specimen side. The second value has notable influence onλ_d.(2) The influence of concrete core area within the range for inner surface of indirect reinforcements on the local compression bearing capacity has not been reflected in the calculation formula in the Current Code. Considering this problem, local compression experiments on 29 concrete prism specimens with indirect reinforcements are completed. The influence of some factors on local compression performance of concrete specimens have been researched, such as the variety of indirect reinforcement, concrete core area and the ratio of the calculated bottom area for local compression to local compression area of concrete. The first-hand experimental data are got, such as failure modes of specimens, features of the wedges, load-displacement curves, characteristics of crack distribution and strain distribution of the indirect reinforcement. Researches show that concrete core area has notable influence on local compression bearing capacity. When the variety, diameter, number, and spacing of mesh indirect reinforcement keep constant, or the variety, diameter, and spacing of spiral indirect reinforcement keep constant, contribution of indirect reinforcements to local compression bearing capacity increases with the increase of concrete core area.The calculation method for local compression bearing capacity considering the influence of concrete core area is brought forward when the ratio of concrete core area (Acor) to local compression area of concrete (Al) is not less than 1.35. The idea is the enhancement coefficient of local compression bearing capacity due to indirect reinforcements (βcor) is replaced by a multinomial (5.91βcor-4.52) in the calculation formula in the Current Code.The calculation method for local compression bearing capacity is brought forward when Acor/Al is less than 1.35. The idea is the contribution of indirect reinforcements to local compression bearing capacity in the Current Code is multiplied by the reduction factor of strength of indirect reinforcements (λ_s). When Acor/Al<1,βcor equals to 1, and the net local compression area (Aln) in the indirect reinforcements contribution is replaced by Acor,n. Acor,n is the residual area of removing the ducts and caves from Acor.λ_s relates to Ab/Al and Acor/Al , and it increases with the increase of the product of the two ratios.(3) Considering the case that prestressed concrete beams are anchored in the side of boundary beam perpendicular to the prestressed concrete beam, local compression experiments on 12 concrete specimens which simulating this case are completed. The influence of boundary beam on local compression performance of anchorage zone of prestressed concrete beams have been researched with length of bearing plate and width of boundary beam varying and width of bearing plate keeping constant. The first-hand experimental data are got, such as failure modes of specimens, load-displacement curves and strain distribution of the indirect reinforcement. Researches show that boundary beam has strong restrictions on end anchorage zone of prestressed concrete beam. When the ratio of length of calculated bottom area outside the section of prestressed concrete beam to width of boundary beam is less than 2 and width of boundary beam is larger than the shorter length of local compression area, the calculated bottom area for local compression can be extended to the side face of boundary beam according to the principle of the local compression area is concentric or symmetric to the calculated bottom area.(4) Considering the applicability of calculation formulas on concrete local compression bearing capacity in present national standards to reactive powder concrete (RPC), local compression experiments on 48 RPC prism specimens are completed. Influences of RPC strength and the ratio of calculated bottom area for local compression to local compression area on RPC local compression performance have been researched. The first-hand experimental data are got, such as failure modes of specimens, characteristics of crack distribution, features of the wedges and load-displacement curves. Researches show that local compression performance of RPC is similar to the ordinary concrete. Local compression bearing capacity of RPC increases with the increases of Ab/Al. The enhancement coefficient of RPC strength for local compression is smaller than the ordinary concrete under the same Ab/Al. Local compression performance of RPC can be improved by mixing steel fiber into RPC, but the dosage of steel fiber has little influence on it.Based on experimental results, two kinds of calculation formulas for local compression bearing capacity of plain RPC and RPC with steel fiber are brought forward. In formula one of plain RPC, influence coefficient of RPC strength (βc) linearly decreases with the increase of Ab/Al, and in formula two, the single influence coefficient of local compression strength is uses to synthetically take into account the influence of strength of RPC and local compression on local compression bearing capacity of specimens. In formula one of RPC with steel fiber,βc is taken as constant and in formula two, the single influence coefficient of local compression strength is used to reflect the influence of factors on local compression bearing capacity of specimens, such as character and dosage of steel fiber, RPC strength and local compression.(5) Suggested methods for calculation of local compression load bearing capacity and placing of indirect reinforcement in end zone are presented.更多还原