施加横向体外预应力加固装配式空心板桥的研究

【作者】 张云娜；

【导师】 陈淮；

【作者基本信息】 郑州大学 ， 结构工程， 2007， 硕士

【摘要】 装配式预应力混凝土空心板桥因建筑高度较低、预制方便、用材经济等优点是桥梁工程广泛采用的桥型。20世纪70、80年代所建造的装配式预应力混凝土空心板桥，存在桥梁承载能力较低，且空心板间多用混凝土小企口缝进行铰接连接的缺陷。随着现代经济高速发展，重型车和超载车出现频繁。所以近些年来，这类桥梁经常出现沿空心板间企口缝的纵向裂缝、坑槽和塌陷，且空心板间铰缝处混凝土破碎、脱落、大面积渗漏，致使板间横向联系失效，出现单板受力，严重影响行车安全，成为整条公路交通的瓶颈。因而，对这类病害桥梁进行加固研究具有重要的工程实用价值。针对上述装配式预应力混凝土空心板桥存在的病害，提出了一种通过施加横向的体外预应力筋来进行治理的加固方法。其加固机理是：通过施加横向的预压应力使装配式预应力混凝上空心板的横向下缘混凝土处于受压状态，平衡了横向弯矩，空心板间可以同时传递竖向剪力和弯矩，变铰接板结构形式为刚接板结构形式，以增强装配式板桥的横向连接能力。同时，由于空心板的横向连接从铰接变为刚接，改善了荷载的横向分布，有利于各空心板协同工作共同分担行车荷载，从而最终提高整个空心板桥的承载能力。该法加固原理简单明确，虽然在一些实际工程中已有所使用，但其实际加固效果在理论上尚缺乏具体数据，使得我们不能定量地认识该法的有效性。在本文中，运用MIDAS／Civil有限元程序，采用三维空间块体单元对装配式预应力混凝土空心板桥进行有限元建模，建立了整桥的三维实体单元计算模型。在有限元建模中，对截面顶板处的普通钢筋区采用钢筋与混凝土的折算弹性模量考虑顶板处普通钢筋的影响，对底部的预应力钢筋采用等效的预应力板带进行模拟；桥面板、铰缝、混凝土铺装及护栏等均用实体单元，横向预应力筋采用只受拉不受压的桁架单元。文中在分析该加固法对空心板桥有效性的同时，也比较了所施加的横向预应力大小、纵桥向不同位置、桥梁宽跨比等因素对桥梁加固效果的影响。对于正交板桥，为了得到横向预应力大小对加固效果的影响，依次将7根横向预应力筋的预应力荷载设为100kN／根、150kN／根、200kN／根三种情况进行分析。为了得到桥梁荷载横向分布影响线，分别在跨中处1～8号板的各板中心处施加单位荷载，对每个单位荷载，再分4种工况：工况1：仅单位荷载；工况2：单位荷载+100kN／根的横向预应力筋荷载；工况3：单位荷载+150kN／根的横向预应力筋荷载；工况4：单位荷载+200kN／根的横向预应力筋荷载，全桥共设有32种工况。文中采用相同的方法研究了斜交空心板桥采用施加横向体外预应力筋进行加固的有效性，以及斜交空心板桥的不同斜度对加固效果的影响。计算结果表明：使用该法对空心板桥进行加固，施工简单，加固效果明显，斜交空心板桥的加固效果没有正交空心板桥的好；所施加横向预应力的大小对加固效果影响不大；在纵桥方向上，同一号板在跨中处的加固效率较两端高；宽跨比越小对加固效果越有利；斜交空心板桥的斜度越大对加固越不利。这些结论对同类桥的加固有一定借鉴作用。由于我国目前装配式预应力空心板桥应用广泛、使用普遍，大量装配式预应力空心板桥存在空心板间企口缝沿纵向开裂等缺陷，所以广泛推广此加固技术，对存在缺陷的装配式预应力空心板桥进行加固将具有较大的社会意义和实用价值。更多还原

【Abstract】 For such advantages as low construction height,being easily prefabricated and economical material using,assembly pre-stressed concrete hollow board bridge is applied widely in bridge engineering. Bridges of the type built in 1970s and 1980s have faults as low load bearing capacity and small tongue-and-groove joint between boards. With modern economy developing highly,heavy vehicles and overload vehicles appear frequently,and cause that longitudinal cracks and pitfalls along tongue-and-groove between boards emerge in bridges of the type recently. Concrete near tongue-and-groove tattered or fallen off,and leakage over large areas lead to fail transverse contact and single plate bearing. As an ultimate result,driving safety and traffic capacity of the whole highway are imperiled. Therefore,reinforcement research on these sick bridges of the type is of great practical engineering value.In connection with diseases as mentioned above existing in assembly pre-stressed concrete hollow board bridges,a strengthening method has been put forward lately,that’s strengthening the bridge by imposing external transverse pre-stressing force on it. The reinforcement mechanism is that,exerting pre-stress on assembly concrete hollow board bridges makes concrete at bottom in compressive station and cancel out transverse moment, enables boards to deliver vertical shear and moment simultaneously,changes contact style form hinge joint to rigid connection,and improves load transverse contribution. It is also beneficial to boards’ teamwork of sharing vehicle loads. Ultimately the load bearing capacity of the whole bridge is increased. The reinforcement mechanism of the method is simple and clear. Now the method has been put into practical project,however,the actual figures of reinforcement effect hasn’t been given out,so we can’t evaluate reinforcement effect of the method quantitatively at the moment.In the text,MIDAS/Civil FEM software is used to build three dimensional FEM computation model of a whole assembly pre-stressed concrete hollow board bridge,using solid element of the FEM program. When building the model,conversion elastic modulus of concrete and steel is adopted in reinforced concrete area at the top of section,in consideration of influence of steel. As to pre-stressed concrete area at the bottom of section,rigidity equivalent pre-stressed plate-belt is adopted to simulate. The bridge deck,tongue-and-groove, concrete pavement and balustrade are all simulated by solid element. Transverse pre-stressed bar is imitated by truss element which can only withstand tension but not compression. In the text,we not only dicuss whether the reinforcement method is useful to hollow board bridge, but also evaluate the influence of factors on reinforcement effect,such as value of transverse pre-stress imposed,variation of location in the direction of longitudinal span,ratio of width to span of the bridge. As for orthogonal slab bridges,we set three cases,that is to say,pre-stress of seven transverse pre-stressed bars are fixed 100kN/stalk,150kN/stalk and 200kN/stalk separately to analyse the influence of the transverse pre-stress value on reinforcement result. To obtain transverse load distribution influence line of the bridge,we exert unit load on No1 to N08 board’s width centre at the mid-span respectively. Each unit load possesses four load cases: 1,unit load only; 2,unit load + transverse pre-stress of 100kN/stalk; 3,unit load + transverse pre-stress of 150kN/stalk; 4,unit load + transverse pre-stress of 200kN/stalk. The whole bridge has 32 load cases in total. The same FEM is applied to study assembly skew slab bridges. Then the text researches whether it’s also effective to skew slab bridges by imposing external transverse pre-stressing force. In the last,the influence of skew angle’s value on reinforcement effect is analysed.The results manifest that: when this method is used to strengthen hollow board bridges, it’s easy in construction and evident in reinforcement effect; It’s more efficient to assembly orthogonal slab bridges than to assembly skew slab bridges; Value of transverse pre-stress has little influence on reinforcement effect; Efficiency is higher at longitudinal mid of span than two ends of the span; Smaller the ratio of width to span is,higher the efficiency of the reinforcement becomes; Larger the skew angle is,lower the efficiency of the reinforcement is. The analytical results may serve as reference to strengthening the other bridges of the type.Since the type of assembly pre-stressed concrete hollow board bridge is used widely at present and a mount of bridges of the type have the faults of tongue-and-groove cracking longitudinally between boards now,it will produce enormous social significance and practical value to popularize this reinforcement technology vigorously to strengthen sick assembly pre-stressed concrete hollow board bridges.更多还原